THE THERMAL AND METALLURGICAL STATE OF STEEL STRIP DURING HOT-ROLLING .1. CHARACTERIZATION OF HEAT-TRANSFER

A technique using intrinsic thermocouples was developed to monitor the thermal response of steel samples during hot rolling. A series of hot-rolling tests was conducted with the thermocouple-instrumented samples on CANMET's pilot mill to simulate individual stands of Stelco's Lake Erie Works hot-strip mill. A mathematical model of heat transfer in the roll bite has been employed to back calculte the roll/strip interface heat-transfer coefficients for lubricated and unlubricated conditions. The influence of reduction, rolling speed, and prerolling on roll-strip heat transfer has also been examined. For unlubricated rolling tests, the heat-transfer coefficient in the roll bite increased with time, reaching a steady-state value of 57 kW/m2-degrees-C. The corresponding number for the lubricated tests was 31 kW/m2-degrees-C. The observed variation in the interface heat-transfer coefficient with increasing strain and interface pressure points to a strong dependence on the real area of contact between the strip and rolls. Therefore, it appears that heat transfer between the two surfaces occurs primarily by conduction across asperity contacts. The high heat-transfer coefficients attained at the roll/strip interface promote chilling of the strip to a depth of approximately one-eighth of the thickness. To validate the overall heat-transfer model, predicted surface temperatures of the strip have been compared with interstand temperature measurements obtained on the industrial mill using pyrometers.