Study of the influence of laser welding parameters on the microstructure of butt welded joints of AISI 304 stainless steel
DOI:
https://doi.org/10.33216/1998-7927-2025-298-12-47-55Keywords:
laser welding, microstructure, sheet metal, butt joints, stainless steels, AISI 304Abstract
Chromium–nickel austenitic stainless steels occupy a leading position among structural materials in modern industry due to the combination of high mechanical properties, corrosion resistance, and good manufacturability. One of the most widely used grades is AISI 304 steel, which is extensively applied in the energy sector, chemical and petrochemical industries, shipbuilding, and mechanical engineering. At the same time, welding, particularly laser welding, is associated with the implementation of nonequilibrium solidification conditions, which significantly affect the weld metal microstructure, phase composition, formation of the heat-affected zone, and non-metallic inclusions. This paper presents the results of an experimental study on the effect of laser welding parameters on the microstructure, phase composition, and characteristics of non-metallic inclusions in butt joints of austenitic stainless steel AISI 304 with a thickness of 1.5 mm. Laser welding was performed using an Nd:YAG laser “DY044” under three welding modes with the same linear energy of 60 J/mm and a laser beam defocusing value of 0 mm, at laser power levels of 1.5, 2.5, and 3.5 kW and corresponding welding speeds of 1.5, 2.5, and 3.5 m/min. Microstructural investigations were carried out by optical microscopy in the magnification range of ×50–×500. The δ-ferrite content was measured using a “Ferritgehaltmesser-1.053” device, while the evaluation of non-metallic inclusions was performed in accordance with DSTU ISO 4967:2017. It was established that the weld metal in all specimens is characterized by a dispersed cast structure with the formation of a central cellular zone, a zone of columnar crystallites, and a zone of equiaxed grains near the fusion line. With increasing laser power, a narrowing of the central cellular band, a reduction in the extent of structural zones, and a decrease in the intensity of mutual penetration between the weld metal and the base metal are observed. The δ-ferrite content in the weld metal shows a clear tendency to decrease from 1.7–1.8% to 0.8–0.9%, indicating a more complete austenitic stabilization at higher welding modes. The highest weld metal purity with respect to non-metallic inclusions was recorded in the specimen welded at a laser power of 3.5 kW, where only dispersed point nitrides and oxynitrides with a rating not exceeding No. 0.5 were detected. The heat-affected zone in all cases is narrow, about 600–900 μm, without austenitic grain growth and with preservation of the rolled structure. The obtained results confirm the effectiveness of optimizing laser welding parameters for the formation of a fine-dispersed microstructure, reduction of δ-ferrite content, and minimization of non-metallic inclusions.
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