Effects of skin pass rolling parameters on mechanical properties of steels

The influence of skin pass rolling on tensile and microstructural properties of three industrial grade steels was investigated. Skin pass rolling was performed on a laboratory mill equipped with a device designed to reproduce the effects of sheet tension and with load cells aimed at measuring the main working parameters. Analysis on tensile properties of skin pass rolled samples showed for an ultralow C grade and a low C grade a decreasing trend of the yield strength down to a minimum, followed by progressive rising values with increasing rolling elongation. This trend was related to changes of the tensile curve shape, leading to a transition from discontinuous to continuous yielding. A zinc-coated mild steel grade featured a tensile curve with a knee at transition from elastic to plastic regime. Accordingly, the change in yield strength with increasing skin pass elongation followed a linear trend. Microstructural and crystallographic information supplied by EBSD analyses suggested that the plastic strain induced by skin pass rolling originated a fairly homogeneous deformation field even on grains directly exposed on the strip surface. Micro-hardness profiles taken across strip thickness highlighted both increasing peak hardness values at strip surfaces and rising values at mid-thickness.