A process for strengthening the coating adhesion of gpa-grade hot-dip galvanized dual-phase steel

Abstract

The application relates to the technical field of metal material surface treatment, in particular to a GPa-grade hot-dip galvanizing dual-phase steel coating bonding force strengthening process, which specifically comprises the following steps: immersing a base material into a plating solution to perform continuous annealing, pre-oxidation, reduction, two-stage cooling and post-plating cooling to obtain the GPa-grade hot-dip galvanizing dual-phase steel coating after strengthening. The technical scheme can inhibit the enrichment of Si and Mn elements in the surface layer of the high-strength automobile steel, reduce the formation of silicon-manganese oxides, strengthen the oxidation capacity in the pre-oxidation section, enhance the zinc liquid wettability, form a continuous and dense inhibiting layer structure for the coating tissue base, make the grain size of the inhibiting layer uniform, present a single-layer inhibiting layer grain morphology, reduce the thickening of the brittle layer phase, and simultaneously reduce the iron loss of the strip steel, so that the production of the zinc pot bottom slag is reduced.

Description

Technical Field

[0001] This invention belongs to the field of metal material surface treatment technology, specifically involving a process for strengthening the adhesion of hot-dip galvanized duplex steel coatings at the GPa level. Background Technology

[0002] With the increasing emphasis on lightweighting and safety standards in the automotive industry, GPa-grade hot-dip galvanized duplex steel (DP980) has become a core material for vehicle body structural components (such as A / B pillars, chassis reinforcements, and pillar reinforcement plates) due to its combination of high strength, good formability, and corrosion resistance. The cathodic protection provided by the hot-dip galvanized layer is a crucial guarantee for ensuring the long service life of the steel in harsh environments.

[0003] However, this grade of steel faces a severe problem of insufficient coating adhesion during production, directly affecting the reliability of components and the safety of the entire vehicle. Specific bottlenecks are as follows: A. The contradiction between high strength and alloying: To achieve 1000MPa high strength, steel typically requires the addition of high levels of alloying elements such as silicon (Si), manganese (Mn), and chromium (Cr). These elements, especially Si and Mn, easily accumulate on the steel surface during continuous annealing, forming an internal oxide layer (such as Si / Mn oxide). This internal oxide layer severely hinders the effective wetting and alloying reaction between the steel substrate and the molten zinc, leading to decreased coating adhesion and even defects such as incomplete coating or coating peeling (powdering). B. Process sensitivity: The continuous annealing process window (temperature, time, atmosphere) for high-strength steel is usually narrow. Even small fluctuations in annealing parameters (such as soaking temperature and dew point control) can significantly affect the morphology and distribution of surface oxides, thus decisively influencing the adhesion of the subsequent galvanized layer. Conventional hot-dip galvanizing process parameters are insufficient to effectively suppress or eliminate these surface problems unique to high-strength steel. C. High Service Reliability Requirements: Automotive components are subjected to complex stresses during forming (stamping, bending) and use. Insufficient coating adhesion can lead to coating cracking and peeling during forming, or accelerated failure due to stress corrosion and fatigue during long-term use, seriously affecting component performance and vehicle safety. Therefore, developing a strengthening method and optimized process specifically for 1000MPa grade hot-dip galvanized duplex steel that can effectively overcome the effects of internal oxidation and significantly improve coating adhesion is a key technological breakthrough to meet the urgent needs of the automotive industry for high-strength, high-corrosion-resistant, and high-reliability steel plates. This invention focuses on solving this core problem, providing technical support for the stable production and application of high-performance hot-dip galvanized duplex steel. Summary of the Invention

[0004] The present invention aims to solve the problems existing in the coating of hot-dip galvanized DP980 steel, such as uneven structure, poor interfacial bonding, poor continuity of the inhibition layer, unstable corrosion resistance, and poor surface.

[0005] According to one aspect of the present invention, a process for strengthening the adhesion of a GPa-grade hot-dip galvanized duplex steel coating is provided, specifically including the following steps: immersing the substrate in a plating solution for continuous stripping, pre-oxidation, reduction, two-stage cooling, and post-plating cooling to obtain a strengthened GPa-grade hot-dip galvanized duplex steel coating.

[0006] Based on the above technical solution, the composition of the substrate is as follows: C: ≤0.18wt%, Mn: 2.00wt%-2.30wt%, Si: 0.40wt%-0.50wt%, P: 0.020wt%-0.035wt%, Cr: 0.35wt%-0.45wt%, Nb: 0.015wt%-0.030wt%, Als: 0.020wt%-0.060wt%, Ti: 0.05wt%-0.06wt%, B: 0.0018wt%-0.0020wt%, La 0.015%~0.025%, Ce 0.016%~0.018%, with the balance being Fe;

[0007] The plating solution uses zinc as a base and controls the aluminum content to be 0.18wt%-0.22wt%.

[0008] Based on the above technical solution, the continuous annealing is a three-stage heating process, specifically: using 0.7-2.0mm low-carbon alloy steel, the first stage of heating is to relieve stress to 685-700℃ at a heating rate of 4.5-5.5℃ / s; the second stage of heating is to heat to 715-735℃ at a heating rate of 9.5-12.5℃ / s, thereby inhibiting the diffusion of silicon and manganese to the surface by shortening the heating time; the third stage of heating is to rapidly heat to 825-855℃ at a heating rate of 19-23℃ / s, and hold at that temperature for 2.2-4.2s.

[0009] Based on the above technical solution, the pre-oxidation specifically involves: pre-oxidation in a mixture of air with a dew point of -33℃ to -28℃ and nitrogen containing water vapor with a dew point of -4℃ to +1℃, wherein the volume ratio of air to nitrogen containing water vapor is 4.8:1-5.2:1, water vapor accounts for 20% to 30% of the nitrogen mixture, and the total gas flow rate of the air and nitrogen mixture is 18-38 m³ / s. 3 / min, the thickness of the pre-oxidized layer is controlled within 0.5μm.

[0010] Based on the above technical solution, the reduction specifically involves: introducing hydrogen gas with a mass fraction of 14-16% and reducing it at 780-840℃ for 50-95 seconds.

[0011] Based on the above technical solution, the two-stage cooling process is as follows: the first stage of cooling reduces the temperature to 715-735℃ at a cooling rate of 4.5-10.5℃ / s, and then the second stage of cooling, i.e., rapid cooling mode, is carried out at a cooling rate of 24-32℃ / s to rapidly cool the temperature to 475-485℃, thereby obtaining a martensitic structure. The zinc liquid temperature is 452-458℃, ensuring the continuous release of the latent heat of the strip steel.

[0012] Based on the above technical solution, the post-plating cooling is a three-stage variable temperature cooling, specifically: the first stage is from 463-472℃ after exiting the zinc pot, using an air knife distance of 22mm-29mm, an air knife pressure of 245-275mbar, and a cooling rate of 4.5-10.5℃ / s to cool to 365-385℃; the second stage is the air cooling stage, with a cooling rate of 33-38℃ / s, cooling to 225-245℃ to eliminate the influence of latent heat release of the strip steel, refine the coating grain structure, and optimize the coating structure; the third stage is the water cooling stage, with a cooling rate of 25~35℃ / s to cool to room temperature to reduce residual stress in the coating, quickly solidify the structure, and improve the adhesion of the coating structure.

[0013] Based on the above technical solution, the substrate of the coating has a continuous and dense inhibition layer structure, and the inhibition layer exhibits a single-layer inhibition layer grain morphology, wherein the size of the inhibition layer grain is 0.5-1.5 micrometers.

[0014] Beneficial effects The technical solution disclosed in this invention addresses the problems of uneven microstructure, poor interfacial bonding, poor continuity of the inhibition layer, unstable corrosion resistance, and poor surface in existing hot-dip galvanized DP980 steel by optimizing the alloy design during smelting, adding rare earth elements such as La and Ce, and then combining continuous annealing, pre-oxidation, reduction, two-stage cooling, and post-plating cooling processes. Through a unique microstructure control and pre-oxidation control process, it inhibits the enrichment of Si and Mn elements from high-strength automotive steel onto the surface of the strip steel, reduces the formation of silicon and manganese oxides, strengthens the oxidation capacity of the pre-oxidation stage, enhances the wettability of the zinc bath, and creates a continuous and dense inhibition layer structure in the coating substrate. This results in uniform grain size in the inhibition layer, exhibiting a single-layer inhibition layer grain morphology, reducing the thickening of the brittle layer phase, and simultaneously reducing strip steel loss, thereby reducing the production of bottom slag in the zinc pot. This technology has made a breakthrough in solving the problem of insufficient adhesion of the zinc layer in traditional hot-dip galvanized high-strength steel, achieving a continuous and dense reaction interface at the microscopic level, while reducing the thickness of the brittle phase layer structure, providing an innovative solution for the formability and corrosion resistance of high-strength steel sheets in automotive body panels, structural components, and other fields. Attached Figure Description

[0015] Figure 1 This is a morphology diagram of the hot-dip galvanized dual-phase GPa steel coating substrate suppression layer in the comparative example of the present invention; Figure 2The morphology of the hot-dip galvanized duplex GPa steel coating substrate inhibition layer after reinforcement in Example 1 of the present invention; Figure 3 The image shows the microstructure of the reinforced hot-dip galvanized duplex steel inhibition layer in Example 1 of this invention. Detailed Implementation

[0016] To make the objectives and technical solutions of this invention clearer, the following embodiments are provided for further explanation. However, the scope of protection of this invention is not limited to these embodiments; the embodiments are merely for illustrative purposes. Those skilled in the art should understand that any changes or equivalent substitutions that do not depart from the concept of this invention are included within the scope of protection of this invention.

[0017] Unless otherwise specified, all reagents and raw materials used in this invention are obtained through purchase.

[0018] Example 1 Plating solution composition: Zinc (Zn) as the base, aluminum (Al) content controlled at 0.21wt%.

[0019] Substrate composition: C: 0.12wt%, Mn: 2.10wt%, Si: 0.40wt%, P: 0.025wt%, Cr: 0.42wt%, Nb: 0.016wt%, Als: 0.030wt%, Ti: 0.05wt%, B: 0.0018wt%, La: 0.015wt%, Ce: 0.016wt%, balance Fe.

[0020] The continuous annealing process employs a three-stage heating process, using 2.0mm low-carbon alloy steel. Stress relief is achieved by heating at 5℃ / s to 688℃, followed by increasing the heating rate to 10℃ / s to 715℃. Shortening the heating time inhibits the diffusion of silicon and manganese to the surface. Rapid heating (21℃ / s) raises the temperature to 855℃, holding for 4.2s. Pre-oxidation is performed using a mixture of air (dew point -30℃) and nitrogen containing water vapor (dew point -3℃, water vapor content 21%), with a gas volume ratio of approximately 4.8:1 and a gas flow rate of 28m³. 3The pre-oxidized layer thickness is controlled at 0.2 μm / min, followed by reduction at 820℃ for 69s with 14% hydrogen by mass to obtain an ideal surface and improve coating adhesion. The cooling process is then divided into two stages: first, cooling at 8℃ / s to 735℃, followed by rapid cooling at 32℃ / s to 485℃ to obtain a martensitic structure. The zinc bath temperature is 455℃ to ensure continuous release of latent heat from the strip. The post-plating cooling process employs a three-stage variable-temperature cooling process. In the first stage, after exiting the zinc bath at 463-472℃, a 26mm air knife distance and 255mbar air knife pressure are used to cool to 365℃ at a rate of 8.5℃ / s. The air-cooling stage cools the steel strip to 228°C at a rate of 35°C / s to eliminate the influence of latent heat release, refine the coating grain size, and optimize the coating structure. Finally, the water-cooling stage cools the strip to room temperature (26°C) at a rate of 30°C / s to reduce residual stress, rapidly solidify the coating, improve adhesion, and suppress the grain size of the inhibition layer to 0.6 micrometers. The morphology of the enhanced hot-dip galvanized duplex GPa steel coating substrate inhibition layer is shown in [Figure number missing]. Figure 2 It can be seen that there are no obvious cracks on the steel substrate surface, forming a continuous and dense inhibition layer structure, and the zinc layer has good adhesion; the microstructure of the inhibition layer of the strengthened hot-dip galvanized duplex steel is shown in the figure. Figure 3 (Red circle: Fe-Al phase grains in the suppression layer).

[0021] Example 2 Plating solution composition: Zinc (Zn) as the base, aluminum (Al) content controlled at 0.21wt%.

[0022] Substrate composition: C: 0.10wt%, Mn: 2.05wt%, Si: 0.44wt%, P: 0.027wt%, Cr: 0.39wt%, Nb: 0.019wt%, Als: 0.050wt%, Ti: 0.06wt%, B: 0.0020wt%, La: 0.020wt%, Ce: 0.017wt%, balance Fe.

[0023] The continuous annealing process employs a three-stage heating process, using 1.7mm low-carbon alloy steel. Stress relief is achieved at a rate of 4.8℃ / s, reaching 695℃. The heating rate is then increased to 12℃ / s, reaching 720℃. Shortening the heating time inhibits the diffusion of silicon and manganese to the surface. Rapid heating (22℃ / s) raises the temperature to 845℃, holding for 38 seconds. Pre-oxidation is performed using a mixture of air (dew point -30℃) and nitrogen containing water vapor (dew point 0℃, water vapor content 26%), with a gas mixture ratio of approximately 5:1 and a gas flow rate of 33m³ / s. 3The pre-oxidized layer thickness is controlled within 0.3 μm at a rate of [per unit weight], followed by a reduction section. Reduction is achieved at 825℃ for 58 seconds using 16% hydrogen by mass to obtain an ideal surface and improve coating adhesion. The cooling process is then divided into two stages: first, cooling at a rate of 9℃ / s to 725℃, followed by rapid cooling at 28℃ / s to 485℃ to obtain a martensitic structure. The zinc bath temperature is 455℃ to ensure continuous release of latent heat from the strip. The post-plating cooling process employs a three-stage variable-temperature cooling process. In the first stage, after exiting the zinc bath at 465℃, a 27mm air knife distance and 260mbar air knife pressure are used to cool to 375℃ at a rate of 8℃ / s. The air-cooling stage cools the strip to 235°C at a rate of 35°C / s to eliminate the influence of latent heat release, refine the coating grain structure, and optimize the coating structure. Finally, the water-cooling stage cools the strip to room temperature (26°C) at a rate of 28°C / s to reduce residual stress, rapidly solidify the structure, improve the adhesion of the coating, and suppress the grain size to 1.1 micrometers.

[0024] Comparative Example Steel plates were prepared according to the preparation method of 1000MPa grade hot-dip galvanized reinforced multiphase steel disclosed in CN116732448A. The chemical composition of the steel plates is as follows: C 0.11%, Si 0.2%, Mn 2.8%, P 0.009%, S 0.005%, Al 1.4%, Nb 0.05%, Cr 0.7%, B 0.004%, balance being iron; hot rolling process parameters are as follows: heating and holding at 1180℃ for 2 hours, roughing mill inlet temperature 1200℃, roughing mill outlet temperature 1000℃, finishing mill start temperature 980℃, finishing mill end temperature 880℃, coiling temperature 500℃, hot-rolled plate thickness 6mm, cold-rolled plate thickness 2.4mm, cold rolling reduction rate 60%; annealing parameters are as follows: preheating temperature 220℃, heating rate 15℃ / s, heating temperature 880℃, soaking temperature 880℃, soaking time 80s, rapid cooling temperature 300℃, rapid cooling rate 45℃ / s, holding temperature 390℃, holding time 50s, galvanizing temperature 455℃, galvanizing time 10s, resulting in a zinc layer thickness of 7mm on the steel plate. The morphology of the inhibition layer of the hot-dip galvanized duplex GPa steel coating substrate is shown in [reference needed]. Figure 1 ,from Figure 1 It can be seen that the substrate is loose, the surface of the steel base is cracked, resulting in a poor reaction interface, and the inhibition layer is discontinuous and has poor adhesion to the substrate.

[0025] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A process for strengthening the adhesion of GPa-grade hot-dip galvanized duplex steel coatings, characterized in that, Specifically, the steps include the following: Plating solution composition: Zinc as the base, aluminum content controlled at 0.21 wt%; Substrate composition: C: 0.12wt%, Mn: 2.10wt%, Si: 0.40wt%, P: 0.025wt%, Cr: 0.42wt%, Nb: 0.016wt%, Als: 0.030wt%, Ti: 0.05wt%, B: 0.0018wt%, La: 0.015wt%, Ce: 0.016wt%, balance Fe; The continuous annealing process employs a three-stage heating process, using 2.0mm low-carbon alloy steel. Stress relief is achieved by heating at 5℃ / s to 688℃, then the heating rate is increased to 10℃ / s to 715℃, followed by rapid heating at 21℃ / s to 855℃, with a holding time of 4.2s. Pre-oxidation is performed using air and nitrogen containing water vapor; the volume ratio of the two gases is 4.8:1, and the gas flow rate is 28m³ / s. 3 The pre-oxidized layer thickness is controlled at 0.2 μm, and then it enters the reduction section, where it is reduced at 820℃ for 69s with 14% mass fraction hydrogen. The temperature is then divided into two stages: first, it is cooled to 735℃ at a cooling rate of 8℃ / s, and then rapidly cooled to 485℃ at a cooling rate of 32℃ / s to obtain a martensitic structure. The zinc bath temperature is 455℃. The post-plating cooling process adopts a three-stage variable temperature cooling process. In the first stage, after exiting the zinc bath at 463-472℃, a 26mm air knife distance and 255mbar air knife pressure are used to cool to 365℃ at a cooling rate of 8.5℃ / s. The second stage is an air cooling stage, where the temperature is cooled to 228℃ at a cooling rate of 35℃ / s. The third stage is a water cooling stage, where the temperature is cooled to room temperature (26℃) at a cooling rate of 30℃ / s to reduce residual stress in the coating, resulting in a strengthened GPa-grade hot-dip galvanized duplex steel coating with a suppressed layer grain size of 0.6 micrometers. The dew point of the air is -30℃, the water vapor content of the nitrogen gas is 21%, and the dew point of the nitrogen gas containing water vapor is -3℃.

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