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WELDING is the most preferred process when it comes to permanent joining of metals for a wide range of industrial applications. Dissimilar metal welding (DMW) is one of the key areas that extends the versatility of the process. Low alloy steels are widely used in low temperature zone of power generation plant. On the other hand, high temperature regions require materials like austenitic alloys for superior corrosion

R. NIVAS, M.Tech. Student, and K. SIVAPRASAD, Assistant Professor, are with the Advanced Materials Processing Laboratory, Department of Metallurgical and Materials Engineering, National Institute of Technology, Tiruchirappalli 620015, India. G. DAS, Sr. Principal Scientist, S.K. DAS, Principal Scientist, B. MAHATO, Technical Officer, and M. GHOSH, Sr. Scientist, are with the Material Science & Technology Division, CSIR-National Metallurgical Laboratory, Jamshedpur 831007, India. Contact e-mail: [email protected] S. KUMAR, Scientific Officer ‘D’, and P.K. SINGH, Scientific Officer ‘G’, are with the Reactor Safety Division, Bhaba Atomic Research Centre, Mumbai 400085, India. Manuscript submitted May 2, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A

resistance and greater creep strength.[1,2] In a typical nuclear power plant, there can be thousands of DMWs, which experience numerous thermal cycling between room temperature and ~623 K (350 C).[3–5] One of the examples is weld joint between low alloy steel (LAS) and austenitic stainless steel (ASS). The nozzle material is ASTM A508 Grade 3 Class 1 (low alloy steel) and connecting piping material is SA312-Type 304LN (austenitic stainless steel). This transition joint is widely used as primary piping of heat transport system in pressurized water reactors (PWR) of nuclear power plants.[3] Besides its unique application, a lot of mechanical and metallurgical hurdles are associated with it. The weld thermal cycle produces heat-affected zone (HAZ) and weld nugget, containing heterogeneous microstructure.[1,5,8] The constitution of joining is critical, because any deviation out of optimum window may lead to deleterious weld due to embrittlement and/or hot/cold cracking. Several factors are collectively responsible for premature failure of such dissimilar metal weld.[6] During fabrication to reduce detrimental effects, different types of welding consumables are introduced.

Inconel welding wires are used to join LAS components to ASS pipes. Inconel wires are promising candidates to minimize the differences in composition and thermal expansion of two different metals.[9–11] Ni-base alloys have an additional advantage of restricting carbon diffusion from low alloy to stainless steel as diffusivity of carbon is very low in face-centered cubic nickel compared with stainless steel.[7] Carbon migration leads to form localized carbon-depleted soft zone and carbon-rich hard zone across fusion boundary. This makes whole region prone to degeneration during service exposure.[3] Concern and interest in the integrity of dissimilar metal welds were raised since the cracking incide