1999 Volume 71 Issue 8 Pages 505-510
High chromium cast iron has a very poor machinability due to its high carbide content. Fe-2.4 mass % C-15 mass % Cr-1 mass % Mo-P-S alloys containing 0 to 0.2 mass % Pb and 0 to 0.4 mass % S were made by casting. The machinability of rodlike these alloys was examined by use of a lathe. Granular MnS was found to be distributed between primary γ dendrites and neighboring chromium carbide (M7C3) in iron containing sulphur. Since MnS became the starting point of rupture of chips and it had the effect which divided chips into small pieces in turning, they diminished in size and the machinability of iron containing sulphur improved. Addition of lead to iron was effective to improve the machinability. The wear of cutting tools decreased largely in turning by addition of lead and sulphur to high chromium cast iron. Since the high chromium as cast iron containing lead and sulphur had austenite matrix, the cutting surface of the cast iron was hardened by machining.
