A cold rolling laser welding machine ultra-high strength steel weld stability control method
By employing a heterogeneous transition cladding process and secondary annealing, the problem of high weld breakage rate in cold-rolled high-strength hot-formed steel was solved, enabling stable and continuous production of ultra-high-strength steel, reducing weld breakage rate, and improving the plasticity and toughness of the welded area.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ANHUI UNIVERSITY OF TECHNOLOGY
- Filing Date
- 2026-04-21
- Publication Date
- 2026-07-24
AI Technical Summary
The high breakage rate of weld seams in cold-rolled high-strength hot-formed steel leads to a decrease in unit production efficiency and makes it difficult to achieve large-scale continuous production. In particular, the breakage rate of thin products with a thickness of ≤2.5mm reaches 100%. The high hardness of the weld seams results in high brittleness, which cannot meet the market's demand for ultra-high-strength steel in large quantities.
A heterogeneous transition cladding process combined with a secondary annealing process is adopted. By covering the weld area with cladding powder of a specific composition and performing laser cladding, followed by two annealing treatments, a plastic buffer layer is formed to reduce weld stress and improve weld toughness.
It effectively reduced the weld breakage rate of hot-formed steel of 1800MPa grade and above, realized the stable and continuous production of ultra-high strength steel, solved the problem of strength mismatch between weld and base material, and improved the ductility and toughness of the welded area.
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Abstract
Description
Technical Field
[0001] This invention relates to a high-strength steel welding technology, and more particularly to a method for controlling the stability of ultra-high-strength steel welds using a cold-rolled laser welding machine. Background Technology
[0002] During the trial production period, the weld breakage rate of 1800MPa grade high-strength hot-formed steel reached 80%, and the breakage rate of thin-specification products with a thickness of ≤2.5mm reached 100%. This resulted in a 15% decrease in the effective operating rate of the unit when producing this product, making it impossible to achieve large-scale continuous production and meet the market's bulk demand for ultra-high-strength steel.
[0003] The high breakage rate is mainly due to weld performance defects. High hardness in the heat-affected zone (HAZ) leads to brittleness; sample hardness tests generally show values above 500 HV, with the HAZ exceeding 600 HV. This high hardness in the HAZ results in rolling forces of up to 2000-2500 tons at both ends of the weld during mill runs, causing brittle fracture at the weld. A brittle layer forms near the fusion line due to martensite coarsening. Simultaneously, cupping tests show insufficient ductility; while the reverse bending test is acceptable, it cannot withstand the impact of rolling forces. For steel grades with a carbon equivalent of 0.61-0.65 (composition: C 0.32-0.34%, Mn 1.3-1.5%, Cr 0.15-0.25%, balance Fe, etc.), conventional annealing cannot overcome its brittleness barrier; the traditional single-pass annealing process can only reduce the weld hardness to 500-550 HV, and the strength matching between the weld and the base metal is unbalanced, with fractures concentrated in the softened zone of the fusion line, which cannot meet the requirements of continuous rolling mills for producing through-plates with welds.
[0004] Although Chinese patent CN112958930A employs alternating welding of high / low carbon equivalent steel combined with annealing to reduce the risk of steel strip fracture and improve the stability of welding quality, this method is less effective in reducing the breakage rate of 1800MPa grade cold-rolled hot-formed strip steel with a carbon equivalent greater than 0.6. It fails to meet the toughness requirements of the weld joints for this type of steel strip, lacks sufficient precision in hardness control, and is prone to fracture at the weld joints of preceding and following strips, thus failing to meet production demands and adapting to high-stress rolling environments. Currently, for ultra-high-strength steel with a carbon equivalent greater than 0.6, conventional processes cannot overcome the brittleness barrier, resulting in a significant mismatch between weld strength and base material strength. Summary of the Invention
[0005] Purpose of the invention: The purpose of this invention is to provide a method for controlling the stability of welds in ultra-high strength steel, thereby solving the problem of high weld breakage rate in cold-rolled high-strength hot-formed strip steel.
[0006] Technical solution: The present invention provides a method for controlling the stability of ultra-high strength steel welds, comprising the following steps: (1) After splicing the tail end of the forward hot-rolled strip steel with the head end of the subsequent hot-rolled strip steel, laser weld it, smooth the weld seam, and then perform the first annealing treatment on the welded area. (2) A layer of cladding powder is uniformly covered on one side of the weld, and then laser cladding is performed on the cladding powder; the same cladding powder is used to perform laser cladding on one side of the weld; (3) Perform a second annealing treatment on the cladding area, and then complete the welding of the hot-rolled strip after cooling.
[0007] This invention innovatively combines a heterogeneous transition cladding process with a secondary annealing process, effectively reducing stress concentration in the weld area during the transition production of 1800MPa grade and above hot-formed ultra-high strength steel. It solves the problem of weld strength mismatch in ultra-high strength steel (Ceq>0.6), optimizes weld quality, and thus significantly reduces the breakage rate of ultra-high strength steel, enabling continuous production of 1800MPa grade hot-formed steel and other steel grades.
[0008] The cladding powder used in the heterogeneous transition cladding process uses 590MPa high-strength steel as the matrix, supplemented with nickel-iron layered double hydroxide, magnesium fluoride, and molybdenum, chromium, and silicon elements. After being clad in the welding area, it can act as a plastic buffer layer, promote the decomposition of coarse martensite at the weld, and, in conjunction with secondary annealing, effectively improve the ductility of the welding area and absorb rolling stress, thereby reducing the risk of strip breakage.
[0009] Preferably, in step (1), the hot-rolled strip steel is a cold-rolled hot-formed strip steel of grade 1800MPa or above with a carbon equivalent of at least 0.6 and a thickness of no more than 3mm.
[0010] Preferably, in step (1), the laser welding method is as follows: the tail end of the preceding hot-rolled strip and the head end of the following hot-rolled strip are cut flat and spliced together, and a CO2 laser with a welding power of 10-12kW is used to laser weld the splice seam, with a welding speed of 1-3m / min.
[0011] Furthermore, the width of the splice seam does not exceed 1mm.
[0012] Preferably, in step (1), the conditions for the first annealing treatment are annealing at 600-650℃ for 1-3 minutes.
[0013] Preferably, in step (2), the composition of the cladding powder, by mass fraction, is as follows: 0.2-0.4% Si, 0.7-1.4% Cr, 0.1-0.5% Mo, 0.1-0.5% magnesium fluoride, 1-5% nickel-iron layered double hydroxide, balance being 590MPa grade hot-rolled pickled steel powder.
[0014] Furthermore, the carbon equivalent of the 590MPa grade hot-rolled pickled steel powder is 0.2-0.3, and the average particle size of the powder is 0.05-0.5 mm.
[0015] Preferably, in step (2), the thickness of the cladding powder covering one side is 0.2-1.0 mm.
[0016] Preferably, in step (2), the laser cladding method is to perform laser cladding under an inert atmosphere with laser power of 2.0-3.0kW, spot diameter of 3-5 mm, and scanning speed of 5-7 mm / s.
[0017] Preferably, in step (3), the conditions for the second annealing treatment are annealing at 720-850℃ for 1-3 minutes.
[0018] The second annealing treatment can promote the full decomposition of coarse martensite in the weld seam and heat-affected zone covered with transition plastic material, and achieve a controllable decrease in hardness. The present invention effectively softens the weld seam area, eliminates residual stress, and significantly improves the ductility and toughness of the material through the second heat treatment after cladding.
[0019] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: This invention overcomes the limitations of conventional annealing by employing an innovative combination of "secondary weld heat treatment and heterogeneous transition cladding with specific strength," fundamentally solving the problem of weld band breakage during continuous production of ultra-high-strength steel. By matching the strength gradient in the weld area, it addresses the strength mismatch between the weld and the base material in high-carbon equivalent steel, reducing the risk of fracture near the fusion line. This enables stable and continuous production of 1800MPa grade hot-formed steel and other steel grades. Detailed Implementation
[0020] The technical solution of the present invention will be further described below.
[0021] Example 1: A method for controlling the stability of ultra-high strength steel welds is as follows: (1) Using 1800MPa grade cold-rolled hot-formed strip steel (composition: 0.33wt% C, 1.4wt% Mn, 0.2wt% Cr, balance Fe, etc.) with a carbon equivalent of 0.63 and a thickness of 2mm as the welding object, the tail end of the preceding cold-rolled hot-formed strip steel and the head end of the following cold-rolled hot-formed strip steel are cut flat and spliced together. The width of the splice seam does not exceed 0.5mm. A CO2 laser with a welding power of 11kW is used to perform laser welding on the splice seam. The welding speed is 2.4m / min. After flattening the weld seam, the welding area is annealed at 630℃ for 2min using a high-frequency induction heating device. (2) Prepare cladding powder according to the following ratio: 0.3 wt% elemental silicon powder, 1.1 wt% metallic chromium powder, 0.3 wt% metallic molybdenum powder, 0.3 wt% magnesium fluoride powder, 3 wt% nickel-iron layered double hydroxide standard powder, and 95 wt% 590 MPa grade hot-rolled pickled steel powder were mixed and ground to obtain a cladding powder with an average particle size of 0.25 mm. The 590 MPa grade hot-rolled pickled steel powder has a carbon equivalent of 0.25 and a composition of: 0.12 wt% C, 1.7 wt% Mn, 0.1 wt% Si, P ≤ 0.02 wt%, S ≤ 0.02 wt%, and the balance Fe.
[0022] (3) A layer of cladding powder with a thickness of 0.6 mm and a width of 4 cm is uniformly covered on one side of the weld. Under an inert atmosphere, laser cladding is performed on the cladding powder with laser power of 2.5 kW, spot diameter of 4 mm, and scanning speed of 6 mm / s. The same cladding powder is used to perform laser cladding on one side of the weld. (4) Perform a second annealing treatment on the cladding area at 780℃ for 3 min. After cooling, complete the welding of the hot-rolled strip.
[0023] Example 2: A method for controlling the stability of ultra-high strength steel welds is as follows: (1) Using 1800MPa grade cold-rolled hot-formed strip steel (composition: 0.32wt%C, 1.3wt%Mn, 0.15wt%Cr, balance Fe, etc.) with a carbon equivalent of 0.61 and a thickness of 2.3mm as the welding object, the tail end of the preceding cold-rolled hot-formed strip steel and the head end of the following cold-rolled hot-formed strip steel are cut flat and spliced together. The width of the splice seam does not exceed 1mm. A CO2 laser with a welding power of 10kW is used to perform laser welding on the splice seam. The welding speed is 2m / min. After flattening the weld seam, the welding area is annealed at 600℃ for 3min using a high-frequency induction heating device. (2) Prepare cladding powder according to the following ratio: 0.2 wt% elemental silicon powder, 0.7 wt% metallic chromium powder, 0.1 wt% metallic molybdenum powder, 0.1 wt% magnesium fluoride powder, 1 wt% nickel-iron layered double hydroxide standard powder, and 97.9 wt% 590 MPa grade hot-rolled pickled steel powder were mixed and ground to obtain a cladding powder with an average particle size of 0.05 mm. The 590 MPa grade hot-rolled pickled steel powder has a carbon equivalent of 0.2 and a composition of: 0.10 wt% C, 1.5 wt% Mn, 0.12 wt% Si, P ≤ 0.02 wt%, S ≤ 0.02 wt%, and the balance Fe.
[0024] (3) A layer of cladding powder with a thickness of 0.2 mm and a width of 3 cm is uniformly covered on one side of the weld. Under an inert atmosphere, laser cladding is performed on the cladding powder with laser power of 2.0 kW, spot diameter of 3 mm, and scanning speed of 5 mm / s. The same cladding powder is used to perform laser cladding on one side of the weld. (4) Perform a second annealing treatment on the cladding area at 720℃ for 2 minutes. After cooling, complete the welding of the hot-rolled strip.
[0025] Example 3: A method for controlling the stability of ultra-high strength steel welds is as follows: (1) Using 1800MPa grade cold-rolled hot-formed strip steel (composition: 0.34wt% C, 1.5wt% Mn, 0.25wt% Cr, balance Fe, etc.) with a carbon equivalent of 0.65 and a thickness of 3mm as the welding object, the tail end of the preceding cold-rolled hot-formed strip steel and the head end of the following cold-rolled hot-formed strip steel are cut flat and spliced together. The width of the splice seam does not exceed 1.5mm. A CO2 laser with a welding power of 12kW is used to perform laser welding on the splice seam. The welding speed is 3m / min. After flattening the weld seam, the welding area is annealed at 650℃ for 1min using a high-frequency induction heating device and then cooled at room temperature. (2) Prepare cladding powder according to the following ratio: 0.4 wt% elemental silicon powder, 1.4 wt% metallic chromium powder, 0.5 wt% metallic molybdenum powder, 0.5 wt% magnesium fluoride powder, 5 wt% nickel-iron layered double hydroxide standard powder, and 92.2 wt% 590 MPa grade hot-rolled pickled steel powder were mixed and ground to obtain a cladding powder with an average particle size of 0.5 mm. The 590 MPa grade hot-rolled pickled steel powder has a carbon equivalent of 0.3 and a composition of: 0.16 wt% C, 1.8 wt% Mn, 0.1 wt% Si, P ≤ 0.02 wt%, S ≤ 0.02 wt%, and the balance Fe.
[0026] (3) A layer of cladding powder with a thickness of 1.0 mm and a width of 5 cm is uniformly covered on one side of the weld. Under an inert atmosphere, laser cladding is performed on the cladding powder with laser power of 3.0 kW, spot diameter of 5 mm, and scanning speed of 7 mm / s. The same cladding powder is used to perform laser cladding on one side of the weld. (4) Perform a second annealing treatment on the cladding area at 850℃ for 1 min. After cooling, complete the welding of the hot-rolled strip.
[0027] Comparative Example 1: Everything else is the same as in Example 1, except that: Skip step (3) and proceed directly to the second annealing process.
[0028] Comparative Example 2: Everything else is the same as in Example 1, except that: Replace the cladding powder in step (3) with 590MPa grade hot-rolled pickled steel powder.
[0029] Comparative Example 3: Everything else is the same as in Example 1, except that: The cladding powder does not contain nickel-iron layered double hydroxide standard powder.
[0030] Comparative Example 4: Everything else is the same as in Example 1, except that: No elemental silicon powder, metallic chromium powder, or metallic molybdenum powder is added to the cladding powder.
[0031] Comparative Example 5: Everything else is the same as in Example 1, except that: Magnesium fluoride powder is not added to the cladding powder.
[0032] Comparative Example 6: Everything else is the same as in Example 1, except that: No 590MPa grade hot-rolled pickled steel powder is added to the cladding powder.
[0033] Comparative Example 7: Everything else is the same as in Example 1, except that: Replace the 590MPa grade hot-rolled pickled steel powder in the cladding powder with hot-rolled pickled steel powder of the following composition: 0.07wt%C, 0.8wt%Mn, P≤0.02wt%, S≤0.02wt%, balance Fe.
[0034] Comparative Example 8: Everything else is the same as in Example 1, except that: The first annealing process in step (1) is not performed.
[0035] Comparative Example 9: Everything else is the same as in Example 1, except that: The second annealing process in step (4) is not performed.
[0036] Comparative Example 10: Everything else is the same as in Example 1, except that: The first annealing process in step (1) and the second annealing process in step (4) are not performed.
[0037] The hardness of the weld area, cladding area and surrounding heat-affected zone in Examples 1-3 and Comparative Examples 1-10 was measured respectively, and three different points were measured in each area.
[0038] In addition, the steel strip breakage rate during continuous processing was measured.
[0039] The results are as follows: Table 1. Hardness test results of different areas at the weld joint
[0040] As shown in Table 1, Comparative Example 1, due to only two heat treatments on the weld without a cladding plastic transition layer, resulted in high hardness in the weld area, making it extremely prone to fracture. Comparative Example 2, using only 590MPa grade hot-rolled pickled steel powder to prepare the cladding plastic transition layer, had a weak effect on improving the plasticity of the weld area, significantly less effective than the cladding powder with compound components. In Comparative Examples 3-7, changes in the composition of the cladding powder failed to improve the high hardness of the weld area, leading to brittle fracture and subsequent band breakage. This indicates that the components in the cladding powder are interdependent and synergistically improve the plasticity of the weld area, effectively reducing the hardness and band breakage rate. Comparative Examples 8-10, using only one annealing treatment or no annealing treatment, resulted in high hardness and brittle fracture in the weld area. This demonstrates that the effect of the cladding plastic transition layer in promoting the decomposition of coarse martensite at the weld depends on both heat treatment operations before and after the cladding treatment, and neither is dispensable.
Claims
1. A method for controlling the stability of ultra-high strength steel welds, characterized in that, Includes the following steps: (1) After splicing the tail end of the forward hot-rolled strip steel with the head end of the subsequent hot-rolled strip steel, laser weld it, smooth the weld seam, and then perform the first annealing treatment on the welded area. (2) A layer of cladding powder is uniformly covered on one side of the weld, and then laser cladding is performed on the cladding powder; the same cladding powder is used to perform laser cladding on one side of the weld; (3) Perform a second annealing treatment on the cladding area, and then complete the welding of the hot-rolled strip after cooling.
2. The method for controlling the stability of ultra-high strength steel welds according to claim 1, characterized in that, In step (1), the hot-rolled strip steel is a cold-rolled hot-formed strip steel of grade 1800MPa or above with a carbon equivalent of at least 0.6 and a thickness of no more than 3mm.
3. The method for controlling the stability of ultra-high strength steel welds according to claim 1, characterized in that, In step (1), The laser welding method is as follows: the tail end of the preceding hot-rolled strip and the head end of the following hot-rolled strip are cut flat and then spliced together. A CO2 laser with a welding power of 10-12kW is used to laser weld the splice seam, and the welding speed is 1-3m / min.
4. The method for controlling the stability of ultra-high strength steel welds according to claim 3, characterized in that, The width of the splice seam shall not exceed 1 mm.
5. The method for controlling the stability of ultra-high strength steel welds according to claim 1, characterized in that, In step (1), the first annealing treatment is performed at 600-650℃ for 1-3 minutes.
6. The method for controlling the stability of ultra-high strength steel welds according to claim 1, characterized in that, In step (2), the composition of the cladding powder by mass fraction is as follows: 0.2-0.4% Si, 0.7-1.4% Cr, 0.1-0.5% Mo, 0.1-0.5% magnesium fluoride, 1-5% nickel-iron layered double hydroxide, balance being 590MPa grade hot-rolled pickled steel powder.
7. The method for controlling the stability of ultra-high strength steel welds according to claim 6, characterized in that, The carbon equivalent of the 590MPa grade hot-rolled pickled steel powder is 0.2-0.3, and the average particle size is 0.05-0.5 mm.
8. The method for controlling the stability of ultra-high strength steel welds according to claim 1, characterized in that, In step (2), the thickness of the cladding powder covering one side is 0.2-1.0 mm.
9. The method for controlling the stability of ultra-high strength steel welds according to claim 1, characterized in that, In step (2), the laser cladding method is to perform laser cladding under an inert atmosphere with laser power of 2.0-3.0kW, spot diameter of 3-5 mm, and scanning speed of 5-7 mm / s.
10. The method for controlling the stability of ultra-high strength steel welds according to claim 1, characterized in that, In step (3), the conditions for the second annealing treatment are annealing at 720-850℃ for 1-3 minutes.