Effect of Co on Microstructure and Stress Rupture Properties of K4750 Alloy
来源期刊：Acta Metallurgica Sinica2019年第12期
论文作者：Xiao-Xiao Li Mei-Qiong Ou Min Wang Xian-Chao Hao Ying-Che Ma Kui Liu
文章页码：1501 - 1510
摘 要：The effects of substituting Co for Fe on the microstructure and stress rupture properties of K4750 alloy were studied.The microstructure of the alloy without Co（K4750 alloy） and the alloy containing Co（K4750-Co alloy） were analyzed.Substitution of Co for Fe inhibited the decomposition of MC carbide and the precipitation of η phase during long-term aging treatment.In K4750-Co alloy,the morphology of MC carbide at the grain boundary（GB） remained dispersed blocky shape and no η phase was observed after aging at 750℃for 3000 h.However,in K4750 alloy,almost all the MC carbides at GBs broke down into granular M23C6 carbide and needle-like η phase.The addition of cobalt could delay the decomposition of MC carbides,which accordingly restricted the elemental supply for the formation of η phase.The stress rupture tests were conducted on two alloys at 750℃/430 MPa.When Co is substituted for Fe in K4750 alloy,the stress rupture life increased from 164.10 to 264.67 h after standard heat treatment.This was mainly attributed to increased concentration of Al,Ti and Nb in γ’ phase in K4750-Co alloy,which further enhanced the strengthening effect of γ’ phase.After aging at 750℃for 3000 h,substitution of Co for Fe can also cause the stress rupture life at 750℃/430 MPa to increase from 48.72 to 208.18 h.The reason was mainly because MC carbide degradation and η phase precipitation in K4750 alloy,which promoted the initiation and propagation of micro-crack during stress rupture testing.
Xiao-Xiao Li1,2，Mei-Qiong Ou1，Min Wang1，Xian-Chao Hao1，Ying-Che Ma1，Kui Liu1
1. Institute of Metal Research,Chinese Academy of Sciences2. School of Materials Science and Engineering,University of Science and Technology of China
摘 要：The effects of substituting Co for Fe on the microstructure and stress rupture properties of K4750 alloy were studied.The microstructure of the alloy without Co（K4750 alloy） and the alloy containing Co（K4750-Co alloy） were analyzed.Substitution of Co for Fe inhibited the decomposition of MC carbide and the precipitation of η phase during long-term aging treatment.In K4750-Co alloy,the morphology of MC carbide at the grain boundary（GB） remained dispersed blocky shape and no η phase was observed after aging at 750℃for 3000 h.However,in K4750 alloy,almost all the MC carbides at GBs broke down into granular M23C6 carbide and needle-like η phase.The addition of cobalt could delay the decomposition of MC carbides,which accordingly restricted the elemental supply for the formation of η phase.The stress rupture tests were conducted on two alloys at 750℃/430 MPa.When Co is substituted for Fe in K4750 alloy,the stress rupture life increased from 164.10 to 264.67 h after standard heat treatment.This was mainly attributed to increased concentration of Al,Ti and Nb in γ’ phase in K4750-Co alloy,which further enhanced the strengthening effect of γ’ phase.After aging at 750℃for 3000 h,substitution of Co for Fe can also cause the stress rupture life at 750℃/430 MPa to increase from 48.72 to 208.18 h.The reason was mainly because MC carbide degradation and η phase precipitation in K4750 alloy,which promoted the initiation and propagation of micro-crack during stress rupture testing.
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