In this study,the carbide precipitation at 925 ℃ in austenite(γ)of a 0.04C–1.5Mn–0.10Ti–0.39 W(wt%)low-carbon steel was investigated by stress relaxation(SR)high-resolution transmission electron microscopy and at...In this study,the carbide precipitation at 925 ℃ in austenite(γ)of a 0.04C–1.5Mn–0.10Ti–0.39 W(wt%)low-carbon steel was investigated by stress relaxation(SR)high-resolution transmission electron microscopy and atom probe tomography.First-principles calculations were employed to reveal the precipitation mechanism.Results indicate that a high dispersion of W-and Fe-rich M C-type ultrafi ne carbides(<10 nm)forms during the very early stage prior to the onset of precipitation determined by SR.These ultrafi ne carbides possess a B1-crystal structure with a lattice parameter of 3.696Å,which is quite close to that ofγ(3.56Å).It can signifi cantly decrease the misfi t of carbide/γinterface with a cube-on-cube relationship,thus assisting the carbide nucleation.As the time prolongs,a few spherical or polygonal Ti-rich(Ti,W)C particles(18–60 nm)are formed at the expense of the ultrafi ne carbides by nucleation and growth on them.These(Ti,W)C particles are identifi ed with a“core–shell”structure(Ti-rich core and Ti,W-rich shell),which leads to a better-coarsening resistance compared with pure TiC in Ti steel.Calculation results show that the composition and structure of carbides at certain stage are closely related to a combined eff ect of W,Fe,and Ti atoms together with interstitial vacancies.展开更多
基金the National Natural Science Foundation of China(No.52001084)the Tianjin Key Laboratory of Materials Laminating Fabrication and Interface Control Technology,the Central University Foundation of Harbin Engineering University(No.GK2100260329)the Jian-Hua Research Foundation of Hebei University of Technology(Nos.HB1921 and HB1920)。
文摘In this study,the carbide precipitation at 925 ℃ in austenite(γ)of a 0.04C–1.5Mn–0.10Ti–0.39 W(wt%)low-carbon steel was investigated by stress relaxation(SR)high-resolution transmission electron microscopy and atom probe tomography.First-principles calculations were employed to reveal the precipitation mechanism.Results indicate that a high dispersion of W-and Fe-rich M C-type ultrafi ne carbides(<10 nm)forms during the very early stage prior to the onset of precipitation determined by SR.These ultrafi ne carbides possess a B1-crystal structure with a lattice parameter of 3.696Å,which is quite close to that ofγ(3.56Å).It can signifi cantly decrease the misfi t of carbide/γinterface with a cube-on-cube relationship,thus assisting the carbide nucleation.As the time prolongs,a few spherical or polygonal Ti-rich(Ti,W)C particles(18–60 nm)are formed at the expense of the ultrafi ne carbides by nucleation and growth on them.These(Ti,W)C particles are identifi ed with a“core–shell”structure(Ti-rich core and Ti,W-rich shell),which leads to a better-coarsening resistance compared with pure TiC in Ti steel.Calculation results show that the composition and structure of carbides at certain stage are closely related to a combined eff ect of W,Fe,and Ti atoms together with interstitial vacancies.
