• Nuclear Engineering and Technology
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• 제53권9호
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• pp.2982-2989
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• 2021

One of the consequences of the 475 ℃ embrittlement of duplex stainless steels is the reduction of the resistance to localized corrosion. Therefore, the detection of this type of embrittlement before the material exhibits significant loss in toughness, and corrosion resistance is important to ensure the structural integrity of critical components under corrosion threats. In this research, conductivity measurements are performed using the alternating current potential drop (ACPD) technique with using a portable four-point probe as a nondestructive evaluation (NDE) method for detecting the embrittlement in a 2507 (UNS S32750) super duplex stainless steel (SDSS) aged at 475 ℃ from as-received condition to 300 h. The electric conductivity results were compared against two electrochemical tests namely double loop electrochemical potentiokinetic reactivation (DL-EPR) and critical pitting temperature (CPT). Mechanical tests and the microstructure characterized using scanning electron microscopy (SEM) imaging are conducted to track the progress of embrittlement. It is shown that the electric conductivity correlates with the changes in impact energy, microhardness, and CPT corrosion tests result demonstrating the feasibility of the four-point probe as a possible field-deployable method for evaluating the 475 ℃ embrittlement of 2507 SDSS.

• 열처리공학회지
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• 제31권6호
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• pp.283-289
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• 2018

This present study deals with the hydrogen embrittlement properties of austenitic Fe-30Mn-0.2C(-1.5Al) high-manganese steels for cryogenic applications. They were electrochemically charged with hydrogen and then subjected to tensile tests for evaluating hydrogen embrittlement behavior. Tensile test results showed that after hydrogen charging the tensile strength and elongation of the Al-free steel were more remarkably decreased with increasing current density when compared to the Al-added steel. After hydrogen charging of the Al-added steel, it was found that the measured hydrogen content was small and silver particles were relatively less decorated. Therefore, the Al-added steel has a superior hydrogen embrittlement resistance to the Al-free steel because the addition of Al suppresses the injection of hydrogen during electrochemical hydrogen charging.

• 한국재료학회지
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• 제22권1호
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• pp.29-34
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• 2012

The hydrogen embrittlement of high strength steel for automobiles was evaluated by small punch (SP) test. The test specimens were fabricated to be 5 series, having various chemical compositions according to the processes of heat treatment and working. Hydrogen charging was electrochemically conducted for each specimen with varying of current density and charging time. It was shown that the SP energy and the maximum load decreased with increasing hydrogen charging time in every specimen. SEM investigation results for the hydrogen containing samples showed that the fracture behavior was a mixed fracture mode having 50% dimples and 50% cleavages. However, the fracture mode of specimens with charging hydrogen changed gradually to the brittle fracture mode, compared to the mode of other materials. All sizes and numbers of dimples decreased with increasing hydrogen charging time. These results indicate that hydrogen embrittlement is the major cause of fracture for high strength steels for automobiles; also, it is shown that the small punch test is a valuable test method for hydrogen embrittlement of high strength sheet steels for automobiles.

• 대한기계학회논문집A
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• 제27권3호
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• pp.455-463
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• 2003

The aim of this study is to investigate the hydrogen embrittlement of Zr-2.5Nb CANDU pressure tube at room temperature. The transverse tensile and fracture toughness tests were performed at various hydrogen concentrations using transverse tensile specimens and CCT (curved compact tension) specimens. These specimens were directly machined from the pressure tube retaining original curvatures. Based on the results of these tests. the hydrogen embrittlement phenomenon was clearly observed and fracture toughness parameters of Zr-2.5Nb pressure tube materials such as, $K_{J(0.2)}$.$J_{ML}$.dJ/da, were dramatically decreased with the increasement of the hydrogen concentration. From microscopic observation by SEM and TEM, it was also revealed that various shapes dimples, fissures and quasi-cleavage were found at the hydrogen-absorbed materials with hydrides while traditional shape dimples were generally located at the as-received materials Through the comparison of the hydride and fissure lengths with the hydrogen concentration the new evaluation method of hydrogen embrittlement was suggested.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.93-98
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• 2000

Unpredictable failures can occur due to the DHC (delayed hydride cracking) or the degradation of fracture toughness by hydride embrittlement in CANDU pressure tube which can result from the absorption of hydrogen or deuterium in the high temperature coolant. To investigate the hydride embrittlement of CANDU Zr-2.5Nb pressure tube, the transverse tensile test and the fracture toughness test were performed from room temperature to $300^{\circ}C$ using three different specimens which have an AR (As Received), 100, and 200 ppm hydrogen. As the amount of absorbed hydrogen was increased, the transverse yield strength and the ultimate tensile strength were also increased. In addition, as the test temperature became higher they were decreased linearly. While, at room temperature, the hydrogenbsorbed specimens represented the embrittlement which resulted in sudden decreasing of fracture toughness, the fracture characteristics became ductile such as AR specimen at high temperatures. Through the observation of fracture surface using SEM, it was found that the stress state of mixed mode could be related to the fissure which was believed to decrease the global fracture toughness.

• 소성∙가공
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• 제29권4호
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• pp.211-217
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• 2020

This paper presents a study on the hydrogen embrittlement of Ti-6Al-4V alloys with different microstructures depending on annealing treatment. They were electrochemically charged with hydrogen and subjected to tensile tests to investigate hydrogen embrittlement behavior. Tensile test results showed that the elongation of Ti-6Al-4V alloy specimens was remarkably decreased with increasing the volume fraction of β phase after hydrogen charging. This is because the β phase with a relatively low diffusivity tends to easily form a hydride at grain boundaries during electrochemical hydrogen charging. After hydrogen charging of the Ti-6Al-4V alloy specimen, it found that silver particles were decorated mostly at the grain boundary, and coarser silver particles were usually formed in the specimen annealed at 950 ℃. Therefore, the specimen having higher β phase fraction shows a poor hydrogen embrittlement resistance because the β phase promotes the formation of coarse hydride during electrochemical hydrogen charging, which leads to a large decrease in ductility.

• 열처리공학회지
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• 제23권3호
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• pp.156-162
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• 2010

The modified 9Cr-1Mo steel (P91 steel) is very popular as a boiler tube material of the USC (Ultra-Supercritical) power plants. The steels were tempered in the temperature range of 400 to $650^{\circ}C$ and the mechanical tests, such as impact and hardness tersts were performed at the room temperature for the tempered steels. A drop in the impact value (embrittlement) and the hardeness increase were simultanously observed in the range of temperature between $475^{\circ}C$ and $600^{\circ}C$, particularly at $550^{\circ}C$. TEM observation shows the hardening was caused by $M_2C$, resulting in the embrittlement. And the maximum volume fraction of $M_3C$ was also observed at $550^{\circ}C$, Therefore, the embrittlement seems to be caused by both the $M_2C$ and $M_3C$.

• 한국전산구조공학회논문집
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• 제35권6호
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• pp.325-331
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• 2022

금속의 취성화는 수소와 접촉하는 구조물을 안정적으로 설계하는데 있어서 큰 문제가 되어왔다. 본 논문에서는 분자동역학 해석을 통해 균열선단 주변에 모인 수소원자들이 전위 이동 현상을 억제하고, 이로 인해 벽개 파괴 현상이 발생하는 것을 확인하였다. 다양한 수소 농도, 하중 속도, 수소 확산 속도 등을 바꾸어가며 분자동역학 해석을 수행하였고, 이에 따른 수소 취성화를 최소화시킬 수 있는 조건들을 조사하였다. 분자동역학 해석 결과는 기존의 실험결과와 잘 일치하였으며 이를 바탕으로 수소 취성화 현상을 정량화하여 평가하였다.

• Corrosion Science and Technology
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• 제22권4호
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• pp.232-241
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• 2023

The mechanical properties of the hydrogen valve responsible for supplying and blocking hydrogen gas in a hydrogen fuel cell electric vehicle (FCEV) were researched. Mechanical properties by hydrogen embrittlement were investigated by coating chromium nitride (CrN) and titanium nitride (TiN) on aluminum alloy by arc ion plating method. The coating layer was deposited to a thickness of about 2 ㎛, and a slow strain rate test (SSRT) was conducted after hydrogen embrittlement to determine the hydrogen embrittlement resistance of the CrN and TiN coating layers. The CrN-coated specimen presented little decrease in mechanical properties until 12 hours of hydrogen charging due to its excellent resistance to hydrogen permeation. However, both the CrN and TiN-coated specimens exhibited deterioration in mechanical properties due to the peeling of the coating layer after 24 hours of hydrogen charging. The specimens coated at 350 ℃ presented a significant decrease in ultimate tensile strength due to abnormal grain growth.

• Corrosion Science and Technology
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• 제22권4호
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• pp.221-231
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• 2023

Interest in aluminum alloys for the hydrogen valves of fuel cell electric vehicles (FCEVs) is growing due to the reduction in fuel efficiency by the high weight. However, when an aluminum alloy is used, deterioration in mechanical characteristics caused by hydrogen embrittlement and wear is regarded as a problem. In this investigation, the aluminum alloy used to prevent hydrogen embrittlement was subjected to surface treatments by performing hard anodizing and plasma ion nitriding processes. The hard anodized Al alloy exhibited brittleness in which the mechanical characteristics rapidly deteriorated due to porosity and defects of surface, resulting in a decrease in the ultimate tensile strength and modulus of toughness by 15.58 and 42.51%, respectively, as the hydrogen charging time increased from 0 to 96 hours. In contrast, no distinct nitriding layer in the plasma ion-nitrided Al alloy was observed due to oxide film formation and processing conditions. However, compared to 0 and 96 hours of hydrogen charging time, the ultimate tensile strength and modulus of toughness decreased by 7.54 and 13.32%, respectively, presenting excellent resistance to hydrogen embrittlement.