STUDY OF THE INFLUENCE OF LASER WELDING PARAMETERS ON THE MICROHARDNESS OF BUTT WELDED JOINTS OF STAINLESS STEEL AISI 304
Abstract
Laser welding is one of the most promising methods for joining austenitic stainless steels, which are widely used in critical structures in modern industry. Particular attention is paid to ensuring stable mechanical properties of welded joints, in particular, uniform microhardness distribution, which is determined by the conditions of heat input and metal crystallization. The purpose of this work is to study the influence of laser welding parameters on the microhardness of butt welded joints of AISI 304 stainless steel with a thickness of 1.5 mm. For this purpose, butt joints were made in three laser welding modes with the same linear energy of 60 J/mm and laser beam defocusing of 0 mm, but with different values of power and welding speed: P = 1.5…2.5…3.5 kW and V = 1.5…2.5…3.5 m/min. Microhardness was determined using the Vickers method both in the cross section of welded joints and vertically along the weld axis. It was found that all the samples studied are characterized by a dispersed cast structure of the weld metal with a clearly defined fusion line and preservation of the rolled structure in the heat-affected zone and base metal. The measurement results showed an uneven distribution of microhardness in both the transverse and vertical directions. All modes are characterized by an increase in microhardness in the weld metal compared to the base metal, which is due to rapid crystallization and the formation of a finer microstructure. The maximum microhardness values in the weld zone reach 2540–2640 MPa depending on the welding mode. It has been shown that at a lower laser power (P = 1.5 kW), the most uniform distribution of microhardness is formed both across the width and height of the weld. With an increase in power to 2.5 and 3.5 kW, the heterogeneity of microhardness distribution increases, with local areas of microhardness reduction appearing in the heat-affected zone and the lower part of the weld, which may be associated with local overheating and slow cooling of the metal. The analysis showed that the maximum microhardness values are usually observed in the upper part of the weld, while a gradual decrease in microhardness is possible towards the root.
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