Martensitic reversion from bcc-martensite to fcc-austenite is an important phase transformation to improve mechanical properties of steels remarkably as well as other phase transformations. However, few studies have undertaken to investigate the martensitic reversion, because it hardly occurs in carbon steels. In the present overview, some characteristics of the martensitic reversion were explained briefly with reference to the previous studies, and a couple of applications of microstructural control for high alloy steels using the martensitic reversion were introduced. Furthermore, a novel heat treatment through the martensitic reversion to improve strength and toughness of low alloy martensitic steel was proposed.

Pure Mg, Mg-0.5 at％Al, Mg-0.5 at％Zn, Mg-0.5 at％Y, Mg-0.9 at％Y, and pure Zn single crystals were applied to indentation tests using a spherical indenter to allow experimental investigation the roles both slips and twinning induce on the formation of indentation. When indented on (0001), all single crystals displayed indentation of circular morphology without slip lines and twins. Mg and Mg alloys' indentation sizes were found dependent on critical resolved shear stress (CRSS) for basal slip in (0001) indentations. Zn (0001) indentation size depends on CRSS for both basal and pyramidal slips. Conversely, when indented on (1010) and (1210), all single crystals had indentations elongated to [0001] with basal slip lines around indentations. Also, {1012} twins were observed in Mg-0.5 at％Al and Mg-0.5 at％Zn but were scarce in Mg-Y. Pure Zn displayed second order pyramidal slips. Sizes of both (1010) and (1210) indentations were found dependent on CRSS for basal slips and for {1012} twins.

Strain-rate dependencies of deformation behavior of commercial purity titanium specimens having different grain sizes were systematically investigated. Ultrafine-grained titanium with an average grain size of 0.07 µm (UFG-Ti) fabricated by multi-directional forging followed by conventional thermo-mechanical processing, and fine-grained (FG-Ti) and coarse-grained (CG-Ti) specimens with an average grain sizes of 0.8 µm and 12 µm attained by its, respectively, annealing at 773 K and 973 K for 1.8 ks were prepared. The FG- and UFG-Ti specimens exhibited strong strain-rate dependence of 0.2％ proof stress, while that of CG-Ti ones were almost constant regardless of applied strain-rate. In-situ X-ray diffraction measurements during tensile tests were also conducted at synchrotron radiation facility, SPring-8. Using the modified Williamson-Hall and the modified Warren-Averbach methods, the activated slip systems and change in dislocation density during deformation were estimated. As a result, it was found that <a> and <c+a> slips were activated in FG- and UFG-Ti specimens. On the other hand, the activation of <c+a> slip was never observed in the CG-Ti ones. It can be, thus, concluded that the different strain-rate dependency of deformation behaviors of specimens with different grain sizes were ascribed to the difference in the deformation mechanisms.

The effect of Nb on microstructure and thermal-shock resistance was investigated for as cast and annealed JIS SCH21 steels. Primary NbC carbide were crystallized together with M₂₃C₆ at grain boundary in as cast steel. Decomposition of primary M₂₃C₆ was detected, while NbC was also hardly decomposed when annealed at elevated temperature. It was found that chromium carbides had low thermal stability but primary NbC carbides played a role in preventing propagation of micro-cracks and restraining shape deformation under condition both heating and quenching. As a result, thermal-shock resistance was improved in the Nb-added steel.