Creep rupture strength of heat affected zone for 9Cr ferritic heat resisting steels

This paper describes creep rupture characteristics of weld heat affected zone, HAZ for 9Cr ferritic steels that are promising materials for nuclear energy uses. In general, creep rupture strength in the heat affected zone of peak temperature between 900 and 1000°C is lower than that in the base metal for ferritic steels. Grain refinement and coagulation of carbides for 9Cr-IMo steels cause decrease in creep rupture strength of the HAZ. The hardness in the simulated HAZ heated to around 1000°C decreases during creep. This seems to be related to weakening of the HAZ at 1000°C. However, substitution of W for Mo is very effective in enhancement of creep rupture strength of the HAZ due to higher stability of carbides and increase in quantity of precipitated carbides during creep rupture test.