Mechanical Properties and Metallurgical Characterization of Dissimilar Welded Joints between AISI 316 and AISI 4340

In the present study, the influence of six different process parameters and three interactions on joint tensile strength, toughness, fusion zone microhardness variation are studied during dissimilar tungsten inert gas welding between austenitic stainless steel AISI 316 and alloy steel AISI 4340. Detailed experimental study using fractional factorial experimental design and subsequent statistical analysis show that higher tensile strength, toughness can be achieved using ER 309 filler material and suitably selecting the other process parameters and heating conditions. Addition of small proportion of hydrogen in shielding gas increases the heat transfer efficiency, melting and subsequent penetration. Preheating of AISI 4340 material reduces the chance of solidification cracking and post-heating helps to improve the joint mechanical property. Microstructural observations show that improper selection of process parameters may lead to micro-pores and degrade the joint quality. Successful joining of the dissimilar materials greatly depends on the selection of optimum process parameters, filler material and shielding gas.