THE EFFECT OF AGING ON THE PROPERTIES AND STRUCTURES OF LOW ACTIVATION MARTENSITIC 9 AND 11-PERCENT CR, W, V STAINLESS-STEELS

The effects on mechanical properties and microstructures of ageing at 500-degrees-C have been established for martensitic 9% and 11% Cr, W, V steels with nominally 0.15% and 0.09% carbon and with additions of tantalum for grain refinement. Samples were aged at 500-degrees-C, after initial tempering at either 675-degrees-C or 750-degrees-C, in order to simulate the thermal conditions likely to be encountered by first wall components in a fusion reactor. Only marginal effects on strength, toughness and microstructure were observed after ageing for times of 1000 and 5000 h, far less than the effect of varying the tempering treatment. Proof strength values of 500-550 MPa were obtained after ageing, with FATT values of -25-degrees-C or lower. Examination of the structures revealed the predominant precipitate to be M23C6, rich in chromium and containing iron and tungsten. In addition, intragranular precipitates of the tantalum/vanadium carbonitride (Ta, V) (C, N) type were found. The work has shown the alloys to be stable for times of at least 5000 h under thermal conditions likely to be experienced in fusion reactors.