Hot Deformation Behavior of P550 Steels for Nonmagnetic Drilling Collars

Abstract

The hot deformation behavior of P550 steels containing different nitrogen contents (0.63 and 0.86 wt% N) is investigated by isothermal compression tests at 900–1200 °C and 0.05–5 s−1. Electron backscattered diffraction (EBSD) is performed to reveal the effects of nitrogen content, deformation temperature, and strain rate on dynamic recrystallization (DRX) behavior of P550 steels. The results indicate that high nitrogen significantly increases the flow stress and apparent activation energy of P550 steels; it also favors the nucleation of DRX by refining the initial grain size. As the deformation temperature is raised, both the fraction and average misorientation angle of DRX grains increase; however, these values first decrease and then increase with increasing the strain rate. The microstructural changes demonstrate that discontinuous DRX (DDRX) plays a dominant role in the nucleation of DRX for the studied steels, whereas continuous DRX (CDRX) is only a coordinated one.