MATHEMATICAL-MODELING OF MEAN FLOW-STRESS DURING THE HOT STRIP ROLLING OF NB STEERS

The mean flow stresses developed during the hot strip rolling of nine grades of Nb steel have been examined. For this purpose, log data obta ined from four different strip mills were converted to mean flow stres s using the Sims approach. The results are analyzed and compared to th e predictions of a mathematical model that takes microstructural evolu tion into account. The model is based on the Misaka equation, but inco rporates the effects of dynamic, metadynamic, and static recrystalliza tion, and also takes the accumulated strain and Nb content into accoun t. Excellent agreement between measured and predicted mean flow stress values is obtained over the whole range of rolling temperatures. In a ddition, the predictions indicate that dynamic, followed by metadynami c, recrystallization takes place in the latter passes of the finishing rolling of some Nb grades. This generalization applies particularly t o the low Si and high Mn grades, indicating that the Si and Mn concent rations and not only the Nb level, determine whether or not dynamic an d metadynamic recrystallization are observed under hot strip rolling c onditions.