Improving fatigue strength of hydromachinery 13Cr-4Ni CA6NM steel with nitriding and thermal spraying surface treatments

In this study, the rotating-bending fatigue behavior in water of a 13Cr-4Ni martensitic stainless steel as substrate, with two different thermochemical treatments and with a thermal sprayed coating was characterized. Hardness profiles were measured by instrumented nanoindentation. X-ray diffraction was used to identify the phases and measure the residual stresses, and the fracture micromechanisms were characterized by scanning electron microscopy. The results show increases of 27%, 74%, and 95% in the fatigue strength from WC-10Co-4Cr coating, plasma nitriding and salt bath nitrocarburizing, respectively, compared with that untreated material at 106 cycles. The good fatigue behavior of the treated surfaces was found to result from an increase in the surface hardness and the generated compressive stresses that delay crack initiation.