980mpa cold-rolled multiphase steel acid pickling process laser welding method

Abstract

The present application relates to the technical field of ultra-high strength steel welding, and particularly relates to a laser welding method for acid-rolling process of 980MPa cold-rolled multiphase steel. The 980MPa cold-rolled multiphase steel is produced by an acid-rolling combined unit, the tail of the front coil strip steel is butt welded with the head of the rear coil strip steel by a laser welding machine, and 780MPa dual-phase steel is used as a transition material. By adjusting and controlling welding process parameters, the welding problem existing in the acid-rolling production process of the 980MPa multiphase steel is solved, the incidence of strip breaking accidents along the weld in the acid-rolling process is reduced, and the production efficiency is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of ultra-high strength steel welding technology, and in particular to a laser welding method for the pickling and rolling process of 980MPa cold-rolled multiphase steel. Background Technology

[0002] With the automotive industry's increasing demands for energy conservation, environmental protection, and safety, the application of gigapascal-grade advanced high-strength steel products in vehicle bodies is gradually increasing. Currently, 980MPa-grade cold-rolled multiphase steel is mostly produced industrially using pickling and rolling mills, and laser welding is used to weld the front and rear coils of strip steel to achieve continuous production. However, due to the special chemical composition system, hot-rolled raw material microstructure, and high carbon equivalent of 980MPa-grade cold-rolled multiphase steel, welding is difficult. In actual production, weld seam breakage is one of the main factors affecting the production efficiency of 980MPa-grade cold-rolled multiphase steel.

[0003] Research has shown that when the welding effect of the same steel grade and the welding of the transition material are poor, weld band breakage accidents are prone to occur during pickling and rolling, seriously affecting production efficiency and yield. To solve the above problems, this invention develops a laser welding method for the pickling and rolling process of 980MPa cold-rolled multiphase steel. Summary of the Invention

[0004] This invention provides a laser welding method for the pickling and rolling process of 980MPa cold-rolled multiphase steel. By adjusting the welding process parameters, the welding problem of 980MPa multiphase steel in the pickling and rolling process is solved, the incidence of weld breakage accidents along the weld is reduced, and the production efficiency is effectively improved.

[0005] To achieve the above objectives, the present invention employs the following technical solution: A laser welding method for the pickling and rolling process of 980MPa cold-rolled multiphase steel is disclosed. The 980MPa cold-rolled multiphase steel is produced by a combined pickling and rolling unit, and the tail end of the front coil strip and the head end of the rear coil strip are butt welded using a laser welding machine.

[0006] 780MPa duplex steel was used as the transition material, and the laser welding process parameters for the transition material are as follows: The pre-welding heating power is 0kW, the post-welding heating power is 40%–65%, and the secondary heating power is 0–20%; the laser focal length is 4–2mm, the welding speed is 30%–45%, and the welding power is 90%–100%. The laser welding process parameters for 980MPa multiphase steel of the same grade are as follows: The pre-welding heating power is 0kW, the post-welding heating power is 40%–60%, and the secondary heating power is 0–20%; the laser focal length is 2–4mm, the welding speed is 30%–40%, and the welding power is 90%–100%. The laser welding process is as follows: The tail of the front coiled strip and the head of the rear coiled strip are fed into the laser welding machine. The centering device of the laser welding machine aligns the head and tail of the strip along the longitudinal center line of the strip. The inlet clamp and outlet clamp clamp the front coiled strip and the rear coiled strip respectively. Using double shears, 20-60mm is cut off from the head and tail of the strip respectively. At the same time, a hole is punched in the middle of the tail of the strip 40-50mm away from the weld seam for subsequent weld seam tracking. The head and tail of the strip are butted together using the inlet clamp and outlet clamp, and the butt gap is controlled to be 0.02-0.1mm. Then the laser head and the rolling wheel are lowered, ready to start welding. During welding, the welding machine carriage moves from the operating side to the transmission side. The strip is preheated by the front heating device. Shielding gas is introduced above and below the strip. The laser head emits laser to melt the butt joint surface to form a weld seam. After welding, the weld seam is annealed using the rear heating device of the laser welding machine.

[0007] The chemical composition of the hot-rolled substrate of 980MPa cold-rolled multiphase steel, by weight percentage, is: C: 0.06%–0.12%, Si: 0.40%–0.50%, Mn: 2.0%–2.2%, Mo: 0.10%–0.20%, Nb: 0.03%–0.06%, Ti: 0.02%–0.06%, B: 0.001%–0.003%, Al: 0.03%–0.05%, P≤0.02%, S≤0.005%, with the balance being Fe and other unavoidable impurities.

[0008] The thickness of the hot-rolled substrate of 980MPa cold-rolled multiphase steel is 2.1 to 4.0 mm.

[0009] The chemical composition of the 780MPa duplex steel hot-rolled substrate, by weight percentage, is: C: 0.110%–0.140%, Si: 0.30%–0.50%, Mn: 1.7%–2.0%, Nb: 0.010%–0.035%, Cr: 0.30%–0.50%, Al: 0.015%–0.065%, P: 0.015%–0.040%, S≤0.010%, with the balance being Fe and other unavoidable impurities.

[0010] The thickness of the 780MPa duplex steel hot-rolled substrate is 2.5 to 4.5 mm.

[0011] Compared with the prior art, the beneficial effects of the present invention are: (1) The weld obtained by the laser welding method described in this invention did not show cracking along the weld in the cupping test, which solved the problem that the accident of strip breakage along the weld is easy to occur during the rolling process of the acid rolling process on the high tension production line, which seriously affects the production efficiency.

[0012] (2) It solved the problems of strip breakage and low yield caused by the welding of transition material.

[0013] (3) The welding process of the transition material adopts the same cross window as the welding of the same steel grade of 980MPa cold-rolled multiphase steel, which improves the welding success rate of the operation and is conducive to mass production and specification transition. Detailed Implementation

[0014] This invention discloses a laser welding method for the pickling and rolling process of 980MPa cold-rolled multiphase steel. The 980MPa cold-rolled multiphase steel is produced using a combined pickling and rolling unit, and the tail end of the front coil strip and the head end of the rear coil strip are butt-welded using a laser welding machine. To ensure welding stability, transition material welding and welding of the same steel grade are carried out using the same cross window.

[0015] 780MPa duplex steel was used as the transition material, and the laser welding process parameters for the transition material are as follows: The pre-welding heating power is 0kW, the post-welding heating power is 40%–65%, and the secondary heating power is 0–20%; the laser focal length is 4–2mm, the welding speed is 30%–45%, and the welding power is 90%–100%. The laser welding process parameters for 980MPa multiphase steel of the same grade are as follows: The pre-welding heating power is 0kW, the post-welding heating power is 40%–60%, and the secondary heating power is 0–20%; the laser focal length is 2–4mm, the welding speed is 30%–40%, and the welding power is 90%–100%. The laser welding process is as follows: The tail of the front coiled strip and the head of the rear coiled strip are fed into the laser welding machine. The centering device of the laser welding machine aligns the head and tail of the strip along the longitudinal center line of the strip. The inlet clamp and outlet clamp clamp the front coiled strip and the rear coiled strip respectively. Using double shears, 20-60mm is cut off from the head and tail of the strip respectively. At the same time, a hole is punched in the middle of the tail of the strip 40-50mm away from the weld seam for subsequent weld seam tracking. The head and tail of the strip are butted together using the inlet clamp and outlet clamp, and the butt gap is controlled to be 0.02-0.1mm. Then the laser head and the rolling wheel are lowered, ready to start welding. During welding, the welding machine carriage moves from the operating side to the transmission side. The strip is preheated by the front heating device. Shielding gas is introduced above and below the strip. The laser head emits laser to melt the butt joint surface to form a weld seam. After welding, the weld seam is annealed using the rear heating device of the laser welding machine.

[0016] After welding is completed, a cupping test is performed. If no cracking occurs along the weld, it is considered qualified. If it is unqualified, it is re-welded (repeat the above steps). A crescent shear is provided at the exit section of the laser welding machine to remove the poor quality area at the edge of the weld.

[0017] The chemical composition of the hot-rolled substrate of 980MPa cold-rolled multiphase steel, by weight percentage, is: C: 0.06%–0.12%, Si: 0.40%–0.50%, Mn: 2.0%–2.2%, Mo: 0.10%–0.20%, Nb: 0.03%–0.06%, Ti: 0.02%–0.06%, B: 0.001%–0.003%, Al: 0.03%–0.05%, P≤0.02%, S≤0.005%, with the balance being Fe and other unavoidable impurities.

[0018] The thickness of the hot-rolled substrate of 980MPa cold-rolled multiphase steel is 2.1 to 4.0 mm.

[0019] The chemical composition of the 780MPa duplex steel hot-rolled substrate, by weight percentage, is: C: 0.110%–0.140%, Si: 0.30%–0.50%, Mn: 1.7%–2.0%, Nb: 0.010%–0.035%, Cr: 0.30%–0.50%, Al: 0.015%–0.065%, P: 0.015%–0.040%, S≤0.010%, with the balance being Fe and other unavoidable impurities.

[0020] The thickness of the 780MPa duplex steel hot-rolled substrate is 2.5 to 4.5 mm.

[0021] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0022] Example 1:

[0023] In this embodiment, the 980MPa cold-rolled multiphase steel is produced by a combined pickling and rolling mill, and the tail end of the front coil strip and the head end of the rear coil strip are butt welded using a laser welding machine.

[0024] The hot-rolled substrate of 980MPa cold-rolled dual-phase steel has a thickness of 2.1mm × 1170mm. The transition material is 780MPa dual-phase steel, and its hot-rolled substrate has a thickness of 2.5mm × 1170mm.

[0025] The laser welding process parameters for transition materials are as follows: The heating power before welding is 0kW, the heating power after welding is 40%, the heating power after the second welding is 0, the laser focal length is 4mm, the welding speed is 40%, and the welding power is 90%.

[0026] The laser welding process parameters for 980MPa multiphase steel of the same grade are as follows: The heating power before welding is 0kW, the heating power after welding is 40%, the heating power after the second welding is 0, the laser focal length is 4mm, the welding speed is 40%, and the welding power is 90%.

[0027] After welding, a cupping test was performed, and no cracking along the weld was observed, nor were any other welding defects found. The strip then passed through the welding machine, the inlet looper, the pickling section, the cold rolling mill, and the coiler, and no strip breakage issues occurred.

[0028] Example 2:

[0029] In this embodiment, the 980MPa cold-rolled multiphase steel is produced by a combined pickling and rolling mill, and the tail end of the front coil strip and the head end of the rear coil strip are butt welded using a laser welding machine.

[0030] The hot-rolled substrate of 980MPa cold-rolled dual-phase steel has a thickness of 2.3mm × 1345mm. The transition material is 780MPa dual-phase steel, and its hot-rolled substrate has a thickness of 2.7mm × 1345mm.

[0031] The laser welding process parameters for transition materials are as follows: The pre-welding heating power is 0kW, the post-welding heating power is 40%, the secondary heating power is 0, the laser focal length is 4mm, the welding speed is 40%, and the welding power is 90%.

[0032] The laser welding process parameters for 980MPa multiphase steel of the same grade are as follows: The heating power before welding is 0kW, the heating power after welding is 40%, the heating power after the second welding is 0, the laser focal length is 4mm, the welding speed is 40%, and the welding power is 90%.

[0033] After welding, a cupping test was performed, and no cracking along the weld was observed, nor were any other welding defects found. The strip then passed through the welding machine, the inlet looper, the pickling section, the cold rolling mill, and the coiler, and no strip breakage issues occurred.

[0034] Example 3:

[0035] In this embodiment, the 980MPa cold-rolled multiphase steel is produced by a combined pickling and rolling mill, and the tail end of the front coil strip and the head end of the rear coil strip are butt welded using a laser welding machine.

[0036] The hot-rolled substrate of 980MPa cold-rolled dual-phase steel has a thickness of 4.0mm × 1335mm. The transition material is 780MPa dual-phase steel, and its hot-rolled substrate has a thickness of 4.5mm × 1335mm.

[0037] The laser welding process parameters for transition materials are as follows: The heating power before welding is 0kW, the heating power after welding is 60%, the heating power after the second welding is 20%, the laser focal length is 4mm, the welding speed is 30%, and the welding power is 99%.

[0038] The laser welding process parameters for 980MPa multiphase steel of the same grade are as follows: The heating power before welding is 0kW, the heating power after welding is 60%, the heating power after the second welding is 20%, the laser focal length is 4mm, the welding speed is 30%, and the welding power is 99%.

[0039] After welding, a cupping test was performed, and no cracking along the weld was observed, nor were any other welding defects found. The strip then passed through the welding machine, the inlet looper, the pickling section, the cold rolling mill, and the coiler, and no strip breakage issues occurred.

[0040] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A laser welding method for the pickling and rolling process of 980MPa cold-rolled multiphase steel, characterized in that, 980MPa cold-rolled multiphase steel is produced by a combined pickling and rolling mill. The tail end of the front coil strip and the head end of the rear coil strip are butt welded using a laser welding machine. 780MPa duplex steel was used as the transition material, and the laser welding process parameters for the transition material are as follows: The pre-welding heating power is 0kW, the post-welding heating power is 40%–65%, and the secondary heating power is 0–20%; the laser focal length is 4–2mm, the welding speed is 30%–45%, and the welding power is 90%–100%. The laser welding process parameters for 980MPa multiphase steel of the same grade are as follows: The pre-welding heating power is 0kW, the post-welding heating power is 40%–60%, and the secondary heating power is 0–20%; the laser focal length is 2–4mm, the welding speed is 30%–40%, and the welding power is 90%–100%. The laser welding process is as follows: The tail of the front coiled strip and the head of the rear coiled strip are fed into the laser welding machine. The centering device of the laser welding machine aligns the head and tail of the strip along the longitudinal center line of the strip. The inlet clamp and outlet clamp clamp the front coiled strip and the rear coiled strip respectively. Using double shears, 20-60mm is cut off from the head and tail of the strip respectively. At the same time, a hole is punched in the middle of the tail of the strip 40-50mm away from the weld seam for subsequent weld seam tracking. The head and tail of the strip are butted together using the inlet clamp and outlet clamp, and the butt gap is controlled to be 0.02-0.1mm. Then the laser head and the rolling wheel are lowered, ready to start welding. During welding, the welding machine carriage moves from the operating side to the transmission side. The strip is preheated by the front heating device. Shielding gas is introduced above and below the strip. The laser head emits laser to melt the butt joint surface to form a weld seam. After welding, the weld seam is annealed using the rear heating device of the laser welding machine.

2. The laser welding method for the pickling and rolling process of 980MPa cold-rolled multiphase steel according to claim 1, characterized in that, The chemical composition of the hot-rolled substrate of 980MPa cold-rolled multiphase steel, by weight percentage, is: C: 0.06%–0.12%, Si: 0.40%–0.50%, Mn: 2.0%–2.2%, Mo: 0.10%–0.20%, Nb: 0.03%–0.06%, Ti: 0.02%–0.06%, B: 0.001%–0.003%, Al: 0.03%–0.05%, P≤0.02%, S≤0.005%, with the balance being Fe and other unavoidable impurities.

3. The laser welding method for the pickling and rolling process of 980MPa cold-rolled multiphase steel according to claim 1 or 2, characterized in that, The thickness of the hot-rolled substrate of 980MPa cold-rolled multiphase steel is 2.1 to 4.0 mm.

4. The laser welding method for the pickling and rolling process of 980MPa cold-rolled multiphase steel according to claim 1, characterized in that, The chemical composition of the 780MPa duplex steel hot-rolled substrate, by weight percentage, is: C: 0.110%–0.140%, Si: 0.30%–0.50%, Mn: 1.7%–2.0%, Nb: 0.010%–0.035%, Cr: 0.30%–0.50%, Al: 0.015%–0.065%, P: 0.015%–0.040%, S≤0.010%, with the balance being Fe and other unavoidable impurities.

5. The laser welding method for the pickling and rolling process of 980MPa cold-rolled multiphase steel according to claim 1 or 4, characterized in that, The thickness of the 780MPa duplex steel hot-rolled substrate is 2.5 to 4.5 mm.