Dynamic recrystallization behavior and coincidence site lattice evolution in thermal deformation of 316H stainless steel used in nuclear systems

The hot deformation behavior of 316H stainless steel used in the 4th-generation nuclear systems was investigated by thermal compression tests at 1000-1150 degrees C and 0.01-10 s(-1). It was found that true stress firstly increased and then decreased with the increasing strain rate with a threshold of 1 s(-1). Electron backscatter diffraction was used to analyze the microstructure evolution. Discontinuous dynamic recrystallization (DDRX) was the dominant dynamic recrystallization (DRX) mechanism, while continuous dynamic recrystallization (CDRX) was the supplementary one. DDRX happened before CDRX and provided additional nucleation sites for the latter. Twin grain boundaries (sigma 3) appeared in DRX grains due to growth accidents. As the length fraction of sigma 3 increased, the coincidence site lattice (CSL) boundary transition began to occur, forming sigma 9 and sigma 27. After the occurrence of full DRX, the growth and annexation of DRX grains were easy to be promoted, in which progress both equiaxed grains and CSL boundaries disappeared. The ideal deformation microstructure with fine and uniform DRX grains, which was accompanied by a high length fraction of CSL boundaries, appeared at 1000 degrees C-0.01 s(-1), 1050 degrees C-0.01-0.1 s(-1), 1100 degrees C-0.1-1 s(-1) and 1150 degrees C-1-10 s(-1). That is, the deformation conditions mentioned above were the preferable thermal forming parameters for 316H stainless steel in actual productions.