Hot-dip aluminized silicon 1000mpa grade dh steel cold forming steel sheet and method of manufacturing the same

Abstract

The application provides a hot-dip aluminized silicon 1000MPa-grade DH steel cold forming steel plate and a preparation method thereof. The steel plate substrate composition is as follows in terms of percentage by weight: C: 0.18%-0.24%, Si: 0.6%-1.4%, Mn: 1.8%-2.4%, Cr: 0.1-0.4%, Mo: 0.05-0.3%, P: less than or equal to 0.02%, S: less than or equal to 0.005%, Ti: less than or equal to 0.03%, and the balance of Fe and inevitable impurities. The microstructure of the cold forming steel plate is ferrite, martensite, bainite and residual austenite; the microstructure is counted by a planar area method, and the ferrite is 25%-45%, the martensite is 20%-50%, the bainite is 15%-30%, and the residual austenite content is 4%-11%. The steel plate produced by the application has a tensile strength of more than 1000MPa, a yield strength of 600-800MPa and an elongation of more than 18%.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal materials, and particularly relates to a hot-dip aluminized-silicon 1000 MPa grade DH steel cold forming steel plate and a preparation method thereof. BACKGROUND

[0002] The fuel consumption of an automobile is closely related to the weight of the automobile body. Research shows that if the weight of an automobile is reduced by 10%, the fuel consumption will be reduced by 6%-10%, and the emissions will be reduced by 4%. In view of this problem, the International Iron and Steel Institute organized a research project on ultra-lightweight steel automobile bodies. After the completion of the project, a plan called the Advanced Concept Vehicle Ultra-Lightweight Steel Body Plan was carried out, the main content of which is the development and application of advanced high-strength steel. According to the fifth edition of the Advanced High-Strength Steel Application Guide published by the International Iron and Steel Institute, advanced high-strength steel generally refers to high-strength steel with a yield strength exceeding 550 MPa, and steel with a tensile strength exceeding 780 MPa is sometimes referred to as ultra-high-strength steel. Dual-phase steel is a typical representative of advanced high-strength steel, and its application is also the most extensive. Plasticized dual-phase (DH) steel is a plasticity upgrade version of dual-phase steel, which can significantly improve the plasticity and formability of the steel plate by introducing a small amount of residual austenite based on the ferrite and martensite structure of dual-phase steel, and has a wide application prospect. The strength level of the DH steel currently produced by the industry is mainly below 800 MPa, and a small number of DH steels have a strength of 1000 MPa. Among them, only a small part of the multiphase steel plates meet the high surface quality requirements. At present, high-surface-quality DH steel is mainly realized by hot-dip galvanizing on the surface of the steel plate, but with the decreasing of zinc resources and the increasing of zinc prices, a new hot-dip method that matches the heat treatment system is urgently needed to meet the market demand for multiphase steel with good surface quality and mechanical properties in the future.

[0003] The relevant documents are as follows:

[0004] A 980 MPa grade high-formability cold-rolled DH steel and a preparation method thereof are disclosed in a Chinese authorized patent with the publication number CN112048681 B. The composition system thereof combines high C, Mn and Si / Al, wherein the Si+Al content is 0.6%-1.7%, which is mainly used to inhibit the decomposition of residual austenite and the precipitation of carbides, and the annealing temperature used in the preparation process is 760-880℃, and the overaging temperature is between 350-450℃. The application is a cold-rolled steel plate, and the performance after heat treatment is a tensile strength of 980-1100 MPa, a yield strength of 550-700 MPa, and an elongation of 16-20%. The product does not involve surface treatment.

[0005] The patent application with the publication number CN112048680 A discloses an alloyed hot-dip galvanized DH980 steel and a preparation method thereof. The composition system of C, Mn, Si+Al and Cr is adopted, and the content of Si+Al is required to be 0.6-1.5%, and the annealing temperature is 760-880℃, the galvanizing temperature is 450-470℃, the alloying temperature is 470-530℃, and the alloying time is 5-60s. The mechanical properties of the steel plate are as follows: the tensile strength is 980-1100MPa, the yield strength is 550-650MPa, the elongation is 16-20%, and the product is an alloyed plated layer.

[0006] The above patent mainly aims at the production and heat treatment process of cold-rolled DH steel and alloyed hot-dip galvanized DH steel, which is obviously different from the heat treatment process of the present application, and both of them do not involve hot-dip aluminum-silicon on the surface of the steel plate. SUMMARY

[0007] The present application aims to overcome the above problems and deficiencies and provide a hot-dip aluminum-silicon 1000MPa grade DH steel cold forming steel plate with excellent mechanical properties and a preparation method thereof.

[0008] The purpose of the present application is achieved as follows:

[0009] A hot-dip aluminum-silicon 1000MPa grade DH steel cold forming steel plate, the composition of the steel plate substrate is as follows in terms of percentage by weight: C: 0.18%-0.24%, Si: 0.6%-1.4%, Mn: 1.8%-2.4%, Cr: 0.1%-0.4%, Mo: 0.05%-0.3%, P≤0.02%, S≤0.005%, Ti: 0.01%-0.03%, Al≤0.005%, and the balance is Fe and unavoidable impurities.

[0010] In the steel plate, Mo / Cr=1 / 3-2 / 3.

[0011] The composition of the plated layer of the steel plate is as follows in terms of percentage by weight: Al: 88%-93%, Si: 7%-12%.

[0012] The microstructure of the cold forming steel plate is ferrite, martensite, bainite and residual austenite; the above microstructure is counted by the planar area method, and the ferrite is 25%-45%, the martensite is 20%-50%, the bainite is 15%-30%, and the residual austenite content is 4%-11%.

[0013] The tensile strength of the cold forming steel plate is more than 1000MPa, the yield strength is 600-800MPa, and the elongation is >18%.

[0014] The reasons for the alloy composition design of the present application are as follows:

[0015] C: C element is a traditional and economical strengthening element of low carbon steel, and the increase of C content in martensite can improve its work hardening capacity. In addition, C atoms can enrich in austenite during intercritical annealing, which plays a role in stabilizing austenite and is beneficial to the retention of retained austenite. However, too high C content will bring difficulties to smelting and welding. Therefore, the C content in the steel plate is controlled to be 0.18% to 0.24% in the application.

[0016] Si: Si element can inhibit cementite precipitation during overaging stage, which is beneficial to the retention of retained austenite, but too high Si element is not conducive to the surface quality of the steel plate. Therefore, the content of Si element is controlled to be 0.6% to 1.4% in the application.

[0017] Mn: Mn is an austenite stabilizing element, has obvious solid solution strengthening effect on high strength steel, can significantly improve the hardenability of steel, has the effects of solid solution strengthening and refining ferrite grains, and is the main strengthening element except C. Since the C content is fixed at about 0.21%, in order to make the strength of the steel plate reach 1000MPa, the content of Mn is controlled to be mainly between 1.8% and 2.4%. Too low Mn content is worried about insufficient strength of the steel plate, and too high Mn content may exist segregation and reduce the plasticity of the steel plate.

[0018] Cr: The effect of Cr element is similar to that of Mn element. The addition of Cr element can significantly expand the austenite phase region, refine the grains, significantly delay the transformation of pearlite and bainite, improve the hardenability of austenite, and has obvious solid solution strengthening effect on high strength steel to improve the strength of the steel. Therefore, Cr element can be used to replace part of Mn element. The content of Cr element is controlled to be 0.1% to 0.4% in the application.

[0019] Mo: The addition of Mo element can effectively reduce the critical cooling rate of martensite formation and reduce the generation of pearlite, thereby improving the hardenability of the steel plate. At the same time, Mo is generally added in combination with Cr in high strength steel, but excessive addition of Mo will significantly increase the cost of the steel. Therefore, the content of Mo is controlled to be 0.05% to 0.3% in the application, and the content of Mo is required to be 1 / 3 to 2 / 3 of the content of Cr.

[0020] Ti: Ti can capture free N atoms in steel, which plays a role in fixing N. At the same time, TiN can precipitate during solidification, which plays a role in pinning grain boundaries. Ti(C, N) precipitates during hot rolling, which plays a role in pinning original austenite grain boundaries and refining original austenite grains. At the same time, a small amount of Ti precipitates during continuous annealing, which plays a role in strengthening ferrite and bainite. However, excessive addition of Ti has limited effect and increases the cost. Therefore, the content of Ti is controlled to be 0.01% to 0.03% in the application.

[0021] Al: Al element has excellent deoxidizing ability, so it is usually used as a deoxidizer in the steelmaking process, and it is an impurity element in the steel plate, so the Al element content is required to be controlled to Al≤0.005% in the present application.

[0022] P: P element is a harmful element in steel, and the lower the content is, the better. Considering the cost, the P element content is controlled to P≤0.02% in the present application.

[0023] S: S element is a harmful element in steel, and the lower the content is, the better. Considering the cost, the S element content is controlled to S≤0.005% in the present application.

[0024] The second technical scheme of the present application provides a preparation method of a hot-dip aluminum-silicon 1000 MPa grade DH steel cold forming steel plate, which comprises smelting, hot rolling, pickling, cold rolling, continuous annealing and aluminum-silicon plating, and finishing.

[0025] Hot rolling: ①The heating temperature is between 1200-1250℃, and the holding time is≥100min. In this stage, Ti and N, C in the steel form Ti(C, N) precipitated phase, which not only fixes N atoms in the steel, but also pinches the original austenite grain boundary, so as to refine the original austenite grain. The holding time can effectively ensure that the Ti precipitation behavior is sufficient.

[0026] ②The opening rolling temperature is between 1100-1150℃, and the final rolling temperature is above 900℃, so as to ensure the rolling temperature in the recrystallization zone and promote the dynamic recrystallization behavior of the original austenite grain in the hot rolling stage.

[0027] ③The coiling temperature is between 560-680℃, so as to prevent the coiling temperature from being too low and increase the cold rolling difficulty. The hot rolling coil thickness is between 2.5-4.0mm.

[0028] Pickling: The iron oxide scale generated on the surface of the hot-rolled steel plate is removed to ensure the surface quality of the cold-rolled steel plate.

[0029] Cold rolling: The cold rolling reduction rate is 50%-58%, so as to ensure that the cold rolling reduction amount is more than 50% and promote the fiberization of the structure in the cold rolling configuration; at the same time, it is prevented that the cold rolling reduction rate is too high, which leads to too large deformation resistance and is difficult to roll to the target thickness.

[0030] Continuous annealing and aluminum-silicon plating:

[0031] ①Isothermal temperature is 780-860℃, isothermal time is 80-150s, slow cooling temperature is 650-700℃, and slow cooling rate is controlled to be 0.5-5℃ / s; in this stage, cold rolling structure is recovered and recrystallized; under the limited isothermal temperature and isothermal time, the steel plate is in austenite zone or two-phase zone, so that element diffusion in the steel plate can be ensured; slow cooling to 650-700℃ can obtain partial ferrite, and C element is enriched in austenite, so that the stability of austenite is enhanced;

[0032] ②After slow cooling, the steel plate is immersed in aluminum-silicon plating solution to obtain an aluminum-silicon plated layer; the temperature of the aluminum-silicon plating solution is 650-700℃, and the aluminum-silicon plating time is 3-10s; the plating temperature can ensure the flowability of the aluminum-silicon plating solution, and the temperature of the aluminum-silicon plating solution is 650-700℃, so that the proportion of ferrite and austenite can be further adjusted, and C element can be diffused to austenite, so that the stability of austenite is ensured.

[0033] ③After aluminum-silicon plating, the steel plate is cooled to overaging temperature 280-350℃ at a cooling rate of >10℃ / s, and then is cooled to room temperature at a cooling rate of >2℃ / s; the cooling rate of >10℃ / s can ensure that austenite can effectively obtain martensite phase, and the limited overaging time can ensure that bainite phase is generated in the overaging stage, so that 15%-30% of bainite is obtained; the generated martensite phase is tempered, so that C element is diffused to austenite from bainite and martensite, the stability of austenite is further ensured, and the plasticity of the steel plate is improved. The cooling rate of >2℃ / s can ensure that austenite in the overaging stage is transformed into martensite phase, and residual austenite is retained.

[0034] Then, the steel plate enters a skin pass mill to adjust the plate shape, and the skin pass elongation is controlled to be 0.1%-0.6%. The mechanism is that: first, a suitable proportion of ferrite and original austenite is obtained by annealing in the austenite zone or two-phase zone; the steel plate is slowly cooled to 650-700℃ for hot aluminum-silicon plating, and then is cooled to 280-350℃ for isothermal treatment to obtain appropriate martensite / bainite structure. Since the hot aluminum-silicon plating is in the slow cooling stage, the overaging time of the present application can be flexibly adjusted according to the phase change requirement, the limitation of high temperature and short time overaging for hot galvanized steel plate is broken, the bainite transformation is sufficient, and the plasticity of the surface quality DH steel is improved. The steel plate produced by the present application has a tensile strength of more than 1000MPa, a yield strength of 600-800MPa, and an elongation of >18%.

[0035] The present application has the following beneficial effects:

[0036] (1) The chemical composition of the steel material of the present application mainly contains C and Mn as main elements, and no obvious noble alloy, and the C content is less than 0.24%, which is beneficial to laser welding and resistance spot welding in the production and application processes;

[0037] (2) The present application realizes high surface quality of DH steel by adopting a new hot aluminizing-siliconizing method, and the hot aluminizing-siliconizing is performed during the slow cooling stage, which is perfectly matched with the heat treatment system, breaks the limitation of high temperature and short time overaging for hot galvanized steel plate, and enables the bainite transformation to be sufficient, which is beneficial to improve the plasticity of DH steel;

[0038] (3) The present application realizes good strength-plasticity and formability of the steel plate by low-cost alloy design and ingenious process design. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The microstructure metallographic chart of the embodiment of the present application. DETAILED DESCRIPTION

[0040] The present application will be further described by examples.

[0041] The embodiment of the present application is smelted, hot-rolled, pickled, cold-rolled, continuously annealed and aluminized-siliconized according to the component ratio of the technical scheme.

[0042] Hot rolling: heating temperature 1200-1250℃, holding time ≥100min; opening rolling temperature 1100-1150℃, final rolling temperature 900℃ or above, coiling temperature 560-680℃, hot rolling coil thickness 2.5-4.0mm;

[0043] Cold rolling: cold rolling reduction rate 50%-58%;

[0044] Continuous annealing and aluminizing-siliconizing:

[0045] ① Isothermal heating temperature 780-860℃, isothermal time 80-150s, slow cooling temperature 650-700℃, slow cooling rate controlled at 0.5-5℃ / s;

[0046] ② Aluminizing-siliconizing: after slow cooling, the steel plate is immersed in aluminizing-siliconizing solution to obtain the surface coating of the steel plate, the temperature of the aluminizing-siliconizing solution is 650-700℃, and the aluminizing-siliconizing time is 3-10s;

[0047] ③ After aluminizing-siliconizing, the steel plate is cooled to overaging temperature 280-350℃ at a cooling rate >10℃ / s, overaging time 200-650s, and then is cooled to room temperature at a cooling rate >2℃ / s;

[0048] Finishing: the steel plate enters the finishing machine to adjust the plate shape, and the finishing elongation is controlled at 0.1%-0.6%.

[0049] The component of the steel of the embodiment of the present application is shown in Table 1. The main process parameters of the hot rolling and cold rolling of the steel of the embodiment of the present application are shown in Table 2. The main process parameters of the annealing and aluminizing-siliconizing of the steel of the embodiment of the present application are shown in Table 3. The performance of the steel of the embodiment of the present application is shown in Table 4.

[0050] Table 1 Composition of the steel of the embodiment of the present application (wt%)

[0051]

[0052] Table 2 Main process parameters of continuous casting and hot rolling of the steel of the embodiment of the present application

[0053]

[0054] Table 3 Main process parameters of annealing and aluminizing of the steel of the embodiment of the present application

[0055]

[0056] Table 4 Properties of the steel of the embodiment of the present application

[0057] Examples Rp0.2 / MPa Rm / MPa A50 / ％ 1 635 1013 19.1 2 653 1012 18.2 3 727 1095 18.7 4 628 1021 18.9 5 712 1087 18.8 6 666 1014 20.5 7 721 1102 18.1 8 706 1013 19.4

[0058] Table 5 Microstructure of the steel of the embodiment of the present application and composition of the plating solution (wt%)

[0059]

[0060] As can be seen from the above, the microstructure of the steel plate produced by the present application is ferrite, martensite, bainite and residual austenite; the above microstructure is counted by the planar area method, the ferrite is 25% to 45%, the martensite is 20% to 50%, the bainite is 15% to 30%, and the residual austenite content is 4% to 11%. The cold forming steel plate has a tensile strength of 1000 MPa or more, a yield strength of 600 to 800 MPa, and an elongation of more than 18%. The hot-dip aluminum-silicon plating is ingeniously carried out in the slow cooling stage, perfectly matches the heat treatment system, breaks the limitation of high temperature and short time overaging for hot-dip galvanized steel plate, and can fully convert bainite, which is beneficial to improve the plasticity of DH steel.

[0061] In order to describe the present application, the above embodiment is appropriately and sufficiently described in the above, the above embodiment is only used to illustrate the present application, and is not limited to the present application. Any modification, equivalent replacement, improvement, etc. made by those skilled in the art without departing from the spirit and scope of the present application shall be included in the protection scope of the present application, and the patent protection scope of the present application shall be defined by the claims.

Claims

1. A hot-dip aluminum-silicon 1000 MPa grade DH steel cold-formed steel sheet, characterized in that, The steel plate substrate component is as follows in terms of weight percentage: C: 0.18%~0.24%, Si: 0.92%~1.4%, Mn: 2.1%~2.4%, Cr: 0.1%~0.4%, Mo: 0.05%~0.3%, P≤0.02%, S≤0.005%, Ti: 0.01%~0.03%, Al≤0.005%, the balance being Fe and inevitable impurities; the microstructure of the cold-formed steel plate is ferrite, martensite, bainite and residual austenite; the above microstructure is counted by the planar area method, ferrite 25%~38%, martensite 23%~50%, bainite 15%~30%, and the residual austenite content 9%~11%.

2. The hot-dip aluminum-silicon 1000 MPa grade DH steel cold forming steel sheet according to claim 1, characterized in that, The Mo / Cr in the steel plate is 1 / 3~2 / 3.

3. The hot-dip aluminum-silicon 1000 MPa grade DH steel cold forming steel sheet according to claim 1, characterized in that, The coating component of the steel plate is as follows in terms of weight percentage: Al: 88%~93%, Si: 7%~12%.

4. The hot-dip aluminum-silicon 1000 MPa grade DH steel cold forming steel sheet according to claim 1, characterized in that, The cold-formed steel plate has a tensile strength of 1000 MPa or more, a yield strength of 600~800 MPa, and an elongation of >18%.

5. A preparation method of the hot-dip aluminum-silicon 1000 MPa grade DH steel cold-formed steel plate according to any one of claims 1~4, comprising smelting, hot rolling, pickling, cold rolling, continuous annealing and aluminum-silicon plating, and finishing; characterized in that: hot rolling: heating temperature 1200~1250℃, holding time≥100 min; opening rolling temperature 1100~1150℃, final rolling temperature≥900℃, coiling temperature 560~680℃, and hot-rolled coil thickness 2.5~4.0mm; cold rolling: cold rolling reduction rate 50%~58%; continuous annealing and aluminum-silicon plating: ① isothermal heating temperature 780~860℃, isothermal time 80~150s, slow cooling temperature 650~700℃, and slow cooling rate 0.5~5℃ / s; ② aluminum-silicon plating: after slow cooling, the steel plate is immersed in an aluminum-silicon plating solution to obtain a coating on the surface of the steel plate, the aluminum-silicon plating solution temperature is 650~700℃, and the aluminum-silicon plating time is 3~10s; ③ after aluminum-silicon plating, the steel plate is cooled to overaging temperature 286~348℃ at a cooling rate of >25℃ / s, overaging time 200~650s, and then cooled to room temperature at a cooling rate of >2℃ / s; finishing: the steel plate enters a finishing machine for shape adjustment, and the finishing elongation is controlled to be 0.1%~0.6%.

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