Surface Cracks in Wire Rod Rolling

Abstract

Surface defects in wire rod and bar rolling are common and well-known to mill people. Nowadays, surface defects are not accepted on high-alloyed steel wire rods. The steel making, casting and rolling processes give rise to defects. Also, the final handling of the wire and bar can destroy the surface. In this work, artificial V-shaped cracks in the longitudinal direction were investigated for different reduction series. The false round-oval series are known as a series for high quality steels and are usually better than square–oval series. Experiments confirmed that in the false round-oval sequences a surface crack in the groove bottom may open up during rolling at the same time as its depth is reduced, which is a beneficial situation. Surface cracks found at 45° to the rolling direction, at groove “corners” and on free surfaces will be closed or reduced in depth. The closing of cracks is detrimental since the cracks usually hide rolled-in oxides beneath the bar surface. The experiments showed that for the subsequent oval–false round sequence the visible crack at the groove bottom will be closed and become shallower. The cracks at 45° and on the free sides will also be closed, but deeper causing a serious surface defect. An FE-analysis was carried out, explaining the experimental results. Flat oval grooves are better than round ovals and false rounds are superior to square for opening and decreasing the depth of a longitudinal crack. It is difficult to eliminate a surface defect constituting a closed crack.