Effects of cold-rolling operation parameters on the surface quality of stainless steel and titanium strips with oil pits

The leading quality indicators of cold-rolled strip products include surface roughness and surface finish. The present study investigates the effects of the reduction ratio and lubrication condition (dry or lubricated) on the surface roughness and surface gloss of S304 stainless steel strips and titanium grade 1 strips processed at room temperature with a rolling speed of 0.33 m/s. The results show that for both materials, the contact ratio between the workpiece and the roller increases with an increasing reduction ratio and gives rise to a higher surface gloss. Moreover, the surface gloss obtained under dry conditions is higher than that obtained under lubricated conditions. The peak cross-sectional and pit cross-sectional areas for both materials decrease as the reduction ratio increases. The corresponding improvement in the surface gloss is particularly apparent under dry conditions due to the absence of oil in the oil pits on the rolled surface. The titanium workpiece has a low yield strength of 170 MPa, and hence a high surface gloss can be obtained under a relatively low reduction ratio of 7%. By contrast, the S304 workpiece has a high yield strength of 215 MPa. As a result, a reduction ratio of at least 17.7% is required to flatten the oil pits and obtain a better surface finish. This study identifies the critical operating parameters of cold rolling affecting surface roughness and glossiness and provides insights into enhancing surface finish. Furthermore, it pinpoints that the valley cross-section area is a critical factor in determining the gloss of a surface with noticeable defects.