Dynamic and static softening behavior of a titanium added ultra-low carbon steel during hot and warm deformation

Abstract

In this work, the mechanical and metallurgical behavior of titanium added ultra-low carbon (ULC-Ti) steel under hot and warm working conditions was studied by means of dilatometer compression tests. Double compression schedules were performed at temperatures between 700 °C and 1000 °C, inter-pass times of 0,5−100 s, and deformations of 0.5 and 0.3 in the first and second stages, respectively, with strain rate of 1 s−1. The analysis of the flow curves obtained allowed the evaluation of the softening characteristics of the steel. The softening and microstructure features indicate different restoration mechanisms depending of the temperature range. Static recrystallization with rapid microstructure restoration is observed at temperatures within the austenitic and intercritical region. Strain induced boundary motion and recovery mechanisms apparently control the restoration process in the ferrite region. In general, flow stress curves showed dynamic recovery behavior. Only the deformation in the intercritical region produced a peak in the flow stress curves. Isothermal holding tests associated with single hit compression indicated the presence of dynamic strain induced transformation, accelerating the softening kinetics at the intercritical region.

Keywords

• Double compression test
• Softening mechanisms
• Warm rolling
• Dynamic transformation
• Recrystallization