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

Abstract

The invention discloses 980MPa-grade hot-dip galvanized DH steel with high surface quality and a preparation method of the 980MPa-grade hot-dip galvanized DH steel. The hot-dip galvanized DH steel comprises the following main chemical components in percentage by mass: 0.17%-0.21% of C, 0.4%-0.7% of Si, 1.8%-2.2% of Mn, 0.01%-0.02% of Nb, 0.01%-0.02% of Ti, 0.4%-0.5% of Cr, 0.14%-0.9% of Als and the balance of Fe. According to the method, a low-carbon design and a high-dew-point annealing process are adopted, and the hot-dip galvanized steel plate which not only meets the low-carbon environment-friendly requirement but also has high surface quality is produced, so that the urgent demand of the market is met. The high-dew-point annealing technology serves as a novel annealing technology, the oxygen partial pressure is increased by increasing the dew point, Si and Mn elements are internally oxidized, and therefore the plating leakage defect is effectively overcome, and the surface smoothness and flatness of the steel plate are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of high-strength steel, and specifically relates to a high-surface-quality 980MPa-grade hot-dip galvanized DH steel and a preparation method thereof. Background Art

[0002] The steel industry is facing unprecedented transformation pressure, and the development of low-carbon, environmentally friendly, and high-performance steel has become an urgent need for the development of the industry; in the field of hot-dip galvanized steel plates, surface quality is one of the key indicators for measuring product quality. Traditional hot-dip galvanizing processes often find it difficult to simultaneously meet the requirements of high strength and good surface quality, especially when producing high-strength steel plates, such as 980MPa hot-dip galvanized DH steel. Due to its high strength, it is easy to cause surface cracks and roughness during processing, and it is easy to have plating defects, which seriously affects the application range and market value of the product.

[0003] In order to solve this problem, the industry has conducted a lot of exploration and practice. Among them, low-carbon design, as an effective strategy, has been widely used in the development of various types of steel. By optimizing the chemical composition and reducing the carbon content, it can not only reduce carbon emissions in the production process, but also improve the processing and welding properties of steel, making it possible to produce hot-dip galvanized steel sheets with high surface quality. In addition, the annealing process, as a key link in the production of hot-dip galvanized steel sheets, has a particularly significant impact on the surface quality of the steel sheets. Traditional annealing processes often make it difficult to accurately control the atmosphere and temperature during the annealing process, resulting in oxidation, decarburization and other problems on the surface of the steel sheets. Summary of the invention

[0004] In order to overcome the defects of the above-mentioned prior art, the present invention adopts low-carbon design and high dew point annealing process to produce hot-dip galvanized steel sheets that meet the requirements of low-carbon environmental protection and have high surface quality to meet the urgent needs of the market. As a new annealing technology, the high dew point annealing process increases the oxygen partial pressure by increasing the dew point, so that Si and Mn elements are internally oxidized, thereby effectively improving the plating leakage defects and improving the surface finish and flatness of the steel plate.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides a high surface quality 980MPa grade hot-dip galvanized DH steel, the chemical composition mass content of the hot-dip galvanized DH steel is C: 0.17% ~ 0.21%, Si: 0.4% ~ 0.7%, Mn: 1.8% ~ 2.2%, Nb: 0.01% ~ 0.02%, Ti: 0.01% ~ 0.02%, Cr: 0.4% ~ 0.5%, Als: 0.14% ~ 0.9%, and the balance is iron and unavoidable impurities.

[0006] In the above technical solution, further, the microstructure of the hot-dip galvanized DH steel contains 20% to 40% ferrite, 40% to 65% martensite, 3% to 12% residual austenite, and 3% to 15% bainite by volume percentage.

[0007] Furthermore, the yield strength of the hot-dip galvanized DH steel perpendicular to the rolling direction is ≥550MPa, the tensile strength is ≥980MPa, and the 80 The elongation after fracture is 15% to 22%, the thickness is 1.0 to 1.6 mm, and the hole expansion rate is ≥23%.

[0008] A method for preparing the above-mentioned high surface quality 980MPa grade hot-dip galvanized DH steel, the preparation method comprising the steps of converter smelting, slab continuous casting, removing defects on the edge of the ingot, hot rolling, pickling and cold rolling, preheating, heating, annealing, slow cooling, rapid cooling, and galvanizing after rapid cooling; wherein,

[0009] Converter smelting: The S of the molten iron after pretreatment is ≤0.003%, and the slag removal rate is ≥94%.

[0010] Scrap steel is added to the converter, with scrap steel accounting for 15% to 18% and molten iron accounting for 82% to 85%; the converter bottom blowing adopts the full-process argon blowing mode, and the terminal oxygen is controlled to be ≤650ppm. The refining LF path is adopted: the slag addition amount is 30 to 40kg; vacuum decarburization treatment, vacuum degree ≤150Pa, decarburization time 18 to 25min; vacuum deoxidation alloying treatment, deoxidation alloying adds ferrosilicon, silicon manganese, aluminum particles, ferroniobium, and the alloying sequence is Al-Mn-Nb.

[0011] Slab continuous casting: continuous casting superheat control: 17℃~27℃; continuous casting maintains a constant pulling speed of 1.0~1.3m / min, and adopts dynamic light pressure. After continuous casting, the edge defects of the slab need to be removed.

[0012] Hot rolling: billet heating temperature 1230℃~1250℃, start rolling temperature 1050℃~1150℃, final rolling temperature 870℃~900℃, coiling temperature 550℃~590℃; descaling water pressure 18~20MPa.

[0013] Galvanizing: Nitrogen humidification equipment is used to accurately control the dew point in the furnace. The dew point of the heating section in the annealing furnace is -10℃~-5℃, the dew point of the annealing section and slow cooling section is -40~-30℃, and the dew point of the furnace nose is -50℃~-40℃; the hydrogen (volume) content in the annealing furnace is 3%~5%.

[0014] The annealing temperature is 830℃~850℃, the slow cooling outlet temperature is 690℃~740℃, the fast cooling outlet temperature is 400℃~430℃, and the strip is first air-knife cooled to 400℃~420℃ after galvanizing; the skin-finishing elongation of the skin-finishing process is controlled in the range of 0.5%~1.0%.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] ① Achieved harmonious unity of high strength and excellent formability: Thanks to the precise material ratio and optimized process flow, the present invention successfully integrates the high strength and excellent formability of steel, fully meeting the strict standards of modern industry for material performance.

[0017] ② High cost-effectiveness: While pursuing high performance, the present invention also takes into account cost control. By optimizing the material ratio and process flow, especially the clever use of chromium and manganese elements, the cost is effectively reduced while ensuring performance.

[0018] ③Excellent surface quality: Through the careful design of Si and Mn content and combined with high dew point annealing process, the surface quality of the product of the present invention is significantly improved.

[0019] ④ Environmental protection and sustainability: While pursuing high performance, the present invention also attaches great importance to environmental protection and sustainability. By optimizing the heating temperature and rolling process, we effectively reduce energy consumption and significantly reduce carbon emissions during the production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The stress-strain curve of the 980MPa grade hot-dip galvanized DH steel with high surface quality obtained in Example 1;

[0021] Figure 2 This is the surface diagram of the galvanized sheet of 980MPa grade hot-dip galvanized DH steel with high surface quality obtained in Example 1. DETAILED DESCRIPTION

[0022] The present invention is further described below in conjunction with specific examples, but the present invention is not limited in any way. To avoid redundant description, the raw materials in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0023] The invention discloses a 980MPa grade hot-dip galvanized DH steel with high surface quality. The chemical composition mass content of the hot-dip galvanized DH steel is C: 0.17%-0.21%, Si: 0.4%-0.7%, Mn: 1.8%-2.2%, Nb: 0.01%-0.02%, Ti: 0.01%-0.02%, Cr: 0.4%-0.5%, Als: 0.14%-0.9%, and the balance is iron and unavoidable impurities.

[0024] A method for preparing the above-mentioned high surface quality 980MPa grade hot-dip galvanized DH steel includes the steps of converter smelting, slab continuous casting, removing defects on the edge of the ingot, hot rolling, pickling and cold rolling, preheating, heating, annealing, slow cooling, rapid cooling, and galvanizing after rapid cooling.

[0025] The matters not described in the following embodiments are the same as the description of the above specific implementation methods.

[0026] Example

[0027] A high surface quality 980MPa grade hot-dip galvanized DH steel, the specific chemical composition of the hot-dip galvanized DH steel described in Examples 1-10 is shown in Table 1.

[0028] Table 1 Chemical composition of hot-dip galvanized DH steel in the embodiment (wt%)

[0029] Example C Mn Si Als Nb Ti Cr 1 0.190 1.9 0.5 0.90 0.020 0.017 0.50 2 0.205 1.8 0.6 0.44 0.018 0.010 0.45 3 0.190 2.1 0.4 0.73 0.016 0.016 0.46 4 0.195 2.0 0.7 0.35 0.019 0.019 0.43 5 0.174 2.2 0.4 0.50 0.020 0.015 0.46 6 0.184 1.9 0.7 0.58 0.016 0.011 0.50 7 0.186 2.2 0.5 0.43 0.013 0.013 0.42 8 0.171 1.8 0.6 0.55 0.019 0.013 0.43 9 0.185 2.1 0.5 0.67 0.020 0.013 0.42 10 0.202 2.0 0.6 0.52 0.016 0.014 0.40

[0030] A method for preparing 980MPa grade hot-dip galvanized DH steel with high surface quality. The specific process flow of Examples 1-10 is as follows, and Table 2 is the hot rolling process parameters; the billet heating temperature is 1230°C to 1250°C, the start rolling temperature is 1050°C to 1150°C, the final rolling temperature is 870°C to 900°C, and the coiling temperature is 550°C to 590°C; the descaling water pressure is 18 to 20MPa.

[0031] Table 2 Hot rolling process parameters of the preparation method of the embodiment

[0032] Example Heating temperature / ℃ Rolling temperature / ℃ Final rolling temperature / ℃ Coiling temperature / ℃ Descaling water pressure / MPa 1 1237 1093 897 588 18 2 1234 1139 888 557 18 3 1234 1092 879 574 19 4 1246 1130 883 587 19 5 1233 1065 883 580 19 6 1246 1121 877 576 18 7 1250 1130 899 585 18 8 1246 1116 878 580 18 9 1237 1093 897 588 18 10 1234 1139 888 557 18

[0033] Table 3 lists the process parameters for cold rolling and hot-dip galvanizing of the example steel. Nitrogen humidification equipment is used to accurately control the dew point in the furnace. The dew point in the annealing furnace is -10°C to -5°C, and the hydrogen (volume) content is 3% to 5%; the dew point of the furnace nose is -50°C to -40°C.

[0034] Galvanizing: annealing temperature 830℃~850℃, slow cooling outlet temperature 690℃~740℃, fast cooling outlet temperature 400℃~430℃. After galvanizing, the strip is first air-knife cooled to 400℃~420℃; the skin-finishing elongation of the skin-finishing process is controlled in the range of 0.5%~1.0%.

[0035] Table 3 Cold rolling and hot dip galvanizing process parameters of the preparation method of the embodiment

[0036]

[0037] The mechanical properties and key parameters of the hot-dip galvanized DH steel with high surface quality of 980 MPa obtained in Example 1-10 are shown in Table 4. The yield strength of the hot-dip galvanized DH steel perpendicular to the rolling direction is ≥550 MPa, the tensile strength is ≥980 MPa, and the A 80 The elongation after fracture is 15% to 22%, the thickness is 1.0 to 1.6 mm, and the hole expansion rate is ≥23%.

[0038] Table 4 Performance parameters of high surface quality 980MPa grade hot-dip galvanized DH steel obtained in Example

[0039]

[0040] The microstructure of the hot-dip galvanized DH steel contains 20% to 40% ferrite, 40% to 65% martensite, 3% to 12% retained austenite, and 3% to 15% bainite by volume percentage. Example 1 The stress-strain curve of the high-surface quality 980-grade hot-dip galvanized DH steel is as follows: Figure 1 As shown; the surface condition of the galvanized sheet, such as Figure 2 As shown, the surface quality is good and there is no precipitation defect.

[0041] For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A high surface quality 980MPa grade hot-dip galvanized DH steel, characterized in that: The chemical composition mass content of the hot-dip galvanized DH steel is C: 0.17%-0.21%, Si: 0.4%-0.7%, Mn: 1.8%-2.2%, Nb: 0.01%-0.02%, Ti: 0.01%-0.02%, Cr: 0.4%-0.5%, Als: 0.14%-0.9%, and the balance is iron and unavoidable impurities.

2. The hot-dip galvanized DH steel according to claim 1, characterized in that: The microstructure of the hot-dip galvanized DH steel contains 20% to 40% ferrite, 40% to 65% martensite, 3% to 12% residual austenite, and 3% to 15% bainite by volume percentage.

3. The hot-dip galvanized DH steel according to claim 1, characterized in that: The yield strength of the hot-dip galvanized DH steel perpendicular to the rolling direction is ≥550MPa, the tensile strength is ≥980MPa, and the 80 The elongation after fracture is 15% to 22%, the thickness is 1.0 to 1.6 mm, and the hole expansion rate is ≥23%.

4. A method for preparing the high surface quality 980MPa grade hot-dip galvanized DH steel as claimed in claim 1, characterized in that: The preparation method comprises the following steps: converter smelting, slab continuous casting, hot rolling, pickling and cold rolling, preheating, heating, annealing, slow cooling, fast cooling, and galvanizing; in, Converter smelting: S of hot metal after pretreatment is ≤0.003%, and slag removal rate is ≥94%; Nitrogen humidification equipment is used to accurately control the dew point in the furnace. The dew point of the heating section in the annealing furnace is -10℃~-5℃, the dew point of the annealing section and slow cooling section is -40℃~-30℃, and the dew point of the furnace nose is -50℃~-40℃; the hydrogen content in the annealing furnace is 3%~5%; Hot rolling: billet heating temperature 1230℃~1250℃, start rolling temperature 1050℃~1150℃, final rolling temperature 870℃~900℃, coiling temperature 550℃~590℃; descaling water pressure 18~20MPa; Galvanizing: annealing temperature 830℃~850℃, slow cooling outlet temperature 690℃~740℃, fast cooling outlet temperature 400℃~430℃. After galvanizing, the strip is first air-knife cooled to 400℃~420℃; the skin-finishing elongation of the skin-finishing process is controlled in the range of 0.5%~1.0%.

5. The method for preparing hot-dip galvanized DH steel according to claim 4, characterized in that: During the converter smelting process, scrap steel accounts for 15% to 18%, and molten iron accounts for 82% to 85%; the converter bottom blowing adopts the full-process argon blowing mode, and the end point oxygen is controlled ≤650ppm; the refining LF path is adopted, and the slag addition amount is 30 to 40kg; vacuum decarburization treatment, vacuum degree ≤150Pa, decarburization time 18 to 25min.

6. The method for preparing hot-dip galvanized DH steel according to claim 4, characterized in that: During the slab continuous casting process, the continuous casting superheat is controlled at 17°C to 27°C; the continuous casting maintains a constant pulling speed of 1.0 to 1.3 m / min, and dynamic light pressure is used to remove edge defects of the cast slab after continuous casting.

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