Comparison of cold formability of cold drawn non-heat-treated steels having similar strength

Abstract

The cold formability of the drawn non-heat-treated steels, i.e. dual phase (DP) steel, low Si steel and ultra low carbon bainitic (ULCB) steel, was examined in terms of the deformation resistance and the forming limit. The present investigation was aimed at elucidating the effect of drawing on the cold formability of non-heat-treated steels which is directly affected by drawing since no heat treatment are involved during forming processes for them. A special care was taken for the present steels to exhibit the similar strength after drawing, so eliminating the strength effect. The present steels after drawing revealed the elastic-near perfect plastic behavior in compression. After drawing, the low Si steel exhibited the lowest deformation resistance estimated by the absorbed energy during deformation. In case of the forming limit in terms of the critical strain under which no cracking occurs during the upsetting test of the drawn steels, the low Si steel and the ULCB steel were better than the conventional heat-treated steel. Accordingly, among several nonheat-treated steels which can replace the conventional heat-treated steel as forging steels, the low Si steel seems to exhibit the best performance if they have the similar strength. The compressive deformation behavior of the present drawn non-heat-treated steels was discussed in association with the strain hardened state and the Bauschinger effect developed by drawing. In addition, their cold formability was explained by the plastic incompatibility between the constituent phases of each steel.