Effect of heat treatment on wear and corrosion behavior of high chromium white cast iron

The abrasive wear and corrosion behavior of as-cast, heat-treated and tempered high chromium white cast iron was studied, and the results were evaluated by means of microstructure, hardness, surface roughness and corrosion resistance. The samples were subjected to wear on the ball-on-flat tribometer test machine under different loads. Corrosion tests were carried out using the potentiodynamic scanning (PDS) technique in both alkaline (3.5 % NaCl) and acidic (0.5 M H2SO4) media. According to the results obtained, the wear rate and hardness of the as-cast alloy were relatively low. After heat treatment higher wear resistance and hardness were achieved thanks to the thinned and elongated primary carbides, excessive amount of secondary carbides and the martensitic matrix. After the tempering process, the primary carbides were rounded and shortened, and all the carbides were homogeneously dispersed. This resulted in lower material hardness. Although the hardness of the tempered sample was lower than that of the heat-treated sample, the wear resistance was higher in virtue of the microstructure. The corrosion results showed that the differences between the corrosion resistance of as-cast, heat-treated and tempered samples are only due to microstructural transformation. The differences are related to the Cr/C ratio, primary carbide content and its form in the matrix, and residual stress. In addition, the study showed that secondary carbides play an influential role at the initialization of corrosion but that the primary carbide content in the alloy are dominant in the progression and orientation of the corrosion in the structure.