A method for producing an austenitic zone weld suppressed laser welded joint

Abstract

The application discloses a preparation method of austenite zone weld seam pressing laser welded joint and belongs to the technical field of metal material processing. Firstly, the welding edges of two steel plates are butted and fixed, laser wire filling welding is carried out, and a welded plate is obtained; the welded plate is kept in a heating furnace at 890-960 DEG C for 3-8 min, and then the welded plate is taken out and sequentially subjected to weld seam pressing and quenching; after quenching, the steel plate and the weld seam both form martensite structure. The laser wire filling welding process is adopted, the weld seam composition is optimized, the deformation amount is provided for the weld seam pressing process, the weld seam structure regulation and control and the pressing performance improvement are realized, the weld seam is pressed and quenched in the austenite phase zone, the uniform and fine martensite structure is obtained, the weld seam structure of hot forming steel is refined and the performance is improved, the tensile test fracture position of the welded joint after quenching is on the base material, the strength is not lower than 1500MPa, and the problems of relatively coarse lath in the weld seam area and low strength are solved successfully.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal material processing, and particularly relates to a preparation method of an austenite zone weld seam pressing laser welded joint. BACKGROUND

[0002] Laser welding is widely used in the welding of steel plates, and the weld seam structure after welding is generally martensite structure. However, after welding, the welded plate is subjected to high-temperature heating and holding and rapid cooling to form a hot-formed part. During the heating and holding stage, the entire welded plate completely enters the austenitizing temperature range, and the structure is transformed into austenite structure. During the subsequent cooling process, the structure of the welded plate is transformed into martensite structure. The hot-formed steel plate has fine original grains due to the rolling deformation, and the formed martensite grains are also fine, the length-width ratio of the martensite lath is small, and the performance of the steel plate is uniform. However, the weld seam area does not undergo the rolling deformation process, and the formed martensite lath is relatively thick, and the length-width ratio of the martensite lath is large. Therefore, the structure of the steel plate is better than that of the weld seam area, and thus the performance is higher than that of the weld seam. Therefore, the weld seam area becomes the weakest link of the hot-formed steel part.

[0003] In order to improve the performance reduction problem of the hot-formed steel welded joint, the invention patent CN115055918B "A continuous rolling method of non-oriented silicon steel" realizes the reduction of the weld seam grain size and the improvement of the weld seam strength by laser wire filling welding of the silicon steel. The patent mainly faces non-oriented silicon steel. Since the silicon content in the silicon steel is high, the weld seam toughness is poor, and the weld seam cracks during the rolling process, which belongs to the normal temperature rolling process. The invention patent CN101658869A "Cold-rolled plate continuous flat weld seam rolling method" realizes the flat rolling of the cold-rolled plate weld seam by first reducing the speed and then reducing the rolling force, and then restoring the rolling force and the strip speed. The patent belongs to the normal temperature rolling, and realizes the weld seam rolling by the cooperation of the rolling force and the strip speed. The above patents are all normal temperature weld seam rolling. So far, there is no related research on pressing and quenching the laser welded weld seam at the austenite temperature to obtain uniform and fine martensite structure and realize the improvement of the weld seam strength and the forming performance. SUMMARY

[0004] In view of this, the purpose of the present application is to provide a preparation method of an austenite zone weld seam pressing laser welded joint. The present application presses the laser welded weld seam at the austenite temperature, refines the austenite grain structure of the weld seam area, and transforms the weld seam structure into fine and uniform martensite structure during the subsequent cooling process, so as to realize the improvement of the weld seam strength and the forming performance.

[0005] The purpose of the present application is achieved in the following way:

[0006] The present application provides a preparation method of an austenite zone weld seam pressing laser welded joint, comprising the following steps:

[0007] (1) butt the welding edges of two steel plates, and then fix them, and laser welding with filling of welding wire is carried out to obtain a welded plate with welding seam excess height;

[0008] (2) the welded plate obtained in step (1) is kept in a heating furnace for 3-8 min, and then the welded plate is immediately subjected to welding seam pressing and quenching in sequence, and the microstructure of the welding seam after quenching is martensite microstructure.

[0009] According to the above technical scheme, further, at least one of the two steel plates in step (1) is hot-formed steel, and the surface of the steel plate is free of plating or is plated with aluminum or aluminum alloy, and the single-side plating weight of the aluminum or aluminum alloy plating is ≤80 g / m 2 .

[0010] According to the above technical scheme, further, the hot-formed steel includes 22MnB5.

[0011] According to the above technical scheme, further, the lower surfaces of the two steel plates in step (1) are located on the same plane.

[0012] According to the above technical scheme, further, the joint gap of the two steel plates in step (1) is 0-0.4 mm.

[0013] According to the above technical scheme, further, the laser power of the laser welding with filling of welding wire in step (1) is 1-10 kW, the defocusing amount is -5-5 mm, the welding speed is 0.02-0.20 m / s, the filling speed of the welding wire is 0.01-0.20 m / s, the diameter of the welding wire is 0.8-1.2 mm, and the protective gas is inert gas.

[0014] According to the above technical scheme, further, the composition and weight percentage of the welding wire for laser welding in step (1) are as follows: C: 0.07%-0.2%, Si: 0.1%-1.0%; Mn: 1.1%-3.0%; Cr: 0.03%-8%, Mo: 0.01%-5.0%, Ti: 0.01%-0.25%, Ni: 0-10%, Nd: 0.002%-1.00%, and 0.5%≤Mo+Cr≤8%, and the balance is Fe and inevitable impurities.

[0015] The action mechanism of each element in the welding wire is as follows:

[0016] C: has certain influence on improving the strength of the weld, increasing the hardenability of the weld in the quenching process, and obtaining the weld with full martensite structure. For the hot forming steel without plating layer, a lower carbon content can be used, and for the hot forming steel with plating layer, the carbon content increases with the increase of the mass of the plating layer. The mass percentage of carbon in the present application is C≥0.07%, and in order to ensure the manufacturability of the welding wire, the maximum value of the carbon content is controlled to be within 0.2%;

[0017] Si and Mn: can improve the strength of the weld and also have the effect of deoxidation, and the functions thereof are mainly deoxidation and deslagging of the steel plate smelting and improvement of the welding process of the welding wire. The Si content in the weld is controlled to be between 0.1% and 1.0%, and the Mn content is controlled to be between 1.1% and 3.0%.

[0018] Cr: improves the strength of the weld metal and the hardenability of the weld in the quenching process, and reduces the activity of Al in the plating layer on the surface of the steel plate, and Al and Cr in the weld pool have a chemical reaction to form the oxide of Al. The higher the mass of the plating layer on the surface of the steel plate is, the more the Cr content required is. The lower limit of the Cr content in the present application is 0.03%, and the upper limit is 8%.

[0019] Mo: can react with Al on the surface of the steel plate in the weld to form a high-temperature stable compound, and reduce the solubility of Al in the weld, and the effect thereof is similar to that of Cr. Meanwhile, Mo has strong hardenability, and a content that is too high is easy to form hard quenched structure in the weld, and reduce the formability of the weld. Therefore, the Mo content is designed to be 0.01% to 5.0%, and 0.5%≤Mo+Cr≤8%. A content that is too low cannot eliminate the influence of the plating layer on the surface of the steel plate on the weld, and a content that is too high has poor formability of the weld.

[0020] Ni: is an element that forms and stabilizes austenite, can expand the austenite phase region, improve the plasticity and toughness of the weld, and can increase the corrosion resistance of the weld. The price of Ni is high, and the Ni content in the present application is 0 to 10% in consideration of the comprehensive situation.

[0021] Ti: hinders the growth of austenite grains in the weld during the heating process of the welded plate, and has an important role in controlling the grain size of the weld. Ti has the effect of refining the grains in the process of the weld pressing deformation and phase change. A content of Ti that is too high will form cracks in the quenching process, and affect the performance of the weld. Therefore, the content of Ti is 0.01% to 0.25%.

[0022] Rare earth Nd: the rare earth Nd element affects the type, quantity and form of non-metallic inclusions in the steel, can refine the martensite lath of the weld, and improve the performance of the weld. The rare earth Nd element forms a compound with Al element, is uniformly distributed in the weld, and improves the strength of the weld. However, the rare earth Nd element is easy to form inclusions in the weld, and the content thereof cannot be too high. Therefore, the content of the rare earth Nd is 0.002% to 1.00%.

[0023] Based on the above technical scheme, further, in step (1), the weld reinforcement h (the height of the weld surface above the surface of the steel plate) is controlled in the range of 0.1mm-2.0mm; the weld reinforcement of the present application is 0.1mm-2.0mm, which provides a reduction amount for the later weld pressing, and the weld reinforcement is less than 0.1mm, the weld pressing reduction amount is less, the weld deformation amount is small, the weld structure is not obviously refined, and the effect of improving the weld strength is not significant; the weld reinforcement is greater than 2mm, the weld wire filling amount is large, the welding material consumption is serious, the heat input of the welded joint is high, and the weld joint is easily softened; the weld deformation amount is large during the weld pressing process, and the weld size precision cannot meet the welding requirements.

[0024] Based on the above technical scheme, further, in step (2), the temperature of the heating furnace is 890-960℃.

[0025] Based on the above technical scheme, further, the present application presses the weld under the condition that the temperature is 890℃-980℃, the weld surface is consistent with the surface of the steel plate after pressing, the steel plate does not occur extrusion deformation during the weld extrusion process, the weld zone metal enters the two-phase zone when the temperature is lower than 890℃, and a complete martensite structure weld cannot be obtained after the weld pressing. When the temperature is higher than 980℃, the weld austenite structure is coarse, and the weld strength and formability are reduced after pressing and quenching.

[0026] Based on the above technical scheme, further, in step (2), the pressing pressure of the weld pressing is 10-1000kN, and the pressing speed is 0.05-1m / s.

[0027] Based on the above technical scheme, further, in step (2), the thickness of the weld after pressing is the same as the thickness of the thicker steel plate in the welded plate.

[0028] Based on the above technical scheme, further, in step (2), the cooling speed of quenching is ≥25℃ / s.

[0029] The present application has the following beneficial effects relative to the prior art:

[0030] 1. The present application realizes the refinement of the weld structure and the improvement of the performance of the hot-formed steel by pressing and quenching the weld in the austenite phase zone, the fracture position of the welded joint after quenching is on the base material, and the strength is not less than 1500MPa, which successfully solves the problems of coarse lath in the weld area and low strength.

[0031] 2. The present application adopts the laser wire filling welding process, optimizes the weld composition, provides a deformation amount for the weld pressing process, and realizes the weld structure control and the improvement of the pressing performance. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present application, the drawings involved in the embodiments will be briefly introduced as follows.

[0033] Figure 1 Metallographic structure diagram of the weld of Example 1. DETAILED DESCRIPTION

[0034] The present application will be described in detail below with reference to the embodiments, but the embodiments of the present application are not limited thereto. Obviously, the embodiments described below are only some of the embodiments of the present application, and other similar embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0035] Two hot-formed steels with the characteristic data of the steel plates as shown in Table 1 were selected as the tailor-welded steels, the welding edges of the two hot-formed steels were butted and fixed by a fixture, the lower surfaces of the two hot-formed steels were kept on a plane, the gap between the steel plates was as shown in Table 2, the fiber laser was used for welding, the defocusing amount, laser power, welding speed, wire feeding speed and wire diameter were as shown in Table 2, the composition of the welding wire was as shown in Table 3, Ar gas was used as the protective gas, and the weld reinforcement (the height of the weld surface above the surface of the steel plate) was as shown in Table 1. The welded plate was placed in a heating furnace for a certain period of time, and then taken out for weld pressing and quenching. The heating condition, pressing and quenching process parameters were as shown in Table 4. After pressing, the thickness of the weld was the same as the thickness of the welded plate. After quenching of the welded piece, the hot-formed steel plate and the weld both formed martensite structure. The strength and fracture position of the weld area of the welded hot-formed steel were tested, and the results were as shown in Table 5.

[0036] Table 1 Data of hot-formed steel plate

[0037]

[0038] Table 2 Parameters of fiber laser welding

[0039]

[0040] Table 3 Chemical composition and weight percentage (wt%) of welding wire

[0041] C Si Mn Cr Mo Ti Ni Neodymium Example 1 0.17 0.21 2.10 0.03 1.54 0.20 1.30 0.003 Example 2 0.14 0.32 1.57 3.50 4.0 0.05 0.21 0.10 Example 3 0.18 0.75 1.25 7.50 0.01 0.05 5.89 0.58 Example 4 0.13 0.89 1.76 4.65 2.70 0.12 8.40 1.00 Example 5 0.19 0.12 2.89 7.05 0.21 0.25 3.50 0.004 Example 6 0.07 0.13 1.64 0.03 4.70 0.01 0 0.008

[0042] Table 4 Heating, pressing and quenching process parameters

[0043]

[0044] Table 5 Strength and fracture position of the weld area of the hot-formed steel

[0045]

[0046]

[0047] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a laser-welded joint with austenitic zone weld seam pressing, characterized in that, Includes the following steps: (1) Fix the welded edges of the two steel plates together and then perform laser filler wire welding to obtain a welded plate with weld reinforcement. (2) The welding plate obtained in step (1) is kept in a heating furnace for 3 to 8 minutes. The welding plate is then removed and immediately subjected to weld pressing and quenching. The weld structure after quenching is martensitic. At least one of the two steel plates mentioned in step (1) is hot-formed steel, and the surface of the steel plate is either uncoated or has an aluminum or aluminum alloy coating, with the single-sided coating weight of the aluminum or aluminum alloy coating being ≤80g / m². 2 ; In step (1), the weld reinforcement height h is controlled within the range of 0.1 to 2.0 mm; The temperature of the heating furnace in step (2) is 890-960℃; the pressing pressure of the weld in step (2) is 700-1000kN and the pressing speed is 0.50-1m / s; In step (2), the quenching cooling rate is ≥25℃ / s.

2. The preparation method according to claim 1, characterized in that, The lower surfaces of the two steel plates mentioned in step (1) are located on the same plane; the splicing gap between the two steel plates is 0 to 0.4 mm.

3. The preparation method according to claim 1, characterized in that, The laser power of the laser wire filler welding described in step (1) is 1 to 10 kW, the defocusing amount is -5 to 5 mm, the welding speed is 0.02 to 0.20 m / s, the wire filler speed is 0.01 to 0.20 m / s, the wire diameter is 0.8 to 1.2 mm, and the shielding gas is an inert gas.

4. The preparation method according to claim 1, characterized in that, The composition and weight percentage of the welding wire used for laser filler wire in step (1) are as follows: C: 0.07%~0.2%, Si: 0.1%~1.0%; Mn: 1.1%~3.0%; Cr: 0.03%~8%, Mo: 0.01%~5.0%, Ti: 0.01%~0.25%, Ni: 0~10%, Nd: 0.002%~1.00%, and 0.5%≤Mo+Cr≤8%, with the balance being Fe and unavoidable impurities.

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