Microstructure and Hardness Properties of 304l Stainless Steel at Varied Gas Tungsten Arc Welding Voltage

Abstract

Establishing optimum range of welding parameters requirements is a sine-quo-non for obtaining weldments with the desired microstructure and mechanical properties. Therefore, in this study efforts were made to investigate the effects of varied gas tungsten arc welding voltage on the microstructure characteristics and hardness property of 304L austenitic stainless steel (ASS). To this end, chemical compositions of the as-received 304L ASS plate was determined by Optical emission spectrometry (AR 4 30 metal analyzer). Weldments with butt –joints configuration were produced, using gas tungsten arc welding (GTAW) at 10 V, 20 V, 30 V and 40 V. Microstructures of the weldments were examined, using metallurgical microscope (OMM) (Olympus GX51), and the weldment were tested on Vickers microhardness testing machine. From the results obtained, chemical compositions of the as-received 304L plate revealed 18.325 wt. % s chromium and 8.469 wt.%  nickel, adding up to 26.794 wt.% of the total elemental content. The microstructures of the weldments are heterogeneous (non-equilibrium), austenite (γ) and ferrite (α) are the major phases. γ is the leading phase, while α grains are found within the γ matrix. Grains of the fusion zone (FZ) microstructures are finer as compared to those of the corresponding heat–affected zone (HAZ). Microstructures of both FZ and HAZ are characterized by δ-ferrite, precipitations, inclusions and dendrites of varied numbers and sizes. Hardness values of weldments were high in the range (20 – 25 V) relative to (30 – 40V). And optimum hardness values 205.8VHN and 192.0VHN were revealed by the FZ and HAZ respectively at the GTAW of 20 V, while least hardness values of 201.4VHN and 188.8VHN were revealed by the FZ and HAZ respectively, at GTAW of 40 V