Study on mechanism of combined action of abrasion and cavitation erosion on some engineering steels

Abstract

The abrasion and cavitation erosion properties as well as the relevant failure mechanisms of several steels to be used for hydraulic turbine parts were investigated. The tests were carried out using rotating disc equipment under simulated working conditions, instead of in the conventionally used venturi tube or vibration apparatus. Different weight loss curves were obtained. The experimental results obtained from our scanning electron microscopy, transmission electron microscopy, light microscopic observations, X-ray analysis and other test methods proved that it is more reasonable to consider the cavitation erosion as a failure of low cycle (plastic strain) fatigue. Hence, it was derived from the Manson-Coffin relation that the resistance to cavitation erosion depends on the square of the product of the hardness and the true fracture strain ϵ f of the steel. Sand—water abrasion is actually a microcutting of the surface layer of the steels and, here, the hardness of the steels is proved to be the main resistance factor. The failure of steels in muddy and sand-carrying water is due to the combined action of abrasion and cavitation erosion, and the consequent weight loss rate is the weighted sum of the individual rates of abrasion and cavitation erosion. Equations that relate the weight loss rate of abrasion and also of cavitation erosion to the mechanical properties of the steels were developed. The calculated values and the experimental data agree well. Conclusions drawn give useful reference principles for the microstructural design of steels to be selected and also for the improvement of their heat treatment.