Effect of cavitation intensity on degradation of X6CrNiTi18-10 stainless steel

Abstract

An influence of cavitation intensity on degradation mechanism of X6CrNiTi18-10 stainless steel has been presented. Investigations have been carried out at various inlet and outlet pressures in a chamber with a system of barricades. Regardless of the test conditions, erosion of the tested steel started with high erosion rate and then decreased indicating on very aggressive cavitating flows. The minimum erosion rate was within a very narrow range, showing little dependence on the inlet pressure, but showing dependence on other processes: the phase transformation and/or the work-hardening process. After 600 min of exposition, the steel was in various erosion stages which were related to the inlet pressure. Degradation of X6CrNiTi18-10 steel was dominated by the process of fatigue crack growth in the surface layer. Slip bands and cracks, as well as voids and dimples were formed, which reduced strength of the exposed surface layer. Hydrodynamic cavitation causes uneven distribution of the erosion over the steel surface, which has been demonstrated by roughness measurements. Roughness measurements also enable visualization of the location, shape and topography of the aggressive and non-aggressive zones. The experimental data shows that the volume loss in a cavitation test fulfills the Paris-Erdogan law in a following form: ∆V(t)=C′(t)∙(v−v0)n(t), where C’(t) and n(t) are the time-dependent functions related to the degradation of the surface layer, v is the flow velocity during the test, v0 is the flow velocity, at which cavitation erosion is initiated.