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Bi Z.,University of Science and Technology Beijing | Dong J.,University of Science and Technology Beijing | Zhang M.,University of Science and Technology Beijing | Zheng L.,University of Science and Technology Beijing | Zhang Q.,Beijing Beiye Functional Materials Corporation
Hangkong Xuebao/Acta Aeronautica et Astronautica Sinica | Year: 2010

Microstructure evolution behavior for 16Cr-4.5Al, a nickel based alloy used for seals, is studied by scanning electron microscope (SEM) observation and image analysis after exposure at 700 °C for 24 h, 96 h, 312 h, 960 h, 1 512 h, 2 904 h and at 750 °C for 16 h, 96 h, 196 h, 288 h, 528 h respectively. In addition, the size growth of carbide and γ' phase is also calculated based on the diffusion dynamics theory.Experimental and computational results both show that, the size stability of M23C6 carbide at grain boundary is generally accepted for the investigated alloy at the tested temperatures.Using diffusion modeling software DICTRA and its mobility database, the size changes of M23C6 carbide at different temperatures could be calculated, which have a good approximation with experimental results. The calculated results also show that carbide grows faster with larger grain size or higher C content of alloy.However, the coarsening of γ' phase is significant, which conforms to the Ostwald ripe formula, and the macro hardness decrease is obvious during its long term exposure at 700 °C.

Yang J.,Yanshan University | Tian J.,Beijing Beiye Functional Materials Corporation | Hao F.,The Aerospace Corporation | Dan T.,The Aerospace Corporation | And 3 more authors.
Applied Surface Science | Year: 2014

Hardfacing (harden-surface-welding) metal of the hypereutectic Fe-Cr-C alloy with different La2O3 additives was developed. The microstructure of the hardfacing metal was observed by optical microscopy. The phase structure was determined by X-ray diffraction. The hardness and wear resistance of the hardfacing metal were measured by hardness tester and dry sand rubber wheel abrasive tester, respectively. The worn surface morphology was observed by field emission scanning electron microscope equipped with energy dispersive X-ray spectrometry. The solidification curve of the hardfacing metal and the relationship between the content of each phase and the temperature were calculated by thermodynamics software Thermo-Calc and Jmatpro, respectively. The results indicate that, with the increase of the La2O3 additives, the dimension of the primary M7C3 carbide in the hypereutectic Fe-Cr-C alloy hardfacing metal decreases gradually. When the La2O3 additive is 0.78 wt.%, it reaches minimum, which is 11.37 μm. The amount of M7C3 carbide (including the primary carbide and the eutectic carbide) decreases firstly then increases. The hardness of the hardfacing metal increases smally, while the wear resistance of it increases firstly then decreases and reaches the most excellent when the La2O3 additive is 0.78 wt.%. The formation temperature of M7C3 carbide is higher than that of austenite in the hypereutectic Fe-Cr-C alloy hardfacing metal. Austenite precipitated in the liquid phase can improve the precipitation rate of M7C3 carbide in a certain extent. As the temperature of the molten pool drops from 870 C to 840 C, γ-Fe transforms into α-Fe completely, so a large number of C atoms precipitate, which promotes the growth of the M 7C3 carbide in short period. © 2013 Elsevier B.V.

Li C.-W.,Beijing Beiye Functional Materials Corporation | Cheng G.-G.,University of Science and Technology Beijing | Wang X.-H.,University of Science and Technology Beijing | Zhu G.-S.,Shougang Qianan Iron and Steel Co. | Cui A.-M.,Shougang Qianan Iron and Steel Co.
Journal of Iron and Steel Research International | Year: 2012

A mathematical model in present study has been established to investigate the effect of Rheinstahl Heraeus (RH) blow argon mode on the decarburization rate in ultra-low carbon steel refining based on the RH equipment of Shougang Qian'an Iron and Steel Co Ltd (SQISCO). The calculated results show that the increase of argon flowrate promotes the carbon elimination from argon gas bubble surface, molten steel free surface in vacuum as well as splash droplet surface, while reduces that from the interior of liquid steel. It has been found the critical turning point of flowrate ascension is at the 5 th minute and the optimum blow argon flowrate in later stage is 2100 L/min in accordance with the 2 stages argon blow mode, which have been confirmed in the commercial production in SQISCO. © 2012 Central Iron and Steel Research Institute.

Xu M.,Northeastern University China | Xu M.,Beijing Beiye Functional Materials Corporation | Wang J.,Northeastern University China | Liu C.,Northeastern University China
Journal Wuhan University of Technology, Materials Science Edition | Year: 2012

The mechanical properties and microstructure evolution of cold-deformed CrMnN austenitic stainless steel annealed in a temperature ranging from 50 °C to 650 °C for 90 min and at 550 °C for different time were investigated by tensile test, micro hardness test, and Transmission Electron Microscope(TEM). The steel was strengthened when it got annealed at temperatures ranging from 100 °C to 550 °C, while it was softened when it got annealed at temperatures ranging from 550 °C to 650 °C. Annealing temperature had stronger effect on mechanical properties than annealing time. TEM observations showed that nano-sized precipitates formed when the steel was annealed at 150 °C for 90 min, but the size and density of precipitates had no noticeable change with annealing temperature and time. Recrystallization occurred when the steel was annealed at temperatures above 550 °C for 90 min, and its scale increased with annealing temperature. Nanosized annealing twins were observed. The mechanisms that controlled the mechanical behaviors of the steel were discussed. © Wuhan University of Technology and Springer Verlag Berlin Heidelberg 2012.

Jiao S.-Y.,University of Science and Technology Beijing | Zhu G.-N.,University of Science and Technology Beijing | Dong J.-X.,University of Science and Technology Beijing | Zhang Q.-Q.,Beijing Beiye Functional Materials Corporation
Cailiao Gongcheng/Journal of Materials Engineering | Year: 2011

The phase evolution and Mo mass fraction variation law when Hastelloy C-276 thermally aged at 550, 750, 800°C for different time were studied. The results show that the carbide is precipitated along grain boundary for short aging time, and the Mo mass fraction firstly decreases to a minimum value about 6% (mass fraction) with carbide precipitation, then increases with aging time duration. Since the Mo content in nickel-based corrosion resistant alloy is vital to the alloy's resistance ability, the carbide precipitation process and Mo mass fraction variation near grain boundary (GB) were simulated according to Thermo-Calc calculation, John-Mel transformations kinetics and Fick second diffusion law. The comparison results between the simulated and measured mass fraction of Mo are in good agreement, this signifies that the Mo mass fraction distribution near GB can be predicted by the model presented in this work. Based on simulation results, proper heat treatment conditions for this alloy can be proposed according to the requirement of Mo content in the service corrosion environments.

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