Thermal Cycling Effects on Microstructural Evolution and Hardness of Martensite 13wt.%Cr–4wt.%Ni Steel

Martensitic 13wt.%Cr–4wt.%Ni steel (13-4 MSS) is widely used in underwater applications where it is exposed to severe fluid velocity. The severe service conditions cause its erosion which leads to a reduction in efficiency and large economic losses. To develop the erosion resistance steel, this is an attempt to strengthen the 13-4 MSS by processing a new heat treatment called thermal cycling treatment (TCT). The as-received steel (as-received) was subjected to TCT by using a thermomechanical simulator (Gleeble 3800). The microstructural characterization of as-received and the microstructural evolution due to TCT was analyzed by optical, electron microscopy, and XRD analysis. The microhardness of each phase and the bulk material hardness were determined to characterize the TCT. The progressive dissolution and the fragmentation of delta ferrite caused the removal of delta ferrite content from 12.7% (for as-received) to 6.3% (for treated). The bulk material hardness was found to be the function of the microhardness of martensite and the volume fraction of the delta ferrite. A 42% increase in the bulk material hardness was obtained by the present TCT.