Cavitation wear behaviour of austenitic stainless steels with different grain sizes

The cavitation erosion behaviour of two different austenitic stainless steels in water with different pH values and room temperature have been studied by means of a 20-kHz ultrasonic vibrator operating at a peak-to-peak amplitude of 40 μm. The austenitic stainless steels used were AISI 304 (18Cr-10Ni) steel and a high nitrogen (HN) containing steel. Each of the steels were fabricated to yield three different grain sizes: 2.5 μm, 20 μm and 45 μm. The grain size in both steels was adjusted by inducing an austenite-martensite-austenite phase transformation. Grain refining results in an improvement of the mechanical properties: hardness, yield strength, tensile strength, fatigue strength as well as an enhancement in the corrosion resistance. The grain size of the steels has an important effect on the nature of damage produced on the surface of the samples. The resistance to cavitation erosion increases continuously with decreasing grain size. It was also found that cavitation erosion resistance of the two steels is sensitive to variations in the pH: a decrease of this value produces an increase in surface damage. This work shows that the HN steel exhibits better cavitation erosion resistance than AISI 304 steel. Also, hardness, tensile strength, yield strength and grain size of both steels can be correlated with the cavitation resistance Re.