Effect of feed rate during induction hardening on the hardening depth, microstructure, and wear properties of tool-grade steel work roll

Abstract

Rolls are the most critical yet vulnerable parts of cold rolling mills. It is crucial for them to withstand long rolling campaigns without losing surface roughness or incurring damage. Newly developed rolls are made from tool-grade steel with high roughness, lower wear, and high damage resistance. One of the most important advantages is the elimination of the need for chrome plating, which is currently widely used on standard steel rolls but is ecologically harmful. We investigated a type of steel with 8% chromium for use in cold rolling using light optical microscopy (LOM), X-ray crystallography (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), hardness measurements, and tribological tests. In this study, a roll with a diameter of 325 mm was electro-slag remelted and forged, machined to a diameter of 305 mm, and quenched and tempered to simulate industrial roll production. A forged roll was induction heated and hardened at four different feed rates (i.e., 24 mm/min, 30 mm/min, 36 mm/min, and 42 mm/min), tempered at 515℃ for 24h and again at 480℃ for 24h, and dissected for in-depth analysis. We identified a clear relationship between the feed rate of the roll during induction hardening and the depth of hardness, the sizes of carbides, and the wear properties of the roll. By reducing the feed rate of the roll through the inductor, we increased the depth of the hardened layer from 16 mm (at a feed rate of 36 mm/min) to 25 mm (at a feed rate of 24 mm/min), which is a 56.25% increase. Such an increase is expected to extend the lifespan of the working roll without having negative effects on the wear resistance and other important parameters. XRD analysis showed that the sample had a 0.4% residual austenite, which means it had a significantly lower risk of roll damage during operation than standard steel grades