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Zhang Z.,Shandong Electric Power Research Institute | Li X.,Shandong University | Du B.,Shandong Electric Power Research Institute | Zou Y.,Shandong University | Wei Y.,Huadian Zouxian Electrical Power Co.
Hanjie Xuebao/Transactions of the China Welding Institution | Year: 2011

Changing of microstructure and impact toughness of welded metal of Super 304H steel aged at (600°C-700°C)×500 h was investigated using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometer and impact test. Results show that microstructure of the welded metal comprises γ phase and precipitates. In the as-received welded metal, precipitates mainly consists of Nb(C, N) and copper-rich phase and after aging treatment M23C6 presents as well. With the increase of aging temperature, amount of precipitates increases accordingly while amount of Nb(C, N) shows a slow increasing trend. The amount of M23C6 increases rapidly at the initial stage and becomes stable later. After aging treatment, impact energy of the welded metal decreases obviously. Occurrence of aging brittleness is attributed to the precipitation of M23C6 along grain boundaries and it is found that the amount of precipitates is a determinate factor.


Zhang Z.,Shandong Electric Power Research Institute | Li X.,Shandong Electric Power Research Institute | Du B.,Shandong Electric Power Research Institute | Wei Y.,Huadian Zouxian Electrical Power Co. | Peng X.,Shandong Electric Power Research Institute
Jinshu Rechuli/Heat Treatment of Metals | Year: 2015

Microstructure evolution of HR3C steel welded joint obtained from creep rupture test at 700℃ was investigated by optical microscopy and scanning electron microscopy. The results show that large amount of M23C6 precipitates in the welded joint during the high temperature creep process. Coarse M23C6 particles are continously distributed along the austenite grain boundaries, inducing the initation of creep cracks. The cellular dendrite welded seam abounds with acicular M23C6, which accelerates the crack propagation and results in the decrease of creep rupture strength. ©, 2015, Chinese Mechanical Engineering Society of Heat Treatment. All right reserved.


Zhang Z.,Shandong Electric Power Research Institute | Li X.,Shandong Electric Power Research Institute | Zou Y.,Shandong University | Wei Y.,Huadian Zouxian Electrical Power Co.
Jinshu Rechuli/Heat Treatment of Metals | Year: 2012

Microstructure and toughness of Super304H steel aged at 600°C was investigated using optical microscopy, scanning electron microscopy, X-ray diffractometer and impact test. The results show that the microstructure of Super304H steel aged at 600°C comprises γ and precipitates. The precipitates mainly consists of Nb(C, N), Cu phase and M 23C 6. The amount, morphology and distribution of precipitating is different with different aging time. Precipitation of M 23C 6 along grain boundaries lead to aging embrittlement of Super304H steel. It is found that the decrease amplitude of impact energy has some connection with the amount of M 23C 6 along grain boundaries.


Li X.-M.,Shandong Electric Power Research Institute | Zhang Z.-W.,Shandong Electric Power Research Institute | Zou Y.,Shandong University | Wei Y.-Z.,Huadian Zouxian Electrical Power Co.
Jinshu Rechuli/Heat Treatment of Metals | Year: 2011

Microstructure variation of Super304H steel aged at 600 °C was investigated using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffractometer. Results show that microstructure of Super304H steel is composed of-γ and precipitates. The precipitates mainly consist of Nb(C, N), copper-rich phase and M 23C6. With the increase of aging time, amount of precipitates increases accordingly while amount of Nb(C, N) shows a slow increasing trend. The amount of M23C6 increases rapidly at the initial stage and become slowly.


Zhang Z.-W.,Shandong Electric Power Research Institute | Li X.-M.,Shandong Electric Power Research Institute | Zou Y.,Shandong University | Wei Y.-Z.,Huadian Zouxian Electrical Power Co.
Jinshu Rechuli/Heat Treatment of Metals | Year: 2011

Effect of microstructure evolution on toughness of Super304H steel was investigated by analyzing the microstructure of Super304H steel experienced by aging treatment. The results show that the amount of precipitates increases with the increase of aging temperature. Moreover, the increasing trend of the amount varies for different kind precipitates. The amount of Nb(C, N) shows a slow increasing trend but the amount of M23C6 increases rapidly then slows down. Corresponding to the increasing trend of M23C 6, the impact toughness of M23C6 decreases. Thus, the aging embrittlement of Super304H steel is due to the intergranular precipitation of M23C6.


Zhang Z.-W.,Shandong Electric Power Research Institute | Li X.-M.,Shandong Electric Power Research Institute | Du B.-S.,Shandong Electric Power Research Institute | Wei Y.-Z.,Huadian Zouxian Electrical Power Co.
Cailiao Rechuli Xuebao/Transactions of Materials and Heat Treatment | Year: 2011

Microstructure and impact toughness of HR3C welded metal aging-treated at 650°C were investigated by means of optical microscopy, scanning electron microscopy, energy dispersive spectrometer, XRD and impact test. Results show that microstructure of the welded metal consists of γ-phase and precipitates of Nb(C, N), M23C6 and Cu-rich phases. With the increase of aging time, the amount of precipitates increases, and it is found that precipitation of M23C6 dominates the amount of precipitates. After aging treatment, impact toughness of the welded metal decreases significantly and shows brittle fracture for aging time over 200 h. The aging brittleness is attributed to the change of amount of M23C6 precipitates.


Zhang Z.,Shandong Electric Power Research Institute | Li X.,Shandong Electric Power Research Institute | Du B.,Shandong Electric Power Research Institute | Zhang D.,Shandong Electric Power Research Institute | Wei Y.,Huadian Zouxian Electrical Power Co.
Jinshu Rechuli/Heat Treatment of Metals | Year: 2015

Embrittlement phenomenon of F12 steel after servicing for 165000 h was investigated by using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometer and impact test. The results show that decomposition and fragmentation occur for the martensitic matrix of F12 steel after running exposure to high temperature. M23C6 carbides precipitate, agglomerate and grow along the grain boundaries, resulting in the distribution morphology of continous chain-spherical and isolated particles, which subsequently causes the grain boundary embrittlement. ©, 2015, Chinese Mechanical Engineering Society of Heat Treatment. All right reserved.

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