Microstructural Improvement of Low Pressure Carburized Low Alloy Sintered Steels

摘要

This paper discusses the effect of the low pressure carburizing treatment on the microstructure of some low alloy sintered steels. The materials were produced by using two different Cr, Mo and Ni pre-alloyed powders, and by adding Cu by diffusion bonding. The carbon content was 0.2% and two densities, 6.8g/cm3 and 7.0g/cm3, were obtained. Sintering was carried out at 1120°C and 1250°C.rnOvercarburizing occurs in both the materials, but there is a great difference between the Cr-containing material and the other one. In the Cr-containing steel overcarburizing results in the formation of a large amount of carbides, whilst in the other material it causes the formation of retained austenite.rnIt is well know that ductility and fatigue resistance of a component decrease significantly in the case of overcarburizing because of either grain boundaries precipitation or retained austenite. However carbides can be solubilized by means of a heat treatment, which distributes carbon more homogeneously in the matrix. Retained austenite can be destabilized by tempering, resulting in an appreciable tempering resistance.