CN105803308B - A kind of the 45MnVS easy-cutting untempered steels and its manufacturing method of the calcium containing magnesium - Google Patents

Abstract

The invention provides a 45MnVS free-cutting non-quenched and tempered steel containing magnesium and calcium and a manufacturing method thereof. The main components of the steel are: C: 0.42%-0.51%, Si: 0.15%-0.6%, Mn: 0.90%-1.50% , P:0.010%～0.035%, S:0.040%～0.080%, V:0.06%～0.13%, Mg: 0.0005%～0.008%, Al: 0.01%～0.04%, Ca:0.0008%～0.005%, and The amount is Fe and unavoidable impurities; the present invention controls the smelting through the converter, LF+VD magnesium-calcium compound treatment to modify the inclusion form, M-EMS+F-EMS combined continuous casting, controlled rolling and controlled cooling, on the basis of the traditional 45MnVS A small amount of magnesium and calcium is added to modify the sulfur-containing inclusions, so that the strength index of the material is equivalent to that of No. 45 steel quenched and tempered, and it has better machinability and fatigue resistance than 45MnVS. It can be used for parts and structures such as automotive connecting rods, crankshafts, knuckle shafts, drive shafts, front axles, etc.

Description

A kind of magnesium-calcium-containing 45MnVS free-cutting non-quenched and tempered steel and its manufacturing method

technical field

The invention relates to the field of iron and steel metallurgy, in particular to a non-quenched and tempered steel and a production process thereof, and relates to a free-cutting non-quenched and tempered steel containing Mg-Ca and a manufacturing method thereof.

Background technique

Free-cutting non-quenched and tempered steel is a kind of steel that has achieved or approached the mechanical properties of quenched and tempered steel and has easy machinability through microalloying, controlled rolling and controlled cooling, etc. Class high-quality or special quality structural steel. Free-cutting non-quenched and tempered steel is widely used in parts and structural parts such as automotive connecting rods, crankshafts, steering knuckle shafts, drive shafts, front axles, etc., and its consumption is increasing day by day. It is a typical representative of automotive steel and caters to continuous machining The development in the direction of automation, high speed and precision puts forward requirements for improved processing performance and higher strength of free-cutting non-quenched and tempered steel. With the development of refining technology, microalloying control technology, controlled rolling and controlled cooling technology, easy Non-quenched and tempered steel is used in a wider range, involving construction, heavy machinery, high-pressure pipelines, bridges and other fields, and has achieved remarkable energy-saving results.

Non-quenched and tempered steel is a kind of high-efficiency and energy-saving steel that has been developed rapidly due to the oil crisis in the 1970s, which led to international energy shortages. attention from all over the world. At present, non-quenched and tempered steel has been widely used for many forgings on foreign automobiles; domestic automobile factories are also developing and applying non-quenched and tempered steel or introducing foreign non-quenched and tempered steel manufacturing technology. Compared with quenched and tempered steel, the strength of traditional non-quenched and tempered steel for hot forging is better, but its toughness is insufficient and difficult to cut, which limits its wide application. Therefore, the development focus of free-cutting non-quenched and tempered steel is to ensure On the basis of strength to improve toughness and endow it with excellent machinability.

The difficulties in the production process are the oxygen content in the steel, the absorption rate and narrow range of sulfur elements, the small inclusions, the uniform harmless treatment and the control of the low-magnification structure of the slab. The sulfur-containing free-cutting steel produced by traditional electric furnace → LF → continuous casting → controlled rolling and controlled cooling or converter → LF → continuous casting → controlled rolling and controlled cooling and Al deoxidation process has poor purity, uneven composition and temperature, nitrogen and hydrogen The flocculent oxides with high content of Al are easy to block the nozzle and have poor pourability. In order to overcome these difficulties and disadvantages, the present invention proposes to adopt converter→LF→VD→continuous casting→controlled rolling and controlled cooling to produce sulfur-containing free-cutting non-quenched and tempered steel by Ca-Mg compound modification process. On the premise of ensuring mechanical properties, In turn, the machinability of steel can be improved, and at the same time, the purity and uniformity of steel can be significantly improved, and the pourability can be improved.

The Chinese patent with publication number CN1667129A discloses a production method of sulfur-containing free-cutting non-quenched and tempered steel. The composition (weight percentage) of the steel is: C 0.10~0.35%, Si 0.15~0.45%, Mn 0.60~1.50% , P≤0.03%, S≤0.045%, Cr 0.80~1.50%, Ti 0.03~0.12%, Al 0.01~0.10%, Ni0~0.30%, Mo0~0.20%, Cu0~0.20%, N 0.004~0.015%, iron balance. The difference between the application of the present invention and the above-mentioned patents lies in that the application of the present invention does not contain Ti and the morphology of inclusions is modified by magnesium and calcium.

The Chinese patent with the publication number CN101255535 discloses a Ca-S composite free-cutting non-quenched and tempered steel and its production process, C: 0.44-0.49%, S: 0.040-0.065%, Si: 0.30-0.60%, P≤0.035 %, Mn: 1.20-1.50%, Ca: 0.001-0.010%, V: 0.08-0.12%, Al: 0.01-0.03%, Cr, Ni, Cu≤0.30%, the rest are Fe and unavoidable impurities. The difference between the application of the present invention and the above-mentioned patents lies in: the magnesium-calcium modification of the present application, Mg: 0.0005%-0.008%, Al: 0.001%-0.04%, Ca: 0.0008%-0.005%, and the application adopts VD in the process deal with.

The publication number is CN104264040A, a non-quenched and tempered steel and its manufacturing method, and a crankshaft made of the non-quenched and tempered steel. The mass percentage ratio of the chemical elements is: C: 0.37-0.43%, Si: 0.55-0.65%, Mn: 1.46～1.56%, V:0.07～0.13%, Nb:0.015～0.035%, N:0.012～0.017%; the balance is iron and other unavoidable impurities. The difference between the application of the present invention and the above-mentioned patents is that the application of the present invention does not add Nb but uses magnesium-calcium modification, Mg: 0.0005%-0.008%, Ca: 0.0008%-0.005%, and this application adopts VD treatment in the process.

Contents of the invention

Aiming at the deficiencies of the existing technology and the higher and higher requirements of the manufacturing industry for materials, the present invention provides a sulfur-containing and magnesium-containing free-cutting non-quenched and tempered steel and its production method through Mg-Ca composite modification treatment, and further modifies the Sulfur is easy to cut the sulfide inclusions in the non-quenched and tempered steel, thereby improving the shape of the inclusions, and then the mechanical properties and cutting performance of the steel. The composition of the non-quenched and tempered steel is calculated by weight percentage: C: 0.42% to 0.51%, Si: 0.15% to 0.6%, Mn: 0.90% to 1.50%, P: 0.010% to 0.035%, S: 0.040% to 0.080%, V: 0.06% to 0.13%, Mg: 0.0005% to 0.008%, Al: 0.01% to 0.04%, Ca: 0.0008% to 0.005%, and the balance is Fe and unavoidable impurities.

The purpose of the present invention is achieved by the following technical solutions:

A free-cutting non-quenched and tempered steel containing sulfur, magnesium, and calcium and its smelting method. The composition of the non-quenched and tempered steel is calculated by weight percentage: C: 0.42%-0.51%, Si: 0.15%-0.6%, Mn : 0.90% to 1.50%, P: 0.010% to 0.035%, S: 0.040% to 0.080%, V: 0.06% to 0.13%, Mg: 0.0005% to 0.008%, Al: 0.01% to 0.04%, Ca: 0.0008 %～0.005%, the balance is Fe and unavoidable impurities.

The effect of each element of the present invention:

C: The level of carbon content has a very important influence on the strength, hardness and ductility of steel. Among all elements, carbon has the greatest ability to increase strength. The strengthening effect of carbon on quenched and tempered steel is about 5 times that of silicon, 9 times that of chromium and 18 times that of manganese. Therefore, in order to ensure that the gear steel has sufficient strength and hardness, Steel must contain a considerable carbon content. General gear steels contain more alloying elements, among which many carbide-forming elements will form carbides such as MoC, (Fe,Cr) ₃ C, Cr ₇ C ₃ and so on with carbon. The precipitation of alloy carbides in the tempering process produces a secondary hardening effect, which can further increase the hardness of the material, so that it has higher strength and good wear resistance.

Si: As a deoxidizer, silicon can control the degree of deoxidation of gear steel. It is a key element that affects the deformation and cutting performance of sulfide inclusions in steel, and is also one of the elements that deteriorate the cutting performance of steel. Silicon can strongly improve the hardenability of the carburized layer, but it is prone to grain boundary oxidation during the carburizing process to form black network defects; with the increase in the addition of alloying elements, the martensitic point of the steel decreases, making the carburized layer after quenching It contains a large amount of retained austenite, which affects the fatigue performance and wear resistance of parts.

Mn: Manganese can increase the nucleation work and transformation activation energy of pearlite, reduce the nucleation rate and growth rate of pearlite, manganese and its carbides dissolve in austenite, and shift the austenite isothermal transformation curve to the right , Increase the stability of supercooled austenite, inhibit pearlite transformation, and improve hardenability. MnS formed by manganese and sulfur in steel is an important easy-cutting phase, which can help improve cutting performance. In order to ensure good cutting performance and mechanical properties, the present invention controls the manganese content at 0.8-1.6%.

P: Phosphorus is considered a harmful element for structural steel, but in cold-rolled sheets, it can be used to dissolve ferrite to significantly increase the strength. At the same time, in order to avoid the cold brittleness of phosphorus, the phosphorus content is generally controlled below 0.10% .

S: S≤0.025% for general low-sulfur steel, S=0.04-0.09% for medium-sulfur steel, and S=0.10-0.30% for high-sulfur steel. Among them, medium-sulfur steel has been widely used in industrial production due to its good cutting performance and mechanical properties, while high-sulfur steel is a steel to meet special cutting performance requirements. For ordinary steel, a slight increase in sulfur can significantly improve the machinability. Studies have shown that spherical or spindle-shaped inclusions are more conducive to cutting than linear inclusions. The purpose of changing the shape of sulfide can be achieved by adding elements such as calcium, rare earth and titanium to free-cutting steel. At the same time, it is necessary to ensure that the steel has a certain ratio of manganese to sulfur, so as to reduce the adverse effects caused by excessive sulfur content in the steel, so as to ensure the mechanical properties of the steel. The principle of composition design is to improve the cutting performance of the steel under the condition that the mechanical properties of the steel are basically unchanged. But at the same time, MnS is easy to elongate along the rolling direction during hot rolling, which reduces the transverse mechanical properties of the steel. Therefore the present invention controls sulfur content to be 0.040%～0.08%.

V: Vanadium is the most commonly used and effective strengthening microalloying element, which mainly affects the structure and properties of steel by forming V (C, N). V (C, N) is mainly precipitated in the ferrite at the austenite grain boundary to refine the ferrite grains and increase the strength of the steel. After a small amount of vanadium is added to the steel, the vanadium combines with carbon and "free" nitrogen to form V(C,N) compounds, which reduces the "free" nitrogen content in the steel and makes the steel non-strain aging. Vanadium carbonitrides have the effect of refining grains and increasing strength, and the strength increases linearly with the increase of vanadium content. If the vanadium content exceeds 0.15%, it is not good for its toughness. The amount of vanadium added in steel is generally controlled at 0.08% to 0.13%.

Al: Aluminum is generally added to the metal as a deoxidizer, but is also a microalloying element used to bind nitrogen in steel. During the cooling process, as the temperature drops, the solubility of aluminum in austenite decreases and aluminum nitrides are precipitated, which prevents the growth of austenite grains. It promotes heterogeneous nucleation during γ→α phase transformation, accelerates austenite transformation and refines ferrite grains. In order to refine the grains better, the method of refining and feeding Al wire is adopted, and the feeding speed and timing of feeding wire are reasonably controlled, so that the content of acid-soluble aluminum can be stably controlled within the internal control range.

Ca: During the solidification process of molten steel, the oxidation product of calcium acts as the nucleation core of sulfide, which can promote the precipitation of sulfide and the uniform distribution of sulfide. By adding sulfide form control elements to the steel, such as tellurium, selenium, titanium, calcium or rare earth metals, etc., and controlling the oxygen content in the steel, the inclusions in the steel are formed into spindles to improve the machinability of the steel. Generally, metal calcium or calcium-silicon alloy deoxidizer is used instead of metal aluminum for deoxidation. Generally, simple calcium free-cutting steel is rarely used, and calcium-sulfur or calcium-sulfur-lead composite free-cutting steel is more common.

Mg: Magnesium is a more active metal element than Al, and it will not form flocculent inclusions like magnesium oxide to block the nozzle. During the solidification process of molten steel, its oxidation products serve as the nucleation core of sulfide, which can promote the precipitation and uniform distribution of sulfide. Magnesium can also change the form of sulfide and form spindle inclusions with magnesium oxide as the core and manganese sulfide as the covering layer, thereby improving the machinability.

(Chemical formula 1) [Mg]+[O]=MgO(s) △G ₁ ^θ =-731400+239.68T

(Chemical formula 2) 2[Al]+3[O]=Al ₂ O ₃ (s) △G ₃ ^θ =-1202070+386.28T

(Chemical formula 3) [Mg]+[S]=MgS(s) △G ₂ ^θ =-537258.5+205.77T

(Chemical formula 4) [Ca]+[S]=CaS(s) △G ₁ ^θ =-541158.26+193.33T

(Chemical Formula 5) MgO(s)+Al ₂ O ₃ (s)=MgO·Al ₂ O ₃ (s) △G ₄ ^θ =-35600-2.09T

(Chemical formula 6) [Mg]+4[O]+2[Al]=MgO·Al ₂ O ₃ (s) △G ₅ ^θ =-1969070+623.87T

From the thermodynamic equilibrium relationship of Mg, Ca, O, and S, the concentration relationship of [Mg], [Ca], [O], and [S] in steel can be obtained at 1873K equilibrium.

A production process for free-cutting non-quenched and tempered steel containing calcium, sulfur and magnesium, characterized in that the process includes smelting, continuous casting and rolling processes, and the process flow is as follows:

(1) Smelting and alloying: desulfurization is not carried out in the molten iron in the converter, only decarburization and phosphorus are carried out, and silicomanganese-ferrosilicon-iron sulfide is added in the order of 1/4 of the steel for weak deoxidation, and the oxygen content is controlled at 30-100ppm;

(2) LF furnace refining: add refining slag, submerged arc slag, add iron sulfide to control sulfur content, and carry out white slag treatment. In the later stage of LF, add silicon-magnesium-calcium alloy wire to the steel for Mg-Ca composite treatment and inclusion modification. The feeding line speed is controlled at 95-120m/min and the appropriate Ca/S and Mg/S are controlled, Ca/S is controlled at 0.010-0.050, and Mg/S is controlled at 0.010-0.050 to ensure that the chemical composition meets the design requirements;

(3) Vacuum refining: In order to ensure the form of easy-cutting inclusions in the steel, vacuum degassing is carried out, so as to realize the stable control of sulfur elements and increase the spindle rate of sulfide inclusions. After breaking the vacuum, add S wire to the steel to make the S content reach the standard ;

(4) Pouring: Protective pouring is carried out throughout the process, the superheat is controlled at 25-40°C, the casting speed is 0.7-1.20m/min, the weak cooling ensures the quality of the continuous casting billet, and the operating current of the electromagnetic stirring of the mold is 250- 280A, the frequency is 2.5-3.5HZ, the best terminal electromagnetic stirring operating current is 150-180A, the frequency is 10.0-13HZ;

(5) Controlled rolling and controlled cooling: the soaking temperature of the billet in the heating furnace is 1050-1200°C, the starting rolling temperature is 1100-1150°C, and the final rolling temperature is 900-1000°C; the cooling rate of the rolled steel is 2°C/s.

A kind of production technological process of the 45MnVS free-cutting non-quenched and tempered steel containing magnesium calcium is:

Converter smelting→LF refining→VD→continuous casting→billet pit cooling→inspection→billet acceptance→heating→descaling→rolling→shearing or sawing→pit cooling→straightening→grinding→finished product inspection→packing mark→ weighing.

The difficulties in the production process are the oxygen content in the steel, the absorption rate and narrow range of sulfur elements, the small inclusions, the uniform harmless treatment and the control of the low-magnification structure of the slab. The sulfur-containing free-cutting steel produced by traditional electric furnace → LF → continuous casting → controlled rolling and controlled cooling or converter → LF → continuous casting → controlled rolling and controlled cooling and Al deoxidation process has poor purity, uneven composition and temperature, nitrogen and hydrogen The flocculent oxides with high content of Al are easy to block the nozzle and have poor pourability. In order to overcome these difficulties and shortcomings, the present invention proposes to adopt converter→LF→VD→continuous casting→controlled rolling and controlled cooling and Mg-Ca compound modification process to produce sulfur-containing free-cutting non-quenched and tempered steel. On the premise of ensuring mechanical properties, In turn, the machinability of steel can be improved, and at the same time, the purity and uniformity of steel can be significantly improved, and the pourability can be improved.

Detailed ways

Example 1:

A production process of 45MnVS free-cutting non-quenched and tempered steel containing magnesium and calcium:

Further preferably, the preparation method of Mg-Ca composite free-cutting non-quenched and tempered steel, in the case of ensuring that the chemical composition of the steel meets the requirements, the following steps are carried out:

(1) Smelting and alloying: desulfurization is not carried out on the molten iron in the converter, only decarburization and phosphorus are carried out, and silicomanganese-ferrosilicon-iron sulfide is added in the order of silicomanganese-ferrosilicon-iron sulfide for weak deoxidation when tapping 1/4 of the steel, and the oxygen content is controlled at 45ppm;

(2) LF furnace refining: add refining slag, submerged arc slag, add iron sulfide to control sulfur content, and carry out white slag treatment. In the later stage of LF, add silicon-magnesium-calcium alloy wire to the steel for Mg-Ca composite treatment and inclusion modification , the feeding line speed is controlled at 100m/min and the appropriate Ca/S and Mg/S are controlled, Ca/S is controlled at 0.040, and Mg/S is controlled at 0.035 to ensure that the chemical composition meets the design requirements;

(3) Vacuum refining: In order to ensure the form of easy-cutting inclusions in the steel, vacuum degassing is carried out, so as to realize the stable control of sulfur elements and increase the spindle rate of sulfide inclusions. After breaking the vacuum, add S wire to the steel to make the S content reach the standard ;

(4) Pouring: Protective pouring is carried out throughout the whole process, the superheat is controlled at 30°C, the casting speed is 1 m/min, the weak cooling ensures the quality of the continuous casting billet, the specific water volume of the secondary cooling is about 0.3L/Kg, the crystallizer The operating current of electromagnetic stirring is 260A, the frequency is 3.0HZ, and the operating current of the optimal terminal electromagnetic stirring is 170A, and the frequency is 12HZ;

(5) Controlled rolling and controlled cooling: the soaking temperature of the billet in the heating furnace is 1200°C, the heating time is 2.5 hours, the rolling start temperature is 1130°C, and the final rolling temperature is 950°C. The cooling rate of the steel after rolling is 2°C/s, and the stack cooling temperature of the lower cooling bed is 700°C.

Claims (2)

1. a kind of 45MnVS easy-cutting untempered steels of calcium containing magnesium, it is characterised in that the composition of steel is by weight percentage：C： 0.42%~0.51%, Si：0.15%~0.6%, Mn：0.90%~1.50%, P:0.010%~0.035%, S: 0.040%~0.080%, V:0.06%~0.13%, Mg：0.0005%~0.008%, Al：0.01%~0.04%, Ca: 0.0008%~0.005%, surplus is Fe and inevitable impurity；The manufacture of the 45MnVS easy-cutting untempered steels of the calcium containing magnesium Method, production technology are as follows：

(1) smelting and alloying：For converter molten iron without desulfurization, only decarburization and phosphorus, when tapping 1/4, presses silicomanganese-ferrosilicon-vulcanization Iron sequence, which is added, carries out weak deoxidation, and Control for Oxygen Content is in 30-100ppm；

(2) LF stoves refine：Be added refining slag, submerged arc slag, be added iron sulfide control sulfur content, carry out white slag processing, the LF later stages to Silicon magnesium calcium alloy line be added in steel carry out Mg-Ca combined processings and field trash and modify, wire-feeding velocity control 95-120m/min simultaneously Suitable Ca/S, Mg/S are controlled, Ca/S controls are controlled in 0.010-0.050, Mg/S in 0.010-0.050, it is ensured that chemical composition Meet design requirement；

(3) vacuum refining：To ensure Cutting free inclusion morphology in steel, vacuum outgas is carried out, and then realize the stabilization of element sulphur Sulphide inculsion spindle rate is controlled and improved, S lines is fed into steel after vacuum breaker, keeps S contents up to standard；

(4) it pours into a mould：Whole process carries out molding casting, and the control degree of superheat is 25-40 DEG C, and continuous casting casting speed is 0.7-1.20m/min, Weak cold cooling ensures continuous casting billet quality, and M-EMS running current is 250-280A, frequency 2.5-3.5HZ, most preferably End electromagnetic agitation running current is 150-180A, frequency 10.0-13HZ；

(5) controlled rolling and controlled cooling：Steel billet is 1050-1200 DEG C in the soaking temperature of heating furnace, 1100-1150 DEG C of start rolling temperature, finish to gauge 900-1000 DEG C of temperature；It is 2 DEG C/s to roll rear steel cooling velocity.

2. a kind of manufacturing method of the 45MnVS easy-cutting untempered steels of calcium containing magnesium as described in claim 1, it is characterised in that tool The production technology of body is as follows：

(1) smelting and alloying：For converter molten iron without desulfurization, only decarburization and phosphorus, when tapping 1/4, presses silicomanganese-ferrosilicon-vulcanization Iron sequence, which is added, carries out weak deoxidation, and Control for Oxygen Content is in 30-100ppm；

(2) LF stoves refine：Be added refining slag, submerged arc slag, be added iron sulfide control sulfur content, carry out white slag processing, the LF later stages to Silicon magnesium calcium alloy line be added in steel carry out Mg-Ca combined processings and field trash and modify, wire-feeding velocity control 95-120m/min simultaneously Suitable Ca/S, Mg/S are controlled, Ca/S controls are controlled in 0.010-0.050, Mg/S in 0.010-0.050, it is ensured that chemical composition Meet design requirement；

(3) vacuum refining：To ensure Cutting free inclusion morphology in steel, vacuum outgas is carried out, and then realize the stabilization of element sulphur Sulphide inculsion spindle rate is controlled and improved, S lines is fed into steel after vacuum breaker, keeps S contents up to standard；

(4) it pours into a mould：Whole process carries out molding casting, and the control degree of superheat is 25-40 DEG C, and continuous casting casting speed is 0.7-1.20m/min, Weak cold cooling ensures continuous casting billet quality, and M-EMS running current is 250-280A, frequency 2.5-3.5HZ, most preferably End electromagnetic agitation running current is 150-180A, frequency 10.0-13HZ；

(5) controlled rolling and controlled cooling：Steel billet is 1050-1200 DEG C in the soaking temperature of heating furnace, 1100-1150 DEG C of start rolling temperature, finish to gauge 900-1000 DEG C of temperature；It is 2 DEG C/s to roll rear steel cooling velocity.