Effect of post weld heat treatment on the crystallographic texture, microstructure, and microhardness of fiber laser beam welded laser powder bed fusion 316L austenitic stainless steel

Abstract

In this study, 316L stainless steel parts produced via laser powder bed fusion (LPBF) under a laser power of 190 W, a scanning speed of 1080 mm/s, and a layer thickness of 20 µm were joined using fiber laser welding at a power of 1.9 kW and a speed of 35 mm/s. The joints were subsequently subjected to post-weld heat treatment (PWHT) at 1080 °C for 1 h, followed by air cooling or water quenching. The as-built LPBF base metal exhibited a fully austenitic phase with columnar and locally equiaxed grains. Following PWHT, cellular grains disappeared, transforming into large columnar and equiaxed-like grains via epitaxial growth, alongside randomly distributed nanosized oxides. Due to rapid cooling during welding, the fusion zone displayed a fine-grained dendritic morphology. Phase maps revealed a nearly fully austenitic microstructure across all conditions, with negligible ferrite. Although heat treatment induced grain coarsening, different austenite morphologies developed depending on the cooling rate. A high fraction of high-angle grain boundaries was observed in all samples except for the water-quenched joint. Furthermore, a Kurdjumov–Sachs (K–S) and Nishiyama–Wassermann (N–W) orientation relationship parallel to (110)FCC // (111)BCC was identified between the austenite and ferrite grains.