In this study, thermal fatigue tests at maximum temperature 1073 K were performed using 13%Cr-Nb-Si and 18%Cr-Nb-Mo steels as representative heat-resistant ferritic stainless steels for automotive exhaust systems. The changes in the microstructure, the crystal orientation and the hysteresis loop during thermal fatigue in the temperature range from 473 K to 1073 K were investigated. As a result of comparing thermal fatigue life under these conditions, 18%Cr-Nb-Mo steel with high temperature strength was found to have a longer thermal fatigue life than 13%Cr-Nb-Si steel. During the thermal fatigue process, the material was softened by reducing of the amount of solute Nb, and the coarsening of Nb precipitation. By this softening, the form of the hysteresis loops changed with the increase in cycles. By considering the softening of the material, the change in the hysteresis loops could be predicted to some extent. Furthermore, by EBSD analysis, it was recognized that the dynamic recovery and recrystallization accompanied by the uniaxial and fine grain formation occurred during the thermal fatigue process. From the viewpoint of change of the microstructure, the thermal fatigue damage was quantified by the ratio of the low-angle grain boundary, and the change of this index with the progress of the cycle in 18%Cr-Nb-Mo steel had a smaller than 13%Cr-Nb-Si steel. It was thought that this point was caused by the retardation of recrystallization by solute Mo.

SUS316LN austenitic stainless steel was simply and heavily cold-rolled up to 92% reduction in thickness. The microstructure developed was composed of complicated heterogeneous nano-structure; “eye-shaped” twin domains, which were surrounded by shear bands, were embedded in low-angle lamellar boundaries. The cold-rolled austenitic steel exhibited marvelous high strength of 1.95 GPa when tensile tested normal to the rolling direction, while lower strength of 1.57 GPa along the rolling direction. Moderate ductility around 10% was still retained in spite of the high strength. The superior mechanical properties of the heavily cold-rolled austenitic stainless steel would be attributed to complicated heterogeneous nano-structures. These achieved strengths were comparable with those obtained by methods of severe plastic deformation.

A {111} texture leads to good deep drawability but does not generally develop in face-centered cubic metals. In this study, rolling and recrystallization textures of austenitic stainless steel with low stacking fault energy have been investigated to reveal whether the {111} texture can be formed by cold rolling, asymmetric warm rolling and subsequent annealing. Rolling texture changes from the α-fiber texture in 70% cold rolled sheets to an asymmetric texture about the TD axis, consisting of an orientation group ranging from {331}<116> to {111}<112> by additional 40% asymmetric warm rolling, which was conducted at 873 K using rolls with different diameters. Correspondingly, pole density at the center of {111} pole figure increased from 2.2 to 3.2. In addition, microstructural observation showed that there were two kinds of shear bands inclined at about ±30° to RD on the longitudinal section. The one is microshear bands within grains and the other is shear bands passing through a number of grains. Recrystallization texture after annealing also shows an asymmetric texture to the TD axis, but consists of an orientation group ranging from {431}<257> to {331}<116>. The 1173 K-1800 s annealing decreases pole density at the center of {111} pole figure to 0.8. In conclusion, the rolling texture with a near-{111}<112> orientation was obtained in cold rolled and asymmetrically warm rolled austenitic stainless steel sheets. However, the recrystallization texture had a near-{110}<112> orientation as a main component.

Temperature gradient annealing has been applied to high purity titanium sheet to investigate microstructural and textural evolutions. The annealing with high temperature gradient was performed through a specially designed apparatus for the titanium sheet subjected to continuous cyclic bending (CCB). EBSD analysis revealed characteristic microstructure on cross-section consisting of coarse grained triangular area, in which coarse grains formed inside deeplier at higher temperature side, resulting from higher stored strain and higher temperature annealing, and non-recrystallized fine grained area held at lower temperature. Textural evolution was also examined for the CCBent and annealed titanium sheets. Further, effects of the temperature gradient annealing were discussed.