Low-cost and high-surface-quality 780MPa-grade alloying hot galvanizing dual-phase steel and production method thereof

Abstract

The invention discloses 780MPa-grade alloyed hot galvanizing dual-phase steel with low cost and high surface quality and a production method of the 780MPa-grade alloyed hot galvanizing dual-phase steel, and relates to the field of advanced high-strength steel. The alloying hot-dip galvanizing dual-phase steel strip steel comprises the following chemical components in percentage by weight: 0.11-0.15% of C, 0.12-0.12% of Cr, 0.12-0.12% of Ni, 0.12-0.12% of Ni and the balance Mn: 1.5 to 2.0%; 0.4 to 0.8 percent of Si; less than or equal to 0.025% of P; s is less than or equal to 0.010%; 0.35 to 0.6 percent of Cr; 0.021% to 0.045% of Nb; ti: 0.01 to 0.021%, and Ti: 0.01 to 0.021%; 0.2 to 0.8 percent of Al; o < = 0.0050%; n is less than or equal to 0.0050%, and the balance is Fe and inevitable impurities. The production method comprises the steps of converter smelting, slab continuous casting, hot rolling, pickling cold rolling and alloying hot galvanizing. The surface quality and corrosion resistance of the product are improved, and the service life of the product is prolonged.

Description

Technical Field

[0001] The present invention relates to the field of advanced high-strength steel, and in particular to a low-cost, high-surface-quality 780MPa-grade alloyed hot-dip galvanized dual-phase steel and a production method thereof. Background Art

[0002] In the field of steel materials, 780MPa grade alloyed hot-dip galvanized duplex steel is widely used in key structural parts such as automobiles and buildings due to its good strength, formability and corrosion resistance. However, with the increasingly stringent requirements on the surface quality of steel, especially in the hot-dip galvanizing process, duplex steel with high silicon (Si) and manganese (Mn) content faces significant surface quality challenges.

[0003] In the traditional hot-dip galvanizing process, high Si and Mn steels are prone to elemental oxidation during high-temperature processing, forming surface oxide precipitation, which not only damages the aesthetics of the product, but may also lead to reduced coating adhesion, plating defects and dezincification, thereby significantly reducing the corrosion resistance and service life of the product. In the prior art, although the humidification process can inhibit oxidation to a certain extent, a long-term high dew point environment is prone to cause the zinc layer to fall off; and if the pre-oxidation process alone is not properly controlled, it may cause surface overoxidation, affecting the subsequent galvanizing effect. Summary of the invention

[0004] In order to solve the problems of the prior art, the present invention provides a low-cost, high-surface-quality 780MPa grade alloyed hot-dip galvanized duplex steel and a production method thereof. The present invention solves the problem of surface oxidation control of high Si and Mn steels during hot-dip galvanizing by precisely controlling the high dew point annealing and pre-oxidation process parameters, thereby preparing a low-cost, high-surface-quality 780MPa grade alloyed hot-dip galvanized duplex steel.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] The invention discloses a low-cost, high-surface-quality 780MPa-grade alloyed hot-dip galvanized dual-phase steel. The chemical composition of the alloy components of the alloyed hot-dip galvanized dual-phase steel strip is as follows by weight percentage: C: 0.11-0.15%; Mn: 1.5-2.0%; Si: 0.4-0.8%; P≤0.025%; S≤0.010%; Cr: 0.35-0.6%; Nb: 0.021-0.045%; Ti: 0.011-0.021%; Al: 0.2-0.8%; O≤0.0050%; N≤0.0050%, and the balance is Fe and unavoidable impurities.

[0007] Furthermore, in the above technical solution, the hot-dip galvanized duplex steel strip has a thickness of 0.8 to 2.5 mm and a width of 900 to 1500 mm.

[0008] Furthermore, in the above technical solution, the finished hot-dip galvanized steel sheet is sampled along a direction perpendicular to the rolling direction, and has a yield strength of 440 to 540 MPa, a tensile strength of 780 to 860 MPa, and an A80 elongation after fracture of 18% to 24%.

[0009] The present invention also provides a production method for the above-mentioned low-cost, high-surface-quality 780MPa-grade alloyed hot-dip galvanized dual-phase steel, the production method comprising: converter smelting, slab continuous casting, hot rolling, pickling and cold rolling, alloyed hot-dip galvanizing; the alloyed hot-dip galvanizing process comprises: a heating section, a heat preservation section, a slow cooling section, a fast cooling section, a galvanizing section, and alloying, wherein the heating section comprises: a humidification section and a pre-oxidation section;

[0010] The conditions of the humidification section are: dew point of -15 to 5°C, hydrogen content of 3% to 5%, and humidification section temperature of 200 to 400°C;

[0011] The conditions of the pre-oxidation stage are: pre-oxidation temperature is 500℃~600℃, dew point is -35~-15℃, oxygen content is 0.6%~1.0%, air flow rate: 30~50Nm 3 / h.

[0012] Furthermore, in the above technical solution, the hot rolling is as follows: the billet entering furnace temperature is between 400 and 650°C, the heating temperature is between 1150 and 1280°C, the start rolling temperature is between 1020 and 1160°C, the final rolling temperature is above 900 to 950°C, and the coiling temperature is between 550 and 700°C.

[0013] Furthermore, in the above technical solution, the reduction rate of the pickling cold rolling is ≥55%.

[0014] Furthermore, in the above technical solution, the temperature of the insulation section of the alloyed hot-dip galvanizing is 810-860°C, the outlet temperature of the slow cooling section is 680-750°C, the cooling rate of the fast cooling section is ≥20°C / s, the outlet temperature of the fast cooling section is between 400-430°C, and the cooling rate of the slow cooling section is lower than that of the fast cooling section.

[0015] Furthermore, in the above technical solution, the strip speed of the alloyed hot-dip galvanized steel strip is 50 to 120 m / min.

[0016] Furthermore, in the above technical solution, the dew point of the furnace nose of the galvanizing section is -50 to -40°C.

[0017] Furthermore, in the above technical solution, the galvanizing temperature of the galvanizing section is 450-460° C., and the composition of the zinc liquid is calculated by weight percentage: Al: 0.13-0.15%, iron <0.05%, and the balance is zinc.

[0018] Furthermore, in the above technical solution, after the strip is galvanized, it is first cooled to 400-420°C by an air knife and then enters into an alloying furnace for alloying. The alloying temperature is 550-585°C.

[0019] Furthermore, in the above technical solution, after alloying, skin finishing is performed, and the skin finishing elongation during the skin finishing process is controlled within the range of 0.5% to 1.0%.

[0020] Beneficial effects of the present invention:

[0021] The present invention improves the surface quality of the alloyed hot-dip galvanized steel sheet through wet annealing and pre-oxidation technology while ensuring the overall performance of the steel, and at the same time, improves the integrity and uniformity of the coating, ultimately improving the surface quality, corrosion resistance and service life of the product.

[0022] In addition, the present invention does not add high-cost elements such as Mo, and thus has lower production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the alloying hot-dip galvanizing process of the present invention.

[0024] Figure 2 The microstructure of the low-cost, high-surface-quality 780MPa grade alloyed hot-dip galvanized dual-phase steel prepared in Example 1. After alloying, the C, Si, and Mn elements diffuse significantly, and the detection effect of the Zn and Fe elements is limited due to the difference in content, but diffusion still occurs. The zinc layer structure is dense and uniform, without Si and Mn external oxidation precipitation defects. DETAILED DESCRIPTION

[0025] The following examples are used to specifically illustrate the present invention. These examples are only general descriptions of the present invention and do not limit the present invention.

[0026] Examples 1-10

[0027] A low-cost, high-surface-quality 780MPa grade alloyed hot-dip galvanized duplex steel. The chemical composition of the alloy components of the alloyed hot-dip galvanized duplex steel strip is shown in Table 1.

[0028] The production method of the above-mentioned low-cost, high-surface-quality 780MPa grade alloyed hot-dip galvanized dual-phase steel comprises, in sequence: converter smelting, slab continuous casting, hot rolling, pickling and cold rolling, and alloyed hot-dip galvanizing; the alloyed hot-dip galvanizing process comprises, in sequence: heating section, insulation section, slow cooling section, fast cooling section, galvanizing section, and alloying, wherein the heating section comprises, in sequence: high dew point annealing section and pre-oxidation section.

[0029] The hot rolling and cold rolling process parameters are shown in Table 2.

[0030] The process parameters of alloy hot-dip galvanizing are shown in Table 3. The temperature of the humidification section is 200-400℃.

[0031] After galvanizing, the strip is first cooled to 400-420℃ by air knife and then enters the alloying furnace for alloying; after alloying, it is subjected to skin finishing.

[0032] The thickness and width of the finished alloyed hot-dip galvanized duplex steel are shown in Table 4. The mechanical properties of the samples taken perpendicular to the rolling direction are shown in Table 4.

[0033] Table 1 Chemical composition of steel in the examples (wt%)

[0034]

[0035] Table 2 Hot rolling and cold rolling process parameters of example steel

[0036]

[0037]

[0038] Table 3 Process parameters of hot-dip galvanizing of steel in the embodiment

[0039]

[0040] Table 4 Mechanical properties of example steel

[0041] Example Thickness / mm Width / mm Yield strength / MPa Tensile strength / MPa Elongation A80 / % 1 2.3 1500 480 805 20 2 0.8 1000 477 849 20 3 1.8 1200 442 801 24 4 1.6 1100 510 823 20 5 2.4 900 532 856 22 6 1.6 1000 525 834 24 7 1.2 900 465 841 23 8 1.4 1000 479 809 23 9 2.0 1200 464 808 20 10 2.5 1200 512 785 24

Claims

1. A low-cost, high-surface-quality 780MPa grade alloyed hot-dip galvanized duplex steel, characterized in that: The chemical composition of the alloyed hot-dip galvanized dual-phase steel strip is as follows by weight percentage: C: 0.11-0.15%; Mn: 1.5-2.0%; Si: 0.4-0.8%; P≤0.025%; S≤0.010%; Cr: 0.35-0.6%; Nb: 0.021-0.045%; Ti: 0.011~0.021%; Al: 0.2~0.8%; O≤0.0050%; N≤0.0050%, the balance is Fe and unavoidable impurities.

2. The low-cost, high-surface-quality 780MPa grade alloyed hot-dip galvanized dual-phase steel according to claim 1, characterized in that: The hot-dip galvanized dual-phase steel has a thickness of 0.8 to 2.5 mm and a width of 900 to 1500 mm.

3. The low-cost, high-surface-quality 780MPa grade alloyed hot-dip galvanized dual-phase steel according to claim 1, characterized in that: The hot-dip galvanized dual-phase steel has a yield strength of 440-540 MPa, a tensile strength of 780-860 MPa, and an A80 elongation after fracture of 18%-24%.

4. The method for producing low-cost, high-surface-quality 780MPa grade alloyed hot-dip galvannealed dual-phase steel according to any one of claims 1 to 3, characterized in that: The production method includes: converter smelting, slab continuous casting, hot rolling, pickling and cold rolling, alloying hot-dip galvanizing; the alloying hot-dip galvanizing process includes: heating section, insulation section, slow cooling section, fast cooling section, galvanizing section, alloying, wherein the heating section includes: humidification section and pre-oxidation section; The conditions of the humidification section are: dew point of -15 to 5°C, hydrogen content of 3% to 5%, and humidification section temperature of 200 to 400°C; The conditions of the pre-oxidation stage are: pre-oxidation temperature is 500-600°C, dew point is -35--15°C, oxygen content is 0.6%-1.0%, air flow rate: 30-50Nm 3 / h.

5. The production method according to claim 4, characterized in that: The hot rolling is as follows: the billet entering furnace temperature is between 400 and 650°C, the heating temperature is between 1150 and 1280°C, the starting rolling temperature is between 1020 and 1160°C, the final rolling temperature is above 900 to 950°C, and the coiling temperature is between 550 and 700°C.

6. The production method according to claim 4, characterized in that: The reduction rate of the pickling cold rolling is ≥55%.

7. The production method according to claim 4, characterized in that: The temperature of the insulation section of the alloyed hot-dip galvanizing is 810-860°C, the outlet temperature of the slow cooling section is 680-750°C, the cooling rate of the fast cooling section is ≥20°C / s, the outlet temperature of the fast cooling section is between 400-430°C, and the cooling rate of the slow cooling section is lower than that of the fast cooling section.

8. The production method according to claim 4, characterized in that: The strip speed of alloyed hot-dip galvanized steel strip is 50-120m / min.

9. The production method according to claim 4, characterized in that: The galvanizing temperature of the galvanizing section is 450-460° C., and the composition of the zinc liquid is calculated by weight percentage: Al: 0.13-0.15%, iron <0.05%, and the balance is zinc.

10. The production method according to claim 4, characterized in that: After galvanizing, the strip is first cooled to 400-420°C by an air knife and then alloyed at a temperature of 550-585°C. After alloying, it is subjected to skin finishing, and the skin finishing elongation is controlled between 0.5% and 1.0%.

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