Failure of high-chromium iron roll in compact strip production MILL

Abstract

A high chromium (HiCr) iron work roll broke in three pieces in finishing stand 4 in a compact strip production (CSP) mill of a steel company. This roll breakage was examined by means of visual inspection, analysis of the mill process data, and chemical and microscopic analysis of a sample from the spheroidal graphite (SG) iron roll core. The roll broke due to inferior quality of the roll core. Due to strong contamination with chromium (1.5%), far above the limit for the CSP mill (max. 0.50%Cr), the core microstructure contained abundant millimeter-sized (Cr,Fe)-carbide clusters, leading to a poor impact toughness.The quality criteria in the test report were adequate, and depending on the data the mill put the roll in service. Unfortunately, the supplied roll contained incorrect data with respect to the chromium level (0.5%Cr) and to a lesser extent the Mo levels in the roll core after solidification. If the test certificate had shown the actual core composition, would have been rejected and the roll failure would have been prevented.The paper describes the causes of the roll failure manufactured from high chrome grade steel along with the precautionary measure.