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  • C21D8/0273—Final recrystallisation annealing
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  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/005—Ferrite

Definitions

• the present invention relates to a ferritic stainless steel having sufficient corrosion resistance and formability and excellent surface properties free from the occurrence of linear flaws due to hot rolling or annealing, and a method for producing the same.
• ferritic stainless steel is inexpensive and has excellent corrosion resistance, it is used in various applications such as building materials, transportation equipment, home appliances, kitchen appliances, and automobile parts, and its application range is expanding further in recent years.
• elongation is sufficiently large
• the average rankford value (hereinafter sometimes referred to as the average r value) is large, and the absolute value of the in-plane anisotropy of the r value (hereinafter sometimes referred to as
• ) is small.
• the absolute value of the in-plane anisotropy of the r value
• Patent Document 1 in mass%, C: 0.02 to 0.06%, Si: 1.0% or less, Mn: 1.0% or less, P: 0.05% or less, S: 0.01% or less, Al: 0.005% or less , Ti: 0.005% or less, Cr: 11-30%, Ni: 0.7% or less, and 0.06 ⁇ (C + N) ⁇ 0.12, 1 ⁇ N / C and 1.5 ⁇ 10 ⁇ 3 ⁇ (V ⁇ N) ⁇ 1.5
• a ferritic stainless steel excellent in formability and ridging resistance, characterized by satisfying ⁇ 10 ⁇ 2 (C, N, and V each represents mass% of each element) is disclosed.
• Patent Document 1 does not mention any anisotropy.
• box annealing for example, annealing at 860 ° C. for 8 hours
• box annealing process has a problem of low productivity because it takes about one week to complete when heating and cooling processes are included.
• Patent Document 2 by mass%, C: 0.01 to 0.10%, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, Ni: 0.01 to 0.50%, Cr: 10 to 20%, Mo: 0.005 to 0.50% , Cu: 0.01 to 0.50%, V: 0.001 to 0.50%, Ti: 0.001 to 0.50%, Al: 0.01 to 0.20%, Nb: 0.001 to 0.50%, N: 0.005 to 0.050% and B: 0.00010 to 0.00500% Hot rolling the contained steel, followed by hot-rolled sheet annealing in the ferrite single-phase temperature range using a box furnace or AP line (annealing and pickling line) continuous furnace, followed by cold rolling and finish annealing Ferritic stainless steels with excellent workability and surface properties characterized by the above are disclosed.
• AP line annealing and pickling line
• Patent Document 2 does not mention any elongation at all.
• a crystal grain group (colony) having a similar crystal orientation is formed during casting or hot rolling, and
• Japanese Patent No. 3588281 (Republication WO00 / 60134)
• Japanese Patent No. 3582001 Japanese Patent Laid-Open No. 2001-3134
• the present invention solves such problems, and provides a ferritic stainless steel having sufficient corrosion resistance and formability, and excellent surface properties free from the occurrence of linear flaws due to hot rolling or annealing, and a method for producing the same.
• the purpose is to provide.
• sufficient corrosion resistance refers to a salt spray cycle test ((Salt spray (35 ° C, 5 ° C (Mass% NaCl, spray 2h) ⁇ Drying (60 ° C, relative humidity 40%, 4h) ⁇ Wet (50 ° C, relative humidity ⁇ 95%, 2h))))
• Salt spray 35 ° C, 5 ° C (Mass% NaCl, spray 2h) ⁇ Drying (60 ° C, relative humidity 40%, 4h) ⁇ Wet (50 ° C, relative humidity ⁇ 95%, 2h)
• the rusting area ratio on the surface is 25% or less.
• sufficient formability means that the elongation at break in a tensile test based on JIS Z 2241 is 25% or more when using a specimen taken in a direction perpendicular to the rolling direction, and a tensile test based on JIS Z2241
• the average r value calculated by the following equation (1) when applying a strain of 15% in the above is 0.65 or more, and the in-plane anisotropy of the r value calculated by the following equation (2) (hereinafter, This means that the absolute value (
• r L is an r value when a tensile test is performed in a direction parallel to the rolling direction
• r D is an r value when a tensile test is performed in a direction of 45 ° with respect to the rolling direction
• r C is a direction perpendicular to the rolling direction. The r value when a tensile test is performed.
• the composition further includes one or more selected from Cu: 0.1 to 1.0%, Ni: 0.1 to 1.0%, Mo: 0.1 to 0.5%, Co: 0.01 to 0.5%
• the composition further includes one or more selected from Mg: 0.0002 to 0.0050%, B: 0.0002 to 0.0050%, REM: 0.01 to 0.10%, Ca: 0.0002 to 0.0020%
• the steel slab having the component composition according to any one of [1] to [4] is hot-rolled and then annealed at a temperature range of 880 to 1000 ° C.
• a method for producing a ferritic stainless steel which is a hot-rolled annealed sheet, followed by cold rolling and then cold-rolled sheet annealing at a temperature range of 800 to 950 ° C. for 5 seconds to 5 minutes.
• all% which shows the component of steel is the mass%.
• a ferritic stainless steel having a sufficient corrosion resistance and formability (elongation and average r value is large,
• Ferritic stainless steel is% by mass, C: 0.005-0.05%, Si: 0.02-0.50%, Mn: 0.05-1.0%, P: 0.04% or less, S: 0.01% or less, Cr: 15.5-18.0%, Al: 0.001 to 0.10%, N: 0.01 to 0.06%, V: 0.01 to 0.25%, Ti: 0.001 to 0.020%, Nb: 0.001 to 0.030%, the balance is Fe and inevitable impurities, and V /(Ti+Nb) ⁇ 2.0.
• the balance of the component composition is important, and in particular, the balance of V, Ti, and Nb is important.
• V 0.01 to 0.25%
• Ti 0.001 to 0.020%
• Nb 0.001 to 0.030%
• V / (Ti + Nb) ⁇ 2.0 are important requirements.
• the inventors examined a technique for obtaining a predetermined formability by short-time hot-rolled sheet annealing using a high-productivity continuous annealing furnace, instead of long-time hot-rolled sheet annealing such as box annealing (batch annealing). did.
• the problem with the prior art using a continuous annealing furnace is that annealing is performed in the ferrite single-phase temperature range, so that sufficient recrystallization does not occur and sufficient elongation cannot be obtained, and after the colony is cold-rolled sheet annealed In other words,
• the inventors performed hot rolling sheet annealing in a two-phase region of a ferrite phase and an austenite phase, and then cold-rolled and cold-rolled sheet annealing by a conventional method, and finally made a ferrite single-phase structure again. I devised that.
• the recrystallization of the ferrite phase is promoted by performing the hot-rolled sheet annealing in the two-phase region of the ferrite phase and austenite which are higher than the ferrite single-phase temperature region.
• the ferrite crystal grains introduced with work strain by hot rolling remain until after cold-rolled sheet annealing, and the elongation after cold-rolled sheet annealing is improved.
• the austenite phase is generated from the ferrite phase by hot-rolled sheet annealing, the austenite phase is generated with a crystal orientation different from that of the ferrite phase before annealing, which effectively destroys the ferrite phase colony. Is done.
• linear wrinkles (hereinafter referred to as linear wrinkles) along the rolling direction after cold-rolled sheet annealing are performed. It has become clear that a new problem arises that surface properties are significantly reduced.
• the inventors investigated the cause of the occurrence of linear flaws by performing hot-rolled sheet annealing in a two-phase region of a ferrite phase and an austenite phase in order to achieve both formability and surface properties.
• the linear wrinkles were caused by a remarkably hard martensite phase present in the surface layer portion of the steel sheet after hot-rolled sheet annealing. That is, if there is a remarkably hard martensite phase in the surface layer of the steel sheet after hot-rolled sheet annealing, strains concentrate at the interface between the remarkably hard martensite phase and the ferrite phase in the subsequent cold rolling, and microcracks are generated.
• the martensite phase is formed by transformation of the austenite phase formed during hot-rolled sheet annealing in the two-phase region of the ferrite phase and the austenite phase during the cooling process.
• HV Vickers hardness
• the inventors clarified the cause of locally forming a significantly hard martensite phase exceeding HV500 after hot-rolled sheet annealing, and intensively studied the countermeasure technique.
• an extremely hard martensite phase is formed when coarse Cr carbonitride is present before hot-rolled sheet annealing.
• This mechanism is considered as follows.
• the austenite phase is formed by the solid solution of Cr carbonitride precipitated by hot rolling.
• the Cr carbonitride before hot-rolled sheet annealing is coarse, the amount of C supplied to the austenite phase increases.
• the C concentration is locally higher than the portion where coarse Cr carbonitride is not dissolved. From this austenite phase having a high C concentration, a remarkably hard martensite phase is produced after hot-rolled sheet annealing.
• V, Ti and Nb should be included in the steel components so that V: 0.01-0.25%, Ti: 0.001-0.020%, Nb: 0.001-0.030%, and V / (Ti + Nb) ⁇ 2.0.
• V 0.01-0.25%
• Ti 0.001-0.020%
• Nb 0.001-0.030%
• Cr carbonitride that precipitates during hot rolling becomes composite carbonitride (Cr, V, Ti, Nb) (C, N) containing V, Ti, and Nb.
• Cr, V, Ti, Nb composite carbonitride
• C, N containing V, Ti, and Nb.
• Ti and Nb have a stronger affinity for C and N than Cr, and form carbonitrides more easily than Cr. Therefore, when Ti or Nb is contained alone, it precipitates as Ti (C, N) or Nb (C, N) different from Cr carbonitride and suppresses the formation of coarse Cr carbonitride. The effect to do is not obtained.
• V is also an element having a strong affinity with C and N.
• Cr carbonitride precipitates as (Cr, V, Ti, Nb) (C, N).
• This (Cr, V, Ti, Nb) (C, N) is a precipitate containing V, Ti, and Nb, which has a lower diffusion rate than Cr, so that the growth or coarsening after precipitation is V, Ti, and Nb. The rate of precipitates is limited, and the precipitate size becomes finer than that of conventional Cr carbonitrides, and the formation of coarse carbonitrides in hot rolling can be effectively suppressed.
• C 0.005-0.05%
• C promotes the formation of the austenite phase and has the effect of expanding the two-phase temperature range where the ferrite phase and the austenite phase appear during hot-rolled sheet annealing. In order to acquire this effect, 0.005% or more needs to be contained. However, if the C content exceeds 0.05%, the steel sheet becomes hard and the ductility decreases. Moreover, even if it has this invention, a remarkably hard martensite phase will produce
• the lower limit is preferably 0.01%, more preferably 0.015%.
• the upper limit is preferably 0.035%, more preferably 0.03%, and even more preferably 0.025%.
• Si 0.02-0.50% Si is an element that acts as a deoxidizer during steel melting. In order to obtain this effect, a content of 0.02% or more is necessary. However, if the Si content exceeds 0.50%, the steel sheet becomes hard and the rolling load during hot rolling increases. Moreover, the ductility after cold-rolled sheet annealing decreases. Therefore, the Si content is in the range of 0.02 to 0.50%. Preferably it is 0.10 to 0.35% of range. More preferably, it is in the range of 0.25 to 0.30%.
• Mn 0.05-1.0% Mn, like C, promotes the formation of an austenite phase and has the effect of expanding the two-phase temperature range in which the ferrite phase and austenite phase appear during hot-rolled sheet annealing. In order to acquire this effect, 0.05% or more needs to be contained. However, if the amount of Mn exceeds 1.0%, the amount of MnS produced increases and the corrosion resistance decreases. Therefore, the Mn content is in the range of 0.05 to 1.0%.
• the lower limit is preferably 0.1%, more preferably 0.2%.
• the upper limit is preferably 0.8%, more preferably 0.35%, and still more preferably 0.3%.
• P 0.04% or less
• P is an element that promotes grain boundary fracture due to grain boundary segregation, so a lower value is desirable, and the upper limit is made 0.04%.
• S 0.01% or less
• S is an element that exists as sulfide inclusions such as MnS and reduces ductility, corrosion resistance, and the like. In particular, when the content exceeds 0.01%, those adverse effects are remarkable. Therefore, it is desirable that the S amount be as low as possible.
• the upper limit of the S amount is 0.01%. More preferably, it is 0.007% or less. More preferably, it is 0.005% or less.
• Cr 15.5-18.0% Cr is an element having an effect of improving the corrosion resistance by forming a passive film on the steel sheet surface. In order to obtain this effect, the Cr content needs to be 15.5% or more. However, if the Cr content exceeds 18.0%, the austenite phase is not sufficiently generated during hot-rolled sheet annealing, and predetermined material characteristics cannot be obtained. Therefore, the Cr content is in the range of 15.5 to 18.0%. Preferably it is 16.0 to 18.0% of range. Furthermore, it is preferably in the range of 16.0 to 17.0%.
• Al 0.001 to 0.10%
• Al is an element that acts as a deoxidizer. In order to acquire this effect, 0.001% or more needs to be contained.
• the Al content is set in the range of 0.001 to 0.10%. Preferably it is 0.001 to 0.07% of range. More preferably, it is 0.001 to 0.05% of range. Even more preferably, it is in the range of 0.001 to 0.03%.
• N 0.01-0.06% N, like C and Mn, promotes the formation of the austenite phase and has the effect of expanding the two-phase temperature range in which the ferrite phase and austenite phase appear during hot-rolled sheet annealing.
• the N content needs to be 0.01% or more.
• the N content is in the range of 0.01 to 0.06%.
• it is 0.01 to 0.05% of range. More preferably, it is in the range of 0.02 to 0.04%.
• V 0.01-0.25%
• V is an extremely important element in the present invention.
• V has a feature that the affinity for C and N is higher than that of Cr.
• V / (Ti + Nb) ⁇ 2.0 it is combined with Cr, Ti and Nb during hot rolling (Cr, V, It precipitates as Ti, Nb) (C, N) and suppresses the precipitation of coarse Cr carbonitride. Due to this effect, the generation of austenite phase in which C is excessively concentrated during hot-rolled sheet annealing is suppressed, and a remarkably hard martensite phase is not generated after hot-rolled sheet annealing, resulting in generation of microcracks during cold rolling. Occurrence of the resulting surface line defects is prevented.
• the V content needs to be 0.01% or more.
• the V amount is in the range of 0.01 to 0.25%.
• it is 0.03 to 0.20% of range. More preferably, it is 0.05 to 0.15% of range.
• Ti and Nb like V, are elements with higher affinity for C and N than Cr, and when steel contains V, V and Cr and (Cr, V, Ti, Nb) (C, N) Has an effect of suppressing the precipitation of coarse Cr carbonitride during hot rolling. In order to obtain this effect, it is necessary to contain 0.001% or more of Ti and 0.001% or more of Nb and satisfy V / (Ti + Nb) ⁇ 2.0.
• the Ti content is in the range of 0.001 to 0.020%, and the Nb content is in the range of 0.001 to 0.030%.
• the amount of Ti is preferably in the range of 0.001 to 0.015%. More preferably, it is in the range of 0.003 to 0.010%.
• the amount of Nb is preferably in the range of 0.001 to 0.025%.
• V / (Ti + Nb) is set to 2.0 or more. Preferably it is 3.0 or more. More preferably, it is 4.0 or more.
• V / (Ti + Nb) exceeds 30.0, even if V, Ti and Nb have a predetermined content, the amount of V existing in a solid solution state without being consumed for formation of composite carbonitride Therefore, the elongation decreases due to the hardening of the steel sheet. Therefore, the upper limit of V / (Ti + Nb) is preferably 30.0.
• the balance is Fe and inevitable impurities.
• Cu and Ni are elements that improve corrosion resistance. In particular, it is effective to contain it when high corrosion resistance is required. Further, Cu and Ni have an effect of promoting the formation of the austenite phase and expanding the two-phase temperature range in which the ferrite phase and the austenite phase appear during hot-rolled sheet annealing. These effects become significant when the content is 0.1% or more. However, if the Cu content exceeds 1.0%, the hot workability is lowered, which is not preferable. Therefore, when it contains Cu, it is 1.0% or less. Preferably it is 0.2 to 0.8% of range.
• Ni is 1.0% or less.
• it is 0.1 to 0.6% of range. More preferably, it is in the range of 0.1 to 0.3%.
• Mo is an element that improves corrosion resistance, and it is effective to contain it particularly when high corrosion resistance is required. This effect becomes significant when the content is 0.1% or more. However, if the Mo content exceeds 0.5%, the austenite phase is not sufficiently generated during hot-rolled sheet annealing, and predetermined material characteristics cannot be obtained. Therefore, when it contains Mo, it is made 0.1 to 0.5 %% or less. Preferably it is 0.1 to 0.3% of range.
• Co is an element that improves toughness. This effect is obtained when the content is 0.01% or more. On the other hand, if the Co content exceeds 0.5%, workability is reduced. Therefore, when it contains Co, it is 0.5% or less. Preferably it is 0.01 to 0.2% of range.
• Mg 0.0002-0.0050%
• B 0.0002-0.0050%
• REM 0.01-0.10%
• Ca One or more selected from 0.0002-0.0020%
• Mg: 0.0002-0.0050% Mg is an element that has the effect of improving hot workability. In order to acquire this effect, 0.0002% or more needs to be contained. However, when the Mg content exceeds 0.0050%, the surface quality decreases. Therefore, when Mg is contained, the content is made 0.0002 to 0.0050%. Preferably it is 0.0005 to 0.0035% of range. More preferably, it is in the range of 0.0005 to 0.0020%.
• B 0.0002-0.0050%
• B is an effective element for preventing low temperature secondary work embrittlement. In order to acquire this effect, 0.0002% or more needs to be contained. However, when the amount of B exceeds 0.0050%, the hot workability decreases. Therefore, when B is contained, the content is made 0.0002 to 0.0050%. Preferably it is 0.0005 to 0.0035% of range. More preferably, it is in the range of 0.0005 to 0.0020%.
• REM 0.01-0.10% REM is an element that improves the oxidation resistance, and in particular has the effect of suppressing the formation of an oxide film at the weld and improving the corrosion resistance of the weld. In order to obtain this effect, a content of 0.01% or more is necessary. However, if the content exceeds 0.10%, productivity such as pickling at the time of cold-rolled sheet annealing is lowered. Moreover, since REM is an expensive element, excessive inclusion causes an increase in manufacturing cost, which is not preferable. Therefore, when REM is contained, the content is made 0.01 to 0.10%.
• Ca 0.0002-0.0020%
• Ca is an effective component for preventing nozzle clogging due to crystallization of Ti-based inclusions that are likely to occur during continuous casting. In order to acquire this effect, 0.0002% or more needs to be contained. However, when the Ca content exceeds 0.0020%, CaS is generated and the corrosion resistance is lowered. Therefore, when Ca is contained, the content is made 0.0002 to 0.0020%. Preferably it is 0.0005 to 0.0015% of range. More preferably, it is 0.0005 to 0.0010% of range.
• the manufacturing method of the ferritic stainless steel of this invention is demonstrated.
• a steel slab having the above composition is hot-rolled and then subjected to hot-rolled sheet annealing in a temperature range of 880 to 1000 ° C. for 5 seconds to 15 minutes to form a hot-rolled annealed sheet.
• it is obtained by performing cold rolled sheet annealing that is held at a temperature range of 800 to 950 ° C. for 5 seconds to 5 minutes.
• the molten steel having the above component composition is melted by a known method such as a converter, electric furnace, vacuum melting furnace or the like, and is made into a steel material (slab) by a continuous casting method or an ingot-bundling method.
• This slab is heated at 1100 to 1250 ° C. for 1 to 24 hours, or directly hot-rolled as cast without heating to form a hot-rolled sheet.
• the winding temperature is preferably 500 ° C. or higher and 850 ° C. or lower. If it is less than 500 ° C., recrystallization after winding is insufficient, and ductility after cold-rolled sheet annealing may be lowered, which is not preferable. When it winds up above 850 degreeC, a particle size will become large and rough skin may generate
• hot-rolled sheet annealing is performed at a temperature of 880 to 1000 ° C., which is a two-phase region temperature of the ferrite phase and the austenite phase, for 5 seconds to 15 minutes.
• Hot-rolled sheet annealing is an important process for the present invention to obtain predetermined surface properties and formability. If the hot-rolled sheet annealing temperature is less than 880 ° C., sufficient recrystallization does not occur and the ferrite single-phase region is formed, so that the effects of the present invention that are manifested by two-phase region annealing may not be obtained. However, if the annealing temperature exceeds 1000 ° C, solid solution of the carbide is promoted, so C concentration in the austenite phase is promoted, and an extremely hard martensite phase is generated after hot-rolled sheet annealing. The property cannot be obtained.
• the hot-rolled sheet annealing temperature exceeds 1000 ° C, the amount of austenite phase produced decreases. Therefore, the amount of martensite phase formed after hot-rolled sheet annealing is reduced, and the metal due to the concentration of rolling strain on the ferrite phase in the vicinity of the martensite phase by cold rolling the metal structure containing the ferrite phase and martensite phase. The effect of relaxing the anisotropic structure cannot be sufficiently obtained, and the predetermined
• the annealing time is less than 5 seconds, even if annealing is performed at a predetermined temperature, the formation of austenite phase and recrystallization of the ferrite phase do not occur sufficiently, so that the desired formability cannot be obtained.
• the annealing time exceeds 15 minutes, a part of (Cr, V, Ti, Nb) (C, N) is dissolved and C concentration in the austenite phase is promoted. A predetermined surface texture cannot be obtained.
• hot-rolled sheet annealing is held at a temperature of 880 to 1000 ° C for 5 seconds to 15 minutes.
• the temperature is maintained at 900 to 1000 ° C. for 15 seconds to 15 minutes. More preferably, the temperature is maintained at 900 to 1000 ° C. for 15 seconds to 3 minutes.
• Cold rolling is preferably performed at a reduction rate of 50% or more from the viewpoint of formability and shape correction.
• cold rolling and annealing may be repeated twice or more, and a stainless steel foil having a thickness of 200 ⁇ m or less may be formed by cold rolling.
• Cold-rolled sheet annealing is performed at a temperature of 800 to 950 ° C for 5 seconds to 5 minutes in order to obtain good formability.
• Cold-rolled sheet annealing is an important process for making a two-phase structure of a ferrite phase and a martensite phase formed by hot-rolled sheet annealing into a ferrite single-phase structure. If the cold-rolled sheet annealing temperature is less than 800 ° C., sufficient recrystallization does not occur and the predetermined ductility and average r value cannot be obtained. On the other hand, when the cold-rolled sheet annealing temperature exceeds 950 ° C, the steel component becomes hard because the martensite phase is formed after the cold-rolled sheet annealing in the steel component in which the temperature is a two-phase temperature range of the ferrite phase and the austenite phase. A predetermined ductility cannot be obtained.
• the glossiness of the steel sheet is lowered due to marked coarsening of crystal grains, which is not preferable from the viewpoint of surface quality.
• the annealing time is less than 5 seconds, even if annealing is performed at a predetermined temperature, the ferrite phase is not sufficiently recrystallized, so that the predetermined ductility and average r value cannot be obtained. If the annealing time exceeds 5 minutes, the crystal grains become extremely coarse and the glossiness of the steel sheet is lowered, which is not preferable from the viewpoint of surface quality. Therefore, cold-rolled sheet annealing is held at 800 to 950 ° C for 5 seconds to 5 minutes.
• the holding is preferably performed at 850 ° C. to 900 ° C. for 15 seconds to 3 minutes.
• BA annealing (bright annealing) may be performed.
• grinding or polishing may be performed.
• Stainless steel having the chemical composition shown in Table 1 was melted in a 50 kg small vacuum melting furnace. These steel ingots were heated at 1150 ° C. for 1 h and then hot rolled to form 3.5 mm thick hot rolled sheets. Subsequently, these hot-rolled sheets were subjected to hot-rolled sheet annealing under the conditions shown in Table 2, and then the surfaces were descaled by shot blasting and pickling.
• the pickling was performed by immersing in a solution of 20 mass% sulfuric acid at a temperature of 80 ° C for 120 seconds, and then immersed in a mixed acid solution consisting of 15 mass% nitric acid and 3 mass% hydrofluoric acid at a temperature of 55 ° C for 60 seconds. Furthermore, after cold-rolled sheet annealing was performed under the conditions shown in Table 2 to a thickness of 0.7 mm by cold rolling, electrolysis under conditions of 25 C / dm 2 in a water temperature of 80 ° C. and an 18 mass% Na 2 SO 4 aqueous solution.
• the cold roll pickling annealed plate thus obtained was evaluated as follows.
• r L , r D , and r C are r values in the L direction, the D direction, and the C direction, respectively.
• 0.65 or more was regarded as acceptable ( ⁇ ), and less than 0.65 was regarded as unacceptable (x).
• 0.30 or less was accepted ( ⁇ ), and more than 0.30 was rejected (x).
• the salt spray cycle test consists of salt spray (35 °C, 5% NaCl, spray 2h) ⁇ drying (60 °C, relative humidity 40%, 4h) ⁇ wet (50 °C, relative humidity ⁇ 95%, 2h) as one cycle. 3 cycles were performed.
• the rusting area ratio after the salt spray cycle test is 10% or less. Corrosion resistance has been further improved.
• Comparative Example No. 24 where the V content is below the range of the present invention and does not satisfy V / (Ti + Nb) ⁇ 2.0
• Comparative Example No. 26 in which Ti and Nb exceed the range of the present invention, Due to insufficient precipitation of (Cr, V, Ti, Nb) (C, N), solid solution C and N were not sufficiently fixed during hot-rolled sheet annealing. Martensite phase was generated, and a large amount of linear flaws were generated after cold-rolled sheet annealing.
• No. 47 and No. 64 are comparative examples in which V / (Ti + Nb) is below the range of the present invention and the hot-rolled sheet annealing temperature is higher than the range of the present invention. Since V / (Ti + Nb) is below the range of the present invention, C concentration in the austenite phase accompanying the solid solution of coarse carbides precipitated during hot rolling is promoted, and extremely hard after hot-rolled sheet annealing. Since the martensite phase was generated, a large amount of linear wrinkles was generated, and the predetermined surface properties could not be obtained.
• the hot-rolled sheet annealing temperature was higher than the range of the present invention, the amount of austenite phase generated during annealing decreased, and the amount of martensite phase generated after hot-rolled sheet annealing decreased.
• the anisotropic relaxation effect of the metal structure could not be obtained, and the predetermined
• No. 48 and No. 65 are comparative examples in which V / (Ti + Nb) is below the range of the present invention and the hot-rolled sheet annealing temperature is lower than the range of the present invention.
• V / (Ti + Nb) is below the range of the present invention, but the hot-rolled sheet annealing temperature was in the ferrite single-phase temperature range and the austenite phase was not generated, resulting in the formation of a significantly hard martensite phase. There was almost no occurrence of linear wrinkles, and good surface properties were obtained.
• the hot-rolled sheet annealing temperature was lower than the range of the present invention, sufficient recrystallization did not occur, and no martensite phase was formed after the hot-rolled sheet annealing, so that the predetermined ductility, average r value and
• No. 66 is a comparative example in which V / (Ti + Nb) is below the range of the present invention and the hot-rolled sheet annealing time is longer than the range of the present invention. Therefore, as a result of excessive C concentration in the austenite phase accompanying the solid solution of coarse carbides precipitated during hot rolling, a remarkably hard martensite phase was generated after hot-rolled sheet annealing, resulting in linear flaws. It was generated in a large amount and a predetermined surface property could not be obtained. Furthermore, because the metal structure after cold-rolled sheet annealing was a mixed grain structure consisting of ferrite crystal grains with excessive carbide in grains and on grain boundaries, and ferrite grains with few carbides on grain boundaries and grain boundaries. During tensile deformation, local strain concentration occurred at the interface between the two crystal grains, and the predetermined ductility was not obtained.
• No. 67 is a comparative example in which V / (Ti + Nb) is below the range of the present invention and the cold-rolled sheet annealing temperature is lower than the range of the present invention. Since V / (Ti + Nb) was below the range of the present invention, a large amount of linear wrinkles occurred, and the predetermined surface properties could not be obtained. Furthermore, because the cold-rolled sheet annealing temperature was lower than the range of the present invention, the recrystallization in the cold-rolled sheet annealing was insufficient and the work structure at the time of cold rolling remained, so the predetermined ductility and average r value could not be obtained. .
• No. 68 is a comparative example in which V / (Ti + Nb) is below the range of the present invention and the cold-rolled sheet annealing temperature is higher than the range of the present invention. Since V / (Ti + Nb) was below the range of the present invention, a large amount of linear wrinkles occurred and the predetermined surface properties could not be obtained. Furthermore, because the cold-rolled sheet annealing temperature was higher than the range of the present invention, it became the annealing in the two-phase temperature range of the ferrite phase and the austenite phase, so the austenite phase was generated again, and after the cold-rolled sheet annealing, the martensite phase Due to the transformation, the steel sheet was remarkably hardened and the predetermined ductility was not obtained.
• the ferritic stainless steel obtained by the present invention is particularly suitable for press-molded products mainly composed of a drawing and applications requiring high surface beauty, such as kitchen utensils and tableware.

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• 2015
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