Laser welding and postweld heat treatment method for producing 2205 duplex stainless steel with specification of 4-6 mm through cold continuous rolling

Abstract

The invention belongs to the technical field of stainless steel cold rolling, and provides a laser welding and postweld heat treatment method for producing 2205 duplex stainless steel with the specification of 4-6 mm through cold continuous rolling. Laser welding parameters are optimized, a nickel-based welding wire material and a multi-pass welding technology are adopted, and the heat cycle process is controlled in combination with induction heating; organizational structures and mechanical properties of welding seams and heat affected zones are effectively improved. According to the innovative process, the toughness and ductility of the welding seam are greatly improved, the requirement for the high deformation rate of 70% or above of the welding seam in the cold continuous rolling process is met, continuous and stable production is ensured, and the strip breakage accident is avoided. The successful application of the technology provides powerful support for stainless steel cold continuous rolling production.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel cold rolling, and relates to the processing of 4-6mm specification 2205 duplex stainless steel, and specifically is a laser welding and post-weld heat treatment method for 4-6mm specification 2205 duplex stainless steel produced by cold continuous rolling. Background Art

[0002] The stainless steel cold rolling production line connects the front and rear steel coils head to tail and connects five racks in series to achieve continuous rolling. The welds are also rolled directly during the process, and then a series of processes such as annealing, pickling, and flattening are carried out directly after rolling. Therefore, the strength and plasticity requirements for the welds are very stringent.

[0003] At the end of using 2205 duplex stainless steel, the conventional welding method uses CO2 laser welding for welding, single-pass welding, double-sided forming and filling with 309 welding wire at the same time. Generally speaking, the standards of the base metal and filler metal do not include requirements for toughness. However, at the production end, especially in the cold rolling process, the control of toughness becomes a key factor, and the thickness of the strip before rolling is relatively thick (4-6mm), and the conventional welding method cannot meet the requirements for continuous rolling toughness. In the actual production process, when the deformation of the weld reaches more than 30%, the probability of the weld breaking is very high, and cold rolling requires the deformation of the weld to reach more than 70%.

[0004] Through the single laser welding weld microstructure analysis of 309 welding wire, a large number of precipitates are dispersed in the weld. According to the composition test, it should be Cr2N. The upper part of the weld metal is basically austenite, and the lower part is coarse ferrite grains. The width of the heat affected zone is 300-400μm, which is not very wide, but the grain growth is obvious, and the grain size reaches more than 250μm. Therefore, the weld has low toughness and poor ductility. The fracture position during rolling is basically near the heat affected zone and the weld fusion line.

[0005] According to the organizational analysis, the main reasons for the poor weld quality of 2205 are as follows: First, the ferrite content in the weld is high and the grain growth is obvious; Second, the ferrite content in the heat-affected zone is much higher than that in the base metal, and the grain growth is obvious; Third, Cr2N is dispersed and precipitated in large quantities in the weld structure and heat-affected zone; When using laser welding technology, due to the highly concentrated energy and extremely rapid heating and cooling processes, this characteristic prevents the N element from effectively diffusing and concentrating in austenite before the temperature drops to the "effective quenching temperature" (about 800°C). As a result, the proportion of austenite is relatively reduced, accompanied by the formation of a large number of Cr2N precipitates.

[0006] For materials with a thickness of 4.0-6.0mm, the heat input applied in single-pass welding is significantly higher, exceeding 0.45KJ / mm, which causes the structure in the weld and its heat-affected zone to stay above the ferrite solution temperature (about 1200℃) for too long, thereby causing the ferrite grains to grow rapidly.

[0007] In the welding parameter design, the weld gap is set to about 0.2mm. This design makes it difficult for the 309 welding wire to fully fuse into the base material in the lower half of the weld, causing the Ni element to be mainly concentrated in the upper half of the weld. This uneven element distribution also causes the lower half of the weld to mainly present a coarse ferrite structure.

[0008] Taking the above three factors into consideration, the toughness of the weld is significantly reduced and the ductility is deteriorated, thus failing to meet the strict requirements of the cold rolling process on weld performance. Summary of the invention

[0009] The purpose of the present invention is to provide a method for laser welding and post-weld heat treatment of 2205 duplex stainless steel with a specification of 4-6 mm produced by cold rolling. By setting a reasonable welding process and a method for controlling the thermal cycle by multiple heat treatments, the composition structure of the weld and the performance of the heat-affected zone are controlled, the toughness of the weld and the heat-affected zone is greatly improved, the requirements for plastic toughness of the weld with a rolling deformation rate of more than 70% of the continuous rolling mill are met, and the occurrence of belt break accidents is avoided.

[0010] The technical solution adopted by the present invention to achieve the above-mentioned purpose is: A method for laser welding and post-weld heat treatment of 4-6 mm 2205 duplex stainless steel produced by cold rolling, comprising: S1. Use two-pass welding to carry out welding operations; S2. The welding materials are nickel-based welding materials for metal filling; S3, increase the weld gap and shear edge gap; S4. After each welding is completed, induction heating is performed, and the target induction heating temperature is 1000°C.

[0011] Furthermore, the parameters of the two-pass welding are set as follows: In the first pass, the laser power is 10KW, the welding speed is 2-3.5m / min, and the heat input is 0.14-0.24KJ / mm; In the second pass, the laser power was 6KW, the welding speed was 4-6m / min, and the heat input was 0.046-0.073KJ / mm.

[0012] Furthermore, the wire feeding speeds of the two welding materials are: The wire feeding speed for the first pass is 4-6m / min, and the wire feeding speed for the second pass is 3-4m / min.

[0013] Furthermore, the weld gap is set to 0.45 mm and the shear gap is set to 0.25 mm.

[0014] Furthermore, the parameters of the two induction heating processes are set as follows: After the first pass, the heating speed is 2-2.5m / min and the heating power is 30-35kw; After the second pass, the heating speed is 2.5-3m / min and the heating power is 25-30kw.

[0015] The beneficial effects of the present invention are: 1. The weld structure is mainly austenite, with only a small amount of ferrite in the lower part and fine grains; 2. The grains in the heat affected zone grow slightly to about 80μm, but a large amount of austenite is distributed in a network at the ferrite grain boundary, and the toughness and ductility are greatly improved. 3. There is almost no Cr2N precipitation in the weld and heat affected zone 4. In actual production, when the maximum deformation of 2205 duplex stainless steel reached 75% during continuous rolling of five stands, the weld did not break, and continuous and stable production was possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the weld organization diagram of conventional welding and post-weld heat treatment of 4-6mm 2205 duplex stainless steel; Figure 2 It is a structural diagram of the weld after being processed by the method of the present invention; Figure 3 This is a grain map of the heat affected zone after being processed by the method of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] A method for laser welding and post-weld heat treatment of 4-6 mm 2205 duplex stainless steel produced by cold rolling, comprising: S1. In order to reduce welding heat input, reduce the time of ferrite staying above the solid solution temperature, and avoid excessive growth of ferrite grains, two-pass welding is adopted; the grains of the weld and heat-affected zone are about 80μm, which is a significant improvement compared with the previous one. At the same time, the second welding interlayer temperature and the two induction heating after welding are used to improve the mechanical properties of the weld, and secondary austenite is formed at the ferrite grain boundary and in the grain.

[0019] The parameters of the two-pass welding were set as follows: for the first pass, the laser power was 10 KW, the welding speed was 2-3.5 m / min, and the heat input was 0.14-0.24 KJ / mm; for the second pass, the laser power was 6 KW, the welding speed was 4-6 m / min, and the heat input was 0.046-0.073 KJ / mm.

[0020] S2. Nickel-based welding material ERNiCr-3 is used for metal filling. The wire feeding speed of the first pass is 4-6m / min, and the wire feeding speed of the second pass is 3-4m / min.

[0021] S3, increase the weld gap and shear edge gap, the weld gap is set to 0.45mm, and the shear edge gap is set to 0.25mm; In order to ensure that the two passes of welding are fully penetrated and the welding wire metal is filled in place, the setting of the weld gap is very critical. It is increased from the conventional 0.2mm to 0.45mm, and the gap setting when the shear blade is sheared is increased from the conventional 0.08mm to 0.25mm. The purpose is to make the shear surface formed by the larger gap shearing inclined. The inclination angle is 3°~5°, which can form a small V-shaped groove with an angle of 6°~10° after the joint, so that the laser in the first welding pass can melt through the steel plate to avoid the situation where the root is not welded through.

[0022] S4. Perform induction heating once after each welding is completed; the purpose of performing weld heating twice during the entire welding process is to increase the insulation time of the weld and heat-affected zone between the effective quenching temperature (about 800°C) and the ferrite solid solution temperature (about 1200°C), and to control the weld cooling rate below 50°C / s, which can prevent excessive growth of ferrite grains and allow the N element to fully diffuse to form austenite, while reducing the formation of Cr2N precipitates. The target induction heating temperature is 1000°C; the parameters of the two induction heatings are set as follows: after the first pass, the heating rate is 2-2.5m / min, and the heating power is 30-35kw; after the second pass, the heating rate is 2.5-3m / min, and the heating power is 25-30kw. Example 1

[0023] 2205 stainless steel width 1256mm, thickness 6.0mm, welding parameters are set as follows: First pass: laser power 10KW, welding speed 2m / min, wire feeding speed 6m / min, weld gap 0.45mm, shear gap 0.25mm, heating speed 2m / min, heating power 35Kw; Second pass: laser power 6KW, welding speed 4m / min, wire feeding speed 4m / min, weld gap 0.45mm, shear gap 0.25mm, heating speed 2.5m / min, heating power 30Kw. Example 2

[0024] 2205 stainless steel width 1306mm, thickness 4.0mm, welding parameters are set as follows: First pass: laser power 10KW, welding speed 3.5m / min, wire feeding speed 4m / min, weld gap 0.45mm, shear gap 0.25mm, heating speed 2.5m / min, heating power 30Kw; Second pass: laser power 6KW, welding speed 6m / min, wire feeding speed 3m / min, weld gap 0.45mm, shear gap 0.25mm, heating speed 3m / min, heating power 25Kw. Example 3

[0025] 2205 stainless steel width 1285mm, thickness 5mm, welding parameters are set as follows: First pass: laser power 10KW, welding speed 2.7m / min, wire feeding speed 5m / min, weld gap 0.45mm, shear gap 0.25mm, heating speed 2.2m / min, heating power 33Kw; Second pass: laser power 6KW, welding speed 4.8m / min, wire feeding speed 3.6m / min, weld gap 0.45mm, shear gap 0.25mm, heating speed 2.7m / min, heating power 28Kw.

[0026] Comparative Example 2205 stainless steel width 1256mm, thickness 6.0mm, welding parameters are set as follows: Single pass welding, laser power 14KW, welding speed 2m / min, heat input 0.35KJ / mm.

[0027] like Figure 1 and Figure 2 Comparison: In conventional welding and post-weld heat treatment of 4-6mm 2205 duplex stainless steel, the grain growth in the heat-affected zone of the material is obvious, 2 / 3 of the weld is ferrite, and only the upper half is austenite; after using the method of the present invention, the weld austenite accounts for more than 80%, and only a small amount of ferrite exists in the lower half with relatively fine grains. The grain growth in the heat-affected zone is as follows Figure 3 As shown in the figure, there is a certain growth but it is basically below 80μm. At the same time, a large amount of grid-like austenite structure is formed at the grain boundaries, which greatly improves the toughness and ductility of the heat affected zone.

[0028] The above descriptions are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for laser welding and post-weld heat treatment of 2205 duplex stainless steel with a specification of 4-6 mm produced by cold rolling, characterized in that: include: S1. Use two-pass welding to carry out welding operations; S2. The welding materials are nickel-based welding materials for metal filling; S3, increase the weld gap and shear edge gap; S4. After each welding is completed, induction heating is performed, and the target induction heating temperature is 1000°C.

2. According to claim 1, a method for laser welding and post-weld heat treatment of 2205 duplex stainless steel with a specification of 4-6 mm produced by cold rolling, characterized in that: The parameters for the two passes of welding are set as follows: In the first pass, the laser power is 10KW, the welding speed is 2-3.5m / min, and the heat input is 0.14-0.24KJ / mm; In the second pass, the laser power was 6KW, the welding speed was 4-6m / min, and the heat input was 0.046-0.073KJ / mm.

3. The method for laser welding and post-weld heat treatment of 2205 duplex stainless steel with a specification of 4-6 mm produced by cold continuous rolling according to claim 1, characterized in that: The speed of the two welding wire feedings is: The wire feeding speed for the first pass is 4-6m / min, and the wire feeding speed for the second pass is 3-4m / min.

4. The method for laser welding and post-weld heat treatment of 2205 duplex stainless steel with a specification of 4-6 mm produced by cold continuous rolling according to claim 1 is characterized in that: The weld gap was set to 0.45 mm and the shear gap was set to 0.25 mm.

5. The method for laser welding and post-weld heat treatment of 2205 duplex stainless steel with a specification of 4-6 mm produced by cold continuous rolling according to claim 1, characterized in that: The parameters of the two induction heating are set as follows: After the first pass, the heating speed is 2-2.5m / min and the heating power is 30-35kw; After the second pass, the heating speed is 2.5-3m / min and the heating power is 25-30kw.

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