STRUCTURE OF CORROSION RUST LAYERS ON SEVERAL LIRHT RAILWAY STEELS AND THEIR EFFECTS ON CORROSION RESISTANCE

Corrosion tests were carried out in simulating coal mine water for three light railway steels. Morphology of the corrosion rust layers was observed by means metallographic microscope and SEM; the structure of them was detected using X-ray diffractometer and the distribution of the alloy elements in the layers were determined by EPMA. The corrosion of these steels in given environments is an electrochemical process, in which cementite plays a role as cathode and ferrite as anode. The rust layers formed on carbon steel are not clearly stratified. A large number of cracks and holes were found in the rust layers, which make the steel protect from corrosion uneffectively. However, the rust layers on the steel 36 CuPCr and that made in Japan are stratified. The interior layer which consists of Fe_3O_4 appears to be very homogeneous, adhesive and compact. In addition, Cu, P and Cr concentrated in the layer and localized on the side nearby matrix. All these improve the corrosion resistance of steels.