Fiber laser beam welding of additive manufactured 316L austenitic stainless steel with wrought 2507 super duplex and wrought 904L super austenitic stainless steels: Crystallographic texture, microstructure, and mechanical properties

Abstract

In this study, 316L parts were produced by selective laser melting (SLM) method, one of the additive manufacturing (AM) processes. Since the size limits of the SLM system prevent large parts from being produced in one piece, there is a need to weld the parts produced with SLM to each other in a final process as an alternative option. For this reason, AM 316L parts are joined with full penetration by fiber laser welding. Welded joints of metals with different properties are widely used in various industries. Accordingly, welding combinations of AM 316L and wrought (W) 2507 super duplex stainless steel (W2507) and wrought (W) 904L super austenitic stainless steel (W904L) sheets, which are stainless steel types with superior mechanical properties, were carried out. Weldability, microstructure, texture, and mechanical properties of AM316L-AM316L, AM316L-W2507, and AM316L-W904L stainless steels welded by fiber laser welding method were investigated in detail. According to the results obtained, it was observed that the as-built AM 316L microstructure consists of cellular grains, and the AM316L-AM316L, AM316L-W2507, and AM316L-W904L laser welded joints are composed of a fine microstructure. While no pores and porosity were observed in As-built AM 316L, nano-sized particles were seen in welded joints' transmission electron microscope (TEM) images. According to EBSD analysis, epitaxial solidification was observed in the weld center of all samples, while grain orientations were mostly random. According to the kernel average misorientation (KAM) analysis, a high dislocation density was detected, especially at the weld metal grain boundaries of the AM316L-W2507 sample. Again in this sample, the lowest grain orientation spread (GOS) value and the highest Taylor Factor value were determined. Depending on the laser welding process, it was determined that some grains in the weld metal center of all samples showed a relatively strong texture (<011>//welding direction). In contrast, the grains in other parts of the weld metal (WM) showed a weaker texture. According to the mechanical test results, the welded joints' mechanical properties were generally lower than the as-built AM316L, W904L, and W2507 base metals. Among welded joints, the highest tensile and yield strength was found in the AM316L-W2507 sample, while the highest ductility was found in the AM316L-W904L sample. It has been determined that the toughness results are very close to each other. As a result of the tensile and impact tests, it was seen that the fractures took place in the ductile mode.