A study on INCONEL617 weld overlay coating on SS 316L by cold metal transfer technique for boiler applications

Hot section components of thermal power plant boilers, gas turbine and chemical and food processing industries are exposed to severe erosive and corrosive conditions leading to premature failure of conventional ferrous based alloy systems. One of the widely accepted methods to impart protection against corrosion, hot oxidation, wear and erosion with cost effectiveness is by cladding or overlay coating of Ni based super alloys. The conventional ways for such overlays are: thermal spray, plasma transferred arc (PTA), arc welding process (GMAW, GTAW), laser and electron beam cladding/welding. Among the arc welding methods, Cold Metal Transfer (CMT) is a newcomer in the industry, well known for its 'pulsed wire feeding' technology. This brings low dilution, defect free claddings, narrow HAZ, highly controlled heat input, spatter free weld beads, strong metallurgical bond between substrate and cladding, energy efficiency and economy. In the present study, Inconel 617 weld overlay coatings were deposited on SS 316L (3 mm thickness) at different current inputs such as 100 A, 90 A and 80 A, using a Fronius VR 7000 CMT machine aided by a CNC automation for overlaying. Micro Vickers hardness profile of the cross section (from substrate end to cladding end) will be discussed in the paper. Detailed SEM analysis of phase changes as well as microstructure evolution is in progress. Micro chemical analysis using EDS, qualitative and quantitative evaluation of weld dilution etc. will be conferred in the advancement of the study. (author)