ASTM International has published an updated version of its Standard Guide for Steam Treatment of Ferrous Powder Metallurgy (PM) Materials, ASTM B935 – 16. Developed by Subcommittee: B09.05, the guide is intended as an aid in establishing and maintaining a procedure for the steam treatment, also referred to as steam blackening, of sintered ferrous PM materials and the appropriate use and evaluation of these materials.

The performance and quality of steam treated materials depends upon the surface cleanliness of the material prior to steam treatment and the adequacy of the processing. Steam treatment can be used as a decorative coating, producing a blue-grey to a blue-black appearance. It can reduce the susceptibility of ferrous PM materials to further oxidation and corrosion, thus providing better shelf life.

More significantly, improvements in apparent hardness, compressive strength, wear characteristics, and some mechanical properties can be observed due to steam treatment. The hardness of magnetite (Fe₃O₄) formed during steam treatment is typically equivalent to 50 HRC and when present in sintered materials wear resistance can be improved significantly.

Steam treatment is also used to seal parts or provide a base material for additional coatings. Steam treated ferrous PM materials are used in many industries, including automotive, marine, home appliances and lawn and garden applications.

http://www.astm.org/cgi-bin/resolver.cgi?B935-16