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WO2016047840A1 - Rolled steel sheet and production method therefor - Google Patents

Rolled steel sheet and production method therefor Download PDF

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Publication number
WO2016047840A1
WO2016047840A1 PCT/KR2014/009415 KR2014009415W WO2016047840A1 WO 2016047840 A1 WO2016047840 A1 WO 2016047840A1 KR 2014009415 W KR2014009415 W KR 2014009415W WO 2016047840 A1 WO2016047840 A1 WO 2016047840A1
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WO
WIPO (PCT)
Prior art keywords
steel sheet
rolled steel
elongation
rolling
boron
Prior art date
Application number
PCT/KR2014/009415
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French (fr)
Korean (ko)
Inventor
김영하
강용식
제복내
Original Assignee
주식회사 포스코
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Publication of WO2016047840A1 publication Critical patent/WO2016047840A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon

Definitions

  • the present invention relates to a rolled steel sheet and a method for manufacturing the same, and more particularly, to a low carbon steel base rolled steel sheet and a method for producing the same by optimizing the steel components and operating conditions to improve material aging and workability.
  • steel sheets used in home appliances and automobiles there must be a property of preventing processing defects due to aging, and thus, steel sheets used in home appliances and automobiles have been used as materials such as ultra low carbon steel containing carbonitride-forming elements having excellent aging resistance. .
  • steel sheets used in home appliances and automobiles are required for bending resistance and workability, etc., and in the case of automotive steel sheets, the steel sheet is prevented from being oxidized due to outside conditions and paint is used to obtain a desired surface color. Since organic matter is coated, management of surface properties of the steel sheet has become an important management factor in terms of paintability.
  • Flucting refers to a phenomenon in which a processed portion at the time of machining is bent into a diamond shape, and when the bending occurs, it is difficult to maintain the shape of the molded part, and thus the bending should be strictly limited in the actual process.
  • Japanese Laid-Open Patent Publication No. 1989-282420 name of the invention: a method of manufacturing a hot rolled steel sheet for processing and a process heat treatment method of a hot rolled steel sheet
  • an ultra low carbon steel base for producing a steel sheet suitable for a high strength member for automobile or industrial equipment.
  • a method for producing a hot rolled steel sheet excellent in workability and aging is disclosed by adding titanium (Ti), niobium (Nb), and some rare earth elements.
  • this method helps to suppress processing defects such as bending by adding carbonitride-forming elements as described above, but decreases productivity due to increased steelmaking time for high clarity and increases production cost by adding expensive alloying elements. There is a problem.
  • Korean Patent Publication No. 1996-23130 name of the invention: a method for manufacturing a high-temperature hot rolled steel sheet having excellent aging resistance
  • a method of improving aging resistance by hot rolling in a temperature range above the Ar 3 transformation point and coarsening ferrite grains is disclosed.
  • Japanese Laid-Open Patent Publication No. 2008-190008 name of the invention: a method for producing a hot rolled steel sheet having excellent aging resistance
  • Hot-rolled steel slabs containing iron and Fe and other unavoidable impurities, cooled to below 400 ° C with an average cooling rate of 60 ° C / s or more, and after winding t / R ⁇ 0.0055 a method of performing a temper rolling (Skin Pass Mill; SPM) having an elongation rate of 0.1 to 1.0% using a small diameter roll satisfying a roll diameter) is disclosed.
  • FGS Ferrite Grain Size
  • the rolled steel sheet according to the present invention is characterized by having a yield point (YP) of 200 to 250 and a yield point-stretching (YP-EL) of 0.01 to 0.05.
  • the low carbon steel satisfies an elongation of 0.7 to 1.6% with respect to the material thickness 0.4 ⁇ T ⁇ 2.4.
  • the manufacturing method of the rolled steel sheet which concerns on another aspect of this invention is carbon (C): 0.035-0.08, silicon (Si): 0.01-0.03, manganese (Mn): 0.15-0.5, phosphorus (P): 0.001-0.015, sulfur (S): 0.001-0.015, solution-aluminum (Sol.-Al): 0.01-0.04, nitrogen (N) 1-40 ppm, residual iron (Fe) and other unavoidable impurities, and boron ( B) forming a steel slab made of low carbon steel added with 1 to 60 ppm; Manufacturing a hot rolled steel sheet by performing a hot rolling process including finishing rolling, cooling, and winding steps on the steel slab; Manufacturing a cold rolled steel sheet by sequentially performing steps of pickling, cold rolling, and continuous annealing of the hot rolled steel sheet; And tempering rolling the continuously annealed cold rolled steel sheet under conditions satisfying an elongation of 0.7 to 1.6% with respect to a material thickness of
  • the finishing rolling is characterized in that it proceeds in a temperature range of 850 ⁇ 950 °C.
  • the cooling is characterized in that it proceeds at a cooling rate of 60 ⁇ 120 °C per second.
  • the said winding is characterized by advancing in the temperature range of 540-640 degreeC.
  • the cold rolling is characterized in that the cold rolling ratio is set to 50 to 90%.
  • the continuous annealing is characterized in that carried out in a temperature range of 720 ⁇ 810 °C.
  • the temper rolling is characterized in that the progress to the conditions that satisfy the elongation according to the following material thickness.
  • the present invention forms a steel slab by adding a certain amount of boron (B) to the components of low carbon steel, and in the hot rolling and cold rolling treatment of the steel slab, finishing rolling and winding in the hot rolling process, and continuous annealing and tempering in the cold rolling process Optimize rolling conditions.
  • B boron
  • the present invention can improve the material aging and workability through the precipitation of the employment elements, so, the present invention can provide a high value-added rolled steel sheet used in home appliances and automobiles.
  • FIG. 1 is a micrograph showing the structure of a rolled steel sheet made of a general low carbon steel without boron (B) added.
  • Figure 2 is a micrograph showing the structure of the rolled steel sheet made of boron (B) addition low carbon steel according to the present invention.
  • FIG 3 is a graph showing the yield point (YP) of a rolled steel sheet made of boron (B) -added low carbon steel prepared according to the present invention and a rolled steel sheet made of ordinary low carbon steel without boron (B) added thereto.
  • YP-EL yield-stretch
  • Carbon (C) is an element added to improve the strength of the steel sheet. As the content increases, the tensile and yield strength increases, but when added excessively, the upper limit is 0.08% by weight because the workability of the material decreases and the bending resistance decreases. Restrict. On the other hand, when the carbon (C) content is less than 0.035% by weight, not only additional operating time is required for decarburization during steelmaking, but also it is difficult to secure stable materials such as target strength. Therefore, the content of carbon (C) is 0.035 to 0.08 wt%.
  • Silicon (Si) is a useful element that can improve the strength without lowering the ductility of the steel sheet. Silicon (Si) contributes to strength as a ferrite stabilizing element employed in ferrite and promotes martensite formation by encouraging carbon enrichment with unmodified austenite. When the silicon (Si) is added in less than 0.01% by weight, it is difficult to secure the martensite fraction, whereas when added in excess, the upper limit is 0.03% by weight because it causes surface defects and degrades the coating adhesion. Limited to
  • Manganese (Mn) is an element widely used as a solid solution strengthening element. It is an important element for increasing the strength of steel and improving hot workability, but is an element that inhibits the ductility and workability of a material due to MnS formation. If the content of the manganese (Mn) is small, the workability is improved, but it is difficult to secure the strength, it should be added 0.15% by weight or more to secure the target strength. On the other hand, excessive addition of manganese (Mn) not only causes economic deterioration and central segregation caused by the addition of a large amount of alloying elements, but also deteriorates weldability, so the upper limit is limited to 0.5% by weight.
  • Phosphorus (P) is an element that serves to improve the strength and corrosion resistance of steel, and it is preferable to add a large amount in order to secure such characteristics, but the element that causes central segregation during casting is a factor that lowers workability when added in large quantities. This content is limited to 0.015% by weight or less. On the other hand, if the content of phosphorus (P) is less than 0.001% by weight, it is difficult to secure strength and corrosion resistance, so the content is 0.001 to 0.015% by weight.
  • S Sulfur
  • Mn manganese
  • S sulfur
  • S combines with manganese (Mn) in steel to form non-metallic inclusions that serve as a starting point for corrosion, as well as acting as a factor of red brittleness, so it is desirable to reduce its content as much as possible. Therefore, the content of sulfur (S) is 0.001 to 0.015% by weight.
  • Aluminum (Al) is generally an element added for deoxidation of molten steel, but has an aspect of improving aging characteristics by combining with solid solution in steel. Therefore, aluminum (Al) is added in a solution-aluminum (Sol.-Al) state, but the lower limit thereof is limited to 0.01% by weight, and when excessively added, the amount of inclusions in the steel is increased, leading to surface defects and degrading workability. Therefore, the upper limit is limited to 0.04% by weight.
  • Nitrogen (N) is an element that is useful in reinforcing materials while being in a solid solution in steel, but since it is a main element causing aging, it is necessary to manage it to a certain amount or less to secure workability, and therefore, the upper limit of addition is limited to 40 ppm. On the other hand, if the addition amount of nitrogen (N) is less than 1 ppm, sufficient rigidity cannot be obtained, and the site for forming precipitates is reduced, so the lower limit of the addition is limited to 1 ppm, and the content is 1 to 40 ppm.
  • Boron (B) is a grain boundary strengthening element, which improves the fatigue properties of welds, prevents grain boundary brittleness of phosphorus (P), and improves high temperature ductility in steels with high content of aluminum (Al) and silicon (Si).
  • boron (B) increases the quenching of the steel, and has the effect of delaying the perlite transformation of austenite and the ferrite reverse transformation of martensite by diffusing to grain boundaries during heat treatment.
  • the boron (B) is added in an excessive amount, the solid solution boron is increased to reduce the elongation, and boron (B) can diffuse on the surface to reduce the plating property, the addition amount is 1 to 60ppm.
  • boron (B) is an element that combines with a solid solution element in steel to improve the aging property and also increases the strength of the material even by adding a small amount as a hardenability enhancing element. At least 1 ppm addition is required. However, if the content exceeds 60ppm, not only does it cause deterioration of material and grain boundary cracking, but also roughens the surface of the hot-rolled steel sheet. Therefore, the content is limited to 1 to 60ppm.
  • boron (B) is added to the low carbon steel of the above-described components, BN is precipitated using MnS precipitate as a seed during the performance and hot rolling, and Precipitation of cementite is encouraged, resulting in reduction of solid solution nitrogen (N) and carbon (C) through refinement and randomization of cementite.
  • N solid solution nitrogen
  • C carbon
  • the precipitation of BN occurs in finishing rolling, in the case of the present invention, the addition of boron (B) enables the BN precipitation at a lower finishing rolling temperature than before, thereby producing a larger amount of BN precipitates than before.
  • the rolled steel sheet according to the present invention can be suppressed from the generation of grains by grain refinement. That is, in the rolled steel sheet according to the present invention, as BN is precipitated at the austenite grain boundary through addition of boron (B), the grain boundary stabilization effect is obtained, and the ferrite transformation is also suppressed in the austenite region. The occurrence of the mixing can be suppressed.
  • the low carbon steel containing a small amount of manganese (Mn) increases the Ar 3 transformation point to promote mixing, and the addition of the transformation delay element is necessary to prevent such mixing.
  • Rolled steel sheet of the present invention can be suppressed by the addition of a certain amount of boron (B) which can play a role of transformation delay element to the components of low carbon steel, as a result, the rolled steel sheet according to the present invention through the suppression of such Silver material aging and poor machining can be improved.
  • the rolled steel sheet according to the present invention adds boron (B) and nitrogen (N) in the steel component to satisfy the conditions of 0.2 ⁇ [B / N] ⁇ 1.1 in order to secure appropriate processing characteristics. This is because if the B / N value is less than 0.2, the bending resistance at room temperature is deteriorated due to excessive solid solution in steel, and the grain restraining effect is insufficient at high temperature, while if the B / N value is over 1.1, the ductility is lowered and the workability is reduced. to be. Therefore, the rolled steel sheet according to the present invention limits the value of B / N in the range 0.2 to 1.1.
  • an embodiment of the present invention performs a hot rolling process in the austenitic region for the steel slab made of the above-described composition components and a certain amount of boron (B) is added.
  • finishing rolling is carried out at a temperature of 850 ⁇ 950 °C, this is, when the finishing rolling temperature is less than 850 °C as the hot rolling is finished in the low temperature region, the crystallization of the grain proceeds rapidly, leading to the deterioration of rollability and workability.
  • the finishing rolling temperature is higher than 950 ° C, since uniform hot rolling is not performed throughout the thickness, grain refinement is not sufficiently achieved, resulting in a drop in impact toughness due to grain coarsening. Therefore, in the Example of this invention, a finishing rolling temperature shall be 850-950 degreeC.
  • Cooling is carried out at the cooling rate of 60-120 degreeC per second in the run-out table (ROT) of steel by which it rolled.
  • ROT run-out table
  • the winding of the hot rolled steel sheet proceeds at a temperature of 540 to 640 ° C.
  • the coiling temperature in the hot rolling process is a temperature for obtaining a structure capable of securing the optimum mechanical properties after the subsequent cold rolling and continuous annealing step, in the case of the rolled steel sheet according to the present invention, if the coiling temperature is less than 540 °C Cold rolling is difficult due to the formation of bainite or martensite structure, and if the temperature exceeds 640 ° C., the final microstructure is coarsened to reduce workability and corrosion resistance, and it is difficult to manufacture a steel sheet having sufficient strength. Therefore, the coiling temperature of the hot rolled steel sheet in the embodiment of the present invention is 540 ⁇ 640 °C.
  • a pickling step and a cold rolling step are sequentially performed on the hot rolled steel sheet obtained through the hot rolling process, and then a continuous annealing step and temper rolling are performed to produce a rolled steel sheet according to the present invention, which is made of a cold rolled steel sheet based on a low carbon steel. do.
  • cold rolling advances with 50-90% of cold rolling rates.
  • Cold rolling deforms the hot rolled tissue, where the strain energy that deforms the tissue becomes energy in subsequent continuous annealing, that is, recrystallization.
  • the cold rolling is less than 50% cold rolling, the effect of the deformation of the tissue is small.
  • the cold rolling is more than 90%, the cold rolling process itself is not very difficult, and the precipitates produced in the hot rolled steel sheet are cold rolled.
  • the development of (100) texture in the early stages of subsequent recrystallization during decomposing deteriorates the drawability, cracks at the edges of the steel sheet, and the probability of breakage in the steel sheet is high. Accordingly, cold rolling controls the cold reduction rate at 50 to 90%.
  • Continuous annealing is performed for 10 to 120 seconds in the temperature range of 720 to 810 ° C.
  • the rolled steel sheet to which boron (B) is added precipitates most of the nitrogen (N) to BN in the hot rolling process, grains are coarsened by decreasing AlN precipitation in the continuous annealing step, and coarsening of grains is lowered in yield point (YP)
  • the annealing temperature must be lowered, and the lowering of the annealing temperature leads to an improvement in productivity.
  • heat treatment below 720 ° C. results in insufficient recrystallization
  • heat treatment above 810 ° C. causes material degradation due to high temperature annealing.
  • the continuous annealing temperature is set to 720 to 810 ° C.
  • Temper rolling is carried out to satisfy the elongation of 0.7 to 1.6% with respect to the material thickness 0.4 ⁇ T ⁇ 2.4, but in the range satisfying the elongation by material thickness as shown in the following Equation 1, Equation 2, Equation 3 and Equation 4. .
  • temper rolling in the embodiment of the present invention is carried out by setting the elongation reference for each material thickness based on the relationship 1, relationship 2, relationship 3 and relationship 4.
  • the steel sheet specimens of the low carbon steel base were prepared with the compositions shown in Table 1 and the operating conditions shown in Table 2, for each specimen The mechanical properties are listed in Table 3.
  • Inventive Examples 1 to 4 are low carbon steel base rolled steel sheets to which boron (B) is added, and Comparative Examples 1 to 4 are low carbon steel base rolled steel sheets to which boron (B) is not added. .
  • Inventive Examples 1 to 4 and Comparative Examples 1 to 4 satisfy all of the operating conditions according to the embodiment of the present invention.
  • Inventive Examples 1 to 4 exhibited good aging resistance because boron (B) was added to the components of low carbon steel so that no yield point-stretching and no bending occurred during processing. Good workability and paintability, such as no cracking, occurred during bending.
  • Comparative Example 1 showed a result that the change in yield point-stretch occurred, the workability and paintability is normal, and the aging resistance is poor. Comparative Example 2 In addition, due to the change in yield point-stretch, poor workability and paintability and normal aging resistance were shown. In Comparative Example 3, no change in yield point-stretching occurred, but the aging resistance and workability were normal, and the paintability was poor. In Comparative Example 4, due to the change in yield point-stretch, the workability was poor, and the aging resistance and paintability were normal.
  • the low carbon steel-based rolled steel sheet to which boron (B) is added is improved in material aging and processing defects as compared with the general low carbon steel-based rolled steel sheet without boron. can see.
  • FIG. 1 and 2 are micrographs showing the structure of the rolled steel sheet made of a general low carbon steel without boron (B) added and the rolled steel sheet made of boron (B) -added low carbon steel according to the present invention, respectively,
  • FIG. And Fig. 4 shows the yield point (YP) and the yield-point (YP-) of the rolled steel sheet made of boron (B) -added low carbon steel and the rolled steel sheet made of ordinary low-carbon steel without boron (B), respectively prepared according to the present invention.
  • EL graphs.
  • the particle size index (FGS) is 10 to 11, that is, the average diameter of the particles is 0.007 to 0.011 mm. It can be seen that a coarse structure of coarse grains having an average number of fragments on the measurement line of 100 to 141 / mm occurred.
  • the boron (B) is added, in the case of the rolled steel sheet made of low carbon steel according to the present invention manufactured according to the optimized operating conditions, the particle size index is 9 to 10, that is, the average diameter of the particles Is 0.011 to 0.015 mm and the average number of sections on the measurement line is 70.7 to 100 / mm, similar to the rolled steel sheet without boron (B) added, but it can be seen that the grains are uniformly formed with little mixed structure. .
  • the rolled steel sheet made of general low carbon steel without boron exhibits a yield point (YP) of about 280 and a yield point-stretching (YP-EL) of about 0.31. have.
  • the FGS is fine and the size of the grains is uniform without generation of a mixed structure.
  • the yield point (YP) 200 to 250, preferably 240
  • the yield point-elongation (YP-EL) 0.01 to 0.05, preferably 0.03, are lower than that of the general low carbon steel without B).
  • the rolled steel sheet according to the present invention manufactured according to the optimized operating conditions with boron (B) added through the growth of uniform grains. It can be seen that it has a relatively low yield point (YP) and yield point-stretching (YP-EL), from this result, it can be seen that the rolled steel sheet according to the present invention is improved in material aging and workability by reducing the potential adhesion.
  • YP yield point
  • YP-EL yield point-stretching
  • the rolled steel sheet made of low carbon steel according to the present invention in which boron (B) is added and manufactured through hot rolling and cold rolling processes according to optimized operating conditions, has good properties in both workability, aging resistance, paintability and corrosion resistance. And, material aging and processing failure is improved, and as a result, the present invention can provide a high value-added rolled steel sheet having excellent material properties and workability used in home appliances and automobiles.

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Abstract

The present invention provides a rolled steel sheet and a production method therefor. The rolled steel sheet according to the present invention consists of low-carbon steel containing 0.035-0.08 wt% of carbon (C), 0.01-0.03 wt% of silicon (Si), 0.15-0.5 wt% of manganese (Mn), 0.001-0.015 wt% of phosphorus (P), 0.001-0.015 wt% of sulfur (S), 0.01-0.04 wt% of solution aluminum (sol. Al), and 1-40 ppm of nitrogen (N) with the remainder being iron (Fe) and other inevitable impurities, wherein a steel slab having 1-60 ppm of boron (B), which satisfies the condition 0.2≤[B/N]≤1.1, added thereto is subjected to finish rolling at 850-950℃, wound at 540-640℃, then continuously annealed at 720-810℃, and temper-rolled satisfying the condition of an elongation of 0.7-1.6% with respect to a material thickness of 0.4≤T＜2.4, thereby uniformly forming crystal grains having a grain size (FGS) of 9-10.

Description

[규칙 제26조에 의한 보정 13.10.2014]　압연강판 및 그의 제조방법13.10.2014 Corrected in accordance with Rule 26.Rolled steel sheet and manufacturing method thereof
본 발명은 압연강판 및 그의 제조방법에 관한 것으로, 더욱 상세하게는, 강 성분 및 조업조건을 최적화하여 재질 시효 및 가공성을 개선한 저탄소강 베이스의 압연강판 및 그의 제조방법에 관한 것이다.The present invention relates to a rolled steel sheet and a method for manufacturing the same, and more particularly, to a low carbon steel base rolled steel sheet and a method for producing the same by optimizing the steel components and operating conditions to improve material aging and workability.
가전 및 자동차 등에 사용되는 강판의 경우, 시효에 의한 가공 결함 발생 방지 특성이 있어야 하기 때문에 가전 및 자동차에 사용되는 강판으로서는 내시효성이 우수한 탄질화물 형성 원소를 첨가한 극저탄소강과 같은 소재들이 사용되어 왔다. In the case of steel sheets used in home appliances and automobiles, there must be a property of preventing processing defects due to aging, and thus, steel sheets used in home appliances and automobiles have been used as materials such as ultra low carbon steel containing carbonitride-forming elements having excellent aging resistance. .
그리고, 가전 및 자동차 등에 사용되는 강판은 필수적으로 내꺽임성 및 가공성 등이 요구되며, 자동차용 강판의 경우 외기 조건에 의해 강판이 산화되는 것을 방지함은 물론 사용자가 원하는 표면 색상을 얻기 위해 페인트 등의 유기물이 도장되므로 강판의 표면 특성 관리가 도장성 측면에서 중요한 관리 인자가 되고 있다.In addition, steel sheets used in home appliances and automobiles are required for bending resistance and workability, etc., and in the case of automotive steel sheets, the steel sheet is prevented from being oxidized due to outside conditions and paint is used to obtain a desired surface color. Since organic matter is coated, management of surface properties of the steel sheet has become an important management factor in terms of paintability.
꺾임(Fluting)은 가공시의 가공부가 다이아몬드 형상으로 꺾이는 현상을 의미하는 것으로, 꺾임이 발생하면, 성형부의 형상 유지가 곤란하기 때문에 실제 공정에서 이러한 꺾임은 엄격히 제한되어야 한다.Flucting refers to a phenomenon in which a processed portion at the time of machining is bent into a diamond shape, and when the bending occurs, it is difficult to maintain the shape of the molded part, and thus the bending should be strictly limited in the actual process.
한편, 꺾임의 원인이 되는 고용원소에 의한 시효 현상은 실질적으로 제한하기 곤란하다. 따라서, 기존에는 제강 단계에서의 고청정화를 통해 제한하거나, 티타늄(Ti) 및 니오븀(Nb) 등과 같은 탄질화물 형성원소를 첨가하여 고용원소들을 고착시키는 방법으로 제한하고 있다. On the other hand, it is difficult to substantially limit the aging phenomenon due to the employment element that causes the bending. Therefore, conventionally, it is limited by high purification in the steelmaking step, or by adding carbonitride-forming elements such as titanium (Ti) and niobium (Nb) to fix solid solutions.
그런데, 탄질화물 형성원소의 첨가는 꺾임과 같은 가공 결함의 억제에는 도움이 되지만, 고청정화를 위한 제강시간을 증가시킴에 따라 생산성 저하를 유발하고, 고가의 합금원소 첨가에 따른 제조원가 상승의 요인이 된다. 특히, 저탄소강에서 꺾임을 억제하는 것이 매우 곤란한 것으로 알려져 있는바, 이러한 저탄소강 베이스의 강판을 가전 및 자동차 등과 같이 엄격한 형상 동결성 및 가공성이 요구되는 제품에 적용하는 경우, 가공시 꺾임을 억제할 수 있는 방안 수립이 절실히 필요하다. By the way, the addition of carbonitride-forming elements is helpful in suppressing processing defects such as bending, but the increase of steelmaking time for high cleanliness causes a decrease in productivity, and the increase in manufacturing cost due to the addition of expensive alloying elements do. In particular, it is known that it is very difficult to suppress the bending in low carbon steel, and when the low carbon steel-based steel sheet is applied to a product requiring strict shape freezing and workability such as home appliances and automobiles, it is possible to suppress the bending during processing. There is an urgent need to establish a plan.
아울러, 최종 제품의 형상 동결성을 향상시키면서 생산성을 높이기 위해서는 소재 측면에서 상술한 내시효성에 의한 꺾임 방지뿐만 아니라, 플랜지성, 밴딩성 및 드로잉성과 같은 다양한 가공 특성이 함께 요구된다. 또한, 이들 제품들은 외부 환경에 노출되어 있어서 내후성 향상을 위해 소재 표면에 페인트 등의 유기물을 도장하는 작업이 이루어져야 하므로, 이와 같은 특성 확보를 위하여 소재 측면에서 도장성 확보가 가능한 강판의 개발이 요구되고 있다.In addition, in order to improve productivity while improving the shape freezing property of the final product, not only the bending prevention by the above-described aging resistance in terms of material, but also various processing characteristics such as flangeability, bending property and drawing property are required. In addition, since these products are exposed to the external environment, the work of coating organic materials such as paint on the surface of the material must be performed to improve weather resistance. Therefore, development of a steel sheet capable of securing paintability in terms of material is required to secure such characteristics. have.
예를 들어, 일본공개특허 제1989-282420호(발명의 명칭: 가공용 열연강판의 제조방법 및 열연강판의 가공열처리법)에는 자동차 또는 산업기기용 고강도 부재에 적합한 강판의 제조를 위해서 극저탄소강 베이스에 티타늄(Ti) 및 니오븀(Nb)과 일부 희토류 원소 등을 첨가하여 가공성 및 시효성이 우수한 열연강판을 제조하는 방법이 개시되어 있다. For example, Japanese Laid-Open Patent Publication No. 1989-282420 (name of the invention: a method of manufacturing a hot rolled steel sheet for processing and a process heat treatment method of a hot rolled steel sheet) includes an ultra low carbon steel base for producing a steel sheet suitable for a high strength member for automobile or industrial equipment. A method for producing a hot rolled steel sheet excellent in workability and aging is disclosed by adding titanium (Ti), niobium (Nb), and some rare earth elements.
그러나, 이 방법은 전술한 바와 같이 탄질화물 형성 원소의 첨가에 의해 꺾임과 같은 가공 결함의 억제에는 도움이 되지만, 고청정화를 위한 제강시간 증가에 따른 생산성 저하 및 고가의 합금원소 첨가에 의한 제조원가 상승의 문제점이 있다.However, this method helps to suppress processing defects such as bending by adding carbonitride-forming elements as described above, but decreases productivity due to increased steelmaking time for high clarity and increases production cost by adding expensive alloying elements. There is a problem.
다른 예로서, 한국공개특허 제1996-23130호(발명의 명칭: 내시효성이 우수한 고가공용 열연강판의 제조방법)에는 극저탄소 알루미늄 킬드강에 탄질화물 형성원소인 지르코늄 등을 미량 첨가하고, 그리고, Ar3 변태점 이상의 온도 범위에서 열간압연하여 페라이트 결정립을 조대화시키는 것에 의해 내시효성을 향상시키는 방법이 개시되어 있다. As another example, Korean Patent Publication No. 1996-23130 (name of the invention: a method for manufacturing a high-temperature hot rolled steel sheet having excellent aging resistance) adds a trace amount of zirconium, a carbonitride-forming element, to ultra-low carbon aluminum killed steel, A method of improving aging resistance by hot rolling in a temperature range above the Ar 3 transformation point and coarsening ferrite grains is disclosed.
그러나, 이 방법은 시효성을 높이기 위하여 지르코늄과 같은 특수원소의 첨가가 필요하므로, 제강 작업성의 악화 및 제조원가 상승의 문제가 있고, 또한, 소재 강도가 낮아짐에 따라 형상 동결성이 나빠지는 문제점이 있다.However, since this method requires the addition of special elements such as zirconium in order to increase aging, there is a problem of deterioration in steelmaking workability and an increase in manufacturing cost, and a problem of deterioration in shape freezing as the material strength is lowered. .
또 다른 예로서, 일본공개특허 제2008-190008호(발명의 명칭: 내시효성이 우수한 열연강판의 제조방법)에는 중량%로, 탄소(C): 0.04∼0.25%, 규소(Si): 0.001∼0.5%, 망간(Mn): 0.05∼1.5%, 인(P): 0.09% 이하, 황(S): 0.015% 이하, 알루미늄(Al): 0.01∼0.08%, 질소(N):0.0005∼0.015%을 함유하고 잔부 철(Fe) 및 기타 불가피한 불순물로 이루어지는 강 슬라브를 열간압연하고, 평균 냉각속도 60℃/s 이상으로 400℃ 미만까지 냉각하며, 권취한 후에 t/R≥0.0055(t는 판 두께, R은 롤 직경)을 만족하는 소경 롤을 이용하여 신장률 0.1∼1.0%의 조질 압연(Skin Pass Mill; SPM)을 행하는 방법이 개시되어 있다. As another example, Japanese Laid-Open Patent Publication No. 2008-190008 (name of the invention: a method for producing a hot rolled steel sheet having excellent aging resistance) in terms of weight%, carbon (C): 0.04-0.25%, silicon (Si): 0.001-- 0.5%, manganese (Mn): 0.05-1.5%, phosphorus (P): 0.09% or less, sulfur (S): 0.015% or less, aluminum (Al): 0.01-0.08%, nitrogen (N): 0.0005-0.015% Hot-rolled steel slabs containing iron and Fe and other unavoidable impurities, cooled to below 400 ° C with an average cooling rate of 60 ° C / s or more, and after winding t / R≥0.0055 (t A method of performing a temper rolling (Skin Pass Mill; SPM) having an elongation rate of 0.1 to 1.0% using a small diameter roll satisfying a roll diameter) is disclosed.
그러나, 이 방법은 권취온도를 400℃ 미만까지 낮추기 때문에 폭 방향 온도의 불균일에 의해 저온 석출물이 생성 거동에 차이를 나타내어 재질 편차가 유발되며, 이로 인해, 형상 불량, 권취 불량 및 후공정 작업성이 저하되는 문제점이 있다. 더욱이, 표면 가동 전위 유발을 위해 강판의 두께에 따라 롤 직경을 일일이 제어해야 하므로, 상용 조업라인과 같이 다양한 크기의 소재를 생산하는 경우에는 적용하기 어려운 문제점이 있다.However, since this method lowers the coiling temperature to less than 400 ° C., the low temperature precipitates show a difference in the production behavior due to the nonuniformity of the width direction, resulting in a material deviation, resulting in poor shape, poor winding and post process workability. There is a problem of deterioration. In addition, since the roll diameter must be controlled in accordance with the thickness of the steel sheet to induce surface movable potential, there is a problem that is difficult to apply when producing a variety of sizes of materials, such as commercial operation line.
본 발명은 강 성분 및 조업조건을 최적화하여 재질 시효 및 가공성을 개선한 저탄소강 베이스의 압연강판 및 그 제조방법을 제공함에 그 목적이 있다.It is an object of the present invention to provide a low carbon steel base rolled steel sheet and a method of manufacturing the same, which optimizes steel components and operating conditions to improve material aging and workability.
본 발명의 일 견지에 따른 압연강판은, 중량%로, 탄소(C): 0.035∼0.08, 실리콘(Si): 0.01∼0.03, 망간(Mn): 0.15∼0.5, 인(P): 0.001∼0.015, 황(S): 0.001∼0.015, 솔루션-알루미늄(Sol.-Al): 0.01∼0.04, 질소(N) 1∼40ppm, 잔부 철(Fe) 및 기타 불가피한 불순물을 함유한 저탄소강으로 이루어지고 보론(B)이 0.2≤[B/N]≤1.1의 조건을 만족하는 범위에서 1∼60ppm이 첨가되어 입도지수(FGS: Ferrite Grain Size)가 9∼10㎛인 결정립들이 균일하게 형성된 것을 특징으로 한다. Rolled steel sheet according to one aspect of the present invention, in weight%, carbon (C): 0.035 to 0.08, silicon (Si): 0.01 to 0.03, manganese (Mn): 0.15 to 0.5, phosphorus (P): 0.001 to 0.015 , Sulfur (S): 0.001 to 0.015, solution-aluminum (Sol.-Al): 0.01 to 0.04, nitrogen (N) 1 to 40 ppm, low carbon steel containing residual iron (Fe) and other unavoidable impurities 1 to 60 ppm is added in a range where (B) satisfies the condition of 0.2 ≦ [B / N] ≦ 1.1, so that crystal grains having a particle size index (FGS: Ferrite Grain Size) of 9 to 10 μm are uniformly formed. .
본 발명에 따른 압연강판은 200∼250의 항복점(YP)과 0.01∼0.05의 항복점-연신(YP-EL)을 갖는 것을 특징으로 한다. The rolled steel sheet according to the present invention is characterized by having a yield point (YP) of 200 to 250 and a yield point-stretching (YP-EL) of 0.01 to 0.05.
본 발명에 따른 압연강판에 있어서, 상기 저탄소강은 소재 두께 0.4≤T＜2.4에 대하여 0.7∼1.6%의 연신율을 만족한다.In the rolled steel sheet according to the present invention, the low carbon steel satisfies an elongation of 0.7 to 1.6% with respect to the material thickness 0.4≤T <2.4.
본 발명의 다른 견지에 따른 압연강판의 제조방법은, 중량%로, 탄소(C): 0.035∼0.08, 실리콘(Si): 0.01∼0.03, 망간(Mn): 0.15∼0.5, 인(P): 0.001∼0.015, 황(S): 0.001∼0.015, 솔루션-알루미늄(Sol.-Al): 0.01∼0.04, 질소(N) 1∼40ppm, 잔부 철(Fe) 및 기타 불가피한 불순물을 함유하고, 보론(B) 1∼60ppm이 첨가된 저탄소강으로 이루어진 강 슬라브를 형성하는 단계; 상기 강 슬라브에 대해 사상 압연, 냉각 및 권취 단계들을 포함하는 열연 공정을 진행하여 열연강판을 제조하는 단계; 상기 열연강판에 대해 산세, 냉간압연 및 연속소둔 단계들을 차례로 진행하여 냉연강판을 제조하는 단계; 및 상기 연속소둔 처리된 냉연강판을 소재 두께 0.4≤T＜2.4에 대하여 0.7∼1.6%의 연신율을 만족하는 조건으로 조질 압연하는 단계;를 포함하는 것을 특징으로 한다.The manufacturing method of the rolled steel sheet which concerns on another aspect of this invention is carbon (C): 0.035-0.08, silicon (Si): 0.01-0.03, manganese (Mn): 0.15-0.5, phosphorus (P): 0.001-0.015, sulfur (S): 0.001-0.015, solution-aluminum (Sol.-Al): 0.01-0.04, nitrogen (N) 1-40 ppm, residual iron (Fe) and other unavoidable impurities, and boron ( B) forming a steel slab made of low carbon steel added with 1 to 60 ppm; Manufacturing a hot rolled steel sheet by performing a hot rolling process including finishing rolling, cooling, and winding steps on the steel slab; Manufacturing a cold rolled steel sheet by sequentially performing steps of pickling, cold rolling, and continuous annealing of the hot rolled steel sheet; And tempering rolling the continuously annealed cold rolled steel sheet under conditions satisfying an elongation of 0.7 to 1.6% with respect to a material thickness of 0.4 ≦ T <2.4.
본 발명에 따른 압연강판의 제조방법에 있어서, 상기 사상 압연은 850∼950℃ 온도 범위에서 진행하는 것을 특징으로 한다. In the method for manufacturing a rolled steel sheet according to the present invention, the finishing rolling is characterized in that it proceeds in a temperature range of 850 ~ 950 ℃.
본 발명에 따른 압연강판의 제조방법에 있어서, 상기 냉각은 초당 60∼120℃의 냉각속도로 진행하는 것을 특징으로 한다. In the method of manufacturing a rolled steel sheet according to the present invention, the cooling is characterized in that it proceeds at a cooling rate of 60 ~ 120 ℃ per second.
본 발명에 따른 압연강판의 제조방법에 있어서, 상기 권취는 540∼640℃의 온도 범위에서 진행하는 것을 특징으로 한다. In the manufacturing method of the rolled steel sheet which concerns on this invention, the said winding is characterized by advancing in the temperature range of 540-640 degreeC.
본 발명에 따른 압연강판의 제조방법에 있어서, 상기 냉간압연은 냉간압하율을 50∼90%로 하여 진행하는 것을 특징으로 한다. In the method for manufacturing a rolled steel sheet according to the present invention, the cold rolling is characterized in that the cold rolling ratio is set to 50 to 90%.
본 발명에 따른 압연강판의 제조방법에 있어서, 상기 연속소둔은 720∼810℃의 온도범위에서 실시하는 것을 특징으로 한다. In the method for producing a rolled steel sheet according to the present invention, the continuous annealing is characterized in that carried out in a temperature range of 720 ~ 810 ℃.
본 발명에 따른 압연강판의 제조방법에 있어서, 상기 조질 압연은 다음의 소재 두께별 연신율을 만족하는 조건으로 진행하는 것을 특징으로 한다. In the method for manufacturing a rolled steel sheet according to the present invention, the temper rolling is characterized in that the progress to the conditions that satisfy the elongation according to the following material thickness.
(관계식 1) 0.4≤T＜0.6에 대하여 0.9±0.2%의 연신율Elongation of 0.9 ± 0.2% for 0.4 ≦ T <0.6
(관계식 2) 0.6≤T＜0.9에 대하여 1.0±0.2%의 연신율Elongation of 1.0 ± 0.2% for 0.6≤T <0.9
(관계식 3) 0.9≤T＜1.1에 대하여 1.1±0.2%의 연신율(Equation 3) Elongation of 1.1 ± 0.2% for 0.9≤T <1.1
(관계식 4) 1.1≤T＜2.4에 대하여 1.4±0.2%의 연신율(Equation 4) Elongation of 1.4 ± 0.2% for 1.1≤T <2.4
본 발명은 저탄소강의 성분에 일정량의 보론(B)을 첨가하여 강 슬라브를 만들고, 이 강 슬라브를 열연 및 냉연 처리함에 있어서 열연 공정에서의 사상 압연 및 권취, 그리고, 냉연 공정에서의 연속소둔 및 조질 압연의 조업조건을 최적화한다. The present invention forms a steel slab by adding a certain amount of boron (B) to the components of low carbon steel, and in the hot rolling and cold rolling treatment of the steel slab, finishing rolling and winding in the hot rolling process, and continuous annealing and tempering in the cold rolling process Optimize rolling conditions.
이렇게 함에 따라, 본 발명은 고용원소들의 석출을 통해 재질 시효와 가공성을 개선할 수 있으며, 그래서, 본 발명은 가전 및 자동차 등에 사용되는 고부가가치의 압연강판을 제공할 할 수 있다.In this way, the present invention can improve the material aging and workability through the precipitation of the employment elements, so, the present invention can provide a high value-added rolled steel sheet used in home appliances and automobiles.
도 1은 보론(B)이 첨가되지 않은 일반적인 저탄소강으로 이루어진 압연강판의 조직을 보여주는 현미경 사진이다. 1 is a micrograph showing the structure of a rolled steel sheet made of a general low carbon steel without boron (B) added.
도 2는 본 발명에 따른 보론(B) 첨가 저탄소강으로 이루어진 압연강판의 조직을 보여주는 현미경 사진이다.Figure 2 is a micrograph showing the structure of the rolled steel sheet made of boron (B) addition low carbon steel according to the present invention.
도 3은 본 발명에 따라 제조된 보론(B) 첨가 저탄소강으로 이루어진 압연강판 및 보론(B)이 첨가되지 않은 일반적인 저탄소강으로 이루어진 압연강판의 항복점(YP) 그래프이다.3 is a graph showing the yield point (YP) of a rolled steel sheet made of boron (B) -added low carbon steel prepared according to the present invention and a rolled steel sheet made of ordinary low carbon steel without boron (B) added thereto.
도 4는 본 발명에 따라 제조된 보론(B) 첨가 저탄소강으로 이루어진 압연강판 및 보론(B)이 첨가되지 않은 일반적인 저탄소강으로 이루어진 압연강판의 항복점-연신(YP-EL) 그래프이다.4 is a yield-stretch (YP-EL) graph of a rolled steel sheet made of boron (B) -added low carbon steel prepared according to the present invention and a rolled steel sheet made of ordinary low carbon steel without boron (B).
이하, 본 발명에 따른 압연강판 및 그 제조방법의 실시 예를 상세하게 설명하도록 한다. Hereinafter, an embodiment of a rolled steel sheet and a method of manufacturing the same according to the present invention will be described in detail.
본 발명의 실시 예에 따른 압연강판은, 중량%로, 탄소(C): 0.035∼0.08, 실리콘(Si): 0.01∼0.03, 망간(Mn): 0.15∼0.5, 인(P): 0.001∼0.015, 황(S): 0.001∼0.015, 솔루션-알루미늄(Sol.-Al): 0.01∼0.04, 질소(N) 1∼30ppm, 잔부 철(Fe) 및 기타 불가피한 불순물을 함유하고, 보론(B) 1∼60ppm을 첨가하되 보론(B) 및 질소(N)가 0.2≤[B/N]≤1.1의 조건을 만족하도록 첨가된 저탄소강으로 이루어질 수 있다. Rolled steel sheet according to an embodiment of the present invention, in weight percent, carbon (C): 0.035 to 0.08, silicon (Si): 0.01 to 0.03, manganese (Mn): 0.15 to 0.5, phosphorus (P): 0.001 to 0.015 , Sulfur (S): 0.001-0.015, solution-aluminum (Sol.-Al): 0.01-0.04, nitrogen (N) 1-30 ppm, residual iron (Fe) and other unavoidable impurities, boron (B) 1 It may be made of low carbon steel added to the addition of ~ 60ppm, but added to meet the conditions of boron (B) and nitrogen (N) of 0.2≤ [B / N] ≤1.1.
이와 같은 본 발명의 실시 예에 따른 압연강판에서의 각 성분의 기능 및 함량 범위를 간략하게 설명하면 다음과 같다. When briefly explaining the function and content range of each component in the rolled steel sheet according to an embodiment of the present invention as follows.
탄소(C)는 강판의 강도 향상을 위해 첨가되는 원소로서, 함량이 증가할수록 인장 및 항복강도는 증가하지만, 과잉 첨가되면 소재의 가공성이 저하되고 내꺾임성이 저하되므로 그 상한을 0.08 중량%로 제한한다. 반면, 탄소(C) 함량이 0.035 중량% 미만이면, 제강시의 탈탄을 위해 추가의 조업시간이 필요할 뿐만 아니라 목표로 하는 강도 등의 안정적인 재질 확보가 곤란한 문제가 있다. 따라서, 탄소(C)의 함량은 0.035∼0.08 중량%로 한다. Carbon (C) is an element added to improve the strength of the steel sheet. As the content increases, the tensile and yield strength increases, but when added excessively, the upper limit is 0.08% by weight because the workability of the material decreases and the bending resistance decreases. Restrict. On the other hand, when the carbon (C) content is less than 0.035% by weight, not only additional operating time is required for decarburization during steelmaking, but also it is difficult to secure stable materials such as target strength. Therefore, the content of carbon (C) is 0.035 to 0.08 wt%.
실리콘(Si)은 강판의 연성을 저하하지 않으면서 강도를 향상시킬 수 있는 유용한 원소이다. 실리콘(Si)은 페라이트에 고용되는 페라이트 안정화 원소로서 강도에 기여하며, 미변태 오스테나이트로의 탄소 농화를 조장하여 마르텐사이트 형성을 촉진시킨다. 이러한 실리콘(Si)을 0.01 중량% 미만으로 첨가할 경우에는 마르텐사이트 분율을 확보하는데 어려움이 있으며, 반면, 과량으로 첨가할 경우에는 표면 결함을 발생시키고 도금 부착성을 저하시키므로 그 상한을 0.03 중량%로 제한한다. Silicon (Si) is a useful element that can improve the strength without lowering the ductility of the steel sheet. Silicon (Si) contributes to strength as a ferrite stabilizing element employed in ferrite and promotes martensite formation by encouraging carbon enrichment with unmodified austenite. When the silicon (Si) is added in less than 0.01% by weight, it is difficult to secure the martensite fraction, whereas when added in excess, the upper limit is 0.03% by weight because it causes surface defects and degrades the coating adhesion. Limited to
망간(Mn)은 고용 강화 원소로 널리 사용되는 원소로서, 강의 강도를 높이고 열간 가공성을 향상시키는 중요한 원소이지만, MnS 형성에 의한 소재의 연성 및 가공성을 저해하는 원소이다. 이러한 망간(Mn)은 그 함량이 적으면 가공성은 개선되지만 강도 확보가 곤란하므로, 목표 강도를 확보하기 위해 0.15 중량% 이상 첨가하여야 한다. 반면, 망간(Mn)이 과다 첨가되면 합금원소 다량 첨가에 의한 경제성 저하 및 중심 편석 발생 요인이 될 뿐만 아니라 용접성을 악화시키므로, 그 상한은 0.5 중량%로 제한한다. Manganese (Mn) is an element widely used as a solid solution strengthening element. It is an important element for increasing the strength of steel and improving hot workability, but is an element that inhibits the ductility and workability of a material due to MnS formation. If the content of the manganese (Mn) is small, the workability is improved, but it is difficult to secure the strength, it should be added 0.15% by weight or more to secure the target strength. On the other hand, excessive addition of manganese (Mn) not only causes economic deterioration and central segregation caused by the addition of a large amount of alloying elements, but also deteriorates weldability, so the upper limit is limited to 0.5% by weight.
인(P)은 강의 강도 향상 및 내식성을 향상시키는 역할을 하는 원소로서, 이러한 특성을 확보하기 위해서는 다량 첨가되는 것이 바람직하지만, 주조시의 중심 편석을 일으키는 원소이므로 다량 첨가할 경우 가공성을 저하시키는 요인이 되므로 그 함량은 0.015 중량% 이하로 제한한다. 반면, 인(P)의 함량이 0.001 중량% 미만이면 강도 및 내식성 확보가 곤란하므로 그 함량을 0.001∼0.015 중량%로 한다. Phosphorus (P) is an element that serves to improve the strength and corrosion resistance of steel, and it is preferable to add a large amount in order to secure such characteristics, but the element that causes central segregation during casting is a factor that lowers workability when added in large quantities. This content is limited to 0.015% by weight or less. On the other hand, if the content of phosphorus (P) is less than 0.001% by weight, it is difficult to secure strength and corrosion resistance, so the content is 0.001 to 0.015% by weight.
황(S)은 강 중에서 망간(Mn)과 결합해 부식 개시점 역할을 하는 비금속 개재물을 형성할 뿐만 아니라 적열 취성의 요인으로 작용하므로, 가능한 그 함량을 감소시키는 것이 바람직하다. 따라서, 황(S)의 함량은 0.001∼0.015 중량%로 한다.Sulfur (S) combines with manganese (Mn) in steel to form non-metallic inclusions that serve as a starting point for corrosion, as well as acting as a factor of red brittleness, so it is desirable to reduce its content as much as possible. Therefore, the content of sulfur (S) is 0.001 to 0.015% by weight.
알루미늄(Al)은 일반적으로 용강 탈산을 위해 첨가되는 원소이지만, 강 중에서 고용원소와 결합하여 시효 특성을 개선하는 측면이 있다. 따라서, 알루미늄(Al)은 솔루션-알루미늄(Sol.-Al) 상태로 첨가하되, 그 하한을 0.01 중량%로 제한하고, 과잉 첨가되면 강 중의 개재물량을 증가시켜 표면 결함을 유발할 뿐만 아니라 가공성을 저하하므로, 그 상한은 0.04 중량%로 제한한다.Aluminum (Al) is generally an element added for deoxidation of molten steel, but has an aspect of improving aging characteristics by combining with solid solution in steel. Therefore, aluminum (Al) is added in a solution-aluminum (Sol.-Al) state, but the lower limit thereof is limited to 0.01% by weight, and when excessively added, the amount of inclusions in the steel is increased, leading to surface defects and degrading workability. Therefore, the upper limit is limited to 0.04% by weight.
질소(N)는 강 중에서 고용 상태로 존재하면서 재질 강화에 유용한 원소이지만, 시효 현상을 일으키는 주된 원소이므로 가공성 확보를 위해 일정량 이하로 관리하는 것이 필요하며, 따라서, 그 첨가 상한선을 40ppm으로 제한한다. 반면, 질소(N)의 첨가량이 1ppm 미만이면, 충분한 강성을 얻을 수 없고, 석출물 형성을 위한 사이트가 감소하게 되므로 그 첨가 하한은 1ppm으로 제한하여, 그 함량을 1∼40ppm으로 한다. Nitrogen (N) is an element that is useful in reinforcing materials while being in a solid solution in steel, but since it is a main element causing aging, it is necessary to manage it to a certain amount or less to secure workability, and therefore, the upper limit of addition is limited to 40 ppm. On the other hand, if the addition amount of nitrogen (N) is less than 1 ppm, sufficient rigidity cannot be obtained, and the site for forming precipitates is reduced, so the lower limit of the addition is limited to 1 ppm, and the content is 1 to 40 ppm.
보론(B)은 입계 강화 원소로서, 용접부의 피로특성을 향상시키고, 인(P)의 입계 취성을 방지하며, 알루미늄(Al) 및 실리콘(Si)의 함량이 높은 강종에서는 고온 연성을 향상시키는 효과가 있다. 또한, 보론(B)은 강의 소입을 증가시키고, 열처리시 결정립계에 확산하여 오스테나이트의 펄라이트 변태 및 마르텐사이트의 페라이트 역변태를 지연시키는 효과가 있다. 반면, 보론(B)은 과량으로 첨가될 경우, 고용 보론이 증가하여 연신율이 감소하고, 보론(B)이 표면상에 확산되어 도금성을 저하시킬 수 있으므로, 그 첨가량을 1∼60ppm으로 한다. Boron (B) is a grain boundary strengthening element, which improves the fatigue properties of welds, prevents grain boundary brittleness of phosphorus (P), and improves high temperature ductility in steels with high content of aluminum (Al) and silicon (Si). There is. In addition, boron (B) increases the quenching of the steel, and has the effect of delaying the perlite transformation of austenite and the ferrite reverse transformation of martensite by diffusing to grain boundaries during heat treatment. On the other hand, when the boron (B) is added in an excessive amount, the solid solution boron is increased to reduce the elongation, and boron (B) can diffuse on the surface to reduce the plating property, the addition amount is 1 to 60ppm.
즉, 보론(B)은 강 중에서 고용 원소와 결합하여 시효성을 개선할 뿐만 아니라, 경화능 향상 원소로서 소량 첨가에 의해서도 소재의 강도를 올려주는 효과를 나타내는 원소이므로, 원하는 재질 특성을 확보하기 위해서는 최소한 1ppm 이상의 첨가가 필요하다. 그러나, 60ppm을 초과하면 오히려 재질 열화 및 연주 시 입계 균열의 요인이 될 뿐만 아니라 열연강판의 표면을 거칠게 하는 문제가 있으므로, 그 함량을 1∼60ppm으로 한정하는 것이다.In other words, boron (B) is an element that combines with a solid solution element in steel to improve the aging property and also increases the strength of the material even by adding a small amount as a hardenability enhancing element. At least 1 ppm addition is required. However, if the content exceeds 60ppm, not only does it cause deterioration of material and grain boundary cracking, but also roughens the surface of the hot-rolled steel sheet. Therefore, the content is limited to 1 to 60ppm.
본 발명의 실시 예에 따른 압연강판은, 상기한 성분의 저탄소강에 보론(B)이 일정량 첨가됨에 따라, 연주 및 열간압연 과정에서 MnS 석출물을 씨드(seed)로 하여 BN이 석출되고, 그리고, 시멘타이트 석출이 조장되어, 시멘타이트의 미세화 및 랜덤화를 통해 고용 질소(N) 및 탄소(C)의 감소가 이루어진다. 특히, BN의 석출은 사상 압연에서 일어나는데, 본 발명의 경우, 보론(B)의 첨가를 통해 기존보다 낮은 사상 압연 온도에서 BN 석출이 가능하게 되어 기존보다 많은 양의 BN 석출물을 생성할 수 있게 되며, 그래서, 본 발명에 따른 압연강판은 결정립 미세화로 혼립 발생이 억제될 수 있다. 즉, 본 발명에 따른 압연강판은, 보론(B) 첨가를 통해 오스테나이트 결정입계에서 BN이 석출됨에 따라 결정입계 안정화 효과를 얻게 되고, 또한, 오스테나이트 영역에서 페라이트 변태를 억제하는 효과를 얻게 되어, 혼립 발생이 억제될 수 있다. In the rolled steel sheet according to the embodiment of the present invention, as a predetermined amount of boron (B) is added to the low carbon steel of the above-described components, BN is precipitated using MnS precipitate as a seed during the performance and hot rolling, and Precipitation of cementite is encouraged, resulting in reduction of solid solution nitrogen (N) and carbon (C) through refinement and randomization of cementite. In particular, the precipitation of BN occurs in finishing rolling, in the case of the present invention, the addition of boron (B) enables the BN precipitation at a lower finishing rolling temperature than before, thereby producing a larger amount of BN precipitates than before. Therefore, the rolled steel sheet according to the present invention can be suppressed from the generation of grains by grain refinement. That is, in the rolled steel sheet according to the present invention, as BN is precipitated at the austenite grain boundary through addition of boron (B), the grain boundary stabilization effect is obtained, and the ferrite transformation is also suppressed in the austenite region. The occurrence of the mixing can be suppressed.
부연하면, 적은 양의 망간(Mn)을 함유한 저탄소강은 Ar3 변태점이 상승하여 혼립이 조장되며, 이러한 혼립 방지를 위해서는 변태 지연 원소의 첨가가 필요하다. 본 발명의 압연강판은 저탄소강의 성분에 변태 지연 원소의 역할을 할 수 있는 보론(B)이 일정량 첨가됨으로써 혼립 발생이 억제될 수 있으며, 결과적으로, 이러한 혼립 발생 억제를 통해 본 발명에 따른 압연강판은 재질 시효 및 가공 불량이 개선될 수 있다. In other words, the low carbon steel containing a small amount of manganese (Mn) increases the Ar 3 transformation point to promote mixing, and the addition of the transformation delay element is necessary to prevent such mixing. Rolled steel sheet of the present invention can be suppressed by the addition of a certain amount of boron (B) which can play a role of transformation delay element to the components of low carbon steel, as a result, the rolled steel sheet according to the present invention through the suppression of such Silver material aging and poor machining can be improved.
부가해서, 가전 및 자동차용 강판의 적절한 가공 특성을 확보하기 위해서는 석출물 및 고용원소의 분율을 적절히 관리하는 것이 필요하다. 따라서, 본 발명에 따른 압연강판은 적절한 가공 특성을 확보하기 위해 강 성분에서의 보론(B)과 질소(N)를 0.2≤[B/N]≤1.1의 조건을 만족하도록 첨가한다. 이는 B/N 값이 0.2 미만이면 강 중의 고용원소 과다로 상온 내꺽임성이 열화되고, 고온에서 결정립 억제 효과가 미흡한 반면, B/N 값이 1.1을 초과하면 연성이 저하되고 가공성이 감소하기 때문이다. 그러므로, 본 발명에 따른 압연강판은 B/N의 값을 0.2∼1.1 범위로 한정한다. In addition, it is necessary to appropriately manage the fractions of precipitates and solid solution elements in order to secure appropriate processing characteristics of the steel sheets for home appliances and automobiles. Therefore, the rolled steel sheet according to the present invention adds boron (B) and nitrogen (N) in the steel component to satisfy the conditions of 0.2≤ [B / N] ≤1.1 in order to secure appropriate processing characteristics. This is because if the B / N value is less than 0.2, the bending resistance at room temperature is deteriorated due to excessive solid solution in steel, and the grain restraining effect is insufficient at high temperature, while if the B / N value is over 1.1, the ductility is lowered and the workability is reduced. to be. Therefore, the rolled steel sheet according to the present invention limits the value of B / N in the range 0.2 to 1.1.
상기한 바와 같은 본 발명에 따른 압연강판을 제조하기 위해, 본 발명의 실시 예에서는 보론(B)이 일정량 첨가된 저탄소강으로 강 슬라브를 만든 후, 연속주조, 조 압연, 사상 압연, 냉각 및 권취 단계들을 통해 열연강판을 제조하는 열연 공정과, 열연강판을 산세, 냉간압연, 연속소둔 및 조질압연 단계들을 통해 냉연 강판을 제조하는 냉연 공정을 차례로 진행하되, 다음과 같은 최적화된 조업조건에 따라 강 슬라브에 대한 열연 및 냉연 공정을 진행해서 재질 시효 및 가공 불량이 개선된 압연강판을 제조한다. In order to manufacture the rolled steel sheet according to the present invention as described above, in the embodiment of the present invention after the steel slab is made of low carbon steel to which a certain amount of boron (B) is added, continuous casting, rough rolling, finishing rolling, cooling and winding The hot rolling process for manufacturing hot rolled steel sheet through the steps, and the cold rolling process for manufacturing cold rolled steel sheet through the steps of pickling, cold rolling, continuous annealing and temper rolling of the hot rolled steel sheet, according to the optimized operating conditions as follows Hot rolled and cold rolled slabs are processed to produce rolled steel sheets with improved material aging and poor machining.
먼저, 중량%로, 탄소(C) 0.035∼0.08, 실리콘(Si) 0.01∼0.03, 망간(Mn) 0.15∼0.5, 인(P) 0.001∼0.015, 황(S) 0.001∼0.015, 솔루션-알루미늄(Sol.-Al) 0.01∼0.04, 질소(N) 0.1∼40ppm, 잔부 철(Fe) 및 기타 불가피한 불순물을 함유하고, 보론(B)이 0.2≤[B/N]≤1.1의 조건을 만족하는 범위에서 1∼60ppm이 첨가된 저탄소강으로 이루어진 강 슬라브를 만든다. First, in weight percent, carbon (C) 0.035 to 0.08, silicon (Si) 0.01 to 0.03, manganese (Mn) 0.15 to 0.5, phosphorus (P) 0.001 to 0.015, sulfur (S) 0.001 to 0.015, solution-aluminum ( Sol.-Al) 0.01 to 0.04, nitrogen (N) 0.1 to 40 ppm, residual iron (Fe) and other unavoidable impurities, and boron (B) satisfies the condition of 0.2≤ [B / N] ≤1.1 Produces a steel slab made of low carbon steel with 1 to 60 ppm added.
그 다음, 이와 같은 조성을 갖는 보론(B)이 일정량 첨가된 저탄소강으로 이루어진 강 슬라브에 대해 연속주조 및 조압연을 차례로 진행한 후, 850∼950℃에서 사상 압연을 진행하고, 이어서, 사상 압연을 거쳐 얻어진 열연 강판을 냉각한 후, 540∼640℃의 온도에서 권취한다.Then, continuous casting and rough rolling were sequentially performed on the steel slab made of low carbon steel to which boron (B) having such a composition was added in a constant amount, followed by finishing rolling at 850 to 950 ° C, followed by finishing rolling. After cooling the hot rolled sheet steel obtained through, it winds up at the temperature of 540-640 degreeC.
여기서, 본 발명의 실시 예는 상기한 조성 성분으로 이루어지고 보론(B)이 일정량 첨가된 강 슬라브에 대해 오스테나이트 영역에서 열연 공정을 진행한다. 특히, 사상 압연은 850∼950℃의 온도에서 진행하는데, 이것은 사상 압연 온도가 850℃ 미만이면 저온 영역에서 열간압연이 마무리됨에 따라 결정립의 혼립화가 급격히 진행되어 압연성 및 가공성의 저하를 초래되고, 반면, 사상 압연 온도가 950℃보다 높으면 두께 전반에 걸쳐 균일한 열간압연이 이루어지지 않아 결정립 미세화가 충분하게 이루어지지 않음으로써 결정립 조대화에 기인한 충격 인성의 저하가 나타나기 때문이다. 따라서, 본 발명의 실시 예에서는 사상 압연 온도를 850∼950℃로 한다.Here, an embodiment of the present invention performs a hot rolling process in the austenitic region for the steel slab made of the above-described composition components and a certain amount of boron (B) is added. In particular, finishing rolling is carried out at a temperature of 850 ~ 950 ℃, this is, when the finishing rolling temperature is less than 850 ℃ as the hot rolling is finished in the low temperature region, the crystallization of the grain proceeds rapidly, leading to the deterioration of rollability and workability, On the other hand, when the finishing rolling temperature is higher than 950 ° C, since uniform hot rolling is not performed throughout the thickness, grain refinement is not sufficiently achieved, resulting in a drop in impact toughness due to grain coarsening. Therefore, in the Example of this invention, a finishing rolling temperature shall be 850-950 degreeC.
냉각은 사상 압연한 강을 런 아웃 테이블(Run out table; 이하, ROT)에서 초당 60∼120℃의 냉각속도로 진행한다. 이것은 ROT에서의 냉각속도가 60℃/초 미만이면 동적 결정립 성장에 의해 상대적으로 조대한 결정립이 형성되어 강도 및 가공성을 저하시키는 원인이 되는 반면, ROT에서의 냉각속도가 120℃/초 이상이면 폭 방향 냉각 불균일에 의한 재질 편차 발생의 원인으로 작용하기 때문이다. 따라서, 본 발명의 실시 예에서는 냉각속도를 60∼120℃/초로 한다. Cooling is carried out at the cooling rate of 60-120 degreeC per second in the run-out table (ROT) of steel by which it rolled. This means that when the cooling rate in ROT is less than 60 ° C / sec, relatively coarse grains are formed by dynamic grain growth, which causes a decrease in strength and workability, while the cooling rate in ROT is more than 120 ° C / sec. This is because it acts as a cause of material deviation caused by directional cooling unevenness. Therefore, in the embodiment of the present invention, the cooling rate is 60 to 120 ° C / sec.
열연강판의 권취는 540∼640℃의 온도에서 진행한다. 즉, 열연 공정에서의 권취 온도는 후속하는 냉간압연 및 연속소둔 단계 후 최적의 기계적 물성을 확보할 수 있는 조직을 얻기 위한 온도로서, 본 발명에 따른 압연강판의 경우, 권취 온도가 540℃ 미만이면 베이나이트 또는 마르텐사이트 조직의 형성으로 인해 냉간압연이 어렵고, 640℃를 초과하면 최종 미세조직이 조대해져 가공성 및 내식성이 저하됨은 물론 충분한 강도를 갖는 강판을 제조하기 어렵다. 따라서, 본 발명의 실시 예에서 열연강판의 권취 온도는 540∼640℃로 한다. The winding of the hot rolled steel sheet proceeds at a temperature of 540 to 640 ° C. In other words, the coiling temperature in the hot rolling process is a temperature for obtaining a structure capable of securing the optimum mechanical properties after the subsequent cold rolling and continuous annealing step, in the case of the rolled steel sheet according to the present invention, if the coiling temperature is less than 540 ℃ Cold rolling is difficult due to the formation of bainite or martensite structure, and if the temperature exceeds 640 ° C., the final microstructure is coarsened to reduce workability and corrosion resistance, and it is difficult to manufacture a steel sheet having sufficient strength. Therefore, the coiling temperature of the hot rolled steel sheet in the embodiment of the present invention is 540 ~ 640 ℃.
계속해서, 열연 공정을 거쳐 얻어진 열연강판에 대해 산세 단계 및 냉간압연 단계를 순차 진행하고, 이어서, 연속소둔 단계 및 조질 압연을 진행하여 저탄소강 베이스의 냉연 강판으로 이루어진 본 발명에 따른 압연강판을 제조한다. Subsequently, a pickling step and a cold rolling step are sequentially performed on the hot rolled steel sheet obtained through the hot rolling process, and then a continuous annealing step and temper rolling are performed to produce a rolled steel sheet according to the present invention, which is made of a cold rolled steel sheet based on a low carbon steel. do.
여기서, 냉간압연은 냉간압하율을 50∼90%로 하여 진행한다. 냉간압연은 열연조직을 변형시키며, 이때, 조직을 변형시키는 변형 에너지는 후속하는 연속소둔, 즉, 재결정 과정에서 에너지가 된다. 이러한 냉간압연은 냉간압하율을 50% 미만으로 하면 조직 변형 효과가 작고, 반면, 냉간압하율을 90% 초과하면 냉간압연 공정 진행 자체가 실질적으로 힘들뿐만 아니라, 열연강판에서 생성된 석출물이 냉간압연 중 분해되어 후속하는 재결정의 초기 단계에서 (100) 집합 조직을 발달시킴으로써 드로잉성이 저하되고, 강판의 가장자리에 균열이 발생하며, 강판에 파단이 일어날 확률이 높다. 따라서, 냉간압연은 냉간압하율을 50∼90%로 관리한다. Here, cold rolling advances with 50-90% of cold rolling rates. Cold rolling deforms the hot rolled tissue, where the strain energy that deforms the tissue becomes energy in subsequent continuous annealing, that is, recrystallization. When the cold rolling is less than 50% cold rolling, the effect of the deformation of the tissue is small. On the other hand, when the cold rolling is more than 90%, the cold rolling process itself is not very difficult, and the precipitates produced in the hot rolled steel sheet are cold rolled. The development of (100) texture in the early stages of subsequent recrystallization during decomposing, deteriorates the drawability, cracks at the edges of the steel sheet, and the probability of breakage in the steel sheet is high. Accordingly, cold rolling controls the cold reduction rate at 50 to 90%.
연속소둔은 720∼810℃의 온도 범위에서 10∼120초간 진행한다. 여기서, 보론(B)이 첨가된 압연강판은 열연 공정에서 질소(N)를 대부분 BN으로 석출시키므로 연속소둔 단계에서 AlN 석출량 감소로 결정립이 조대화되고, 결정립의 조대화는 항복점(YP) 하향을 초래하며, 이를 보상하기 위해서는 소둔 온도를 낮추어야 하고, 이와 같은 소둔 온도의 하향은 생산성 향상을 가져온다. 또한, 720℃ 미만의 열처리는 재결정 생성 미흡을 가져오고, 810℃를 초과한 열처리는 고온 소둔에 의한 재질 열화를 야기한다. 다시 말해, 소둔 온도가 720℃ 미만일 경우 AlN 석출이 거의 일어나지 않아 질소(N)에 의한 시효가 발생할 수 있고, 소둔 온도가 810℃를 초과할 경우 AlN 석출은 충분히 일어나지만 결정립 성장이 과도하여 강판 재질이 저하될 수 있다. 따라서, 본 발명의 실시 예에서 연속소둔 온도는 720∼810℃로 한다. Continuous annealing is performed for 10 to 120 seconds in the temperature range of 720 to 810 ° C. Here, since the rolled steel sheet to which boron (B) is added precipitates most of the nitrogen (N) to BN in the hot rolling process, grains are coarsened by decreasing AlN precipitation in the continuous annealing step, and coarsening of grains is lowered in yield point (YP) In order to compensate for this, the annealing temperature must be lowered, and the lowering of the annealing temperature leads to an improvement in productivity. In addition, heat treatment below 720 ° C. results in insufficient recrystallization, and heat treatment above 810 ° C. causes material degradation due to high temperature annealing. In other words, when the annealing temperature is less than 720 ℃ AlN precipitation hardly occurs and aging by nitrogen (N) may occur, and when the annealing temperature exceeds 810 ℃ AlN precipitation occurs sufficiently, but the grain growth is excessive, the steel sheet material This can be degraded. Therefore, in the embodiment of the present invention, the continuous annealing temperature is set to 720 to 810 ° C.
조질 압연은 소재 두께 0.4≤T＜2.4에 대하여 0.7∼1.6%의 연신율을 만족하도록 진행하되, 다음의 관계식 1, 관계식 2, 관계식 3 및 관계식 4와 같이 소재 두께별 연신율을 만족하는 범위로 실시한다. Temper rolling is carried out to satisfy the elongation of 0.7 to 1.6% with respect to the material thickness 0.4≤T <2.4, but in the range satisfying the elongation by material thickness as shown in the following Equation 1, Equation 2, Equation 3 and Equation 4. .
(관계식 1) 0.4≤T＜0.6에 대하여 0.9±0.2%의 연신율Elongation of 0.9 ± 0.2% for 0.4 ≦ T <0.6
(관계식 2) 0.6≤T＜0.9에 대하여 1.0±0.2%의 연신율Elongation of 1.0 ± 0.2% for 0.6≤T <0.9
(관계식 3) 0.9≤T＜1.1에 대하여 1.1±0.2%의 연신율(Equation 3) Elongation of 1.1 ± 0.2% for 0.9≤T <1.1
(관계식 4) 1.1≤T＜2.4에 대하여 1.4±0.2%의 연신율(Equation 4) Elongation of 1.4 ± 0.2% for 1.1≤T <2.4
이것은 연신율이 0.7% 미만일 경우 고착 탄소량이 증가하여 항복점-연신(YP-EL) 및 가공시 주름이 발생할 수 있고, 반면, 1.6%를 초과할 경우 소재의 웨이브 및 가공 경화에 의해 항복점(YP)이 높아져서 가공시 가공크랙이 발생할 수 있기 때문이다. 따라서, 본 발명의 실시 예에서 조질 압연은 관계식 1, 관계식 2, 관계식 3 및 관계식 4를 토대로 하는 소재 두께별 연신율 기준을 설정하여 실시한다. If the elongation is less than 0.7%, the amount of fixed carbon may increase and yield point-stretch (YP-EL) and wrinkles may occur during processing, whereas if the elongation exceeds 1.6%, the yield point (YP) may be reduced due to wave and work hardening of the material. This is because processing cracks may occur during processing. Therefore, temper rolling in the embodiment of the present invention is carried out by setting the elongation reference for each material thickness based on the relationship 1, relationship 2, relationship 3 and relationship 4.
상기한 바와 같은 강 성분 및 조업조건에 따라 제조된 본 발명에 따른 압연강판의 특성은 다음과 같다. The characteristics of the rolled steel sheet according to the present invention manufactured according to the steel components and operating conditions as described above are as follows.
본 발명에 따른 압연강판의 조성 및 제조방법의 효과를 확인하기 위하여, 하기의 표 1에 기재된 조성들 및 표 2에 기재된 조업조건들로 저탄소강 베이스의 강판 시편들을 제작하였고, 각 시편들에 대한 기계적 특성을 표 3에 기재하였다. In order to confirm the effect of the composition and manufacturing method of the rolled steel sheet according to the present invention, the steel sheet specimens of the low carbon steel base were prepared with the compositions shown in Table 1 and the operating conditions shown in Table 2, for each specimen The mechanical properties are listed in Table 3.
즉, 하기 표 1의 조성들을 갖는 강 슬라브들에 대해 표 2에 기재된 공정조건에 따라 850∼950℃ 온도에서 사상 압연을 진행한 후, 540∼640℃의 온도에서 권취하여 열연강판을 제조하고, 그런 다음, 이 열연강판에 대해 산세 및 50∼90%의 압하율로 냉간압연을 실시하며, 이어서, 냉간압연된 강판을 720∼810℃ 온도에서 연속소둔 처리한 후, 냉연강판 두께 0.4≤T＜2.4에 대하여 0.7%∼1.6%의 연신율을 만족하는 범위로 조질 압연을 하여 시편들을 제조하고, 이어서, 각 시편들에 대해 기계적 특성을 측정하였다. That is, according to the process conditions shown in Table 2 for the steel slabs having the compositions of Table 1 after finishing rolling at a temperature of 850 ~ 950 ℃, it is wound at a temperature of 540 ~ 640 ℃ to produce a hot rolled steel sheet, Then, the hot rolled steel sheet is subjected to pickling and cold rolling at a reduction ratio of 50 to 90%, followed by continuous annealing of the cold rolled steel sheet at a temperature of 720 to 810 ° C, followed by a thickness of 0.4≤T < Specimens were prepared by temper rolling in a range satisfying an elongation of 0.7% to 1.6% with respect to 2.4, and then mechanical properties were measured for each specimen.
표 1
구분 C Si Mn P S Sol.-Al N* B*
발명예1 0.04 0.018 0.2 0.007 0.006 0.01 27 10
발명예2 0.045 0.02 0.25 0.009 0.009 0.02 29 15
발명예3 0.05 0.025 0.3 0.011 0.011 0.03 31 20
발명예4 0.055 0.027 0.35 0.014 0.014 0.04 33 25
비교예1 0.04 0.018 0.2 0.007 0.006 0.01 27 -
비교예2 0.045 0.02 0.25 0.009 0.009 0.02 29 -
비교예3 0.05 0.025 0.3 0.011 0.011 0.03 31 -
비교예4 0.055 0.027 0.35 0.014 0.014 0.04 33 -
Table 1
division C Si Mn P S Sol.-Al N * B *
Inventive Example 1 0.04 0.018 0.2 0.007 0.006 0.01 27 10
Inventive Example 2 0.045 0.02 0.25 0.009 0.009 0.02 29 15
Inventive Example 3 0.05 0.025 0.3 0.011 0.011 0.03 31 20
Inventive Example 4 0.055 0.027 0.35 0.014 0.014 0.04 33 25
Comparative Example 1 0.04 0.018 0.2 0.007 0.006 0.01 27 -
Comparative Example 2 0.045 0.02 0.25 0.009 0.009 0.02 29 -
Comparative Example 3 0.05 0.025 0.3 0.011 0.011 0.03 31 -
Comparative Example 4 0.055 0.027 0.35 0.014 0.014 0.04 33 -
표 1에서, * 표시된 성분의 함량 단위는 ppm이며, 나머지 성분들의 함량 단위는 중량%이다.In Table 1, the content units of the * components are ppm and the content units of the remaining components are% by weight.
표 2
구 분 사상압연 온도 (℃) 권취 온도 (℃) 연속소둔 온도(℃) 연신율 (%)
발명예1 870 560 750 41
발명예2 875 580 760 43
발명예3 880 600 770 45
발명예4 890 620 780 47
비교예1 870 560 750 41
비교예2 875 580 760 43
비교예3 880 600 770 45
비교예4 890 620 780 47
TABLE 2
division Finish rolling temperature (℃) Coiling temperature (℃) Continuous Annealing Temperature (℃) Elongation (%)
Inventive Example 1 870 560 750 41
Inventive Example 2 875 580 760 43
Inventive Example 3 880 600 770 45
Inventive Example 4 890 620 780 47
Comparative Example 1 870 560 750 41
Comparative Example 2 875 580 760 43
Comparative Example 3 880 600 770 45
Comparative Example 4 890 620 780 47
표 3
구 분 항복점-연신 가공성 내시효성 도장성
발명예1 미발생 양호 양호 양호
발명예2 미발생 양호 양호 양호
발명예3 미발생 양호 양호 양호
발명예4 미발생 양호 양호 양호
비교예1 발생 보통 불량 보통
비교예2 발생 불량 보통 불량
비교예3 미발생 보통 보통 불량
비교예4 발생 불량 보통 보통
TABLE 3
division Yield Point-Elongation Machinability Anti-aging Paintability
Inventive Example 1 Not Occurred Good Good Good
Inventive Example 2 Not Occurred Good Good Good
Inventive Example 3 Not Occurred Good Good Good
Inventive Example 4 Not Occurred Good Good Good
Comparative Example 1 Occur usually Bad usually
Comparative Example 2 Occur Bad usually Bad
Comparative Example 3 Not Occurred usually usually Bad
Comparative Example 4 Occur Bad usually usually
상기한 표 1 내지 표 3에서, 발명예 1 내지 4는 보론(B)이 첨가된 저탄소강 베이스의 압연강판이고, 비교예 1 내지 4는 보론(B)이 첨가되지 않은 저탄소강 베이스 압연강판이다. 그리고, 발명예 1 내지 4, 그리고, 비교예 1 내지 4는 본 발명의 실시 예에 따른 조업조건들 모두를 만족한다. In the above Tables 1 to 3, Inventive Examples 1 to 4 are low carbon steel base rolled steel sheets to which boron (B) is added, and Comparative Examples 1 to 4 are low carbon steel base rolled steel sheets to which boron (B) is not added. . Inventive Examples 1 to 4 and Comparative Examples 1 to 4 satisfy all of the operating conditions according to the embodiment of the present invention.
표 3을 참조하면, 발명예 1 내지 4는 저탄소강의 성분들에 보론(B)이 첨가됨에 따라 가공 시에 항복점-연신이 발생하지 않고 꺾임이 발생하지 않아 모두 양호한 내시효성을 나타내었고, 또한, 밴딩 가공시에도 가공 균열이 발생하지 않는 등 양호한 가공성 및 도장성을 나타내었다. Referring to Table 3, Inventive Examples 1 to 4 exhibited good aging resistance because boron (B) was added to the components of low carbon steel so that no yield point-stretching and no bending occurred during processing. Good workability and paintability, such as no cracking, occurred during bending.
반면, 비교예 1은 항복점-연신의 변화가 발생한 것으로 인해 가공성 및 도장성이 보통이고 내시효성이 불량인 결과를 나타내었다. 비교예 2 또한 항복점-연신의 변화가 발생한 것으로 인해 가공성 및 도장성이 불량하고, 내시효성이 보통인 결과를 나타내었다. 비교예 3은 항복점-연신의 변화가 발생하지 않았으나 내시효성 및 가공성이 보통이고 도장성이 불량한 결과를 나타내었다. 비교예 4는 항복점-연신의 변화가 발생한 것으로 인해 가공성이 불량하고 내시효성 및 도장성이 보통인 결과를 나타내었다. On the other hand, Comparative Example 1 showed a result that the change in yield point-stretch occurred, the workability and paintability is normal, and the aging resistance is poor. Comparative Example 2 In addition, due to the change in yield point-stretch, poor workability and paintability and normal aging resistance were shown. In Comparative Example 3, no change in yield point-stretching occurred, but the aging resistance and workability were normal, and the paintability was poor. In Comparative Example 4, due to the change in yield point-stretch, the workability was poor, and the aging resistance and paintability were normal.
그러므로, 표 1 내지 표 3으로부터, 본 발명에 따라 보론(B)이 첨가된 저탄소강 베이스의 압연강판은 보론이 첨가되지 않은 일반적인 저탄소강 베이스의 압연강판과 비교해서 재질 시효 및 가공 불량이 개선됨을 볼 수 있다. Therefore, from Tables 1 to 3, according to the present invention, the low carbon steel-based rolled steel sheet to which boron (B) is added is improved in material aging and processing defects as compared with the general low carbon steel-based rolled steel sheet without boron. can see.
도 1 및 도 2는 각각 보론(B)이 첨가되지 않은 일반적인 저탄소강으로 이루어진 압연강판의 조직 및 본 발명에 따른 보론(B) 첨가 저탄소강으로 이루어진 압연강판의 조직을 보여주는 현미경 사진들이고, 도 3 및 도 4는 각각 본 발명에 따라 제조된 보론(B) 첨가 저탄소강으로 이루어진 압연강판 및 보론(B)이 첨가되지 않은 일반적인 저탄소강으로 이루어진 압연강판의 항복점(YP) 및 항복점-연신(YP-EL) 그래프들이다. 1 and 2 are micrographs showing the structure of the rolled steel sheet made of a general low carbon steel without boron (B) added and the rolled steel sheet made of boron (B) -added low carbon steel according to the present invention, respectively, FIG. And Fig. 4 shows the yield point (YP) and the yield-point (YP-) of the rolled steel sheet made of boron (B) -added low carbon steel and the rolled steel sheet made of ordinary low-carbon steel without boron (B), respectively prepared according to the present invention. EL) graphs.
도 1을 참조하면, 보론(B)이 첨가되지 않은 일반적인 저탄소강으로 이루어진 압연강판의 경우, 입도지수(FGS; Ferrite Grain Size)가 10∼11인, 즉, 입자의 평균 직경이 0.007∼0.011㎜이고, 측정선상의 절편의 평균 수가 100∼141/㎜인 조대한 결정립들의 혼립 조직이 발생하였음을 볼 수 있다. Referring to FIG. 1, in the case of a rolled steel sheet made of general low carbon steel to which boron (B) is not added, the particle size index (FGS) is 10 to 11, that is, the average diameter of the particles is 0.007 to 0.011 mm. It can be seen that a coarse structure of coarse grains having an average number of fragments on the measurement line of 100 to 141 / mm occurred.
반면, 도 2를 참조하면, 보론(B)이 첨가되고, 최적화된 조업조건에 따라 제조된 본 발명에 따른 저탄소강으로 이루어진 압연강판의 경우, 입도지수는 9∼10, 즉, 입자의 평균 직경이 0.011∼0.015㎜이고, 측정선상의 절편의 평균 수가 70.7∼100/㎜인 정도로 보론(B)이 첨가되지 않은 압연강판과 유사하지만, 결정립들이 혼립 조직이 거의 없이 균일하게 형성하였음을 볼 수 있다. On the other hand, referring to Figure 2, the boron (B) is added, in the case of the rolled steel sheet made of low carbon steel according to the present invention manufactured according to the optimized operating conditions, the particle size index is 9 to 10, that is, the average diameter of the particles Is 0.011 to 0.015 mm and the average number of sections on the measurement line is 70.7 to 100 / mm, similar to the rolled steel sheet without boron (B) added, but it can be seen that the grains are uniformly formed with little mixed structure. .
도 3 및 도 4를 참조하면, 보론(B)이 첨가되지 않은 일반적인 저탄소강으로 이루어진 압연강판은 280 정도의 항복점(YP)과, 0.31 정도의 항복점-연신(YP-EL)을 나타냄을 볼 수 있다.3 and 4, it can be seen that the rolled steel sheet made of general low carbon steel without boron (B) exhibits a yield point (YP) of about 280 and a yield point-stretching (YP-EL) of about 0.31. have.
반면, 본 발명에 따라 보론(B)이 첨가되고 최적화된 조업조건에 따라 제조된 저탄소강으로 이루어진 압연강판의 경우, FGS가 미세하고 혼립 조직의 발생없이 결정립들의 크기가 균일한 것으로 인해, 보론(B)이 첨가되지 않은 일반적인 저탄소강 보다 낮은 200∼250, 바람직하게 240의 항복점(YP)과, 0.01∼0.05, 바람직하게 0.03의 항복점-연신(YP-EL)을 나타냄을 볼 수 있다.On the other hand, in the case of a rolled steel sheet made of low carbon steel, in which boron (B) is added according to the present invention and manufactured according to optimized operating conditions, the FGS is fine and the size of the grains is uniform without generation of a mixed structure. It can be seen that the yield point (YP) of 200 to 250, preferably 240, and the yield point-elongation (YP-EL) of 0.01 to 0.05, preferably 0.03, are lower than that of the general low carbon steel without B).
따라서, 보론(B)이 첨가되지 않은 일반 저탄소강으로 이루어진 압연강판과 비교해서, 보론(B)이 첨가되고 최적화된 조업조건에 따라 제조된 본 발명에 따른 압연강판은 균일한 결정립들의 성장을 통해 상대적으로 낮은 항복점(YP) 및 항복점-연신(YP-EL)을 갖게 됨을 볼 수 있으며, 이 결과로부터, 본 발명에 따른 압연강판은 전위 고착이 감소됨으로써 재질 시효 및 가공성이 개선됨을 알 수 있다. Therefore, compared with the rolled steel sheet made of ordinary low carbon steel without boron (B) added, the rolled steel sheet according to the present invention manufactured according to the optimized operating conditions with boron (B) added through the growth of uniform grains. It can be seen that it has a relatively low yield point (YP) and yield point-stretching (YP-EL), from this result, it can be seen that the rolled steel sheet according to the present invention is improved in material aging and workability by reducing the potential adhesion.
그러므로, 보론(B)이 첨가되고 열연 및 냉연 공정을 최적화된 조업조건에 따라 거쳐 제조된 본 발명에 따른 저탄소강으로 이루어진 압연강판은 가공성, 내시효성, 도장성 및 내식성 모두에서 양호한 특성을 가지므로, 재질 시효 및 가공 불량이 개선되며, 결과적으로, 본 발명은 가전 및 자동차 등에 사용되는 우수한 재질 특성 및 가공성을 갖는 고부가가치의 압연강판을 제공할 할 수 있다.Therefore, the rolled steel sheet made of low carbon steel according to the present invention, in which boron (B) is added and manufactured through hot rolling and cold rolling processes according to optimized operating conditions, has good properties in both workability, aging resistance, paintability and corrosion resistance. And, material aging and processing failure is improved, and as a result, the present invention can provide a high value-added rolled steel sheet having excellent material properties and workability used in home appliances and automobiles.
이상, 여기에서는 본 발명을 특정 실시예에 관련하여 도시하고 설명하였지만, 본 발명이 그에 한정되는 것은 아니며, 이하의 특허청구의 범위는 본 발명의 정신과 분야를 이탈하지 않는 한도 내에서 본 발명이 다양하게 개조 및 변형될 수 있다는 것을 당업계에서 통상의 지식을 가진 자가 용이하게 알 수 있다. As mentioned above, although the present invention has been illustrated and described with reference to specific embodiments, the present invention is not limited thereto, and the following claims are not limited to the scope of the present invention without departing from the spirit and scope of the present invention. It can be easily understood by those skilled in the art that can be modified and modified.

Claims (10)

  1. 중량%로, 탄소(C): 0.035∼0.08, 실리콘(Si): 0.01∼0.03, 망간(Mn): 0.15∼0.5, 인(P): 0.001∼0.015, 황(S): 0.001∼0.015, 솔루션-알루미늄(Sol.-Al): 0.01∼0.04, 질소(N) 1∼40ppm, 잔부 철(Fe) 및 기타 불가피한 불순물을 함유한 저탄소강으로 이루어지고, By weight%, carbon (C): 0.035 to 0.08, silicon (Si): 0.01 to 0.03, manganese (Mn): 0.15 to 0.5, phosphorus (P): 0.001 to 0.015, sulfur (S): 0.001 to 0.015, solution Aluminum (Sol.-Al): 0.01 to 0.04, nitrogen (N) 1 to 40 ppm, consisting of low carbon steel containing residual iron (Fe) and other unavoidable impurities,
    보론(B)이 0.2≤[B/N]≤1.1의 조건을 만족하는 범위에서 1∼60ppm이 첨가되어 입도지수(FGS; Ferrite Grain Size))가 9∼10인 결정립들이 균일하게 형성된 것을 특징으로 하는 압연강판.1 to 60 ppm is added in the range where boron (B) satisfies the condition of 0.2 ≤ [B / N] ≤ 1.1, so that grains having a grain size index (FGS) of 9 to 10 are uniformly formed. Rolled steel sheet.
  2. 제 1 항에 있어서, 200∼250의 항복점(YP)과 0.01∼0.05의 항복점-연신(YP-EL)을 갖는 것을 특징으로 하는 압연강판.The rolled steel sheet according to claim 1, having a yield point (YP) of 200 to 250 and a yield point-stretching (YP-EL) of 0.01 to 0.05.
  3. 제 1 항에 있어서, 상기 저탄소강은 소재 두께 0.4≤T＜2.4에 대하여 0.7∼1.6%의 연신율을 만족하는 것을 특징으로 하는 압연강판의 제조방법. The method of manufacturing a rolled steel sheet according to claim 1, wherein the low carbon steel satisfies an elongation of 0.7 to 1.6% with respect to a material thickness of 0.4≤T <2.4.
  4. 중량%로, 탄소(C): 0.035∼0.08, 실리콘(Si): 0.01∼0.03, 망간(Mn): 0.15∼0.5, 인(P): 0.001∼0.015, 황(S): 0.001∼0.015, 솔루션-알루미늄(Sol.-Al): 0.01∼0.04, 질소(N) 1∼40ppm, 잔부 철(Fe) 및 기타 불가피한 불순물을 함유하고, 보론(B) 1∼60ppm이 0.2≤[B/N]≤1.1의 조건을 만족하도록 첨가된 저탄소강으로 이루어진 강 슬라브를 형성하는 단계; By weight%, carbon (C): 0.035 to 0.08, silicon (Si): 0.01 to 0.03, manganese (Mn): 0.15 to 0.5, phosphorus (P): 0.001 to 0.015, sulfur (S): 0.001 to 0.015, solution -Aluminum (Sol.-Al): 0.01 to 0.04, nitrogen (N) 1 to 40 ppm, residual iron (Fe) and other unavoidable impurities, and boron (B) 1 to 60 ppm is 0.2≤ [B / N] ≤ Forming a steel slab made of low carbon steel added to satisfy the condition of 1.1;
    상기 강 슬라브에 대해 사상 압연, 냉각 및 권취 단계들을 포함하는 열연 공정을 진행하여 열연강판을 제조하는 단계; Manufacturing a hot rolled steel sheet by performing a hot rolling process including finishing rolling, cooling, and winding steps on the steel slab;
    상기 열연강판에 대해 산세, 냉간압연 및 연속소둔 단계들을 차례로 진행하여 냉연강판을 제조하는 단계; 및 Manufacturing a cold rolled steel sheet by sequentially performing steps of pickling, cold rolling, and continuous annealing of the hot rolled steel sheet; And
    상기 연속소둔 처리된 냉연강판을 소재 두께 0.4≤T＜2.4에 대하여 0.7∼1.6%의 연신율을 만족하는 조건으로 조질 압연하는 단계; Tempering rolling the continuously annealed cold rolled steel sheet under conditions satisfying an elongation of 0.7 to 1.6% with respect to a material thickness of 0.4 ≦ T <2.4;
    를 포함하는 것을 특징으로 하는 압연강판의 제조방법.Method for producing a rolled steel sheet comprising a.
  5. 제 4 항에 있어서, 상기 사상 압연은 850∼950℃ 온도 범위에서 진행하는 것을 특징으로 하는 압연강판의 제조방법.The method of claim 4, wherein the finishing rolling is carried out at a temperature range of 850 to 950 ℃.
  6. 제 4 항에 있어서, 상기 냉각은 초당 60∼120℃의 냉각속도로 진행하는 것을 특징으로 하는 압연강판의 제조방법.The method of claim 4, wherein the cooling is performed at a cooling rate of 60 to 120 ℃ per second.
  7. 제 4 항에 있어서, 상기 권취는 540∼640℃의 온도 범위에서 진행하는 것을 특징으로 하는 압연강판의 제조방법.The method of manufacturing a rolled steel sheet according to claim 4, wherein the winding proceeds in a temperature range of 540 to 640 ° C.
  8. 제 4 항에 있어서, 상기 냉간압연은 냉간압하율을 50∼90%로 하여 진행하는 것을 특징으로 하는 압연강판의 제조방법.The method for manufacturing a rolled steel sheet according to claim 4, wherein the cold rolling is performed with a cold reduction ratio of 50 to 90%.
  9. 제 4 항에 있어서, 상기 연속소둔은 720∼810℃의 온도범위에서 실시하는 것을 특징으로 하는 압연강판의 제조방법.The method of manufacturing a rolled steel sheet according to claim 4, wherein the continuous annealing is performed at a temperature range of 720 to 810 캜.
  10. 제 4 항에 있어서, 상기 조질 압연은 다음의 소재 두께별 연신율을 만족하는 조건으로 진행하는 것을 특징으로 하는 압연강판의 제조방법. The method of claim 4, wherein the temper rolling is carried out under a condition that satisfies elongation according to the following material thickness.
    (관계식 1) 0.4≤T＜0.6에 대하여 0.9±0.2%의 연신율Elongation of 0.9 ± 0.2% for 0.4 ≦ T <0.6
    (관계식 2) 0.6≤T＜0.9에 대하여 1.0±0.2%의 연신율Elongation of 1.0 ± 0.2% for 0.6≤T <0.9
    (관계식 3) 0.9≤T＜1.1에 대하여 1.1±0.2%의 연신율(Equation 3) Elongation of 1.1 ± 0.2% for 0.9≤T <1.1
    (관계식 4) 1.1≤T＜2.4에 대하여 1.4±0.2%의 연신율(Equation 4) Elongation of 1.4 ± 0.2% for 1.1≤T <2.4
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