Yasuya Ohmori1 and Yasuhiro Maehara1
1Central Research Laboratories, Sumitomo Metal Industries, Ltd., Amagasaki
The effect of NbC precipitation on hot deformation of austenitic stainless steels has been studied with particular emphasis on ductility. The mechanism for reducing ductility in the temperature range where NbC precipitation occurs can also explain the surface cracking mechanism of continuously cast low alloy steel slabs. The ductility trough in slow strain rate tensile tests at around 1073 K in Nb-bearing steels is accompanied by the intergranular microvoids coalescence mode of fracture. This ductility loss is induced by rather coarse NbC particles precipitated on the grain boundaries, the precipitation free zones along the grain boundaries and the dynamic precipitation of fine NbC particles within the grains. That is, when an external stress is applied, the strain will be concentrated within the soft layers of precipitation free zones by the matrix strengthening due to fine dispersion of NbC. This will lead to the decohesion of the NbC/matrix interfaces on grain boundaries, resulting in the intergranular microvoid coalescence.
niobium-carbide, hot deformation, austenitic stainless steels, surface cracking of continuously cast slab, ductility trough, slow straining, intergranular ductile fracture, precipitation free zone, dynamic precipitation, strain concentration
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