A hot-dip galvanizing structural steel based on micro-alloying regulation and a preparation method thereof

Abstract

The application discloses a hot galvanizing structural steel based on micro-alloy regulation and a preparation method thereof. The steel plate base material and the zinc plating layer attached to the surface of the steel plate base material are included. The chemical components of the steel plate base material are as follows in terms of percentage by weight: C: 0.18-0.21%, Mn: 0.50-0.65%, Si: 0.08-0.12%, P: less than or equal to 0.02%, S: less than or equal to 0.01%, N: less than or equal to 0.01%, V: 0.02-0.10%, Nb: 0.015-0.060%, Ti: 0.02-0.10%, and the rest is Fe and inevitable impurities. The chemical components of the zinc plating solution are as follows in terms of percentage by weight: Al: 0.18-0.22%, and the rest is Zn and inevitable impurities. The preparation method meets the requirements of high strength and stable bending performance through a micro-alloy strengthening mechanism, solves the contradiction between the cost of high-strength steel and the elongation, improves the uniformity of the inhibition layer phase structure, and reduces the bending corrosion risk.

Description

Technical Field

[0001] This invention relates to the field of metal material manufacturing and processing technology, and more particularly to a hot-dip galvanized structural steel based on microalloy control and its preparation method. Background Technology

[0002] The core demands of the home appliance manufacturing industry for structural steel focus on the synergistic improvement of high strength, excellent formability, corrosion resistance, and surface quality. Home appliance components such as washing machine drums, refrigerator frames, and air conditioner casings need to withstand mechanical stress and frequent bending, requiring materials with a yield strength ≥340MPa and high elongation. Simultaneously, the hot-dip galvanized layer must meet the requirements for the appearance quality and long-term use of the appliances.

[0003] Traditional structural steel is strengthened with C and Mn to improve its strength, but it often exhibits high anisotropy and poor plasticity, making it prone to springback and cracking during bending, thus failing to simultaneously achieve high yield strength and complex forming requirements. Furthermore, traditional galvanizing processes are susceptible to coating uniformity issues due to alloy element segregation. For example, excessive Mn precipitation at the substrate-coating interface during galvanizing significantly inhibits the wettability of the zinc bath, interfering with coating formation and bonding quality, such as affecting adhesion, uniformity, and density. This becomes a core problem limiting the effectiveness of galvanizing. Therefore, to address the challenges of synergistically achieving high yield strength and excellent bending performance, and the interference of microalloying elements on coating quality, a microalloy-controlled hot-dip galvanized structural steel and its preparation method are needed. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a hot-dip galvanized structural steel based on microalloying control. This hot-dip galvanized structural steel, by adding trace amounts of Nb, Ti, and V, induces the dispersion precipitation of nano-sized carbonitrides during traditional hot and cold rolling processes, effectively inhibiting austenite grain growth and achieving refined and uniform grain size in the substrate, thereby significantly improving the yield strength of the steel. Simultaneously, by reducing the Mn content, the formation of Mn precipitates can be avoided, effectively improving the bonding quality of the zinc coating. Furthermore, through a three-stage temperature control process and a three-stage variable-temperature cooling process, the interfacial reaction time is extended and the reaction rate is increased, further enhancing the interfacial bonding strength between the zinc coating and the substrate, preventing zinc layer peeling at bending points during bending, while simultaneously meeting the stringent surface quality requirements of appliance panels.

[0005] Another objective of this invention is to provide a method for preparing hot-dip galvanized structural steel based on microalloying regulation. In this method, the cooling stage of a three-stage temperature-controlled process cools the steel to 450-480°C at a rate of 10-15°C / s, ensuring that a small amount of carbides precipitate at the grain boundaries, thereby obtaining a strip steel with a nanoscale microalloying strengthening phase structure. In the three-stage variable-temperature cooling process, the first stage cools the steel to 370-380°C at a rate of 5-10°C / s to eliminate the influence of latent heat release in the strip steel, refine the zinc coating grain structure, and optimize the zinc coating microstructure.

[0006] To achieve the above objectives, the present invention is accomplished through the following technical solutions.

[0007] A hot-dip galvanized structural steel based on microalloy control includes a steel plate substrate and a zinc coating attached to the surface of the steel plate substrate.

[0008] The chemical composition of the steel plate substrate, by weight percentage, is as follows: C: 0.18%~0.21%, Mn: 0.50%~0.65%, Si: 0.08%~0.12%, P≤0.02%, S≤0.01%, N≤0.01%, V: 0.02%~0.10%, Nb: 0.015%~0.060%, Ti: 0.02%~0.10%, with the remainder being Fe and unavoidable impurities; The chemical composition of the zinc plating solution used for the zinc coating, by weight percentage, is: aluminum (Al): 0.18~0.22%, with the remainder being Zn and unavoidable impurities.

[0009] In the above technical solution, the thickness of the steel plate substrate is 0.7~1.5mm, and the grain size of the steel plate substrate is 5~10μm.

[0010] In the above technical solution, the thickness of the zinc coating is 13~15 μm.

[0011] The above-mentioned method for preparing hot-dip galvanized structural steel based on microalloying control involves the following process route for cold-rolled steel sheet substrate: continuous annealing → hot-dip galvanizing → post-galvanizing cooling. The continuous annealing process employs a three-stage temperature control process, which includes: heating to 690-700℃ at a rate of 5-8℃ / s to relieve stress; then heating to 740-760℃ at a rate of 8-10℃ / s and holding at that temperature for 2-4 seconds, followed by pre-oxidation under a mixture of air and nitrogen containing water vapor; then reduction with 12-15wt% hydrogen to improve the adhesion of the zinc coating; and finally cooling to 450-480℃ at a rate of 10-15℃ / s to obtain a strip steel with a nanoscale microalloyed reinforced phase structure. The post-plating cooling adopts a three-stage variable temperature cooling process, which includes: the first stage is after the strip steel exits the zinc pot, it is cooled to 370~380℃ using an air knife distance of 23~30mm, an air knife pressure of 250~280mbar, and a cooling rate of 5~10℃ / s; the air cooling stage increases the cooling rate to 35~40℃ / s and cools to 230~240℃; finally, it is cooled to room temperature through a water cooling stage.

[0012] In the above technical solution, pre-oxidation is carried out under a mixed gas of air and nitrogen containing water vapor to obtain a pre-oxidized layer with a thickness of 0.2~0.6μm on the steel plate substrate.

[0013] In the above technical solution, the temperature difference between the hot-dip galvanizing process and the zinc plating solution is controlled to be 10~15℃, which maintains the continuous release of latent heat after the strip steel leaves the zinc pot. This helps to inhibit the dense and continuous formation of the reaction interface, while ensuring the fluidity of the zinc liquid on the zinc plating surface and improving the quality of air knife scraping.

[0014] In the above technical solution, the process route to obtain the cold-rolled steel plate substrate is: steelmaking → continuous casting → hot rolling → pickling → cold rolling → degreasing and cleaning.

[0015] In the above technical solution, the running speed of the steel plate substrate during continuous annealing is controlled to be 65~95m / min.

[0016] In the above technical solution, the temperature is raised to 740-760℃ at a heating rate of 8-10℃ / s and then briefly held for 2-4 seconds. By increasing the heating rate and shortening the time, the diffusion of silicon and manganese to the surface is suppressed.

[0017] In the above technical solution, the dew point of the air is -35~-30℃, the dew point of the nitrogen containing water vapor is -5~0℃, and the water vapor content in the nitrogen is 0.003~0.020 vol.

[0018] In the above technical solution, the volume ratio of air to nitrogen containing water vapor is (5~6):1.

[0019] In the above technical solution, the gas flow rate of the mixed gas is 15~20m³. 3 / min.

[0020] In the above technical solution, the hot-dip galvanizing temperature of the zinc plating solution is 450~460℃.

[0021] In the above technical solution, the water-cooling section cools to room temperature to reduce residual stress in the zinc coating, rapidly solidify the structure, and improve the adhesion of the zinc coating structure.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The preparation method of the present invention effectively improves the bonding quality of zinc coating by reducing the Mn content in high-strength steel and avoiding the formation of Mn precipitate phase.

[0023] (2) The preparation method of the present invention adds a small amount of V, Ti and Nb through microalloying technology to obtain a composite nanoscale microalloyed reinforced structure. The microalloying elements pin the grain boundaries and increase the grain boundary slip resistance, so that the steel has good bending and stamping performance on the basis of low cost, with a maximum tensile strength of 459.0 MPa and an elongation of more than 36%.

[0024] (3) Compared with hot-dip galvanized structural steel prepared by traditional methods, the present invention can significantly improve its yield strength without sacrificing elongation, with the highest yield strength reaching 401.7 MPa, and significantly improve its corrosion resistance. Attached Figure Description

[0025] Figure 1 The microstructure of the hot-dip galvanized structural steel prepared in Example 1 of this invention is shown by transmission electron microscopy (TEM) under a 0.2 μm scale. Figure 2 The morphology of the inhibition layer of the hot-dip galvanized structural steel prepared in Example 2 of the present invention; Figure 3 The morphology of the inhibition layer of the hot-dip galvanized structural steel prepared in Comparative Example 1. Detailed Implementation

[0026] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0027] This invention achieves the following key functions through microalloying technology: Microstructure regulation mechanism: Through the combined effect of microalloying elements, grain refinement, precipitation strengthening and inclusion control are synergistically regulated to optimize the microstructure of the matrix.

[0028] Grain refinement strengthening: Microalloying elements inhibit the growth of austenite or ferrite grains by pinning grain boundaries, increase the resistance to grain boundary slip, and improve the strength and toughness of the material while refining the grains; Precipitation strengthening: Nanoscale (V, Ti, Nb)C precipitates are dispersed in the matrix, effectively hindering dislocation movement and enhancing the matrix strength.

[0029] Example 1 A hot-dip galvanized structural steel based on microalloy control includes a steel plate substrate and a zinc coating attached to the surface of the steel plate substrate. The chemical composition of the steel plate substrate, by weight percentage, is as follows: C: 0.19%, Mn: 0.55%, Si: 0.10%, P: 0.015%, S: 0.007%, N: 0.006%, V: 0.04%, Nb: 0.016%, Ti: 0.05%, with the remainder being Fe and unavoidable impurities; The chemical composition of the zinc plating solution used for zinc plating, by weight percentage, is: aluminum (Al): 0.18%, with the remainder being Zn and unavoidable impurities. The thickness of the zinc plating is 14 μm.

[0030] The above-mentioned method for preparing hot-dip galvanized structural steel based on microalloying control includes the following steps: Based on the chemical composition and weight percentage of the steel plate substrate, the following process route is adopted: steelmaking → continuous casting → hot rolling → pickling → cold rolling → degreasing and cleaning → continuous annealing → hot-dip galvanizing → post-galvanizing cooling. The continuous annealing process employs a three-stage temperature control process, which includes: controlling the running speed of the steel substrate to 75 m / min; heating a 1.0 mm thick low-carbon alloy steel (i.e., the steel substrate with a grain size of 8 μm) obtained after degreasing and cleaning to 695 °C at a rate of 8 °C / s to relieve stress; then heating it to 745 °C at a rate of 8 °C / s and holding it briefly for 4 seconds (by increasing the heating rate and shortening the time, the diffusion of silicon and manganese to the surface is suppressed); and pre-oxidizing it with a mixed gas to obtain a 0.5 μm thick pre-oxidized layer on the low-carbon alloy steel. The mixed gas is a mixture of air (dew point -35 °C) and nitrogen containing water vapor (dew point -4 °C), with a volume ratio of air to nitrogen containing water vapor of 6:1, a water vapor content of 0.012 vol% in the nitrogen, and a gas flow rate of 18 m³ / min. 3 / min; then enter the reduction section, where 15wt% hydrogen is used for reduction to improve the adhesion of zinc coating; finally, the cooling section cools down to 470℃ at a cooling rate of 12℃ / s to ensure that a small amount of carbides precipitate to the grain boundaries, thereby obtaining strip steel with nanoscale microalloyed reinforced phase structure. Hot-dip galvanizing process: The strip steel with nanoscale microalloyed reinforced phase structure is placed in a zinc plating bath at 455℃ for zinc plating. The temperature difference between the strip steel and the zinc plating bath is controlled at 15℃ to maintain the continuous release of latent heat after the strip steel leaves the zinc pot. This helps to inhibit the dense and continuous formation of the layer reaction interface on the surface of the strip steel, while ensuring the fluidity of the zinc liquid on the surface of the zinc plating layer and improving the quality of air knife scraping. The post-galvanizing cooling process employs a three-stage variable-temperature cooling process to obtain hot-dip galvanized structural steel. The three-stage variable-temperature cooling process includes: the first stage, after the strip exits the zinc bath, uses an air knife distance of 28mm, an air knife pressure of 280mbar, and a cooling rate of 7℃ / s to cool to 370℃, in order to eliminate the influence of latent heat release in the strip, refine the zinc coating grain structure, and optimize the zinc coating microstructure; the air cooling stage increases the cooling rate to 38℃ / s, cooling to 240℃; finally, a water cooling stage cools to room temperature to reduce residual stress in the zinc coating, rapidly solidify the microstructure, and improve the adhesion of the zinc coating microstructure.

[0031] Figure 1 TEM microstructure of the hot-dip galvanized structural steel prepared in Example 1. Figure 1 It can be seen that the hot-dip galvanized structural steel obtained by the process of the present invention has a composite nano-precipitated phase.

[0032] Example 2 A hot-dip galvanized structural steel based on microalloy control includes a steel plate substrate and a zinc coating attached to the surface of the steel plate substrate. The chemical composition of the steel plate substrate, by weight percentage, is as follows: C: 0.21%, Mn: 0.65%, Si: 0.08%, P: 0.015%, S: 0.006%, N: 0.005%, V: 0.05%, Nb: 0.03%, Ti: 0.04%, with the remainder being Fe and unavoidable impurities; The chemical composition of the zinc plating solution used for zinc plating, by weight percentage, is: Al: 0.18%, with the remainder being Zn and unavoidable impurities. The thickness of the zinc plating is 14 μm.

[0033] The above-mentioned method for preparing hot-dip galvanized structural steel based on microalloying control includes the following steps: Based on the chemical composition and weight percentage of the steel plate substrate, the following process route is adopted: steelmaking → continuous casting → hot rolling → pickling → cold rolling → degreasing and cleaning → continuous annealing → hot-dip galvanizing → post-galvanizing cooling. The continuous annealing process employs a three-stage temperature control process, which includes: controlling the running speed of the steel substrate to 85 m / min; heating a 1.0 mm thick low-carbon alloy steel (i.e., the steel substrate with a grain size of 8 μm) obtained after degreasing and cleaning to 700℃ at a rate of 8℃ / s to relieve stress; then heating it to 760℃ at a rate of 8℃ / s and holding it briefly for 4 seconds (by increasing the heating rate and shortening the time, the diffusion of silicon and manganese to the surface is suppressed); and pre-oxidizing it with a mixed gas to obtain a 0.4 μm thick pre-oxidized layer on the low-carbon alloy steel. The mixed gas is a mixture of air (dew point -30℃) and nitrogen containing water vapor (dew point -3℃), with a volume ratio of air to nitrogen containing water vapor of 6:1, a water vapor content of 0.012 vol% in the nitrogen, and a gas flow rate of 20 m³ / min. 3 / min; then enter the reduction section, where 13wt% hydrogen is used for reduction to improve the adhesion of zinc coating; finally, the cooling section cools down to 470℃ at a cooling rate of 15℃ / s to ensure that a small amount of carbides precipitate to the grain boundaries, thereby obtaining strip steel with nanoscale microalloyed reinforced phase structure. Hot-dip galvanizing process: Steel strip with a nanoscale microalloyed reinforced phase structure is placed in a 455℃ zinc plating bath for zinc plating. The temperature difference between the steel strip and the zinc plating bath is controlled at 15℃ to maintain the continuous release of latent heat after the steel strip exits the zinc bath. This helps to form a dense and continuous inhibitory layer on the surface of the steel strip (such as...). Figure 2 (As shown), while ensuring the fluidity of the zinc liquid on the zinc coating surface, the air knife scraping quality is improved; Post-galvanizing cooling employs a three-stage variable-temperature cooling process to obtain hot-dip galvanized structural steel. The three-stage variable-temperature cooling process includes: In the first stage, after the strip exits the zinc bath, it is cooled to 380℃ using a 25mm air knife distance, 270mbar air knife pressure, and a cooling rate of 10℃ / s. This eliminates the influence of latent heat release in the strip, refines the zinc coating grain structure, and optimizes the zinc coating microstructure. In the air-cooling stage, the cooling rate is increased to 40℃ / s, cooling to 235℃. Finally, it passes through a water-cooling stage to cool to room temperature to reduce residual stress in the zinc coating, rapidly solidify the microstructure, and improve the adhesion of the zinc coating.

[0034] Figure 2 The image shows the morphology of the inhibition layer on the hot-dip galvanized structural steel prepared in Example 2. Figure 2 It can be seen that the present invention can effectively solve the interference of Mn precipitation on the uniformity of zinc coating and has no porosity defects.

[0035] Comparative Example 1 A hot-dip galvanized structural steel includes a steel plate substrate and a zinc coating adhered to the surface of the steel plate substrate. The chemical composition of the steel plate substrate, by weight percentage, is as follows: C: 0.21%, Mn: 0.85%, Si: 0.08%, P: 0.015%, S: 0.007%, N: 0.006%, with the remainder being Fe and unavoidable impurities; The chemical composition of the zinc plating solution used for zinc plating, by weight percentage, is: aluminum (Al): 0.18%, with the remainder being Zn and unavoidable impurities.

[0036] The preparation method of the above-mentioned hot-dip galvanized structural steel includes the following steps: Based on the chemical composition and weight percentage of the steel plate substrate, the following process route is adopted: steelmaking → continuous casting → hot rolling → pickling → cold rolling → degreasing and cleaning → continuous annealing → hot-dip galvanizing → post-galvanizing cooling.

[0037] The process used in Comparative Example 1 is basically the same as that used in Example 1.

[0038] Figure 3The inhibition layer morphology of hot-dip galvanized structural steel prepared by the traditional C and Mn strengthening method is shown in Comparative Example 1.

[0039] The mechanical property test results of the hot-dip galvanized structural steel prepared in Examples 1-2 and Comparative Example 1 are shown in Table 1.

[0040] Table 1

[0041] The corrosion resistance test results of the hot-dip galvanized structural steel prepared in Examples 1-2 and Comparative Example 1 (under neutral salt spray corrosion environment) are shown in Table 2.

[0042] Table 2

[0043] This invention achieves the following objectives through a complete process innovation encompassing component design, microstructure control, and coating technology: The preparation method of the present invention can solve the interference of Mn precipitation on the uniformity of zinc coating, effectively improve the bonding quality of zinc coating, and achieve high reliability of zinc coating. Compared with Comparative Example 1, the white rust appearance time of Example 2 of the present invention is increased by about 46.6%, and the red rust appearance time is increased by about 39.0%. While ensuring the yield strength of hot-dip galvanized structural steel with microalloy control is ≥340MPa, it can prevent cracking under extreme bending conditions (R / t≤0.5), achieving a combination of high strength and easy formability, which can meet the high-precision stamping requirements of complex structural parts such as washing machine inner drum and refrigerator bracket.

[0044] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A hot-dip galvanized structural steel based on microalloying regulation, characterized in that, This includes the steel plate substrate and the zinc coating attached to the surface of the steel plate substrate; The chemical composition of the steel plate substrate, by weight percentage, is as follows: C: 0.18%~0.21%, Mn: 0.50%~0.65%, Si: 0.08%~0.12%, P≤0.02%, S≤0.01%, N≤0.01%, V: 0.02%~0.10%, Nb: 0.015%~0.060%, Ti: 0.02%~0.10%, with the remainder being Fe and unavoidable impurities; The chemical composition of the zinc plating solution used for the zinc plating layer, by weight percentage, is: Al: 0.18~0.22%, with the remainder being Zn and unavoidable impurities.

2. The hot-dip galvanized structural steel according to claim 1, characterized in that, The thickness of the steel plate substrate is 0.7~1.5mm, and the grain size of the steel plate substrate is 5~10μm.

3. The hot-dip galvanized structural steel according to claim 1, characterized in that, The thickness of the zinc coating is 13~15 μm.

4. The method for preparing hot-dip galvanized structural steel according to any one of claims 1 to 3, characterized in that, The preparation method involves the following process route for cold-rolled steel sheet substrate: continuous annealing → hot-dip galvanizing → post-galvanizing cooling. The continuous annealing process employs a three-stage temperature control process: heating to 690-700℃ at a rate of 5-8℃ / s, then heating to 740-760℃ at a rate of 8-10℃ / s and holding at that temperature for 2-4s, followed by pre-oxidation under a mixture of air and nitrogen containing water vapor, then reduction with 12-15wt% hydrogen; and finally cooling to 450-480℃ at a rate of 10-15℃ / s. The post-plating cooling adopts a three-stage variable temperature cooling process. The first stage is after the strip steel exits the zinc pot, it is cooled to 370~380℃ using an air knife distance of 23~30mm, an air knife air pressure of 250~280mbar, and a cooling rate of 5~10℃ / s. In the air cooling stage, the cooling rate is increased to 35~40℃ / s, and it is cooled to 230~240℃. Finally, it is cooled to room temperature through a water cooling stage.

5. The preparation method according to claim 4, characterized in that, The process route for obtaining the cold-rolled steel plate substrate is as follows: steelmaking → continuous casting → hot rolling → pickling → cold rolling → degreasing and cleaning.

6. The preparation method according to claim 4, characterized in that, Pre-oxidation is carried out in a mixture of air and nitrogen containing water vapor to obtain a pre-oxidized layer with a thickness of 0.2~0.6μm on the steel plate substrate.

7. The preparation method according to claim 4, characterized in that, The hot-dip galvanizing process controls the temperature difference between the steel substrate and the zinc plating solution to be 10~15℃.

8. The preparation method according to claim 4, characterized in that, The running speed of the steel plate substrate during continuous annealing is controlled to be 65~95m / min.

9. The preparation method according to claim 4, characterized in that, The air has a dew point of -35 to -30°C, and the nitrogen containing water vapor has a dew point of -5 to 0°C; the nitrogen contains 0.003 to 0.020 vol% water vapor, and the volume ratio of air to nitrogen containing water vapor is (5 to 6):

1.

10. The preparation method according to claim 4, characterized in that, The gas flow rate of the mixed gas is 15~20m³. 3 / min.

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