Influence of smelting processes on precipitation behaviors and mechanical properties of low activation ferrite steels

▶ Creep properties could be improved dramatically by control of smelting process. ▶ VIM + ESR smelting process could improve the W macrosegregation. ▶ W could accelerate the transition of M 7C 3 to M 23C 6 in RAFM steel. ▶ The synergetic effect of carbides and tungsten depletion of solid solution lead to the decrease in creep resistance. In this paper, the influence of smelting processes on precipitation behaviors and mechanical properties of CLF-1 (China low activation ferrite) steel was investigated. Mechanical properties of CLF-1 steels melted by vacuum induction melting (VIM, CS25 steel) and vacuum induction melting followed by consumable electrode remelting (VIM + ESR, CS350 steel) had been studied. The results indicated that the steels showed similar values of hardness and tensile strength, however, creep properties of CLF-1 steel were obviously improved by VIM + ESR process. M 23C 6 and M 7C 3 Carbides were precipitated in the CS25 steel, and M 23C 6 carbides were precipitated in CS350 steel after high-temperature tempering at 1013 K for 90 min. Creep properties of CS25 steel were shown to be dramatically deteriorated by the existence of rod M 7C 3 precipitates, which was due to W macrosegregation in the CS25 steel melted by VIM. M 7C 3 was replaced by M 23C 6 after ageing at 823 K for 5000 h.