Dynamic strain aging and serrated flow behavior of Cr-Ti-B low carbon steel during warm deformation

Abstract

The compression behavior of Cr-Ti-B low carbon steel was studied over the temperature range from 250 to 650 °C at three strain rates: 0.01 s−1, 0.1 s−1, and 1 s−1. Moreover, the serrated plastic flow was analyzed during compression, which revealed that type A serrations occurred at high strain rates, while types B or B + C serrations formed at low strain rates. The temperature range (250–350 °C) of negative strain rate sensitivity (NSRS) was slightly lower than that (300–400 °C) of dynamic strain aging (DSA). A pronounced increase of peak stress was observed at 350 °C deformation temperature and a 1 s−1 strain rate, which was attributed to the interactions between the interstitial atoms or atmospheres and movable dislocations. The average diffusion activation energy (73 kJ/mol) at low temperature (250–350 °C) also indicated that the serration mechanism was associated with the diffusion of interstitial atoms. The serration behavior at high temperatures (550–650 °C) was attributed to the pinning of dislocations by precipitates. The steel tended to exhibit planar slip of dislocations in the DSA region, and dynamic recovery was dominant during deformation at 550 °C and above.