What is the real mechanism of stress relaxation phenomenon in steel at room temperature ?

Dear Mechanicians,

Does anyone know about the mechanism of stress relaxation phenomenon in steel at room temperature ? I am studying the influence of residual stresses on stress relaxation of steel wire, particularly in Duplex stainless steel, with classcial test of stress relaxation at room temperature, higher residual stress amplitude the higher stress loss after some time (720 hours). So far this kind of influence has been studied practically by some series of experiments. I would like to model this phenomenon by numerical method (such as FEM) but I do need to know the mechanism in microstructure of the target material especially the complex one like Duplex steel. In shorter words, in the steel wire, the experiment is in 1-D but the residual stresses are in 3-D eventhough the stress component in the direction of the 1-D test have been proven experimentally to be the by far more important than the others in other directions.

Thank you in advance

Regards

Hamanh