• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.7
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• pp.637-646
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• 2016

This study is to investigate the influence of hydrogen attack and UNSM on fatigue behaviors of the Inconel 718 alloy. The decrease of the fatigue life between the untreated and the hydrogen attacked material is 10-20%. The fatigue lives of hydrogen attacked specimen decreased without a fatigue limit, similar to those of nonferrous materials. Due to hydrogen embrittlement, about 80% of the surface cracks were smaller than the average grain size of $13{\mu}m$. Many small surface cracks caused by the embrittling effect of hydrogen attack were initiated at the grain boundaries and surface scratches. Cracks were irregularly distributed, grew, and then coalesced through tearing, leading to a reduction of fatigue life. Results revealed that the fatigue lives of UNSM-treated specimens were longer than those of the untreated specimens.

• Journal of Welding and Joining
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• v.8 no.3
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• pp.39-52
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• 1990

The research is to insure the soundness of the stainless steel overlaid weld metal(21/4Cr-IMo steel + SUS 309L) for a pressure vessel application. Detail studies were conducted for the PWHT influence on the micrstructure and intergranular corrosion characteristics of the overlaid weld metal as well as initiation of hydrogen embrittlement crack(or Disbonding) when welded metal are exposed to the hydrogen atmosphere. Hydrogen was experimentally charged to the overlaid weld metal in order to study PWHT effect on the susceptibility of hydrogen embrittlement crack. The results of this research are as follows: 1. At the bond region, austenite grain of the stainless steel side became coarsed and Cr23C6 type carbide was precipitated at the coarsed austenitic grain boundaries. Intergranular Corrosion width(by Straiss test) increased with increasing PWHT temperature and PWHT time.

• Journal of Welding and Joining
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• v.8 no.1
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• pp.2-11
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• 1990

오-스테나이트계 스테인레스강을 용접육성한 강판의 박리균열의 원인에 대하여 강중의 수소거동을 중심으로 고찰해 보았다. 강중의 수소온도 분포를 추정하는데는 확산 방정식을 기초로하여 수치해석이 유력하며 그 기초적사항에 대해 제문헌을 인용하여 설명했으며, 또 시험편에 대하여 계산과 실험치의 결과를 이용하여 비교하였다. 이들로부터 박리균열의 발생에 대한 미시적 임계조건을 도출하여, 이들이 한정된 실험의 범위내이지만 실증할 수 있음을 나타내었다. 그러나 박리균열의 원인의 하나인 잔류응력에 대해서는 아직 불명한 점이 많으나, 냉각속도에 따라 변화하며 그것이 수소농도라고 하는 관점에서 미시적 임계조건에 영향을 미칠 수 있음을 시사하고 있다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.11
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• pp.1377-1382
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• 2011

Recently, alternative and novel energy resources have been developed for use in the future because of the current environmental problems and exhaustion of fossil energy resources. Hydrogen energy has many merits, such as its environmental friendliness, easy storage, and easy production, but it also has disadvantages, in that it is highly combustible and explosive. In this study, a test procedure using a simple SP test under highly pressurized hydrogen gas conditions was established. In order to evaluate its applicability, SP tests were carried out using a stainless steel (SUS316L) sample under atmospheric, pressurized helium, and pressurized hydrogen gas conditions. The results under the pressurized hydrogen gas condition showed fissuring and produced a reduction of the elongation in the plastic instability region due to hydrogen embrittlement, showing the effectiveness of the current in-situ SP test.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.11
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• pp.1011-1020
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• 2017

This study was conducted to investigate the material properties of stainless steel 316L specimens of untreated and UNSM treated material, hydrogen attacked material(100 bar, $300^{\circ}C$ at 120 h) and UNSM treated hydrogen attacked material at room temperature. Results demonstrated that the hydrogen attacked materials showed a tendency toward a slightly decreased fatigue strength, while the hydrogen embrittlement effect was smaller than the S-N curve of conventional untreated material. As compared to untreated material, the fatigue limit of the UNSM treated material increased by 43.8%, while it was 57.1％ higher in the UNSM treated hydrogen attacked material than in untreated hydrogen attacked material. The plastic deformation layer was ${\sim}152{\mu}m$ thick, as confirmed by maps showing the level of local plastic deformation affected by the UNSM treatment in three ways: an image quality map, inverse pole figure map, and kernel average misorientation map captured via electron back scatter diffraction. Owing to hydrogen embrittlement, about 90％ of surface cracks were smaller than the average grain size of $35{\mu}m$.

• Korean Journal of Materials Research
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• v.6 no.9
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• pp.885-899
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• 1996

초강인 AISI 4340강을 85$0^{\circ}C$에서 2시간 동안 오스테나이징 처리 후 수냉하고, 250, 400, $600^{\circ}C$에서 각각 2시간 동안 템퍼링 처리를 하였다. AISI 4340강의 인장 특성은 상온에서 측정되었다. AISI 4340강 위에 니켈 전해도금된 것과 도금되지 않은 시편의 분극 특성이 3.5wt%NaCI 수용액과 인공해수에서 측정되었다. AISI 4340강위에 니켈 전해도금된 시편은 500mV(vs. Ag/AgCI)이하의 전위에서 부식 저항이 크게 향상되었다. 그러나 1A/$\textrm{cm}^2$의 전류밀도에서 30분 이상 니켈 전해도금된 시편은 도금층에 불순물과 기공이 형성되었기 때문에 AISI 4340강의 부식 저항은 감소되었다. AISI 4340강의 수소취화형 응력부식균열을 여러 작용 응력과 음극인가전력에서 U-bend 시편을 이용하여 IN 3.5 wt% NaCI 수용액에서 조사되었고, 수소취화형 응력부식균열 거동은 주사전자현미경으로 조사되었다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.11a
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• pp.65-66
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• 2008

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.97-98
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• 2006

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.573-578
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• 2001

For the corrosion protect ion of the natural gas transmission pipelines, two methods are used, cathodic protection and coating technique. In the case of cathodic protection, defects are embrittled by occurring hydrogen at the crack tip or material surface. It is however very important to evaluate whether cracks in the embrittled area can grow or not, especially in weld metal. In this work, on the basis of elastic plastic fracture mechanics, we performed CTOD test ing with varying test conditions, such as the potential and current density. The CTOD of the base steel and weld metal showed a strong dependence of the test conditions. The CTOD decreased with increasing cathodic potential and current density. The morphology of the fracture surface showed quasi-cleavage. Hydrogen introduced fractures, caused by cathodic overprotection.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1192-1197
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• 2003

The aim of this study is to investigate the hydride embrittlement when the LBB evaluation is carried out for the integrity of PHWR Pressure Tubes. The transverse tensile and CCT tests were performed at three hydrogen concentrations while the test temperatures were changed (RT to $300^{\circ}C$). The specimens were directly machined from the pressure tube retaining original curvature. Both the transverse tensile and the fracture toughness tests showed the hydrogen embrittlement clearly at RT but this phenomenon was disappeared while the test temperature arrived over $250^{\circ}C$. Using the DHC test results, the CCL and LBB time were calculated and compared. The hydride embrittlement behavior at the LBB evaluation was definitely showed.