18%Crフエライト鋼における動的再結晶

抄録

Polycrystals of 18% Cr ferritic stainless steel were hot-compressed at various strain rates and various temperatures, and immediately cooled by water. Equiaxed grains surrounded by clearly etched boundaries were observed in the specimens deformed at higher temperatures or lower strain rates. The detailed microstructural observations by optical microscopy and TEM and the crystallographic determinations by TEM/Kikuchi-line analysis and SEM/EBSP analysis showed that these equiaxed grains are the dynamically recrystallized grains with both large angle grain boundaries and dislocation substructures. In spite of the occurrence of dynamic recrystallization, a large drop in stress was not observed in stress-strain curves. At a constant strain, the occurrence of dynamic recrystallization was generally determined by Zener-Hollomon parameter (Z). For example, it appeared under the condition of Z<10¹⁴s^-1 at a true strain of 0.8. The dynamically recrystallized grains were very much larger than that of the subgrains formed under the same deformation condition, which suggests that the dynamic recrystallization occurred by nucleation and growth mechanism. Such characteristics of dynamic recrystallization of ferrite is quite similar to that in the IF steel previously reported. On the other hand, the Z<10¹⁴s^-1 rule did not stand at 700°C, at which a number of carbides precipitated at initial grain boundaries and pinned the boundaries. It was also clarified that the size of the dynamically recrystallized grains is considerablly smaller than that of the grains statically or meta-dynamically recrystallized during cooling after the same hot-deformation condition.