The austenite in many austenitic stainless steels is meta-stable. That is, the phase(crystal structure) with the lower free energy would be the ferritic structure, but the diffusion required to effect this transformation is much too slow too ever occur by itself at room temperature. If mechanical energy can cause the shearing of the crystal lattice than accompanies the transformation of austenite to martensite, then the stable martensite , a structure that is a distorted ferrite which is magnetic, forms.
 The temperature at which 50% transformation occurs with 30% deformation is called the Md30 tempeature. It is around room temerature for 301 and 304 and can be accurately calculated from a formula I'll put in FAQ.

Thank you very much. I have asked this question to many people but really never had the chance to ask someone with materials experise. Thank you very much

Gerald Austin
Iuka, Miss.