It has been previously demonstrated that yttrium can improve the resistance of stainless steel to sliding wear in corrosive environment. However, the mechanism responsible for the beneficial effect of yttrium on corrosive wear is not well understood. In this work, the erosion behavior of Y-free and Y-containing 304 stainless steel in a dilute H2SO4 slurry containing silica sand was investigated, with the aim of exploring the role that yttrium plays. The failure and self-healing of passive films on Y-free and Y-containing 304 stainless steel samples under combined attack by corrosion and mechanical scratch were studied, using an electrochemical scratch technique. The failure of the passive films during dry scratch and identation was also investigated using a micro-mechanical probe with in situ monitoring changes in the electrical contact resistance. In addition, effect of yttrium on electron work function was investigated. All the results demonstrated that yttrium effectively improved properties of the passive film, including corrosion resistance, mechanical behavior and the film stability, resulting in enhanced resistance to corrosion-erosion.