CN107619993B - Cold-rolled martensite steel plate with yield strength of 750MPa and manufacturing method thereof - Google Patents
Cold-rolled martensite steel plate with yield strength of 750MPa and manufacturing method thereof Download PDFInfo
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Abstract
The invention relates to a cold-rolled martensite steel plate with 750 MPa-grade yield strength and a manufacturing method thereof, and mainly solves the technical problem that the existing cold-rolled martensite steel plate with 750 MPa-grade yield strength is high in manufacturing cost. The invention provides a cold-rolled martensite steel plate which comprises the following chemical components in percentage by weight: c: 0.12-0.22%, Si: 0.30-0.90%, Mn: 1.30-1.90%, Cr: 0.20 to 0.80%, Ti: 0.010-0.050%, Al: 0.020-0.060%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, N is less than or equal to 0.006%, and Ca: 0.0015-0.004%, and the balance of iron and inevitable impurities. The yield strength of the steel plate is 790-830 MPa, the tensile strength is more than or equal to 980MPa, and the elongation percentage A after fracture80Not less than 6 percent. The method is mainly used for manufacturing the side beams, the square tube columns and the like of the trucks.
Description
Technical Field
The invention relates to cold-rolled high-strength steel, in particular to a cold-rolled martensite steel plate with yield strength of 750MPa and a manufacturing method thereof, belonging to the technical field of iron-based alloy.
Background
With the great development of the global automobile industry, energy conservation, environmental protection and safety become the leading trend of future research and development, and a series of experiments show that: the energy consumption of the automobile is in a linear relation with the self weight of the automobile, and the automobile has great significance for saving energy and reducing emission of the automobile obviously because the energy consumption can be reduced by 8 percent and the emission can be reduced by 4 percent for common passenger vehicles such as the self weight is reduced by 10 percent. In addition, the requirement of people on driving safety tends to be improved, the automobile industry is forced to adopt a large number of high-strength plates, and the automobile steel is required to have high strength and good ductility at the same time in order to avoid great personal injury caused by collision. Modern cold-rolled high-strength steel mainly comprises DP steel, TRIP steel, MP steel, MART steel and the like. The production of high-strength steel can be realized only by two ways at present, one is by adding alloy elements, the other is by improving the rapid cooling rate and improving the strength of the steel plate by utilizing phase change strengthening. The former can deteriorate the coating performance of the strip steel, the process requirement is complex, expensive production equipment is required to be added, and the investment cost and the production cost of a production line are increased. The latter requires that the strip steel is heated to a two-phase region or an austenite single-phase region, is rapidly cooled after short-time heat preservation, and forms ferrite-martensite dual-phase steel, martensite-bainite complex-phase steel or martensite single-phase steel and the like through phase transformation strengthening. Although the problem of obtaining the steel grade with expected strength without adding expensive alloy elements can be solved, and the production process cost is also reduced, the rapid cooling technology of continuous annealing has high requirements, and the rapid cooling technology mainly comprises the following modes: roll Cooling (Rolling Cooling), Gas Jet Cooling (Gas Jet Cooling), aerosol Cooling (atomizing Cooling), water quench Cooling (WaterQuench Cooling), nitrogen and water mixed Cooling (Wet Flashcooling), pentane super-Dry Cooling (Pentane ultra-Dry Cooling), and the like. The cold-rolled martensite steel is generally produced by a continuous annealing unit with a water quenching function, so that the equipment investment is large and the process precision requirement is high. For a continuous annealing unit without a water quenching function, a proper component design and hot rolling and cold rolling production process are adopted, so that the high-strength martensitic steel is significant work.
Chinese patent document CN103305762A discloses a cold-rolled high-strength dual-phase steel plate for an automobile with 400 MPa-level tensile strength and a preparation method thereof, wherein the structure of the steel plate is mainly a ferrite-martensite dual-phase structure, the martensite content is 4-9%, and the steel plate comprises the following chemical components: c: 0.01 to 0.05%, Si: 0.1-0.4%, Mn: 1.2-1.6%, Cr: 0.1-0.4%, Als: 0.02-0.05%, N is less than or equal to 0.005%, P is less than or equal to 0.02%, S is less than or equal to 0.01%, and the balance is Fe and inevitable residual impurity elements. The technical method disclosed in the document comprises the steps of hot rolling, pickling, cold rolling, heat treatment and the like. The annealing heat treatment process comprises the following steps: firstly, heating a cold-rolled sheet to an annealing temperature of 740-800 ℃, preserving heat for 90-120 s, then slowly cooling to 640-680 ℃ at a speed of 5-8 ℃/s, then rapidly cooling to 260-320 ℃ at a speed of more than 40 ℃/s for overaging treatment, wherein the overaging treatment time is 400-600 s, and finally naturally cooling to room temperature.
Chinese patent document CN104419877A discloses a cold-rolled martensitic steel with weather resistance and a manufacturing method thereof, wherein the chemical components are as follows: c: 0.10 to 0.20%, Si: 0.20 to 0.80%, Mn: 1.4-2.2%, Cr: 0.3-0.8%, Ni: 0.08-0.20%; cu: 0.20-0.50%; v: 0.08-0.15%; ti: 0.01-0.03%; b: 0.0005 to 0.003%; al: 0.015-0.045%, P is less than or equal to 0.020%, S is less than or equal to 0.007%, N is less than or equal to 0.008%, and the balance is iron and inevitable impurities. The technology disclosed in the document has the advantages that the finish rolling temperature is 910-950 ℃, the coiling temperature is 660-700 ℃, the annealing temperature is 780-840 ℃, the slow cooling outlet temperature is 680 ℃, the fast cooling speed is 35-60 ℃/s, the fast cooling finishing temperature is 240-300 ℃, and the annealing heat preservation time is 110-170 s; the overaging temperature is 380-430 ℃, the overaging time is 200-400 s, and the flat elongation is not higher than 0.6%. The steel plate produced in the embodiment is suitable for producing 1.0-1.4 mm cold-rolled martensite steel with weather resistance, the yield strength reaches more than 1000MPa, the tensile strength is more than 1100MPa, and the elongation A50mm% is above 5%.
Chinese patent document CN103981440A discloses a 700 MPa-grade industrial atmosphere corrosion resistant martensitic steel plate and a preparation method thereof, wherein the martensitic steel plate comprises the following chemical components: 0.17-0.25% of C; 0.10-0.40% of Si; 0.50-0.80% of Mn0.50; p is less than or equal to 0.020%; s is less than or equal to 0.001 percent; 0.015-0.040% of Al0; nb0.02-0.05%; 0.010-0.030% of Ti0.010; the balance of Fe and inevitable impurities. The method for manufacturing a technical steel sheet disclosed in this document comprises the steps of: (1) carrying out VD vacuum weak degassing for one time; (2) carrying out secondary VD vacuum strong degassing; (3) heating the plate blank; (4) rough rolling; (5) fine rolling; (6) performing sub-temperature quenching; (7) primary high-temperature tempering; (8) and (5) performing secondary low-temperature tempering. According to the technology, the sub-temperature quenching temperature is 750-800 ℃, the cooling speed is 30-50 ℃/s, a small amount of free carbide, martensite and residual austenite are obtained, the primary high-temperature tempering temperature is 600-650 ℃, the heat preservation time is 120-150 min, the carbide is eliminated through aggregation, the martensite is lathed, the toughness and plasticity are improved, the secondary high-temperature tempering temperature is 200-250 ℃, the heat preservation time is 80-120 min, the brittleness is reduced, the internal stress is eliminated, and the mixed tempered martensite structure is obtained.
Although some cold-rolled dual-phase steel or martensitic steel plates disclosed in the above patent documents have corresponding chemical compositions and certain alloys added thereto, the yield strength and tensile strength of the produced dual-phase steel are low due to the difference in the amount of the alloys added and the continuous annealing process, and the strength requirements of high-strength steel cannot be met. Some martensite steels reach the strength requirement of high-strength martensite steel, the yield strength is more than or equal to 1000MPa, but alloy elements such as Ni, V, B and the like are required to be added to improve the strength, the production cost is high, the addition of the B element is easy to cause defects of continuous casting slabs and reduce the welding performance of steel plates, and meanwhile, because the finish rolling temperature is higher, iron scales are easy to generate on the surfaces of strip steels to influence the surface quality. In addition, expensive Nb element (0.02-0.05%) is added to improve the strength, and the annealing process needs two times of tempering to obtain the tempered martensite steel with the yield strength of 700MPa, so that the production process is complex, and the production cost is correspondingly increased.
Disclosure of Invention
The invention aims to provide a cold-rolled martensite steel plate with 750MPa grade yield strength and a manufacturing method thereof, mainly solves the technical problem that the existing cold-rolled martensite steel plate with 750MPa grade yield strength is high in manufacturing cost, and produces the cold-rolled martensite steel plate with 750MPa grade yield strength in a continuous annealing unit without quenching cooling capacity.
The technical scheme adopted by the invention is as follows: a cold-rolled martensite steel plate with yield strength of 750MPa comprises the following chemical components in percentage by weight: c: 0.12-0.22%, Si: 0.30-0.90%, Mn: 1.30-1.90%, Cr: 0.20 to 0.80%, Ti: 0.010-0.050%, Al: 0.020-0.060%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, N is less than or equal to 0.006%, and Ca: 0.0015 to 0.0040 percent, and the balance of iron and inevitable impurities.
the reason why the chemical composition of the cold-rolled martensitic steel sheet having a yield strength of 750MPa grade according to the present invention is limited to the above range is as follows:
C: c is a solid-solution strengthening element and is an important index that affects the strength and weldability of steel. When the content of C is low, the steel does not have enough carbide and solid solution carbon, and the austenite can not generate enough distortion to strengthen the martensite when being transformed into the martensite so as to obtain higher strength; when the content of C is too high, the ductility and toughness are reduced, and the welding performance is also remarkably reduced. Therefore, the content of C in the steel is controlled to be 0.12-0.22%.
Si: si is also a solid solution strengthening element, can expand the critical zone range, purify ferrite, improve hardenability and the like, but the high content of Si is not favorable for weldability and the surface quality of strip steel. Comprehensively considered, the content of Si in the steel is controlled to be 0.30-0.90%.
Mn: mn can improve the strength of the quenched steel plate. Mn is an element for stabilizing austenite, can reduce the transformation temperature of austenite, promote the dissolution of C in austenite, increase the enrichment of C and delay the formation of pearlite, thereby expanding the application range of the cooling rate of forming a martensite structure by quenching. However, too high Mn reduces the activity of C and tends to segregate, deteriorating the properties of the steel. Therefore, the content of Mn in the steel is controlled to be 1.30-1.90%.
Cr: cr can obviously improve the oxidation resistance of steel, the hardenability of steel, the tempering stability and the like. The Cr content exceeding 0.80% causes crevice corrosion, and also increases the production cost, while being disadvantageous in delayed fracture properties. Comprehensively considered, the Cr content in the steel is controlled to be 0.20-0.80%.
Ti: ti is a strong carbonitride forming element, a proper amount of Ti can fix N in steel and form fine TiN particles, the effect of grain refinement cannot be achieved due to too low Ti content, and the proper amount of Ti can remarkably refine grains and improve welding performance. The Ti content is controlled to be 0.010-0.050%.
al: al is a main deoxidizing element in steel, and contributes to grain refinement, but too much Al increases the number of inclusions in steel, and deteriorates the workability thereof. The Al added in the invention is mainly used for deoxidizing and refining grains, so the content of the Al is controlled to be 0.020-0.060%.
N: n in the steel is combined with Ti to form TiN, and a second phase is precipitated at high temperature to strengthen the matrix, but when the content of N is too high, coarse TiN is formed in the steel or N is dissolved in the steel, so that the plasticity and the toughness are damaged. The content of N in the steel is controlled to be less than or equal to 0.006 percent
P and S: p is a harmful element of steel grade, and seriously damages the plasticity and toughness of the steel plate; s combines with Mn and the like in steel to form a plastic inclusion MnS, which is detrimental to transverse plasticity and toughness of the steel, so the content of S should be as low as possible. In the invention, P is controlled to be less than or equal to 0.015 percent and S is controlled to be less than or equal to 0.008 percent.
Ca: as a result of the Ca treatment, fine spherical composite inclusions which are centered on CaO-Al2O3 and coated with (Ca, Mn) S are formed, and elongated MnS inclusions are replaced, so that the number and size of the inclusions are reduced, and the bending performance is improved. Therefore, the content of Ca in the invention is controlled to be 0.0015-0.004%.
A method for manufacturing a cold-rolled martensite steel plate with the yield strength of 750MPa, which comprises the following steps:
Continuously casting molten steel to obtain a continuous casting slab, wherein the molten steel comprises the following chemical components in percentage by weight: c: 0.12-0.22%, Si: 0.30-0.90%, Mn: 1.30-1.90%, Cr: 0.20 to 0.80%, Ti: 0.010-0.050%, Al: 0.020-0.060%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, N is less than or equal to 0.006%, and Ca: 0.0015-0.0040% and the balance of iron and inevitable impurities;
Heating the continuous casting plate blank to 1220-1260 ℃, and then carrying out hot rolling, wherein the hot rolling is a two-section rolling process, rolling is carried out at the temperature above the austenite recrystallization temperature, and the rough rolling finishing temperature is 1040-1100 ℃; rolling in an austenite non-recrystallization temperature region, wherein the finish rolling temperature is 840-900 ℃, the thickness of the steel plate after finish rolling is 2.0-4.0 mm, laminar cooling after finish rolling adopts front-section cooling, and the hot rolled steel coil is obtained when the coiling temperature is 530-610 ℃.
The hot rolled steel coil is uncoiled again and then is subjected to acid pickling, cold rolling, annealing in a vertical continuous annealing furnace, flattening and coiling to obtain a finished steel plate with the thickness of 1.0-2.0 mm, the cold rolling reduction is 50-68%, the temperature of the cold rolled hard strip steel in the annealing section of the vertical continuous annealing furnace after cold rolling is 840-880 ℃, the annealing time of the strip steel in the annealing section is 160-180 s, the quick cooling starting temperature of the strip steel is 680-730 ℃, the quick cooling ending temperature is 200-260 ℃, the quick cooling speed is 30-50 ℃/s, the temperature rising and overaging section stabilizing temperature after quick cooling is 280-330 ℃, the overaging time is 600-680 s, and the flattening elongation is 0.1-0.2%.
The production process adopted by the invention has the following reasons:
1. Continuous casting slab heating temperature setting
In consideration of the requirements for homogenization of the austenite structure of a continuously cast slab and stability of the finish rolling force of alloy steel, the slab needs to be heated in a relatively high temperature range. The higher furnace-out temperature can partially dissolve the coarse (Ti, Mn) S and other second phase particles, and generate dispersed and fine precipitates in the subsequent cooling process, thereby improving the product strength, but when the heating temperature is too high, the scale defects can be formed on the surface of the strip steel, and the surface quality is influenced. Therefore, the heating temperature of the continuous casting plate blank is 1220-1260 ℃.
2. Roughing finish temperature setting
The rough rolling process is carried out at the temperature above the austenite recrystallization temperature, so that austenite grains in the casting blank can be refined. The finishing temperature of rough rolling is too high, the grain refining effect is poor, and the finishing temperature is too low, so that the finish rolling difficulty is increased, and the rolling stability is influenced. Therefore, the rough rolling finishing temperature is set to be 1040-1100 ℃.
3. Finish rolling finish temperature setting
finishing temperature of finish rolling needs to be controlled at Ar3The transformation point is higher than the transformation point so as to ensure the rolling in an austenite area, but the high finishing rolling temperature is controlled to easily generate scale defects, thereby influencing the surface quality of a cold-rolled product. Therefore, the finish rolling finishing temperature is set to be 840-900 ℃.
4. Setting of laminar cooling mode
after finishing the finish rolling, the ferrite phase transformation is slow due to slow cooling, ferrite grains are coarse, the yield strength is low, and the ferrite grains are properly refined through fast laminar cooling to obtain other strengthening structures. The subsequent cold rolling and annealing processes of the hot rolled strip steel need to inherit certain hot rolling strength, so that a laminar cooling mode is set as front-stage cooling.
5. Hot rolling coiling temperature setting
The proper coiling temperature can ensure that the hot-rolled strip steel obtains certain strength, and the precipitation of the second phase particles can meet the requirements of subsequent cold rolling and annealing. The coiling temperature is high, the recrystallized grains are easy to grow after cold rolling annealing, the strength is reduced, the coiling temperature is low, the strength of the hot rolled strip steel is high, the load upper limit of a cold rolling mill is exceeded, and the rolling is unstable. Therefore, the laminar flow coiling temperature is set to be 530-610 ℃ in the invention.
6. Cold rolling reduction setting
The cold rolling of the invention adopts a 5-stand continuous rolling unit for rolling, the increase of the cold rolling deformation can promote the recrystallization of continuous annealing and obtain a fine grain structure, thereby improving the strength of the steel plate, but the deformation is improved to a certain degree, the load of a rolling mill is increased sharply, and the production difficulty and the rolling stability are increased. Therefore, the cold rolling reduction is set to be 50-68%.
7. Annealing temperature and annealing time settings
The annealing heating is mainly to realize austenitizing of the cold-rolled steel plate and prepare for the subsequent quenching process, and the austenitizing temperature of the cold-rolled steel plate needs to be controlled at Ar3In order to ensure that the internal structure is transformed into austenite as completely as possible. The high heating temperature exceeds the upper limit of the heating capacity of the annealing furnace on one hand, and on the other hand, austenite grains can grow sufficiently, which is not beneficial to improving the strength after quenching. Therefore, the annealing temperature of the steel strip in the soaking section of the vertical continuous annealing furnace is set to be 840-880 ℃, and the time in the soaking section is set to be 160-180 s.
8. Setting of technological parameters of quick cooling and overaging stages
The magnitude of the rapid cooling start temperature mainly affects the amount of super-cooled austenite, and thus the martensite content in the high-strength steel. When the cooling rate is 30 ℃/s or more, the amount of super-cooled austenite increases with the increase of the rapid cooling start temperature, and the amount of martensite finally formed also increases, which is a main factor for satisfying the strength.
The lower the rapid cooling termination temperature is, not only can the supercooled austenite be fully transformed into martensite, but also the strength reduction caused by the excessive decomposition of the martensite due to the overhigh tempering temperature in the overaging process of the martensite can be avoided.
The rapid cooling speed is important for whether the supercooled austenite is converted into bainite and martensite, when the cooling speed is low, the supercooled austenite is preferentially converted into ferrite, carbon enrichment occurs in the supercooled austenite, carbides can be separated out, and the amount of the final martensite is small. When the rapid cooling speed is higher, more undercooled austenite is converted into martensite in the cooling process, so that the strength is improved.
The martensite steel after rapid cooling needs to be subjected to overaging treatment to improve the uniformity of internal structure, and the plasticity and toughness of the martensite steel are improved under the condition of not reducing or having no obvious influence on strength. When the sample is overaged in a low-temperature area, the structure of the sample is basically unchanged, and martensite in the structure is distributed on a ferrite matrix in a lath shape. And when the overaging temperature is higher, martensite is decomposed, the decomposition degree is higher along with the increase of the overaging temperature, the volume fraction is reduced, the strength is obviously reduced, and the requirement on high strength performance cannot be met.
Therefore, the technological parameters of the fast cooling and overaging sections of the invention are as follows: the rapid cooling starting temperature of the strip steel is 680-730 ℃, the rapid cooling ending temperature is 200-260 ℃, the rapid cooling speed is 30-50 ℃/s, the temperature-raising and overaging section stabilizing temperature after rapid cooling is 280-330 ℃, and the overaging time is 600-680 s, so that the uniformity of the internal structure of the maraging steel plate after overaging treatment is ensured.
9. Flat elongation setting
The main purpose of flattening is to eliminate a material yield platform, measured by an elongation index, the elongation is too low to eliminate the yield platform, and the defect of wrinkles is easily generated on the part during punching. The elongation is too high, crystal grains are obviously elongated, the difference of transverse and longitudinal properties of the material is large, the processing property is poor, and the punching is easy to crack. The flat elongation of the invention is 0.1-0.2%.
The microstructure of the cold-rolled martensite steel plate with the yield strength of 750MPa grade obtained by the invention is martensite + a small amount of ferrite and crystal grainsThe degree grade is I11-I13 grade, and the yield strength Rp0.2790 to 830MPa, tensile strength RmNot less than 980MPa, elongation after breakage A80Not less than 6%, and qualified in 180 DEG bending test with d being 0 a.
The cold-rolled martensite steel plate with the yield strength of 750MPa is used for manufacturing side beams, square tube columns and the like of trucks (trucks), can replace high-strength steel plates with the thickness of 2.5-3.0 mm, is remarkable in light weight effect, and has high market competitiveness.
Compared with the prior art, the invention has the following positive effects: 1. the invention improves the chemical composition design of steel, adds proper Cr and Ti alloy elements on the basis of C, Mn steel, does not remarkably improve the alloy cost, and produces qualified high-strength cold-rolled martensitic steel by utilizing a strong cooling fan and overaging treatment equipment on a continuous annealing production line without quenching capacity, and the like, and has good product manufacturability and low manufacturing cost. 2. The cold-rolled martensitic steel produced by the method has the thickness of 1.0-2.0 mm, the yield strength of more than or equal to 750MPa, the tensile strength of more than or equal to 980MPa and the elongation percentage A after fracture80The steel plate has the advantages that the steel plate is more than or equal to 6 percent, the d is qualified as 0a in a 180-degree bending test, the steel plate can replace a high-strength steel plate with the thickness of 2.5-3.0 mm, the light weight effect is obvious, and the market competitiveness is high. 3. In the invention, Ca is added for steel making, so that MnS inclusions are changed into spheres from long strips, and the bending cracking defect is improved; the stable temperature of the heating overaging section after rapid cooling is 280-330 ℃, enough overaging time is ensured, the uniformity of the internal structure of the martensite steel plate after strong cooling is improved, and better bending performance is ensured, which is better than that of general high-strength cold-rolled martensite steel.
Drawings
FIG. 1 is a metallographic structure photograph of a cold-rolled martensitic steel sheet according to example 2 of the present invention.
Detailed Description
the present invention is further described in examples 1 to 4.
Table 1 shows the chemical composition (in weight percent) of the steels of the examples of the invention, with the balance being iron and unavoidable impurities.
Table 1 chemical composition of martensitic steel of examples of the present invention, unit: weight percent/%.
according to the design requirements of the material components, the converter top and bottom is adopted to compound and blow molten steel with qualified components, and a continuous casting slab is obtained through slab continuous casting, wherein the thickness of the continuous casting slab is 210-230 mm, the width is 900-1600 mm, and the length is 8500-11000 mm.
And (3) sending the fixed-length plate blank produced in the steel-making process to a heating furnace for reheating, taking out the plate blank from the furnace for descaling, and sending the plate blank to a hot continuous rolling mill for rolling. The rolling is controlled by a rough rolling and finish rolling continuous rolling unit, the coiled steel is cooled by laminar flow, the laminar flow adopts front section cooling, qualified hot rolled steel coils are produced, and the thickness of the hot rolled steel plates is 2.0-4.0 mm. The main process control parameters of hot rolling are shown in Table 2.
TABLE 2 Hot Rolling Process control parameters of the inventive examples
And (2) after the hot rolled steel coil is uncoiled again and is subjected to acid washing, the hot rolled steel coil is subjected to primary cold rolling on a 6-roller UCM (universal convexity with intermediate roller shifting) 5-stand cold continuous rolling mill, the reduction rate of the cold rolling is 50-68%, and the cold rolled steel coil is subjected to annealing, overaging, flattening and coiling to obtain a finished steel plate with the thickness of 1.0-2.0 mm. The annealing process comprises the following steps: the temperature of the strip steel in the soaking section of the annealing of the vertical continuous annealing furnace is 840-880 ℃, and the annealing time of the strip steel in the soaking section is 160-180 s; the rapid cooling starting temperature of the strip steel is 680-730 ℃, the rapid cooling ending temperature is 200-260 ℃, the rapid cooling speed is 30-50 ℃/s, the stabilizing temperature of the temperature rising and overaging section after rapid cooling is 280-330 ℃, the overaging time is 600-680 s, and the flat elongation is 0.1-0.2%. The cold rolling, annealing and flattening process parameters are shown in Table 3.
TABLE 3 control parameters of the cold rolling, annealing and leveling processes of the examples of the present invention
The cold-rolled martensite steel plate with the yield strength of 750MPa grade obtained by the method. Referring to FIG. 1, the structure is martensite and a small amount of ferrite, the grain size grade is I11-I13, and the yield strength Rp0.2Not less than 750MPa, tensile strength RmNot less than 980MPa, elongation after breakage A80Not less than 6%, and qualified in 180 DEG bending test with d being 0 a.
The cold-rolled martensite steel plate obtained by the invention is subjected to a part 1 of a GB/T228.1-2010 metal material tensile test: room temperature test method, the mechanical properties are shown in Table 4.
TABLE 4 mechanical Properties of martensitic steels according to examples of the invention
In addition to the above embodiments, the present invention may have other embodiments. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.
Claims (3)
1. A cold-rolled martensite steel plate with yield strength of 750MPa comprises the following chemical components in percentage by weight: c: 0.12-0.22%, Si: 0.30-0.90%, Mn: 1.30-1.90%, Cr: 0.20 to 0.80%, Ti: 0.010-0.050%, Al: 0.020-0.060%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, N is less than or equal to 0.006%, and Ca: 0.0015-0.004%, and the balance of iron and inevitable impurities, wherein the microstructure of the cold-rolled martensitic steel plate is martensite and a small amount of ferrite, and the grain size grade of the structure is I11-I13 grade; the yield strength R of the cold-rolled martensite steel plate with the thickness of 1.0-2.0 mmp0.2Not less than 750MPa, tensile strength Rmnot less than 980MPa, elongation after breakage A80Not less than 6%, and qualified in 180 DEG bending test with d being 0 a.
2. A manufacturing method of a cold-rolled martensite steel plate with the yield strength of 750MPa comprises the following steps:
Continuously casting molten steel to obtain a continuous casting slab, wherein the molten steel comprises the following chemical components in percentage by weight: c: 0.12-0.22%, Si: 0.30-0.90%, Mn: 1.30-1.90%, Cr: 0.20 to 0.80%, Ti: 0.010-0.050%, Al: 0.020-0.060%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, N is less than or equal to 0.006%, and Ca: 0.0015-0.004%, and the balance of iron and inevitable impurities;
Heating the continuous casting plate blank to 1220-1260 ℃, and then carrying out hot rolling, wherein the hot rolling is a two-section rolling process, rolling is carried out at the temperature above the austenite recrystallization temperature, and the rough rolling finishing temperature is 1040-1100 ℃; rolling in an austenite non-recrystallization temperature region, wherein the finish rolling temperature is 840-900 ℃, laminar cooling adopts front-section cooling after finish rolling, and a hot rolled steel coil is obtained when the coiling temperature is 530-610 ℃;
The hot rolled steel coil is uncoiled again and then is annealed, leveled and coiled by an acid washing, cold rolling and vertical continuous annealing furnace to obtain a finished steel plate with the thickness of 1.0-2.0 mm, the cold rolling reduction is 50-68%, the temperature of the rolled hard strip steel after cold rolling in the soaking section of annealing of the vertical continuous annealing furnace is 840-880 ℃, the annealing time of the strip steel in the soaking section is 160-180 s, the quick cooling starting temperature of the strip steel is 680-730 ℃, the quick cooling ending temperature is 200-260 ℃, the quick cooling speed is 30-50 ℃/s, the temperature rising and overaging section stabilizing temperature after quick cooling of the strip steel is 280-330 ℃, the overaging time is 600-680 s, and the leveling elongation is 0.1-0.2%.
3. The method for manufacturing a cold-rolled martensitic steel sheet having a yield strength of 750MPa according to claim 2, wherein the thickness of the hot-rolled steel sheet after the hot-rolling and finish-rolling is controlled to be 2.0 to 4.0 mm.
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