MECHANISM ON THE EFFECT OF AL UPON THE GAMMA-]EPSILON MARTENSITE-TRANSFORMATION IN THE FE-MN ALLOYS

The structure of the solid solution treated and deformed Fe-25Mn-(0-3. 11)Al-0.15C alloys was examined by means of metallograph and X-ray dif fraction, which has confirmed that Al restrains the gamma --> epsilon transformation in the Fe-Mn alloys. The mechanism on the restraining e ffect of Al has been discussed on the basis of the effect of Al upon t he stacking fault energy in the Fe-Mn alloys. Aluminium increases ther modynamically the stability of the Fe-Mn austenite and the driving for ce limit necessitated to be overcome for the gamma --> epsilon transfo rmation, because the thermodynamical calculation indicates that Al inc reases the stacking fault energy in the Fe-Mn alloys at 300 K. Al will decrease the number and the size for the epsilon-martensite nucleus a ccording to the stacking fault mechanism of the epsilon-martensite nuc leation.