THE THERMAL AND METALLURGICAL STATE OF STEEL STRIP DURING HOT-ROLLING .2. FACTORS INFLUENCING ROLLING LOADS

Traditional models for computing roll forces during hot rolling generally ignore the steep thermal gradients set up in the through-thickness direction due to roll chilling and deformation heat. In this paper, Alexander's model has been modified to account for the effect of thermal gradients on roll forces. Flow stress data have been obtained by conducting tests on a cam plastometer and a Gleeble 1500 for a 0.05 pct carbon, a 0.34 pct carbon, and a 0.07 pct carbon with 0.024 pct niobium steel for temperatures and strain rates attained in each of the stands on Stelco's Lake Erie Works (LEW) hot-strip mill. The hyperbolic sine equation has been shown to fit the data and is capable of predicting flow stress over a range of temperatures and strain rates. Simulations of the industrial operation have been conducted on the pilot mill at CANMET, and it has been shown by comparing predicted and measured roll forces that the friction coefficient is reduced from 0.3 to approximately 0.35 to 0.25 in the presence of a lubricant. It has also been shown that incorporating the steep thermal gradients in the roll-bite zone increases predicted roll forces by 6 to approximately 10 pct over the values computed based on centerline temperatures. The model has been validated also by comparing predictions with roll forces measured on the industrial mill.