EFFECTS OF ALLOYING ELEMENTS ON THERMAL AGING EMBRITTLEMENT OF 15Cr FERRITIC ALLOYS

摘要

Oxide dispersion strengthened (ODS) ferritic steels with Cr content exceed 13wt% often suffer aging embrittlement while exhibiting high temperature strength and high resistance to corrosion and radiation. The effects of carbon and minor elements, such as Si, Mn and Ni, on the age-hardening behavior of 15Cr ferritic alloys were investigated. The tensile properties, Vickers-hardness and microstructures of Fe-15Cr, Fe-C-15Cr, Fe-15Cr-(Si, Mn, Ni) and Fe-C-15Cr-(Si, Mn, Ni) ferritic alloys were compared before and after thermal aging at 475 °C up to 2000 h. After thermal aging, a significant increase in hardness, yield and ultimate tensile strength was observed, which was attributed primarily to the formation of α'-phase that includes the alloying elements such as Si, Mn and Ni. The addition of carbon accelerated the age-hardening of Fe-15Cr alloys by the formation of carbides, which enhanced the nucleation and growth of α'-phase. The addition of Mn, Si and Ni appears to accelerate the phase separation of Fe-15Cr alloys, which is interpreted in terms of site competition mechanism that the grain boundary segregation of alloying elements suppress the Cr-segregation and keep the Cr concentration in the matrix. Quite a few G-phase precipitates were observed in the matrix and on grain boundaries after 2000 h aging.