Performance characteristics of mill rolls from graphite chromium cast iron

The main requirements for the development of a new grade for the later finishing section of the mill are : good oxidation and thermal behaviour, high wear resistance, good resistance to rolling incidents. The approach of Marichal Ketin to improve the rolling performances in the last finishing stands is presented. The Hi-Cr cast iron possesses excellent wear resistance due to the presence of hard chromium carbides, but its thermal conductivity and sticking properties are fairly low. A graphite precipitation could contribute to an improvement in thermal conductivity and serve as lubricant preventing sticking. The new material, called graphitic chromium iron, shows good oxidation, wear and thermal behaviour allowing its use as work roll in the last stands of the finishing section of a HSM. In the as-cast condition, graphite precipitation in high Ni and Si chromium cast iron occurs at a temperature of 950 degrees C. Moreover, the amount and volume of free graphite may be increased by secondary graphite precipitation during suitable heat treatment.