Aging of a cast 35Cr-45Ni heat resistant alloy

摘要

The microstructural evolution during aging and its effect on the mechanical properties of a centrifugally cast 35Cr-45Ni heat resistant alloy was studied by means of optical and electron microscopy, and by mechanical testing in samples aged in air at 750℃ for a period of time of up to 1000h. The as-cast microstructure consisted of an austenitic matrix and a network of two types of primary carbides that were identified as NbC and M_7C_3 by their light and dark tones when viewed in backscattered electron mode in a scanning electron microscope. Aging promoted the occurrence of different phenomena such as the transformation of primary M_7C_3 to M_(23)C_6 carbides, precipitation of secondary M_(23)C_6 carbides and the transformation of NbC to Nb_3Ni_2Si. It was found that aging promoted an increase in Vickers microhardness of more than 50%, the increment in tensile strength of around 20% and the reduction in ductility of close to 70%.