Continuous Cooling Transformation Behavior of a Microalloyed Spring Steel

A laboratory study was carried out, using deformation dilatometry, to determine the effects of processing schedule on the continuous cooling transformation behavior of a microalloyed spring steel. The scope of the study was to determine CCT diagrams, microstructures and hardness for the steel under processing conditions, which simulate commercial hot rolling and controlled cooling. It was found, that by reducing reheating temperature and deformation temperature, the amount of large (>50nm) un-dissolved (V,Nb,Ti)(C,N) precipitates in austenite increased and the austenite grain size following deformation decreased. The amount of small (<30nm) strain-induced (Nb,V,Ti)(C,N) precipitates in austenite decreased following deformation, and the transformation of austenite to ferrite and pearlite was accelerated. Hardness was unaffected by the changes in processing.