CN105568145B - A kind of strong dual phase sheet steel of automobile cold-rolled superelevation with decay resistance and preparation method thereof - Google Patents

Abstract

A cold-rolled ultra-high-strength dual-phase steel sheet for automobiles with corrosion resistance and a preparation method thereof, the chemical composition and mass percentage of the steel sheet are: 0.13%~0.16%C, 1.8%~2.0%Si, 2.3%~2.5% Mn, 1.8%~2.2%Cr, 0.010%~0.025%Al, 0.001%~0.008%S, 0.002%~0.012%P, 0.001%~0.004%N, and the rest are Fe and unavoidable impurity elements. The preparation method has simple process and low production cost, and the prepared steel plate has excellent comprehensive mechanical properties and corrosion resistance, and has good welding performance and formability, and meets the requirements of the automobile industry on the strength and corrosion resistance of high-strength steel.

Description

A cold-rolled ultra-high-strength dual-phase steel plate for automobiles with corrosion resistance and its preparation method

technical field

The invention relates to a composition and a preparation method of a cold-rolled ultra-high-strength dual-phase steel plate for automobiles with excellent corrosion resistance, belonging to the field of metal materials, and in particular to the technical field of production and application of steel for automobiles.

Background technique

As the downward pressure on China's economic situation increases, the steel industry, which is the basis of China's manufacturing industry, is getting colder. The production capacity of ordinary steel products is seriously overcapacitated, and the price continues to drop. However, high-quality steel products still need to be imported. This kind of "big but not strong" has already It has become an obvious feature of the development of my country's iron and steel industry, and many high-end steel production technology problems need to be solved urgently.

As a kind of advanced high-strength steel for automobiles, dual-phase steel has attracted much attention because of its excellent strong plasticity, low yield ratio, high hardening index and good formability, and because of its relatively small alloy content, It has excellent welding performance and low cost. For a period of time, people have carried out a large number of new species development and research work on dual-phase steel. At present, the highest strength of commercially produced dual-phase steel has reached 1200MPa, and the scope of application is continuously expanding. Among the commonly used alloying elements, Al has a significant effect on improving the stability of austenite, but the current Al content in the existing technology is too high (about 1.0 to 2.0%), resulting in a significant decrease in smelting castability, which is not conducive to continuous production , this paper controls the Al content below 0.025%. The present invention improves the comprehensive mechanical properties of dual-phase steel by adding a certain amount of Cr elements, and makes it have better corrosion resistance, thereby replacing part of the galvanized sheet, thereby reducing production costs and improving economic benefits. first.

CN104419878 A discloses "ultra-high-strength cold-rolled dual-phase steel with weather resistance and its manufacturing method". The mass percentage of its chemical composition is: C: 0.10%-0.16%, Si: 0.10%-0.50%, Mn: 1.4%-2.2%, Cr: 0.30%-0.79%, Ni: 0.08%-0.20%, Cu: 0.20%～0.50%, Nb: 0.01%～0.05%, Ti: 0.02%～0.05%, Al: 0.015%～0.045%, P≤0.020%, S≤0.007%, N≤0.008%, the balance is Fe and unavoidable impurities. A weather-resistant ultra-high-strength cold-rolled dual-phase steel with a yield strength of more than 700 MPa, a tensile strength of more than 800 MPa, and an elongation of more than 5% can be obtained. However, this type of steel has many alloy elements, high production cost, low strength, and relatively high yield strength, which is not conducive to stamping and forming in the process of manufacturing auto parts. Compared with it, the steel of the invention has less alloy element content, low alloy cost, simple process, the most important thing is that its tensile strength is nearly 1000MPa higher than that, and its corrosion resistance is excellent.

CN 104328348 A discloses "800MPa grade cold-rolled dual-phase steel and its production method". The mass percentage of its chemical composition is: C: 0.14-0.17%, Si: 0.45-0.55%, Mn: 1.6-1.8%, Cr: 0.55-0.65%, P: ≤0.016%, S: ≤0.008%, Als: 0.02 to 0.05%, N: ≤0.004%, and the balance is Fe. A cold-rolled dual-phase steel with a tensile strength of 800-850MPa, a yield strength of 450-550MPa, and an elongation of 15-17% has been produced, with reduced strength levels and no corrosion resistance.

CN 103469097 A discloses "high-strength martensitic ferritic duplex stainless steel corrosion-resistant oil casing and its manufacturing method". The weight percent of its chemical composition is: C: 0.05-0.10%, Si: 0.1-0.4%, Mn: 0.20-1.0%, P: less than 0.03%, S: less than 0.01%, Cr: 13.5-15.0%, Ni: 0.5 ～1.5%, Mo: 0.2～1.0%, Nb: 0.005～0.02%, N: 0.01～0.10%, O: below 0.004%, and satisfy Cr+1.5Mo+2Ni+16N≥17 and Ni+30(C+ N)+8Nb≥3.5, wherein Cr, Ni, Mo, Si, Nb, Mn, C, N are the weight percentage content of elements, and the rest are Fe and unavoidable impurities, and a high yield strength of 110ksi level is obtained. Strength and vTrs: martensitic seamless stainless steel for oil country tubular goods with excellent low temperature toughness below -60°C, but the tensile strength and other mechanical properties of the steel types in the examples involved are not disclosed. It belongs to the field of stainless steel, and its alloy element content is relatively high, its cost is too high, its production process and performance requirements are obviously different from the steel of the present invention, and it is not suitable for the manufacture of auto parts.

In this paper, by changing the composition design of the traditional cold-rolled high-strength steel, the cold-rolled ultra-high-strength dual-phase steel with corrosion resistance is developed by adding Cr elements. In the two simulated atmospheric environments, the steel of the present invention shows excellent corrosion resistance. performance. The process of the invention is simple, and the prepared steel plate has excellent comprehensive mechanical properties and corrosion resistance, and meets the requirements of the dual-phase steel for the use of auto parts in different environments. The invention aims to accumulate beneficial experimental data for the research and development of high-quality ultra-high-strength automotive steel, and at the same time change the current situation that ultra-high-strength automotive steel only focuses on strength and ignores its comprehensive performance.

Contents of the invention

The object of the present invention is to provide a cold-rolled ultra-high-strength dual-phase steel with low cost, good plasticity, low yield ratio and excellent corrosion resistance and a preparation method thereof.

In order to achieve the above purpose, the cold-rolled ultra-high-strength dual-phase steel designed by the present invention has a specific composition of 0.13%-0.16%C, 1.8%-2.0%Si, 2.3%-2.5%Mn, 1.8%-2.2%Cr, 0.010% %-0.025% Al, 0.001%-0.008% S, 0.002%-0.012% P, 0.001%-0.004% N, and the rest are Fe and unavoidable impurity elements.

The cold-rolled ultra-high-strength steel involved in the present invention is smelted in a vacuum induction furnace, and its manufacturing method comprises the following steps:

Carry out smelting and casting according to the above composition to obtain a billet satisfying the above chemical composition, cool the billet to room temperature, and use it as a raw material for hot rolling;

Heating the billet with the furnace to 1200°C-1250°C, keeping it warm for 2 hours, and then performing hot rolling, the rough rolling start temperature of the hot rolling process is 1050°C-1110°C, and the finish rolling temperature is 840°C-880°C, The total reduction rate of the hot-rolled sheet is 80% to 90%, and the reduction rate of the last pass is 20% to 30%. After the final rolling, the hot-rolled sheet is cooled to 630°C to 680°C and coiled. The coiling temperature 630℃～680℃, keep warm for half an hour after coiling, then air-cool to room temperature with the furnace;

Uncoiling the coiled steel plate for pickling cold rolling, the cold rolling process needs to control the cold rolling reduction between 50% and 80% to obtain cold rolled steel plate;

The cold-rolled steel sheet is continuously annealed, and the preheating section is heated to 100°C-200°C at a heating rate of 6.0°C/s-10.0°C/s, and then the steel plate is heated at a heating rate of 2.0°C/s-5.0°C/s Heating to the two-phase zone for heat preservation, the heat preservation temperature is 760°C-820°C, the heat preservation time is 160s-190s, and then the steel plate is slowly cooled to 620°C-650°C at a cooling rate of 4°C/s-8°C/s, and then Then cool the steel plate rapidly at a cooling rate of 35°C/s-50°C/s to 250°C-270°C, over-aging for 300s-400s, and then slowly cool the steel plate at a cooling rate of 3°C/s-8°C/s to room temperature.

Preferably, the starting rolling temperature in the hot rolling process is 1070°C-1100°C, the finishing rolling temperature is 815-835°C, and the rolling reduction in the last pass of hot rolling is controlled between 22%-26%.

Preferably, the annealing temperature is 785°C-825°C, and the holding time is 165s-185s. Then cool rapidly at a cooling rate of 38°C/s~45°C/s to 255°C~265°C, perform overaging treatment for 320s~380s, and then cool slowly to room temperature.

The structure of the steel is mainly martensite and a small amount of dispersed ferrite.

The steel has good comprehensive mechanical properties, Rp _0.2 = 1020-1100MPa, _Rm = 1600MPa-1850MPa, A ₅₀ = 4.55%-9.50%, Rp _0.2 / _Rm = 0.52-0.65.

The dual-phase steel has excellent corrosion resistance. When simulating the industrial atmospheric environment in the uniform corrosion full immersion test, the corrosive solution used is _0.005mol /L NaHSO solution (0.52g/L), and the corrosion rate of the steel of the present invention obtained is 0.17g m ^-2 h ^{- 1} , significantly better than the 0.25g·m ^-2 ·h ^-1 of the traditional dual-phase steel DP780; in the neutral salt spray test to simulate the marine atmospheric environment, the corrosion solution used is 50g/L±5g/L NaCl solution, The corrosion rates of the steel of the present invention in the test period of 96h and 144h are respectively 1.26g·m ^-2 ·h ^-1 and 1.11g·m ^-2 ·h ^-1 , significantly better than the corresponding 1.87g of the traditional dual-phase steel DP780 Corrosion rates of ·m ^-2 ·h ^-1 and 1.90 g·m ^-2 ·h ^-1 .

Beneficial effects of the present invention

(1) The composition of the alloy of the present invention is only basic C, Si, Mn and a certain amount of Cr elements. Through reasonable process control, its mechanical properties can reach Rp _0.2 = 1020 ~ 1100MPa, R _m = 1600MPa ~ 1850MPa, A ₅₀ = 4.55% to 9.50%, Rp _0.2 /R _m =0.52 to 0.65.

(2) The present invention adopts low-temperature heating and hot-rolling process control technology to effectively refine the hot-rolled structure.

(3) the present invention controls Mn content in the scope of 2.3%～2.5%, but can not be too high, can not exceed Mn content (5%<Mn%<8%) of medium manganese TRIP steel, not only reduces cost, and improves Process performance, convenient for testing steel continuous casting and cold rolling.

(4) The present invention effectively refines the microstructure of the steel of the present invention through the rational addition of Cr elements, and at the same time makes the steel of the present invention have corrosion resistance. In the simulated industrial atmospheric environment and the marine atmospheric environment, it is more effective than DP780. For superior corrosion resistance.

Description of drawings

Fig. 1 is the steel hot rolling process of this embodiment.

Fig. 2 is the steel heat treatment process of this embodiment.

Fig. 3 is a macroscopic photo of the corrosion morphology of the steel in the neutral salt spray test of this embodiment for 96 hours (a macroscopic photo of the corrosion morphology of the 96-hour test period (a) the steel of the present invention (b) DP780 steel, as shown in Fig. 3).

Fig. 4 is the SEM photo of the corrosion appearance of the steel in the neutral salt spray test of this embodiment for 96 hours (the SEM photo of the corrosion appearance of the test period of 96 hours (a) the steel of the present invention (b) DP780 steel, as shown in Fig. 4).

Fig. 5 is a macroscopic photo of the corrosion morphology of the steel in the neutral salt spray test of this embodiment for 144h test period (the macroscopic photo of the corrosion morphology of the 144h test period (a) the steel of the present invention (b) DP780 steel, as shown in Fig. 5).

Fig. 6 is the SEM photo of the corrosion appearance of the steel in the neutral salt spray test of this embodiment for 144h test period (the SEM photo of the corrosion appearance of the 144h test period (a) the steel of the present invention (b) DP780 steel, as shown in Fig. 6).

detailed description

The technical solutions of the present invention will be further described below in conjunction with specific embodiments.

The embodiment of the present invention is a cold-rolled ultra-high-strength dual-phase steel for automobiles with corrosion resistance. The mass percentages of its components are shown in Table 1, and the rest are iron and unavoidable impurities.

Table 1 specific embodiment steel chemical composition (mass percentage, %)

The test steel billet was smelted and cooled to room temperature, then the billet was heated to 1200°C, held for 2 hours, rolled at 1100°C, and hot-rolled plates with a thickness of 2mm to 4mm were obtained after six passes of hot rolling. The reduction ratio of the last pass 25%, the final rolling temperature is 850℃～880℃, and then water cooled to 640～660℃ for half an hour, and the coiling is simulated with the furnace cooling. The hot-rolled sheet that has been pickled to remove the surface oxide layer is cold-rolled on a four-roller double-stand rolling mill at a reduction rate of 50% to 70%, and the thickness of the finally obtained cold-rolled sheet is 0.8mm to 1.5mm. After cold rolling, the steel plate is annealed on a continuous annealing machine, and the annealing process is shown in Figure 2.

The annealing process of Example 1 (component 1) is as follows: the preheating section is heated to 150°C at 7.4°C/s, the heating section is heated to 800°C at the holding temperature of the two-phase zone at 2.6°C/s, and the two-phase zone is kept at the holding temperature for 180s. In the slow cooling section, the steel is slowly cooled to 640°C, then rapidly cooled to 260°C at a cooling rate of 40°C/s, overaged for 368s, and then slowly cooled to room temperature.

The annealing process of embodiment 2 (component 2) is that the preheating section is heated to 180°C at 7.4°C/s, the heating section is heated to the two-phase zone holding temperature of 810°C at 2.6°C/s, and the two-phase zone is kept warm for 180s. In the slow cooling section, cool slowly to 640°C, then quickly cool to 250°C at a cooling rate of 40°C/s, perform overaging treatment for 320s, and then slowly cool to room temperature.

The annealing process of embodiment 3 (component 1) is that the preheating section is heated to 150°C at 7.4°C/s, the heating section is heated to 820°C at the holding temperature of the two-phase zone at 2.6°C/s, and the two-phase zone is kept at the holding temperature for 180s. In the slow cooling section, the steel is slowly cooled to 620°C, then rapidly cooled to 260°C at a cooling rate of 40°C/s, overaged for 368s, and then slowly cooled to room temperature.

The mechanical properties of the steel in this example are shown in Table 2. When the annealing temperature is 820°C, Rp _0.2 = 1020MPa, _Rm = 1760MPa, A ₅₀ = 8.06%, and Rp _0.2 / _Rm = 0.58 cold-rolled ultra-high-strength dual-phase steel. According to "Metal Materials Laboratory - Uniform Corrosion Full Immersion Test Method JB/T 7901-2001", the uniform corrosion full immersion test is used to simulate the industrial atmospheric environment, and the corrosion solution is 0.005mol/L NaHSO ₃ solution (0.52g/L ), in the 130h test period, the corrosion rate of the steel of the present invention is 0.17g·m ^-2 ·h ^-1 , significantly better than 0.25g·m ^-2 ·h ^-1 of DP780; according to "Artificial Atmosphere Corrosion Test - Salt Spray In the test GB/T 10125-2012", the marine atmospheric environment is simulated through the neutral salt spray test, and the NaCl solution with a concentration of 50g/L±5g/L is used, and the corrosion rate is 1.26g during the 96h and 144h test periods. m ^-2 ·h ^-1 , 1.11g·m ^-2 ·h ^-1 , the corresponding corrosion rates of DP780 in the same test period are 1.87g·m ^-2 ·h ^-1 , 1.90g·m ^-2 ·h ^{- 1} . Fig. 3 and Fig. 4 are the macrophotographs and SEM photographs of the corrosion morphology of the steel in the neutral salt spray test for 96 hours in the test period of this embodiment. Fig. 5 and Fig. 6 are the macrophotographs and SEM photographs of the corrosion morphology of the steel in the neutral salt spray test of this embodiment for 144 hours.

Table 2 Steel mechanical properties of this embodiment

The contents not described in detail in the description of the present invention belong to the prior art known to those skilled in the art.

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (7)

1. A cold-rolled ultra-high-strength dual-phase steel sheet for automobiles with corrosion resistance, characterized in that the chemical composition of the steel sheet is calculated in mass percentage: 0.13% to 0.16% C, 1.8% to 2.0% Si, 2.3% ～2.5%Mn, 1.8%～2.2%Cr, 0.010%～0.025%Al, 0.001%～0.008%S, 0.002%～0.012%P, 0.001%～0.004%N, and the rest are Fe and unavoidable impurity elements. 2. The method for preparing a dual-phase steel plate as claimed in claim 1, wherein the above-mentioned components are smelted and cast to obtain a steel slab satisfying the above-mentioned chemical composition, and the steel slab is cooled to room temperature and is used as a hot-rolled raw material; Heating the billet with the furnace to 1200°C-1250°C, keeping it warm for 2 hours, and then performing hot rolling, the rough rolling start temperature of the hot rolling process is 1050°C-1110°C, and the finish rolling temperature is 840°C-880°C, The total reduction rate of the hot-rolled sheet is 80% to 90%, and the reduction rate of the last pass is 20% to 30%. After the final rolling, the hot-rolled sheet is cooled to 630°C to 680°C and coiled. The coiling temperature 630℃～680℃, keep warm for half an hour after coiling, then air-cool to room temperature with the furnace; Uncoiling the coiled steel plate for pickling cold rolling, the cold rolling process needs to control the cold rolling reduction between 50% and 80% to obtain cold rolled steel plate; The cold-rolled steel sheet is continuously annealed, and the preheating section is heated to 100°C-200°C at a heating rate of 6.0°C/s-10.0°C/s, and then the steel plate is heated at a heating rate of 2.0°C/s-5.0°C/s Heating to the two-phase zone for heat preservation, the heat preservation temperature is 760°C-820°C, the heat preservation time is 160s-190s, and then the steel plate is slowly cooled to 620°C-650°C at a cooling rate of 4°C/s-8°C/s, and then Then cool the steel plate rapidly at a cooling rate of 35°C/s-50°C/s to 250°C-270°C, over-aging for 300s-400s, and then slowly cool the steel plate at a cooling rate of 3°C/s-8°C/s to room temperature. 3. The method for preparing dual-phase steel sheets according to claim 2, characterized in that: the starting temperature of the hot rolling process is 1070°C to 1100°C, the finishing temperature is 815°C to 835°C, and the last hot rolling The reduction rate of the second time is controlled between 22% and 26%. 4. The preparation method of dual-phase steel plate according to claim 2, characterized in that: the annealing holding temperature is 785°C-825°C, the holding time is 165s-185s, and then the annealing temperature is 38°C/s-45°C/s Rapid cooling to 255°C-265°C, overaging treatment for 320s-380s, and then slow cooling to room temperature. 5. The preparation method of dual-phase steel plate according to claim 2, characterized in that: the structure of the steel is mainly martensite and a small amount of dispersed ferrite. 6. The preparation method of dual-phase steel plate according to claim 2, characterized in that: the steel has good comprehensive mechanical properties, R _p0.2 =1020-1100MPa, R _m =1600MPa-1850MPa, A ₅₀ =4.55 % to 9.50%, R _p0.2 /R _m =0.52 to 0.65. 7. The preparation method of dual-phase steel plate as claimed in claim 2, characterized in that: the dual-phase steel has excellent corrosion resistance, and when the uniform corrosion full immersion test simulates the industrial atmospheric environment, the corrosive solution used is 0.005mol /L of NaHSO ₃ solution, the corrosion rate of the steel of the present invention obtained is 0.17g m ^-2 h ^-1 ; when the neutral salt spray test simulates the marine atmosphere environment, the corrosive solution used is 50g/L ± 5g/ L of NaCl solution, the corrosion rates of the steel of the present invention in the 96h and 144h test periods were 1.26g·m ^-2 ·h ^-1 and 1.11g·m ^-2 ·h ^-1 respectively.