CN108486494A - The production method of vanadium micro-alloying 1300MPa grade high-strengths hot rolled steel plate and cold-rolled biphase steel plate - Google Patents

Abstract

The invention discloses a production method of a vanadium microalloyed 1300MPa high-strength hot-rolled steel plate and a cold-rolled dual-phase steel plate, which is used to solve the technical problem of insufficient strength of the dual-phase steel plate prepared by the existing method. The technical solution is to obtain 1300MPa-level high-strength hot-rolled steel plates through smelting and solidification of steel, continuous hot rolling and controlled cooling after casting slabs or ingots, and after coiling at a certain temperature in hot continuous rolling, pickling and cooling at room temperature Roll to a thickness of 1-3mm, and then hold at a certain temperature in the two-phase region of 720-780°C for a short time and immediately quench to obtain a vanadium microalloyed 1300MPa grade high-strength dual-phase cold-rolled steel plate. The preparation process combines the precipitation strengthening of nano-vanadium carbide particles with the martensitic transformation strengthening, which significantly improves the strength of the existing dual-phase steel, and at the same time ensures high production efficiency.

Description

Production of vanadium microalloyed 1300MPa grade high-strength hot-rolled steel sheet and cold-rolled dual-phase steel sheet production method

technical field

The invention relates to a preparation method of a dual-phase steel plate, in particular to a production method of a vanadium microalloyed 1300MPa grade high-strength hot-rolled steel plate and a cold-rolled dual-phase steel plate.

Background technique

High-strength and high-plastic materials have always been pursued by material workers. At present, the automotive steel industry is facing the need to improve product performance to ensure safety. At the same time, it requires the development of lightweight body and new technology to reduce energy consumption standards and reduce pollutant emissions. Meet the corresponding social norms of energy conservation and environmental protection. In recent years, the development of dual-phase (martensitic + ferrite) steels has met the performance requirements of automotive steels at low cost and has been widely used.

For a long time, the mechanical properties of dual-phase steel mainly rely on martensite to provide strength, and ferrite to provide plasticity. At present, the highest strength level is DP1180 grade, its tensile strength is about 1200MPa, yield strength is about 750MPa, and the total elongation is about 10% (Data source: Strain hardening behavior and mechanism of DP1180 dual-phase steel under high strain rate deformation conditions; Acta Metall Sinica; 2012(48):1160-1160). The preparation of dual-phase steel mainly goes through technological processes such as smelting, forging, hot rolling, cold rolling, two-phase zone annealing, and quenching. Compared with the second-generation and third-generation advanced high-strength automotive steels, dual-phase steels are typical representatives of the first-generation advanced high-strength automotive steels due to their low production cost and excellent performance. The production process of cold-rolled dual-phase steel is continuous cold rolling and continuous annealing process. Its tensile strength is determined by the martensite fraction in the annealed structure. The higher the martensite fraction, the higher the tensile strength, which requires high strength. Martensitic steel requires higher annealing temperature to form more martensite fraction, but the highest strength grade of dual-phase steel that can be commercially produced at present is 1180MPa, that is, DP 1180 steel.

Contents of the invention

In order to overcome the problem of insufficient strength of the dual-phase steel plate prepared by the existing method, the invention provides a production method of a vanadium microalloyed 1300MPa high-strength hot-rolled steel plate and a cold-rolled dual-phase steel plate. This method obtains 1300MPa high-strength hot-rolled steel plates through smelting and solidification of steel, continuous hot rolling and controlled cooling after billet or ingot opening, and after coiling at a certain temperature in hot continuous rolling, pickling and cold rolling at room temperature to a thickness of 1-3mm, and then immediately quenched at a certain temperature in the two-phase region of 720-780°C for a short time to obtain a vanadium microalloyed 1300MPa grade high-strength dual-phase cold-rolled steel plate. The preparation process combines the precipitation strengthening of nano-vanadium carbide particles with the martensitic transformation strengthening, which significantly improves the strength of the existing dual-phase steel, and at the same time ensures high production efficiency.

The technical scheme adopted by the present invention to solve the technical problem: a production method of vanadium microalloyed 1300MPa grade high-strength hot-rolled steel plate and cold-rolled dual-phase steel plate, which is characterized in that it includes the following steps:

(1) Smelting and solidification of steel: steelmaking by converter, electric furnace or induction furnace, continuous casting to produce billets or die casting to produce ingots;

(2) Continuous hot rolling after casting slab or ingot: heating the slab or ingot at 1100-1250°C, rolling by rough rolling mill for 5-20 passes, hot rolling to 40-80mm thickness specification, Then the hot rolling unit will carry out 5-7 passes of rolling to 4-15mm, and the final rolling temperature will be controlled at 800-850°C

(3) After final rolling, there are two cooling methods. One is to rapidly cool to 500-550°C at a cooling rate of >4°C/s after final rolling, and then cool to <150°C at a cooling rate of 0.5-1°C/s and then coil at a low temperature. ; The second is to coil at a high temperature of >4°C/s to 450-650°C, and the coil weight is more than 10 tons. The above two hot-rolled coils are finally air-cooled to room temperature, and the former process can obtain 1300MPa hot-rolled steel sheets.

(4) The two kinds of hot-rolled plates obtained in step (3) are subjected to pickling treatment, and cold-rolled to 0.5-3.0 mm at room temperature. Due to the different rolling resistance, the hot-rolled sheet coiled at low temperature <150°C in step (3) is finally cold-rolled to a thickness of 1.0-3.0mm, while the hot-rolled sheet coiled at 450-650°C can be cold-rolled to 0.5-2mm .

(5) Annealing the cold-rolled steel sheet obtained in step (4). Step (3) Coil the hot-rolled sheet <150°C at low temperature and after cold rolling, heat it to 600-700°C at a heating rate of >10°C/s and keep it for 3-10 minutes, then heat it to 720-780°C for 80 minutes Rapid cooling after -150s, cooling rate > 30 ℃ / s; and for step (3) after high-temperature coiling of 450-650 ℃ hot-rolled sheet cold rolling, directly heated to 720-780 at a heating rate of > 10 ℃ / s ℃, fast cooling after holding time for 20-60s, cooling rate>30℃/s. Both processes can obtain high-strength cold-rolled dual-phase steel sheets.

The chemical composition of the slab or ingot obtained in step (1) is 0.10-0.30wt% C, 1.50-4.50wt% Mn, 0.00-0.120wt% Al, 0.00-0.90wt% Si, 0.05-0.50% V, P ≤0.020wt%, S≤0.02wt%, and the balance is Fe.

According to the hot-rolled steel plate prepared in step (3), the microstructure of the hot-rolled steel plate coiled at low temperature (<150° C.) after final rolling is mainly bainite.

After annealing according to the step (5), the microstructure characteristics of the product are all martensite, ferrite and vanadium carbide, and the deformed microstructure remains.

In addition, one or more of the following elements can be added to the cast billet or ingot composition to further improve performance: Ni: 0.1-3.0wt%, Cr: 0.2-3.0wt%, Mo: 0.1-0.8wt%, Si: 0.3-2.3wt%, Cu: 0.5-2.0wt%, B: 0.0005-0.005wt%, Nb: 0.02-0.10wt%, [N]: 0.002-0.25wt%, Ti: 0.05-0.25wt%, RE (rare earth): 0.002-0.005wt%, Ca: 0.005-0.03wt%. Among them, the addition of Ni, Mo, Cr, B, etc. can further improve the hardenability or low-temperature impact toughness of the steel; the addition of Nb, Ti, etc. to refine the original austenite grains leads to the final microstructure refinement; adding Cu, through precipitation strengthening, improves the steel strength; adding Si, etc. to increase strength and inhibit carbide precipitation, etc.; adding [N] to adjust the stability of austenite.

The beneficial effects of the present invention are: the method obtains 1300MPa grade high-strength hot-rolled steel plate through smelting and solidification of steel, continuous hot rolling and controlled cooling after casting slab or ingot, or after coiling at a certain temperature in hot continuous rolling, After pickling and cold rolling at room temperature to a thickness of 1-3mm, and then quenching immediately at a certain temperature in the two-phase region of 720-780°C for a short time, the vanadium microalloyed 1300MPa grade high-strength dual-phase cold-rolled steel plate is obtained. The preparation process combines the precipitation strengthening of nano-vanadium carbide particles with the martensitic transformation strengthening, which significantly improves the strength of the existing dual-phase steel, and at the same time ensures high production efficiency.

The present invention obtains 1300MPa grade high-strength hot-rolled steel plate by using vanadium microalloying, controlled rolling and controlled cooling; obtains non-equilibrium structure by deforming and storing the cold-rolled plate, and then precipitates vanadium nanoparticles and martensitic phase Combined with variable strengthening, 1300MPa grade cold-rolled steel plate can be obtained. Compared with the traditional cold-rolled dual-phase steel plate, the cold-rolled dual-phase steel plate obtained in the present invention can increase the index of tensile strength by 10% or even higher and the index of yield strength without reducing the total elongation. 12% or even higher.

The present invention redesigns the basic composition on the basis of the existing dual-phase steel, forms martensite through rapid cooling after conventional annealing to improve strength, and also combines the microalloying composition design of vanadium to skillfully form The combination of austenite and the precipitation of fine vanadium-containing particles further increases the yield strength and tensile strength of the cold-rolled steel sheet, while the steel sheet also maintains good elongation.

The invention discloses a preparation method of a hot-rolled plate with a strength level of 1300MPa. At present, most of the existing hot-rolled low-alloy high-strength steel sheets have a strength level of no more than 1000 MPa, while the hot-rolled steel sheet obtained by the present invention has a tensile strength of 1300 MPa through the combination of composition optimization design and controlled cooling process. And the elongation rate exceeds 10%, which has obvious advantages in mechanical properties.

In the above technical scheme, a large number of nano-sized vanadium carbide particles can be precipitated in the high-temperature coiling process after hot rolling. After cold rolling, it can be directly heated to the two-phase region for short-term heat preservation, and martensite strengthened by vanadium carbide precipitation can be obtained after quenching. Ferrite dual-phase structure, so that the yield strength and tensile strength can be effectively improved without loss of plasticity; and for the hot-rolled sheet coiled at low temperature after hot rolling, most of the V has not yet precipitated after cold rolling, and it needs Heating to a temperature lower than the annealing temperature and keeping it warm to allow VC to precipitate, and then annealing in the two-phase region, this process can obtain finer and dispersed VC particles, so the yield strength of the steel plate is higher, while the tensile strength and elongation It is similar to the previous process.

According to the hot-rolled steel plate prepared in step (3) of the technical solution, the microstructure of the hot-rolled steel plate coiled at low temperature (<150°C) after final rolling is mainly bainite, and the mechanical properties are tensile strength 1200-1400MPa, yield strength ≥900MPa, total elongation ≥10%, uniform elongation ≥4%.

According to the technical scheme step (5) after annealing, the product microstructure features are martensite, ferrite and vanadium carbide, and the deformed structure remains; 700°C heat preservation and then heating to 720-780°C heat preservation and rapid cooling), the yield strength of the steel plate is ≥950MPa, the tensile strength is ≥1300MPa, the uniform elongation is ≥5%, and the total elongation is 9-15%. On the premise that the uniform elongation and total elongation do not decrease, compared with DP1180 steel, the index of tensile strength is increased by 10%, and the yield strength is increased by 26%. The rolled plate is directly heated to 720-780°C and then quickly cooled), the yield strength of the obtained steel plate is ≥800MPa, the tensile strength is ≥1300MPa, the uniform elongation is ≥5%, and the total elongation is 8-13%. Under the premise of not reducing the elongation, compared with DP1180 steel, the index of tensile strength is increased by 10%, and the yield strength is increased by 12%. The yield strength of the steel plate obtained by the former process is higher.

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Description of drawings

Fig. 1 is the scanning electron microscope photograph of the hot-rolled steel plate that obtains after 1-B-3 group hot rolling in the method embodiment of the present invention;

Fig. 2 is the optical metallographic microscope photograph of the hot-rolled steel plate obtained after 2-B-3 group hot rolling in the embodiment of the method of the present invention;

Fig. 3 is the scanning electron microscope photograph of the cold-rolled steel plate obtained after 1-B-3 group cold rolling and annealing in the method embodiment of the present invention;

Fig. 4 is the scanning electron microscope photograph of the cold-rolled steel plate obtained after 2-B-3 group cold rolling and annealing in the method embodiment of the present invention;

Fig. 5 is a typical engineering stress-strain curve obtained from tensile experiments of two kinds of hot-rolled steel sheets and two kinds of cold-rolled steel sheets in the embodiment of the method of the present invention.

Detailed ways

The following examples refer to Figures 1-5. A kind of production method of vanadium microalloyed 1300MPa grade high-strength hot-rolled steel plate and cold-rolled dual-phase steel plate, concrete steps are as follows:

(1) Smelting and solidification of steel: steelmaking by converter, electric furnace or induction furnace, continuous casting to produce billets or die casting to produce ingots;

(2) Continuous hot rolling after casting slab or ingot: heating the slab or ingot at 1100-1250°C, rolling by rough rolling mill for 5-20 passes, hot rolling to 40-80mm thickness specification, Then the hot rolling unit will carry out 5-7 passes of rolling to 4-15mm, and the final rolling temperature will be controlled at 800-850°C

(3) There are two cooling methods after the final rolling, one is to rapidly cool to 500-550 °C at a cooling rate of >4 °C/s after the final rolling, and then cool to <150 °C at a rate of 0.5-1 °C/s and then coil; The second is to coil by cooling to 450-650°C at >4°C/s, and the coil weight must be greater than 15 tons to ensure a slow cooling rate, or to simulate the actual slowness of the industrial coil by heating the furnace for heat preservation and furnace cooling during the pilot test simulation cooling rate. The above two kinds of hot-rolled coils are finally air-cooled to room temperature to provide base materials for subsequent cold rolling. But the former process can obtain 1300MPa grade hot rolled steel plate.

(4) The two kinds of hot-rolled plates obtained in step (3) are subjected to pickling treatment, and cold-rolled to 0.5-3.0 mm at room temperature. Due to the different rolling resistance, the hot-rolled sheet coiled at low temperature (<150°C) in step (3) is finally cold-rolled to a thickness of 1.0-3.0mm, while the hot-rolled sheet coiled at 450-650°C can be cold-rolled to a thickness of 0.5mm -2mm.

(5) Annealing the cold-rolled steel sheet obtained in step (4). Step (3) After cold-rolling the hot-rolled sheet coiled at low temperature (<150°C), heat it to 600-700°C at a heating rate of >10°C/s and keep it warm for 3-10 minutes, then heat it to 720-780°C and keep it warm Fast cooling after 80-150s, cooling rate > 30°C/s; and for step (3) hot-rolled coils (450-650°C) after cold rolling, directly heat at a heating rate > 10°C/s To 720-780°C, hold for 20-60s and then cool quickly, and the cooling rate is >30°C/s. Both processes can obtain high-strength dual-phase cold-rolled steel sheets.

Example 1:

Chemical composition (wt%) of table 1 invention steel

Element C mn al V Si P S A 0.10 1.84 0.080 0.08 0.20 <0.005 <0.005 B 0.16 2.62 0.053 0.15 0.33 <0.005 <0.005 C 0.25 4.13 0.120 0.35 0.80 <0.005 <0.005

The test in this example adopts the chemical composition shown in Table 1. After smelting, it is cast into an ingot, hot-forged into a slab with a thickness of 50 mm, heated to 1200 ° C for 3 hours, and then hot-rolled to about 4.7 mm by a pilot single-stand rolling mill to obtain a hot Rolled products, the final rolling temperature is about 850°C, and then divided into 1 and 2 coiling methods according to the cooling process and coiling temperature, which are marked as 1 group and 2 groups respectively. , in which group 1 is rapidly cooled to about 530°C at a cooling rate of about 5°C/s after final rolling, and then cooled to 150°C at a rate of about 0.6-0.8°C/s, and then coiled; group 2 is cooled at a cooling rate of about 5°C/s s is cooled to 550°C for coiling, and then placed in a heat treatment furnace at 550°C for 5 hours and then cooled with the furnace to simulate the slow cooling process of industrial hot-rolled coils. The mechanical properties of the hot-rolled plates of the above two cooling methods are shown in Table 2. It can be seen that the mechanical properties of the steel plates coiled at low temperature after the former rapid cooling can reach 1300MPa.

Cold-roll the hot-rolled sheet obtained in Group 1 to a thickness of 2mm, heat it at 15°C/s to 630-670°C and keep it for 300-600s, then heat it to different temperatures in the range of 720-760°C, and hold it for 120-150s After different times, take it out and cool it with oil, and the cooling rate exceeds 30°C/s; cold-roll the hot-rolled plate obtained in the second group to a thickness of 1.2mm, and directly heat it to different temperatures in the range of 720-760°C at 15°C/s, Keep warm for 30-60s, take it out and cool it with oil at a cooling rate >30°C/s. Both processes can obtain high-strength dual-phase cold-rolled steel sheets, and their properties are shown in Table 3.

Through the characterization of the microstructure, it can be seen from the scanning electron microscope photo in Figure 1 that the bainite structure is obtained after cooling in group 1 after hot rolling. It can be seen from the scanning electron microscope photos in Figure 2 that the microstructure obtained by cooling after hot rolling in the two groups is pearlite microstructure, ferrite is the matrix, and cementite particles are distributed. This is mainly due to the difference in hot rolling process. From the scanning electron microscope photos in Figure 3, it can be seen that the final microstructure after group 1 annealing is ferrite + martensite, and it is distributed in bands along the rolling direction, and the original austenite grain size and ferrite grain size The particle size is between 1 and 3 microns. It can be seen from the scanning electron microscope photos in Figure 4 that the final microstructure after annealing in the two groups is ferrite + martensite, and it is distributed in bands along the rolling direction, and the original austenite grain size and ferrite grain size The particle size is between 1 and 3 microns. It can be seen from the engineering stress-strain curve in Figure 5 that there are huge differences in the tensile mechanical properties of hot-rolled steel sheets obtained by different coiling methods; in addition, the tensile strength of the final microstructure after group 1 annealing is higher than 1300MPa, and the yield strength is higher than 800MPa , The uniform elongation is higher than 6%, and the total elongation is higher than 10%. The tensile strength of the final structure after annealing in the two groups is higher than 1300MPa, the yield strength is higher than 800MPa, the uniform elongation is higher than 6%, and the total elongation is higher than 9%.

Table 2 Mechanical properties of hot-rolled sheet

Table 3 Mechanical properties of the hot-rolled sheets in Table 2 after undergoing different annealing processes after cold rolling

The yield strength of the cold-rolled steel plate after annealing basically exceeds 800MPa, and the yield strength of the first group of hot-rolled low-temperature coiling process is higher, exceeding 950MPa; the tensile strength of both is above 1300MPa, and the strength-plastic product is above 12GPa%. Compared with the traditional DP1180, the obtained performance has been significantly improved, and it is expected to be put into actual production.

Claims (6)

1. a kind of production method of vanadium micro-alloying 1300MPa grade high-strengths hot rolled steel plate and cold-rolled biphase steel plate, feature exist In including the following steps：

(1) smelting and solidification of steel：By converter, electric furnace or induction furnace steel-smelting, using continuous casting strand or molding production casting Ingot；

(2) hot continuous rolling after strand or ingot formation：Strand or ingot casting are heated through 1100-1250 DEG C, 5- is carried out by roughing mill 20 passes, hot rolling carry out 5-7 passes to 4-15mm, finishing temperature to 40-80mm thickness specifications, then by heat even unit Control is at 800~850 DEG C；

(3) be divided to two kinds of types of cooling after finish to gauge, when after finish to gauge with>4 DEG C/s cooling rates are cooled to 500-550 DEG C soon, then with 0.5-1 DEG C/s is cooled to<Low temperature batches after 150 DEG C；Second is that with>4 DEG C/s is cooled to 450-650 DEG C of high temperature coiling, and volume is great in 10 tons；On It states two kinds of hot rolled coils and is finally air-cooled to room temperature, former technique obtains 1300MPa rank hot rolled steel plates；

(4) step (3) is obtained into two kinds of hot rolled plates and passes through pickling processes, at room temperature cold continuous rolling to 0.5-3.0mm；Due to rolling Drag is different, in step (3)<To thickness 1.0-3.0mm, 450-650 DEG C is batched for 150 DEG C of hot rolled plate final cold rollings batched Hot rolled plate is cold-rolled to 0.5-2mm；

(5) cold-rolled steel sheet obtained in step (4) is made annealing treatment；In step (3)<150 DEG C of hot rolled plate cold rollings batched Afterwards, with>The rate of heat addition of 10 DEG C/s is heated to 600-700 DEG C of heat preservation 3-10min, is then again heated to 720-780 DEG C, when heat preservation Between rapid cooling after 80-150s, cooling rate>30℃/s；And for the 450-650 DEG C of hot rolled plate cold rolling batched in step (3) after, with >The rate of heat addition of 10 DEG C/s is directly heated to 720-780 DEG C, rapid cooling after soaking time 20-60s, cooling rate>30℃/s.

2. the life of vanadium micro-alloying 1300MPa grade high-strengths hot rolled steel plate and cold-rolled biphase steel plate according to claim 1 Production method, it is characterised in that：The chemical composition of gained strand or ingot casting is 0.10-0.30wt%C, 1.50- in the step (1) 4.50wt%Mn, 0.00-0.120wt%Al, 0.00-0.90wt%Si, 0.05-0.50%V, P≤0.020wt%, S≤ 0.02wt%, surplus Fe.

3. the life of vanadium micro-alloying 1300MPa grade high-strengths hot rolled steel plate and cold-rolled biphase steel plate according to claim 1 Production method, it is characterised in that：Prepared hot rolled steel plate in the step (3), after finish to gauge<The hot rolled plate that 150 DEG C of low temperature batches Tissue based on bainite, mechanical property be tensile strength 1200-1400MPa, yield strength >=900MPa, breaking elongation >= 10%, uniform elongation >=4%.

4. the life of vanadium micro-alloying 1300MPa grade high-strengths hot rolled steel plate and cold-rolled biphase steel plate according to claim 1 Production method, it is characterised in that：Product tissue is characterized as martensite, ferrite and vanadium carbide after step (5) annealing, and remains Deformation structure.

5. the life of vanadium micro-alloying 1300MPa grade high-strengths hot rolled steel plate and cold-rolled biphase steel plate according to claim 1 Production method, it is characterised in that：After hot rolled plate cold rolling being batched for the low temperature described in step (5), with>The rate of heat addition of 10 DEG C/s It is heated to a certain temperature 3-10min within the scope of 600-700 DEG C, is then again heated to a certain temperature in 720-780 DEG C, is kept the temperature Rapid cooling after 80-150s, cooling rate>30 DEG C/s, yield strength >=950MPa of cold-rolled steel sheet, tensile strength >=1300MPa, Uniform elongation >=5%, breaking elongation 9-15%；And for the high temperature coiling hot rolled plate cold rolling described in step (5) after, with> The rate of heat addition of 10 DEG C/s is directly heated to 720-780 DEG C, rapid cooling after soaking time 20-60s, cooling rate>It is 30 DEG C/s, cold Rolled steel plate yield strength >=800MPa, tensile strength >=1300MPa, uniform elongation >=5%, breaking elongation 8-13%.

6. the life of vanadium micro-alloying 1300MPa grade high-strengths hot rolled steel plate and cold-rolled biphase steel plate according to claim 1 Production method, it is characterised in that：Separately it is subject to a kind of lower or multiple element in strand or ingot casting ingredient obtained by step (1), into one Step improves performance：Ni:0.1-3.0wt%, Cr:0.2-3.0wt%, Mo:0.1-0.8wt%, Si:0.3-2.3wt%, Cu: 0.5-2.0wt%, B：0.0005-0.005wt%, Nb:0.02-0.10wt%, [N]:0.002-0.25wt%, Ti：0.05- 0.25wt%, RE (rare earth):0.002-0.005wt%, Ca:0.005-0.03wt%；Wherein addition Ni, Mo, Cr, B is further Improve the quenching degree or low-temperature impact toughness of steel；The refinement original austenite grain such as addition Nb, Ti leads to final structure refinement；Addition Cu, the intensity that steel is improved by precipitation strength；Si etc. is added to improve intensity and inhibit Carbide Precipitation；It adds [N] and adjusts Ovshinsky The stability of body.