Impact properties of modified 9Cr 1Mo steel welds: Comparison between cold wire and hot wire gas tungsten arc welding processes

Abstract

Modified 9Cr 1Mo steel is used for the manufacture of Steam Generators (SG) for Prototype Fast Breeder Reactor at Kalpakkam, India. The hot wire Gas Tungsten Arc Welding (GTAW) process was selected for the manufacture of SGs wherever feasible in addition to the conventional cold wire GTAW process due to various advantages. Drop weight tests on modified 9Cr 1Mo steel welds produced by hot wire and cold wire GTAW processes were carried out in accordance with ASTM E208. It is found that the Nil Ductility Transition (NDT) behavior of the hot wire and cold wire GTA welds were similar during drop weight tests performed up to −10 °C. Subsequently, Charpy V notch impact tests were carried out at +18 °C and 0 °C in accordance with ASME Boiler and Pressure Vessel Code. The impact strength at 0 °C of welds produced by cold wire GTAW process was found to be superior compared to the welds of hot wire GTAW process. Subsequently, the analysis of impact strength was carried out using a two-sided students t-test. With a 95% confidence level, the results of the t-test revealed that there is a genuine difference in impact strength at 0 °C between the welds of hot wire and cold wire GTAW processes.