The partitioning of substitutional solute elements during the tempering of martensite in Cr and Mo containing steels

The partitioning of substitutional solute elements between cementite and ferrite during the tempering of martensite both in a commercial 2.2Cr1Mo0.15C wt% steel and in a novel 2.2Cr1Mo0.4C wt% steel has been studied using atom probe field ion microscopy. No partitioning of Cr, Mo and Mn was observed between the cementite and ferrite in the early stages of tempering. No concentration spikes of substitutional solute elements were found at the transformation interface on an atomic scale. The enrichment of Cr, Mn and Mo in the cementite during prolonged ageing, before the onset of soft impingement, was found to be the same in both the low and high carbon alloys. The results provide further support for the theory that cementite precipitates from supersaturated ferrite via a paraequilibrium displacive transformation mechanism.