Preparation method of welding seam pressing laser welding joint in austenite area

Abstract

The invention discloses a preparation method of an austenite area welding seam pressing laser welding joint, and belongs to the technical field of metal material machining. The method comprises the steps that firstly, the welding edges of two steel plates are fixed after being in butt joint, laser wire filling welding is conducted, a welded plate is obtained, the welded plate is placed in a heating furnace at the temperature of 890-960 DEG C to be subjected to heat preservation for 3-8 min, the welded plate is taken out and immediately subjected to weld joint pressing and quenching in sequence, and the quenched steel plates and weld joints form martensitic structures. The laser wire filling welding technology is adopted, meanwhile, welding seam components are optimized, deformation is provided for the welding seam pressing process, welding seam structure regulation and control and pressing performance improvement are achieved, meanwhile, pressing and quenching are conducted on a welding seam in an austenite phase region through control, and a uniform and small martensite structure is obtained; according to the method, the structure refinement and performance improvement of the hot forming steel welding seam are achieved, the tensile detection fracture position of a welding joint after quenching is located on base metal, the strength is not lower than 1500 MPa, and the problems that a batten in a welding seam area is thick and large and the strength is low are successfully solved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material processing, and in particular relates to a method for preparing an austenite zone weld pressed laser welded joint. Background Art

[0002] Laser welding is widely used in the welding of steel plates. After welding, the weld structure is generally martensitic. However, after hot-formed steel is welded, the weld plate is heated and insulated at high temperature and cooled rapidly to form hot-formed parts. During the heating and insulation stage, the entire weld plate completely enters the austenitizing temperature range, and the structure is transformed into austenitic structure. In the subsequent cooling process, the structure of the weld plate is transformed into martensitic structure. Due to the rolling deformation of hot-formed steel plates, the original grains are relatively fine, the martensitic grains formed are also relatively fine, the aspect ratio of the martensitic lath is small, and the performance of the steel plate is uniform. However, the weld area has not undergone the rolling deformation process, and the martensitic laths formed are relatively coarse, and the aspect ratio of the martensitic laths is large. Therefore, the structure of the steel plate is better than that of the weld area, so the performance is higher than that of the weld, and the weld area becomes the weakest link of hot-formed steel parts.

[0003] In order to improve the problem of reduced performance of hot-formed steel welded joints, the invention patent CN115055918 B "A method for continuous rolling of non-oriented silicon steel" achieves reduced weld grain size and improved weld strength by laser wire welding of silicon steel. This patent is mainly for non-oriented silicon steel. Due to the high silicon content in silicon steel, the weld toughness is poor, and the weld cracks during rolling, which belongs to the normal temperature rolling process. The invention patent CN101658869A "Cold-rolled plate continuous flat weld rolling method" realizes cold-rolled plate weld flat rolling by first slowing down and then reducing the rolling force, first restoring the rolling force and then restoring the strip speed. This patent belongs to normal temperature rolling, and the weld rolling is achieved by combining the rolling force and the strip speed. The above patents are all for normal temperature weld rolling. So far, there has been no report on the relevant research on pressing and quenching the laser weld at austenite temperature to obtain a uniform and fine martensitic structure to achieve improved weld strength and forming performance. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a method for preparing a laser welded joint in an austenitic zone weld. The present invention presses the laser welded weld at an austenitic temperature, refines the austenite grain structure in the weld zone, and in the subsequent cooling process, the weld structure is transformed into a martensite structure with fine and uniform grains, thereby improving the weld strength and formability.

[0005] The object of the present invention is achieved by the following methods:

[0006] The present invention provides a method for preparing an austenite zone weld pressed laser welded joint, comprising the following steps:

[0007] (1) The welding edges of two steel plates are butted and fixed, and laser wire welding is performed to obtain a welded plate with a weld excess height;

[0008] (2) The welded plate obtained in step (1) is kept warm in a heating furnace for 3 to 8 minutes, and the welded plate is taken out and immediately subjected to weld pressing and quenching in sequence, wherein the weld structure after quenching is a martensitic structure.

[0009] Based on the above technical solution, further, at least one of the two steel plates in step (1) is hot-formed steel, the surface of the steel plate is uncoated or the surface of the steel plate is aluminum-coated or aluminum-alloy-coated, and the weight of the single-sided coating of the aluminum or aluminum-alloy coating is g≤80g / m 2 .

[0010] Based on the above technical solution, further, the hot-formed steel includes 22MnB5.

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

[0012] Based on the above technical solution, further, the splicing gap between the two steel plates described in step (1) is 0 to 0.4 mm.

[0013] Based on the above technical solution, further, the laser power of the laser wire filling welding described in step (1) is 1-10 kW, the defocus amount is -5-5 mm, the welding speed is 0.02-0.20 m / s, the wire filling speed is 0.01-0.20 m / s, the welding wire diameter is 0.8-1.2 mm, and the shielding gas is an inert gas.

[0014] Based on the above technical solution, further, the composition and weight percentage of the welding wire for laser filling in step (1) are: 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 unavoidable impurities.

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

[0016] C: It has a certain influence on improving the strength of the weld, increasing the hardenability of the weld during the quenching process, and obtaining a weld with a complete martensitic structure. For uncoated hot-formed steel, a lower carbon content can be used. For coated hot-formed steel, as the coating quality increases, the carbon content requirement increases. The mass percentage of carbon in the present invention is: C ≥ 0.07%. In order to ensure the manufacturability of the welding wire, the maximum carbon content is controlled within 0.2%;

[0017] Si and Mn: can improve the strength of the weld and play a role in deoxidation. Their main functions are deoxidation and slag removal during steel plate smelting and improving the welding processability of the welding wire. The Si content in the weld of the present invention is controlled between 0.1% and 1.0%, and the Mn content is controlled between 1.1% and 3.0%.

[0018] Cr: improves the strength of the weld metal and the hardenability of the weld during the quenching process, reduces the activity of Al in the steel plate surface coating, and chemically reacts with chromium in the weld pool to form aluminum oxide. The higher the quality of the steel plate surface coating, the more Cr content is required. The lower limit of the Cr content in the present invention is 0.03% and the upper limit is 8%.

[0019] Mo: It can react with Al on the surface of the steel plate in the weld to form a high-temperature stable compound, reducing the solubility of Al in the weld. Its effect is similar to that of Cr. At the same time, Mo has strong hardenability. If the content is too high, it is easy to form a hardened structure in the weld, reducing the formability of the weld. Therefore, the Mo content is designed to be 0.01% to 5.0%, and 0.5% ≤ Mo + Cr ≤ 8%. If the content is too low, it cannot eliminate the influence of the steel plate surface coating on the weld. If the content is too high, the weld forming performance is poor.

[0020] Ni: an element that forms and stabilizes austenite, can expand the austenite phase region, improve the weld plasticity and toughness, and increase the weld's corrosion resistance. However, it is expensive. Considering all factors, the weld of the present invention contains 0-10% Ni.

[0021] Ti: It hinders the growth of austenite grains in the weld during the heating process of the welding plate, plays an important role in controlling the grain size of the weld, and has the effect of refining grains during the compression deformation and phase transformation of the weld. Too high Ti content in the weld will form cracks during the quenching process, affecting the performance of the weld. Therefore, the Ti content is 0.01% to 0.25%.

[0022] Rare earth Nd: Rare earth Nd element affects the type, quantity and form of non-metallic inclusions in steel, can refine the martensitic lath of welds, improve weld performance, and forms compounds with Al elements, which are evenly distributed in welds to improve weld strength. However, it is easy to form weld inclusions, so the content cannot be too high. Therefore, the content of Nd is 0.002% to 1.00%.

[0023] Based on the above technical scheme, further, in step (1), the weld excess height h (the height of the weld surface above the steel plate surface) is controlled within the range of 0.1mm to 2.0mm; the weld excess height described in the present invention is 0.1mm to 2.0mm, which provides a thinning amount for the later weld pressing. If the weld excess height is lower than 0.1mm, the weld pressing thinning amount is small, the weld deformation is small, the weld structure is not obviously refined, and the effect on improving the weld strength is not significant; if the weld excess height is greater than 2mm, the welding wire filling amount is large, and the welding material consumption is serious; the heat input of the welding joint is high, which is easy to cause the weld joint to soften; the weld deformation during the weld pressing process is large, which is easy to cause metal accumulation in the weld area, and the weld size accuracy cannot meet the welding requirements.

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

[0025] Based on the above technical solution, the present invention further presses the weld at a temperature of 890°C to 980°C. After pressing, the weld surface is consistent with the steel plate surface. During the weld extrusion process, the steel plate does not undergo extrusion deformation. When the temperature is lower than 890°C, the metal in the weld zone enters the two-phase zone, and a complete martensitic weld cannot be obtained after the weld is pressed. When the temperature is higher than 980°C, the austenite structure of the weld is coarse, and the strength and formability of the weld are reduced after pressing and quenching.

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

[0027] Based on the above technical solution, 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 solution, further, the cooling rate of quenching in step (2) is ≥25°C / s.

[0029] The beneficial effects of the present invention compared with the prior art are as follows:

[0030] 1. The present invention obtains a uniform and fine martensitic structure by pressing and quenching the weld in the austenite phase region, thereby achieving refinement of the weld structure and improvement of the performance of the hot-formed steel. The fracture position of the weld joint in tensile testing after quenching is on the parent material, and the strength is not less than 1500MPa, which successfully solves the problem of relatively thick laths and low strength in the weld area.

[0031] 2. The present invention adopts a laser wire-filling welding process and optimizes the weld composition, providing deformation for the weld pressing process, thereby achieving weld structure regulation and improved pressing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0033] Figure 1 This is the metallographic structure diagram of the weld in Example 1. DETAILED DESCRIPTION

[0034] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative labor all fall within the protection scope of the present invention.

[0035] Select two hot-formed steels with steel plate characteristic data as shown in Table 1 as tailor-welded steel plates, butt the welding edges of the two hot-formed steel plates and fix them with clamps to keep the lower surfaces of the two hot-formed steel plates on the same plane. The gap between the steel plates is shown in Table 2. Fiber laser welding is used. The defocus amount, laser power, welding speed, wire filling speed and welding wire diameter are shown in Table 2. The composition of the welding wire is shown in Table 3. Ar gas is used as the protective gas. The weld excess height (the height of the weld surface above the steel plate surface) is shown in Table 1. The welded plate is placed in a heating furnace for insulation for a period of time, and then taken out for weld pressing and quenching. The heating conditions, pressing and quenching process parameters are shown in Table 4. The thickness of the weld after pressing is the same as that of the welded plate. After quenching of the welded part, the hot-formed steel plate and the weld both form martensitic structure. The strength and fracture position of the weld area of ​​the welded hot-formed steel are tested. The results are shown in Table 5.

[0036] Table 1 Hot-formed steel plate data

[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 Rare Earth 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 location of the weld area of ​​hot-formed steel

[0045]

[0046]

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing austenite zone weld pressed laser welded joint, It is characterized in that The following steps are involved: (1) The welding edges of two steel plates are butted and fixed, and laser wire welding is performed to obtain a welded plate with a weld excess height; (2) The welded plate obtained in step (1) is kept warm in a heating furnace for 3 to 8 minutes, and the welded plate is taken out and immediately subjected to weld pressing and quenching in sequence, wherein the weld structure after quenching is a martensitic structure.

2. The preparation method according to claim 1, It is characterized in that At least one of the two steel plates in step (1) is hot-formed steel, the surface of the steel plate is uncoated or the surface of the steel plate is coated with aluminum or aluminum alloy, and the weight of the single-sided coating of the aluminum or aluminum alloy is ≤80g / m 2 .

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

4. The preparation method according to claim 1, It is characterized in that The laser power of the laser wire-filling welding described 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 wire-filling speed is 0.01-0.20 m / s, the welding wire diameter is 0.8-1.2 mm, and the shielding gas is an inert gas.

5. The preparation method according to claim 1, It is characterized in that The composition and weight percentage of the welding wire for laser filling in step (1) are: 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 unavoidable impurities.

6. The preparation method according to claim 1, It is characterized in that In step (1), the weld excess height h is controlled within the range of 0.1 to 2.0 mm.

7. The preparation method according to claim 1, It is characterized in that In step (2), the pressing pressure of the weld is 10 to 1000 kN, and the pressing speed is 0.05 to 1 m / s.

8. The preparation method according to claim 1, It is characterized in that The temperature of the heating furnace in step (2) is 890-960°C.

9. The preparation method according to claim 1, It is characterized in that The cooling rate of quenching in step (2) is ≥25°C / s.

Images