Effects of the laser parameters on the mechanical properties and microstructure of weld joint in dissimilar pulsed laser welding of AISI 304 and AISI 420

Abstract

Dissimilar laser welding of AISI 304 and AISI 420 stainless steel sheets was performed with pulsed Nd: YAG laser so as to evaluate the temperature distribution, microstructure and mechanical properties of the welded zone. The effects of pulsed laser process parameters including (pulse duration, frequency, current, focal length and welding speed) on the fusion zone temperature variation were investigated. Furthermore, the weld joint microstructure and mechanical properties were evaluated according to the temperature distribution of the fusion zone. Different thermal conductivity of the austenitic and ferritic stainless steel resulted in higher temperature of the welded zone for austenitic sample because of more heat concentration. The focal length and peak power had the significant influence on the AISI 304 temperature rise. The fusion zone microstructure composed of coarse ferrite grains austenitic grains. The heat affected zone (HAZ) was including coarse ferrite grains near the ferritic side and austenitic grains with stringers of ferrite δ adjacent to the austenitic side of the weld. The fracture of the welded joint initiated at the HAZ region of AISI 420 stainless steel. Increasing the welding speed decreased the peak temperature of the fusion zone which clearly reduced the strength of the joint. Increasing the welding speed remarkably reduced the weld tensile strength of the about 30% and the temperature of the melt pool adjacent area about 140 °C. Also, the porosity formed at the melt pool region when the temperature of the ferritic sample decreased from 250 °C to 130 °C during welding process. The fusion zone microstructure analysis shows that the predominant microstructure was composed of coarse ferritic grains that include more than 70% of the melt pool total volume.