Effect of partial solution treatment on martensitic transformation of 12%Cr steels

When high chromium martensitic steels are subjected to partial solution treatment in (austenite +M₂₃C₆ carbide) two -phase region, not only the coarsening of austenite grains is effectively suppressed by insoluble-carbide particles, but also martensitic structure, which has formed during cooling, is refined through the treatment. In this study, the mechanism of refining of martensitic structure was discussed in Fe-12%Cr-C ternary alloys by investigating the relation between Ms temperature and solution treatment conditions, and the effect of insoluble-carbide particles on the substructures such as martensite-lath or -block. The Ms temperature of steels with full solution treatment simply depends on the content of C and Cr, but that of steels with partial solution treatment is dependent on the effective chemical composition of matrix, which is evaluated by taking the amount of C and Cr in insoluble-carbide away from their total content. Refining of martensite-block structure within grains is not caused directly by insoluble-carbide particles, but done indirectly through the refining of austenite grain size. While, on the martensite-lath structure, insoluble-carbide particles supply nucleation sites for laths, and work also as obstacles for growing laths. As a result, martensite-laths in steels with partial solution treament are divided finely by insoluble carbide particles, and the arrangement of laths is tend to be confused.