The microstructural evolution of casting porosities and creep-induced cavities for a damaged nickel-based superalloy under different hot isostatic pressing （HIP） conditions was investigated in order to understand th...The microstructural evolution of casting porosities and creep-induced cavities for a damaged nickel-based superalloy under different hot isostatic pressing （HIP） conditions was investigated in order to understand the effects of HIP parameters on the healing behavior of micropores. A number of small-sized creep cavities formed during long-term service and large-sized porosities formed during the casting process were observed. These microdefects were partially healed after treated at high temperature of 1100 ℃ combined with 150 MPa pressure for 2 h, together with the formation of the so- called concentrically oriented γ rafting structure. When HIP temperature was increased to 1150 and 1175 ℃, both the amount and the size of the microdefects were decreased. The concentrically oriented γ rafting around creep cavities became more remarkable, and the primary γ denuded zone was also formed between the raft structure and the cavity. Energy-dispersive X-ray spectroscopy analysis revealed that the γ matrix solute atoms diffused toward the cavity under the concentration gradient, whereas the γ-forming elements diffused in a negative direction. When increasing HIP temperature up to 1200 ℃, the micropores were hardly observed, indicating that both casting porosities and creep-induced cavities had almost been healed. Meanwhile, theγ rafting structure disappeared since HIP temperature was beyond theγ solvus temperature. It is revealed by the experimental results that the atomic diffusion could mainly dominate the healing process of micropores.展开更多
There are significant effects of process parameters on internal qualities of bloom, and these process parameters are as follows. position and reduction amount, reduction distribution, reduction rate, and so on. Develo...There are significant effects of process parameters on internal qualities of bloom, and these process parameters are as follows. position and reduction amount, reduction distribution, reduction rate, and so on. Developing a control model is the key to apply soft reduction technology successfully. As the research object, 360 mm ×450 mm bloom caster in PISCO （Panzhihua Iron and Steel Co. ） has been studied, and the research method for control model of dynamic soft reduction has been proposed. On the basis of solidification and heat transfer model, the position of soft reduction and reduction distribution of each frame are determined according to the bloom temperature distribution and solid fraction in bloom center calculated. Production practice shows that the ratio of center porosity which is less than or equal to 1.0, increased to 97.27%, ratio of central segregation which is less than or equal to 0.5, increased to 80.91%, and ratio of central carbon segregation index which is more than or equal to 1.10, decreased to 4% with the applying model of dynamic soft reduction.展开更多
基金financially supported by the University–Industry cooperation project sponsored by Aviation Industry Corporation of China(No.cxy2010BH06)the National Natural Science Foundation of China(No.51301001)
文摘The microstructural evolution of casting porosities and creep-induced cavities for a damaged nickel-based superalloy under different hot isostatic pressing （HIP） conditions was investigated in order to understand the effects of HIP parameters on the healing behavior of micropores. A number of small-sized creep cavities formed during long-term service and large-sized porosities formed during the casting process were observed. These microdefects were partially healed after treated at high temperature of 1100 ℃ combined with 150 MPa pressure for 2 h, together with the formation of the so- called concentrically oriented γ rafting structure. When HIP temperature was increased to 1150 and 1175 ℃, both the amount and the size of the microdefects were decreased. The concentrically oriented γ rafting around creep cavities became more remarkable, and the primary γ denuded zone was also formed between the raft structure and the cavity. Energy-dispersive X-ray spectroscopy analysis revealed that the γ matrix solute atoms diffused toward the cavity under the concentration gradient, whereas the γ-forming elements diffused in a negative direction. When increasing HIP temperature up to 1200 ℃, the micropores were hardly observed, indicating that both casting porosities and creep-induced cavities had almost been healed. Meanwhile, theγ rafting structure disappeared since HIP temperature was beyond theγ solvus temperature. It is revealed by the experimental results that the atomic diffusion could mainly dominate the healing process of micropores.
文摘There are significant effects of process parameters on internal qualities of bloom, and these process parameters are as follows. position and reduction amount, reduction distribution, reduction rate, and so on. Developing a control model is the key to apply soft reduction technology successfully. As the research object, 360 mm ×450 mm bloom caster in PISCO （Panzhihua Iron and Steel Co. ） has been studied, and the research method for control model of dynamic soft reduction has been proposed. On the basis of solidification and heat transfer model, the position of soft reduction and reduction distribution of each frame are determined according to the bloom temperature distribution and solid fraction in bloom center calculated. Production practice shows that the ratio of center porosity which is less than or equal to 1.0, increased to 97.27%, ratio of central segregation which is less than or equal to 0.5, increased to 80.91%, and ratio of central carbon segregation index which is more than or equal to 1.10, decreased to 4% with the applying model of dynamic soft reduction.
