ANALYSING EFFECT OF QUENCHING AND TEMPERING INTO MECHANICAL PROPERTIES AND MICROSTRUCTURE OF 304-SS WELDED PLATES

The present work deals with analysis of mechanical performance and microstructural appearance of quenched and tempered SS-304 welded joints made by MIG welding technique. Since welding involves a critical solidification and thereby lots of internal stresses. Hence, heat treatment becomes important for removing stresses. In the present work, two SS-304 welded plates were heat treated. First plate was in quenched condition, and another was in tempered state. In both the plates, mechanical properties like tensile strength, impact strength, and hardness were analyzed. In addition, the microstructural attributes of base metal, heat affected zone and welded joints in both the welded plates were analyzed through optical microscope. The fractography analysis was also carried out in this study to get information about failure characteristics of samples after tensile testing. A significant change in mechanical properties, such as, 150% improvement in toughness, 7% reduction in weld-zone hardness, 3% improvement in yield strength and 6% reduction in ultimate tensile strength was obtained after tempering work. Also, the tempering process had reformed the grain structure by creating twins in base metal, and lathy δ ferrite & γ+δ lamella in HAZ. The martensite formed in quenched specimen had been completely recovered into fine γ+δ matrix.