Welding process method for improving corrosion resistance of 304 stainless steel weld joint

Abstract

The invention provides a welding process method for improving corrosion resistance of a 304 stainless steel weld joint. According to the welding process method, the weld joint with excellent corrosion resistance is successfully prepared by adjusting parameters such as a laser welding path and scanning frequency of a galvanometer system. Experimental results show that compared with a traditional laser welding method, the laser welding method can improve the corrosion performance of a welded joint in a 3.5% NaCI solution.

Description

Technical Field

[0001] The invention relates to the technical field of laser welding, in particular to laser welding of 304 stainless steel sheets. Background Art

[0002] 304 stainless steel has excellent mechanical properties and corrosion resistance. Its output and usage account for more than 50% of the total output of stainless steel. It has been widely used in the engineering field, and is often connected by welding. At present, welding is mainly carried out by methods such as metal arc welding (SMAW), gas metal arc welding (GMAW), argon tungsten arc welding (GTAW), laser welding (LBW) and cold metal welding (CMT). Although 304 stainless steel has good welding performance, in engineering applications, welded joints often fail due to corrosion. For example, in July 2020, the first batch of units of the Wudongde Hydropower Station began to generate electricity. At the end of July, it was discovered that the fire water pipes of the 811 m turbine layer of the main powerhouse of the underground power station began to leak. By the end of September, the number of leaking points in the left and right bank power station pipelines increased dramatically, totaling more than 270. For typical clean water, measurement, and fire water systems, the leaking points (about 90%) are concentrated in the welds. During the welding process, the weld area has undergone rapid heating, melting, and solidification. Compared with the parent material, the weld structure has changed greatly: the weld of 304 stainless steel is mainly composed of "austenite phase" and "ferrite phase", and the austenite phase is the main phase, accounting for more than 90%. The grain morphology of the weld is mainly columnar crystals, and equiaxed crystals appear in rare cases. The parent material only has an austenite phase, and the rolled steel grains are often in the form of equiaxed crystals. According to the literature, corrosion often occurs at the interface of "austenite phase" and "ferrite phase". This is because the two phases have different compositions and structures, resulting in differences in the potential of the two phases. The service environment of 304 stainless steel is often liquid, and the galvanic effect formed by the two phases is generated, which will produce electrochemical corrosion. At the same time, through literature research, it was found that the grain orientation and grain size of stainless steel welds will also affect corrosion. Therefore, how to improve the corrosion resistance of 304 stainless steel plate welds has become an urgent problem to be solved in this field. Summary of the invention

[0003] The invention provides a galvanometer scanning laser welding process method for improving the corrosion resistance of a 304 stainless steel thin plate butt weld, so as to solve the problem that the 304 stainless steel welding weld is easily corroded.

[0004] In order to achieve the above object, the present invention provides the following technical solutions: S1. Use 800-grit sandpaper to grind the surface of the 2mm thick stainless steel plate to remove the oxide film, and then use 1200-grit sandpaper to grind the welding surface to make the 2mm thick stainless steel surface brighter; S2. Use acetone to clean the 2mm thick stainless steel surface to be welded to ensure that the welding area is free of pollution and there is no gap when connecting; S3. Place the 2mm thick 304 stainless steel on the welding table in a butt-jointed manner and tighten it with a clamp to ensure that the 2mm thick 304 stainless steel will not deform during the welding process; S4. Adjust the angle of the galvanometer scanning system so that the laser beam irradiates the stainless steel surface to be welded vertically. Then, with the galvanometer scanning system as the origin, rotate the galvanometer scanning system 10° clockwise in the plane formed by the welding speed direction and the laser beam direction, that is, the laser beam emission direction forms an angle of 80° with the stainless steel surface, and the component of the laser beam emission direction in the welding speed direction is opposite to the welding speed direction; S5. Adjust the process parameters of the galvanometer scanning laser welding system as follows: laser power: 800 watts, scanning type of the galvanometer scanning system is circular, frequency is 115 Hz, welding speed in the welding direction is 10 mm / s, shielding gas is argon gas with a purity of 99.9%, gas flow rate is 20 L / min, and defocus is 0; The shielding gas is transported by a 1 mm thick cylindrical copper tube. The shielding gas outlet is 5 cm away from the surface of the stainless steel plate, and the laser beam is coaxial with the cylindrical copper tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 It is the polarization curve of the laser welded joint surface of the 304 stainless steel sheet prepared in Example 1 in 3.5% NaCl solution, the galvanometer laser welding S1 is the polarization curve of the welded joint prepared by the method of the present invention, the conventional laser welding S01 is the polarization curve of the welded joint prepared by the conventional laser welding method, and the base material is the polarization curve of the unwelded part of 304 stainless steel. DETAILED DESCRIPTION

[0006] First, use 800-mesh sandpaper to grind the surface of the 2mm-thick stainless steel plate to remove the oxide film, and further use 1200-mesh sandpaper to grind the welding surface to make the 2mm-thick stainless steel surface brighter; then use acetone to clean the 2mm-thick stainless steel surface to be welded to ensure that the welding is free of pollution and there is no gap when docking; further, place the 2mm-thick 304 stainless steel on the welding operating table in the form of docking, and use a clamp to tighten it to ensure that the 2mm-thick 304 stainless steel will not deform during welding; then adjust the angle of the galvanometer scanning system so that the laser beam irradiates the stainless steel surface to be welded vertically, and then use the galvanometer scanning system as the origin, and adjust the galvanometer scanning system in the welding speed direction and the laser beam direction. The plane formed by the direction of the optical beam is rotated 10° clockwise, that is, the laser beam emission direction forms an angle of 80° with the stainless steel surface, and the component of the laser beam emission direction in the welding speed direction is opposite to the welding speed direction; finally, the process parameters of the galvanometer scanning laser welding system are adjusted as follows: laser power is 800 watts, the scanning type of the galvanometer scanning system is circular, the frequency is 115 Hz, the welding speed in the welding direction is 10 mm / s, the shielding gas is argon with a purity of 99.9%, the gas flow rate is 20 L / min, and the defocus amount is 0; it is worth noting that the shielding gas is transported in a 1 mm thick cylindrical copper tube, the shielding gas outlet is 5 cm away from the surface of the stainless steel plate, and the laser beam is coaxial with the cylindrical copper tube.

[0007] In order to verify the corrosion resistance of the 304 stainless steel weld prepared by the present invention, the scanning type of the galvanometer scanning system in step S5 of the present invention is changed to straight line welding, that is, conventional welding method. The welded joint sample prepared by the present invention is recorded as: galvanometer laser welding S1; the welded joint sample prepared by the conventional welding method is recorded as: conventional laser welding S01; it is placed in a 3.5% NaCl solution for electrochemical corrosion performance test. According to the polarization curve test results of the electrochemical test, it can be found that the corrosion resistance of the 304 stainless steel welded joint prepared by the present invention is much better than that of the welded joint prepared by the conventional laser welding method.

Claims

1. A welding process method for improving the corrosion resistance of 304 stainless steel welds, characterized in that: The following steps are involved: S1. Use 800-grit sandpaper to grind the surface of the 2mm thick stainless steel plate to remove the oxide film, and then use 1200-grit sandpaper to grind the welding surface to make the 2mm thick stainless steel surface brighter; S2. Use acetone to clean the 2mm thick stainless steel surface to be welded to ensure that the welding area is free of pollution and there is no gap when connecting; S3. Place the 2mm thick 304 stainless steel on the welding table in a butt-jointed manner and tighten it with a clamp to ensure that the 2mm thick 304 stainless steel will not deform during the welding process; S4. Adjust the angle of the galvanometer scanning system so that the laser beam irradiates the stainless steel surface to be welded vertically. Then, with the galvanometer scanning system as the origin, rotate the galvanometer scanning system 10° clockwise in the plane formed by the welding speed direction and the laser beam direction, that is, the laser beam emission direction forms an angle of 80° with the stainless steel surface, and the component of the laser beam emission direction in the welding speed direction is opposite to the welding speed direction; S5. Adjust the process parameters of the galvanometer scanning laser welding system as follows: laser power: 800 watts, scanning type of the galvanometer scanning system is circular, frequency is 115 Hz, welding speed in welding direction is 10 mm / s, shielding gas is argon with a purity of 99.9%, gas flow rate is 20 L / min, and defocus is 0.

2. A welding process method for improving the corrosion resistance of 304 stainless steel welds according to the claims, characterized in that: The shielding gas is transported by a 1 mm thick cylindrical copper tube. The shielding gas outlet is 5 cm away from the surface of the stainless steel plate, and the laser beam is coaxial with the cylindrical copper tube.

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