At last year’s PowderMet2013, held in Chicago, USA, Hoeganaes Corporation was presented with the Howard I Sanderow Outstanding Technical Paper award for its paper “The Influence of Silicon on the Mechanical Properties and Hardenability of PM Steels.” During this year’s PM2014 World Congress in Orlando, Florida, Hoeganaes will explore the topic further with a presentation entitled “Diffusion Behavior and Microstructural Transformations of PM Steels Containing Silicon.”
In the award winning presentation, the Hoeganaes team studied the effects of silicon additions to PM alloy systems. Silicon is an abundant alloying element, being the second most available element in the earth’s crust and therefore a very cost effective element for use in steel.
The microstructures, mechanical properties and hardenability of Powder Metallurgy alloy systems were investigated and it was demonstrated that the addition of silicon can increase strength in both the sintered and heat treated conditions. In the sintered condition silicon strengthens the ferrite of the pearlitic microstructure by solid solution hardening. In the heat treated condition silicon was found to increase the hardenability of low alloy steels and when used in combination with chromium, manganese or molybdenum was seen to increase hardenability over that if these elements were used alone. The increase in hardenability was such that alloys containing silicon were able to be sinter-hardened using accelerated cooling.
In this year’s presentation, Hoeganaes will explore this topic more fully. The effectiveness of the silicon is dependent on the distribution of the element throughout the material volume, which is determined by the diffusion during sintering. The distribution of silicon and interaction with other elements are quantified using energy dispersive spectroscopy on multiple compositions prepared using different alloying methods.
In addition, the effects of the diffusion on hardenability are being addressed by estimating the volume percent of the various transformation products in cross-sections of hardenability samples. This increased knowledge of the diffusion of silicon in PM alloys, and its interaction with other alloying elements, will lead to a better understanding of the sintering requirements for the end user, states Hoeganaes.