PM structural steels having lower or cheaper alloy contents were the subject of a one-day special program at POWDERMET 2016 in Boston.
A very impressive and comprehensive review of PM ferrous alloy developments over the past few decades was presented at the POWDERMET2016 conference in Boston during a special interest program devoted to “Lean Alloys”. The three-part program of invited papers was organized by Roger Lawcock, Stackpole International (Canada), Sydney Luk, North American Höganäs Inc. (USA), and Blaine Stebick, Phoenix Sintered Metals (USA). It drew on the expertise of leading global experts in industry and the academic world. Sadly, these were oral presentations that are not included in the conference proceedings volume. Some of the key papers are summarized in this article, not necessarily in the order they were presented.
Bruce Lindsley, Hoeganaes Corp. (USA), and currently president of APMI International, began his talk with an historical review of how PM ferrous alloys came to be developed, initially by admixing elemental alloy powders with sponge iron, then by diffusion alloying, and with the appearance of water-atomized steel powders, the emergence of pre-alloyed powders. With conventional sintering the choice of alloys was largely limited to copper, nickel, and molybdenum, due to oxidation issues with other elements such as chromium and manganese that are widely used in wrought alloy steels. While the cost of traditional alloy elements remained relatively low, there was little incentive to develop new alloy systems. That all changed with the commodity price shock in the early to mid-2000s and the extraordinary escalation in the prices of nickel, copper and molybdenum. With a 4–10-fold increase in some cases, this led to a re-assessment of alloy compositions and numerous attempts to offset the rise. Since then, prices have come back down – but this could all happen again. The resulting design challenge: how to design cost-effective, i.e. “lean” alloy systems that have satisfactory and reproducible properties and behavior. (As an aside, Lindsley commented that just because something worked in the laboratory, it doesn’t mean you can make parts out of it.) This led to two approaches: either optimize the current alloy contents, or try something really different, such as a change in material processing such as high-temperature sintering, or alternative alloys such as chromium and manganese.
This article appeared in the Jan/Feb issue of Metal Powder Report.
