Development of novel mechanical processing method of GA steel sheets using stress-induced phase transformation

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Based on the hypothesis that plastic deformability appears by the stress-induced transformation from the Fe-Zn intermetallic compounds to hcp/fcc phase, X-ray powder diffraction analysis using a diamond anvil was carried out to estimate the critical pressure of transformation and bulk modulus of the Fe-Zn intermetallics at low- and high-pressure conditions. The samples of zeta and Gamma1 phases collected as the dross phase in the previous study, were examined for the possible presence of phase transitions. No phase transition was observed for the Gamma1 phase up to 30GPa at room temperature, while clear evidence of the phase transition to the hcp phase for the zeta phase was obtained. The phase stability was estimated based on the calculation of the assessed free energy change of mixing (chemical energy) for the Fe-Zn system and estimated values of the bulk modulus and molar volume for the low- and high-pressure phase, and the critical pressures for the phase transitions are proposed.