Effect of Stacking Fault Precipitation on Hot Deformation of Austenitic Stainless Steel

抄録

The hot deformation characteristics of Nb-bearing austenitic stainless steel have been studied by means of tensile test and transmission electron microscopy in reflection to the stacking fault precipitation of NbC. Tensile tests were carried out at temperature ranging from 823 to 1173K at an initial strain rate of 2.1×10^-4s^-1.
Although the yield strength of the solution-treated specimen was quite low, remarkable work hardening occurred at temperature ranging from 1023 to 1123K. In this temperature region, a deep ductility trough accompanied by intergranular ductile fracture was also observed. This can be explained in terms of the dynamic precipitation of NbC within the grains as well as on the grain boundaries.
In the aged specimen, on the other hand, the yield strength was much higher than that of solution treated, but the work hardening was less significant. Such a high yield strength is probably due to the refinement of the average effective grain size, i.e., an austenite grain being separated into several regions by the hard platelets of stacking faults with fine NbC particles. The ductility trough in this case was rather shallow because of the reduction of dynamic NbC precipitation.
At temperatures above 1123K, the ductility of the solution-treated specimen increased with increasing deformation temperature, but that of the aged specimen was lamely reduced. This ductility loss could arise from local dynamic recrystallization in the vicinity of grain boundaries.