A method for laser welding and post-weld heat treatment of 4-6 mm specification 2205 duplex stainless steel in cold continuous rolling production

Abstract

The present application belongs to the technical field of stainless steel cold rolling, and provides a method for laser welding and post-welding heat treatment of 4-6 mm specification 2205 duplex stainless steel in cold continuous rolling, which effectively improves the microstructure and mechanical properties of the weld and heat-affected zone by optimizing the laser welding parameters, using nickel-based welding wire material and multi-pass welding technology, combined with induction heating to control the heat cycle process. The innovative process greatly improves the toughness and ductility of the weld, meets the requirements of more than 70% high deformation rate of the weld in the cold continuous rolling process, ensures continuous and stable production, and avoids belt breakage accidents. The successful application of the technology provides strong support for stainless steel cold continuous rolling production.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of stainless steel cold rolling, and relates to a 4-6mm specification 2205 duplex stainless steel processing, in particular to a cold continuous rolling production 4-6mm specification 2205 duplex stainless steel laser welding and post-weld heat treatment method. BACKGROUND

[0002] The stainless steel cold continuous rolling production line realizes continuous rolling by connecting the front and rear steel coil heads in series through five racks, and the weld is directly rolled in the process, and a series of processes such as annealing, pickling, and leveling are directly carried out after rolling, so the strength and plasticity requirements of the weld are very strict.

[0003] In the 2205 duplex stainless steel use end, the conventional welding method adopts CO2 laser welding, single pass welding double-sided forming while filling 309 welding wire. Generally speaking, the standard of base metal and filler metal does not include the requirement for toughness. However, in the production end, especially the toughness control in the process of cold continuous rolling weld becomes a key factor, and the thickness of the strip before rolling is relatively thick (4-6mm), so the conventional welding method cannot meet the requirements of continuous rolling toughness. In the actual production process, when the weld deformation reaches more than 30%, the probability of weld fracture is extremely high, and the cold continuous rolling requires the deformation of the weld to be more than 70%.

[0004] Through the analysis of the microstructure of the single laser welding weld of the filler 309 welding wire, a large number of precipitates are dispersedly distributed in the weld, which should be Cr2N according to the composition detection. The upper half of the weld metal is basically austenite, and the lower half is coarse ferrite grains. The width of the heat affected zone is not very wide, but the grain growth is obvious, and the grain size reaches more than 250μm. Therefore, the weld toughness is low, the ductility is poor, and the fracture position is basically near the heat affected zone and the weld fusion line in the rolling process.

[0005] According to the microstructure analysis, the reasons for the poor 2205 weld mainly include the following aspects:

[0006] First, the ferrite content in the weld is relatively high and the grain growth is obvious;

[0007] Second, the ferrite content in the heat affected zone is much higher than that in the base metal, and the grain growth is obvious;

[0008] Third, a large amount of Cr2N is dispersedly precipitated in the weld structure and the heat affected zone;

[0009] When laser welding technology is used, due to the high energy concentration and the extremely rapid heating and cooling process, this characteristic makes N element unable to effectively diffuse and enrich in austenite before the temperature drops below the "effective quenching temperature" (about 800℃). As a result, the proportion of austenite is relatively reduced, and a large amount of Cr2N precipitates are formed.

[0010] For the material with thickness of 4.0-6.0mm, when single-pass welding is implemented, the applied heat input is significantly higher, exceeding 0.45KJ / mm, which causes the microstructure in the weld and its heat affected zone to stay above the ferrite solid solution temperature (about 1200℃) for too long, and thus promotes the rapid increase of ferrite grains.

[0011] In the design of welding parameters, the gap between the welds is set to about 0.2mm, which makes it difficult for the 309 welding wire to fully fuse into the base material in the lower half of the weld, resulting in the Ni element mainly concentrating in the upper half of the weld. This uneven distribution of elements also causes the lower half of the weld area to mainly present a coarse ferrite structure.

[0012] In combination of the above three factors, the toughness of the weld is significantly reduced, and the ductility is poor, so as to fail to meet the strict requirements of the cold continuous rolling process on the performance of the weld. SUMMARY

[0013] The purpose of the present application is to provide a laser welding and post-weld heat treatment method for cold continuous rolling production of 4-6mm specification 2205 duplex stainless steel, which controls the composition and microstructure of the weld and the performance of the heat affected zone by setting reasonable welding process and multiple heat treatment control heat cycle method, greatly improves the toughness of the weld and the heat affected zone, meets the requirements of more than 70% of the weld for plastic toughness of the rolling deformation rate of the continuous rolling mill, and avoids the occurrence of strip breaking accidents.

[0014] The technical scheme adopted by the present application to achieve the above purpose is:

[0015] A laser welding and post-weld heat treatment method for cold continuous rolling production of 4-6mm specification 2205 duplex stainless steel, comprising:

[0016] S1, welding operation is performed in two-pass welding mode;

[0017] S2, metal filling is performed by using nickel-based welding material;

[0018] S3, the gap between the welds and the gap between the blades are increased;

[0019] S4, after each welding is completed, induction heating is performed once, and the target induction heating temperature is 1000℃.

[0020] Further, the parameters of the two-pass welding are set as follows:

[0021] 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;

[0022] The second pass is carried out at a laser power of 6 KW, a welding speed of 4-6 m / min, and a heat input of 0.046-0.073 KJ / mm.

[0023] Further, the wire feeding speeds of the two passes are as follows:

[0024] The wire feeding speed of the first pass is 4-6 m / min, and the wire feeding speed of the second pass is 3-4 m / min.

[0025] Further, the gap between the welds is set to 0.45 mm, and the gap between the blades is set to 0.25 mm.

[0026] Further, the parameters of the two induction heating are as follows:

[0027] After the first pass, the heating speed is 2-2.5 m / min, and the heating power is 30-35 KW;

[0028] After the second pass, the heating speed is 2.5-3 m / min, and the heating power is 25-30 KW.

[0029] The present application has the following beneficial effects:

[0030] 1. The weld structure is mainly austenitic, and only a small amount of ferrite is present in the lower half, and the grains are fine;

[0031] 2. The grains in the heat-affected zone are slightly grown to about 80 μm, but a large amount of austenite is distributed in a network at the ferrite grain boundaries, and the toughness and ductility are greatly improved

[0032] 3. There is almost no Cr2N precipitation in the weld and the heat-affected zone

[0033] 4. In actual production, the weld does not break even when the maximum deformation of the five-stand continuous rolling 2205 duplex stainless steel reaches 75%, and continuous and stable production can be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a weld structure diagram of a conventional welding and post-weld heat treatment method for 4-6 mm specification 2205 duplex stainless steel;

[0035] Figure 2 is a weld structure diagram after the method of the present application is used;

[0036] Figure 3 is a grain diagram of the heat-affected zone after the method of the present application is used. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present application more clear and explicit, the present application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0038] A cold continuous rolling production method of 4-6mm specification 2205 duplex stainless steel laser welding and post-weld heat treatment, comprising:

[0039] S1, in order to reduce the welding heat input, reduce the ferrite solid solution temperature above the residence time, avoid the ferrite grain excessive growth, adopt two pass welding method; Through detection, the weld and heat affected zone grain is about 80μm, which is greatly improved compared with the previous. At the same time, the second welding layer temperature and the two induction heating after welding are used to improve the mechanical properties of the weld, and the secondary austenite is formed in the ferrite grain boundary and intracrystalline.

[0040] The parameter setting of two pass welding is: first pass, laser power 10KW, welding speed 2-3.5m / min, heat input 0.14-0.24KJ / mm; second pass, laser power 6KW, welding speed 4-6m / min, heat input 0.046-0.073KJ / mm.

[0041] S2, the welding material adopts nickel-based welding material ERNiCr-3 for metal filling, the first pass welding material wire feeding speed is 4-6m / min, and the second pass welding material wire feeding speed is 3-4m / min.

[0042] S3, increase the weld gap and shear blade gap, the weld gap is set to 0.45mm, and the shear blade gap is set to 0.25mm;

[0043] Here, in order to ensure that the two pass welding is completely penetrated, the weld gap is set to be very critical, which is increased from the conventional 0.2mm to 0.45mm, and the shear blade gap is set from the conventional 0.08mm to 0.25mm. The purpose is that the shear surface formed by the larger gap shear is inclined, and the inclination angle is 3°~5°, which can form a small V-shaped groove with an included angle of 6°~10° after the gap is welded, so that the first pass welding laser can melt through the steel plate to avoid the root unpenetrated.

[0044] S4, after each welding is completed, induction heating is carried out; the whole welding process is carried out twice to increase the holding time of the weld and heat affected zone organization between the effective quenching temperature (about 800℃) and the ferrite solid solution temperature (about 1200℃), and the cooling speed of the weld is controlled below 50℃ / s, which can avoid the excessive growth of ferrite grain and make N element diffuse to form austenite, and at the same time reduce the formation of Cr2N precipitates. The target induction heating temperature is 1000℃; the parameter setting of two times induction heating is: 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. Example 1

[0045] 2205 stainless steel width 1256mm, thickness 6.0mm, welding parameters are set as:

[0046] First pass: laser power 10KW, welding speed 2m / min, wire feeding speed 6m / min, weld gap 0.45mm, shear blade gap 0.25mm, heating speed 2m / min, heating power 35Kw;

[0047] Second pass: laser power 6KW, welding speed 4m / min, wire feeding speed 4m / min, weld gap 0.45mm, shear blade gap 0.25mm, heating speed 2.5m / min, heating power 30Kw. Example 2

[0048] 2205 stainless steel width 1306mm, thickness 4.0mm, welding parameters are set as:

[0049] First pass: laser power 10KW, welding speed 3.5m / min, wire feeding speed 4m / min, weld gap 0.45mm, shear blade gap 0.25mm, heating speed 2.5m / min, heating power 30Kw;

[0050] Second pass: laser power 6KW, welding speed 6m / min, wire feeding speed 3m / min, weld gap 0.45mm, shear blade gap 0.25mm, heating speed 3m / min, heating power 25Kw. Example 3

[0051] 2205 stainless steel width 1285mm, thickness 5mm, welding parameters are set as:

[0052] First pass: laser power 10KW, welding speed 2.7m / min, wire feeding speed 5m / min, weld gap 0.45mm, shear blade gap 0.25mm, heating speed 2.2m / min, heating power 33Kw;

[0053] Second pass: laser power 6KW, welding speed 4.8m / min, wire feeding speed 3.6m / min, weld gap 0.45mm, shear blade gap 0.25mm, heating speed 2.7m / min, heating power 28Kw.

[0054] Comparative Example

[0055] 2205 stainless steel width 1256mm, thickness 6.0mm, welding parameters are set as:

[0056] Single-pass welding, laser power 14KW, welding speed 2m / min, heat input 0.35KJ / mm.

[0057] As Figure 1 And Figure 2 Comparison: 4-6mm specification 2205 duplex stainless steel conventional welding and post-weld heat treatment, material heat affected zone grain growth is obvious, weld 2 / 3 organization is ferrite, only the upper half is austenite; after using the method of the application, the weld austenite accounts for more than 80%, only the lower half exists a small amount of ferrite and the grain is relatively small, the heat affected zone grain growth is as Figure 3 Shown, there is a certain growth but basically below 80μm, at the same time a large number of grid-shaped austenite organization is formed in the grain boundary, which greatly improves the toughness and ductility of the heat affected zone.

[0058] The above only describes the embodiments of the application and is not intended to limit the application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for laser welding and post-weld heat treatment of 4-6mm specification 2205 duplex stainless steel produced by cold continuous rolling, characterized in that: include: S1. Welding operation is performed using a two-pass welding method; the parameters for the two-pass welding are set as follows: For 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; For the second pass, the laser power is 6KW, the welding speed is 4-6m / min, and the heat input is 0.046-0.073KJ / mm; S2. Nickel-based welding materials are used for metal filler. S3. The weld gap is set to 0.45mm, and the shear blade gap is set to 0.25mm. S4. After each welding operation, induction heating is performed once, with a target induction heating temperature of 1000℃; the parameters for the two induction heating operations are set as follows: After the first pass, the heating rate is 2-2.5 m / min, and the heating power is 30-35 kW; After the second pass, the heating rate is 2.5-3 m / min, and the heating power is 25-30 kW.

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

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