Dissimilar laser beam welding of AISI 2507 super duplex stainless to AISI 317L austenitic stainless steel

Abstract

In this research, AISI 2507 super duplex/AISI 317L austenitic stainless steels were joined by laser beam welding technique. The effects of heat input and post weld heat treatment (PWHT) on surface, texture, microstructure and mechanical properties were investigated. Based on the experimental results, it has been determined that the weld metal (WM) exhibits a duplex microstructure. Ferrite grains, grain boundary austenite, intragranular austenite and widmanstatten austenite and dislocation formations were detected in WM. In addition, ferrite, austenite grains and stacking faults were detected in the base metal (BM) of 2507 super duplex and 317L austenitic stainless steels. While dislocation and stacking fault formations disappeared after PWHT, Cr23C6 precipitates were formed. While a K-S and N-W orientation relationship (OR) was generally seen in the samples with and without PWHT, no OR was seen in the BM of the 317L side. In addition, the PWHT result of the Bain OR seen in the WM of the welded sample was not seen. The findings showed that while the Oxygen core on the WM surface of the sample without PWHT and PWHT was at the highest level at first, it then became zero as it descended deeper. Moreover, it was determined that the levels of Fe, Cr, Ni and Mo nuclei, which were at low levels at first, increased as one went deeper. It has been determined that as the heat input increases, the tensile strength, hardness and bending force decrement, while the toughness values increase in the welded samples. Based on PWHT, there is a reduction in tensile strength, hardness and bending force; [111] orientation to the grains [101] and [001] grains, a rise in the proportion of grains with a Schmid Factor (SF) value greater than 0.4, a decrement in kernel average misorientation (KAM) values and coincidence site lattice (CSL) boundary ratios, (001)<100> and (112)<111> this component has been caused by changes such as the emergence of recrystallized γ grains causing a rise in austenite content, increase in grain size, disappearance of stacking fault occurrences and dislocations. It was determined that the rise in toughness was caused by the emergence of (113)<332> component and the increase in low angle grain boundary ratios.