Effect of heat input and post weld heat treatment on the texture, microstructure and mechanical properties of laser beam welded AISI 317L austenitic stainless steel

Abstract

In this study, AISI 317L austenitic stainless steel sheets were welded using laser beam welding method and post-welding heat treatment (PWHT) was applied to the joints. The effect of PWHT and welding heat input on texture, microstructure and mechanical properties was examined. According to the results obtained in the study, it was observed that the microstructure of the weld metal of the samples welded with the lowest and highest heat input consisted largely of austenite and a small amount of ferrite grains. Mechanical properties were directly affected by such microstructural changes. With the exception of impact notch results, higher tensile strength and micro-hardness was observed for most welded joints compared to the base metal for heat-treated and non-heat-treated conditions. It was found that the bending strength decreased due to softening of the microstructure after heat treatment. High mechanical properties were achieved in the samples joined with low heat input thanks to the microstructure with finer grains. According to the electron backscatter diffraction result (EBSD); the austenite (FCC) ratio in the base metal and weld metal of the sample welded with the highest heat input was found to be approximately 98% and 92%, while the ferrite (BCC) ratio in the base metal and weld metal was determined as 2% and 8%. It was determined that austenite volume ratio increases with PWHT. Austenite grains showed a random orientation in the base metal, while in the weld metal they showed orientation in the direction of [111] and more often [100]. Generally K–S and N–W orientation relationship (OR) was observed in the samples. In the weld metal of the C4H sample, transmission electron microscopy (TEM) determined the spinodal decomposition of ferrite, but G-phase was not observed.