Papers by Author: Chang Seok Oh

Abstract: Low alloy transformation induced plasticity (TRIP) steels have a complex microstructure consisting of ferrite, bainite and retained austenite. Their excellent mechanical properties are ascribed to the martensitic transformation of retained austenite during plastic deformation. In the present contribution, the crystallographic texture of fcc and bcc phases in TRIP steels was measured by means of orientation mapping. The austenite texture was close to a typical rolling texture of fcc metals. For bcc phase, the effects of orientation and grain size on the distribution of pattern quality were investigated. The texture of transformation product phase was separated by grain size. The transformation texture showed stronger α fiber including {113}<110> component than the recrystallization texture. It showed a good agreement with a transformation texture predicted by Kurdjmov-Sachs (KS) relationship without any variant selection.

Abstract: The effect of Cr2N precipitation on deformed microstructure in high nitrogen austenitic Fe-18Cr-18Mn-2Mo-0.9N steel was investigated with a particular emphasis on deformation twinning. Based on the crystallographic analysis in the stereographic projection, the orientation relationship between austenite (γ) matrix and Cr2N was determined to be Cr2N [110]γ //[1100] and Cr2N (111) γ //(0001) . The deformation twinning had {111} < 112 > crystallographic component similar to that of cellular Cr2N. The cellular Cr2N precipitates caused a different orientation dependence of deformation twinning: only one twinning system in the <111 > grain was activated almost parallel to the growth direction of Cr2N.

Abstract: The thermodynamic assessment of the Al-Ir binary system, one of the key sub-systems of the Ir-based alloys, was performed using the CALPHAD technique. The AlIr(B2) phase was described using the two sublattice model with the formula (Al,Ir)0.5(Ir,Va)0.5, while other intermetallic phases were treated as stoichiometric compounds. The calculated data of the phases in the Al-Ir system can be used to accurately reproduce experimental data, such as phase equilibria, invariant reactions, and formation enthalpies of the intermetallic phases.