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

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. M23C6 and M7C3 Carbides were precipitated in the CS25 steel, and M23C6 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 M7C3 precipitates, which was due to W macrosegregation in the CS25 steel melted by VIM. M7C3 was replaced by M23C6 after ageing at 823 K for 5000 h.