Tailored blank laser welding method for 1500MPa-grade antioxidant hot forming steel

Abstract

The invention discloses a tailored blank laser welding method for 1500 MPa-grade anti-oxidation hot forming steel. The tailored blank laser welding method comprises the following steps that two anti-oxidation hot forming steel plates are provided; the two anti-oxidation hot forming steel plates are fixed, and the two anti-oxidation hot forming steel plates are aligned; under the protective atmosphere, the two anti-oxidation hot forming steel plates are subjected to tailor-welding treatment through a laser to obtain a tailor-welded plate; and after heat treatment is conducted on the tailor-welded blank, the tailor-welded blank is transferred to a flat plate mold for mold cooling. Quantitative Si and Cr elements are added on the basis of a conventional hot-formed steel plate bare plate, the hardenability and the product of strength and elongation of the material are improved, laser self-melting tailor welding is performed, a welding seam can be converted into martensite under the air cooling condition, the toughness of the welding seam after heat treatment is improved by 30% or above compared with the conventional bare plate, the fracture position is not located at the welding seam, and the anti-oxidation hot-formed steel plate has the good anti-oxidation performance. The method can be applied to 1500MPa anti-oxidation hot forming steel plates; and a single laser beam is adopted, so that the operation is simple, and the cost is low.

Description

Technical Field

[0001] The invention relates to the technical field of laser welding, and in particular to a laser welding method for 1500MPa-grade oxidation-resistant hot-formed steel. Background Art

[0002] Lightweighting is a method of reducing the weight of parts while ensuring the strength of the parts remains unchanged. High-strength hot-formed steel is an indispensable material for achieving lightweighting in the automotive industry.

[0003] Compared with traditional welding technology, laser welding technology can improve the utilization rate of raw materials and reduce production costs. It can perform laser welding on hot-formed steels of different strengths and thicknesses, which can greatly reduce tooling costs, reduce the overall weight of parts, and improve part dimensional accuracy in the subsequent hot stamping process.

[0004] At present, there are two types of hot-formed steel: bare plate and coated plate, and oxidation-resistant hot-formed steel is a type of bare plate. Anti-oxidation hot-formed steel adds Si and Cr elements to ordinary hot-formed steel to improve the hardenability of the steel, so that the material can reach martensite even in air-cooled state and can produce a layer of oxide layer of about 1 micron on the surface of the steel matrix to protect the steel matrix from oxidation. In the actual production process, oxidation-resistant hot-formed steel can achieve: lower heating temperature, shorter heating time, and reduced energy consumption; shorter stamping cycle, improved production efficiency; and elimination of shot blasting steps, reducing production process costs.

[0005] Based on the above research, antioxidant hot-formed steel has great value in the automotive industry under the premise of lightweighting, cost reduction and efficiency improvement. Therefore, it is necessary to find a suitable welding process for laser welding of antioxidant hot-formed steel. Systematic research on the laser welding process of antioxidant hot-formed steel has certain theoretical and practical value.

[0006] Patent CN116967608A discloses a method for manufacturing high-strength steel laser welding. The high-strength steel matrix contains 5-15% residual austenite structure. Two high-strength steel workpieces to be welded are butt-jointed, and a large-size spot first laser beam and a small-size spot second laser beam are used to synchronously weld the upper surface of the welded part and the lower surface of the welded part. This can not only improve the high-strength steel laser welding yield, but also improve the forming performance of the welded joint, meeting the needs of efficient production and use. However, this method requires two laser beams, which is complicated to operate and costly. Moreover, for oxidation-resistant hot-formed steel, the austenite in the matrix is ​​less than 5%, so this technical solution is not suitable for laser welding of oxidation-resistant hot-formed steel.

[0007] Patent CN113736983A discloses a method for improving the toughness of high-strength steel welds. The welds of high-strength steel are subjected to laser heat treatment twice. The first laser heat treatment is used to form a martensitic weld. The second laser heat treatment is to temper the martensitic weld to obtain a tempered martensitic structure to improve the toughness of the weld. This method can achieve an efficient, high-precision, high-quality weld softening heat treatment technical solution, reduce the risk of weld fracture, and avoid various forms of weld fracture problems caused by low weld toughness, hydrogen embrittlement, or excessive weld hardness. However, this method requires two laser heat treatments, which is complicated to operate, inefficient, and costly.

[0008] Patent CN117583852A discloses a method for preparing a hot-formed joint of Al-Si coated hot-formed steel. Since it is Al-Si coated hot-formed steel, it is necessary to use filler wire welding for laser welding. If autogenous welding is used, the Al element in the coating will penetrate into the weld, hindering the transformation of the structure to produce ferrite (soft phase), resulting in low strength at the weld and cracking at the weld. This method requires specific welding wire and is costly. As for oxidation-resistant hot-formed steel, it is a type of bare plate and does not have an Al-Si coating on the surface, so filler wire welding is not required during the laser welding process. 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 of the invention

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

[0011] S1. Provide two anti-oxidation hot-formed steel plates, each of which has a thickness of 1.0-2.0 mm;

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

[0013] S3. Under a protective atmosphere, two anti-oxidation hot-formed steel plates are welded by laser to obtain a welded plate;

[0014] Among them, the parameters of laser welding are:

[0015] When the thickness t of the thickest of the two anti-oxidation hot-formed steel plates is 1.0-1.4 mm, t+0.2≤Q≤t+0.4, where Q is the laser welding power in kW, the welding speed is 30-50 mm / s, and the defocus is 8-12 mm;

[0016] When the thickness t of the thickest of the two oxidation-resistant hot-formed steel plates is 1.6-2.0 mm, t+0.1≤Q≤t+0.2, where Q is the laser welding power in kW, the welding speed is 10-30 mm / s, and the defocus is 3-8 mm;

[0017] S4, after heat treatment, the tailor-welded blank is transferred to a flat mold for mold cooling.

[0018] Furthermore, the oxidation resistant hot-formed steel plate comprises the following components by 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 unavoidable impurities.

[0019] The present invention adopts an anti-oxidation hot-formed steel plate and performs laser self-melting welding. 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, thereby improving the hardenability and strength-ductility product of the material. During the laser welding process, the weld can be transformed into martensite under air cooling, and the toughness of the weld after heat treatment is increased 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 will not be at the weld, which can be applied to 1500MPa anti-oxidation hot-formed steel plates. And the mechanical properties of the anti-oxidation hot-formed steel plate welded components are much greater than those of ordinary bare plate welded components. The self-melting welding method of the present invention solves the problem of welding anti-oxidation hot-formed steel plates of different thicknesses. The laser welding power is 1.4-2.2kW, and a single-beam laser is used, which is low in cost.

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

[0021] When the thickness t of the thickest of the two anti-oxidation hot-formed steel plates is 1.0-1.4 mm, the heating temperature is 880-900°C and the holding time is 200-240s;

[0022] When the thickness t of the thickest of the two oxidation-resistant hot-formed steel plates is 1.6-2.0 mm, the heating temperature is 900-930°C and the holding time is 260-300 s.

[0023] Furthermore, in S4, the cooling rate of the mold cooling is 5-80°C / s, and after cooling to room temperature, a specific cooling treatment process is adopted, so that the weld can be transformed into martensite during cooling, and the toughness of the weld is increased by more than 30% compared with the conventional bare plate, and the strength of the weld is even greater than that of the bare plate.

[0024] Furthermore, in S3, during the tailor-made welding process, the laser beam is swung along the weld in a zigzag shape to perform flat welding.

[0025] Furthermore, in S2, the gap between the two anti-oxidation hot-formed steel plates is 0-5 mm.

[0026] Furthermore, S1 also includes a pretreatment step of the anti-oxidation hot-formed steel plate: flattening the steel plate by wire cutting or laser cutting, and decontaminating and air-drying the surface and welding interface thereof;

[0027] Wherein, the decontamination adopts one or more of dry ice snowflakes, anhydrous ethanol and acetone.

[0028] Furthermore, in S2, the fixing is specifically: placing the anti-oxidation hot-formed steel plate on a workbench and fixing it with a welding fixture, or placing the anti-oxidation hot-formed steel plate in a fixture and fixing it after spot welding.

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

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

[0031] Beneficial effects of the present invention:

[0032] The oxidation-resistant hot-formed steel plate of the present invention adds a certain amount of Si and Cr elements to the conventional hot-formed steel plate bare plate, thereby improving the material hardenability and strength-ductility product. Laser self-melting welding is adopted, and the weld can be transformed into martensite under air cooling during the laser welding process. After laser welding heat treatment, the toughness of the weld is increased by more than 30% compared with the conventional bare plate, and the strength of the weld is even greater than that of the bare plate, and the fracture position will not be at the weld, which can be applied to 1500MPa oxidation-resistant hot-formed steel plates. And the mechanical properties of the oxidation-resistant hot-formed steel plate welded components are much greater than those of ordinary bare plate welded components.

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

[0034] In order to more clearly illustrate the technical solution of the present invention, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] Figure 1 This is a metallographic diagram of the weld position of Example 1 of the present invention;

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

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

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

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

[0040] Figure 6 It is a tensile test photograph of Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be described clearly and completely below in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] This embodiment provides a laser welding method for 1500MPa grade oxidation-resistant hot-formed steel, comprising the following steps:

[0043] S1. Provide two anti-oxidation hot-formed steel plates, the thickness of the anti-oxidation hot-formed steel plates is 1.0-2.0 mm, and the anti-oxidation hot-formed steel plates include the following components by 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 unavoidable impurities;

[0044] S2. Fixing the two anti-oxidation hot-formed steel plates, wherein the two anti-oxidation hot-formed steel plates are aligned with a gap of 0-5 mm;

[0045] S3. Under a protective atmosphere, two anti-oxidation hot-formed steel plates are welded by laser to obtain welded plates; wherein the parameters of laser welding are:

[0046] When the thickness t of the thickest of the two anti-oxidation hot-formed steel plates is 1.0-1.4 mm, t+0.2≤Q≤t+0.4, where Q is the laser welding power in kW, the welding speed is 30-50 mm / s, and the defocus is 8-12 mm;

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

[0048] S4, after heat treatment of the tailor-welded blank, transfer it to a flat die for die cooling; the heat treatment parameters are:

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

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

[0051] Preferably, S1 also includes a pretreatment step of the anti-oxidation hot-formed steel plate: the steel plate is smoothed by wire cutting or laser cutting, and its surface and welding interface are decontaminated and air-dried; the decontamination is carried out by one or more of dry ice snowflakes, anhydrous ethanol and acetone.

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

[0053] Preferably, in S3, during the tailor-made welding process, the laser beam performs zigzag swing flat welding along the weld; the shielding gas is nitrogen or argon with a flow rate of 20 L / min; and the laser is a fiber laser, a solid-state laser or a carbon dioxide laser.

[0054] Preferably, in S4, the cooling rate of the mold cooling is 5-80°C / s, and after cooling to room temperature, a specific cooling treatment process is adopted, so that the weld can be transformed into martensite during cooling, and the toughness of the weld is increased by more than 30% compared with the conventional bare plate, and the strength of the weld is even greater than that of the bare plate.

[0055] In this embodiment, the oxidation-resistant hot-formed steel plate adds a certain amount of Si and Cr elements on the basis of the conventional hot-formed steel plate bare plate, which improves the hardenability and strength-ductility product of the material. Laser self-melting welding is adopted. During the laser welding process, the weld can be transformed into martensite under air cooling, and the toughness at the weld is increased 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 will not be at the weld. It can be applied to 1500MPa oxidation-resistant hot-formed steel plates. And the mechanical properties of the oxidation-resistant hot-formed steel plate welded components are much greater than those of ordinary bare plate welded components. The self-melting welding method solves the problem of welding oxidation-resistant hot-formed steel plates of different thicknesses. The laser welding power is 1.4-2.2kW, and a single-beam laser is used, which is simple to operate and low in cost.

[0056] The following is a specific embodiment, in which the oxidation-resistant hot-formed plate is a 1500MPa grade oxidation-resistant hot-formed steel plate. The steel plate components include, by mass: 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 rest is Fe and unavoidable impurities.

[0057] Example 1

[0058] This embodiment relates to a method for welding a 1500MPa grade anti-oxidation hot-formed steel plate, comprising the following steps:

[0059] (1) Two anti-oxidation hot-formed steel plates, each with a thickness of 1.0 mm, were provided. The steel plates were processed flat by laser cutting, and their surfaces and welding interfaces were decontaminated by anhydrous ethanol and then air-dried;

[0060] (2) Place the air-dried anti-oxidation hot-formed steel plate on a workbench and fix it with a welding fixture with a gap of 0 mm;

[0061] (3) Under the protection of nitrogen with a flow rate of 20 L / min, two anti-oxidation hot-formed steel plates were welded by laser. The laser beam swung in a zigzag shape along the weld. The welding parameters were: welding power of 1.4 KW, welding speed of 40 mm / s, and defocus of 10 mm.

[0062] (4) After heat treatment, the welded steel plate is transferred to a flat mold and cooled to room temperature at a cooling rate of 5-80°C / s. The heat treatment parameters are: temperature 900°C, holding time 200s. The metallographic image of the weld position of the welded component of this embodiment is as follows: Figure 1 As shown, it can be seen that there are no cracks or bubbles at the weld position.

[0063] Example 2

[0064] This embodiment relates to a method for welding 1500MPa grade anti-oxidation hot-formed steel plates. The difference from Implementation 1 is that the thickness of the two steel plates is 2.0mm, the welding parameters are: welding power is 2.2KW, welding speed is 20mm / s, defocus is 5mm, heat treatment parameters are: temperature is 930℃, insulation time is 300s, and other parameters and steps are the same.

[0065] Example 3

[0066] This embodiment relates to a method for welding 1500MPa grade anti-oxidation hot-formed steel plates. The difference from Implementation 1 is that the thicknesses of the two steel plates are 1.4mm and 1.6mm respectively, and the welding parameters are: welding power is 1.7KW, welding speed is 30mm / s, defocus is 7mm, heat treatment parameters are: temperature is 920°C, insulation time is 260s, and other parameters and steps are the same.

[0067] Example 4

[0068] This embodiment relates to a method for welding 1500MPa grade anti-oxidation hot-formed steel plates. The difference from Implementation 1 is that the thicknesses of the two steel plates are 1.6mm and 2.0mm respectively, and the welding parameters are: welding power is 2.2KW, welding speed is 20mm / s, defocus is 4mm, heat treatment parameters are: temperature is 930°C, holding time is 260s, and other parameters and steps are the same.

[0069] Comparative Example 1

[0070] This comparative example relates to a method for welding 1500MPa grade anti-oxidation hot-formed steel plates. The difference from implementation 1 is that the thickness of the two steel plates is 1.6mm, the welding parameters are: welding power is 1.6KW, welding speed is 25mm / s, defocus is 7mm, heat treatment parameters are: temperature is 930℃, insulation time is 260s, and other parameters and steps are the same.

[0071] Comparative Example 2

[0072] This comparative example relates to a method for welding 1500MPa grade anti-oxidation hot-formed steel plates. The difference from implementation 1 is that the thickness of the two steel plates is 1.6mm, the gap is 6mm, the welding parameters are: welding power is 1.6KW, welding speed is 25mm / s, defocus is 7mm, heat treatment parameters are: temperature 930℃, insulation time 260s, and other parameters and steps are the same.

[0073] Comparative Example 3

[0074] This comparative example relates to a method for welding 1500MPa grade anti-oxidation hot-formed steel plates. The difference from implementation 1 is that the thickness of the two steel plates is 1.6mm, the welding parameters are: welding power is 3KW, welding speed is 25mm / s, defocus is 7mm, heat treatment parameters are: temperature is 930℃, insulation time is 260s, and other parameters and steps are the same.

[0075] Comparative Example 4

[0076] This comparative example relates to a method for welding 1500MPa grade anti-oxidation hot-formed steel plates. The difference from implementation 1 is that the thickness of the two steel plates is 1.6mm, the welding parameters are: welding power is 1.7KW, welding speed is 40mm / s, defocus is 7mm, heat treatment parameters are: temperature is 930℃, insulation time is 260s, and other parameters and steps are the same.

[0077] The welding parameters and welding results of Examples 1-4 and Comparative Examples 1-3 are shown in Table 1.

[0078] Table 1

[0079]

[0080] As can be seen from Table 1, the tensile strength of the welded components of Examples 1-4 of the present invention is relatively large, the weld structure is a martensitic structure, and the fracture positions of the mechanical tests are all parent materials. The tensile specimens of the welded components of Examples 1-4 are as follows: Figure 2-5 As shown, it can be seen that the strength of the weld exceeds the strength of the steel plate itself.

[0081] Comparative Example 1 The laser power during the welding process is low, resulting in the presence of martensite and ferrite in the weld, which has low strength. The fracture position of the tensile test is at the weld, such as Figure 6 As shown; in Example 2, the gap during the welding process is too large, resulting in poor weld quality and inability to perform tensile testing; in Example 3, the laser power during the welding process is too high, resulting in welding deformation and cracking, and inability to perform tensile testing; in Example 4, the welding rate is too fast, resulting in cold welds.

[0082] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

Claims

1. A laser welding method for 1500MPa grade oxidation resistant hot-formed steel, characterized in that: The steps include: S1. Provide two anti-oxidation hot-formed steel plates, each of which has a thickness of 1.0-2.0 mm; S2, fixing the two anti-oxidation hot-formed steel plates, wherein the two anti-oxidation hot-formed steel plates are aligned; S3. Under a protective atmosphere, two anti-oxidation hot-formed steel plates are welded by laser to obtain a welded plate; Among them, the parameters of laser welding are: When the thickness t of the thickest of the two anti-oxidation hot-formed steel plates is 1.0-1.4 mm, t+0.2≤Q≤t+0.4, where Q is the laser welding power in kW, the welding speed is 30-50 mm / s, and the defocus is 8-12 mm; When the thickness t of the thickest of the two oxidation-resistant hot-formed steel plates is 1.6-2.0 mm, t+0.1≤Q≤t+0.2, where Q is the laser welding power in kW, the welding speed is 10-30 mm / s, and the defocus is 3-8 mm; S4, after heat treatment, the tailor-welded blank is transferred to a flat mold for mold cooling.

2. The laser welding method of 1500MPa grade oxidation resistant hot-formed steel according to claim 1, characterized in that: The oxidation resistant hot-formed steel plate comprises the following components by mass percentage: C 0.15-0.30%, Si 1.40-1.70%, Cr3.10-3.40%, 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 laser welding method of 1500MPa grade oxidation resistant hot formed steel according to claim 1, characterized in that: In S4, the parameters of the heat treatment are: When the thickness t of the thickest of the two anti-oxidation hot-formed steel plates is 1.0-1.4 mm, the heating temperature is 880-900°C and the holding time is 200-240s; When the thickness t of the thickest of the two oxidation-resistant hot-formed steel plates is 1.6-2.0 mm, the heating temperature is 900-930°C and the holding time is 260-300 s.

4. The laser welding method of 1500MPa grade oxidation resistant hot formed steel according to claim 1, characterized in that: In S4, the mold is cooled at a cooling rate of 5-80°C / s to room temperature.

5. The laser welding method of 1500MPa grade oxidation resistant hot formed steel according to claim 1, characterized in that: In S3, during the tailor-made welding process, the laser beam is swung along the weld in a zigzag shape to perform flat welding.

6. The laser welding method of 1500MPa grade oxidation resistant hot formed steel according to claim 1, characterized in that: In S2, the gap between the two anti-oxidation hot-formed steel plates is 0-5 mm.

7. The laser welding method of 1500MPa grade oxidation resistant hot formed steel according to claim 1, characterized in that: S1 also includes a pretreatment step of the anti-oxidation hot-formed steel plate: flattening the steel plate by wire cutting or laser cutting, and decontaminating and air-drying the surface and welding interface; Wherein, the decontamination adopts one or more of dry ice snowflakes, anhydrous ethanol and acetone.

8. The laser welding method for 1500MPa grade oxidation resistant hot formed steel according to claim 1, characterized in that: In S2, the fixing specifically includes: placing the anti-oxidation hot-formed steel plate on a workbench and fixing it with a welding fixture, or placing the anti-oxidation hot-formed steel plate in a fixture and fixing it after spot welding.

9. The laser welding method of 1500MPa grade oxidation resistant hot formed steel according to claim 1, characterized in that: In S3, the laser is a fiber laser, a solid-state laser or a carbon dioxide laser.

10. The laser welding method of 1500MPa grade oxidation resistant hot formed steel according to claim 1, characterized in that: In S3, the protective gas is nitrogen or argon, and the flow rate is 20 L / min.

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