Second phases in steel: a review of the concept, origin, and their relevance for properties

Steels are multiphase alloys with an increasingly complex constitution. This complexity of steel microstructures has been recognized since the birth physical metallurgy. Non-metallic inclusions have also very early as relevant to understanding behavior. With advances in precipitation hardening and grain size control, many precipitate phases gained importance design. Around 1950-70 term “second phases” was coined all-encompassing definition that would cover non-metallic well fine precipitates such nitrides carbonitrides even steels already had a multi-phase While this classification may be practical some cases, we argue it hinders proper origin effects particles unduly complicates phenomena which they take part. In work, briefly review second phase particle concept discuss critical properties respect their influence on Through several examples, propose volume fraction main variables evaluating how affect steels. chemical composition is key particles, suggest these are, together interface properties, most understand effect