Flow Curves for C45 Steel at Abrupt Changes in the Strain Path

Many industrial forming processes involve a non-straight strain path. In general, a deviation from a straight strain path is accompanied by a change in the flow curve. The deviations that lead to a reduced flow stress are especially important because they may lead to instability. In order to get more information about flow stress behaviour at abrupt changes in the deformation mode, two types were examined: the first for compression-to-tension (“Bauschinger effect”) and the second for tension-to-torsion. Experiments were performed with C45 steel. The amount of strain before the change (“pre-strain”) was varied. The observed flow curve changes are recorded in three so-called “flow curve change characteristics”. One is based on the initial change, the second on the permanent change and the third on an intermediate value. These three characteristics display simple relationships with the pre-strain. The results are discussed from a metallurgical point of view.