PRECIPITATION OF NbC AND HOT DUCTILITY OF AUSTENITIC STAINLESS STEELS.

Abstract

The mechanism for reducing ductility in the temperature range where NbC precipitation occurs can explain surface cracking of continuously cast low alloy steel slabs. The ductility trough in slow strain rate tensile tests at around 1073 K is accompanied by the intergranular microvoid coalescence mode of fracture. This ductility loss is induced by coarse NbC particles precipitated on grain boundaries, the precipitation free zones along the grain boundaries and the dynamic precipitation of fine NbC particles within the grains. When an external stress is applied, the strain will be concentrated within the soft layers of precipitation-free zones by matrix strengthening due to fine dispersion of NbC. This will lead to the decohesion of NbC/matrix interfaces on grain boundaries.