Deformation Behavior of Fe-36Ni Steel during Cryogenic (123-173 K) Rolling

Microstructural evolution and mechanical properties of cryogenic rolled Fe-36Ni steel were investigated. The annealed Fe-36Ni steel was rolled at cryogenic temperature (123-173 K) with 20%-90% rolling reduction in thickness. The deformation process was accompanied by twinning at cryogenic temperature, and the mean thickness of deformation twins was about 200 nm with 20% rolling reduction. When the rolling reduction was above 40%, twinning was suppressed due to the stress concentration in the tested steel. Deformation microstructure of Fe-36Ni steel consisted of both twin boundaries and dislocations by cryogenic rolling (CR), while it only contained dislocations after rolling at room temperature (RT). The tensile strength of Fe-36Ni steel was improved to 930 MPa after 90% reduction at cryogenic temperature, while the tensile strength after 90% reduction at RT was only 760 MPa. More dislocations could be picidticed as the nucleation sites of recrysialization during CR process.