ABSTRACT

Microstructure refinement is one of the best metallurgical solutions to decrease alloying elements at given mechanical properties or increase mechanical properties at a given chemical composition, allowing cost reduction, recyclability, weldability and toughness improvement, especially in high strength steels. At the hot rolling stage, grain refinement is promoted by the use of high reductions in the last stands. However in the conventional rolling practice the possibility to apply high reduction is limited due to the high rolling loads restrictions. Asymmetric hot rolling could be an interesting way to solve the problems related to high reductions in the last finishing stands of the hot strip mill. The object of this paper is to study the metallurgical impact of hot asymmetric rolling of steel strips of low-C steels to define the hot rolling procedure for microstructure refinement, for decreasing rolling forces and for modifying textures. Specific solutions to perform hot asymmetric rolling (different roll speed and different roll diameter or roll) were investigated. The strain and stress distribution during rolling was modelled through finite element technique and correlated with the microstructure. Several asymmetric configurations were studied by FEM modelling and one experimental configuration (twin drive asymmetric rolling) was tested. As suggested by the numerical simulations and even from experiments the rolling force in asymmetric rolling is lower than that for symmetric rolling. It turned out that asymmetric hot rolling clearly reduce rolling force and torque. The gain in rolling force increases with increasing reduction and is superior for single drive rolling with different roll diameters. A better homogeneity of the microstructure through thickness has been observed, and the effect of hot asymmetric rolling with respect to grain refinement has been verified.