EFFECTS OF TA AND NB ON MICROSTRUCTURES AND MECHANICAL-PROPERTIES OF LOW ACTIVATION FERRITIC 9CR-2W-0.2V STEEL FOR FUSION-REACTOR

In order to develop low activation high chromium ferritic steels for fusion reactors, the effects of 0.05-0.16 wt% Ta and 0.05 wt% Nb alloyings, and heat treatments on elevated temperature strength, toughness and microstructures of 0.1C-9Cr-2W-0.2V-0.04N steels were investigated. Normalizing and tempering conditions were determined as heating at 1 050°C for 30 min and at 800°C for 1 h through observing the dissolution of carbonitrides of Ta and As temperatures, respectively. The optimum amount of Ta in consideration of creep-rupture strength and toughness was approximately 0.10 wt%. Delta-ferrite formed in 0.16 wt% Ta steel of which Cr-equivalent was approximately 10 wt%. The steels alloyed with Ta showed only slightly lower creep-rupture strength than that of the steel alloyed with the optimum amount of Nb, 0.05 wt%. Toughness of the steels alloyed with Ta was superior to that of the steel alloyed with Nb. Hence, Ta-addition can be recommended over Nb-addition in view of the improved toughness. © 1990, The Iron and Steel Institute of Japan. All rights reserved.