| Effects of bending temperature and thermal cycle on SME in Fe-X%Mn alloy were studied. As the bending temperature was decreased from room temperature to-196℃, the SME of Fe-17%Mn, Fe-21%Mn, and Fe-24%Mn alloys were increased. The reason is considered that the mechanical driving force required for stress induced a martensite transformation is lowered due to the increase in chemical driving force for the martensite transformation in accordance with decrease in the bending temperature. However, since Fe-28%Mn alloy is stable, the SME of the alloy was very small regardless of the bending temperature up to-196℃. The SME was increased with increase in number of thermal cycle, showing a peak value at around 5 cycles, and then decreased with further thermal cycle. This effect of thermal cycle on the SME became greater with decrease in Mn content. After the 17%Mn alloy was controlled to have various a martensite contents by holding at temperatures below Ms temperature, the SME of the alloy was measured with respect to a martensite content after bending at 170℃ and heating to 350℃. The measured SME of the alloy showed tendency to increase with increase in a martensite content. From this result, it is concluded that the presence of more or less a martensite content improves the SME at high bending temperature such as 170℃, because the yield strength of γ is increased with the presence of some ε martensite content and the usual slip off {111} $lt;110$gt;γ is γ estrained during bending. |
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