Comparative study of cavitation erosion resistance of austenitic steels with different levels of metastability

Abstract

Introduction. Reliability-critical components of equipment working in contact with high-speed liquid media (for example, turbine blades of hydroelectric power stations, pump impellers, ship propellers) are subjected to one of the types of wear – cavitation erosion. The current study aims to select and scientifically substantiate the type of coating and its structural-phase state for the effective protection of parts from cavitation erosion. Research methods. The study carries out a comparative analysis of differences in the cavitation erosion resistance of characteristic austenitic steels, in the form of bulk material (316L) and coatings (E308L, 60Cr8TiAl), used for protection against cavitation Arc surfacing, i.e. MMA and MIG, is used for depositing the coatings. The tests are carried out on an original installation for evaluating the cavitation resistance of materials with applying ultrasound and the electrical potential difference. Results and Discussion. The results show that the 60Cr8TiAl has a higher resistance to cavitation erosion than that of E308L and 316L by 4 and 10 times, respectively. The structural factors that determine the resistance to cavitation erosion damage are identified to analyze the reasons for the differences in material resistance. Firstly, a strong dependence of the cavitation erosion resistance of austenitic steels on the intensity of the deformation martensitic transformation, developing under the influence of cavitation, is confirmed. This structural transformation contributes to an increase in cavitation resistance of the surface layer. In metastable austenitic steel, a deformation martensite (α′) is formed in the surface layer during the initial test period. This causes an increase in hardness, dissipation of the energy of external action, and the appearance of compressive stresses that prevent the occurrence of microcracks. Subsequently, additional hardening of the previously formed dispersed crystals of α′-martensite occurs. In 60Cr8TiAl, these effects are significantly stronger than that of E308L and 316L due to the higher level of metastability of austenite and formation of carbon deformation martensite.