• Title, Summary, Keyword: T91 Steel

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Corrosion Behavior and Oxide Film Formation of T91 Steel under Different Water Chemistry Operation Conditions

  • Zhang, D.Q.;Shi, C.;Li, J.;Gao, L.X.;Lee, K.Y.
    • Corrosion Science and Technology
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    • v.16 no.1
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    • pp.8-14
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    • 2017
  • The corrosion behavior of a ferritic/martensitic steel T91 exposed to an aqueous solution containing chloride and sulfate ions is investigated depending on the stimulated all-volatile treatment (AVT) and under oxygenated treatment (OT) conditions. The corrosion of T91 steel under OT condition is severe, while the corrosion under AVT condition is not. The co-existence of chloride and sulfate ions has antagonistic effect on the corrosion of T91 steel in both AVT and OT conditions. Unlike to corrosion resistance in the aqueous solution, OT pretreatment provides T91 steel lower oxidation-resistance than VAT pretreatment. From scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) and X-ray diffraction (XRD) analysis, the lower corrosion resistance in the aqueous solution by VAT conditions possibly is due to the formation of pits. In addition, the lower oxidation resistance of T91 steel pretreated by OT conditions is explained as follows: the cracks formed during the immersion under OT conditions accelerated peeling-off rate of the oxide film.

Effects of hardness values on the creep rupture strength in a Mod. 9Cr1Mo Steel (Mod. 9Cr1Mo 강의 크리프 강도에 미치는 경도의 영향)

  • Lee, Yeon-Su;Yu, Seok-Hyeon;Gong, Byeong-Uk;Kim, Jeong-Tae
    • Proceedings of the KSME Conference
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    • pp.637-642
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    • 2003
  • The Modified 9Cr-1Mo steel identified as T91, P91 and F91 in the ASME specification has been widely used for the construction of modern power plants. The available data on the influence of process parameters during manufacturing and fabrication on its properties are not sufficient. In this study, the influence of various thermal cycles on the hardness and the creep rupture strength was analyzed in the base metal and the weldments made in tube and pipe of a Mod.9Cr-1Mo steel. The low hardness, 155Hv, showed low creep rupture strength below the allowable stresses of T91 base metal in the ASME specification. This low value was attributed to the fully recovered dislocation structure and the weakening of precipitation hardening associated with the abnormal thermal cycles.

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Enhancing Effects of NaHSO3 on Corrosion of T91 Steel

  • Wu, Tangqing;Tan, Yao;Wang, Jun;Xu, Song;Liu, Lanlan;Feng, Chao;Yin, Fucheng
    • Journal of Electrochemical Science and Technology
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    • v.11 no.4
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    • pp.368-378
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    • 2020
  • In the paper, corrosion behavior of T91 steel in different concentrations of NaHSO3 solution was studied in combination with scanning electron microscope (SEM) and electrochemical measurements. The results showed that the steel exhibited active anodic dissolution characteristics in the solution, and NaHSO3 concentration affected both cathodic and anodic behaviors. The steel surface was covered by intact corrosion products in the solutions, but the compactness and mechanical properties of the corrosion products degraded with the increase of NaHSO3 concentration. In low-concentration NaHSO3 solution the steel tended to undergo uniform corrosion with slight corrosion pits, but its corrosion mode gradually transited to localized corrosion as the NaHSO3 concentration increased. The mechanical property degradation of the corrosion products caused by sulfur compounds and the pH decrease of the solution are the important factors to accelerating its corrosion process.

Corrosion Prevention of Cr steels in $SO_2$ Atmosphere for Electrial Power Plants (화력발전소의 장수명화를 위한 Cr 강(鋼)의 고온 $SO_2$가스 부식저감 대책 기술)

  • Lee, Dong-Bok;Choe, Jeong-Ho
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • pp.114-115
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    • 2007
  • The corrosion characteristics of Cr steels were investigated to protect Cr steels from the SO2-gas corrosion in the coal-fired power plant. The samples tested were low alloy ferritic steel (ASTM T22, 23), martensitic steel (ASTM T91, 92, 122), and austenitic stainless steel (ASTM 347HFG). The corrosion tests were performed between 600oC and 1000oC in Ar + (0.2, 1)%SO2 gas for 100 hr. Chromium was quite beneficial to corrosion resistance, while iron was not. The corrosion resistance increased in the order of T22, T23, T91, T92, T122, and 347HFG.

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Corrosion of Fe-9%Cr-1%Mo Steel at 600 and 700℃ in N2/(0.5, 2.5)%H2S-mixed Gas

  • Lee, Dong Bok;Abro, Muhammad Ali;Yadav, Poonam;Bak, Sang Hwan;Shi, Yuke;Kim, Min Jung
    • Journal of the Korean institute of surface engineering
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    • v.49 no.2
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    • pp.147-151
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    • 2016
  • The T91 steel (Fe-9%Cr-1%Mo) was corroded at 600 and $700^{\circ}C$ for 5 - 70 h in the $N_2$/(0.5, 2.5)%$H_2$Smixed gas at one atm. It was corroded fast, forming the outer FeS layer and the inner (FeS, $FeCr_2O_4$)-mixed layer. The formation of the outer FeS layer facilitated the oxidation of Cr to $FeCr_2O_4$ in the inner layer. Since the nonprotective FeS scale was present over the whole scale, T91 steel displayed poor corrosion resistance.

Reliability Prediction of Long-term Creep Strength of Gr. 91 Steel for Next Generation Reactor Structure Materials (미래형 원자로 구조 재료용 Gr. 91 강의 장시간 크리프 강도의 신뢰성 예측)

  • Kim, Woo-Gon;Park, Jae-Young;Yin, Song-Nan;Kim, Dae-Whan;Park, Ji-Yeon;Kim, Seon-Jin
    • Korean Journal of Metals and Materials
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    • v.49 no.4
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    • pp.275-280
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    • 2011
  • This paper focuses on reliability prediction of long-term creep strength for Modified 9Cr-1Mo steel (Gr. 91) which is considered as one of the structural materials of next generation reactor systems. A "Z-parameter" method was introduced to describe the magnitude of standard deviation of creep rupture data to the master curve which can be plotted by log stress vs. The larson-Miller parameter (LMP). Statistical analysis showed that the scattering of the Z-parameter for the Gr. 91 steel well followed normal distribution. Using this normal distribution of the Z-parameter, the various reliability curves for creep strength design, such as stress-time temperature parameter reliability curves (${\sigma}$-TTP-R curves), stress-rupture time-reliability curves (${\sigma}-t_{r}-R$ curves), and allowable stress-temperature- reliability curves ([${\sigma}$]-T-R curves) were reasonably drawn, and their results are discussed.

On-Site Corrosion Behavior of T91 Steel after Long-Term Service in Power Plant

  • He, Yinsheng;Chang, Jungchel;Lee, Je-Hyun;Shin, Keesam
    • Korean Journal of Materials Research
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    • v.25 no.11
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    • pp.612-615
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    • 2015
  • In this work, on-site corrosion behavior of heat resistant tubes of T91, used as components of a superheater in a power plant for up to 25,762 h, has been investigated using scanning electron microscopy(SEM), energy dispersive X-ray spectroscopy (EDS), and electron backscattered diffraction(EBSD), with the objectives of studying the composition, phase distribution, and evolution during service. A multi-layer structure of oxide scale was found on both the steamside and the fireside of the tube surface; the phase distribution was in the order of hematite/magnetite/spinel from the outer to the inner matrix on the steamside, and in the order of slag/magnetite/spinel from the outer to the inner matrix on the fireside. The magnetite layer was found to be rich in pores and cracks. The absence of a hematite layer on the fireside was considered to be due to the low oxygen partial pressure in the corrosion environment. The thicknesses of the hematite and of the slag-deposit layer were found to exhibit no significant change with the increase of the service time.

Corrosion of Fe-Cr Steels at 600-800℃ in NaCl Salts

  • Lee, Dong Bok;Kim, Min Jung;Yadav, Poonam;Xiao, Xiao
    • Journal of the Korean institute of surface engineering
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    • v.51 no.6
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    • pp.354-359
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    • 2018
  • NaCl-induced hot corrosion behavior of ASTM T22 (Fe-2.25Cr-1Mo), T91 (Fe-9Cr-1Mo), T92 (Fe-9Cr-1.8W-0.5Mo), 347HFG (Fe-18-Cr-11Ni), and 310H (Fe-25Cr-19Ni) steels was studied after spraying NaCl on the surface. During corrosion at $600-800^{\circ}C$ for 50-100 h, thick, non-adherent, fragile, somewhat porous oxide scales formed. All the alloys corroded fast with large weight gains owing to fast scaling and destruction of protective oxide scales. Corrosion rates increased progressively as the corrosion temperature and time increased. Corrosion resistance increased in the order of T22, T91, T92, 347HFG, and 310H, suggesting that the alloying elements of Cr, Ni, and W beneficially improved the corrosion resistance of steels. Basically, Fe oxidized to $Fe_2O_3$, and Cr oxidized to $Cr_2O_3$, some of which further reacted with FeO to form $FeCr_2O_4$ or with NiO to form $NiCr_2O_4$.

Study of the Microstructural Evolution of Tempered Martensite Ferritic Steel T91 upon Ultrasonic Nanocrystalline Surface Modification

  • He, Yinsheng;Yang, Cheol-Woong;Lee, Je-Hyun;Shin, Keesam
    • Applied Microscopy
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    • v.45 no.3
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    • pp.170-176
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    • 2015
  • In this work, various electron microscopy and analysis techniques were used to investigate the microstructural evolution of a 9% Cr tempered martensite ferritic (TMF) steel T91 upon ultrasonic nanocrystalline surface modification (UNSM) treatment. The micro-dimpled surface was analyzed by scanning electron microscopy. The characteristics of plastic deformation and gradient microstructure of the UNSM treated specimens were clearly revealed by crystal orientation mapping of electron backscatter diffraction (EBSD), with flexible use of the inverse pole figure, image quality, and grain boundary misorientation images. Transmission electron microscope (TEM) observation of the specimens at different depths showed the formation of dislocations, dense dislocation walls, subgrains, and grains in the lower, middle, upper, and top layers of the treated specimens. Refinement of the $M_{23}C_6$ precipitates was also observed, the size and the number density of which were found to decrease as depth from the top surface decreased. The complex microstructure and microstructural evolution of the TMF steel samples upon the UNSM treatment were well-characterized by combined use of EBSD and TEM techniques.

Strength of Axially Loaded Concrete-Filled Tubular Stub Column. (중심축하중을 받는 콘크리트충전 각형강관단주의 내력)

  • Kang, Chang-Hoon;Oh, Young-Suk;Moon, Tae-Sup
    • Journal of Korean Society of Steel Construction
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    • v.13 no.3
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    • pp.279-287
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    • 2001
  • This paper presents an experimental and analytical study on the behavior of concrete-filled tubular stub columns concentrically loaded in compression to fail. Total eleven specimens were tested and test parameters are the depth-to-thickness ratios of steel tube and the ratio of concrete cylinder strength-to-yield stress of steel tube. Depth-to-thickness ratios of steel tube between 20.22

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