On a Sliding Wear Resistance by a Sulphurized Layer of Cast Iron

Abstract

This study was made to scrutinize the influence or effect on the wear resistance by a sulphurized layer which produces on the outer surface of cast iron subjected to sulphurization.
A piece of spheroidal graphite cast iron used as a stator was treated in a reducing salt bath containing 5%Na₂S₂O₃, and the reaction products produced on the outer surface was observed by X-ray diffraction. It was noticed that in addition to FeS, Fe_1−xS and Fe₃S₄, carbides and nitrides such as Fe₃C, Fe₂N and Fe₃N coexisted with α-Fe on the sulphurized layer of cast iron treated by a normal salt bath. Whereas, when cast iron had been treated with an inferior bath, porous and brittle reaction products consisting of FeS and Fe₃O₄ appeared around the outer surface, and in the underlayer the reaction products similar to those mentioned above were detected.
The study was further conducted on a dry-sliding wear of these two kinds of sulphurized cast iron in connection with a rotor of S 45 C. As a result, it was recognized that sulphurized iron revealed excellent wear resistance in the compositional range where the adhesive or thermal wear appeared. It seems that such a phenomenon was due to the existence of a sulphurized layer which suppressed adhesion and welding between the stator and rotor, and also due to the said sulphurized layer which tended to produce an oxidized wear under a wide range of wear condition.
In the cast iron treated with an inferior bath, there appeared heterogeneous reaction products on its outer surface as mentioned above, and the wear loss was comparatively great until the reaction products were removed from the surface. When the products were removed, a normal sulphurized layer came to appear on the surface, rapidly improving the wear resistance of cast iron.
It has been made clear that the above observations coincide well with the distribution of sulpheric constituents on the sliding face examined by an X-ray microanalyzer.