Resistance to tempering of 9Cr-ODS ferritic steel

Chikada, Nobuyoshi*; Hayashi, Shigenari*; Ukai, Shigeharu*; Kono, Yutaka*; Otsuka, Satoshi   ; Kaito, Takeji 

The mechanistic study was carried out on high-temperature strength of 9Cr-ODS ferritic steel that has a duplex microstructure of tempered martensite and residual-alpha ferrite. Microstructure characterizations were performed by micro and nano-hardness tests and microstructure observations after normalizing and tempering. Resistance to tempering was shown to increase with volume fraction of residual-alpha ferrite. This result is consistent with creep rupture test result. Individual strength of tempered martensite and residual-alpha ferrite was estimated from nano-hardenss and inter-particle spacing. In the presentation, discussion will be performed on the mechanism of residual-alpha ferrite formation as well as the effect of residual-alpha ferrite on high-temperature strength improvement.