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Cheng X.,Jiangsu University | Wang C.,Jiangsu University | Zhang N.,Jiangsu University | Li D.,Jiangsu University | And 2 more authors.
Jinshu Rechuli/Heat Treatment of Metals | Year: 2016

Creep property of a novel Cr18Ni9NbTiN austenitic stainless steel at 650 ℃ and different stresses was investigated by RDL100 high temperature electrical creep machine. Microstructure of the Cr18Ni9NbTiN steel at different creep stage under 220 MPa were observed and analyzed by using SEM, TEM and EDS. The results show that during initial-state creep stage, intracrystalline dislocation density increases dramatically, tangled dislocation is found, tiny NbN precipitates disperse distribute within the grain. During steady-state creep stage, dislocations form reticular structure, TiN particles separates out from the grains, chain (Cr, Fe)23C6 precipitates along grain boundaries, reticular dislocation and precipitated second phase not only reduce the mobility of dislocation together, but also improve the creep resistance of the alloy. During accelerate-state creep stage, a large number of extended dislocations appeared which extend the creep life of the steel. Creep rupture of Cr18Ni9NbTiN steel belongs to intergranular brittle fracture, some of (Cr, Fe)23C6 precipitates on the grain boundary exfoliated, wedge cracks are found at trigeminal grain boundary. © 2016, Chinese Mechanical Engineering Society of Heat Treatment. All right reserved.

Li D.-S.,Jiangsu University | Li D.,Jiangsu University | Dou H.,Jiangsu Yinhuan Precision Steel Tube Co Ltd | Gao P.,Jiangsu Yinhuan Precision Steel Tube Co Ltd | And 4 more authors.
Key Engineering Materials | Year: 2014

The oxidation kinetic curves of four kinds of austenitic stainless steel at 700? was measured by weighting method. It is showed that the oxidation curves of those austenitic stainless steels follow the parabolic law. The mass gain of 800Al steel. is the least of all. The surfacemorphology and structure of the oxide scale were studied by scanning electron microscopy and X-ray diffraction methods. It is found that adense oxide scale formed at 700? in all four austenitic stainless steels. In austenitic stainless steel with high Mn content, scales are mainly composed of Mn2O3 and the spinel MnFe2O4. Scales of austenitic stainless steel with high Cr content but without element Al are composed by Cr2O3 and the small amount of spinel FeCr2O4 . Scales of austenitic stainless steel with element Al and Cr are composed of(Fe0.6Cr0.4)2O3 and Al oxide, showing the excellent oxidation resistance property. ©2014 Trans Tech Publications Ltd, Switzerland.

Li D.,Jiangsu University | Dai Q.,Jiangsu University | Wang R.,Jiangsu University | Wang G.,Jiangsu Yinhuan Precision Steel Tube Co Ltd | Liu Y.,Jiangsu Yinhuan Precision Steel Tube Co Ltd
Jinshu Rechuli/Heat Treatment of Metals | Year: 2013

The unqualified TP304L pipes applied to ultra-supercritical thermal power units were analyzed by the JSM-7001F scanning electron microscope, Inca Energy350X energy spectrometer, etc. It is found a certain depth of corrosion occurred on the inside surface of the unqualified TP304L pipes in form of intergranular corrosion cracking. Microstructure analysis shows that there are more carbides precipitated at the grain boundaries on the inner surface of the pipes, and fewer on the outer surface or in the center of the pipes. It is considered that the intergranular corrosion cracking and carbide precipitation are due to high temperature and rapid carburizing during production.

Li D.,Jiangsu University | Dai Q.,Jiangsu University | Wang G.,Jiangsu Yinhuan Precision Steel Tube Co Ltd | Shao X.,Jiangsu Yinhuan Precision Steel Tube Co Ltd | Wang R.,Jiangsu University
Jiangsu Daxue Xuebao (Ziran Kexue Ban)/Journal of Jiangsu University (Natural Science Edition) | Year: 2012

The high-temperature oxidation properties of Super304H and Super304HS austenitic heat-resis-tance stainless steels at various temperatures were investigated by weighting method. The results indicate that the dynamic oxidation curves of both Super304H and Super304HS show parabolical figure. The oxidation resistance property of Super304HS is markedly better than that of Super304H, and the oxidation scale of Super304H is obviously chipped off after the treatment at 900°C for 100 h. Surface morphologies and structure of oxidation scales were analyzed by SEM and XRD. The results show that similar composition of Cr 2O 3 with small FeCr 2O 4 was detected in the two types of oxidation scales at 700°C and 800°C. The oxidation scale of Super304H at 900°C mainly contains Cr 2O 3, Fe 2O 3 and FeCr 2O 4, while only Cr 2O 3 and FeCr 2O 4 are observed in oxidation sacle of Super304HS.

Li D.-S.,Jiangsu University | Dai Q.-X.,Jiangsu University | Cheng X.-N.,Jiangsu University | Shao X.-Z.,Jiangsu Yinhuan Precision Steel Tube Co Ltd | Wang G.-J.,Jiangsu Yinhuan Precision Steel Tube Co Ltd
Cailiao Rechuli Xuebao/Transactions of Materials and Heat Treatment | Year: 2012

Based on the experimental data and the extensive results of the author's research, the author studied the relation between elements and mechanical properties of austenitic stainless steels at room temperature. According to a large number of experimental results, the quantitative calculational equation of strength and elongation are obtained by computer processing.

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