FACTORS INFLUENCING AUSTENITE GRAIN SIZE IN SINTER-HARDENED LOW-ALLOY STEELS

It is well known that the austenite-grain size is important vis-a-vis the mechanical properties of heat-treated wrought steels. However, for powder metallurgy (PM) steels these relationships have not been studied in detail, primarily because of the difficulties in clearly revealing the prior austenite grain boundaries. In this work a universal method for etching the grain boundaries was tested that enabled investigation of the primary parameters influencing OH grain size, namely, sintering temperature and time, the starting powder-particle size, and the density of the sintered parts. For sinter-hardened chromium-containing steels (Astaloy CrM) the method is simple and reliable. The specimens experience exactly the same heat treatment for hardening that is necessary for visualization of the grain boundaries, and any artifacts or other undesirable changes of the microstructure can be avoided.