Effect of nitrogen on microstructure and high temperature creep strength of 9Cr-ODS steel

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

The effect of nitrogen concentration on microstructure and high temperature creep strength of 9Cr-ODS ferritic/martensitic steel was investigated. The results showed that the tensile strength and high temperature creep strength decreased with increasing nitrogen concentration. The microstructural analysis suggests that the non-uniform dispersion of Y-Ti-O particles due to the increase in nitrogen concentration may have been the cause of the decrease in high temperature creep strength. The non-uniform dispersion of Y-Ti-O particles is probably the result of the consumption of Ti by the formation of Ti nitrides, which weakened its refinement effect on the nano-sized oxide particles.