Effect of nitrogen concentration on nano-structure and high-temperature strength of 9Cr-ODS steel

Oka, Hiroshi   ; Tanno, Takashi  ; Otsuka, Satoshi   ; Yano, Yasuhide  ; Kaito, Takeji 

In determining the nitrogen concentration specifications, nano-structure and high-temperature strength of 9Cr-ODS steel have been investigated as a function of the nitrogen content with the aim of obtaining technical knowledge that makes the specification reasonable. The hardness and tensile strength showed degradation with increasing nitrogen content. For a microstructure, the decrement of residual ferrite phase was confirmed. Since the nitrogen is an austenite stabilizer, the increment of nitrogen enhanced an alpha to transformation, resulted in the decrease of the residual ferrite phase. It is considered that the reduction of the strength is due to the decrease of the residual ferrite phase.