CN104942439B - 907A high-strength steel T-shaped joint laser welding and machining method - Google Patents

Abstract

The invention discloses a process method for laser welding of 907A high-strength steel T-shaped joints. It is a double-pass laser welding process. Speed 1.2～2.1m/min, defocus amount -10mm～-25mm, side blowing argon or helium is used as welding shielding gas during welding, the air flow direction is opposite to the welding direction, and the distance between the centers of spots is 0.3 during double-pass welding ~0.7mm. Compared with the single-pass laser welding, the microhardness of the weld is higher and the joint strength is insufficient. When the double-pass welding is used, due to the effect of the first welding waste heat, the martensite content is reduced, thereby improving the strength of the joint. toughness. The invention can be used to improve the strength and toughness of laser welding of 907A high-strength steel, so as to improve the service life of parts.

Description

A 907A high-strength steel T-joint laser welding processing method

technical field

The invention relates to material processing engineering technology, in particular to the field of metal processing, and relates to a material laser welding processing method.

Background technique

Lightweight shipbuilding is an inevitable trend for humans to cope with environmental degradation and energy shortages. Welded sandwich panels that combine the advantages of low-alloy high-strength steel with excellent performance and laser welding have broad application prospects in the shipbuilding industry. Energy conservation and emission reduction, and the establishment of a resource-saving and environment-friendly society are a major consensus in the development of human society. At present, in the shipbuilding process, one of the main measures to effectively reduce energy consumption, reduce emissions and ensure safety is the application of lightweight technology, which must be given sufficient attention. The laser welding speed is fast, the production efficiency is high, and there is no mechanical contact; when deep penetration welding is used, the depth-to-width ratio of the laser weld is large; the heat input is small, the weld width is small, the heat-affected zone is small, and the workpiece after welding is deformed It is also small; the heating and cooling speed is very fast, the weld grains are fine, and the weld quality is high. Fiber lasers have many advantages such as good beam quality, high output power, compact structure, and the ability to use optical fiber transmission. They have good application prospects in many fields such as welding. Laser welding can not only improve welding production efficiency, but also greatly reduce the width of the heat-affected zone of the weld, reduce the internal defects of the weld such as pores, incomplete penetration, slag inclusions, etc., and significantly improve the overall performance of the welded joint.

The present invention takes fiber laser welding of high-strength steel sandwich plates as the main research object, through methods such as hardness testing, mechanical performance testing, optical and scanning electron microscopy for microstructure observation, etc. The law, microstructure and mechanical properties have been systematically studied, and good-quality laser-welded sandwich panels have been obtained through appropriate welding processes, providing reliable basic data and suggestions for subsequent laser-welded manufacturing of sandwich structural panels and other related fields.

Contents of the invention

The invention aims to provide a laser welding processing method for T-shaped joints of 907A high-strength steel. This process is a T-joint laser double-pass welding process, which can improve the strength and toughness of 907A high-strength steel T-joint laser welding to improve the service life of parts.

A process method for laser welding of 907A high-strength steel T-joints, the process comprising:

(1) The T-joint is composed of the upper base plate, the lower base plate and the web between the upper and lower base plates. A shallow groove is milled at the position to be welded on the upper base plate or the lower base plate, and the paint on the position to be welded is removed and ground; a grinding wheel can be used Remove the paint on the position to be welded, and then smooth it with sandpaper; the upper and lower bottom plates and webs are 907A thin steel plates, which can be obtained by machining.

(2) Clean the welding surface to remove dirt, oil, etc., preferably with acetone. Grease can cause defects such as pores, cracks, and hydrogen embrittlement. Therefore, use acetone to clean the welding surface before welding to remove dirt, oil, etc. Then; fix the upper bottom plate, lower bottom plate and web to form a 907A high-strength steel T-joint.

Install and fix the panel and core board on the workbench through the pre-established fixture;

(3) Laser welding is performed on 907A high-strength steel T-joints, which is double-pass laser welding. The process parameters are: laser power 3000-5000W, focus position spot diameter 280-320μm, focal length 300-320mm, welding speed 1.2- 2.1m/min, defocus amount -10mm～-25mm, side-blown argon or helium is used as welding shielding gas during welding, the airflow direction is opposite to the welding direction, and the distance between spot centers during double-pass welding is 0.3～0.7mm .

Preferably, the spot diameter at the focus position is 300 μm, and the focal length is 310 mm.

Preferably, the center-to-center distance of the spots is 0.5 mm during the double-pass welding in step (3).

Preferably, the protective gas flow rate in step (3) is 15-30 L/min, more preferably 25 L/min.

The 907A high-strength steel T-joint obtained by the above-mentioned laser processing method is stronger and tougher, which can increase the service life of the parts. In single-pass welding, the structure of the laser welding seam is fine, which is lath martensite; the welding heat-affected zone is very narrow, about 1mm, and its structure transitions from thicker lath martensite and a small amount of retained austenite to plate martensite. Strip martensite, retained austenite and a small amount of precipitated carbide; the microhardness of the weld seam and the heat-affected zone are higher than that of the base metal, the microhardness of the weld seam is between 330 and 360HV _0.2 , and the T-joint pulls off and fractures There are both ductile fracture and brittle fracture, and the cracks gradually expand from both sides to the center, and finally cleavage fracture occurs in the center of the weld. Compared with the single-pass laser welding, the microhardness of the weld is higher and the joint strength is insufficient. When the double-pass welding is used, due to the effect of the first welding waste heat, the martensite content is reduced, thereby improving the strength of the joint. toughness. The invention can be used to improve the strength and toughness of laser welding of 907A high-strength steel, so as to improve the service life of parts.

Description of drawings

Fig. 1 is the appearance of single-pass and double-pass laser welding of T-joints in the present invention, wherein (a) is the appearance of single-pass laser welding of T-joints, and (b) is the appearance of double-pass laser welding of T-joints.

Fig. 2 is the SEM photo of the T-joint laser welding seam structure of the present invention, (a) is the SEM photo of the single-pass laser welding seam structure, (b) is the SEM photo of the double-pass laser welding seam structure.

Fig. 3 is the SEM photo of the fracture structure of the T-joint laser welding seam of the present invention, (a) is the SEM photo of the fracture structure of the single-pass laser welding seam, and (b) is the SEM photo of the fracture structure of the double-pass laser welding seam.

Fig. 4 is a hardness curve diagram of a single-pass laser welding seam of a T-shaped joint.

Fig. 5 is a hardness curve diagram of the double-pass laser welding seam of the T-shaped joint.

detailed description

Embodiments of the present invention will be described in detail below. This embodiment is carried out on the premise of the technical solution of the present invention, and the detailed implementation and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

Example 1

(1) The 907A thin steel plate is obtained by mechanical processing, and its original size is 300mm×200mm×3mm (upper bottom plate, lower bottom plate) and 200mm×120mm×3mm (web plate). Mill shallow grooves at the position to be welded, use a grinding wheel to remove the paint at the position to be welded, and then smooth it with sandpaper.

(2) Dirt, dust, and grease will cause defects such as pores, cracks, and hydrogen embrittlement. Therefore, use acetone to clean the welding surface before welding to remove dirt, oil, etc. Then, install and fix the upper and lower base plates (panels) and core plates (web plates) on the workbench through the pre-established fixtures.

(3) Perform single-pass laser welding on 907A high-strength steel T-joints. The process parameters are: laser power 4500W, focal spot diameter 300um, focal length 310mm, welding speed 1.5m/min, and defocus of -15mm When welding, side-blown argon gas is used as the welding shielding gas, the air flow direction is opposite to the welding direction, and the shielding gas flow rate is 25L/min.

The results show that the heat-affected zone of laser welding is very narrow, as shown in Fig. 1(a). The high-magnification SEM photo of the structure is shown in Figure 2(a). The structure transitions from coarser lath martensite and a small amount of retained austenite to lath martensite, retained austenite and a small amount of precipitated carbides. Figure 3(a) shows the morphology characteristics of the tensile fracture of the sample, and the single-pass weld fracture has both brittle and plastic fracture characteristics.

The micro-Vickers hardness test is carried out on the welded joint, the loading time is 15s, the hardness load is 200gf, and the distance between two points is 0.1mm. The test curve is shown in Figure 4. Due to the formation of martensite during the laser heating and cooling process, Make its hardness value higher than the base metal itself.

Example 2

(1) The 907A thin steel plate is obtained through mechanical processing, and its original size is 300mm×200mm×3mm (upper and lower bottom plates) and 200mm×120mm×3mm (web), and three waiting plates on one side of the panel (upper and lower bottom plates) Mill shallow grooves at the welding position, use a grinding wheel to remove the paint at the position to be welded, and then smooth it with sandpaper.

(2) Dirt, dust, and grease will cause defects such as pores, cracks, and hydrogen embrittlement. Therefore, use acetone to clean the welding surface before welding to remove dirt, oil, etc. Then, install and fix the panels (upper and lower base plates) and core plates (web plates) on the workbench through the pre-established fixtures.

(3) Double-pass laser welding is performed on the 907A high-strength steel T-joint, the parameter setting is the same as in Example 1, and the spot center distance is 0.5mm during double-pass welding.

The results show that the heat-affected zone of laser welding is very narrow, as shown in Fig. 1(b). The SEM photo of the high-magnification structure is shown in Figure 2(b), and its structure transitions from coarser lath martensite and a small amount of retained austenite to lath martensite, retained austenite and a small amount of precipitated carbides, and It is more uniform and finer than single pass welding. Figure 3(b) shows the tensile fracture morphology of the sample, showing obvious dimple features, which belong to ductile fracture. The results show that, compared with the single-pass laser welding process in Example 1, the strength and toughness of the T-shaped joint obtained by double-pass welding is improved.

The hardness of the weld seam is tested on the welded joint. Compared with single-pass laser welding, due to the effect of residual heat from the previous pass, the hardness value decreases and is closer to the base metal. The hardness test curve is shown in Figure 5.

Claims (5)

1. a kind of 907A high-strength steel T connector laser welding processing method, it is characterised in that step includes：

(1) 907A sheet metals are taken respectively as base plate and web, shallow slot are milled out in base plate position to be welded, are removed the oil of position to be welded Paint, is polished with sand paper；

(2) face of weld is cleaned, and base plate and web fixation is made into T connector；

(3) laser welding is carried out to the junction of the base plate and web of T connector, is two pass time laser welding, technological parameter is： 3000～5000W of laser power, 280～320 μm of focal position spot diameter, focal length are 300～320mm, and speed of welding is 1.2 ～2.1m/min, defocusing amount -10mm～-25mm, adopt side-blown argon or helium as welding protection gas, air-flow side during welding To with welding direction conversely, and hot spot center distance is 0.3～0.7mm during double pass welds.

2. 907A high-strength steel T connector laser welding processing methods described in claim 1, it is characterised in that step (3) two pass During secondary welding, hot spot center distance is 0.5mm.

3. 907A high-strength steel T connector laser welding processing methods described in claim 1, it is characterised in that the guarantor of step (3) Shield throughput is 15～30L/min.

4. 907A high-strength steel T connector laser welding processing methods described in claim 1, it is characterised in that in step (3), 300 μm of focal position spot diameter, focal length is 310mm.

5. 907A high-strength steel T connector laser welding processing methods described in claim 1, it is characterised in that the guarantor of step (3) Shield throughput is 25L/min.