• 한국해양공학회지
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• 제5권2호
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• pp.207-207
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• 1991

The crack length measurements by electrical potential(EP) method for 1% Cr-Mo-V and 12%Cr steel of 0.5T-CT specimen were performed at $500^{\circ}C, 600^{\circ}C 700^{\circ}C$, and an applicability of stress intensity factor($K_I$), net section stress($\sigma_{net}$), $C^*$-ingegral and $C_t$ parameter was studied to measure creep crack growth rate(da/dt) with side groove and without side groove under static and cyclic loading condition. The experimental result could be summarized as follows: 1) Crack measurement by EP method was available and coincided with the Johnson,s analytical equation. 2) da/dt by $K_I$ and $\sigma_{net}$ was not adequate because of the wide scatter band according to load and temperature, but $C^*$-integral, except for transition region, was adequate. 3) $C_t$ parameter showed the best fitted line through total creep region without relating with both temperature and load condition. 4) Under the cyclic loading condition, $C_t$ parameter was proper to extimate da/dt. And it was shown that da/dt for 1% Cr-Mo V steel under the static condition(R=1) was 1.16 times faster than the case under cyclic loading(R=0), and for 12% Cr steel, 1.43 times.

• 한국해양공학회지
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• 제5권2호
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• pp.67-75
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• 1991

The crack length measurements by electrical potential(EP) method for 1% Cr-Mo-V and 12%Cr steel of 0.5T-CT specimen were performed at $500^{\circ}C, 600^{\circ}C 700^{\circ}C$, and an applicability of stress intensity factor($K_I$), net section stress($\sigma_{net}$), $C^*$-ingegral and $C_t$ parameter was studied to measure creep crack growth rate(da/dt) with side groove and without side groove under static and cyclic loading condition. The experimental result could be summarized as follows: 1) Crack measurement by EP method was available and coincided with the Johnson, s analytical equation. 2) da/dt by $K_I$ and $\sigma_{net}$ was not adequate because of the wide scatter band according to load and temperature, but $C^*$-integral, except for transition region, was adequate. 3) $C_t$ parameter showed the best fitted line through total creep region without relating with both temperature and load condition. 4) Under the cyclic loading condition, $C_t$ parameter was proper to extimate da/dt. And it was shown that da/dt for 1% Cr-Mo V steel under the static condition(R=1) was 1.16 times faster than the case under cyclic loading(R=0), and for 12% Cr steel, 1.43 times.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 추계학술대회 논문집 학회본부 A
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• pp.265-268
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• 2000

In this study, a small punch creep (SP-Creep) test using miniaturized specimen has been described for the development of the new creep test method for high temperature structural components such as headers and tubes of boiler, turbine casing and rotor, and reactor vessel. The SP-Creep testing technique has been applied to 1Cr-0.5Mo steel used widely as boiler header material and the creep test temperature are varied at $550^{\circ}C{\sim}600^{\circ}C$. From the experimental results, e.g. SP-Creep curve behaviors, the creep rate in steady state and creep rupture life with test temperature and load, the load exponential value(n, m), the activation energy($Q_{spc}$), the Monkman-Grant relation and the creep life assessment equation etc., it can be summarized that the SP-Creep test may be a useful test method to evaluate the creep properties of the heat resisting material such as boiler header.

• 한국가스학회지
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• 제2권4호
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• pp.42-46
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• 1998

소형 시험편 기술은 최소량의 재료를 사용하여 그 재료의 물리적인 거동을 특성화할 수 있기 때문에 산업설비로부터 많은 재료를 수집할 수 없는 경우에 유용한 방법이다. 본 연구에서 사용한 재료는 화력발전소 터빈로터 소재로 많이 사용되고 있는 1Cr-1Mo-0.25V강이었으며, $^630{\circ}C$에서 등온열화처리하여 5종류의 가속 열화 모사재를 만들었다. 충격시험에는 표준 시험편과 소형 시험편이 사용되었으며, 일부 소형 시험편에 소성 구속을 증가시키기 위해 측면흠을 만들어 넣었다. 표준 시험편과 소형 시험편의 충격특성을 비교하였으며 크기효과를 고찰하였고, 소형 시험편의 연성취성천이온도와 표준 시험편의 연성취성천이온도와의 상관관계를 만들었다. 따라서 소형 시험편의 충격시험결과로부터 표준 시험편의 충격특성을 추정하는 것이 가능하게 되었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.43-48
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• 2000

In this study, a small punch creep(SP-Creep) test using miniaturized specimen$(10{\times}10{\times}0.5mm)$ has been described for the development of the newly semi-destructive creep test method for high temperature structural components such as headers and tubes of boiler turbine casino and rotor and reactor vessel. The SP-Creep testing technique has been applied to 2.25Cr-1Mo(STBA24) steel used widely as boiler tube material and the creep test temperature are varied at $550^{\circ}C{\sim}600^{\circ}C$. The overall deformations of SP-Creep curves are definitely depended with applied load and creep test temperature and show the creep behaviors of three steps like conventional uniaxial creep curves. The steady state creep rate${\delta}_{ss}$ of SP-Creep curve for miniaturized specimen increases with increasing creep temperature, but the exponential value with creep loading is decreased. The activation energy$(Q_{spc})$ during SP-Creep deformation with various test temperatures shows 605.7kJ/mol that is g.eater than 467.4kJ/mol reported in uniaxial creep test. This may be caused by the difference of stress states during creep deformation In two creep test. But from the experimental results, e.g. SP-Creep curve behaviors, the steady state creep rate${\delta}_{ss}$ with creep temperature, and the exponential value(n) with creep loading, it can be summarized that the SP-Creep test may be a useful test method to evaluate the creep properties of the heat resisting material.

• 한국자기학회지
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• 제16권4호
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• pp.211-215
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• 2006

구조 강이나 터빈로터 강의 기계적 물성은 자기적 특성과 관계되므로, 비파괴적으로 자기적 특성을 측정하여 기계적 물성을 평가하는 연구가 많이 수행되었다. 따라서 자동차용 강판으로 사용되는 냉연강판에서도 비파괴적으로 자기적 특성을 측정함으로써 냉연강판의 기계적 물성을 유추할 수 있을 것이고, 냉연강판 생산 라인에서 자기적 특성을 측정하여 온라인상에서 냉연강판의 기계적 특성을 모니터할 수 있을 것이다. 기계적 특성이 다른 세 종류의 냉연강판 CBQ 3060, CBQ 3041 및 CBQ 3036의 시편을 준비하고 교류 섭동 자기장을 인가하여 자기적 특성인 가역투자율을 비파괴적으로 측정함으로서 기계적 물성인 경도와의 상관관계를 규명하였다. 세 종류의 냉연강판 시편에서 기계적 물성인 비커스 경도, 항복강도 및 인장강도를 측정하였다. 주파수가20 Hz일 때, surface type 프로브로 측정한 섭동자기장의 제 1차 고조파인 가역투자율의 피크 간 간격에서 구한 보자력은 비커스경도, 항복강도 및 인장강도가 증가할 때 선형적으로 증가하였다. 주파수 20 Hz에서 lift-off에 대한 가역투자율 측정을 하였는데,lift-off가 증가함에 따라 고조파의 amplitude가 급격히 감소하였다.