مهدی شبان غازانی

In the present study, the AISI 321 austenitic stainless steel was cold rolled and annealed at 700, 800, and 900 ͦC for 15 min to obtain different microstructures. After annealing, tensile tests were conducted at ambient temperature and the yield ratio was calculated using the engineering stress-strain curves. Also, the yield ratio of samples with different initial microstructures was predicted using the material constants of Hollomon and Voce equations. The results of microstructural analysis showed that the initial microstructure after annealing at 700 ͦC is consisted of elongated austenite grains with high dislocation densities and the ultrafine grains obtained as a result of inverse transformation of martensite to austenite phase. Also, after annealing at 800 and 900 ͦC, the equiaxed microstructure of dislocation free grains is obtained. It is concluded that after annealing at 700 ͦC, the minimum work hardening exponent (nmin) obtained from ∂lnσ/∂lnε curves can be used successfully to predict the correct YR using the Hollomon equation. In this condition, the austenite to martensite transformation is suppressed during tensile testing. Whereas, the austenite to martensite transformation occurs during tensile testing of samples annealed at 800 and 900 ͦC, and results in the increase of strain hardening exponent with applied strain. In this case, the correct YR can be predicted using the average work hardening exponent (navg) determined from ∂lnσ/∂lnε curves. The constants of Voce equation were also calculated and used to predict the YR of austenitic stainless steels. Results indicate that the YR of AISI 321 austenitic stainless steel at different initial conditions can be predicted accurately using the constants of Voce equation.