Effect of alloying elements on the hardenability of PM steels

Abstract: In an effort to broaden the use of powder metallurgy components to high load applications it is necessary to increase the mechanical properties. One way of doing so is to optimize the chemical composition and increase the hardenability. In this report a hardenability evaluation is performed on Astaloy™ CrA (Fe+1,8wt.%Cr) with 0,6 wt.% admixed carbon in the form of graphite with 1 wt.% or 2 wt.% of admixed copper or nickel. CCT diagrams are constructed for five compositions and said materials are evaluated regarding mechanical performance to try to evaluate what influence the hardenability of the material have on the performance. The hardenability evaluation consist of dilatometry where the samples are austenitized followed by 15 different cooling rates, evaluated by the means of metallography to confirm the transformation products achieved. This data is used to construct CCT diagrams. The evaluation of the mechanical properties is performed on sintered samples with three different cooling rates. Admixed nickel and copper have a positive influence on the hardenability of low alloyed PM-steel. The areas of the transformation products in the CCT diagrams are altered depending on quality and quantity of added element. Additional alloying element have a significant impact on the mechanical performance of materials consisting of high temperature transformation products but is of less significance if the materials consist of low temperature transformation products. Copper and nickel increase the hardenability of the material and give the opportunity to get fully martensitic structures with lower cooling rates e.g. sinter hardening making it more practical and economical compared to quenching, thus getting components with enhanced mechanical performance.