Inter-phase corrosion of chromium white cast irons in dynamic state

In the present paper, chromium white cast irons were prepared by the unidirectional solidification. The carbide sample was extracted for the corrosion and wear test. The inter-phase corrosion mechanism and the electrochemical behavior of chromium white cast irons in corrosion medium were discussed from the viewpoints of electrochemistry and erosion wear. The inter-phase corrosion rates between carbide and matrix were obtained for chromium white cast irons. It can be concluded from the investigation that the inter-phase corrosion rate of the alloy is more than half of the total corrosion rate in the medium. The electrochemical behavior of carbide is quite different from the test alloys and the matrixes, and the carbide always is in the self-passive state. The corrosion resistance of type M7C3 carbide is higher than that of type M3C carbide. The free corrosive potential difference between carbide and matrix is the driving force of the inter-phase corrosion. In the present corrosive environment, the carbide is protected, but the matrix is corroded rapidly. Increasing the free corrosion potentials of the matrix can not only reduce the inter-phase corrosion rates, but also raise the corrosion resistance of chromium white cast irons greatly. (C) 2004 Published by Elsevier B.V.