• Journal of the KSME
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• v.26 no.4
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• pp.284-289
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• 1986

이들 기기, 장치는 대부분 철강재가 그 근간을 이루고 있지만, 특히 고온부를 형성하는 부재는 내열용 철강과 합금이다. 강을 모재로 하고 고온에서의 강도유지를 위하여 유용한 소랴의 Cr, Mo 등을 합금시킨 저합금내열강이 1차적으로 사용되어 왔으나 사용조건이 고도화 되면서 이들 합금성분 량이 늘어나 주로 Cr 성분을 증가시킨 고 Cr 페라이트계, 그리고 Ni 성분을 다량으로 첨가한 오스테나이트계 내열강이 제 2차, 제 3차대상이 되어 연구 발전되어 왔다. 그 사용한계는 사용 가스등 환경의 영향과 고온의 크리이프나 피로, 파괴에 대한 저항성등에 크게 좌우되지만, 대개 2.25Cr-1Mo 강의 저합금강에서 $550^{\circ}C$, 9~12% Cr인 페라이트계 내열강에서 $^650{\circ}C$ 까지가 한도이며 그 이상온도에서는 오스테나이트계 내열강이 고려의 대상이 되고 있는 것 같다. 이들 고온부에 사용되는 철강 재료를 중심으로 최근의 동향을 주로 금속학적 입장에서 살펴보기로 한다.

• Journal of Power System Engineering
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• v.17 no.6
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• pp.115-121
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• 2013

This study was carried out to investigate the effect of hot forging on the hardness and impact value of ultra high carbon low alloy steel. With increasing hot forging ratio, thickness of the network and acicular proeutectoid cementite decreased, and than were broken up into particle shapes, when the forging ratio was 80%, the network and acicular shape of the as-cast state disappeared. Interlamellar spacing and the thickness of eutectoid cementite decreased with increasing forging ratio, and were broken up into particle shapes, which then became spheroidized. With increasing hot forging ratio, hardness, tensile strength, elongation and impact value were not changed up 50%, and then hardness rapidly decreased, while impact value rapidly increased. Hardness and impact value was greatly affected by the disappeared of network and acicular shape of proeutectoid cementite, and became particle shape than thickness reduction of proeutectoid and eutectoid cementite.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.189-194
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• 2003

It is important to evaluate strength of dissimilar weld zone to use dissimilar materials safely. This study examines mechanical characteristics of dissimilar weld zone between low alloy steel and austenitic stainless steel that satisfies welding related requirements of ASME Code, experimentally reviews metallurgical and mechanical properties at and adjacent to weld interface. It is confirmed that hardness singularity occurs at the weld interface, and that optimum buttering thickness is more than 5㎜ from view points of tensile & yield strength. From a macroscopic view, brittle fracture characteristics is observed in buttering weld zone by tensile test.

• Transactions of Materials Processing
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• v.14 no.3 s.75
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• pp.215-223
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• 2005

A numerical analysis program is developed by FDM scheme for the prediction of microstructural transformation during heat treatment of steels. In this study, multi-phase model was used fur description of diffusional austenite transformations in low-alloy hypoeutectoid steels during cooling after austenitization. A fundamental property of the model consisting of coupled differential equations is that by taking into account the rate of austenite grain growth, it permits the prediction of the progress of ferrite, pearlite, and bainite transformations simultaneously during quenching and estimate the amount of martensite also by using K-M eq. In order to simulate the microstructural evolution during tempering process, another Avrami-type eq. was adopted and method for vickers hardness prediction was also proposed. To verify the developed program, the calculated results are compared with experimental ones of casting product. Based on these results, newly designed heat treatment process is proposed and it was proved to be effective for industry.

• Transactions of Materials Processing
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• v.15 no.8 s.89
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• pp.581-585
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• 2006

Effects of V on both the formation of Ti-Nb-V carbonitrides and mechanical properties of Ti-Nb bearing low carbon HSLA steels were investigated. Hot rolling process was simulated by using Gleeble 3500 system with the steels containing three different levels of V ($0{\sim}0.1wt.%$). Vanadium precipitated as Ti-Nb-V carbonitrides at austenite region but it did not precipitate as VC during austenite to acicular ferrite or bainitic ferrite phase transformation. As V content increased, the amount of Nb precipitates was decreased but the average size of Ti-Nb-V carbonitrides was increased due to larger diffusivity of V than that of Nb. Coarsened Ti-Nb-V carbonitrides could act as heterogeneous nucleation site during ${\gamma}{\rightarrow}{\alpha}$ phase transformation, thus, acicular ferrite transformation was promoted as V content increased, resulting in increase of upper shelf energy.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.477-482
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• 2001

A study was performed to determine the optimum height for an arc air gouging of temporary attachments, which were attached at the pressure vessel made of low alloy steel. Frequently, the crack occurred in the base metal by the excessive heat input during an arc air gouging process to remove the temporary attachments. A numerical analysis by 2-dimensional finite element method was performed to calculate the temperature distribution in the base metal during the removal of temporary attachments. And then the mock-up test was performed to verify the numerical results. Numerical values showed good agreement with the experimental results. These results indicated that the defects due to the excessive heat input during an arc air gouging were dependent on the height of temporary attachments remained above hie main products.

• Journal of the Korea Safety Management & Science
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• v.6 no.4
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• pp.239-248
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• 2004

Likelihood of failure for the external corrosion of carbon and low alloy steels, which affect to a risk of facilities, was analyzed quantitatively through the risk based inspection using API-581 BRD. We found that the technical module subfactor (TMSF) decreased as the inspection number increased and it increased as the Inspection effectiveness and the used year increased. In this condition, the TMSF showed high value for the case of the marine/cooling tower drift area as a corrosion driver, poor quality of coating, no insulation, and low insulation condition.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05b
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• pp.709-714
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• 1995

영광 3, 4호기에 사용되고 있는 원전 압력용기용 SA-508 IH 강의 미세구조 및 상온 피로균 열성장 특성을 고찰하였다. 본 강재의 미세구조, 석출물 분포 및 형상을 투과전자현미경을 통하여 관찰하였으며 임계영역에서의 거동 및 균열닫힘에 주목하여 피로균열성장 특성을 연구하였다. 다양한 형태의 (Fe, MR)$_3$C 세멘타이트 및 Mo$_2$C 석출물이 입계, 래스경계면 및 입내에 분포되고 있음을 확인하였다. Paris 영역에서의 피로균열성장 속도는 ASME 기준선과 유사하였으며, 임계 영역에서는 일반적인 저합금강의 경우보다 다소 낮게 나타났다. 파면조사 결과 입내 연성파괴현상이 전 $\Delta$K 영역에서 나타나고 있으며, $\Delta$K$_{th}$ 부터 $\Delta$K가 12 Mpa√m 영역에서는 입계파괴 및 입내 평활면이 관찰되었다.

• Plant Journal
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• v.6 no.4
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• pp.56-62
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• 2010

This study investigated characteristics of the post-weld heat treatment of SA213-T23, which was developed for water wall of the ultra super critical power boiler. The temperature of post weld heat treatment should be $730^{\circ}C$ or higher to reduce hardness of the deposit metal and heat affected zone. Coincidently, the temperature should remain $760^{\circ}C$ or lower to prevent hardness of the base metal from dropping. Hardness decline of deposit metal was trivial according to time when the holding time of heat treatment at $740^{\circ}C$ of post-weld heat treatment gradually increased from initial 15 minutes.

• Nuclear Engineering and Technology
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• v.26 no.2
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• pp.312-323
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• 1994

1986년 12월 미국의 Surry Unit 2 발전소에서 발생한 급수배관의 대형 파손사고가 침식-부식(erosion-corrosion) 현상에 의해 일어난 것으로 밝혀진 이후, 조사 결과 2차계통에 광범위하게 사용되는 탄소강, 저합금강 재질에서 이와 유사한 손상사례가 많이 나타나는 것으로 밝혀졌다. 이러한 침식-부식 손상은 물-증기로 이루어진 계의 단상(water) 또는 2상(water-wet steam) 조건에서 발생된다. 국내의 원자력 발전소 2차계통에서도 이러한 침식-부식 손상이 나타나고 있으며, 현재 손상원인 해석과 이에 대한 대책 수립이 시급히 요청되고 있다. 본 기고문은 국내 원전의 침식-부식 손상조사와 이의 대책수립을 위한 연구에 활용될 수 있는 침식-부식 손상의 개념, 현상학적 양상, 주요인자의 영향 및 해외 원전의 손상경험 사례 등을 종합하여 정리한 것이다.