A laser welding method for 1500mpa grade antioxidant hot forming steel

Abstract

The application discloses a laser welding method of 1500MPa-grade antioxidant hot forming steel, which comprises the following steps: providing two pieces of antioxidant hot forming steel plates; fixing the two pieces of antioxidant hot forming steel plates, wherein the two pieces of antioxidant hot forming steel plates are aligned; under a protective atmosphere, performing laser welding treatment on the two pieces of antioxidant hot forming steel plates by using a laser to obtain a laser-welded plate; and after heat treatment of the laser-welded plate, transferring the laser-welded plate to a flat die for die cooling. The antioxidant hot forming steel plate adds a certain amount of Si and Cr elements on the basis of a conventional hot forming steel plate bare plate, improves the hardenability and strength-plastic product of the material, and is laser-welded, so that the weld can be transformed into martensite under air cooling, the toughness at the weld is improved by more than 30% after heat treatment compared with the conventional bare plate, the fracture position is not at the weld, and the laser-welded plate can be applied to 1500MPa antioxidant hot forming steel plates; the laser power is small, a single laser is adopted, and the operation is simple and low in cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser welding, in particular to a laser welding method of 1500MPa-grade antioxidant hot forming steel. BACKGROUND

[0002] Lightweight refers to a method of reducing the weight of a part while ensuring that the strength of the part remains unchanged. High-strength hot forming steel is an indispensable material for achieving lightweight in the automotive industry.

[0003] Compared with traditional welding technology, laser welding technology can improve material utilization and reduce production costs. It can also be used to laser weld hot forming steels of different strengths and thicknesses, which can greatly reduce tooling costs, reduce the overall weight of the parts, and improve the dimensional accuracy of the parts during subsequent hot stamping.

[0004] Currently, hot forming steel comes in two types: bare sheet and plated sheet. Antioxidant hot forming steel is a type of bare sheet. Antioxidant hot forming steel adds Si and Cr elements to the base hot forming steel to improve the hardenability of the steel, allowing the material to achieve martensite in an air-cooled state and a 1-micron-thick oxidation layer on the surface of the steel matrix to protect the steel matrix from oxidation. In actual production, antioxidant hot forming steel can achieve lower heating temperatures, shorter heating times, lower energy consumption, shorter stamping cycles, and higher production efficiency, as well as the elimination of the shot blasting step and the reduction of production process costs.

[0005] Based on the above research, antioxidant hot forming steel has great value in the lightweight and cost reduction of the automotive industry. Therefore, it is necessary to find a suitable welding process for laser welding of antioxidant hot forming steel, and systematic research on the laser welding process of antioxidant hot forming steel has certain theoretical and practical value.

[0006] Patent CN116967608A discloses a high-strength steel laser welding manufacturing method. The high-strength steel base contains 5-15% residual austenite structure. The two high-strength steel workpieces are butted at the welding site. A large-size spot first laser beam is used to weld the upper surface of the welding site, and a small-size spot second laser beam is used to weld the lower surface of the welding site. This method can improve the yield of high-strength steel laser welding and the forming performance of the welded joint, meeting the needs of efficient production. However, this method requires two laser beams, which is complex and expensive. Moreover, for antioxidant hot forming steel, the base contains less than 5% austenite, so this technical solution is not suitable for laser welding of antioxidant hot forming steel.

[0007] Patent CN113736983A discloses a method for improving the weld toughness of high-strength steel, which performs twice laser heat treatment on the weld of high-strength steel, the first laser heat treatment is used to form a martensitic weld, and the second laser heat treatment is a tempering treatment for the martensitic weld to obtain a tempered martensitic structure, thereby improving the weld toughness, and realizing an efficient, high-precision and high-quality weld softening heat treatment technical solution, which can reduce the risk of weld fracture and avoid various forms of weld fracture problems caused by low weld toughness, hydrogen embrittlement or high weld hardness. However, this method requires twice laser heat treatment, which is complex, low in efficiency and high in cost.

[0008] Patent CN117583852A discloses a method for preparing a hot-formed joint of Al-Si coated hot-formed steel. Since it is an Al-Si coated hot-formed steel, it needs to use wire filling welding for laser welding. If self-fusion welding is used, the Al element in the coating will penetrate into the weld, hinder the transformation of the structure to produce ferrite (soft phase), and thus cause low strength at the weld and cracking position on the weld. This method requires a specific welding wire, which is high in cost. For oxidation-resistant hot-formed steel, it belongs to a kind of bare plate, and the surface layer does not have an Al-Si coating, so it does not need to use wire filling welding during laser welding. Therefore, this technical solution is not suitable for laser welding of oxidation-resistant hot-formed steel.

[0009] Therefore, it is of great significance to develop an efficient and low-cost laser welding method for 1500MPa-grade oxidation-resistant hot-formed steel. SUMMARY

[0010] To solve the above technical problems, the present application provides a laser welding method for 1500MPa-grade oxidation-resistant hot-formed steel, comprising the following steps:

[0011] S1, providing two oxidation-resistant hot-formed steel plates, the thickness of the oxidation-resistant hot-formed steel plates being 1.0-2.0mm;

[0012] S2, fixing the two oxidation-resistant hot-formed steel plates, wherein the two oxidation-resistant hot-formed steel plates are aligned;

[0013] S3, under a protective atmosphere, performing laser welding treatment on the two oxidation-resistant hot-formed steel plates by a laser to obtain a laser-welded plate;

[0014] The parameters of laser welding are as follows:

[0015] When the thickness t of the thickest steel plate among the two oxidation-resistant hot-formed steel plates is 1.0-1.4mm, t+0.2≤Q≤t+0.4, the Q is the laser welding power, the unit is kW, the welding speed is 30-50mm / s, and the defocusing amount is 8-12mm;

[0016] when the thickness t of the thickest steel plate in the two pieces of the anti-oxidation hot-formed steel plate is 1.6-2.0 mm, t+0.1≤Q≤t+0.2, the laser welding power is Q, the unit is kW, the welding speed is 10-30 mm / s, and the defocusing amount is 3-8 mm;

[0017] S4, after the tailor-welded plate is heat treated, the tailor-welded plate is transferred to a flat die for die cooling.

[0018] Further, the anti-oxidation hot-formed steel plate comprises the following components in percentage by mass: C 0.15-0.30%, Si 1.40-1.70%, Cr 3.10-3.40%, Mn 1.10-1.80%, B 0.001-0.010%, Ti 0.02-0.08%, Nb 0.05-0.10%, and the rest is Fe and inevitable impurities.

[0019] The anti-oxidation hot-formed steel plate is used in the present application, and laser self-fusion tailor-welding is performed. The anti-oxidation hot-formed steel plate adds a certain amount of Si and Cr elements on the basis of a conventional hot-formed steel plate bare plate, so as to improve the hardenability and the product of strength and ductility. In the process of laser tailor-welding, the weld can be transformed into martensite under air cooling, and the toughness at the weld is improved by more than 30% compared with that of a conventional bare plate after heat treatment. The strength of the weld is even greater than that of the bare plate, and the fracture position is not at the weld. The anti-oxidation hot-formed steel plate can be applied to 1500 MPa anti-oxidation hot-formed steel plate. The mechanical properties of the anti-oxidation hot-formed steel plate tailor-welded component are much greater than those of an ordinary bare plate tailor-welded component. The self-fusion tailor-welding mode solves the problem of tailor-welding of anti-oxidation hot-formed steel plates with different thicknesses. The laser welding power is 1.4-2.2 kW, and a single laser beam is used, so the cost is low.

[0020] Further, in S4, the parameters of the heat treatment are as follows:

[0021] when the thickness t of the thickest steel plate in the two pieces of the anti-oxidation hot-formed steel plate is 1.0-1.4 mm, the heating temperature is 880-900℃, and the holding time is 200-240 s;

[0022] when the thickness t of the thickest steel plate in the two pieces of the anti-oxidation hot-formed steel plate is 1.6-2.0 mm, the heating temperature is 900-930℃, and the holding time is 260-300 s.

[0023] Further, in S4, the cooling rate of the die cooling is 5-80℃ / s, and the cooling is to room temperature. A specific cooling treatment process is used, so that the weld can be transformed into martensite under cooling, and the toughness at the weld is improved by more than 30% compared with that of a conventional bare plate. The strength of the weld is even greater than that of the bare plate.

[0024] Further, in S3, the laser beam is zigzag oscillated along the weld for flat welding.

[0025] Further, in S2, the gap between the two pieces of the anti-oxidation hot-formed steel plate is 0-5mm.

[0026] Further, in S1, the anti-oxidation hot-formed steel plate further comprises a pretreatment step: the steel plate is processed flat by using a wire cutting or laser cutting method, and the surface and welding interface are subjected to dirt removal and air drying treatment.

[0027] The dirt removal uses one or more of dry ice snowflakes, anhydrous ethanol and acetone.

[0028] Further, in S2, the fixing specifically refers to placing the anti-oxidation hot-formed steel plate on a workbench and fixing it with a welding clamp, or placing the anti-oxidation hot-formed steel plate in a clamp after spot welding.

[0029] Further, in S3, the laser is a fiber laser, a solid-state laser or a carbon dioxide laser.

[0030] Further, in S3, the protective gas is nitrogen or argon, and the flow rate is 20L / min.

[0031] Advantages of the present application:

[0032] The anti-oxidation hot-formed steel plate of the present application adds a certain amount of Si and Cr elements to the conventional hot-formed steel plate, thereby improving the hardenability and the product of strength and ductility. The laser self-fusion tailor-welding can convert the weld into martensite under air cooling during the laser tailor-welding process. After laser tailor-welding heat treatment, the toughness at the weld is improved by more than 30% compared with the conventional bare plate, the strength of the weld is even greater than that of the bare plate, and the fracture position is not at the weld, so it can be applied to 1500MPa anti-oxidation hot-formed steel plate. The mechanical properties of the anti-oxidation hot-formed steel plate tailor-welded component are much greater than those of the ordinary bare plate tailor-welded component.

[0033] The self-fusion tailor-welding method solves the problem of tailor-welding of anti-oxidation hot-formed steel plates with different thicknesses, the laser welding power is 1.4-2.2 kW, and a single beam laser is used, which is simple to operate and low in cost. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings described below are only embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0035] Figure 1 is the metallographic phase diagram of the weld position of the embodiment 1 of the present application.

[0036] Figure 2is a tensile test photo of Example 1 of the present application;

[0037] Figure 3 is a tensile test photo of Example 2 of the present application;

[0038] Figure 4 is a tensile test photo of Example 3 of the present application;

[0039] Figure 5 is a tensile test photo of Example 4 of the present application;

[0040] Figure 6 is a tensile test photo of Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0041] The technical solutions of the present application will be described clearly and completely below in conjunction with specific embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0042] The present embodiment provides a laser welding method of 1500MPa grade antioxidant hot forming steel, comprising the following steps:

[0043] S1, providing two antioxidant hot forming steel plates, the thickness of the antioxidant hot forming steel plate is 1.0-2.0mm, the antioxidant hot forming steel plate comprises the following components in mass percentage: C 0.15-0.30%, Si 1.40-1.70%, Cr 3.10-3.40%, Mn 1.10-1.80%, B 0.001-0.010%, Ti 0.02-0.08%, Nb 0.05-0.10%, and the rest is Fe and inevitable impurities;

[0044] S2, fixing the two antioxidant hot forming steel plates, wherein the two antioxidant hot forming steel plates are aligned with a gap of 0-5mm;

[0045] S3, under a protective atmosphere, laser welding treatment is performed on the two antioxidant hot forming steel plates to obtain a laser welded plate; wherein the laser welding parameters are as follows:

[0046] When the thickness t of the thickest steel plate among the two antioxidant hot forming steel plates is 1.0-1.4mm, t+0.2≤Q≤t+0.4, the Q is the laser welding power, unit: kW, the welding speed is 30-50mm / s, and the defocusing amount is 8-12mm;

[0047] When the thickness t of the thickest steel plate in the two anti-oxidation hot-formed steel plates is 1.6-2.0 mm, t+0.1≤Q≤t+0.2, the laser welding power Q is in kW, the welding speed is 10-30 mm / s, and the defocusing amount is 3-8 mm;

[0048] S4, after the tailor-welded plate is heat treated, the tailor-welded plate is transferred to a flat die for die cooling; the parameters of the heat treatment are:

[0049] When the thickness t of the thickest steel plate in the two anti-oxidation hot-formed steel plates is 1.0-1.4 mm, the heating temperature is 880-900℃, and the holding time is 200-240 s;

[0050] When the thickness t of the thickest steel plate in the two anti-oxidation hot-formed steel plates is 1.6-2.0 mm, the heating temperature is 900-930℃, and the holding time is 260-300 s.

[0051] Preferably, in S1, a pretreatment step of the anti-oxidation hot-formed steel plate is further included: the steel plate is processed flat by using a line cutting or laser cutting method, and the surface and welding interface thereof are subjected to dirt removal and air drying treatment; the dirt removal uses one or more of dry ice snowflakes, anhydrous ethanol, and acetone.

[0052] Preferably, in S2, the fixing specifically refers to placing the anti-oxidation hot-formed steel plate on a workbench and fixing it with a welding clamp, or placing the anti-oxidation hot-formed steel plate in a clamp after spot welding and fixing it.

[0053] Preferably, in S3, the laser beam is zigzag oscillated along the weld to perform flat welding during the tailor-welding treatment; the protective gas is nitrogen or argon, and the flow rate is 20 L / min; the laser is a fiber laser, a solid-state laser, or a carbon dioxide laser.

[0054] Preferably, in S4, the cooling rate of the die cooling is 5-80℃ / s, and the cooling is to room temperature; a specific cooling treatment process is used, so that the weld can be transformed into martensite under cooling, the toughness at the weld is improved by more than 30% compared with a conventional bare plate, and the strength of the weld is even greater than that of the bare plate.

[0055] The anti-oxidation hot-formed steel plate in this embodiment adds a certain amount of Si and Cr elements on the basis of a conventional hot-formed steel plate bare plate, improves the hardenability and strength-plasticity product of the material. Laser self-fusion tailor-welding is adopted, and the weld can be transformed into martensite under air cooling during laser tailor-welding, and the toughness at the weld is improved by more than 30% compared with the conventional bare plate, the strength of the weld is even greater than that of the bare plate, and the fracture position is not at the weld, which can be applied to 1500MPa anti-oxidation hot-formed steel plate. The mechanical properties of the tailor-welded component of the anti-oxidation hot-formed steel plate are much greater than those of the ordinary bare plate tailor-welded component. The self-fusion tailor-welding mode solves the problem of tailor-welding of anti-oxidation hot-formed steel plates with different thicknesses, the laser welding power is 1.4-2.2 kW, and a single laser beam is adopted, which is simple to operate and low in cost.

[0056] The following is a specific embodiment, in which the anti-oxidation hot-formed plate is a 1500MPa grade anti-oxidation hot-formed steel plate, and the components of the steel plate include, by mass fraction: C 0.186-0.196%, Si 1.46-1.61%, Cr 3.17-3.36%, Mn 1.24-1.31%, B 0.0032-0.0037%, Ti 0.034-0.037%, Nb 0.057-0.072%, and the balance is Fe and unavoidable impurities. Example 1

[0057] This embodiment relates to a tailor-welding method of a 1500MPa grade anti-oxidation hot-formed steel plate, which comprises the following steps:

[0058] (1) Two anti-oxidation hot-formed steel plates with a thickness of 1.0mm are provided, the steel plates are processed flat by laser cutting, and the surface and welding interface are treated by anhydrous ethanol and then air-dried;

[0059] (2) The air-dried anti-oxidation hot-formed steel plates are placed on a workbench and fixed with a welding clamp, and the gap is 0mm;

[0060] (3) The two anti-oxidation hot-formed steel plates are tailor-welded by a laser under the protection of nitrogen gas with a flow rate of 20L / min, the laser beam is zigzag oscillated along the weld, and the tailor-welding parameters are as follows: the welding power is 1.4KW, the welding speed is 40mm / s, and the defocusing amount is 10mm;

[0061] (4) After heat treatment, the tailor-welded steel plates are transferred to a flat die, cooled to room temperature at a cooling rate of 5-80℃ / s, and the heat treatment parameters are as follows: the temperature is 900℃, and the holding time is 200s. The metallographic image of the weld position of the tailor-welded component in this embodiment is shown in Figure 1 It can be seen that there is no crack or bubble at the weld position. Example 2

[0062] The present example relates to a tailor-welding method of an oxidation-resistant hot-formed steel plate of 1500 MPa level, which differs from example 1 in that the thickness of the two steel plates is 2.0 mm, the tailor-welding parameters are: welding power is 2.2 KW, welding speed is 20 mm / s, defocusing amount is 5 mm, and the heat treatment parameters are: temperature is 930 ℃, holding time is 300 s, and other parameters and steps are the same. Example 3

[0063] The present example relates to a tailor-welding method of an oxidation-resistant hot-formed steel plate of 1500 MPa level, which differs from example 1 in that the thickness of the two steel plates is 2.0 mm, the tailor-welding parameters are: welding power is 2.2 KW, welding speed is 20 mm / s, defocusing amount is 5 mm, and the heat treatment parameters are: temperature is 930 ℃, holding time is 300 s, and other parameters and steps are the same. Example 4

[0064] The present example relates to a tailor-welding method of an oxidation-resistant hot-formed steel plate of 1500 MPa level, which differs from example 1 in that the thickness of the two steel plates is 2.0 mm, the tailor-welding parameters are: welding power is 2.2 KW, welding speed is 20 mm / s, defocusing amount is 5 mm, and the heat treatment parameters are: temperature is 930 ℃, holding time is 300 s, and other parameters and steps are the same.

[0065] Comparative Example 1

[0066] The present example relates to a tailor-welding method of an oxidation-resistant hot-formed steel plate of 1500 MPa level, which differs from example 1 in that the thickness of the two steel plates is 2.0 mm, the tailor-welding parameters are: welding power is 2.2 KW, welding speed is 20 mm / s, defocusing amount is 5 mm, and the heat treatment parameters are: temperature is 930 ℃, holding time is 300 s, and other parameters and steps are the same.

[0067] Comparative Example 2

[0068] The present example relates to a tailor-welding method of an oxidation-resistant hot-formed steel plate of 1500 MPa level, which differs from example 1 in that the thickness of the two steel plates is 2.0 mm, the tailor-welding parameters are: welding power is 2.2 KW, welding speed is 20 mm / s, defocusing amount is 5 mm, and the heat treatment parameters are: temperature is 930 ℃, holding time is 300 s, and other parameters and steps are the same.

[0069] Comparative Example 3

[0070] The comparative example relates to a butt welding method of the 1500MPa grade antioxidant hot forming steel plate, and the difference from example 1 is that the thickness of the two steel plates is 1.6mm, the butt welding parameters are: the welding power is 3KW, the welding speed is 25mm / s, the defocusing amount is 7mm, the heat treatment parameters are: the temperature is 930℃, the holding time is 260s, and the other parameters and steps are the same.

[0071] Comparative example 4

[0072] The comparative example relates to a butt welding method of the 1500MPa grade antioxidant hot forming steel plate, and the difference from example 1 is that the thickness of the two steel plates is 1.6mm, the butt welding parameters are: the welding power is 3KW, the welding speed is 25mm / s, the defocusing amount is 7mm, the heat treatment parameters are: the temperature is 930℃, the holding time is 260s, and the other parameters and steps are the same.

[0073] The welding parameters and welding result tests of examples 1-4 and comparative examples 1-3 are shown in table 1.

[0074] Table 1

[0075]

[0076] From table 1, it can be seen that the tensile strength of the butt welding components of examples 1-4 is larger, the weld structure is martensite structure, and the fracture position of the mechanical test is the base material. The tensile test samples of examples 1-4 are shown in Figures 2-5 It can be seen that the strength of the weld exceeds the strength of the steel plate body.

[0077] The laser power is low during the butt welding process of comparative example 1, which results in the existence of martensite and ferrite in the weld, and the strength is low. The fracture position of the tensile test is in the weld, as shown in Figure 6 The gap is too large during the butt welding process of comparative example 2, which results in poor weld quality and cannot be tested by tensile test; the laser power is too high during the butt welding process of comparative example 3, which results in welding deformation and cracking, and cannot be tested by tensile test; in comparative example 4, the welding speed is too fast, which results in false welding.

[0078] The above detailed description of the present application is made in combination with specific embodiments and exemplary examples, but these descriptions cannot be understood as limitations of the present application. Those skilled in the art understand that the technical solutions and embodiments of the present application can be variously replaced, modified or improved without deviating from the spirit and scope of the present application, and these all fall within the scope of the present application. The protection scope of the present application is subject to the appended claims.

Claims

1. A laser welding method of an oxidation-resistant hot-formed steel of the 1500 MPa grade, characterized in that, It comprises the following steps: S1, providing two pieces of antioxidant hot forming steel plates, the thickness of the antioxidant hot forming steel plates is 1.0-2.0mm; S2, fixing the two pieces of antioxidant hot forming steel plates, wherein the two pieces of antioxidant hot forming steel plates are aligned; S3, under a protective atmosphere, laser is used to perform tailor-welding treatment on the two pieces of antioxidant hot forming steel plates to obtain a tailor-welded plate; Wherein, the parameters of laser tailor-welding are as follows: When the thickness t of the thickest steel plate among the two pieces of antioxidant hot forming steel plates is 1.0-1.4mm, t+0.2≤Q≤t+0.4, Q is the laser tailor-welding power, unit: kW, the welding speed is 30-50mm / s, and the defocusing amount is 8-12mm; When the thickness t of the thickest steel plate among the two pieces of antioxidant hot forming steel plates is 1.6-2.0mm, t+0.1≤Q≤t+0.2, Q is the laser tailor-welding power, unit: kW, the welding speed is 10-30mm / s, and the defocusing amount is 3-8mm; S4, after the heat treatment of the tailor-welded plate, the tailor-welded plate is transferred to a flat die for die cooling; The parameters of the heat treatment are as follows: When the thickness t of the thickest steel plate among the two pieces of antioxidant hot forming steel plates is 1.0-1.4mm, the heating temperature is 880-900℃, and the holding time is 200-240s; When the thickness t of the thickest steel plate among the two pieces of antioxidant hot forming steel plates is 1.6-2.0mm, the heating temperature is 900-930℃, and the holding time is 260-300s; The cooling rate of the die cooling is 5-80℃ / s, and the cooling is to room temperature.

2. The method of laser welding of 1500 MPa grade oxidation resistant hot formed steel of claim 1, wherein, The antioxidant hot forming steel plate comprises the following components in mass percentage: C 0.15-0.30%, Si 1.40-1.70%, Cr 3.10-3.40%, Mn 1.10-1.80%, B 0.001-0.010%, Ti 0.02-0.08%, Nb 0.05-0.10%, and the rest is Fe and inevitable impurities.

3. The method of laser welding of 1500 MPa grade oxidation resistant hot formed steel of claim 1, wherein, In S3, the laser beam is zigzag oscillated along the weld to perform flat welding.

4. The method of laser welding the 1500 MPa grade oxidation resistant hot formed steel of claim 1, wherein, In S2, the gap between the two pieces of antioxidant hot forming steel plates is 0-5mm.

5. The method of laser welding the 1500 MPa grade of oxidation resistant hot formed steel of claim 1, wherein, In S1, the pretreatment step of the antioxidant hot forming steel plate is further included: the steel plate is processed flat by using wire cutting or laser cutting, and the surface and welding interface are subjected to dirt removal and air drying treatment; Wherein, the dirt removal adopts one or more of dry ice snowflakes, anhydrous ethanol and acetone.

6. The method of laser weld bonding of the 1500 MPa grade oxidation resistant hot formed steel of claim 1, wherein, In S2, the fixing is specifically that the antioxidant hot forming steel plates are placed on a workbench and fixed by welding clamps, or the antioxidant hot forming steel plates are fixed in the clamps after spot welding.

7. The method of laser welding the 1500 MPa grade of oxidation resistant hot formed steel of claim 1, wherein, In S3, the laser is a fiber laser, a solid-state laser or a carbon dioxide laser.

8. The method of laser welding the 1500 MPa grade of oxidation resistant hot formed steel of claim 1, wherein, In S3, the protective gas is nitrogen or argon, and the flow rate is 20L / min.

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