• 한국산업융합학회 논문집
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• 제22권1호
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• pp.11-20
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• 2019

This study dealt with the tensile strength characteristics of stainless steel 304L steel by hydrogen charging. Especially, the effect of hydrogen charging time on the tensile strength and ductility of 304L stainless steels was evaluated, in conjunction with the observation of their fracture surfaces. The tensile properties of hydrogen-charged 304L stainless steels were also investigated with the variation of tensile loading speeds. The hydrogen amount of 304L stainless steels obviously increased with the increase of hydrogen charging time. The tensile properties of 304L stainless steels were clearly affected by the short term charging of hydrogen. In particular, the elongation of 304L stainless steels decreased with increasing hydrogen charging time, due to the hydrogen embrittlement. It was also found that the tensile properties of hydrogen-charged 304L stainless steels were very sensitive to the crosshead speed for tensile loading.

• 열처리공학회지
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• 제36권6호
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• pp.382-388
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• 2023

In this study, hydrogen embrittlement (HE) behavior of a SA-723 steel via controlling gaseous hydrogen pre-charging condition has been analyzed. The gaseous hydrogen charging of the SA-723 steel was performed under a constant pressure of 20 MPa of gaseous H₂ at 150℃ and 300℃ for 2 and 6h, and TDS, SSRT and Charpy tests were conducted to analyze the hydrogen embrittlement (HE) behavior of the SA-723 steel. Furthermore, prior to commencing the test, these specimens were coated with Zn to prevent hydrogen from diffusing out of a specimen during the tests. The TDS results showed that the 300℃-6h and 150℃-6h charged steels contain larger amounts of hydrogen than 300℃-2h and 150℃-2h charged steel. The SSRT and Charpy test results also showed the similar trends that the mechanical properties of the steels deteriorate as the amount of hydrogen charged in the steel increases. Therefore, this study suggests that, for SA-723 steel, the charging time parameter is more effective to charge more amount of hydrogen into SA-723 steel, rather than the charging temperature.

• 한국재료학회지
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• 제20권11호
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• pp.581-585
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• 2010

High strength sheet steels for automobile are seriously compromised by hydrogen embrittlement. This issue has been continuously studied, but the field of interest, which lies between microstructural characteristics and hydrogen behavior with hydrogen charging, has not yet been thoroughly investigated. This study was done to investigate the behavior of hydrogen according to the hydrogen volume fraction on 590MPa grade DP steels, which are developed under hydrogen charging conditions as high strength sheet steels for automobiles. The penetration depths and the mechanical properties, according to charging conditions, were investigated through the distribution of micro-hardness and the microstructural observation of the subsurface zone. It was found that the amount of hydrogen trapping in 590MPa DP steels was related to the austenite volume fraction. It was confirmed that the distribution of micro-hardnesses according to the depth of the subsurface zone under the free surface showed the relationship of the depth of the hydrogen saturation between the charging conditions.

• 한국수소및신에너지학회논문집
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• 제30권4호
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• pp.356-361
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• 2019

Since the government announced the roadmap to revitalize the hydrogen economy, we are constantly making the effort to expand the use of fuel cell electric vehicles (FCEV) and hydrogen charging stations. There is however a significant issue to build and operate the hydrogen charging station due to the lack of the profit model. Many researchers believe that the supply of FCEV will be increased in the near future and finally ensure the economy of hydrogen charging stations. This study shows that the sales changes of hydrogen gas and consumption patterns by the operation of the hydrogen charging station in Changwon City. The results will be used as the evidence to support for operating the hydrogen charging station by private businesses and the validity of additional establishment of hydrogen charging stations.

• 한국수소및신에너지학회논문집
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• 제32권3호
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• pp.163-171
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• 2021

Securing energy sources is a key element essential to economic and industrial development in modern society, and research on renewable energy and hydrogen energy is now actively carried out. This research was conducted through experiments and analytical methods on the hydrogen filling process in the hydrogen storage tank of the hydrogen charging station. When low-temperature, high-pressure hydrogen was injected into a high-pressure tanks where hydrogen is charged, the theoretical method was used to analyze the changes in temperature and pressure inside the high-pressure tanks, the amount of hydrogen charge, and the charging time. The analysis was conducted in the initial vacuum state, called the First Cycle, and when the residual pressure was present inside the tanks, called the Second Cycle. As a result of the analysis, the highest temperature inside the tanks in the First Cycle of the high-pressure tank increased to 442.11 K, the temperature measured through the experiment was 441.77 K, the Second Cycle increased to 397.12 K, and the temperature measured through the experiment was 398 K. The results obtained through experimentation and analysis differ within ±1%. The results of this study will be useful for future hydrogen energy research and hydrogen charging station.

• 대한기계학회논문집A
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• 제26권6호
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• pp.1107-1113
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• 2002

This study presents the hydrogen emblittlement in the metal, which decreases the ductility and then induces the brittle fracture. The contribution deals with the effect of strain rate and notch geometry on hydrogen emblittlement of 1.25Cr-0.5Mo and 2.25Cr-1Mo steels, which are in use at high pressure vessel. Smooth and notched specimens were examined to obtain the elongation and tensile strength. For charging the hydrogen in the metal, the cathodic electrolytic method was used. In this process, current density is maintained constant. The amount of hydrogen penetrated in the specimen was detected by the hydrogen determenator(LECO RH404) with the various charging time. The distribution of hydrogen concentration penetrated in the specimen was obtained by finite element analysis. The amount of hydrogen is high in smooth specimen and tends to concentrate in the vicinity of surface. The elongation and tensile strength decreased with the passage of charging time in 1.25Cr-0.5Mo and 2.25Cr-1Mo steels. The elongation increased and tensile strength decreased as strain rate increased. As a result of this study, it is supposed that 1.25Cr-0.5Mo steel is more sensitive than 2.25Cr-lMo steel in hydrogen embrittlement. Hydrogen embrittlement susceptibility of notched specimen after hydrogen charging is more remarkable than that of smooth specimen.

• 한국가스학회지
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• 제18권1호
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• pp.61-67
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• 2014

고강도 DP강의 수소취성 거동을 소형펀치시험을 통해 평가하였다. 이를 위해 첨가원소가 각기 다른 3종의 DP강 시험편에 전기화학적 방법으로 수소를 강제 주입시켰다. 수소주입 후, 수소주입량을 측정하였다. 수소주입량은 마르텐사이트 부피분율에 크게 의존하는 것으로 조사되었다. 전류밀도 150, $200mA/cm^2$ 조건에서 25시간이 포화상태에 도달하는 수소주입조건으로 나타났다. SP시험 후 SP에너지와 SP bulb 형상을 비교한 결과, 수소주입량의 증가에 따라 SP에너지와 SP bulb 높이가 감소하는 것으로 나타났다. 또한 SP bulb 파단면에서는 뚜렷한 facet와 층상형태의 벽개 파단면이 관찰되어 수소취성화를 관찰할 수 있었다.

• Archives of Metallurgy and Materials
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• 제67권4호
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• pp.1491-1495
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• 2022

The present research deals with the effect of pre-strain on the hydrogen embrittlement behavior of intercritically annealed medium-Mn steels. A slow strain-rate tensile test was conducted after hydrogen charging by an electrochemical permeation method. Based on EBSD and XRD analysis results, the microstructure was composed of martensite and retained austenite of which fraction increased with an increase in the intercritical annealing temperature. The tensile test results showed that the steel with a higher fraction of retained austenite had relatively high hydrogen embrittlement resistance because the retained austenite acts as an irreversible hydrogen trap site. As the amount of pre-strain was increased, the hydrogen embrittlement resistance decreased notably due to an increase in the dislocation density and strain-induced martensite transformation.

• 한국가스학회지
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• 제18권5호
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• pp.40-46
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• 2014

전기화학적 방법으로 수소 주입시킨 5종의 고강도 DP강의 수소취성화 정도를 소형펀치시험으로 평가하였다. SP시험 후 SP흡수에너지는, $200mA/cm^2$ 전류밀도 조건의 DP5 시험편에서 수소주입시간이 5hr에서 50hr으로 증가함에 따라 363 kgf-mm에서 209 kgf-mm로 현저히 저하되는 것을 알 수 있었다. 전류밀도와 수소주입시간의 증가에 따라 수소주입량과 SP에너지 저하는 선형적인 상관관계를 갖는 것으로 조사되었다. 또한 SP시험에 의해 생성된 bulb의 높이 변화는 1.79 mm에서 1.59 mm로 낮아지는 것으로 조사되었다. 이는 앞서의 SP 흡수에너지 결과와 유사한 경향으로 나타나, 수소취성평가의 지표로 활용 가능할 것으로 사료된다. 균열 파단부위의 SEM 관찰에서 수소주입량 증가에 따라 파단면은 취성파면 형태로 진행되는 것을 확인할 수 있었다.

• 한국수소및신에너지학회논문집
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• 제30권6호
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• pp.479-484
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• 2019

Environmental problems were related to human life from second industrial revolution. Recently, peoples are interested in solving global warming problem and improving air quality. Therefore, we request for eco-friendly vehicles such as fuel cell electric vehicles using eco-friendly hydrogen energy. In order to reduce particulate matter in Korea, we have established a plan to promote the deployment of eco-friendly vehicles. In this paper, we analyzed the average monthly charging status and hydrogen consumption by introducing fuel cell bus.