Influence of heat treatments on the mechanical properties and microstructure of a 50Cr-50Ni niobium containing alloy

Abstract
A heat resisting 50Cr-50Ni niobium-containing casting alloy, particularly developed for petrochemical plants was studied. The alloy combines high temperature strength with fuel ash corrosion resistance. However, during service, the exposure to high temperatures gives rise to precipitation of embrittling phases, strongly depleting the material ductility. Therefore, studies on the thermal aging at 700° C were carried out either in the as cast condition or after heat treatments at 1000, 1075, 1150° C. Alloy modifications were analyzed from a microstructural point of view and through hardness measurements, with the aim of relating them to other mechanical properties. It was found that the thermal treatments, providing a coarse precipitation, were effective in preventing excessive embrittlement levels to be reached.