Dissimilar Laser Welding of Austenitic Stainless Steel and Abrasion-Resistant Steel: Microstructural Evolution and Mechanical Properties Enhanced by Post-Weld Heat Treatment

Abstract

In this study, ultra-high-strength steels, namely, cold-hardened austenitic stainless steel AISI 301 and martensitic abrasion-resistant steel AR600, as base metals (BMs) were butt-welded using a disk laser to evaluate the microstructure, mechanical properties, and effect of post-weld heat treatment (PWHT) at 250 °C of the dissimilar joints. The welding processes were conducted at different energy inputs (EIs; 50–320 J/mm). The microstructural evolution of the fusion zones (FZ) in the welded joints was examined using electron backscattering diffraction (EBSD) and laser scanning confocal microscopy. The hardness profiles across the weldments and tensile properties of the as-welded joints and the corresponding PWHT joints were measured using a microhardness tester and universal material testing equipment. The EBSD results showed that the microstructures of the welded joints were relatively similar since the microstructure of the FZ was composed of a lath martensite matrix with a small fraction of austenite. The welded structure exhibited significantly higher microhardness at the lower EIs of 50 and 100 J/mm (640 HV). However, tempered martensite was promoted at the high EI of 320 J/mm, significantly reducing the hardness of the FZ to 520 HV. The mechanical tensile properties were considerably affected by the EI of the as-welded joints. Moreover, the PWHT enhanced the tensile properties by increasing the deformation capacity due to promoting the tempered martensite in the FZ.

Microstructure Evolution at Ni/Fe Interface in Dissimilar Metal Weld between Ferritic Steel and Austenitic Stainless Steel

“…There is a steep chemical composition gradient in the interior of the PMZ and a composition interface between the PMZ and unmolten BM, which results in complex microstructure evolution near the Ni/Fe interface. In addition, the microstructures near the Fe/Ni interface might evolve further during the post-weld heat treatment (PWHT) process [ 20 ]. Special microstructures were observed near the Ni/Fe interface in early years, i.e., the martensite layer [ 21 , 22 ] and interfacial precipitates [ 3 , 13 , 16 , 23 ].…”

Effect of High-Temperature Tempering on Microstructure and Mechanical Strength of Laser-Welded Joints between Medium-Mn Stainless Steel and High-Strength Carbon Steel

“…Meanwhile, some detrimental effects, thermal residual stresses, and heterogeneous microstructure could be associated with the dissimilar metal joints owing to the variations in melting point temperatures, different chemistry, different mechanical strength, and physical properties, such as thermal conductivity, and coefficient of thermal expansion [12]. Hence, Post-weld heat treatment (PWHT) is desired to improve the mechanical performance of the weldments, such as the mechanical strength and toughness [13,14], and overcome the heterogeneity in microstructures across the weld structure [15]. In the present manuscript, the strengthening effect due to high-temperature tempering (HTT) at 700 °C was studied on LWed butt joints of MMn-SS and HS-CS.…”

Studying the strengthening mechanisms and mechanical properties of dissimilar laser-welded butt joints of medium-Mn stainless steel and automotive high-strength carbon steel

“…It is well established that a post-weld heat treatment (PWHT) is applied to weldments to improve their mechanical performance, such as in terms of the tensile strength and toughness [17][18][19][20][21][22], overcome the heterogeneity in microstructures across the weld structure [23], and relieve the weld-induced residual stresses arising from rapid cooling, phase transformation in the FZ, and different thermal expansion coefficients of the BMs and weldments [2,[24][25][26][27].…”