Study on the mechanism of de-embrittlement based on the theory of grain boundary segregation for 2.25Cr–1Mo steel

The mechanism of embrittlement and de-embrittlement for 2.25Cr–1Mo steel was studied based on the theory of grain boundary segregation, and the idea of critical temperature of embrittlement for embrittled material was proposed according to the iso-segregation curve in this paper. There is one critical embrittlement temperature corresponding to each degree of embrittlement. When further heat treating temperature is higher than critical temperature, it is a de-embrittlement process. Otherwise, it is an embrittlement process. The model of segregation that element P segregates to intragranular from grain boundary in the de-embrittlement process was deduced based on the theory of atom diffusion. The de-embrittled test and Auger electron spectroscopy analysis were conducted for the matrix of hydrogenation reactor served for 12 years, and the theoretical calculation is consistent with the experimental results, which indicates that the further embrittlement or de-embrittlement mechanism can be explained both qualitatively and quantitatively with combination of the theory of iso-segregation curve and the de-embrittled model derived.

Research highlights
► Mechanism of embrittlement and de-embrittlement for 2.25Cr–Mo steel was studied.
► The critical temperature of embrittlement for embrittled material was proposed firstly.
► Segregation model that element P segregates to intragranular from grain boundary was deduced.
► Auger electron spectroscopy analysis were conducted for hydrogenation reactor after 12 years.
► Discussing de-embrittled process and method of embrittled heat treating.