Impact of quenching temperature and isothermal holding time during austempering on bainite content in high-silicon steel

Abstract

Silicon plays an important role in the manufacture and processing of steel. It is involved in metallurgical processes in the melt, improves castability, and, together with aluminium, belongs to the elements which suppress cementite formation during heat treatment of steels. The last-named aspect offers a great potential for developing high-strength steels with excellent ductility. The amount of bainite in the microstructure has a substantial impact in this respect. Bainite fraction depends mainly on temperature and on the isothermal holding time in the bainitic transformation region. In steels with low silicon levels, isothermal bainitic transformation continues until all austenite has transformed to bainite. At higher silicon levels, approximately 2 weight percent, the bainitic transformation is expected to be incomplete. The resulting bainite fraction would then be dictated by the thermodynamic equilibrium in the austenite-bainite system. As a result, one could control microstructural evolution, and thus the mechanical properties in high-strength bainitic-martensitic steels.