A Comparative Analysis among Quenched, Tempered, and Stepped Cooled TIG Welded SS-304 Plates Based on Tensile Strength, Hardness, and Microstructural Appearance

Abstract

The present experimental work critically analyses the changes in microstructural orientation and mechanical properties of TIG (tungsten inert gas) welded AISI-304 (SS) plates which have undergone through various heat treatments. The characteristics of heat-treated samples have been compared with those of untreated samples which is denoted by the original sample in this study. Five SS-304 plates were welded by the TIG method. Out of five, four plates were heat treated and one plate was put in the original condition. Four heat treatment includes quenching, stepped heat treating (sand + water), tempering-1 (quick quench then sand cooling), and tempering-2 (quick quench then air cooling). In all the five plates, the tensile test and microhardness test have been performed. In addition, microscopic observation of cross-sectional surfaces has also been carried out. The base metal (BM) zone of all five plates mainly consists of equiaxed γ-grains, although twin can be observed only in the original sample. The heat-affected zone (HAZ) imparts both lathy and dendritic type δ-ferrite at the transition of the BM and welded zone (WZ). At the welded zone, the γ-matrix has become coarse with numerous spots and dendrites of δ-ferrite could be seen. Sample 3, tempered by means by water sprinkling for a very short time and then cooling in sand, has shown satisfactory results among all. The sample has achieved the 23% higher extension value and 10% higher hardness at WZ than these of the original sample, although a negligible loss (0.2%) of ultimate tensile strength (UTS) is also reported in sample 3.