Influence of austenite grain size on overaging treatment of continuous annealed dual phase steels

A dual phase steel with an initial coarse microstructure was refined, by means of a thermal treatment, to study the influence of the austenite grain size reached during an intercritical annealing treatment on the martensite start temperature. Thus, the effect of the austenite grain size on a subsequent overaging treatment was also investigated. It was found that a coarser austenite grain size leads to a higher martensite start temperature and a lower amount of non-tempered martensite and/or austenite (MA constituents) volume fraction after a continuous annealing and overaging treatment. The non-tempered martensite and/or austenite volume fraction always was higher for the highest overaging temperature.