A surface treatment liquid, a shot-blasting-free hot press steel sheet, a hot press component, and a method for manufacturing the same

Abstract

This invention relates to the field of high-strength steel surface treatment technology, and particularly to a surface treatment liquid, a steel plate for hot stamping without shot blasting, hot stamped parts, and a method for preparing the same. The invention provides a surface treatment liquid, with a total mass of 100 parts, comprising 5-30 parts of water-based resin, 1-60 parts of nano-aluminosilicate and / or modified nano-aluminosilicate, 1-10 parts of surfactant, and the balance being water; the nano-aluminosilicate and / or modified nano-aluminosilicate simultaneously contains Si and Al elements. Applying the surface treatment liquid provided by this invention to the surface of a metal-coated hot stamping steel plate results in a uniform and controllable oxide layer on the surface of the parts obtained after hot stamping, eliminating the need for an additional shot blasting process and avoiding related problems associated with shot blasting, while also meeting the requirements for subsequent welding and electrophoresis.

Description

Technical Field

[0001] This invention relates to the field of high-strength steel surface treatment technology, and in particular to a surface treatment liquid, a steel plate for hot stamping without shot blasting, hot stamped parts, and a method for preparing the same. Background Technology

[0002] In the context of automotive lightweighting, high-strength hot-formed steel sheets can solve energy conservation and emission reduction problems while also improving vehicle safety performance, leading to a gradual increase in their usage. However, ultra-high-strength hot-formed steel sheets with strengths above 1000MPa suffer from problems such as easy cracking, severe springback, and difficulty in forming complex parts during cold stamping. Hot stamping processes can avoid these problems, but bare hot-formed steel sheets suffer from severe surface oxidation, decarburization, and poor corrosion resistance during heating. Therefore, a series of coated hot-formed steels, such as aluminum-silicon coatings and zinc-based coatings, have been developed.

[0003] Among them, zinc-based coated hot-formed steel can achieve a protective effect through sacrificial anodes, and its corrosion resistance is superior to that of aluminum-silicon coated hot-formed steel. Furthermore, compared to aluminum-silicon coatings, zinc-based coated hot-formed steel requires lower heating temperatures and shorter heating times, resulting in greater energy savings and lower production costs. However, during the heating process (heating is required during forming), the zinc-based coating surface continuously oxidizes in the heated atmosphere, leading to a thicker oxide layer. The difference in element diffusion rates between the coating and the substrate results in uneven oxide layer composition distribution. This oxide layer undergoes ionization during electrophoresis, with different compositions exhibiting different ionization states. This can easily lead to pinholes during electrophoresis, negatively impacting the surface quality of the coating and affecting subsequent welding stability.

[0004] Currently, shot blasting is widely used to solve the problem of uneven oxide layer on the surface. In addition to requiring additional specialized equipment and increasing process costs, shot blasting also increases the environmental pressure on parts manufacturers due to the dust emissions generated during the process. Furthermore, for large parts (such as central channels, door rings, etc.), the impact of the shot used in shot blasting on the steel surface can easily cause stress release inside the parts, leading to loss of precision control and reduced parts yield. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a surface treatment liquid, a steel plate for hot stamping without shot blasting, hot stamped parts, and a method for preparing the same. By coating the surface treatment liquid provided by this invention onto the surface of the metal-plated hot stamping steel plate, the oxide layer on the surface of the parts obtained after hot stamping is uniform and controllable, eliminating the need for an additional shot blasting process and avoiding the aforementioned problems caused by shot blasting. Simultaneously, it can meet the requirements of subsequent welding and electrophoresis.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The present invention provides a surface treatment liquid, which, in a total mass of 100 parts, comprises 5-30 parts of aqueous resin, 1-60 parts of nano-aluminosilicate and / or modified nano-aluminosilicate, 1-10 parts of surfactant, and the balance being water; wherein the nano-aluminosilicate and / or modified nano-aluminosilicate contains both Si and Al elements.

[0007] Preferably, it also includes 1 to 10 parts of surface lubricant.

[0008] Preferably, the mass ratio of Al and Si elements in the nano-aluminosilicate and / or modified nano-aluminosilicate, calculated as Al2O3 and SiO2 respectively, is (0.5~10):1.

[0009] The present invention provides a hot-formed steel for hot stamping that does not require shot blasting, comprising a hot-formed steel substrate, a zinc-based coating attached to the surface of the hot-formed steel substrate, and a post-treatment layer for which shot blasting is not required coated on the surface of the zinc-based coating; the post-treatment layer for which shot blasting is not required is formed by drying and curing the surface treatment liquid described in the above scheme.

[0010] Preferably, the single-sided dry film weight of the shot-blasting-free post-treatment layer is 0.1~3 g / m³. 2 .

[0011] Preferably, the surface of the hot-formed steel contains Al and Si elements, wherein the mass percentage of Si element is not higher than 65%.

[0012] Preferably, the drying and curing temperature is 80~120℃.

[0013] This invention provides a shot-blast-free preparation method for hot-stamped parts, comprising the following steps: heating the hot-stamping shot-blast-free hot-forming steel described in the above scheme to AC3 or above, and after complete austenitization, transferring it to a hot-stamping die for forming, holding pressure, and quenching, without shot blasting, to obtain the hot-stamped parts.

[0014] Preferably, the heating temperature is 850~950℃ and the heating time is 200~600s.

[0015] The present invention provides hot-stamped parts prepared by the above-described method, with a contact resistance ≤5mΩ.

[0016] The present invention provides a surface treatment liquid, comprising, by mass parts, 5-30 parts of aqueous resin, 1-60 parts of nano-aluminosilicate and / or modified nano-aluminosilicate, 1-10 parts of surfactant and the balance being water; wherein the nano-aluminosilicate and / or modified nano-aluminosilicate simultaneously contains Si and Al elements.

[0017] The surface treatment liquid provided by this invention, in which nano-aluminosilicate and / or modified nano-aluminosilicate are uniformly dispersed in an aqueous resin as functional substances, is coated on the surface of a hot-formed steel metal coating and dried and cured to obtain a shot-blast-free post-treatment layer, thereby obtaining a steel plate for hot stamping without shot blasting. During the heat treatment of the steel plate for shot blasting-free hot stamping, the aqueous resin, as the dispersed phase, undergoes thermal decomposition and volatilization at high temperatures. Meanwhile, the nano-aluminosilicate and / or modified nano-aluminosilicate, as functional materials, rapidly combine with oxygen elements and undergo cross-linking reactions at high temperatures, forming a long-chain molecular ceramic structure with high molecular weight and high polymerization degree (the nano-aluminosilicate and / or modified nano-aluminosilicate combine with O atoms at high temperatures, forming Al-O-Si chemical bonds through atomic rearrangement, thus forming a long-chain molecule with high polymerization degree). This ceramic structure, with a microporous mesh framework protective layer covering the plate surface, reduces the driving force for the diffusion of elements from the matrix to the coating surface, inhibits the diffusion of elements (such as Mn and Al) from the matrix to the coating surface during heating, and suppresses uneven oxidation on the zinc-based coating surface, reducing the thickness of the oxide layer on the component surface. Simultaneously, the rapidly formed oxide protective layer (including aluminum oxide and silicon oxide) can block the volatilization of low-melting-point liquid zinc during heating, reducing zinc-based coating loss at high temperatures and ensuring the surface quality of the coating during heat treatment. The surface treatment liquid of the present invention is used to form a shot-blast-free post-treatment layer on the surface of zinc-based coated hot stamping steel plates. This can effectively control the uneven diffusion and continuous oxidation process of coating and matrix elements to the surface during the heat treatment of traditional zinc-based coated steel plates, reduce the thickness of the oxide layer on the material surface, and meet the subsequent welding and electrophoresis requirements of the OEM without the need for additional shot blasting, thus saving process and environmental protection costs.

[0018] Furthermore, the surface treatment liquid provided by the present invention also contains a surface lubricant. By introducing the surface lubricant into the post-processing layer without shot blasting, the processing lubrication performance of the steel plate surface can be improved, effectively reducing surface damage to the steel coil during storage, transportation, blanking and other processes.

[0019] In addition, the present invention also has the following beneficial effects: The shot blasting-free treatment liquid provided by this invention uses environmentally friendly water-based resin as the dispersed phase, which has the advantages of easy dispersion, easy spreading, and easy coating. It is suitable for post-treatment equipment of continuous production lines in steel plants without the need for new equipment or production line modifications. The resin, surfactant, and surface lubricant in the shot blasting-free post-treatment layer obtained after drying and curing can volatilize without residue during heat treatment. The Si and Al in nano-aluminosilicate and / or modified nano-aluminosilicate are conventional constituent elements in the hot-formed steel matrix, and no other heavy metals or participating elements are introduced, making it environmentally friendly.

[0020] The steel for hot stamping without shot blasting provided by this invention has a post-treatment layer that can effectively reduce the surface reflectivity of the zinc-based coating, improve the radiation heating efficiency in the heat treatment furnace by about 20%, significantly shorten the heating time when preparing hot stamped parts, reduce production energy costs, and effectively improve production cycle time. Attached Figure Description

[0021] Figure 1 Heating curves of the hot-formed steel with zinc-based coating that is not shot-blasted in Examples 2-3, 5 and 7 and the hot-formed steel in Comparative Example 1 are shown. Figure 2 The electrophoretic coating results of hot-formed steels in Comparative Examples 1-3 after heating at 870℃ for 240s are shown in the figure. Figure 3 The images show the electrophoretic coating results of the shot-blast-free zinc-based coated hot-formed steel in Examples 2-3, 5 and 7 after heating at 870°C for 240 seconds. Figure 4 The electrophoretic coating results of hot-formed steels in Comparative Examples 1-3 after heating at 900℃ for 300s are shown in the figure. Figure 5 The images show the electrophoretic coating results of the zinc-based coated hot-formed steel without shot blasting in Examples 2-3, 5 and 7 after heating at 900°C for 300s. Figure 6 The electrophoretic coating results of hot-formed steels in Comparative Examples 1-3 after heating at 930℃ for 300s are shown in the figure. Figure 7 The images show the electrophoretic coating results of the shot-blast-free zinc-based coated hot-formed steel in Examples 2-3, 5 and 7 after heating at 930°C for 300 seconds. Figure 8 Friction coefficient curves for the shot-blast-free zinc-based coated hot-formed steel of Examples 2-3, 5 and 7 and the hot-formed steel of Comparative Example 1; Figure 9 The image shows the surface microstructure of the zinc-based coated hot-formed steel without shot blasting in Example 2. Figure 10 The image shows the surface microstructure of the zinc-based coated hot-formed steel without shot blasting in Example 3. Figure 11 The image shows the surface microstructure of the zinc-based coated hot-formed steel without shot blasting in Example 5. Figure 12 The image shows the surface microstructure of the zinc-based coated hot-formed steel without shot blasting in Example 7. Figure 13 The image shows the surface microstructure of the hot-formed steel in Comparative Example 1. Figure 14 The image shows the surface microstructure of the hot-formed steel in Comparative Example 2. Figure 15 The image shows the surface microstructure of the hot-formed steel in Comparative Example 3. Detailed Implementation

[0022] The present invention provides a surface treatment liquid, which, in a total mass of 100 parts, comprises 5-30 parts of aqueous resin, 1-60 parts of nano-aluminosilicate and / or modified nano-aluminosilicate, 1-10 parts of surfactant, and the balance being water; wherein the nano-aluminosilicate and / or modified nano-aluminosilicate contains both Si and Al elements.

[0023] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0024] The surface treatment liquid provided by this invention comprises 5 to 30 parts of aqueous resin per 100 parts by total mass, and in specific embodiments, it can be 5, 10, 15, 20, 25, or 30 parts. In this invention, the aqueous resin is preferably one or more of aqueous epoxy resin, aqueous acrylic resin, aqueous alkyd resin, and aqueous polyester resin. In this invention, the aqueous resin serves as a dispersed phase to disperse the nano-silica-alumina components.

[0025] The total mass is 100 parts. The surface treatment liquid provided by the present invention includes 1 to 60 parts of nano-aluminosilicate and / or modified nano-aluminosilicate. In specific embodiments, it can be 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 or 60 parts.

[0026] In this invention, the nano-aluminosilicate is preferably a natural nano-aluminosilicate and / or a synthetic nano-aluminosilicate; the natural nano-aluminosilicate can specifically be one or more of halloysite, attapulgite, diaspore, montmorillonite, kaolinite, palygorskite, and sepiolite; the synthetic nano-aluminosilicate can specifically be one or more of ultrafine aluminum silicate, amorphous aluminum silicate, and zeolite. The modified nano-aluminosilicate is a product obtained by modifying the above-mentioned natural or synthetic nano-aluminosilicates, and the modification methods include, but are not limited to, intercalation modification, carboxyl modification, alkyl modification, or amino modification. In the embodiments of this invention, the nano-aluminosilicate is specifically commercially available nano-modified kaolin.

[0027] In this invention, the preferred mass ratio of Al and Si elements in the nano-aluminosilicate and / or modified nano-aluminosilicate, calculated as Al2O3 and SiO2 respectively, is (0.5~10):1. In specific embodiments, it can be 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1. The conventional heat treatment temperature for zinc-based coated hot-formed steel is 850~950℃. The thermal stability of simple alumina or silicon dioxide is insufficient to maintain the stability of oxides above 700℃. This invention uses nano-aluminosilicate and / or modified nano-aluminosilicate, which still exhibit good thermal stability at high temperatures of 800~1000℃.

[0028] In this invention, the nano-aluminosilicate and / or modified nano-aluminosilicate, as functional materials, can rapidly combine with oxygen and undergo cross-linking reactions under high-temperature conditions to form a long-chain molecular ceramic structure with high molecular weight and high degree of polymerization. This ceramic structure covers the surface of the plate with a mesh-like framework of micropores, inhibiting the diffusion of elements (Mn, Al, etc.) from the matrix to the coating surface and the uneven oxidation on the zinc-based coating surface during heating, thus reducing the thickness of the oxide layer on the surface of the parts. At the same time, the rapidly formed oxide protective layer (including aluminum oxide and silicon oxide) can block the volatilization of low-melting-point liquid zinc during heating, reduce the loss of the zinc-based coating at high temperatures, and ensure the surface quality of the coating during heat treatment. Al and Si are oxygen-loving elements that can rapidly combine with oxygen and react to form a protective layer. Applying the surface treatment solution to the steel plate surface in advance can effectively reduce the element concentration difference between the coating surface and the matrix, reduce the driving force for the diffusion of elements from the matrix to the coating surface, and thus achieve the purpose of inhibiting excessive oxidation of elements on the surface. This invention utilizes nano-aluminosilicates and / or modified nano-aluminosilicates. Silicon and aluminum are common elements in hot-formed steel matrices, and no other heavy metals or impurities are introduced, making it environmentally friendly. Furthermore, the nano-silicon-aluminum components do not react with the zinc-based coating, eliminating the risk of damaging the zinc layer's grain boundaries.

[0029] The surface treatment liquid provided by this invention comprises 1 to 10 parts of surfactant, based on a total mass of 100 parts. In specific embodiments, the amounts can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 parts. In this invention, the surfactant preferably includes one or more of organosilicon surfactants, polyether block surfactants, and polyacrylate surfactants. This invention does not specifically limit the type of surfactant; organosilicon surfactants, polyether block surfactants, and polyacrylate surfactants well-known in the art are all acceptable. For example, the organosilicon surfactant can specifically be a polysiloxane surfactant, the polyether block surfactant can specifically be a block copolymer of ethylene oxide and propylene oxide, and the polyacrylate surfactant can specifically be a vinylpyridine copolymer of acrylate. In this invention, the surfactant's function is to balance the aqueous resin, promote the uniform dispersion of the nano-silica-alumina component in the aqueous resin, and prevent its aggregation.

[0030] The total mass is 100 parts. The surface treatment liquid provided by this invention preferably also includes 1 to 10 parts of a surface lubricant, and in specific embodiments, this can be 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 parts. In this invention, the surface lubricant preferably includes one or more of polyethylene wax, oxidized polyethylene wax, polypropylene wax, oxidized polypropylene wax, and polytetrafluoroethylene wax. In this invention, the surface lubricant can improve the processing lubrication performance of the steel plate surface and effectively reduce surface damage to steel coils during storage, transportation, and blanking processes.

[0031] The surface treatment solution provided by this invention, in units of 100 parts by weight, includes water as the remainder. In this invention, the water is preferably pure water.

[0032] This invention does not impose special requirements on the preparation method of the surface treatment liquid; the components can be directly mixed evenly. In an embodiment of this invention, the aqueous resin is first dispersed in water and stirred for the first time. Then, nano-aluminosilicate and / or modified nano-aluminosilicate are added and stirred for the second time. Finally, the remaining components are added and stirred for the third time to obtain the surface treatment liquid. In this invention, the stirring time for each stirring step is sufficient to achieve uniform dispersion.

[0033] The present invention provides a hot-formed steel for hot stamping that does not require shot blasting, comprising a hot-formed steel substrate, a zinc-based coating attached to the surface of the hot-formed steel substrate, and a post-treatment layer for which shot blasting is not required coated on the surface of the zinc-based coating; the post-treatment layer for which shot blasting is not required is formed by drying and curing the surface treatment liquid described in the above scheme.

[0034] In this invention, the preferred chemical element composition of the hot-formed steel matrix is: C 0.05~0.4wt%, Si≤1.3wt%, Mn 0.5~2.2wt%, Cr≤1.5wt%, Mo≤0.5wt%, Ni≤0.5wt%, Ti≤0.04wt%, Nb≤0.2wt%, V≤0.2wt%, B 0.002~0.006wt%, P≤0.020wt%, S≤0.003wt%, Al≤0.8wt%, N≤0.006wt%, with the balance being Fe.

[0035] The present invention does not have any special requirements for the zinc-based coating. Any zinc-based coating well known in the art is acceptable, such as a pure zinc coating, a zinc-iron alloy coating, or a zinc-aluminum-magnesium coating.

[0036] The present invention does not impose a special limitation on the thickness of the zinc-based coating; any thickness known in the art is acceptable. In the present invention, the preferred single-sided mass of the zinc-based coating is 30~120 g / m². 2 In specific embodiments, the concentration can be 30, 50, 70, 90, 100, or 120 g / m³. 2 .

[0037] In this invention, the single-sided dry film weight of the shot-blasting-free post-treatment layer is preferably 0.1~3 g / m³. 2 In specific embodiments, the concentration can be 0.1, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.3, 2.5, 2.8, or 3 g / m³. 2 In this invention, the post-treatment layer without shot blasting is formed by drying and curing the aforementioned surface treatment liquid; the drying and curing temperature is preferably 80~120℃, and in specific embodiments it can be 80, 90, 100, 110 or 120℃. The drying and curing is preferably achieved by hot air drying. This invention does not impose a special limitation on the drying and curing time, as long as the surface treatment liquid is completely dry.

[0038] In this invention, the surface of the hot-formed steel contains Al and Si elements, wherein the mass percentage of Si element is not higher than 65%, preferably 0.1~65%, and in specific embodiments it can be 5%, 8%, 18%, 20%, 25%, 30%, 35%, 40%, 42%, 45%, 50%, 55% or 60%.

[0039] The present invention provides a method for preparing the hot-formed steel for hot stamping without shot blasting as described above, comprising the following steps: coating a surface treatment liquid on the surface of a hot-formed steel substrate with a zinc-based coating, and then drying and curing to obtain the hot-formed steel for hot stamping without shot blasting.

[0040] The present invention does not have any special requirements for the coating method; any coating method well known in the art is acceptable, such as spraying or roller coating.

[0041] This invention provides a shot-blast-free preparation method for hot-stamped parts, comprising the following steps: heating the above-mentioned hot-stamping shot-blast-free hot-forming steel to AC3 or above, and after complete austenitization, transferring it to a hot-stamping die for forming, holding pressure, and quenching, without shot blasting, to obtain the hot-stamped parts.

[0042] In this invention, AC3 refers to the lowest heating temperature at which steel is continuously heated from room temperature, and the internal ferrite structure is completely transformed into austenite structure, forming a single uniform austenite phase.

[0043] In this invention, the heating temperature is preferably 850~950℃, and the heating time is preferably 200~600s; in specific embodiments, the heating temperature can be 850, 870, 900, 920, or 950℃; and the heating time can be 200, 300, 400, 500, or 600s. Conventional zinc-based coatings have a boiling point of 908℃, and the heating temperature is not higher than 910℃. This invention, by constructing a post-shot blasting layer, broadens the heat treatment temperature window. Furthermore, zinc-based coatings, due to their smooth surface, high reflectivity, and low thermal radiation coefficient, have insufficient heat absorption efficiency in the early stages of heating, resulting in a slow heating rate. Conventional heating of the substrate to above AC3 requires at least 300s, while this invention can achieve a heating time of less than 300s, specifically 200~600s. In this invention, the heating time refers to the time interval from when the sheet enters the heating furnace to when it exits the furnace. During the process of heating the hot-formed steel for hot stamping of the present invention to AC3, the heating rate can reach 5~15℃ / s in the stage of heating to 500℃, and the heating rate can reach 2~8℃ / s in the stage of heating from 500℃ to the austenitizing temperature.

[0044] This invention does not have special requirements for the forming process; a well-known hot bath forming process can be used. Specifically, the lower die of the hot stamping mold is placed in a water tank filled with hot water, a high-temperature hot bath medium. Partial or complete immersion of the lower die surface in the hot water allows the part to complete the forming process within the hot bath medium. This invention also does not have special requirements for the pressure holding and quenching processes and conditions; conventional operations can be followed.

[0045] The present invention provides hot-stamped parts prepared by the above-described method, with a contact resistance ≤5mΩ.

[0046] In this invention, the surface of the hot-stamped parts has an oxide layer; the oxide layer is generated by the chemical reaction of the metal elements on the coating surface and the post-treatment layer without shot blasting with oxygen elements in the air at a high temperature.

[0047] In this invention, the oxide layer preferably comprises zinc oxide products, zinc-manganese composite oxide products, and aluminum oxide products. The Zn element in the oxide layer originates from the zinc-based plating layer, and the Mn element originates from the substrate, diffusing to the surface during heating; the Al element mainly originates from the post-treatment layer without shot blasting. The oxide layer formed by this invention has a uniform composition, with minimal differences in elemental composition at different locations on the surface, meeting the requirements for subsequent welding and electrophoretic coating even without shot blasting. In this invention, the thickness of the oxide layer preferably does not exceed 3 μm.

[0048] The following detailed description, in conjunction with embodiments, of the surface treatment liquid, shot-blast-free hot stamping steel plate, hot stamping parts, and their preparation methods provided by the present invention, should not be construed as limiting the scope of protection of the present invention.

[0049] In the following examples, the waterborne acrylic resin / waterborne epoxy resin / waterborne polyurethane resin used were purchased from Wanhua Chemical. The nano-modified kaolin (20000 mesh, Xintu Mineral Products Co., Ltd.), halloysite nanotubes, ultrafine aluminum silicate (Maclean reagent), polysiloxane surfactant (WANALYST® SC703, Wanhua Chemical), acrylic block polymer (Dispex® Ultra PX 4585, BASF), polyethylene wax / polypropylene wax (Keim-Additec, Germany), and nano alumina were all commercially available.

[0050] Example 1 This embodiment provides a surface treatment liquid for zinc-based coated hot-formed steel that does not require shot blasting. Based on a total mass of 100 parts, it includes: 30 parts of water-based acrylic resin, 35 parts of nano-modified kaolin (calculated as oxides, with an Al2O3 to SiO2 mass ratio of 2:1), 3 parts of polysiloxane surfactant, and 2 parts of polyethylene wax as a lubricant, with the remainder being pure water.

[0051] The preparation method is as follows: add waterborne acrylic resin to pure water at room temperature (no need to adjust pH, pH is about 6) and stir thoroughly for 15 minutes. Then add nano-modified kaolin, stir at a speed of not less than 300 rpm and stir thoroughly for 30 minutes. After thorough dispersion, add polysiloxane surfactant and polyethylene wax and stir for 30 minutes to obtain surface treatment liquid.

[0052] Example 2 In this embodiment, the surface treatment liquid from Example 1 was applied to the surface of zinc-based coated hot-formed steel (1500MPa level, AC3 at 840℃) by roller coating. After hot air drying, zinc-based coated hot-formed steel without shot blasting was obtained. During drying, the strip speed was 90m / min, the plate temperature was 100℃, and the dry film weight of the coating on one side after drying was 0.5g / m². 2 The Si element mass percentage on the coating surface is 20%.

[0053] Example 3 In this embodiment, the surface treatment liquid from Example 1 was applied to the surface of zinc-based coated hot-formed steel (1500MPa level, AC3 at 840℃) by roller coating. After hot air drying, zinc-based coated hot-formed steel without shot blasting was obtained. During drying, the strip speed was 65m / min, the plate temperature was 100℃, and the dry film weight of the coating on one side after drying was 1g / m². 2 The Si content on the coating surface is 42% by mass.

[0054] Example 4 This embodiment provides a surface treatment liquid for zinc-based coated hot-formed steel that does not require shot blasting. Based on a total mass of 100 parts, it comprises: 25 parts water-based epoxy resin, 20 parts halloysite nanotubes (calculated as oxides, with an Al2O3 to SiO2 mass ratio of 1:1), 2 parts polysiloxane surfactant, and 4 parts polyethylene wax as a lubricant; the remainder is pure water. The preparation method of the surface treatment liquid is the same as in Example 1.

[0055] Example 5 In this embodiment, the surface treatment liquid from Example 4 was applied to the surface of zinc-based coated hot-formed steel (1500MPa level, AC3 at 840℃) by roller coating. After hot air drying, zinc-based coated hot-formed steel without shot blasting was obtained. During drying, the strip speed was 75m / min, the plate temperature was 90℃, and the dry film weight of the coating on one side after drying was 0.8g / m². 2 The Si element mass percentage on the coating surface is 18%.

[0056] Example 6 This embodiment provides a surface treatment liquid for zinc-based coated hot-formed steel that does not require shot blasting. By weight, it comprises: 10 parts waterborne polyurethane resin, 55 parts ultrafine aluminum silicate (calculated as oxides, with an Al2O3 to SiO2 mass ratio of 5:1), 2 parts acrylic block polymer as a surfactant, and 4 parts polypropylene wax as a lubricant; the remainder is pure water. The preparation method of the surface treatment liquid is the same as in Example 1.

[0057] Example 7 In this embodiment, the surface treatment liquid from Example 6 was applied to the surface of zinc-based coated hot-formed steel (1500MPa level, AC3 at 840℃) by roller coating. After hot air drying, zinc-based coated hot-formed steel without shot blasting was obtained. During drying, the strip speed was 80m / min, the plate temperature was 95℃, and the dry film weight of the coating on one side after drying was 1.2g / m². 2 The Si element content on the coating surface is 8% by mass.

[0058] Comparative Example 1 Compared with Examples 2-3, this comparative example omits the post-treatment coating and is a conventional zinc-based coated hot-formed steel (1500MPa level, AC3 is 840℃).

[0059] Comparative Example 2 This comparative example provides a surface treatment liquid for zinc-based coated hot-formed steel that does not require shot blasting. It does not use nano-aluminosilicate or modified nano-aluminosilicate. Based on a total mass of 100 parts, it specifically includes: 50 parts of water-based acrylic resin, 3 parts of acrylic block polymer as a surfactant, and 2 parts of polyethylene wax as a lubricant, with the remainder being pure water.

[0060] The above-mentioned surface treatment liquid was applied to the surface of zinc-based coated hot-formed steel (1500MPa level, AC3 at 840℃) by roller coating. After hot air drying, zinc-based coated hot-formed steel without shot blasting was obtained. During drying, the strip speed was 70m / min, the plate temperature was 100℃, and the dry film weight of the coating on one side after drying was 0.8g / m². 2 .

[0061] Comparative Example 3 This comparative example provides a surface treatment liquid for zinc-based coated hot-formed steel that does not require shot blasting. The only difference from Example 1 is that the nano-modified kaolin is replaced with nano-alumina. Based on a total mass of 100 parts, it specifically includes: 30 parts of water-based acrylic resin, 35 parts of nano-alumina, 3 parts of polysiloxane surfactant as a surfactant, and 2 parts of polyethylene wax as a lubricant, with the remainder being pure water.

[0062] The above-mentioned surface treatment solution was applied to the surface of zinc-based coated hot-formed steel (1500MPa level, AC3 at 840℃) by roller coating. After hot air drying, zinc-based coated hot-formed steel without shot blasting was obtained. During drying, the strip speed was 70m / min, the plate temperature was 100℃, and the dry film weight of the coating on one side after drying was 0.6g / m². 2 .

[0063] Performance testing: The sheet metals from Examples 2-3, 5, and 7, as well as Comparative Example 1, were placed in an 890°C box furnace and connected to thermocouples. The furnace temperature rise rate of the sheet metals was tested, and the heating curves are shown below. Figure 1 As shown. By Figure 1 It can be seen that the heating rate of Examples 2-3, 5 and 7 is significantly higher than that of Comparative Example 1. This is because the shot-blast-free coating can effectively reduce the surface reflectivity of the zinc-based coating, thereby improving the heating efficiency.

[0064] The sheet metals from Examples 2-3, 5, and 7, and Comparative Examples 1-3, were placed in a box-type heating furnace and treated with different heat treatment processes followed by quenching. The mechanical properties of the steel sheets were tested, as well as the contact resistance data of the welded surfaces and the electrophoretic quality between the heat-treated sheets. The mechanical property testing followed the standard GB / T 228.1-2010 "Metallic materials, tensile testing—Part 1: Tests at room temperature." The weld contact resistance testing method followed ISO 18594-2007 "Resistance spot welding, resistance projection welding and resistance gap welding—Determination of transition resistance in aluminum and steel materials." The electrophoretic quality testing method followed JB / T10242-2013 "General Technical Specification for Cathodic Electrophoretic Coating." The results are summarized in Table 1, and the electrophoretic coating result diagram is shown below. Figures 2-7 , Figure 2 The electrophoretic coating results of hot-formed steels in Comparative Examples 1-3 after heating at 870℃ for 240s are shown in the figure. Figure 3The images show the electrophoretic coating results of the shot-blast-free zinc-based coated hot-formed steel in Examples 2-3, 5 and 7 after heating at 870°C for 240 seconds. Figure 4 The electrophoretic coating results of hot-formed steels in Comparative Examples 1-3 after heating at 900℃ for 300s are shown in the figure. Figure 5 The images show the electrophoretic coating results of the zinc-based coated hot-formed steel without shot blasting in Examples 2-3, 5 and 7 after heating at 900°C for 300s. Figure 6 The electrophoretic coating results of hot-formed steels in Comparative Examples 1-3 after heating at 930℃ for 300s are shown in the figure. Figure 7 The images show the electrophoretic coating results of the zinc-based hot-formed steel without shot blasting in Examples 2-3, 5 and 7 after heating at 930°C for 300 seconds.

[0065] Table 1 shows the mechanical properties, welding resistance, and electrophoretic quality of Examples 2-3, 5, 7, and Comparative Examples 1-3.

[0066] In Table 1, ○, △, and × represent excellent, qualified, and poor electrophoresis quality, respectively. Welding requirements are met when the welding contact resistance is ≤5mΩ and the tensile strength standard is 1300~1700MPa.

[0067] As shown in Table 1, although the plates in Examples 2-3, 5, and 7 were not shot-blasted, their contact resistance was ≤5mΩ, meeting the welding requirements, and their electrophoresis quality was also qualified. Comparative Examples 1-3 could not simultaneously meet the requirements of qualified electrophoresis quality and contact resistance less than 5mΩ; the tensile strength of Comparative Examples 1-3 was unqualified (less than 1300MPa) under the 870℃ heating process for 240s.

[0068] The sheet metals of Examples 2, 3, 5, and 7, and Comparative Example 1, in their supplied state (untreated), were characterized using a friction testing machine to determine their surface friction coefficients. The friction coefficient curves are shown in the figure. Figure 8 The data is shown in Table 2.

[0069] Table 2 shows the average coefficients of friction for Examples 2-3, 5, 7 and Comparative Example 1.

[0070] As shown in Table 2, by constructing a shot-blast-free post-treatment layer and introducing a surface lubricant into the post-treatment layer, the present invention can improve the processing lubrication performance of the steel plate surface and effectively reduce surface damage to the steel coil during storage, transportation, blanking and other processes.

[0071] The sheet metals from Examples 2-3, 5, and 7, and Comparative Examples 1-3, were placed in an 890℃ box furnace and heated for 300 seconds. After quenching, the surface microstructure of the heated sheet metals was observed using a scanning electron microscope. The results are as follows: Figures 9-15As shown, the surface of the example is covered with a continuous, clustered zinc oxide layer, which is uniform and free of other oxide components, proving that the post-treatment coating can effectively improve the uniformity of the oxide layer on the surface of the material after heat treatment. The comparative example, however, has a small or partial distribution of clustered zinc oxide on its surface, with other flat areas consisting of an Al oxide layer. This uneven surface oxide layer affects the surface quality of the electrophoretic coating and the uniformity of the surface contact resistance. Using a scanning electron microscope at 200x magnification, five points were taken every 100 μm from the left to the right of the center line of the field of view for elemental EDS point scanning. The elemental content results are shown in Table 3. The difference between the minimum and maximum content of each element was calculated and recorded as the maximum difference, as listed in Table 3.

[0072] Table 3. Surface oxide layer composition test results for Examples 2-3, 5, 7 and Comparative Examples 1-3

[0073] As shown in Table 3, the content of the same element at different locations on the surface of the hot-formed steel in Examples 2-3, 5, and 7 varies little. Taking the Zn element distribution in Example 2 as an example, the maximum difference in Zn element content at different locations is only 4.7 wt%, proving that the oxide layer on its surface is uniformly distributed. In contrast, the distribution of the same element at different locations on the surface of the hot-formed steel in Comparative Examples 1-3 varies greatly, indicating that the oxide layer is not uniformly distributed.

[0074] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A surface treatment liquid, characterized in that, The total mass, in units of 100 parts, includes 5-30 parts of water-based resin, 1-60 parts of nano-aluminosilicate and / or modified nano-aluminosilicate, 1-10 parts of surfactant, and the balance being water; the nano-aluminosilicate and / or modified nano-aluminosilicate simultaneously contain Si and Al elements.

2. The surface treatment liquid according to claim 1, characterized in that, It also includes 1 to 10 parts of surface lubricant.

3. The surface treatment liquid according to claim 1 or 2, characterized in that, The mass ratio of Al and Si elements in the nano-aluminosilicates and / or modified nano-aluminosilicates, calculated as Al2O3 and SiO2 respectively, is (0.5~10):

1.

4. A type of hot-formed steel for hot stamping that does not require shot blasting, characterized in that, It includes a hot-formed steel substrate, a zinc-based coating attached to the surface of the hot-formed steel substrate, and a shot-blast-free post-treatment layer coated on the surface of the zinc-based coating; the shot-blast-free post-treatment layer is formed by drying and curing the surface treatment liquid according to any one of claims 1 to 3.

5. The hot-formed steel for hot stamping without shot blasting according to claim 4, characterized in that, The single-sided dry film weight of the shot-blasting-free post-treatment layer is 0.1~3 g / m³. 2 .

6. The hot-formed steel for hot stamping without shot blasting according to claim 4, wherein the surface of the hot-formed steel contains Al and Si elements, wherein the mass percentage of Si element is not higher than 65%.

7. The hot-formed steel for hot stamping without shot blasting according to claim 4, characterized in that, The drying and curing temperature is 80~120℃.

8. A method for preparing hot-stamped parts without shot blasting, characterized in that, The process includes the following steps: heating the hot-formed steel for hot stamping without shot blasting as described in any one of claims 4 to 7 to AC3 or higher, and after complete austenitization, transferring it to a hot stamping die for forming, pressure holding, and quenching, without shot blasting, to obtain the hot-stamped parts.

9. The preparation method according to claim 8, characterized in that, The heating temperature is 850~950℃, and the heating time is 200~600s.

10. The hot-stamped part prepared by the method according to any one of claims 8 to 9, characterized in that, Contact resistance ≤ 5mΩ.

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