Obvious different formability and mechanical properties of warm caliber rolling Q345 steel with normalized and tempered states

Abstract

The formability and strengthening-toughening behaviors of the warm rolled steels are highly dependent on the raw heat treatment state. Herein, the normalized and tempered Q345 steels were both subjected to caliber rolling at 500 °C with different rolling reduction ratios (18%, 44%, and 68%) to obtain elongation grains and carbide particles with different distribution and size. With the increase of caliber rolling reduction ratio, the strength and fracture elongation of the rolled normalized Q345 steels are gradually decreased, whereas the rolled tempered Q345 steels exhibit obvious improvement in these properties. The warm rolled normalized steel contains severe uneven grain distribution and coarse carbides, which leads to high stress concentration and low mechanical properties, as well as poor formability. On the other hand, warm rolled tempered steel contains nanoscale carbides and homogeneous elongation grains that help to release high stress and strain concentration, resulting in improved formability and mechanical properties to a certain extent. Moreover, the warm rolled tempered steel (Tempformed/TF) exhibited a significant improvement in the impact absorb energy, about 3.1 and 47 times higher than those of the quenched and tempered (QT) state at 20 °C and −80 °C, respectively. This remarkable improvement in low-temperature impact toughness can be attributed to the delamination behavior and subsequent induced super-high plastic deformation energy. These findings have important implications for the design and development of high-performance materials with superior strength-toughness combinations.