The microstructure evolution of secondary austenite in 2507 duplex stainless steel was investigated by means of optical metallography,scanning electron microscopy and confocal scanning laser microscopy.Four types of s...The microstructure evolution of secondary austenite in 2507 duplex stainless steel was investigated by means of optical metallography,scanning electron microscopy and confocal scanning laser microscopy.Four types of secondary austenite(γ2)morphologies including partially transformed austenite,grain boundary austenite,Widmannstätten austenite(WA)and intragranular austenite could be formed during cooling after solution treatment.It was concluded that secondary austenite morphology was mainly dependent on cooling rates.Two mechanisms of WA formation were proposed.WA nucleated at grain boundary of ferrite or at the formed phase boundary.Transmission electron microscopy(TEM)analysis displayed that WA grew in parallel to the ferrite.The effects of Cr_(2)N on secondary austenite precipitation were discussed in detail.Once Cr_(2)N was involved,a mechanism was proposed that secondary austenite formed by element diffusion,leading to the migration of the austenite–ferrite interface.Cr_(2)N acted as the nucleation sites forγ2 and provided the nitrogen for the transformation;meanwhile,the precipitation of Cr_(2)N during the rapid cooling was captured by TEM.A process of nucleation followed by diffusion was concluded to be the formation of secondary austenite with no Cr_(2)N precipitated.The decomposition of secondary austenite was also studied,which was found to be a diffusion mechanism followed by displacement in connection with the element distribution.展开更多
基金This work was supported by the National Key Research and Development Program of China(No.2016YFB0300201)has received funding from the Key Research and Innovation Program in Zhejiang Province,China(Grant agreement No.2020C01007).
文摘The microstructure evolution of secondary austenite in 2507 duplex stainless steel was investigated by means of optical metallography,scanning electron microscopy and confocal scanning laser microscopy.Four types of secondary austenite(γ2)morphologies including partially transformed austenite,grain boundary austenite,Widmannstätten austenite(WA)and intragranular austenite could be formed during cooling after solution treatment.It was concluded that secondary austenite morphology was mainly dependent on cooling rates.Two mechanisms of WA formation were proposed.WA nucleated at grain boundary of ferrite or at the formed phase boundary.Transmission electron microscopy(TEM)analysis displayed that WA grew in parallel to the ferrite.The effects of Cr_(2)N on secondary austenite precipitation were discussed in detail.Once Cr_(2)N was involved,a mechanism was proposed that secondary austenite formed by element diffusion,leading to the migration of the austenite–ferrite interface.Cr_(2)N acted as the nucleation sites forγ2 and provided the nitrogen for the transformation;meanwhile,the precipitation of Cr_(2)N during the rapid cooling was captured by TEM.A process of nucleation followed by diffusion was concluded to be the formation of secondary austenite with no Cr_(2)N precipitated.The decomposition of secondary austenite was also studied,which was found to be a diffusion mechanism followed by displacement in connection with the element distribution.
