Experimental investigations on weldability issues of gas metal arc welded aisi 3i6l stainless steel welded joints for imroving their mechancial metallurgical and corrosion performance

Abstract

ABSTRACT newlineAISI 316L grade austenitic stainless steels (ASS) belong to a group of chromium-nickel- molybdenum grades and is an industrially very important grade as they are used in a wide variety of applications like nuclear, petrochemical, aerospace, chemical, dairy industry etc. These grades are intended to provide improved corrosion resistance relative to the standard chromium-nickel steel grades used in corrosive process environments. The ASS structures when fabricated using welding suffers from the problem of mechanical as well as corrosion property degradation. Because of this, there is a strong need to develop welding procedures capable of giving sound quality joints which would perform satisfactorily in actual service conditions. Based upon this the present work was undertaken that involved using Multipass welding technique for fabricating AISI 316 L austenitic stainless steel welds using GMA (gas metal arc) welding process. Two types of weld procedural variations were used viz. a three-pass weld and a five pass welding procedure for fabricating sound butt joints. The welded joints were subjected to two post thermal ageing treatments viz. 750°C/2hr and 750°C/12 hr. Metallurgical studies, transverse tensile testing studies and impact toughness studies were carried out to investigate the role of heat input variation that resulted due to multipass effect as well as due to short and long term thermal ageing treatments. The results of this investigation reveal that the five pass welding procedure resulted in higher yield and UTS of the joints, besides giving higher ductility (%age elongation), as compared to the three pass weld. Post weld thermal ageing treatments increased the yield and the UTS of the joints but reduced ductility due to precipitation that resulted due to ageing effects. Five weld pass technique also resulted in higher impact toughness than the three weld pass technique in the as-welded condition. Thermal ageing resulted in a loss of toughness in both the welds. Ageing condition of 750°C/12 hou