The Cu-containing austenitic heat-resistant steel 18Cr9Ni3CuNbN, which is being used as superheater and reheater tube material for modern ultra-super-critical （USC） power plants all over the world, has been investig...The Cu-containing austenitic heat-resistant steel 18Cr9Ni3CuNbN, which is being used as superheater and reheater tube material for modern ultra-super-critical （USC） power plants all over the world, has been investigated at 650 ℃ long time aging till 10 000 h. SEM, TEM and 3DAP （three dimensional atom probe） have been used to follow microstructural changes with mechanical property variations. Experimental results show that Cu-rich phase and MX precipitate in the grains as well as M 23 C 6 precipitates at grain boundaries are the main precipitation strengthening phases in this steel. Among them Cu-rich phase is the most important strengthening phase. Homogeneous distribution of very fine nano-size Cu-rich phase has been formed at very early stage of 650 ℃ aging （less than 1 h）. Cu atoms gradually concentrate to Cu-rich particles and the other elements （such as Fe, Cr, Ni etc） diffuse away from Curich particles to γ-matrix with the increasing of aging time at 650 ？ C. The growth rate of Cu-rich phase at 650 ℃ long time aging is very slow and the average diameters of Cu-rich phase have been determined by TEM method. Cu-rich phase keeps in about 30 nm till 650 ℃ aging for 10 000 h. It shows that nano-size Cu-rich phase precipitation strengthening can be kept for long time aging at 650 ℃ because of its excellent stability at high temperatures. According to structure stability study and mechanical properties determination results the Cu-rich phase precipitation sequence and its strengthening mechanism model have been suggested and discussed.展开更多
Thermodynamic calculation,thermal analysis,and identification and observation of precipitates have been carried out on a W-alloyed 10 wt pct Cr steel by means of ThermoCalc program,differential thermal analysis（DTA）...Thermodynamic calculation,thermal analysis,and identification and observation of precipitates have been carried out on a W-alloyed 10 wt pct Cr steel by means of ThermoCalc program,differential thermal analysis（DTA）,X-ray diffraction（XRD） and transmission electron microscopy（TEM） with an energy dispersive Xray spectrometer,respectively.Several critical phase transformation points were determined by combining experimental results with calculations.Two individually stable phases of Nb（C,N） and VN,instead of one single phase MX（X：C,N）,M23C6 or Laves phases,were predicted in the calculated equilibrium phase diagram.An unstable elongated M7C3 with relatively higher Cr was detected unexpectedly in the normalized and tempered steel.Two kinds of spherical Nb（C,N） with different size were recognized as the primary and the secondary precipitates of Nb（C,N） which contain different V contents.It was observed that one kind of complex precipitate in a special V-wing shape was resulted from two plate-like VN adhering to coarse primary spherical Nb（C,N）.展开更多
基金supported by the National Natural Science Foundation of China (No.50931003)
文摘The Cu-containing austenitic heat-resistant steel 18Cr9Ni3CuNbN, which is being used as superheater and reheater tube material for modern ultra-super-critical （USC） power plants all over the world, has been investigated at 650 ℃ long time aging till 10 000 h. SEM, TEM and 3DAP （three dimensional atom probe） have been used to follow microstructural changes with mechanical property variations. Experimental results show that Cu-rich phase and MX precipitate in the grains as well as M 23 C 6 precipitates at grain boundaries are the main precipitation strengthening phases in this steel. Among them Cu-rich phase is the most important strengthening phase. Homogeneous distribution of very fine nano-size Cu-rich phase has been formed at very early stage of 650 ℃ aging （less than 1 h）. Cu atoms gradually concentrate to Cu-rich particles and the other elements （such as Fe, Cr, Ni etc） diffuse away from Curich particles to γ-matrix with the increasing of aging time at 650 ？ C. The growth rate of Cu-rich phase at 650 ℃ long time aging is very slow and the average diameters of Cu-rich phase have been determined by TEM method. Cu-rich phase keeps in about 30 nm till 650 ℃ aging for 10 000 h. It shows that nano-size Cu-rich phase precipitation strengthening can be kept for long time aging at 650 ℃ because of its excellent stability at high temperatures. According to structure stability study and mechanical properties determination results the Cu-rich phase precipitation sequence and its strengthening mechanism model have been suggested and discussed.
文摘Thermodynamic calculation,thermal analysis,and identification and observation of precipitates have been carried out on a W-alloyed 10 wt pct Cr steel by means of ThermoCalc program,differential thermal analysis（DTA）,X-ray diffraction（XRD） and transmission electron microscopy（TEM） with an energy dispersive Xray spectrometer,respectively.Several critical phase transformation points were determined by combining experimental results with calculations.Two individually stable phases of Nb（C,N） and VN,instead of one single phase MX（X：C,N）,M23C6 or Laves phases,were predicted in the calculated equilibrium phase diagram.An unstable elongated M7C3 with relatively higher Cr was detected unexpectedly in the normalized and tempered steel.Two kinds of spherical Nb（C,N） with different size were recognized as the primary and the secondary precipitates of Nb（C,N） which contain different V contents.It was observed that one kind of complex precipitate in a special V-wing shape was resulted from two plate-like VN adhering to coarse primary spherical Nb（C,N）.
