Anti-decarburization coating, preparation method thereof, anti-decarburization coating and application of anti-decarburization coating

Abstract

The invention discloses an anti-decarburization coating and a preparation method thereof, an anti-decarburization coating and application, and relates to the technical field of coatings, the anti-decarburization coating comprises the following material components by mass: 36 to 38 wt% of SiO2, 7 to 10 wt% of B2O3, 7 to 10 wt% of Al2O3, 0.9 to 1.2 wt% of MgO, 0.1 to 1.3 wt% of CaO, 8 to 10 wt% of Fe2O3, 6 to 8 wt% of Na2O, 1 to 3 wt% of K2O, 0.1 to 0.5 wt% of graphite, and the balance of water glass. The anti-decarburization coating provided by the invention is applied to the preparation process of the steel product, so that the double effects of oxidation decarburization resistance and surface active recarburization can be simultaneously realized in the hot working process of the steel product, and the surface quality and fatigue performance of the steel product can be further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coatings, in particular to a decarburization-preventing coating, a preparation method thereof, a decarburization-preventing coating layer and applications. BACKGROUND

[0002] Steel products are prone to oxidation decarburization during heat treatment and rolling, which seriously damages the surface quality of the steel products. The presence of decarburized layer, especially full decarburized layer, can reduce the fatigue performance of the steel products by more than 50%, and further cause early fatigue fracture of the steel products during service. Therefore, inhibiting the oxidation decarburization of steel products during hot working has become a key research direction in the field of steel product manufacturing. At present, two means are mainly adopted, i.e., raw material alloying and decarburization-preventing coating. The former enhances the anti-decarburization ability by adding alloying elements such as Ni, Mo and Cr to improve the oxidation resistance, but significantly increases the material cost; the latter has become the mainstream technology widely used in industry due to its better economy and feasibility.

[0003] Among various high-temperature anti-oxidation coatings, glass-ceramic-based coatings have been widely used in industrial production due to low raw material cost and simple preparation process, and can effectively reduce the oxidation and decarburization on the surface of steel parts in the range of 700-1000℃. However, nano-coatings and composite coatings are still in the laboratory research stage due to high cost and complex process. In recent years, a number of patents have proposed different types of protective coatings, such as CN 118359948A which provides a protective coating for high manganese steel with excellent oxidation resistance, decarburization resistance and crack resistance; CN 117736597A uses a double-layer coating structure to control the decarburization and oxidation defects of high-carbon steel; and CN 119752225A develops a decarburization-preventing coating which can be quickly solidified and low-temperature glazing. However, these coatings all focus on isolating oxygen diffusion to inhibit decarburization, and do not achieve active carbonation on the surface of steel, thus having limitations in improving the existing decarburized layer.

[0004] In actual production, the surface of spring flat steel supplied by the steel plant usually has a decarburized layer of about 0.2 mm, and the depth often meets the requirements of GB / T 1222 standard (the decarburized layer depth of general spring steel is not less than 1.2% of the thickness, and that of silicon spring steel is not less than 1.6%). The decarburized layer may further intensify during subsequent hot rolling or heat treatment, and even form a full decarburized layer, which seriously reduces the fatigue life of the leaf spring. Although the existing protective coating can inhibit the decarburization process to some extent, it cannot compensate the carbon in the surface decarburized area, and therefore cannot fundamentally improve the decarburized layer depth.

[0005] Therefore, there is an urgent need for a new functional coating which can simultaneously achieve the dual effects of anti-oxidation decarburization and active surface carbonation during the hot working of steel products. SUMMARY

[0006] The application provides a decarburization-preventing coating, a preparation method thereof, a decarburization-preventing coating layer and application. The decarburization-preventing coating is applied to the preparation process of a steel product, and can realize the double effects of anti-oxidation decarburization and surface active recarburization during the hot working process of the steel product, thereby improving the surface quality and fatigue performance of the steel product.

[0007] In a first aspect, the application provides a decarburization-preventing coating, which comprises the following material components in mass percentage: SiO2: 36-38 wt%, B2O3: 7-10 wt%, Al2O3: 7-10 wt%, MgO: 0.9-1.2 wt%, CaO: 0.1-1.3 wt%, Fe2O3: 8-10 wt%, Na2O: 6-8 wt%, K2O: 1-3 wt%, graphite: 0.1-0.5 wt%, and the balance is water glass.

[0008] In some embodiments, the particle size of the decarburization-preventing coating is 100-300 mesh.

[0009] In a second aspect, the application provides a preparation method of the decarburization-preventing coating of the first aspect, comprising: part of SiO2 and a liquid medium are first mixed, and then crushed to obtain a crushed standby material; the crushed standby material, another part of SiO2, B2O3, Al2O3, MgO, CaO, Fe2O3, Na2O, K2O, graphite and water glass are second mixed to obtain the decarburization-preventing coating.

[0010] In some embodiments, the liquid medium comprises dehydrated oil.

[0011] In some embodiments, the second mixing time is 30-60 min.

[0012] In a third aspect, the application provides a decarburization-preventing coating layer, which is obtained by curing the decarburization-preventing coating of the first aspect or the decarburization-preventing coating obtained by the preparation method of the second aspect.

[0013] In a fourth aspect, the application provides a steel product, wherein the surface of a steel blank is coated with the decarburization-preventing coating layer of the third aspect before heat treatment of the steel blank or before rolling of the steel blank during the preparation process of the steel product.

[0014] In some embodiments, the steel product comprises a steel plate spring.

[0015] In some embodiments, the heat treatment comprises quenching, the temperature of the quenching is 820-930 ℃, the holding time is 60-120 min, and nitrogen gas is introduced as a protective atmosphere to reduce the oxygen partial pressure during the quenching.

[0016] In some embodiments, the rolling temperature is 950-1050℃, the holding time is 60-120min, and nitrogen is introduced as a protective atmosphere during the rolling to reduce the oxygen partial pressure.

[0017] In some embodiments, the billet is further subjected to a dephosphorization treatment before being rolled.

[0018] Compared with the prior art, the above technical solutions provided by the embodiments of the present application have the following advantages: (1) The anti-decarburization coating provided by the present application is formed by precisely matching and synergistically acting the components of the materials, and is coated on the surface of the steel product to form a protective coating. The coating can simultaneously achieve the dual functions of anti-oxidation decarburization and surface active recarburization during the hot working process of the steel product, thereby improving the surface quality of the steel product and enhancing its fatigue performance. Practical application shows that the surface decarburization layer depth of the steel plate spring treated by the coating can be reduced by more than 90%, and the fatigue life can be increased by 100%.

[0019] (2) SiO2 and Al2O3 can form a dense mullite structure at high temperatures, effectively blocking the invasion of oxygen, thereby significantly inhibiting the oxidation and decarburization of the steel surface. In addition, SiO2 can also improve the mechanical strength and chemical stability of the coating, preventing the coating from cracking. Further, the content of SiO2 is limited to between 36-38wt%, and too high SiO2 content may lead to sintering difficulty, decreased corrosion resistance, or increased sintering temperature. When the content of SiO2 is too high, due to the large difference in the thermal expansion coefficient between Al2O3 and SiO2, stress concentration will occur, resulting in coarse cracks and reducing the thermal shock resistance of the coating. If the content of SiO2 is too low, it may affect the formation and density of the mullite structure. Therefore, the content of SiO2 needs to be within a certain range to balance the material properties. The content of Al2O3 is limited to between 7-10wt%, and too high Al2O3 content may lead to sintering difficulty, excessive grain growth, or decreased density. If the content of Al2O3 is too low, it may affect the formation and performance of mullite. Therefore, the content of Al2O3 needs to be within a certain range to balance the material properties.

[0020] (3) B2O3 can reduce the chemical and corrosion activity of alkaline oxides (such as Na2O and K2O) in the coating, and melt to form a vitreous viscous liquid at high temperature, which tightly covers the surface of the billet and isolates it from the oxidizing atmosphere. Further, the content of B2O3 is limited to between 7-10wt%, and too high or too low content of B2O3 will affect the melting property and chemical corrosion resistance of the glass. If the content of B2O3 is too low, the flowability of the glass phase is poor, and micro-pores and cracks are easily formed in the coating, resulting in a decrease in the density of the coating and poor adhesion of the coating. If the content of B2O3 is too high, the viscosity of the glass phase is too low, and micro-cracks are easily formed during the cooling process, resulting in stress concentration in the coating and increasing the risk of cracking, and the thermal shock stability and adhesion are decreased. The content of Na2O is limited to between 6-8wt%, and when the content of Na2O is too low, the melting acceleration effect of the glass is poor; and when the content of Na2O is too high, the durability of the glass is decreased. The content of K2O is limited to between 1-3wt%, which is economical, and if the content of K2O is too high, it may inhibit the formation of lithium silicate, affecting the performance of the product.

[0021] (4) MgO not only increases the melting temperature of the coating, but also enhances the density of the coating by generating spinel structures such as MgAl 0.6 Fe 1.4 O4 and MgFe2O4, inhibits the oxidation and diffusion of iron elements, reduces oxidation loss, and makes the coating easy to peel off after cooling. Further, the content of MgO is limited to between 0.9-1.2wt%, and when the content of MgO is too high, the thermal expansion coefficient decreases and the thermal shock resistance of the coating is poor; and when the content of MgO is too low, the density of the coating is poor and it may not effectively prevent oxidation, resulting in a decrease in the performance of the coating.

[0022] (5) The addition of CaO improves the flowability and wettability of the glass liquid phase at high temperature, ensuring uniform coating of the coating on the surface of the steel. Further, the content of CaO is limited to between 0.1-1.3wt%, and when the content of CaO is too high, the glass may easily crystallize and the thermal expansion coefficient increases, resulting in easy peeling of the coating; and when the content of CaO is too low, it is difficult to play its role in reducing viscosity, improving melting property and controlling thermal expansion coefficient.

[0023] (6) Fe2O3 helps to adjust the viscosity and solidification temperature of the coating, further optimizing its wetting and covering performance. Further, the content of Fe2O3 is limited to between 8-10wt%, and when the content of Fe2O3 is too low, the covering performance of the coating is poor; and when the content of Fe2O3 is too high, the coating has more bubbles and the ability to prevent oxygen from entering is reduced.

[0024] (7) The graphite added in the coating serves as a high-temperature carburant, which can provide a carbon source to the surface of the leaf spring at 1000°C or below, actively carburate the decarburized area, fundamentally reduce the decarburization tendency, and make up for the deficiency of the traditional protective coating which can only isolate oxygen but cannot compensate for the loss of carbon. Further, the content of the graphite is limited to 0.1-0.5wt%, when the content of the graphite is too low, the carburating effect cannot be achieved; when the content of the graphite is too high, the mixing of the coating is difficult, and the uniformity is poor. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0026] Figure 1 A comparison chart showing the total decarburized layer chart of the present application comparative example 1 (a) without anti-decarburization coating after heat treatment and the total decarburized layer chart of example 1 (b) with anti-decarburization coating after heat treatment is shown.

[0027] Figure 2 A comparison chart showing the total decarburized layer chart of the present application comparative example 2 (a) without anti-decarburization coating after heat treatment and the total decarburized layer chart of example 2 (b) with anti-decarburization coating after heat treatment is shown.

[0028] Figure 3 A comparison chart showing the total decarburized layer chart of the present application comparative example 3 (a) without anti-decarburization coating after heat treatment and the total decarburized layer chart of example 3 (b) with anti-decarburization coating after heat treatment is shown. DETAILED DESCRIPTION

[0029] In order to make the person skilled in the art better understand the present application, the technical solutions in the embodiments of the present application are described clearly and completely. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0030] Spring steel will be oxidized and decarburized during heat treatment and rolling, which seriously affects the surface quality of the leaf spring. The existence of the decarburized layer, especially the total decarburized layer, will cause the fatigue performance of the leaf spring to decrease by more than 50%, resulting in fatigue fracture of the leaf spring during use. Therefore, reducing the oxidation and decarburization of spring steel during heat treatment and rolling is a research hotspot in the production process of leaf springs.

[0031] Currently, the main measures include raw material alloying and anti-decarburization coatings. Raw material alloying involves adding a large amount of alloying elements, such as Ni, Mo, and Cr, to the steel to improve its oxidation resistance. However, because the addition of alloying elements significantly increases the cost of raw materials, anti-decarburization coatings are currently more commonly used for high-temperature oxidation and decarburization protection. There are many types of commonly used high-temperature anti-oxidation coatings, mainly divided into: glass-ceramic materials, nanomaterials, and composite coating materials. Nanomaterials and composite material coatings are still largely in the research stage due to their high material costs and complex manufacturing processes. Glass-ceramic materials are widely used in industrial production due to their low raw material costs and simple manufacturing processes. Ceramic materials have excellent high-temperature performance and are commonly used high-temperature anti-decarburization coatings for steel. They can reduce oxidation and decarburization on the surface of parts within a temperature range of 700-1000℃.

[0032] CN 118359948A – "High-Temperature Anti-Oxidation, Anti-Decarburization, and Anti-Cracking Protection for High-Manganese Steel" describes a high-temperature anti-oxidation, anti-decarburization, and anti-cracking protective coating for high-manganese steel and its preparation method. The technical solution involves uniformly mixing α-Al₂O₃ micro powder, fused magnesia fine powder, potassium feldspar fine powder, manganese oxide powder, iron oxide powder, boron carbide powder, and lanthanum oxide powder to obtain a composite powder. Metakaolin and silica micro powder are mixed, and NaOH and KOH solutions are added and mixed. The resulting mixture is placed in a plastic container, stirred, and deionized water is added, followed by water bath stirring to obtain an aluminosilicate gel. The aluminosilicate gel, styrene-acrylic emulsion, deionized water, and silane coupling agent are mixed and stirred in a water bath to obtain a high-strength binder. The composite powder and high-strength binder are mixed evenly and stirred to obtain a high-temperature anti-oxidation, anti-decarburization, and anti-cracking protective coating for high-manganese steel. The coating produced by this patent, when applied to high-manganese steel, exhibits excellent high-temperature oxidation resistance, a thin decarburized layer, and superior crack resistance, meeting the protection requirements during the heat treatment process of high-manganese steel. However, this patent does not provide a surface carburizing effect.

[0033] CN 117736597 A-"High-carbon steel anti-decarburization coating structure and high-carbon steel decarburization and surface oxidation defect control method", discloses a high-carbon steel anti-decarburization coating structure, including a first coating and a second coating coated on the surface of the steel material in turn, the first coating includes mass percentage components: graphite powder 40%~60%, alumina powder 20%~40%, zinc oxide powder 10%~20% and binder 5%~20%, the second coating includes mass percentage components: alumina powder 40%~60%, silicon oxide powder 30%~50% and binder 5%~20%. The application also discloses a high-carbon steel heat treatment method for controlling decarburization and surface oxidation defects, after the first coating and the second coating are coated on the surface of the workpiece and dried, quenching treatment is carried out, the surface coating is removed after cooling to room temperature, and then tempering treatment is carried out. The application can effectively control the decarburization and oxidation problems on the surface of high-carbon steel. However, the patent process is complex, requires two coatings, and has no surface carbon enrichment effect.

[0034] CN 119752225A-"High-carbon steel anti-decarburization coating and its preparation method and application". The coating of the patent application includes the following raw materials by weight: SiO2 30~35 parts, Al2O3 4~6 parts, talc powder 0.5~1 part, gypsum powder 1~2 parts, ZrO2 1~5 parts, potassium feldspar powder 1~3 parts, sodium feldspar powder 1~3 parts, ZnO 5~10 parts, Cr2O3 1~4 parts, SiC 5~8 parts, B2O3 5~9 parts, graphite 1~4 parts, solvent 30~40 parts; wherein, the Al / Si ratio is 1:6~8; the solvent is composed of 0.1~0.6% methyl cellulose, 5~10% sodium silicate / potassium silicate, 0.3~1% polyethylene glycol, 0.01~0.03% sodium hexadecyl sulfonate and the balance of water. The coating of the application has the advantages of rapid curing, low-temperature glazing and simple phosphorus removal. However, the coating has no surface carbon enrichment effect.

[0035] In summary, the above coating patents all have certain anti-decarburization and oxidation effects, but do not have surface carbon enrichment effect.

[0036] However, in actual production, the surface of the spring flat steel supplied by the steel plant usually has a decarburized layer of about 0.2 mm, and the depth often meets the requirements of GB / T 1222 standard (the decarburized layer depth of general spring steel is not less than 1.2% of the thickness, and the decarburized layer depth of silicon spring steel is not less than 1.6%). The decarburized layer may further intensify during subsequent hot rolling or heat treatment, or even form a full decarburized layer, which seriously reduces the fatigue life of the leaf spring. Although the existing protective coating can inhibit the decarburization process to some extent, it cannot compensate for the carbon in the surface decarburized area, so it cannot fundamentally improve the decarburized layer depth.

[0037] Therefore, there is an urgent need for a new functional coating to achieve the dual effects of anti-oxidation decarburization and surface active recarburization during the hot working process of steel products.

[0038] In view of this, the application provides a decarburization-resistant coating, a preparation method thereof, a decarburization-resistant coating and application. The application of the decarburization-resistant coating provided by the application to the preparation process of steel products can achieve the dual effects of anti-oxidation decarburization and surface active recarburization during the hot working process of steel products, thereby improving the surface quality and fatigue performance of the steel products.

[0039] In a first aspect, the application provides a decarburization-resistant coating, which comprises the following material components in mass percentage: SiO2: 36-38wt%, B2O3: 7-10wt%, Al2O3: 7-10wt%, MgO: 0.9-1.2wt%, CaO: 0.1-1.3wt%, Fe2O3: 8-10wt%, Na2O: 6-8wt%, K2O: 1-3wt%, graphite: 0.1-0.5wt%, and the balance is water glass.

[0040] The decarburization-resistant coating provided by the application can achieve the dual effects of anti-oxidation decarburization and surface active recarburization during the hot working process of steel products through the precise proportioning and synergistic effect of the material components, thereby improving the surface quality and fatigue performance of the steel products.

[0041] Specifically, SiO2 and Al2O3 can form a dense mullite structure at high temperatures, effectively blocking the invasion of oxygen, thereby significantly inhibiting the oxidation and decarburization of the steel surface. In addition, SiO2 can also improve the mechanical strength and chemical stability of the coating, preventing the coating from cracking. Further, the content of SiO2 is limited to between 36-38wt%, and a too high SiO2 content can lead to sintering difficulties, decreased corrosion resistance, or increased sintering temperature. Moreover, when the SiO2 content is too high, due to the large difference in the thermal expansion coefficient of Al2O3 and SiO2, stress concentration will occur, resulting in coarse cracks and reducing the thermal shock resistance of the coating. If the SiO2 content is too low, it can affect the formation and density of the mullite structure. Therefore, the content of SiO2 needs to be within a certain range to balance the material properties. The content of Al2O3 is limited to between 7-10wt%, and a too high Al2O3 content can lead to sintering difficulties, excessive grain growth, or decreased density. If the Al2O3 content is too low, it can affect the formation and performance of mullite. Therefore, the content of Al2O3 needs to be within a certain range to balance the material properties.

[0042] B2O3 can reduce the chemical and corrosion activity of alkaline oxides (such as Na2O and K2O) in the coating, and melt to form a vitreous viscous liquid at high temperature, tightly covering the surface of the billet and isolating it from the oxidizing atmosphere. Further, limiting the content of B2O3 to between 7-10wt%, too high or too low content of B2O3 will affect the melting and chemical corrosion resistance of the glass. If the content of B2O3 is too low, the flowability of the glass phase is poor, and micro-pores and cracks are easily formed in the coating, resulting in a decrease in the density of the coating and poor adhesion of the coating. If the content of B2O3 is too high, the viscosity of the glass phase is too low, and micro-cracks are easily formed during the cooling process, resulting in stress concentration in the coating, increasing the risk of cracking, and decreasing the thermal shock stability and adhesion. Limiting the content of Na2O to between 6-8wt%, when the content of Na2O is too low, the melting acceleration effect of the glass is poor; and when the content of Na2O is too high, the durability of the glass decreases. Limiting the content of K2O to between 1-3wt%, which is economical, and if the content of K2O is too high, it may inhibit the formation of lithium silicate, affecting the performance of the product.

[0043] MgO not only increases the melting temperature of the coating, but also enhances the density of the coating by generating spinel structures such as MgAl 0.6 Fe 1.4 O4 and MgFe2O4, enhances the density of the coating, effectively inhibits the oxidation and diffusion of iron elements, reduces oxidation loss, and at the same time makes the coating easy to peel off after cooling. Further, limiting the content of MgO to between 0.9-1.2wt%, when the content of MgO is too high, the thermal expansion coefficient decreases, and the thermal shock resistance of the coating becomes poor; when the content of MgO is too low, the density of the coating is poor, which may not effectively prevent oxidation, resulting in a decrease in the performance of the coating.

[0044] The addition of CaO improves the flowability and wettability of the glass liquid phase at high temperature, ensuring uniform coating of the coating on the surface of the steel. Further, limiting the content of CaO to between 0.1-1.3wt%, when the content of CaO is too high, the glass may easily crystallize and the thermal expansion coefficient may increase, resulting in easy peeling of the coating; when the content of CaO is too low, it is difficult to play its role in reducing viscosity, improving melting and controlling thermal expansion coefficient.

[0045] Fe2O3 helps to adjust the viscosity and solidification temperature of the coating, further optimizing its wetting and covering performance. Further, limiting the content of Fe2O3 to between 8-10wt%, when the content of Fe2O3 is too low, the covering performance of the coating is poor; when the content of Fe2O3 is too high, the coating has more bubbles, and the ability to prevent oxygen invasion decreases.

[0046] The graphite added in the coating serves as a high-temperature carburant and can stably provide a carbon source to the surface of the plate spring below 1000 DEG C, actively carburate the decarburized area, and fundamentally reduce the decarburization tendency and make up for the deficiency of the traditional protective coating which can only isolate oxygen but cannot compensate for the carbon loss. Further, the content of the graphite is limited to 0.1-0.5wt%, when the content of the graphite is too low, the carburating effect cannot be achieved; when the content of the graphite is too high, the mixing difficulty of the coating is greater and the uniformity is poor.

[0047] Therefore, the anti-decarburization coating provided in the application not only effectively reduces the oxidation and decarburization degree of the steel product during the heat treatment process, but also improves the surface carbon content, thereby significantly improving the surface quality and fatigue performance of the steel product.

[0048] In combination with the first aspect, in some embodiments provided in the application, the particle size of the anti-decarburization coating is 100-300 mesh. The particle size of the anti-decarburization coating is limited in the above range, so as to ensure the performance of the coating (such as adhesion, wear resistance, and dispersibility), and take into account the production cost and process feasibility.

[0049] It should be explained that the "particle size of the anti-decarburization coating" refers to the size of the solid particles (such as SiO2, Al2O3, graphite, and other powders) in the coating.

[0050] In the second aspect, the application provides a preparation method of the anti-decarburization coating of the first aspect, comprising: S100, a part of SiO2 and a liquid medium are first mixed and then crushed to obtain a crushed standby material.

[0051] In this step, since the densities of the components are greatly different, the uniformity of the mixture can be improved by first mixing a part of SiO2 with a liquid medium and crushing.

[0052] In combination with the second aspect, in some embodiments provided in the application, the liquid medium comprises dehydrated oil. The liquid medium described above can uniformly mix the powder and improve the adhesion and oxidation resistance of the coating.

[0053] It should be explained that the "dehydrated oil" refers to an oil obtained by mixing a rust inhibitor, a base oil, an antioxidant, and a dehydrating agent. In the application, the dehydrated oil includes but is not limited to dehydrated oil and dehydrating agent.

[0054] It needs to be explained that "part of SiO2" refers to the total amount of SiO2 in the formula is divided into two or more parts, and is processed in different processes. In this application, the total amount of SiO2 in the formula is divided into two parts, one part is crushed in step S100, and the amount of this part is not specially limited, and the application takes about 20% of the total amount of SiO2 in step S100; and the other part of SiO2 is used in the subsequent mixing step. Thus, it is beneficial to improve the uniformity of mixing.

[0055] S200, the crushed standby material, another part of SiO2, B2O3, Al2O3, MgO, CaO, Fe2O3, Na2O, K2O, graphite and water glass are mixed to obtain a decarburization resistant coating.

[0056] In this step, the pretreated crushed SiO2 standby material is secondly mixed with the remaining solid raw materials and water glass. The fine particle SiO2 slurry formed by pre-crushing is used as a dispersion medium, which effectively alleviates the problem of uneven mixing caused by large differences in the densities of various components, and ensures the uniformity of the chemical composition and particle distribution of the coating system.

[0057] In combination with the second aspect, in some embodiments provided by the application, the second mixing time is 30-60 min. Limiting the second mixing time to the above range can ensure uniform mixing of the coating.

[0058] In a third aspect, the application provides a decarburization resistant coating, which is obtained by curing the decarburization resistant coating of the first aspect or the decarburization resistant coating obtained by the preparation method of the second aspect.

[0059] The decarburization resistant coating is realized based on the above-mentioned decarburization resistant coating. The specific technical features of the decarburization resistant coating can be referred to the above-mentioned embodiments. Since the decarburization resistant coating adopts part or all of the technical solutions of the above-mentioned embodiments, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be repeated here.

[0060] In a fourth aspect, the application provides a steel product. In the process of preparing the steel product, before the steel blank is heat treated or before the steel blank is rolled, the surface of the steel blank is coated with the decarburization resistant coating of the third aspect.

[0061] The steel product is realized based on the above-mentioned decarburization resistant coating. The specific technical features of the decarburization resistant coating can be referred to the above-mentioned embodiments. Since the steel product adopts part or all of the technical solutions of the above-mentioned embodiments, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be repeated here.

[0062] In some embodiments provided by the present application in combination with the fourth aspect, the steel product comprises a leaf spring.

[0063] In some embodiments provided by the present application in combination with the fourth aspect, the heat treatment comprises quenching, the quenching temperature is 820-930℃, the holding time is 60-120min, and nitrogen is introduced during the quenching to reduce the damage of oxygen to the coating.

[0064] In some embodiments provided by the present application in combination with the fourth aspect, the rolling temperature is 950-1050℃, the holding time is 60-120min, and nitrogen is introduced during the rolling to reduce the damage of oxygen to the coating.

[0065] In some embodiments provided by the present application in combination with the fourth aspect, the steel billet is further subjected to phosphorus removal treatment before rolling.

[0066] In some embodiments provided by the present application in combination with the fourth aspect, before the step of coating the surface of the steel billet with the decarburization-resistant coating, the surface of the steel billet is further shot blasted, specifically, before coating the coating, the surface of the leaf spring is subjected to strong shot blasting with steel shots with a diameter of 0.7mm to remove surface impurities and activate the surface, thereby promoting subsequent surface recarburization.

[0067] The technical solutions provided by the present application will be described in detail below in combination with embodiments.

[0068] Embodiment 1 1) The present application provides a kind of anti-decarburization coating, the anti-decarburization coating includes the following mass percentage of material components: SiO2 37wt%, B2O3 8wt%, Al2O3 9%, MgO 1.0wt%, CaO 1.0wt%, Fe2O3 9wt%, Na2O 7wt%, K2O 2wt%, graphite 0.3wt%, the balance is water glass.

[0069] 2) The present application provides a kind of anti-decarburization coating preparation method, which includes: ①SiO2 powder of total amount about 20% of formula is weighed, and with appropriate amount of dehydrated grease (such as castor oil or special polymer dispersant) is placed in grinding container, and the mixture is ground and sheared by hand or mechanically, until the grinding standby material is uniformly fine and has no obvious grain feeling.

[0070] ②The grinding standby material obtained in the first step, the remaining SiO2 and all other components are added to the mixing machine according to the predetermined ratio, mixed for 50min, to ensure that the overall particle size range is stable between 100 and 300 meshes, and the anti-decarburization coating slurry is obtained.

[0071] 3) The application embodiment 1 provides a preparation method of the anti-decarburization coating. ① Dongfeng Commercial Vehicle Company develops a certain heavy vehicle steel plate spring. The material specification of the part is 90*13mm, the material is 60Si2Mn, the raw material decarburization layer depth is 0.3mm, and the full decarburization layer depth is 0.05mm.

[0072] ②Before the anti-decarburization coating is coated, the surface of the steel plate spring is activated and cleaned, specifically, a steel shot with a diameter of 0.7mm is used to strongly shot blast the surface of the steel plate spring, the shot blasting intensity must cover the entire surface to be coated, and the surface is ensured to be in a uniform activated state, and the residual shot and dust must be removed after shot blasting.

[0073] ③The anti-decarburization coating obtained in step 2) is uniformly coated on the surface of the spring leaf treated by shot blasting in a spraying or dipping manner, and is left to dry at room temperature after coating for not less than 30 minutes, so as to form an anti-decarburization coating on the surface of the steel plate spring.

[0074] ④The steel plate spring coated with the anti-decarburization coating is sent into a heating furnace, the rolling temperature is 950℃, nitrogen gas is introduced into the furnace as a protective atmosphere to reduce the oxygen partial pressure, the holding time is 90 minutes, the surface oxide skin is removed (dephosphorization treatment) after taking out of the furnace by using high-pressure water jet, then the anti-decarburization coating is applied on the surface of the plate spring again, the step is the same as ③, then the steel plate spring is quenched, the quenching heating temperature is 900℃, the holding time is 60 minutes, nitrogen gas is introduced into the furnace as a protective atmosphere to reduce the oxygen partial pressure, the quenching into oil temperature is 850℃, the tempering temperature is 480℃, and the holding time is 1.5 hours, so as to obtain a finished steel plate spring.

[0075] Embodiment 2 1) The application embodiment 2 provides an anti-decarburization coating, which is the same as that in embodiment 1.

[0076] 2) The application embodiment 2 provides a preparation method of the anti-decarburization coating, which is the same as that in embodiment 1.

[0077] 3) The application embodiment 2 provides a preparation method of the anti-decarburization coating, which is similar to that in embodiment 1, and the difference lies in that: ① Dongfeng Commercial Vehicle Company develops a certain heavy vehicle steel plate spring. The material specification of the part is 90*27mm, the material is 51CrV4, the raw material decarburization layer depth is 0.31mm, and there is no full decarburization layer.

[0078] ④The rolling temperature is 1000℃, the heat treatment temperature of the plate spring is 930℃, the quenching temperature is 870℃, the tempering temperature is 440℃, and the holding time is 1.5 hours.

[0079] Embodiment 3 1) Embodiment 3 of the present application provides a decarburization-preventing coating, which is the same as that of embodiment 1.

[0080] 2) Embodiment 3 of the present application provides a preparation method of the decarburization-preventing coating, which is the same as that of embodiment 1.

[0081] 3) Embodiment 3 of the present application provides a preparation method of the decarburization-preventing coating, which is similar to that of embodiment 1, and the difference lies in that: ① A heavy truck steel plate spring developed by Dongfeng Commercial Vehicle Company. The material specification of the part is 90x33mm, the material is DFS49600 (a material independently developed by Dongfeng Automobile Company, wherein the Si content is 1.2-1.4%), and the original material decarburization layer depth is 0.35mm, wherein the full decarburization layer depth is 0.03mm.

[0082] ④ The rolling temperature of the above spring steel blank is 1000℃, the heat treatment temperature of the spring is 900℃, the quenching temperature is 860℃, the tempering temperature is 420℃, and the holding time is 1.5h.

[0083] Embodiment 4 1) Embodiment 4 of the present application provides a decarburization-preventing coating, which is similar to that of embodiment 1, and the difference lies in that the decarburization-preventing coating comprises the following material components in mass percentage: SiO2 is 36wt%, B2O3 is 7wt%, Al2O3 is 7wt%, MgO is 0.9wt%, CaO is 0.1wt%, Fe2O3 is 8wt%, Na2O is 6wt%, K2O is 1wt%, graphite is 0.1wt%, and the balance is water glass.

[0084] 2) Embodiment 4 of the present application provides a preparation method of the decarburization-preventing coating, which is similar to that of embodiment 1.

[0085] 3) Embodiment 4 of the present application provides a preparation method of the decarburization-preventing coating, which is similar to that of embodiment 1.

[0086] Embodiment 5 1) Embodiment 5 of the present application provides a decarburization-preventing coating, which is similar to that of embodiment 1, and the difference lies in that the decarburization-preventing coating comprises the following material components in mass percentage: SiO2 is 38wt%, B2O3 is 10wt%, Al2O3 is 10wt%, MgO is 1.2wt%, CaO is 1.3wt%, Fe2O3 is 10wt%, Na2O is 8wt%, K2O is 3wt%, graphite is 0.5wt%, and the balance is water glass.

[0087] 2) Embodiment 5 of the present application provides a preparation method of the decarburization-preventing coating, which is the same as that of embodiment 1.

[0088] 3) Embodiment 5 of the present application provides a preparation method of the decarburization-preventing coating, which is the same as that of embodiment 1.

[0089] Comparative Example 1 The steel plate spring is directly heated without spraying the anti-decarburization coating on the surface of the steel plate spring, and the rest is similar to Example 1.

[0090] Comparative Example 2 The steel plate spring is directly heated without spraying the anti-decarburization coating on the surface of the steel plate spring, and the rest is similar to Example 2.

[0091] Comparative Example 3 The steel plate spring is directly heated without spraying the anti-decarburization coating on the surface of the steel plate spring, and the rest is similar to Example 3.

[0092] Comparative Example 4 1) The present application provides an anti-decarburization coating, which is similar to Example 1, except that the material composition of the anti-decarburization coating does not contain Fe2O3.

[0093] 2) The present application provides a preparation method of an anti-decarburization coating, which is similar to Example 1.

[0094] 3) The present application provides a preparation method of an anti-decarburization coating, which is similar to Example 1.

[0095] Comparative Example 5 1) The present application provides an anti-decarburization coating, which is similar to Example 1, except that the mass percentage of Fe2O3 in the material composition of the anti-decarburization coating is 5wt%.

[0096] 2) The present application provides a preparation method of an anti-decarburization coating, which is similar to Example 1.

[0097] 3) The present application provides a preparation method of an anti-decarburization coating, which is similar to Example 1.

[0098] Comparative Example 6 1) The present application provides an anti-decarburization coating, which is similar to Example 1, except that the mass percentage of Fe2O3 in the material composition of the anti-decarburization coating is 20wt%.

[0099] 2) The present application provides a preparation method of an anti-decarburization coating, which is similar to Example 1.

[0100] 3) The present application provides a preparation method of an anti-decarburization coating, which is similar to Example 1.

[0101] Performance test (1) The steel plate spring of Example 1 and Comparative Example 1 is respectively tested for decarburized layer and hardness gradient of finished steel plate spring and fatigue performance, and the specific test method and steps are: Decarburized layer test: The surface of the finished steel plate spring (leaf spring) is removed for metallographic sample, and the sample surface decarburized layer is detected according to the national standard GB / T 224 "Steel Decarburized Layer Depth Determination Method", and the carbon content from the surface to the center is measured by a scanning electron microscope.

[0102] Hardness gradient detection: The sample is taken from the finished leaf spring, and the hardness gradient test from the surface to the center of the sample is carried out according to GB / T 4340.1 "Metallic Materials Vickers Hardness Test".

[0103] Fatigue performance test: The specific test method is: GB / T19844 "Steel Plate Spring", loading mode: loading stress is 520±330MPa; loading frequency is 1.5HZ.

[0104] The specific test results are shown in Table 1: Table 1

[0105] It can be proved from Table 1 that the use of the decarburization prevention coating can effectively reduce the decarburized layer, especially avoid the appearance of full decarburized layer, the hardness gradient of the steel plate spring is better, and the fatigue performance is better.

[0106] Figure 1 The comparison chart of the total decarburized layer chart of the present application comparative example 1 (a) without applying the decarburization prevention coating after heat treatment and the total decarburized layer chart of example 1 (b) with the decarburization prevention coating after heat treatment is shown. It can be proved from the comparison chart that the use of the decarburization prevention coating can significantly reduce the decarburized layer depth and avoid the appearance of full decarburized layer.

[0107] (2) The decarburized layer and hardness gradient detection and fatigue performance test of the finished steel plate spring of example 2 and comparative example 2 are carried out respectively, and the test method is the same as the steps in (1), wherein the loading mode in the fatigue performance test (1, loading stress 650±350MPa; 2, loading frequency 1.0HZ).

[0108] The specific test results are shown in Table 2: Table 2

[0109] It can be proved from Table 2 that the use of the decarburization prevention coating can effectively reduce the decarburized layer, especially avoid the appearance of full decarburized layer, the hardness gradient of the steel plate spring is better, and the fatigue performance is better.

[0110] Figure 2 The comparison chart of the total decarburized layer chart of the present application comparative example 2 (a) without applying the decarburization prevention coating after heat treatment and the total decarburized layer chart of example 2 (b) with the decarburization prevention coating after heat treatment is shown. It can be proved from the comparison chart that the use of the decarburization prevention coating can significantly reduce the decarburized layer depth and avoid the appearance of full decarburized layer.

[0111] (3) The steel plate spring of Example 3 and Comparative Example 3 was respectively subjected to decarburized layer and hardness gradient detection of finished steel plate spring and fatigue performance test, and the test method steps were the same as those in step (1), wherein the loading mode in the fatigue performance test was (1, loading stress 800±400 MPa; 2, loading frequency 0.8HZ).

[0112] The specific test results are shown in Table 3: Table 3

[0113] It can be proved from Table 3 that the use of the anti-decarburization coating can effectively reduce the decarburized layer, especially avoid the appearance of full decarburized layer, the hardness gradient of the steel plate spring is better, and the fatigue performance is better.

[0114] Figure 3 The comparative diagram of the total decarburized layer diagram of the anti-decarburization coating after heating treatment of the present application Comparative Example 3 (a) without coating and the total decarburized layer diagram of Example 3 (b) with anti-decarburization coating after heating treatment is shown. It can be proved from the comparative diagram that the use of the anti-decarburization coating can significantly reduce the depth of the decarburized layer and avoid the appearance of full decarburized layer.

[0115] (4) The anti-decarburization coating of Examples 1-5 and Comparative Examples 1-6 was respectively applied to the preparation process of steel products, for example, forming the anti-decarburization coating of the present application on the surface of the steel plate spring before heat treatment of the steel plate spring, and then testing the anti-oxidation decarburization performance and surface active carbonization performance, and the specific test steps are as follows: Anti-oxidation decarburization performance: The sample surface decarburized layer was detected according to the national standard GB / T 224 “Steel Decarburized Layer Depth Determination Method”.

[0116] Surface active carbonization performance: The carbon content of the plate spring sample surface to the center was tested by scanning electron microscopy.

[0117] The specific test results are shown in Table 4: Table 4

[0118] From Table 4, the effects of anti-decarburization are as follows: 1) Compared with the uncoated protection plate spring (Comparative Example 1-3), the use of the anti-decarburization coating can effectively reduce the decarburized layer depth by more than 90%, and full decarburized layer does not appear, and through the carbon content test, it can be seen that the coating has a certain carbon supplement to the surface of the plate spring.

[0119] 2) The plate spring with coating protection all passed the bench test, compared with the uncoated protection plate spring (Comparative Example 1-3), the use of the coating can improve the fatigue life of the plate spring by more than 100%.

[0120] 3) The composition inside the coating has a greater effect on the anti-decarburization effect, the use of Fe2O3 can increase the coverage and wettability of the coating, and the use of graphite in combination with nitrogen protection during the heat treatment process can play a role in supplementing the surface carbon, greatly improving the surface quality of the leaf spring.

[0121] In conclusion, the anti-decarburization coating provided by the present application can be coated on the surface of a steel product and form a protective coating through the precise proportioning and synergistic effect of various material components. The coating can simultaneously achieve the dual functions of oxidation and decarburization resistance and surface active recarburization during the heat processing of the steel product, thereby improving the surface quality of the steel product and enhancing its fatigue performance. Practical application shows that the surface decarburization layer depth of the steel plate spring treated by the coating can be reduced by more than 90%, and the fatigue life can be increased by more than 100%.

[0122] In the description of the present specification, the description of the terms "one embodiment / way", "some embodiments / ways", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment / way or example are included in at least one embodiment / way or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment / way or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments / ways or examples. In addition, the skilled person in the art can combine and combine the different embodiments / ways or examples described in the present specification and the features of the different embodiments / ways or examples, without contradiction.

[0123] It should be noted that in the present application, the relationship terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitations, the element defined by the statement "including a" does not exclude the presence of another identical element in the process, method, article or device including the element. In the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise explicitly specified.

[0124] The foregoing detailed description of the application has been presented for purposes of illustration and description. Various modifications and changes can be made to these embodiments without departing from the spirit and scope of the application. It is intended that the scope of the application should not be limited by the particular representative embodiments described above.

Claims

1. A decarburization-resistant coating, characterized in that, The anti-decarburization coating comprises the following material components by mass percentage: SiO2: 36-38wt%, B2O3: 7-10wt%, Al2O3: 7-10wt%, MgO: 0.9-1.2wt%, CaO: 0.1-1.3wt%, Fe2O3: 8-10wt%, Na2O: 6-8wt%, K2O: 1-3wt%, graphite: 0.1-0.5wt%, with the balance being water glass.

2. The anti-decarburization coating as described in claim 1, characterized in that, The particle size of the anti-decarburization coating is 100-300 mesh.

3. A method for preparing the anti-decarburization coating as described in claim 1 or 2, characterized in that, include: After mixing a portion of SiO2 with the liquid medium, the mixture is crushed to obtain crushed material for later use. The crushed spare material, another portion of SiO2, B2O3, Al2O3, MgO, CaO, Fe2O3, Na2O, K2O, graphite and water glass are mixed a second time to obtain the anti-decarburization coating.

4. The preparation method according to claim 3, characterized in that, The liquid medium includes dehydrated oil; and / or, The second mixing time is 30-60 minutes.

5. A decarburization-resistant coating, characterized in that, The anti-decarburization coating is formed by curing the anti-decarburization coating as described in claim 1 or 2, or by curing the anti-decarburization coating obtained by the preparation method of the anti-decarburization coating as described in claim 3 or 4.

6. A steel product, characterized in that, During the preparation of the steel product, before heat treatment or rolling of the steel billet, the anti-decarburization coating as described in claim 5 is applied to the surface of the steel billet.

7. The steel product as described in claim 6, characterized in that, The steel products include leaf springs.

8. The steel product as described in claim 6, characterized in that, The heat treatment includes quenching, the quenching temperature is 820-930℃, the holding time is 60-120min, and nitrogen gas is introduced as a protective atmosphere to reduce the oxygen partial pressure during the quenching process.

9. The steel product as described in claim 6, characterized in that, The rolling temperature is 950-1050℃, the holding time is 60-120min, and nitrogen gas is introduced during the rolling process as a protective atmosphere to reduce the oxygen partial pressure.

10. The steel product as described in claim 6, characterized in that, The process of dephosphorizing the steel billet before rolling also includes the steel billet.

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