• Title/Summary/Keyword: Stainless Steels

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ENVIRONMENTAL FATIGUE OF METALLIC MATERIALS IN NUCLEAR POWER PLANTS - A REVIEW OF KOREAN TEST PROGRAMS

  • Jang, Changheui;Jang, Hun;Hong, Jong-Dae;Cho, Hyunchul;Kim, Tae Soon;Lee, Jae-Gon
    • Nuclear Engineering and Technology
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    • v.45 no.7
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    • pp.929-940
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    • 2013
  • Environmental fatigue of the metallic components in light water reactors has been the subject of extensive research and regulatory interest in Korea and abroad. Especially, it was one of the key domestic issues for the license renewal of operating reactors and licensing of advanced reactors during the early 2000s. To deal with the environmental fatigue issue domestically, a systematic test program has been initiated and is still underway. The materials tested were SA508 Gr.1a low alloy steels, 316LN stainless steels, cast stainless steels, and an Alloy 690 and 52M weld. Through tests and subsequent analysis, the mechanisms of reduced low cycle fatigue life have been investigated for those alloys. In addition, the effects of temperature, dissolved oxygen level, and dissolved hydrogen level on low cycle fatigue behaviors have been investigated. In this paper, the test results and key analysis results are briefly summarized. Finally, an on-going test program for hot-bending of 347 stainless steel is introduced.

Effect of Rolling Conditions on the Sticking Phenomena of Ferritic Stainless Steel (페라이트계 스테인레스강의 Sticking 현상에 미치는 열간압연조건의 영향)

  • Jin, Won;Choi, Joem-Yong
    • Transactions of Materials Processing
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    • v.6 no.2
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    • pp.110-117
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    • 1997
  • Sticking behavior under the hot rolling conditions for ferritic stainless steels have been studied. Sticking, which is a phenomenon that the naked metal exposed to the surface by scale breakaway during hot rolling sticks to the roll surface, was affected by both high temperature tensile strength and oxidation resistance of the steels. A steel having higher tensile strength and lower oxidation resistance exhibits better resistance to the sticking. It is due to that higher tensile strength increases localized deformation resistance and lower oxidation resistance creates lower friction between steel and roll by forming thicker scale as a lubricant during hot rolling. So, the sticking tends to occur more severely in the order of 430J1L, 436L, 430 and 409L. The most sensitive temperature to the sticking was found to be 90$0^{\circ}C$ for all grade of steels. It was also found that the high speed steel(HSS) roll compared to the Hi-Cr roll was more beneficial to prevent sticking. Because higher surface hardness of HSS roll compared to that of Hi-Cr roll provides less nucleation sites for sticking such as scratch on the roll surface.

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Corrosion behaviors of 18Cr Stainless Steels in Selective Catalytic Reduction Environments (Selective Catalytic Reduction (SCR) 환경에서 18% 크롬 스테인리스강의 부식 거동)

  • Heesan Kim
    • Corrosion Science and Technology
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    • v.22 no.3
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    • pp.175-186
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    • 2023
  • Effects of high-temperature environment and low-temperature environment on corrosion behaviours of 18Cr stainless steels (type 304L, type 441) in simulated selective catalytic reduction (SCR) environments were studied using weight loss test in each environment and rust analysis. With time to exposure to the high-temperature environment, type 441 was more resistant to corrosion than type 304L due to both higher diffusivity of Cr and lower thermal expansion coefficient in α-iron. The former provides a stable protective Cr2O3 layer. The latter leaded to low residual stress between scale and steel, reducing the spallation of the scale. With time to exposure to the low-temperature environment, on the other hand, type 304L was more resistant to corrosion than type 441. The lower resistance of type 441 was caused by Cr-depleted zone with less than 11% formed during the pre-exposure to a high-temperature environment, unlike type 304L. It was confirmed by results from the crevice corrosion test of sensitised 11Cr steel. Hence, to achieve higher corrosion resistance in simulated SCR environments, ferritic stainless steels having lower thermal expansion coefficient and higher diffusivity of Cr but containing more than 18% Cr are recommended.

EVALUATION OF HYDROGEN INDUCED DISBONDING FOR CR-MO-V STEEL/AUSTENITIC STAINLESS OVERLAY

  • Kim, Byung-Hoon;Kim, Dong-Jin;Kim, Jeong-Tae
    • Proceedings of the KWS Conference
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    • 2002.10a
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    • pp.211-216
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    • 2002
  • To investigate transition region in welded overlay relating to disbonding crack, the effect of vanadium addition on disbonding of Cr-Mo steels overlay welded with austenitic stainless steel was studied. V modified Cr-Mo steels have a higher resistance to disbonding than V free Cr-Mo steel. One reason is due to the fact that fine vanadium carbide precipated in base metal traps hydrogen and thus decreases the susceptibility to the disbonding. The second is related to the higher stability of the vanadium and stable carbides formed during PWHT, in which the carbon diffusion to the interface is lower than for V free Cr-Mo steel. Decreasing the carbon content at the interface of the weld overlay shows good resistance to the disbonding. Hence, it is important to control the carbon content at the interface of the weld overlay.

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Effect of Alloying Elements of Si, Mn, Ni, and Cr on Oxidation of Steels between 1050℃ and 1200℃ in Air (강의 대기 중 1050~1200℃의 산화에 미치는 합금원소 Si, Mn, Ni, Cr의 영향)

  • Lee, Dong Bok
    • Korean Journal of Metals and Materials
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    • v.50 no.4
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    • pp.300-309
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    • 2012
  • Low-carbon steels and a stainless steel were oxidized isothermally and cyclically between $1050^{\circ}C$ and $1200^{\circ}C$ for up to 100 min in air to find the effect of alloying elements of Si, Mn, Ni, and Cr on their oxidation. The most active alloying element of Si was scattered inside the oxide scale, at the scale-alloy interface and as internal oxide precipitates beneath the oxide scale. Manganese, which could not effectively improve the oxidation resistance, was rather uniformly distributed in the oxide scale. Nickel and chromium tended to present at the lower part of the oxide scale. Excessively thick porous scales formed on the low-carbon steels, whereas thin but non-adherent scales containing $Cr_2O_3$ formed on the stainless steel.

UNDERLIGNING THERMOCAPILLARY EFFECTS BY ELECTRON BEAM MELTING OF THIN SPECIMENS

  • Domergue, L.;Camel, D.;Marya, S.
    • Proceedings of the KWS Conference
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    • 2002.10a
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    • pp.199-204
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    • 2002
  • Extensive investigations on cast to cast variations observed in steels have underlined the role of thermocapillary or surface tension driven fluid flow in welding operations. The behavior of weld pool under the electric arc is however affected by possible arc modifications linked to microchemistry variations in materials & this limits to some extent the real contribution from surface tension effects. Thus, electron beam welding with high vacuum was used to investigate thermo-capillary effects on thin austenitic stainless steels & nickel based alloys. The weld pool was monitored by video observations to estimate the importance of fluid flow during the melting & solidification phase. The results underline the importance of fluid flow on [mal solidification.

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Aging Evaluation of Duplex Cast Stainless Steel Using Ball Indentation Test (볼 압입시험을 이용한 2상 주조 스테인리스강의 열화 평가)

  • Kim Jin-Weon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.9 s.240
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    • pp.1253-1261
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    • 2005
  • Cast stainless steel (CSS) is thermally aged by a long term exposure in the range of nuclear power plant operating temperature. The thermal aging is a cause of concern for the continued safe and reliable operation of CSS nuclear components. Therefore, an assessment of degradation in material properties of these components has been importantly considered. In this study the ball indentation tests were performed on four cast stainless steels aged at $400^{\circ}C$ for 3600 hours, to investigate the applicability of ball indentation test to the assessment of aging degradation of cast stainless steels. Thus, the reliability of ball indentation test for aged CSS was analyzed by evaluating the scattering of data tested from each material and by comparing tensile properties obtained from ball indentation test and standard tensile test. Also, the tensile properties of aged CSS obtained from ball indentation test were compared with those predicted by the evaluation procedure developed on the basis of material database for aged CSS.

Effects of Rare Earth Metals Addition and Aging Treatment on the Corrosion Resistance and Mechanical Properties of Super Duplex Stainless Steels

  • 박용수;김순태;이인성;송치복
    • Transactions of Materials Processing
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    • v.8 no.3
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    • pp.309-309
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    • 1999
  • Effects of rare earth metals addition and aging treatment on corrosion resistance and mechanical properties of super duplex stainless steels were investigated using optical/SEM/TEM metallographic examination, an X-ray diffraction test, a potentiodynamic anodic polarization test and a tensile test. The performance of the experimental alloy with 0.32% REM addition was compared with commercial super duplex stainless steel such as SAF 2507 when they were exposed to solution annealing heat treatment and aging treatment. The corrosion resistance in CF environments and mechanical properties of the experimental alloy were found superior to those of the commercial duplex stainless steel. The REM with larger atomic radii than those of Cr, Mo and W may fill vacancies inside the matrix and around the grain boundaries, retarding formation of harmful intermetallic σ and χ phases. In addition, fine REM oxides/oxy-sulfides (1-3㎛) seemed to enhance the retardation effects. With REM additions, strength and ductility increased due to the phase and grain refinement caused by fine REM oxides and oxy-sulfides.

A Study of Metallurgical Phenomena in Austenitic Stainless Steel Fusion Welds (I) -Weldability of Commercial Austenitic Stainless Steels- (오스테나이트계 스테인리스강 용접부의 금속학적 현상에 관한 연구(I) - 시판 오스테나이트계 스테인리스강의 용접성 -)

  • 이종섭;김숙환
    • Journal of Welding and Joining
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    • v.16 no.3
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    • pp.111-120
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    • 1998
  • To predict and evaluate metallurgical and mechanical behavior of th welds, it is essential to understand solidification behavior and microstructural evolution experienced in the welds, neither of which follows the equilibrium phase diagram because of rapid heating and cooling conditions. Metallurgical phenomena in austenitic stainless steel fusion welds, types 304, 309S, 316L, 321 and 304N, were investigated in this study. Autogenous GTA welding was performed on weld coupons, and primary solidification mode and phase distribution were investigated from the welds. Varestraint test was employed to evaluate solidification cracking susceptibilities of the alloys. GTA weld fusion zones in type 304, 321 and 304N stainless steels experienced primary ferrite solidification while those in type 309S primary austenite solidification. Type 316L exhibited a mixed type of primary ferrite and primary austenite solidification. The primary solidification mode strongly depended on $Cr_{eq}/Ni_{eq}$ ratio. In terms of solidification cracking susceptibility, type 309S that solidified as primary austenite exhibited high cracking susceptibility while the alloys experienced primary ferrite solidification showed low cracking susceptibility. The relative ranking in solidification cracking susceptibility was type 304=type 304N < type 321 < type 316L < type 309S.

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Forming Phases and corrsion properties of Nitride layer During the Ion Nitriding for AISI 304 Stainless Steels (AISI 304 스테인리스 강의 이온질화에 의한 질화성의 생성 상과 부식특성)

  • Shin, D. H.;Choi, W.;Lee, J. H.;Kim, H. J.;Nam, S. E.
    • Journal of the Korean institute of surface engineering
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    • v.31 no.1
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    • pp.54-62
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    • 1998
  • In this study, the behaviorof ion nitriding of AISI 304 stainless steel was investigated using plasma ion nitriding system. The characteristics of ion nitriding, and their micsoctrucyures, and physical properties were investigated as a function of process parmeteds. important conclusions can be summarzied as follows. Firstly, it was found that growth of nitride layer in ion nitriding are mainly affected by N2 partial pressures and nitriding temperatures for AISI 304 stainless steel. The $N_2$<\TEX> partial pressure plays on important role in ion nitriding since it determiness the incoming flux of nitrogen species onto specimen surface. Nitriding thmprrature is also important besauseit determines the diffusion rates of nitrogen through nitride layers. While both parameters affects the characteristics rateding are controlled by nitridingen diffusion nitration profiles of N and alloying elements such as Cr and Ni are observed through niride layers. Secondly, nitride layer consists of the upper white laywe having various nitride phases and the underneath diffusion layers. The thickness of white layer increases with $N_2$<\TEX> partial pressures and nitriding temperatures. The thinkness of diffusion layer is increasting nitriding temperatures. Finally, nitriding of stainless steels steel show slighly low their corrsionce prorerties. However, passivation properties, which is normally observed in stainless steels, were still observed aftre ion nitriding.

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