Resistance upset butt welding of austenitic to martensitic stainless steels

In this research, joining austenitic to martensitic stainless steels and effect of welding power on microstructure and mechanical properties of the joint were investigated. Microstructure of the weld was studied using optical microscopy (OM) and scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) linked to SEM was used to determine chemical composition of phases and distribution of chromium (Cr), nickel (Ni) and iron (Fe) at the joint interface. Microhardness and tensile strength tests were performed. Finally fracture surface of samples were studied by SEM. Results showed that an interlayer composed of 80% ferrite and 20% martensite has formed at the joint interface and there were three different zones in the heat affected zone (HAZ) of two steels. Different forms of austenite phase including widmanstatten austenite (W_γ), allotriomorphic austenite (A_γ) and intergranular austenite (I_γ), delta ferrite (δ-ferrite) and chromium carbide (Cr₂₃C₆) have formed in the HAZ of austenitic stainless steel. Fractography of tension samples indicated that in all samples fracture occurred in austenitic stainless steel HAZ. The strength and hardness of the joint increased and HAZ length decreased with increasing of welding power.