Stacking fault energy and fcc→hcp transformation driving force in Fe-Mn-C-Cr-Si high manganese steels and experimental investigation

Abstract

Abstract In order to improve the strength and work hardening capacity of high manganese steel, the effects of alloying elements on the stacking fault energy (SFE) and driving force of fcc→hcp transformation in Fe-Mn-C-Cr-Si high manganese steels were explored in detail. Based on the thermodynamic calculations, the Fe-0.6C-15Mn-(4,6)Cr-(0,3)Si (wt.%) steels were prepared to investigate the microstructure and mechanical properties. The calculated results show that the Cr reduces the SFE of Fe-C-Mn-Cr high Mn steels linearly and the reduction rate of SFE is greater as the C content increasing. With increasing the Si concentration, the SFE of Fe-C-Mn-Si steels decreases when the Mn content is higher than 18 wt.%. However, when carbon content is less than 1 wt.% and Mn content less than 18 wt.%, the SFE reaches to a maximum value and then declines with the increase of Si content. The combined effect of Cr and Si on the SFE of Fe-C-Mn-Si-Cr steels appears the similar behaviors to that of Si. Generally, the value of driving force, Δ G γ → ε , of fcc→hcp transformation in Fe-Mn-C-2Cr-Si (wt.%) steels increases with the increase of C and Mn and decreases with the Si content increasing. However, for 0.6 wt.% C and 7 wt.% Mn steels, the value of Δ G γ → ε first increases and then decreases with the increase of Si content. The results of tensile test indicated that the Fe-15Mn-0.6C-6Cr-3Si (wt.%) high manganese steel demonstrates a better combination of the ultimate strength of 987 MPa, yield strength of 470 MPa, fracture elongation of 41.5% and high work hardening capacity because of the ε-martensitic transformation caused by the great Δ G γ → ε (large negative value) and low SFE under stress.