Microstructure Property Correlation of Partial Penetration Weld Deposited Stainless Steels for Weld Repair of Investment Castings

Cast stainless steels 14X (14X18H4г4, austenitic), 08X (08X14H7MЛ, martensitic) and 04X (04X13H5M5Ҡ9Л, stainless maraging steel) are extensively used in investment castings of aerospace systems. Weld deposit is mostly required on investment castings to repair the cast defects, which are mostly partial penetration welds. In the present work, gas tungsten arc welding (GTAW) has been used for the weld deposit on the cast coupons of three stainless steels 14X, 08X and 04X with specific filler wires. For 14X alloy, 316L filler wire, and for 08X as well as for 04X alloy, 03X filler wires were used. As a part of weld procedure establishment for investment castings, study has been carried out for different applicable thicknesses (3–25 mm) with multiple numbers of weld deposits (repairs) up to 3 times, as required for the actual castings. Welded coupons were subjected to specific heat treatments applicable for the respective alloys. Weld deposited and heat-treated coupons were characterized for mechanical properties, microstructure and fracture analysis. Weld deposit microstructure of 14X and 08X alloy showed mainly cast austenitic structure, whereas it has martensitic cast structure for 04X alloys. Small amount of martensite was also found in 08X weld. Significant change in tensile strength and % elongation was not observed with respect to change in thickness or multiple weld repairs except minor scatter normally found in cast alloys and its welds. ~ 90% or higher weldment strength was observed with respect to their parent metal properties. Microhardness measurement across the weld showed marginally lower value compared to parent metal, and failure of tensile test specimens was found at the weld or at the weld parent metal interface. Ductile fracture was observed on tested specimens of all the three steels.