Effects of Tungsten and Tantalum on Creep Deformation and Rupture Properties of Reduced Activation Ferritic-Martensitic Steel

Reduced Activation Ferritic-Martensitic (RAFM) steels are actively considered as structural material for blanket module of fusion reactor for its adequate creep rupture strength and better void swelling resistance than austenitic stainless steels. This paper presents the effect of tungsten and tantalum on the creep deformation and rupture properties of RAFM steel. Four heats of RAFM steel containing 1-2 wt. % tungsten and 0.06 - 0.14 wt. % tantalum have been melted. Creep tests were carried out on the steels at 823 K over a stress range of 180 – 260 MPa. The creep deformation of the steels was found to proceed with relatively shorter primary regime followed by an extended tertiary regime with virtually no secondary regime. The minimum creep rate of the steel was found to decrease with the increase in tungsten content and to increase with the increase in tantalum content. Creep rupture life of the steel increased appreciably with the increase in tungsten content from 1 wt. % to 2 wt. %. The increase in tantalum content from 0.06 wt. % to 0.14 wt. % was found to decrease the creep rupture strength of the steel.