A steel plate is one of the critical components of a scroll expander system that usually experiences cavitation in service. An experimental study is conducted to study the behaviour of the scroll’s steel plate subjected to cavitation erosion. For this purpose an ultrasonic transducer is utilised to produce cavitation bubbles. Micrographs of damaged surfaces were observed, showing the nature of the cavitation mechanism and the morphology alterations across the steel sample. Experimental results are explained in terms of the cavitation erosion rates, roughness profile, accumulated strain energy, and hardness of the matrix.