Effects of Stacking Fault Precipitation of NbC on Hot Deformation of Austenitic Stainless Steel
1985 Volume 71 Issue 8 Pages 978-985
Details
1985 Volume 71 Issue 8 Pages 978-985
The hot deformation of Nb-bearing austenitic stainless steel has been studied by means of tensile test with particular attention to both stacking fault precipitation and dynamic precipitation of NbC. Tensile test was carried out at temperatures ranging from 823 to 1173 K at an initial strain rate of 2.1 × 10-4 s-1.
The results obtained are as follows:
(1) Although the yield strength of the solution-treated specimen was quite low, remarkable work hardening during the deformation occurred at temperatures ranging from 1023 to 1123 K. In this temperature region large 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.
(2) In the aged specimen, on the other hand, the yield strength was much larger than that of solutiontreated one and work hardening during the deformation was less significant. Such a high yield strength can be explained in terms of the "small grains" formed by the hard stacking faults where the fine NbC particles precipitated. The ductility trough in this case was rather shallow because of suppression of dynamic NbC precipitation.
(3) At the temperatures above 1123 K the ductility of the solution-treated specimen increased with increasing deformation temperature, but that of the aged specimen was largely reduced. This ductility loss could be ascribed to the crack formation observed along coherent twin boundaries.
