Other events

Title

FUNDAMENTAL STUDY OF LUBRICATION CHARACTERISTICS OF HIGH STRENGTH STEEL IN COLD ROLLING

Authorship

Shimura, Masahiro; Kasai, Daisuke; Shiraishi, Toshiyuki; Takahama, Yoshiki

Shimura, Masahiro

I am this author

Kasai, Daisuke

I am this author

Shiraishi, Toshiyuki

I am this author

Takahama, Yoshiki

I am this author

DOI

10.5151/9785-9785-32189

Downloads

Abstract

Due to the increasing demand for fuel efficiency and collision safety, Advanced High Strength Steel (AHSS) has been applied to vehicles. When AHSS is rolled at a high reduction ratio, the forward slip ratio in cold rolling tends to be lower than that of other softer strips like low-carbon steels and the work roll sometimes skids the strip. This skid causes defects on the strip surface. When the reduction ratio increases, then the bite angle also becomes larger. This large bite angle increase leads to a decrease of the inlet oil film thickness and the friction coefficient increases with the increase in the forward slip ratio. To identify why the forward slip ratio of AHSS at a high reduction ratio becomes smaller than that of low-carbon steel, the relationship between the reduction ratio and forward slip ratio was investigated by a rolling experiment. For this trial, a 4Hi laboratory cold mill was used. AHSS and low-carbon steel coils were rolled by two different rolls that set to be 0.3 and 0.6 μmRa in order to make two kinds of friction conditions. Furthermore, the rolling conditions were numerically analyzed to determine the influence of the friction coefficient and flow stress on the relationship between the forward slip ratio and reduction ratio. These experiments and numerical analysis revealed that the forward slip ratio was reduced with increasing rolling reduction ratio in a low friction state, on the other hand, it increased with increasing rolling reduction ratio in a high friction state. This feature was clearly seen when harder materials were rolled.

Keywords

cold rolling; friction; forward slip ratio; AHSS