Papers by Author: Innocent Shuro

Abstract: SUS316L austenitic stainless steel was subjected to severe plastic deformation (SPD) by the method of high pressure torsion (HPT). From a fully austenitic matrix (γ), HPT resulted in phase transformation from g®a¢. The largest volume fraction of 70% a¢ was obtained at 0.2 revolutions per minute (rpm) while was limited to 3% at 5rpm. Pre-straining of g by HPT at 5rpm decreases the volume fraction of a¢ obtained by HPT at 0.2rpm. By HPT at 5rpm, a¢®g reverse transformation was observed for a¢ produced by HPT at 0.2rpm.

Abstract: SUS 304 austenitic stainless steel (ASS) was deformed by high pressure torsion (HPT) to obtain 100% volume fraction of martensite (α') from a fully austenitic (γ) matrix. Deformation caused an increase in hardness (Hv) from 1.6 GPa in the as annealed state to 6.4 GPa　after HPT. Deformed samples were then annealed in the range 200 – 600oC and peak hardness of 7.8 GPa was observed after annealing at 400oC for 1 hour. Differential scanning calorimetry (DSC) and electrical resistivity tests showed that the deformed alloy undergoes a two stage phase transformation on heating from room temperature up to 700oC. The first stage of transformation was associated with hardening behavior while the second one which is reverse α' → γ transformation resulted in a reduction in hardness. Annealing at 400oC after deformation was found to increase the magnetization saturation (Msat) values.

Abstract: SUS 304 austenitic stainless steel was subjected to severe plastic deformation (SPD) by the method of high pressure torsion (HPT). From a fully austenitic matrix (γ), HPT resulted in phase transformation to give a two phase structure of austenite (γ) and martensite (α') by the transformation γα'. The phase transformation was accompanied by an increase in hardness (Hv) from 1.6 GPa in the as annealed form to 5.4 GPa in the deformed state. Subsequent annealing in temperature range 250oC to 450oC resulted in an increase in both α' volume fraction and hardness (6.4 GPa). Annealing at 600oC resulted in a decrease in α' volume fraction hardness.

Abstract: Two unique characteristics of HPT as a SPD process, namely deformation with strain gradient and deformation under high pressure, were investigated. The effect of strain gradient was examined using low carbon steel. HPTed samples showed hardening at the center of the specimen where shear strain is principally zero and saturation hardness was higher than those without strain gradient such as ECAP or ARB. HPT experiments using specimen with different radial strain gradient in one sample also showed strain gradient hardening. The effect of high pressure during HPT was examined using pure Ti which transformed from α phase to ω phase when HPTed at high pressure. The volume fraction of ω phase increases with strain and with decreasing oxygen content. The ω phase is metastable at ambient conditions and it transforms back to α phase during heating.