The Effect of Heat Treatment on the Properties of Astaloy Cra Powder Alloys

Abstract

In this study, the effect of heat treatment on the mechanical properties and microstructures of several prealloyed Astaloy CrA (Fe-1.8%Cr) powder alloys with 1% copper or nickel and 0.5% graphite additions was investigated. The powder alloys were compacted under 600 MPa and sintered at 1120°C in a gas mixture of nitrogen and hydrogen for 45 minutes. Sintered samples were austenitized at 1070°C under nitrogen for 20 minutes, followed by cooling in air, quenching in water and tempering at 200°C for 60 minutes in air. Hardness and transverse rupture strength values of the sintered and heat treated samples were determined. Microstructural characterization of the samples was done with optical microscopy. The results showed that normalizing led to primarily pearlitic structures, whereas fully martensitic structures, and tempered martensitic structures formed in the quenched and tempered samples. In all the alloys, austenitizing at 1070°C led to decarburization. Increase in the hardness of quenched and tempered samples was correlated to the formation of martensitic microstructures. Increase in the transverse rupture strength of quenched and tempered samples was correlated to the prevention of crack initiation via through the formation of ductile decarburized layer after austenitizing.