Papers by Author: Tae Ho Lee

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: Deformation behavior of high nitrogen austenitic Fe-18Cr-18Mn-2Mo-0.9N stainless steel was investigated utilizing electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). During deformation, the <110> grains rotated and the trace of these grains moved towards into the dodecahedral plane (the line connecting (001) and (111) planes). Misorientation mapping in EBSD showed that the special boundaries (almost Σ3) gradually diminished whereas the low-angle boundaries were developed. TEM observation showed that (i) the low-angle boundaries developed corresponded to the deformation twinning with {111}<112> component, (ii) the deformation twinning showed the strong orientation dependence relative to tensile axis, and (iii) the deformed microstructure was characterized by extended stacking faults, planar dislocation array in low strain regime, and by well-developed deformation twinning in high strain region, respectively.

Abstract: In order to simplify the production routine and to save cost of hot-rolled TRIP steels, the intercritical rolling process was investigated using thermo-mechanical simulation technology. Both 0.2C-1.5Mn-1.5Si and 0.2C-1.5Mn-1.5Si-0.5Cu TRIP steels were chosen so as to study the effect of 0.5 pct Cu addition on microstructure and retained austenite volume fraction of 0.2C-1.5Mn-1.5Si TRIP steel. It is found that grain size refinement happened during intercritical deformation, and multi-phase microstructure could be achieved after isothermal treatment, so intercritical annealing can be eliminated to avoid grain size coarse and to keep the refine grain size in intercritical-deformed TRIP steels.