Influence of heat input on microstructure and mechanical behaviour of austenitic stainless steel 316L processed in wire and arc additive manufacturing

Abstract

Wire arc additive manufacturing (WAAM) has long been considered an efficient method for producing medium- and large-sized components, due to its minimal material consumption, high deposition, superior structural quality and environmental friendliness. The ER 316L wire was employed as the filler metal in the fabrication process with varying heat input by altering welding current (C), wire feed speed (WFS) and travel speed (TS). The first portion of the studies involved producing single-bead welds by adjusting the heat input condition, while the second part involved fabricating three single-bead walls using optimum parameters determined in the first part of the research. The mechanical properties of SS316L samples remained impressively constant when WFS and TS were varied. The macroscopic morphology and microstructure of a thick-walled component were studied using a metallurgical microscope and optical electron microscopy. The mechanical properties of tensile study and micro-hardness analysis were reported. From a microstructural study, it can be observed that the deposited weld beads consist of a columnar structure with primary dendrites. The cooling rate and heat dissipation during the weld deposition process affect the variance of microstructure in different areas. The average micro-hardness value of various linear heat input manufactured components demonstrated stability, with values of 313, 249 and 398 HV, respectively. The hardness results of as-deposited walls provide a higher value in bottom regions due to heat accumulation. Tensile properties were determined parallel and perpendicular to the deposition directions; decreased heat input resulted in superior mechanical properties in terms of tensile characteristics. From the tensile properties, the mean values of various heat input SS 316L ultimate tensile strength, yield strength and elongation were found to be 426 MPa, 304 MPa and 20%, respectively. Fractography showed typical dimple fracture characteristics in all the specimens. It is clear from the current research that parts made by WAAM exceed their 316L casting parts and wrought alloy.