Effects of water cooling on microstructural evolution, hardness and anti-corrosion properties of Inconel 52 fusion-cladded AISI 316L stainless steel

Abstract

The structural integrity and repair of piping systems in the reactor vessels of ocean structures and nuclear power plants have attracted considerable interest in recent years; particularly with regard to the clad welding of austenitic stainless steel (SS) components. This study conducts an experimental investigation into the effects of water cooling on the microstructure, hardness, tensile strength and electro-corrosion resistance properties of AISI 316L SS specimens clad with Inconel 52M alloy by means of a GTAW process. The results show that the application of water cooling during the welding process produces a matrix with a lower dilution ratio than that produced under the un-water-cooled condition. In addition, the water-cooling process results in a finer matrix structure with a smaller dendrite spacing, and hence increases the specimen hardness. The water-cooled sample has a high volume fraction of Nb-rich precipitates, but a low volume fraction of Cr23C6 phase. Conversely, the un-water-cooled sample has a low volume fraction of Nb-rich precipitates, but a high volume fraction of Cr23C6 phase. Consequently, the two samples have a similar tensile strength. Finally, the electro-corrosion resistance of the water-cooled specimen is lower than that of the un-water-cooled specimen since the higher cooling rate induced in the GTAW process prompts a larger volume fraction of grain boundaries (defects) in the matrix and a greater residual stress. In general, the results presented in this study serve as a useful source of reference for the cladding repair of AISI 316L SS piping systems in the ocean engineering and nuclear power generation fields.