Abstrakt

The erosion resistance of S235JR steel to flow cavitation was investigated. In order to understand an influence of steel properties and cavitation intensities on the degradation mechanisms, low-carbon S235JR steel was tested in the as-received state and after thermal treatment (annealing) under four different flow velocities. Annealing decreased steel hardness, which made S235JR steel less resistant to cavitation erosion. The performed investigations showed that the state of this steel affects the degradation process, e.g. erosion rate and development of surface roughness. An increase in flow velocity caused a linear increase in erosion rate of S235JR steel in as-received state, and an exponential increase in erosion rate of S235JR steel after thermal treatment. Regardless of the state of S235JR steel, an increase in the flow velocity caused a logarithmic increase in the area with increased roughness for Ra > 0.5 μm, where Ra parameter is the arithmetic average of all profile deviations from the mean line over the evaluation length. The increase in surface roughness and the Ra parameter depended on the flow velocity. However, for high flow rates, the Rp parameter, which is the mean of the five maximum profile peak heights from the mean line over the evaluation length, represented an effect of micro-jets impacts on the surface development better than the Ra parameter. A new parameter P, which combines elongation, impact energy and hardness, has been proposed. With increased value of this parameter, the resistance to cavitation erosion decreases. The performed investigations showed that the volume loss can be described by equation in the form of ΔV = C(t)∙(v-v0)n(t), where the function C(t) describes the development of cracks in the surface layer and the function n(t) describes the development of the hardened surface layer.

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