Mechanisms of Slip Generation in Cold Rolling of AHSS

Abstract

The skidding between rolls and steel strip is more likely to occur in the cold rolling process in accordance with an increase of tensile strength of the material following the customers’ demand. This happens when the work rolls rotates faster than the longitudinal speed of the strip at the exit of the roll-bite. This phenomenon leads to not only the strip surface defection but the thickness nonuniformity and thus the aim of this study is defined to clarify the mechanism behind the phenomenon. In order to clarify the factor causing the skidding, the cold rolling experiments using two different steel grades, namely the Low Carbon Steel (LCS) and the Advanced High Strength Steel (AHSS) having respectively 270 and 980 MPa tensile strength, have been conducted, which was then assessed by the numerical analyses and the comparison of the forward slip characteristics was made between these two steel grades. It has been revealed that the forward slip is decreased under the low friction coefficient condition with an increase of the rolling reduction. In addition, the friction coefficient of the AHSS is lower than that of the LCS. The existence of the micro-plasto-hydrodynamic lubrication in the AHSS suggests a decrease in friction coefficient, which results in the exhibit of skidding, which was not observed in the LCS.