ASTM-B935 › Standard Guide for Steam Treatment of Ferrous Powder Metallurgy (PM) Materials
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1.1 This 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 P/M materials and the appropriate use and evaluation of these materials. Additional information concerning the effect of this process on ferrous P/M material properties is contained in Appendix X1.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Significance and Use
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-gray to a blue-black appearance. It can reduce the susceptibility of ferrous P/M 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 (see Appendix X1) 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, their 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 P/M materials are used in many industries, including automotive, marine, home appliances and lawn and garden applications.
blackening; black oxide; ferrous P/M parts; iron oxide; magnetite; steam; ICS Number Code 77.160 (Powder metallurgy)
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Nov. 5, 2020