B addition, including simultaneous addition of B and C in plain Fe, low alloy steels and stainless steels is effective to promote sintering. A small amount of added B forms steepened liquidus of Fe-B, Fe-B-C or other eutectic reactions in phase diagrams of those alloy systems. Following the formation of the eutectic liquids in the alloys, rapid densification and spherodization of pores proceed leading to the improvements of mechanical properties. In plain Fe and Fe-C steels, B is detected only in the particle boundary area; forming eutectic boride or borocarbide. B addition to a eutectoid Fe-C steel forms a ferritic surface layer on particles together with boundary borocarbide network, while in Cr and/or Mo containing steels, B exists both in the boundary area and within the matrix particles; forming (Fe, Cr, Mo)2B precipitates in the matrix. B will react with N in commercial sintering atmospheres forming hexagonal BN, which may become the site for the epitaxial precipitation of secondary graphite from the matrix containing C.