Hot stamping steel with enhanced oxide layer bonding strength and manufacturing method thereof

Abstract

The present invention relates to a hot stamping steel with enhanced oxide layer bonding strength and a manufacturing method thereof. The hot stamping steel comprises the following chemical components in weight percentage: C: 0.08-0.38%, Si: 0.1-1.2%, Mn: 0.5-3.0%, P≤0.10%, S≤0.05%, Al: 0.01-0.30%, Ti: 0.01-0.15%, B: 0.001-0.05%, N≤0.01%, and the remainder is Fe and other inevitable impurities. In the manufacturing method, the hot stamping steel surface is selectively oxidized by controlling the dew point of the atmosphere in the annealing furnace to ≤0°C and the H2 content to 2-10%, so that the Si element enrichment within 100nm of the steel plate surface is not less than 120%·nm, and the enriched products mainly include composite oxides including SiO2, Mn2SiO4 and MnSiO3. The hot stamping steel and the manufacturing method thereof of the present invention effectively enhance the bonding force between the substrate and the oxide layer during the subsequent reheating and hot stamping process, improve the problem of oxide layer shedding of the hot stamping steel, and are beneficial to improving the service life of the hot stamping die and the hot stamping production cycle.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, and in particular to a hot stamping steel with enhanced oxide layer bonding strength and a manufacturing method thereof. Background Art

[0002] With the deterioration of the natural environment and the increasing shortage of petroleum resources, environmental protection, safety, and energy conservation have become key development priorities for the automotive manufacturing industry. Hot-stamped parts, characterized by high performance reinforcement, excellent high-temperature ductility, strong formability, and low springback, have become a key technical solution for lightweighting automotive structures. Hot-stamped products are widely used in safety components such as body-in-white (BIW) A / B-pillars, anti-collision beams, and center tunnels, leading to increasing demand for hot-stamped steel in the automotive market. During the production of hot-stamped parts, the steel sheets must be heated to the austenitic temperature range and insulated. Although nitrogen is used in the heating furnaces, the hot-stamped steel is exposed to the atmosphere during the hot-stamping process from the furnace to the die. This unavoidable formation of iron oxide scale on the steel surface is a major pain point in hot-stamped part production. This scale can fall off during the subsequent stamping phase, causing mold wear and tear. This requires the machine to be stopped during the stamping process for mold purging and repair, slowing production.

[0003] Currently, two groups of ideas have been announced to solve the above-mentioned difficulties. On the one hand, surface treatment such as galvanizing, aluminum-silicon plating, and organic coatings have the problem of zinc layer melting LME and aluminum-silicon coating melting and sticking to the roller during the reheating process of zinc-based and aluminum-silicon coated hot stamping steel respectively; on the other hand, the degree of shedding of surface iron oxide scale is reduced and the bonding strength between the iron oxide scale and the substrate is increased, but the manufacturing process is complex and stable production is difficult to achieve.

[0004] Chinese patent CN103614640B discloses "a non-coated hot stamping steel resistant to high-temperature oxidation". Its chemical composition by weight is "C 0.18-0.28, Si 0.05-0.50%, Mn 0.20-0.90%, P≤0.010%, S≤0.005%, Cr 0.20-1.5%, Mo 0.010-0.30%, B 0.0006-0.0030%, Nb+V+Ti 0.02-0.25%, Al 0.010-0.100%, and the balance is Fe and unavoidable impurity elements." Its design idea is to improve the high-temperature oxidation resistance of the steel plate by adding expensive high-temperature oxidation-resistant alloying elements such as Cr and Mo, resulting in a high product cost.

[0005] Chinese patent CN107427889B discloses "hot stamping steel sheet and its manufacturing method, and hot stamping formed body", which mainly controls the surface roughness Rz of hot stamping steel sheet to be greater than 2.5μm and the surface oil coating amount to be 50-1500mg / m 2 The process of forming more than three concave and convex points with a depth of 0.2 to 8.0 μm per 100 μm at the interface between the iron oxide scale and the substrate is realized through the steps of the above steps, thereby improving the bonding strength between the iron oxide scale and the substrate. The manufacturing process is complex and difficult to achieve. Summary of the Invention

[0006] The present invention aims to overcome the shortcomings of the prior art and provide a hot stamping steel with enhanced oxide layer adhesion and a method for manufacturing the same. The present invention aims to provide a new hot stamping steel by enhancing the oxide layer adhesion to effectively address the above-mentioned difficulties, thereby improving the adhesion between the oxide layer and the substrate and improving the shedding of iron oxide scale.

[0007] In order to achieve the above-mentioned invention purpose, the technical solution provided by the patent of this invention is as follows:

[0008] A hot stamping steel with enhanced oxide layer bonding strength, wherein the Si element enrichment within a 100nm depth range on the surface of the hot stamping steel is not less than 120% / nm, and the enriched material is a composite oxide including SiO2, Mn2SiO4, and MnSiO3. The enriched material is located between the steel substrate and the oxide layer to enhance the oxide layer bonding strength.

[0009] In a hot stamping steel for enhancing the bonding strength of an oxide layer according to the present invention, the hot stamping steel comprises the following chemical components in weight percentage: C: 0.08-0.38%, Si: 0.1-1.2%, Mn: 0.5-3.0%, P≤0.10%, S≤0.05%, Al: 0.01-0.30%, Ti: 0.01-0.15%, B: 0.001-0.05%, N≤0.01%, and the remainder being Fe and other unavoidable impurities.

[0010] In the hot stamping steel for enhancing the bonding strength of the oxide layer according to the present invention, the chemical composition of the hot stamping steel further includes one or more of the following: Cr: 0.01-2.0%, Ni: 0.01-1.0%, Mo: 0.01-1.0%, Cu: 0.01-1.0%, Nb: 0.01-0.10%; V: 0.01-0.2%.

[0011] In the hot stamping steel for enhancing the bonding strength of the oxide layer according to the present invention, the chemical composition weight percentage of the hot stamping steel satisfies Si / Mn<1 / 2.

[0012] In the hot stamping steel with enhanced oxide layer bonding strength of the present invention, when calculating the Si element enrichment, a glow discharge method is used to detect the element depth distribution on the surface of the hot stamping steel, and the Si element integration within a surface depth of 100 nm is performed according to the GDS curve to obtain the enrichment data.

[0013] In the composition design of the above hot stamping steel:

[0014] Carbon (C) is a key element for increasing strength and hardness, ensuring that the tensile strength of hot-stamped parts meets the target requirements. However, increasing carbon content deteriorates the plasticity, toughness, and weldability of hot-stamped parts. Therefore, the present invention limits the C content to 0.08-0.38%.

[0015] Si: It acts as a reducing agent and deoxidizer during steelmaking, and can also improve strength and hardness. Si is a key element in the present invention. During the annealing process, Si in the steel plate selectively oxidizes and concentrates on the surface of the steel plate. During subsequent hot stamping and heating, Si oxides such as SiO2 further form complex phase structures, such as Fe2SiO4. This complex phase structure is located at the interface between the substrate and the iron oxide scale and exhibits excellent adhesion, thereby improving the bonding between the oxide layer and the substrate and improving the shedding of the iron oxide scale. A Si content below 0.1% makes it difficult to form surface oxides during the annealing process, failing to achieve the intended effect of the present invention. A Si content above 1.2% saturates the effect and reduces weldability. Therefore, the Si content in the present invention is controlled to 0.1-1.2%.

[0016] Mn: It has deoxidizing and desulfurizing properties and is a strong austenite stabilizer, second only to Ni. Therefore, it significantly increases the hardenability of steel. To ensure the strength and hardenability of steel sheets, the Mn content in hot stamping steel must be no less than 0.5%. However, a Mn content above 3.0% significantly degrades the steel's manufacturability and weldability. Therefore, the present invention controls the Mn content to between 0.5% and 3.0%.

[0017] P and S: Both P and S are harmful elements in steel. P segregation can cause the steel to crack easily during cold working, a phenomenon known as cold brittleness. S segregation at high temperatures can reduce plasticity and even lead to hot brittleness. Therefore, the steel in this invention contains P ≤ 0.10% and S ≤ 0.05%.

[0018] Al: As a deoxidizing element, it is best to contain more than 0.01% Al in the steel. However, if the steel contains too much Al, it will cause coarse oxides to form in the steel, deteriorating the overall performance of the steel. Therefore, the Al content of the present invention is controlled to 0.01-0.3%.

[0019] Ti: Combines with nitrogen in the steel to form TiN, which inhibits boron from forming BN nitrides. Furthermore, Ti precipitates to form TiC, which refines grains and strengthens the steel through precipitation. Ti contents above 0.01% achieve significant results, but excessive Ti contents can lead to the formation of massive nitrides, which degrade toughness and ductility. Therefore, the Ti content in this invention is controlled between 0.01% and 0.15%.

[0020] B: Its primary function in steel is to significantly increase its hardenability, thereby conserving other, less expensive metals. The addition of B has an optimal range for improving hardenability; above a certain level, the effect is insignificant. Therefore, in the present invention, the B content is controlled between 0.001 and 0.05%.

[0021] When the N content exceeds 0.01%, coarse nitrides will be formed, resulting in reduced blanking performance and hardenability of the substrate steel plate. Therefore, the present invention controls N≤0.01%.

[0022] Cr, Ni, Mo, Cu: All are effective elements to ensure the toughness of hot stamping parts. Cr effectively improves the hardenability of steel, further improves the strength and toughness of steel, and prevents high-temperature surface oxidation. Ni can improve the strength of steel and reduce the low-temperature brittle transition temperature of steel. Mo can significantly improve the hardenability of steel, refine austenite grains, and prevent temper brittleness. Cu improves the hardenability and strength of steel while also improving the corrosion resistance of steel. Taking into account the alloy cost of steel and the saturation of element effects, the present invention also contains one or more alloy components of Cr: 0.01~2.0%, Ni: 0.01~1.0%, Mo: 0.01~1.0%, V: 0.01~0.2%, and Cu: 0.01~1.0%.

[0023] Nb and V are important microalloying elements in steel. Forming NbC and VC effectively refines grains, improving steel's strength and toughness while also imparting excellent cold bending properties. The precipitation of fine carbides acts as hydrogen traps, reducing sensitivity to hydrogen-induced delayed cracking. Microalloying elements require an addition of 0.01% or more to achieve significant effects. These effects are saturated when Nb content reaches 0.1% and V content reaches 0.2%. Therefore, in the present invention, Nb is 0.01-0.10% and V is 0.01-0.2%.

[0024] The present invention also relates to a method for manufacturing a hot stamping steel for enhancing the bonding strength of an oxide layer, wherein the hot stamping steel comprises the following chemical components in weight percentage: C: 0.08-0.38%, Si: 0.1-1.2%, Mn: 0.5-3.0%, P≤0.10%, S≤0.05%, Al: 0.01-0.30%, Ti: 0.01-0.15%, B: 0.001-0.05%, N≤0.01%, and the remainder is Fe and Other unavoidable impurities: the chemical composition of the hot stamping steel also includes one or more of the following: Cr: 0.01-2.0%, Ni: 0.01-1.0%, Mo: 0.01-1.0%, Cu: 0.01-1.0%, Nb: 0.01-0.10%; V: 0.01-0.2%. The manufacturing method includes the following steps: smelting, continuous casting, hot rolling, pickling, cold rolling and annealing. During the annealing step, the dew point in the furnace is ≤0°C.

[0025] In the method for manufacturing hot stamping steel with enhanced oxide layer bonding strength of the present invention, as one implementation form of hot stamping steel, if the chemical composition weight percentage is 0.1≤Si≤0.6%, then in the annealing step, the furnace dew point is ≤-20°C.

[0026] In the method for manufacturing hot stamping steel with enhanced oxide layer bonding strength of the present invention, as another implementation form of hot stamping steel, if the chemical composition weight percentage is 0.6<Si≤1.2%, then in the annealing step, the furnace dew point is ≤0°C.

[0027] The present invention also relates to a method for manufacturing hot stamping steel with enhanced oxide layer bonding strength. In the annealing step, the H2 atmosphere in the furnace is controlled to be 2-10%.

[0028] The present invention also relates to an annealing step in a method for manufacturing hot stamping steel with enhanced oxide layer bonding strength. In the annealing step, the annealing temperature is controlled at 720-800°C.

[0029] Based on the above technical solution, the hot stamping steel with enhanced oxide layer bonding strength and the manufacturing method thereof of the present invention have achieved the following beneficial effects in practice:

[0030] 1. The present invention provides a hot stamping steel with enhanced oxide layer adhesion. Si is a key element in the composition of the hot stamping steel. During the annealing process, the Si element in the steel plate is selectively oxidized and enriched on the steel plate surface. During the subsequent hot stamping heating, Si oxides such as SiO2 further form a complex phase structure, such as Fe2SiO4. This complex phase structure is formed at the interface between the substrate and the iron oxide scale and has excellent adhesion. Therefore, it is beneficial to improve the adhesion of the oxide layer to the substrate and improve the shedding of the iron oxide scale.

[0031] 2. The present invention achieves Si element enrichment by oxidation on the steel plate surface through a special manufacturing method. Specifically, in the annealing step of the manufacturing method, the selective oxidation of the hot stamping steel surface is controlled by controlling the atmosphere in the annealing furnace, thereby promoting a certain amount of Si oxide enrichment on the hot stamping steel surface. This effectively enhances the bonding strength between the substrate and the oxide layer during the subsequent reheating and hot stamping process, improves the problem of oxide layer shedding on the hot stamping steel, and is beneficial to improving the service life of the hot stamping die and the hot stamping production cycle. It has the advantages of being environmentally friendly and energy-saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a graph showing the depth distribution of Si elements on the surface of the GDS detection example and the comparative example sample in the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the accompanying drawings and examples to more clearly illustrate its composition and manufacturing method, but this is not intended to limit the scope of protection of the present invention.

[0034] The present invention first provides a hot stamping steel with enhanced oxide layer adhesion. The hot stamping steel has a Si enrichment of no less than 120% / nm within a 100nm depth on the steel surface. The enriched materials are composite oxides including SiO2, Mn2SiO4, and MnSiO3, located between the steel substrate and the oxide layer to enhance the oxide layer's adhesion. By enriching the Si-containing composite oxides, the surface of the steel sheet can be enriched with oxides such as SiO2 to form complex phase structures, such as Fe2SiO4, during heating or hot stamping. This complex phase structure forms at the interface between the substrate and the iron oxide scale and exhibits excellent adhesion, thereby improving the adhesion of the oxide layer to the substrate and reducing the shedding of the iron oxide scale. In the present invention, the element depth distribution on the surface of the hot stamping steel is measured using a glow discharge (GDS) method. Si enrichment data is obtained by integrating the GDS curve within a 100nm depth range. The present invention conducted annealing production experiments with different processes, especially adjusting the dew point, for multiple groups of chemical compositions. Products with different surface Si enrichments were obtained according to the above calculation method. Parts were subsequently obtained through a hot stamping process. The results showed that hot stamped parts with Si enrichment within 100 nm of not less than 120%·nm had good adhesion to the surface oxide scale and showed no obvious shedding.

[0035] In the above-mentioned hot stamping steel for enhancing the bonding strength of the oxide layer, the hot stamping steel includes the following chemical components in weight percentage: C: 0.08-0.38%, Si: 0.1-1.2%, Mn: 0.5-3.0%, P≤0.10%, S≤0.05%, Al: 0.01-0.30%, Ti: 0.01-0.15%, B: 0.001-0.05%, N≤0.01%, and the remainder is Fe and other unavoidable impurities.

[0036] The hot stamping steel composition further includes one or more of the following components in weight percentage: Cr: 0.01-2.0%, Ni: 0.01-1.0%, Mo: 0.01-1.0%, Cu: 0.01-1.0%, Nb: 0.01-0.10%; V: 0.01-0.2%.

[0037] In the above-mentioned hot stamping steel, the chemical composition weight percentage satisfies Si / Mn < 1 / 2. Studies have shown that when the substrate composition Si / Mn ≥ 1 / 2, the enrichment of Si and Mn elements on the surface of the annealed sample tends to decrease with the decrease of dew point, and the enrichment pattern is not obvious. Therefore, it cannot be guaranteed that the required amount of oxide enrichment is generated on the surface.

[0038] The present invention also relates to a method for manufacturing the hot stamping steel with enhanced oxide layer adhesion, comprising the following steps: smelting, continuous casting, hot rolling, pickling, cold rolling, and annealing. To achieve the oxide layer adhesion-enhancing effect of the present invention, the furnace dew point must be controlled to ≤ 0°C during the annealing step. In meteorology, the dew point, also known as the dew point temperature, refers to the temperature at which gaseous water in air reaches saturation and condenses into liquid water under a fixed pressure. Research has found that the atmosphere within the annealing furnace is crucial for the selective oxidation of Si. A dew point above 0°C results in a lower degree of Si oxidation, meaning less surface enrichment. Furthermore, hot stamping steels with high Si content are susceptible to internal Si oxidation, forming Si enrichment within 250nm of the steel sheet surface. This internal oxidation, resulting in Si oxide enrichment, makes it difficult to form a complex surface phase structure during the subsequent hot stamping heating process, resulting in insufficient improvement in the adhesion between the substrate and the oxide scale. Research results confirm that element enrichment within a depth of 100nm from the surface is significantly effective. Combined with the requirement of a corresponding surface enrichment of Si of 120%·nm, the dew point is controlled to be no higher than 0°C.

[0039] Research has shown that if the Si content in the hot stamping steel matrix is ​​0.1-0.6%, and the furnace dew point is preferably ≤-20°C, the Si oxidation enrichment depth is approximately 100 nm. Therefore, integrating the Si content within a 100 nm depth on the surface yields a Si enrichment of at least 120% / nm. If the Si content in the hot stamping steel matrix is ​​0.6-1.2%, Si oxides are more likely to form on the hot stamping steel surface. This surface Si oxidation enrichment requirement is achieved by preferably keeping the furnace dew point ≤0°C.

[0040] The main purpose of controlling the H2 content in the furnace during the above-mentioned annealing step is to increase the reducing atmosphere. An H2 content of 2-10% can effectively reduce the Fe oxides on the steel plate surface, resulting in pure Fe, Si oxides, and other metal oxides on the steel plate surface. An H2 content below 2% is not very effective, while an H2 content above 10% may reduce Si oxides, preventing sufficient Si oxide enrichment from forming on the surface of the hot stamping steel. Therefore, the H2 content is controlled within a range of 2-10%.

[0041] In the aforementioned annealing step, the annealing temperature is controlled between 720°C and 800°C. If the steel plate is annealed in a furnace below 720°C, the Si element will not have sufficient momentum to migrate toward the steel plate surface, failing to form effective oxide enrichment, thus failing to achieve the effects of the present invention. If the annealing temperature exceeds 800°C, the strength of the annealed sample will be low, failing to stably meet factory performance requirements, and energy consumption will be high. Therefore, the present invention controls the annealing temperature between 720°C and 800°C.

[0042] According to the method of the present invention, the hot stamping steel meeting the above-mentioned surface Si element enrichment is prepared. The oxide layer formed during the subsequent reheating and hot stamping process has good bonding strength with the substrate and is not prone to falling off.

[0043] Example 1

[0044] This embodiment is a hot stamping steel for enhancing the bonding strength of the oxide layer. The chemical composition of the hot stamping steel is as follows by weight: C: 0.20%, Si: 0.30%, Mn: 1.2%, P: 0.01%, S: 0.005%, Al: 0.03%, Ti: 0.03%, B: 0.005%, Cr: 0.2%, N: 0.005%, and the balance is Fe and unavoidable inclusions.

[0045] This embodiment provides a method for manufacturing the hot stamping steel with enhanced oxide layer bonding strength, comprising the steps of smelting, continuous casting, hot rolling, pickling, cold rolling, and annealing, wherein smelting, continuous casting, hot rolling, pickling, and cold rolling are conventional production operations for the steel plate with the above chemical composition. Specifically, the following operations are performed in the annealing step:

[0046] (1) Example 1: Annealing process: furnace dew point controlled at -25°C, H2 content 4%;

[0047] (2) Comparative Example 1-1: Annealing process controlled the furnace dew point at -5°C and the H2 content at 4%;

[0048] (3) Comparative Example 1-2: Annealing process controlled furnace dew point -25°C, H2 content 15%;

[0049] In the annealing step, the annealing temperature is selected to be 780°C.

[0050] The glow discharge GDS method is used to detect the depth distribution of elements on the surface of hot stamping steel. According to the test element depth distribution curve, the Si element content is integrated within the surface depth range of 0 to 100 nm. According to the mathematical area integral calculation method, the enrichment data is obtained. Taking Example 1 as an example, the Si enrichment within the range of 0 to 100 nm is the area of ​​the area surrounded by the obtained curve and the X-axis and Y-axis. The Si enrichment in Example 1 is 132%·nm, the Si enrichment in Comparative Example 1-1 is 70%·nm, and the Si enrichment in Comparative Example 1-2 is 86%·nm. Figure 1 As shown, Figure 1 The depth distribution curves of Si elements along the thickness of the surface of the example and comparative example samples detected by GDS in the present invention clearly show that the Si element enrichment within 100nm of the surface of the example is significantly higher than that of the comparative example. According to the above-mentioned method, the enrichment of the example meets the requirement of no less than 120% / nm. Surface oxide analysis of the samples combined with scanning electron spectroscopy and Auger electron spectroscopy confirmed that the surface oxides include Mn-Si composite oxides such as SiO2, Mn2SiO4, and MnSiO3.

[0051] The hot stamping steel was heated to 930° C. and kept at this temperature for 4 minutes before hot stamping. The iron oxide scale on the surface of the hot stamped parts of the embodiment was well bonded, while the iron oxide scale on the surface of the hot stamped parts of the comparative example fell off significantly.

[0052] Example 2

[0053] This embodiment is a hot stamping steel for enhancing the bonding strength of the oxide layer. The chemical composition of the hot stamping steel is as follows by weight: C: 0.15%, Si: 0.75%, Mn: 2.5%, P: 0.01%, S: 0.004%, Al: 0.10%, Ti: 0.08%, Nb: 0.05%, Cr: 0.5%, N: 0.005%, and the balance is Fe and unavoidable inclusions.

[0054] A method for manufacturing a steel plate having the above chemical composition to produce a hot stamping steel with enhanced oxide layer adhesion, the method comprising the steps of smelting, continuous casting, hot rolling, pickling, cold rolling and annealing, wherein smelting, continuous casting, hot rolling, pickling and cold rolling are conventional production operations for the steel plate having the above chemical composition. In particular, the following operations are performed in the annealing step:

[0055] (1) Example 2: Annealing process: furnace dew point controlled at -15°C, H2 content 6%;

[0056] (2) Comparative Example 2: Annealing process controlled the furnace dew point at 5°C and the H2 content at 6%;

[0057] In the above annealing step, the annealing temperature is selected to be 750°C.

[0058] The glow discharge GDS method was used to detect the depth distribution of elements on the surface of hot stamping steel. The Si element content was integrated within the surface depth range of 0 to 100 nm according to the test element depth distribution curve. The enrichment data was obtained according to the above-mentioned mathematical area integration method. The Si enrichment in the example was 156%·nm, and the Si enrichment in the comparative example was 92%·nm.

[0059] The surface oxide analysis of the samples was carried out by combining scanning electron spectroscopy and Auger electron spectroscopy, confirming that the surface oxides included Mn-Si composite oxides such as SiO2, Mn2SiO4, and MnSiO3.

[0060] The hot stamping steel was heated to 950° C. and kept at this temperature for 3 minutes before hot stamping. The iron oxide scale on the surface of the hot stamped parts of the embodiment was well bonded, while the iron oxide scale on the surface of the hot stamped parts of the comparative example fell off significantly.

[0061] Example 3

[0062] This embodiment is a hot stamping steel for enhancing the bonding strength of the oxide layer. The chemical composition of the hot stamping steel is as follows by weight: C: 0.35%, Si: 1.0%, Mn: 3.0%, P: 0.01%, S: 0.004%, Al: 0.10%, Ti: 0.05%, Mo: 0.2%, V: 0.15%, B: 0.03%, N: 0.005%, and the balance is Fe and unavoidable inclusions.

[0063] A method for manufacturing a steel plate having the above chemical composition to produce a hot stamping steel with enhanced oxide layer adhesion, the method comprising the steps of smelting, continuous casting, hot rolling, pickling, cold rolling and annealing, wherein smelting, continuous casting, hot rolling, pickling and cold rolling are conventional production operations for the steel plate having the above chemical composition. In particular, the following operations are performed in the annealing step:

[0064] (1) Example 3: Annealing process: furnace dew point controlled at -5°C, H2 content 5%;

[0065] (2) Comparative Example 3: Annealing process controlled the furnace dew point at 5°C and the H2 content at 5%;

[0066] In the above annealing step, the annealing temperature is selected to be 730°C.

[0067] The glow discharge GDS method was used to detect the depth distribution of elements on the surface of the hot stamping steel. The Si element content was integrated within the surface depth range of 0 to 100 nm according to the test element depth distribution curve. The enrichment data was obtained according to the above-mentioned mathematical area integration calculation method. The Si enrichment in Example 3 was 178%·nm, and the Si enrichment in the comparative example was 105%·nm.

[0068] The surface oxide analysis of the samples was carried out by combining scanning electron spectroscopy and Auger electron spectroscopy, confirming that the surface oxides included Mn-Si composite oxides such as SiO2, Mn2SiO4, and MnSiO3.

[0069] The hot stamping steel was heated to 900° C. and kept at this temperature for 6 minutes before hot stamping. The iron oxide scale on the surface of the hot stamped parts of the embodiment was well bonded, while the iron oxide scale on the surface of the hot stamped parts of the comparative example fell off significantly.

[0070] The present invention designs a hot stamping steel for strengthening the oxide layer. The hot stamping steel is manufactured according to the designed components. The manufactured hot stamping steel effectively strengthens the bonding force between the substrate and the oxide layer during the subsequent reheating and hot stamping processes, improves the problem of oxide layer shedding of the hot stamping steel, and is beneficial to improving the service life of the hot stamping die and the hot stamping production cycle.

Claims

1. A hot stamping steel with enhanced oxide layer bonding strength, characterized in that: The hot stamping steel comprises the following chemical components in weight percentage: C: 0.08-0.38%, Si: 0.1-1.2%, Mn: 0.5-3.0%, P≤0.10%, S≤0.05%, Al: 0.01-0.30%, Ti: 0.01-0.15%, B: 0.001-0.05%, N≤0.01%, and the rest is Fe and other inevitable impurities, and the chemical composition weight percentage Si / Mn is <1 / 2; the Si element enrichment within the 100nm depth range on the surface of the hot stamping steel is not less than 120%·nm, and the enriched substances include SiO 2、 Composite oxides including Mn2SiO4 and MnSiO3 are located between the steel substrate and the oxide layer to enhance the bonding strength of the oxide layer.

2. The hot stamping steel with enhanced oxide layer bonding strength according to claim 1, characterized in that: The chemical composition of the hot stamping steel also includes one or a combination of the following: Cr: 0.01-2.0%, Ni: 0.01-1.0%, Mo: 0.01-1.0%, Cu: 0.01-1.0%, Nb: 0.01-0.10%; V: 0.01-0.2%.

3. The hot stamping steel with enhanced oxide layer bonding strength according to claim 1, characterized in that: When the Si element enrichment is counted, the glow discharge method is used to detect the depth distribution of elements on the surface of the hot stamping steel, and the Si element content is integrated within a surface depth of 100 nm according to the GDS curve to obtain its enrichment data.

4. A method for manufacturing the hot stamping steel with enhanced oxide layer bonding strength according to claim 1, characterized in that: The hot stamping steel includes the following chemical components in weight percentage: C: 0.08-0.38%, Si: 0.1-1.2%, Mn: 0.5-3.0%, P≤0.10%, S≤0.05%, Al: 0.01-0.30%, Ti: 0.01-0.15%, B: 0.001-0.05%, N≤0.01%, and the rest is Fe and other inevitable impurities. The chemical composition of the hot stamping steel also includes one or more combinations of the following: Cr: 0.01-2.0%, Ni: 0.01-1.0%, Mo: 0.01-1.0%, Cu: 0.01-1.0%, Nb: 0.01-0.10%; V: 0.01-0.2%. The manufacturing method thereof includes the following steps: smelting, continuous casting, hot rolling, pickling, cold rolling and annealing. In the annealing step, the dew point in the furnace is ≤0°C.

5. The method for manufacturing hot stamping steel with enhanced oxide layer bonding strength according to claim 4, characterized in that: In the hot stamping steel, if the chemical composition weight percentage is 0.1≤Si≤0.6%, then in the annealing step, the furnace dew point is ≤-20°C.

6. The method for manufacturing hot stamping steel with enhanced oxide layer bonding strength according to claim 5, characterized in that: In the hot stamping steel, if the chemical composition weight percentage is 0.6<Si≤1.2%, then in the annealing step, the dew point in the furnace is ≤0°C.

7. The method for manufacturing hot stamping steel with enhanced oxide layer bonding strength according to claim 5, characterized in that: In the annealing step, the H2 atmosphere in the furnace is controlled at 2-10%.

8. The method for manufacturing hot stamping steel with enhanced oxide layer bonding strength according to any one of claims 4 to 7, characterized in that: In the annealing step, the annealing temperature is controlled at 720-800°C.

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