Study On Non-equilibrium Grain Boundary Segregation And The Mechanism Of Intermediate Temperature Embrittlement

After half century of theoretical and experimental research, non-equilibrium grain-boundary segregation (NGS) has been a complete theoretical system and widely used to analyze intermediate temperature embrittlement (ITE). In order to develop processing and service potential of materials, three following aspects have been carried out based on the theory of NGS in this paper:1. The theoretical study on NGSThe progress in the theory of grain boundary anelastic relaxation has been discussed. According to the peak temperature and its movement of NGS induced by grain boundary anelastic relaxation, the character of intermediate temperature embrittlement in17Cr ferritic stainless steel has been analyzed which reported by Sun et al. The result showed that the temperature of ductility minimum increased with the strain rate incresing, which was induced by the movement of peak temperature.2. The research of hot ductility loss in C-Mn steels based on NGSThe experimental hot ductility datum in C-Mn steels are analyzed from the perspective of thermally-induced non-equilibrium grain-boundary segregation (TNGS). This involves considerations of the ductility trough, the ductility healing phenomenon, the effect of temperature difference between solution treatment temperature and test temperature in tensile test on ductility trough, the effect of cooling rate on hot ductility, and the formation of cavities at grain boundaries. Based on analysis, we conclude that:the loss in hot ductility of C-Mn steels is ascribed to thermally-induced non-equilibrium grain boundary segregation of impurities.3. The experimental study on the ITE in17Cr ferritic stainless steel with NGSAfter solution treatment at high temperature of1100℃for30min, the17Cr ferritic stainless steel was hold at300-500℃for10min and measured by elevated temperature tensile test. The experimental results showed that a ductility minimum occurred at400℃. The ductility recovered with the holding time increasing at400℃. These results have verified the ITE of17Cr ferritic stainless steel based on NGS. According to the critical time from the experimental results, the effective diffusion distance of P in NGS has been calculated in this paper.