High-surface-quality 980MPa-grade hot-dip galvanized dual-phase steel and preparation method thereof

Abstract

The invention discloses high-surface-quality 980MPa-grade hot-dip galvanized dual-phase steel and a preparation method thereof. The high-surface-quality 980MPa-grade hot-dip galvanized dual-phase steel is prepared from the following components in percentage by mass: 0.05 percent to 0.11 percent of C, 0.5 percent to 0.9 percent of Si, 2.1 percent to 2.5 percent of Mn, 0.03 percent to 0.05 percent of Nb, 0.04 percent to 0.06 percent of Ti, 0.13 percent to 0.28 percent of Mo, 0.02 percent to 0.05 percent of Als and the balance of iron and inevitable impurities. According to the method, through innovative humidification annealing and oxidation-reduction dual-process collaborative parameter design, the annealing dew point and the oxygen content are controlled in a segmented mode, stable control over the galvanized surface quality of the high-Si and Mn dual-phase steel is achieved, the effect of improving thick-specification products is obvious, the overall qualification rate is greatly increased, element external oxidation is inhibited, the coating quality is optimized, the production efficiency is improved, and the method is suitable for large-scale popularization and application. The problem of surface peroxidation or zinc layer falling easily caused by a traditional single process is solved, and the high-end requirement for high-performance steel is met.

Description

Technical Field

[0001] The present invention relates to the fields of materials and metallurgy, and more specifically, to a high-surface-quality 980MPa-grade hot-dip galvanized dual-phase steel and a preparation method thereof. Background Art

[0002] In the field of steel materials, 980MPa grade hot-dip galvanized duplex steel is widely used in key structural components such as automobiles and buildings due to its high strength, good formability and excellent corrosion resistance. However, with the continuous improvement of the surface quality requirements of steel, especially duplex steel with high silicon (Si) and manganese (Mn) content, it faces many significant challenges in the hot-dip galvanizing process.

[0003] In the traditional hot-dip galvanizing process, high Si and Mn steels are prone to elemental oxidation during high-temperature processing, resulting in surface oxide precipitation. This phenomenon not only reduces the adhesion of the coating, but also causes plating defects and dezincification. These problems not only damage the aesthetics of the product, but also significantly reduce its corrosion resistance and service life.

[0004] In order to solve these problems, the industry has tried a variety of improved processes. For example, the humidification process can inhibit oxidation to a certain extent, but the high dew point can easily cause the zinc layer to fall off; and if the pre-oxidation process alone is not properly controlled, it will cause surface overoxidation. In addition, when the product specifications are thicker (≥2mm), the pre-oxidation process will be more restricted. This is because more iron oxide may remain during the acid rolling process. At this time, if the air flow in the pre-oxidation process is increased, the subsequent reduction effect will be poor, which will in turn affect the subsequent galvanizing effect. The limitations of these traditional single processes have made the surface quality problem of high-strength steel a bottleneck restricting its high-end applications. Summary of the invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects of the prior art, provide a high surface quality 980MPa grade hot-dip galvanized duplex steel and a preparation method thereof, through the innovative "humidification annealing + oxidation-reduction" dual process collaborative parameter design, adopt the segmented control of annealing dew point and oxygen content, for the first time to achieve stable control of the galvanized surface quality of high Si, Mn dual-phase steel, inhibit elemental external oxidation, optimize the coating quality, improve production efficiency, solve the problem of surface overoxidation or zinc layer shedding easily caused by the traditional single process, and meet the high-end demand for high-performance steel in the fields of automobiles, construction, etc.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A high surface quality 980MPa grade hot-dip galvanized dual-phase steel comprises the following components in mass percentage: C: 0.05%-0.11%, Si: 0.3%-0.5%, Mn: 2.1%-2.5%, Nb: 0.03%-0.05%, Ti: 0.04%-0.06%, Mo: 0.13%-0.28%, Als: 0.02%-0.05%, and the balance is iron and unavoidable impurities.

[0008] Optionally, the hot-dip galvanized duplex steel has a thickness of 1.0 mm to 2.0 mm and a width of 900 mm to 1500 mm.

[0009] Optionally, the hot-dip galvanized dual-phase steel has a yield strength of ≥550 MPa, a tensile strength of ≥980 MPa, and an A80 elongation after fracture of 20% to 24%.

[0010] The present invention also discloses a method for preparing the high surface quality 980MPa grade hot-dip galvanized dual-phase steel as mentioned above, comprising the following steps: converter smelting, slab continuous casting, hot rolling, pickling and cold rolling, and hot-dip galvanizing; the hot-dip galvanizing includes a heating section, a heat preservation section, a slow cooling section, a fast cooling section, and a galvanizing section; the heating section includes a humidification section and a pre-oxidation section.

[0011] Optionally, during the hot rolling, the ingot entering furnace temperature is 400°C to 650°C, the heating temperature is 1230°C to 1250°C, the start rolling temperature is 1020°C to 1160°C, the final rolling temperature is 870°C to 900°C, and the coiling temperature is 550°C to 570°C.

[0012] Optionally, in the pickling cold rolling, the cold rolling reduction rate is 60% to 80%.

[0013] Optionally, in the humidification section, the dew point is -15°C to -5°C, and the hydrogen content is 3% to 5%; in the pre-oxidation section, the pre-oxidation temperature is 500°C to 600°C, the dew point is -32°C to -17°C, the oxygen content is 0.6% to 1.0%, and the air flow rate is 30Nm3 / h to 50Nm3 / h.

[0014] Optionally, in the insulation section, the annealing temperature is 840℃~880℃; in the slow cooling section, the slow cooling outlet temperature is 740℃~760℃, and the hydrogen content is 3%~5%; in the fast cooling section, the fast cooling outlet temperature is between 350℃~380℃; in the galvanizing section, the dew point of the furnace nose is -50℃~-40℃; the belt speed is 50m / min~120m / min; the galvanizing temperature is 450℃~460℃, and the zinc liquid includes iron with a mass percentage of less than 0.05% and Al with a mass percentage of 0.13%~0.15%; after the strip is galvanized, it is first cooled to 400℃~430℃ by an air knife, and the finishing elongation of the finishing process is 0.5%~0.9%.

[0015] Implementing the embodiments of the present invention will have the following beneficial effects:

[0016] The present invention aims to provide a high surface quality 980MPa grade hot-dip galvanized dual-phase steel and a preparation method thereof, which effectively solves the surface oxidation control problem faced by high Si and Mn steels during hot-dip galvanizing by innovatively combining the synergistic effect of the "humidification annealing + oxidation-reduction" process, so that the yield strength of the hot-dip galvanized dual-phase steel is ≥550MPa, the tensile strength is ≥980MPa, and the A80 elongation after fracture is 20% to 24%, achieving significant technical progress and practical application value. Specifically embodied in the following aspects:

[0017] 1. Significantly improved surface quality: effectively inhibit the external oxidation of Si and Mn elements, reduce surface oxide precipitation, and eliminate plating defects.

[0018] 2. Optimize coating quality: The uniform oxide film formed by pre-oxidation improves the adhesion of the zinc layer, and the coating uniformity reaches the international advanced standards.

[0019] 3. Enhanced process stability: The dew point control in the humidified annealing section is precisely matched with the oxygen content in the pre-oxidation section to avoid dezincification and overoxidation problems, significantly improving process stability.

[0020] 4. Low-carbon component design: low-carbon component design is adopted, which conforms to the concept of green production.

[0021] 5. Improve production efficiency: By optimizing process parameters, shorten the production cycle, reduce energy consumption, and achieve efficient and stable production.

[0022] 6. Meet high-end needs: Ensure that the product has high strength, high surface quality and excellent corrosion resistance to meet the stringent requirements of high-performance steel in the automotive, construction and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of hot-dip galvanizing process according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0025] 1. Chemical composition design

[0026] The invention discloses a high surface quality 980MPa grade hot-dip galvanized dual-phase steel, comprising the following components in mass percentage: C: 0.05%-0.11%, Si: 0.3%-0.5%, Mn: 2.1%-2.5%, Nb: 0.03%-0.05%, Ti: 0.04%-0.06%, Mo: 0.13%-0.28%, Als: 0.02%-0.05%, and the balance is iron and inevitable impurities.

[0027] In a specific embodiment, the hot-dip galvanized dual-phase steel has a thickness of 1.0 mm to 2.0 mm and a width of 900 mm to 1500 mm.

[0028] In a specific embodiment, the hot-dip galvanized dual-phase steel has a yield strength of ≥550 MPa, a tensile strength of ≥980 MPa, and an A80 elongation after fracture of 20% to 24%.

[0029] 2. Preparation process design

[0030] The present invention also discloses a method for preparing 980MPa grade hot-dip galvanized dual-phase steel with high surface quality as in any embodiment of the present invention, comprising the following steps: converter smelting, slab continuous casting, hot rolling, pickling and cold rolling, and hot-dip galvanizing.

[0031] S1. The converter smelting and slab continuous casting steps of the present invention can be operated according to conventional preparation methods.

[0032] S2. During hot rolling, the billet entering furnace temperature is 400°C ~ 650°C, the heating temperature is 1230°C ~ 1250°C, the starting rolling temperature is 1020°C ~ 1160°C, the final rolling temperature is 870°C ~ 900°C, and the coiling temperature is 550°C ~ 570°C.

[0033] S3. In the pickling cold rolling, the cold rolling reduction rate is 60% to 80%.

[0034] S4. Hot-dip galvanizing includes heating section, insulation section, slow cooling section, fast cooling section and galvanizing section; the heating section includes humidification section and pre-oxidation section; in the humidification section, the dew point is -15℃~-5℃, and the hydrogen content is 3%~5%; in the pre-oxidation section, the pre-oxidation temperature is 500℃~600℃, the dew point is -32℃~-17℃, the oxygen content is 0.6%~1.0%, and the air flow rate is 30Nm3 / h~50Nm3 / h; in the insulation section, the annealing temperature is 840℃~880℃; in the slow cooling section, the slow cooling outlet temperature is The temperature is 740℃~760℃, and the hydrogen content is 3%~5%; in the rapid cooling section, the rapid cooling outlet temperature is 350℃~380℃; in the galvanizing section, the dew point of the furnace nose is -50℃~-40℃; the belt speed is 50m / min~120m / min; the galvanizing temperature is 450℃~460℃, and the zinc liquid includes iron with a mass percentage of less than 0.05% and Al with a mass percentage of 0.13%~0.15%; after the strip is galvanized, it is first cooled to 400℃~430℃ by an air knife, and the finishing elongation of the finishing process is 0.5%~0.9%.

[0035] In a specific embodiment, when the thickness specification is ≥2mm, the dew point is -10℃~-5℃; the oxygen content is 0.6%~1.0%, and the air flow rate is 30Nm 3 / h~40Nm 3 / h.

[0036] Specifically, the present invention precisely controls the dew point and atmosphere composition of the humidified annealing section to preliminarily inhibit the oxidation behavior of Si and Mn at high temperatures and reduce the precipitation of surface oxides, thereby effectively avoiding the problems of missed plating and dezincification. At the same time, a uniform and dense oxide film is formed in the pre-oxidation stage, and reduced iron is generated through a subsequent reduction process, which serves as an ideal substrate for galvanizing, significantly improving the bonding strength and uniformity of the coating. In addition, by optimizing process parameters, shortening the production cycle, and reducing energy consumption, efficient and stable production is achieved.

[0037] The present invention not only solves the surface quality problem of high Si, Mn dual-phase steel, but also provides a reliable technical path for the industrial production of hot-dip galvanized high-strength steel, and has significant social and economic benefits and industry promotion value.

[0038] The following are specific embodiments

[0039] The chemical composition of Examples 1-10 is shown in Table 1, the converter smelting, slab continuous casting and hot rolling process, pickling and cold rolling parameters of Examples 1-10 are shown in Table 2, the hot-dip galvanizing process parameters of Examples 1-10 are shown in Table 3, and the mechanical properties of Examples 1-10 are shown in Table 4.

[0040] Table 1 Chemical composition of Examples 1-10 (%)

[0041] Example C Mn Si Als Mo Nb Ti 1 0.069 2.3 0.5 0.02 0.26 0.041 0.054 2 0.083 2.1 0.3 0.03 0.22 0.039 0.044 3 0.051 2.3 0.3 0.04 0.14 0.044 0.051 4 0.097 2.4 0.3 0.05 0.18 0.037 0.044 5 0.067 2.4 0.3 0.03 0.26 0.047 0.046 6 0.056 2.1 0.4 0.03 0.23 0.05 0.048 7 0.08 2.1 0.3 0.03 0.16 0.036 0.041 8 0.057 2.3 0.4 0.03 0.2 0.035 0.043 9 0.078 2.5 0.4 0.05 0.17 0.047 0.047 10 0.084 2.4 0.5 0.04 0.14 0.036 0.056

[0042] Table 2 Converter smelting, slab continuous casting and hot rolling process, pickling and cold rolling parameters of Examples 1-10

[0043] Example Furnace temperature / ℃ Oven temperature / ℃ Rolling temperature / ℃ Final rolling temperature / ℃ Coiling temperature / ℃ Cold rolling reduction ratio / % 1 425 1250 1125 885 554 60 2 469 1250 1156 875 552 65 3 469 1236 1141 886 556 80 4 406 1237 1122 883 565 64 5 477 1237 1120 897 562 65 6 590 1242 1153 880 561 70 7 644 1236 1150 888 551 72 8 424 1230 1136 892 554 72 9 507 1246 1146 882 565 70 10 413 1233 1137 895 563 75

[0044] Table 3 Hot-dip galvanizing process parameters of Examples 1-10

[0045]

[0046] Table 4 Mechanical properties of Examples 1-10

[0047]

[0048]

[0049] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A high surface quality 980MPa grade hot-dip galvanized dual-phase steel, characterized in that: The following components are included in mass percentage: C: 0.05% to 0.11%, Si: 0.3% to 0.5%, Mn: 2.1% to 2.5%, Nb: 0.03% to 0.05%, Ti: 0.04% to 0.06%, Mo: 0.13% to 0.28%, Als: 0.02% to 0.05%, and the balance is iron and inevitable impurities.

2. The high surface quality 980MPa grade hot-dip galvanized dual-phase steel according to claim 1, characterized in that: The yield strength of the hot-dip galvanized dual-phase steel is ≥550MPa, the tensile strength is ≥980MPa, and the A80 elongation after fracture is 20% to 24%.

3. The high surface quality 980MPa grade hot-dip galvanized dual-phase steel according to claim 1, characterized in that: The hot-dip galvanized dual-phase steel has a thickness of 0.7 mm to 2.5 mm and a width of 900 mm to 1500 mm.

4. A method for preparing a high surface quality 980MPa grade hot dip galvanized dual phase steel as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: Converter smelting, slab continuous casting, hot rolling, pickling and cold rolling, hot-dip galvanizing; The hot-dip galvanizing includes a heating section, a heat preservation section, a slow cooling section, a fast cooling section, and a galvanizing section; the heating section includes a humidification section and a pre-oxidation section.

5. The preparation method according to claim 4, characterized in that: In the hot rolling, the ingot furnace temperature is 400°C to 650°C, the heating temperature is 1230°C to 1250°C, the start rolling temperature is 1020°C to 1160°C, the final rolling temperature is 870°C to 900°C, and the coiling temperature is 550°C to 570°C.

6. The preparation method according to claim 4, characterized in that: In the pickling cold rolling, the cold rolling reduction rate is 60% to 80%.

7. The preparation method according to claim 4, characterized in that: In the humidification section, the dew point is -15°C to -5°C, and the hydrogen content is 3% to 5%; In the pre-oxidation stage, the pre-oxidation temperature is 500°C to 600°C, the dew point is -32°C to -17°C, the oxygen content is 0.6% to 1.0%, and the air flow rate is 30Nm 3 / h~50Nm 3 / h.

8. The preparation method according to claim 4, characterized in that: In the heat preservation section, the annealing temperature is 840°C to 880°C; In the slow cooling section, the slow cooling outlet temperature is 740°C to 760°C, and the hydrogen content is 3% to 5%; In the rapid cooling section, the rapid cooling outlet temperature is between 350°C and 380°C; In the galvanizing section, the dew point of the furnace nose is -50℃~-40℃; the belt speed is 50m / min~120m / min; the galvanizing temperature is 450℃~460℃, the zinc liquid includes iron with a mass percentage of less than 0.05% and Al with a mass percentage of 0.13%~0.15%, and the finishing elongation of the finishing process is 0.5%~0.9%.

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