980MPa-grade hot-dip galvanized quenched partition steel capable of improving surface precipitation defect and preparation method of 980MPa-grade hot-dip galvanized quenched partition steel

Abstract

The invention discloses 980MPa-grade hot-dip galvanized quenched partition steel for improving surface precipitation defects and a preparation method thereof. The 980MPa-grade hot-dip galvanized quenched partition steel comprises the following components in percentage by mass: 0.10-0.21% of C, 1.7-2.4% of Mn, 1.3-2.4% of Si, less than or equal to 0.024% of P, less than or equal to 0.024% of S, 0.2-0.6% of Mo, 0.04-0.08% of Nb, 0.5-1.0% of Al, less than or equal to 0.0040% of O, less than or equal to 0.0040% of N, more than or equal to 3.0% and less than or equal to 4.1% of Si and Mn, and the balance of Fe and inevitable impurities. According to the method, the high dew point annealing process and the pre-oxidation process are ingeniously combined, so that the problems of surface precipitation and plating leakage occurring in the production process of high-Si and high-Mn steel are effectively solved, the production efficiency and the product surface quality are remarkably improved, and a new development direction is developed for the production technology of the high-strength hot-dip galvanized steel.

Description

Technical Field

[0001] The invention relates to the fields of materials and metallurgy, and more specifically to a 980MPa grade hot-dip galvanized quenching and partitioning steel with improved surface precipitation defects and a preparation method thereof. Background Art

[0002] In the field of steel materials, 980MPa grade hot-dip galvanized quenched and partitioned steel is widely used in key structural components such as automobiles, buildings, and bridges due to its high strength, good formability, and excellent corrosion resistance. However, with the continuous improvement of the performance requirements for this type of steel, especially the strict requirements for its surface quality, its production process faces many technical challenges. In particular, when the content of silicon (Si) and manganese (Mn) in the steel is high, their external oxidation behavior during hot working becomes a key factor affecting product quality.

[0003] Si and Mn are important alloying elements that play a significant role in improving the strength and toughness of steel. However, high content of Si and Mn also brings production difficulties. During hot-dip galvanizing and subsequent quenching and partitioning, Si and Mn elements easily diffuse to the steel surface and oxidize to form oxide precipitation. This will not only damage the surface quality of the steel, but may also lead to subsequent plating defects, seriously affecting the corrosion resistance and aesthetics of the product.

[0004] At present, the industry mainly uses the following two processes to deal with this problem: 1. High dew point annealing process: This process can effectively inhibit the oxidation of the steel surface by controlling the high dew point of the furnace atmosphere, thereby reducing the precipitation of oxides. However, the effect of using the high dew point annealing process alone on steels with high Si and Mn content is limited. In addition, long-term exposure to a high dew point environment may cause the zinc layer in the steel to fall off (dezincification), thereby reducing the corrosion resistance of the product. 2. Pre-oxidation process: This process helps to improve the wettability and coating adhesion in subsequent treatments by forming a thin and uniform oxide film on the steel surface in advance. However, when the pre-oxidation process is used alone, for high Si and Mn steels, if it is not properly controlled, it is easy to cause surface overoxidation, thereby affecting the reduction effect of subsequent processes and the surface quality of the final product.

[0005] In the face of the special challenges faced by high Si and Mn content steels during hot dip galvanizing quenching and partitioning, an innovative process method is urgently needed. This new method should not only effectively inhibit the external oxidation of Si and Mn elements, but also avoid dezincification and overoxidation problems, while ensuring efficient production and high-quality products. The limitations of traditional single processes have prompted the industry to explore more sophisticated and complex process control strategies. Summary of the invention

[0006] The purpose of the present invention is to overcome the above-mentioned defects of the prior art, provide a 980MPa grade hot-dip galvanized quenching and partitioning steel with improved surface precipitation defects and a preparation method thereof, design for the high Si and Mn content characteristics of the 980MPa grade hot-dip galvanized quenching and partitioning steel, by combining the composite treatment technology of high dew point annealing process and pre-oxidation process, accurately control the parameters and sequence of the two-stage process, first use the high dew point annealing process to preliminarily inhibit the oxidation of Si and Mn elements, and then form an oxide film of suitable thickness on the steel surface through the pre-oxidation process. This oxide film can protect the steel matrix and provide good surface conditions for subsequent hot-dip galvanizing and quenching and partitioning processes. This composite process not only effectively solves the surface precipitation and leakage plating problems of high Si and Mn steel grades in the production process, but also significantly improves production efficiency and product surface quality, opening up a new development direction for the production technology of high-strength hot-dip galvanized steel.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A 980MPa grade hot-dip galvanized quenching and partitioning steel for improving surface precipitation defects comprises the following components in mass percentage: C: 0.10%-0.21%, Mn: 1.7%-2.4%, Si: 1.3%-2.4%, P≤0.024%, S≤0.024%, Mo: 0.2%-0.6%, Nb: 0.04%-0.08%, Al: 0.5%-1.0%, O≤0.0040%, N≤0.0040%, 3.0%≤Si+Mn≤4.1%, and the balance is Fe and unavoidable impurities.

[0009] Optionally, the hot-dip galvanized quenched and partitioned steel has a thickness of 0.8 mm to 2.5 mm and a width of 900 mm to 1300 mm.

[0010] Optionally, the hot-dip galvanized quenched and partitioned steel has a yield strength of 550-650 MPa, a tensile strength of 980-1100 MPa, and an A80 elongation after fracture of 15%-25%.

[0011] The present invention also discloses a method for preparing the 980MPa grade hot-dip galvanized quenching and partitioning steel with improved surface precipitation defects, comprising the following steps: converter smelting, slab continuous casting, hot rolling, bell annealing, pickling and cold rolling, and hot-dip galvanizing;

[0012] The hot-dip galvanizing heating section includes a high dew point annealing section and a pre-oxidation section;

[0013] In the high dew point annealing section, the dew point is -10°C to 8°C, and the hydrogen content is 3% to 5%;

[0014] 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 1.2%, and the air flow rate is 30Nm 3 / h~50Nm 3 / h.

[0015] Optionally, the hot-dip galvanizing also includes a heat preservation section, a slow cooling section, a fast cooling section, an equalization section, and a galvanizing section; the annealing temperature is 845°C to 875°C, the slow cooling outlet temperature is 740°C to 760°C; the fast cooling outlet temperature is 300°C to 330°C; the furnace nose dew point is -50°C to -40°C; the belt speed is 50m / min to 120m / min; the galvanizing temperature is 460°C to 470°C, and the finishing elongation of the finishing process is 0.6% to 0.9%.

[0016] Optionally, during the hot rolling, the billet exit temperature is 1220°C to 1260°C, the rough rolling outlet temperature is 1050°C to 1100°C, the finishing rolling inlet temperature is 980°C to 1010°C, the final rolling temperature is 870°C to 920°C, and the coiling temperature is 570°C to 600°C.

[0017] Optionally, in the hood annealing, the hood annealing temperature is 600° C. to 620° C., and the holding time is 5 h to 7 h.

[0018] Implementing the embodiments of the present invention will have the following beneficial effects:

[0019] The present invention proposes a 980MPa grade hot-dip galvanized quenching and partitioning steel with improved surface precipitation defects and a preparation method thereof, which achieves significant technical progress and practical application value by cleverly combining a high dew point annealing process with a pre-oxidation process, which is specifically embodied in the following aspects:

[0020] (1) Significantly improved the surface quality of steel: By precisely controlling the parameters of the two-stage process, the external oxidation of Si and Mn elements is effectively suppressed, the surface precipitation defects and plating leakage are greatly reduced, and the surface quality of the product is improved.

[0021] (2) Improved production efficiency and economic benefits: High-quality products also enhance market competitiveness and bring higher economic benefits to the enterprise.

[0022] (3) Satisfying the needs of high-end application fields: The high-surface quality 980MPa grade hot-dip galvanized quenched and partitioned steel produced by the present invention is successfully applied to key structural components such as automobiles, buildings, and bridges due to its excellent mechanical properties, corrosion resistance, and surface quality, meeting the strict requirements of these fields for high-strength, high-toughness, and high-corrosion-resistant steels.

[0023] (4) Promoted technological progress in the steel industry: The successful implementation of the present invention has provided the steel industry with new technical ideas and methods for the production and processing of high-strength steel, promoted the industry's technological progress and industrial upgrading, and is of great significance for enhancing the overall competitiveness of my country's steel industry.

[0024] In summary, the present invention not only significantly improves the quality and performance of the product, but also improves production efficiency and economic benefits, meets the needs of high-end application fields, and promotes technological progress in the steel industry. It has broad social and economic benefits and important industry value. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the hot-dip galvanizing process of the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0027] 1. Chemical composition and mechanical properties

[0028] A 980MPa grade hot-dip galvanized quenching and partitioning steel for improving surface precipitation defects comprises the following components in mass percentage: C: 0.10%-0.21%, Mn: 1.7%-2.4%, Si: 1.3%-2.4%, P≤0.024%, S≤0.024%, Mo: 0.2%-0.6%, Nb: 0.04%-0.08%, Al: 0.5%-1.0%, O≤0.0040%, N≤0.0040%, 3.0%≤Si+Mn≤4.1%, and the balance is Fe and unavoidable impurities.

[0029] In a specific embodiment, the hot-dip galvanized quenched and partitioned steel has a thickness of 0.8 mm to 2.5 mm and a width of 900 mm to 1300 mm.

[0030] In a specific embodiment, the yield strength of the hot-dip galvanized quenched and partitioned steel is 550-650 MPa, the tensile strength is 980-1100 MPa, and the A80 elongation after fracture is 15%-25%.

[0031] 2. Production technology

[0032] The present invention also discloses a method for preparing a 980MPa grade hot-dip galvanized quenched and partitioned steel with improved surface precipitation defects as in any embodiment of the present invention, comprising the following steps: converter smelting, slab continuous casting, hot rolling, hood annealing, pickling and cold rolling, and hot-dip galvanizing.

[0033] S1. The converter smelting and slab continuous casting steps of the present invention can be operated according to conventional preparation methods.

[0034] S2. During hot rolling, the billet exit temperature is 1220℃~1260℃, the rough rolling outlet temperature is 1050℃~1100℃, the finishing rolling inlet temperature is 980℃~1010℃, the final rolling temperature is 870℃~920℃, and the coiling temperature is 570℃~600℃.

[0035] S3. In the hood annealing, the hood annealing temperature is 600°C to 620°C, and the holding time is 5h to 7h.

[0036] S4. Pickling and cold rolling can be carried out according to conventional preparation methods.

[0037] S6. The heating section of hot-dip galvanizing includes a high dew point annealing section and a pre-oxidation section; in the high dew point annealing section, the dew point is -10℃~8℃, 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%~1.2%, and the air flow rate is 25Nm2 / h~45Nm2 / h.

[0038] In a specific embodiment, hot-dip galvanizing also includes a holding section, a slow cooling section, a fast cooling section, an equalization section, and a galvanizing section; the annealing temperature is 845°C to 875°C, the slow cooling outlet temperature is 740°C to 760°C; the fast cooling outlet temperature is 300°C to 330°C; the furnace nose dew point is -50°C to -40°C; the belt speed is 50m / min to 120m / min; the galvanizing temperature is 460°C to 470°C, and the finishing elongation of the finishing process is 0.6% to 0.9%.

[0039] In a specific embodiment, when the thickness specification is ≥2mm, the dew point is -5℃~5℃, the oxygen content is 0.6%~0.8%, and the air flow rate is 30Nm 3 / h~40Nm 3 / h.

[0040] Specifically, the present invention, by precisely controlling the parameters of the high dew point annealing process, preliminarily inhibits the oxidation behavior of Si and Mn elements in steel at high temperatures, reduces the precipitation of oxides, and lays a good foundation for subsequent processes. In addition, on the basis of preliminarily inhibiting oxidation, a thin and uniform oxide film is formed on the steel surface through a pre-oxidation process, which can not only protect the steel matrix from further oxidation, but also serve as a high-quality substrate for subsequent hot-dip galvanizing, avoid dezincification, and prevent surface overoxidation, thereby ensuring the surface quality and corrosion resistance of the final product. In addition, by optimizing the combination mode and parameter setting of the two-stage process, efficient production is achieved, and the residence time of the strip in each process section is reduced, which not only ensures production efficiency, but also avoids potential problems caused by long-term processing. The 980MPa grade hot-dip galvanized quenching and partitioning steel prepared by the present invention has excellent mechanical properties, corrosion resistance and surface quality, and can meet the urgent needs of key structural components such as automobiles, buildings, bridges, etc. for high-strength, high-toughness, and high-corrosion-resistant steel.

[0041] The following are specific embodiments

[0042] The chemical composition of Examples 1-10 is shown in Table 1, the converter smelting, slab continuous casting and hot rolling process parameters of Examples 1-10 are shown in Table 2, the hood annealing, pickling cold rolling and 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.

[0043] Table 1 Chemical composition of Examples 1-10 (%)

[0044]

[0045] Table 2 Process parameters of converter smelting, slab continuous casting and hot rolling of Examples 1-10

[0046] Example Oven temperature / ℃ Rough rolling outlet temperature / ℃ Finishing rolling inlet temperature / ℃ Final rolling temperature / ℃ Coiling temperature / ℃ 1 1240 1060 980 870 570 2 1251 1052 985 912 593 3 1238 1073 996 906 572 4 1251 1053 1000 900 573 5 1259 1066 1010 915 575 6 1243 1074 1008 890 590 7 1260 1082 1005 917 586 8 1260 1090 995 918 595 9 1220 1100 992 887 574 10 1256 1083 994 915 579

[0047] Table 3 Process parameters of bell annealing, pickling cold rolling and hot dip galvanizing of Examples 1-10

[0048]

[0049]

[0050] Table 4 Mechanical properties of Examples 1-10

[0051]

[0052] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it 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 980MPa grade hot-dip galvanized quenching and partitioning steel with improved surface precipitation defects, characterized in that: The invention comprises the following components in mass percentage: C: 0.10% to 0.21%, Mn: 1.7% to 2.4%, Si: 1.3% to 2.4%, P≤0.024%, S≤0.024%, Mo: 0.2% to 0.6%, Nb: 0.04% to 0.08%, Al: 0.5% to 1.0%, O≤0.0040%, N≤0.0040%, and 3.0%≤Si+Mn≤4.1%, and the balance is Fe and unavoidable impurities.

2. The 980MPa grade hot-dip galvanized quenching and partitioning steel with improved surface precipitation defects according to claim 1, characterized in that: The hot-dip galvanized quenched and partitioned steel has a thickness of 0.8 mm to 2.5 mm and a width of 900 mm to 1300 mm.

3. The 980MPa grade hot-dip galvanized quenching and partitioning steel with improved surface precipitation defects according to claim 1, characterized in that: The yield strength of the hot-dip galvanized quenched partitioning steel is 550-650MPa, the tensile strength is 980-1100MPa, and the A80 elongation after fracture is 15%-25%.

4. A method for preparing a 980MPa grade hot dip galvanized quenching and partitioning steel with improved surface precipitation defects 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, bell annealing, pickling and cold rolling, hot-dip galvanizing; The hot-dip galvanizing heating section includes a high dew point annealing section and a pre-oxidation section; In the high dew point annealing section, the dew point is -10°C to 8°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 1.2%, and the air flow rate is 25Nm 2 / h~45Nm 2 / h.

5. The preparation method according to claim 4, characterized in that: The hot-dip galvanizing also includes a heat preservation section, a slow cooling section, a fast cooling section, an equalization section, and a galvanizing section; the annealing temperature is 845°C to 875°C, the slow cooling outlet temperature is 740°C to 760°C; the fast cooling outlet temperature is 300°C to 330°C; the furnace nose dew point is -50°C to -40°C; the belt speed is 50m / min to 120m / min; the galvanizing temperature is 460°C to 470°C, and the finishing elongation rate of the finishing process is 0.6% to 0.9%.

6. The preparation method according to claim 4, characterized in that: During the hot rolling, the billet furnace exit temperature is 1220°C to 1260°C, the rough rolling outlet temperature is 1050°C to 1100°C, the finishing rolling inlet temperature is 980°C to 1010°C, the final rolling temperature is 870°C to 920°C, and the coiling temperature is 570°C to 600°C.

7. The preparation method according to claim 4, characterized in that: In the hood annealing, the hood annealing temperature is 600° C. to 620° C., and the holding time is 5 h to 7 h.

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