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An integrated model for predicting recrystallization, phase transformation and yield strength of vanadium-microalloyed carbon steel (V-steel) is developed. Two effects of vanadium addition on recrystallization are assumed: one is the solute-drag effect on mobility of grain boundary, the other is pinning-effect on austenite grain growth due to vanadium carbide (VC) precipitate in austenite. The austenite grain size is considered as the control variable for nucleation density in grain corner, grain boundary, and grain interior during phase transformation. Thermodynamic data for transformation including para-equilibrium of carbon concentration and driving force were calculated using ThermoCalc software. The vanadium addition leads to α/γ -interphase VC precipitation in ferrite, which accelerates the diffusion rate of carbon in austenite at α/γ interface and increases nucleation sites for intragranular ferrite transformation. In consequence, the ferrite fraction and grain size are increased. Brandt model 27) is conducted to predict pearlite transformation. The lamellar spacing is considered as a function of carbon concentration and undercooling. The alloying elements, ferrite and pearlite fractions, ferrite grain size, and lamellar spacing were taken into account for predicting strength of V-free steels. Modified Ashby-Orowan equation is then used to calculate the VC precipitation strengthening of V-steels. Using this model the calculated results obtained are in good agreement with experimental results.

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.

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.