Influence of preheating temperature and post-weld heat treatment on microstructural and mechanical characteristics of the heat-affected zone in nodular cast irons with ferritic-pearlitic matrix

Abstract

Cast irons are a class of iron-carbon alloys that are extensively utilized owing to their cost-effectiveness, excellent machinability, and high damping capacity. Nodular cast irons, also known as ductile irons and spheroidal graphite cast irons exhibit superior tenacity, ductility, and mechanical strength, thereby making them suitable for more demanding applications, particularly in the automotive industry and wind power generation. However, welding cast iron is a more complex, difficult, and meticulous process than welding steel mainly due to the high carbon content present in the alloy. Nevertheless, welding of these alloys is important and has various industrial applications. Gas tungsten arc welding has been employed but is not a common alternative. However, the high control over the energy transferred, simplicity of mechanization and presence of an inert protective atmosphere are interesting factors when considering the effect of the welding thermal cycle on the heat-affected zone (HAZ). Thus, this study aims to investigate the effect of the preheating temperature and post-weld heat treatment (PWHT) of nodular cast iron blocks partially remelted by the tungsten inert gas welding process on the microstructure and mechanical behavior of the HAZ. Notably, the use of higher preheating temperatures promotes improvements in the microstructure and, consequently, in the hardness of the HAZ. However, the optimum condition was achieved in the sample preheated at 350 °C and subjected to PWHT.