Can the volume percentage of deformation induced ferrite (DIF) increase during cold rolling in TWIP (High Mn) steel? It is generally formed in low carbon steel during hot/warm rolling and slow cooling. But I have done the microstructural as well as XRD studies of a low carbon (0.06 wt.%) TWIP steel, where I have observed that the volume percentage of DIF is increasing with the application of cold deformation. If anyone has the explanation, please help me.
If the specific volume of the DIF is less than the specific volume of the parent phase (matrix) then the enlargement of DIF regions during the transformation relaxes the total strain energy generated by the coldworking, which creates equal amount of reduction in the total Helmholtz free energy of the system. DELF = DELFo(T) +1/2 DELW, which may take the following form for the isothermal reactions; DELF = 1/2 DELW
where DEL W becomes negative due to the total strain energy reduction induced by the cold work initially. Therefore there will be enhancement of DIF formation since this results negative change in Helmholtz free energy variation. Otherwise cold work hinders the formation of DIF.
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