• Title/Summary/Keyword: Corrosion fatigue crack growth rate

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A Study on Corrosion Fatigue Properties of Welded Joints for TMCP High Strength Steels (TMCP 고장력강 용접부의 부식도영 특성에 관한 연구)

  • 이택순;이휘원;김영철
    • Journal of Ocean Engineering and Technology
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    • v.10 no.3
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    • pp.14-23
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    • 1996
  • The corrosion fatigue test were carried out to evaluate the fatigue characteristics of accelerated cooled (ACC) TMCP high tensile strength steels and weld joint with high heat input by one side one run submerged are welding. In this paper, the fatigue crack growth behaviors were investigated with the center crack tension specimen of base metal and heat affected zone in substitute sea water and air, respectively Main results obtained are sunnarized as follows: 1. The fatigue crack growth rates in sea water faster than those in air environment for the different heat input values, crack growth rate of base metal is very fast and effect of heat input is not remarkable. 2. In HAZ (82kJ/cm, 116kJ/cm), the crack branching phenomena were observed in both air and sea water environment, 3. In SEM observation, the corrosion effect on base metal was larger than that on HAZ in corrosion environment.

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Fatigue Crack Propagation Characteristics in HAZ of A106 Gr B Steel Weldments (A106 Gr B강 용접열영향부에서의 피로균열성장특성)

  • 김철한;조선영;김복기;배동호
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 1999.05a
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    • pp.263-268
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    • 1999
  • With HAZ of A 106 Gr B steel weldment, fatigue test in air, electrochemical polarization test and corrosion fatigue test in 3.5wt.% NaCl solution were performed changing load ratio. Obtained results are as follows. 1) K$\sub$op/ was independent of K$\sub$max/ and load ratio in fatigue crack growth. 2) In variation of load ratio, the scatter band of crack growth curve was reduced by half considering crack closure 3) In the result of electrochemical polarization test, current density was increased abruptly when potential was larger than corrosion potential. 4) Fatigue crack growth rate in corrosive environment was markly higher than the rate in air because of corrosion characteristics of the material and anodization of inner surface crack.

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Research for the Evaluation of Corrosion Fatigue Crack Initiation Life (해수환경중 부식피로균열 발생수명 평가에 관한 연구)

  • Kim, Won-Beom;Paik, Jeom-Kee;Yajima, Hiroshi
    • Journal of the Society of Naval Architects of Korea
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    • v.44 no.4
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    • pp.417-424
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    • 2007
  • With regard to corrosion fatigue crack initiation life (Nc), it has been treated ambiguously for the member which doesn't have stress concentration area. In this research, in order to clarify the corrosion fatigue crack initiation life (Nc), corrosion fatigue tests were carried out. Reasonable and universal corrosion fatigue crack initiation life (Nc) was defined and corrosion fatigue crack initiation/propagation model was suggested also. As the fatigue crack which emanates from the pit is usually small, accordingly it is treated as a small crack. In addition, the observation of the corrosion fatigue fracture surfaces using SEM was conducted. And the fracture mechanics analysis using an intrinsic crack model was conducted for the treatment of the small crack. Finally, the followings were obtained. When there is no clear stress concentration point which seems to fall into a corrosion fatigue crack initiation life, the significance of the definition and suggestion of the moment of the reasonable and universal corrosion fatigue crack initiation life (Nc), at which the fatigue crack propagation rate becomes faster than the corrosion pit growth rate so that the fatigue crack initiates from the pit and propagates in earnest, has been clarified.

Fatigue Crack Growth Behavior of Ni-Cr-Mo Steel under Acid Fog Environment (산성안개 환경하에서 Ni-Cr-Mo 강의 피로크랙전파거동)

  • Kim, Min-Geon;Im, Yong-Ho;Kim, Man-Gu
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.7 s.178
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    • pp.1841-1846
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    • 2000
  • To examine the effect of acid fog on the corrosion fatigue behavior in structural steel, fatigue tests under acid fog atmosphere were carried out in comparison with distilled water. The corrosive c omponents contained in acid fog pile up the corrosion products on crack face and show a crack branching and crack tip blunting. Therefore, due to these workings crack growth rate was reduced by decreasing the effective stress range in crack tip rather than under distilled water. Also the effect of sulfuric acid, which is the main component of acid fog, and testing speed on fatigue crack growth were examined. It was found that corrosion behavior was remarkably dependent upon pH and Hz rather than components of acid fog. According as pH and testing speed decrease below a specific value, crack growth was accelerated in comparison with distilled water. This reveals that due to liquid having strong acidity and slow speed of test the crack face dissolution was promoted, so crack closure was disturbed in the process of stress descent.

Effect of Specimen Thickness to Corrosion Fatigue Crack Propagation Behavior of Structure Rolled Steel (일반구조용 압연강재의 부식피로균열전파거동에 미치는 시험편 두께의 영향)

  • 조약래
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.28 no.3
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    • pp.286-294
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    • 1992
  • In this paper, the corrosion fatigue crack propagation behavior of structure rolled steel (SWS 41C) was investigated by changing the thickness, and this experiment was done by the three point bending corrosion fatigue tester. The main results obtained are as follows: 1) As the thickness of specimen becomes thicker, the corrosion sensitivity to initial stage crack becomes some sensitive, and that the fatigue life becomes more sensitive. 2) The crack growth rate to initial stage crack (da/dN) was retarded as the thickness of specimen becomes thicker. But after initial stage crack, as the thickness of specimen is more thicker, da/dN is more rapid. 3) As the corrosion fatigue crack length grows, the accelerative factor of thick specimen (t=12mm) is more higher than that of thin specimen (t=6mm). 4) As the corrosion fatigue crack length grows, the corroson potential of both thick specimen and thin specimen becomes more less noble potential, however thick specimen (t=12mm) tends to more less noble potential than that of thin specimen(t=6mm).

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Fatigue Fracture Characteristics by Corrosion Degradation of 12Cr Alloy Steel (12Cr합금강의 부식열화에 의한 피로파괴 특성)

  • Jo, Seon-Yeong;Kim, Cheol-Han;Bae, Dong-Ho
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.6
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    • pp.996-1003
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    • 2001
  • In order to investigate the fatigue fracture characteristics by corrosion degradation of 12Cr alloy steel, both the fatigue characteristics in air of them artificially degraded during long period and the corrosion fatigue characteristics were experimentally evaluated in various environments which were determined from electro-chemical polarization tests. And also, their fracture mechanisms were analyzed and compared, fractographyically. From their results, the fracture mechanical characteristics of it artificially degraded during long period in the distilled water, 3.5 wt.% NaCl solution and 12.7wt.%(1M) Na$_2$SO$_4$solution of 25, 60 and 90$\^{C}$ did not show distinguishable difference comparing with non-corroded one in regardless of temperature and degradation period. It means that degradation of the material by just surface corrosion does not remarkably affect to fatigue crack growth. On the other hand, the crack growth rates by corrosion fatigue increased due to activity increase of corrosive factors such as OH(sub)-,Cl(sup)- and SO$_4$(sup)- at the crack tip with temperature increase. Therefore, the crack growth rates by corrosion fatigue were more faster than that in air of the artificially degraded specimen due to the such difference of crack growth mechanism.

A study on the characteristics of corrosion-fatigue-crack propagation in the welded parts of high tensile steels under sea water (고장력강 용접부의 해수중 부식피로균열 성장특성에 관한 연구)

  • 김영식;박무창
    • Journal of Ocean Engineering and Technology
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    • v.1 no.2
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    • pp.113-122
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    • 1987
  • Ships and offshore strrctures are exposed to the corrosive surroundings, and the extablishment of the design criteria and the elucidation on the influence by this environment are requested to maintain the safety and to demonstrate the function of the structure. In this paper, the fatigue-crack-growth behavior on the compact tension specimens of quenched, tempered HT80 grade steels and RA36 high tensile steels having a single edge fatigue cracked notch respectively, were investigated under the repeated tensile stress with constant stroke in sea water for the welded parts by shielded metal arc welding. Main results obtained are summerized as follows; 1. The fatigue-crack-growth rates da/dN in sea water appeared to be greater behavior than those in air environment at the same stress intensisy factor range $\DeltaK$. 2. The correlation data of da/dN$\DeltaK$ of the two kinds of high tensile steels in sea water showed no great difference, however, the correlation data of da/dN$\DeltaK/\sigma_y$($\sigma_y$ stands for yield strength of the material) showed that the fatigue-crack-growth behavior of RA36 plate is affected by active path corrosion(APC) mechanism, while that of HT80 grade plate is mainly affected by hydrogen embrittlement mechanism.

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Stress Corrosion Crack Rate of STS 304 Stainless Steel in High Temperature Water (고온수중에서 STS 304 스테인리스강의 응력부식균열 성장속도)

  • Kim, Jeong-Gi
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.1 s.173
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    • pp.156-162
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    • 2000
  • Sensitized STS 304 stainless steel crack growth rate(CGR) in high temperature water was investigated under trapezoidal wave loading test using fracture mechanics techniques. The CGR, due to stress corrosion cracking(SCC), were systematically measured as a function of the stress intensity factor and stress. holding time under trapezoidal wave loading. In high temperature water, CGR was enhanced by a synergistic effects in combination with an aggressive environment and mechanical damage. The CGR, $(da/dN)_{env}$ was basically described as a summation of the environmentally assisted crack growth rate $(da/dN)_{SCC}$, $(da/dN)_{CF}$ and fatigue crack growth rate in air $(da/dN)air,. The CGR, $(da/dN)_{env}$, increased linearly with increasing stress holding time. The CGR, $(da/dN)_{SCC}$ decreased linearly with increasing stress holding time. Fracture surface mode varied from trans-granular cracking to inter-granular cracking with increasing stress holding time.

A Study on the Corrosion Susceptibility and Corrosion Fatigue Characteristics on the Material of Turbine Blade (Turbine Blade재료의 부식민감성과 부식피로특성에 관한 연구)

  • Jo, Seon-Yeong;Kim, Cheol-Han;Ryu, Seung-U;Kim, Hyo-Jin;Bae, Dong-Ho
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.3 s.174
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    • pp.603-612
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    • 2000
  • Corrosion characteristics on the 12Cr alloy steel of turbine blade was electro-chemically investigated in 3.5wt% NaCI and 12.7wt% Na2S04 solution, respectively. Electro-chemical polarization test, Huey test and Oxalic acid etching test were previously conducted to estimate corrosion susceptibility of the material. And, using the horizontal corrosion fatigue tester, corrosion fatigue characteristics of 12Cr alloy steel in distilled water, 3.5wt% NaCI solution, and 12.7wt%(1M) Na2S04 solution were also fracture-mechanically estimated and compared their results. Parameter considered was room temperature, 60'C and 90'C. Corrosion fatigue crack length was measured by DC potential difference method.Obtained results are as follows,1) 12Cr alloy steel showed high corrosion rate in 3.5wt% NaCI solution and Na2S04 solution at high tempratue.2) Intergranular corrosion sensitivity of 12 Cr alloy was smaller than austenitic stainless steel.3) Corrosion fatigue crack growth rate in 3.5wt% NaCI and 12.7wt%(IM) Na2S04 solution is entirely higher than in the distilled water, and also increased with the temperature increase.

A study on the application of electrochemical method for degradation evaluation (열화평가에 전기화학적 방법의 응용에 관한 연구)

  • Kwon, Jae-Do;Moon, Yun-Bae;Kim, Sang-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.22 no.1
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    • pp.44-51
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    • 1998
  • In order to develop the evaluation methods of degradation for the Ni-Cr-Mo-V steel, which is in use for turbine rotor in nuclear power plant, the degraded materials were prepared by simulated degradation methods. The result of impact test and fatigue crack growth test shows that the FATT(Fracture Appearance Transition Temperature) and fatigue crack growth rate increased with the increase of degradation. And the result of new electrochemical polarization test method was suggested for the evaluating FATT, fatigue crack growth exponent and coefficient C values based on the results of relationship between corrosion current density(Icorr) & FATT, and the m & C and Icorr.