• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.6
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• pp.325-331
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• 2022

Hydrogen embrittlement in metals has been a serious issue with regard to structural safety. In this study, molecular dynamics simulations revealed that the aggregation of hydrogen atoms at the crack tips suppresses the dislocation emission and thus results in cleavage fracture. A series of molecular dynamics simulations were performed considering factors such as the concentration of hydrogen atoms, loading rate, and diffusion coefficient. We investigated the conditions that minimize hydrogen embrittlement. The simulation results were consistent with the experimental results and used to quantify hydrogen embrittlement.

• Journal of the Korean Institute of Gas
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• v.19 no.1
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• pp.57-63
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• 2015

The hydrogen was charged TRIP steel by electrochemical method under 0.5M $H_2SO_4$ electrolyte and 0.5M NaOH electrolyte with hydrogen charging conditions respectively. The degree of hydrogen embrittlement of TRIP steel was evaluated by using micro Vickers hardness tests. These results showed that the degree of hydrogen embrittlement in acidic electrolyte with hydrogen penetration and hydrogen diffusion through the depth of specimen was more sensitive than its alkaine electrolyte between two type electrolytes. However, it was investigated that micro Vickers hardnesses of surface in acidic electrolyte under two electrolyte were higher than those of alkaine electrolyte. It was thought that in case of hydrogen embrittlement in acid-ice electrolyte, hydrogen charging time was more effective than current density, in case of alkaine electrolyte, hydrogen current density was more effective than charaging time.

• Journal of the Korean Institute of Gas
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• v.19 no.1
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• pp.64-70
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• 2015

In order to evaluate the degree of hydrogen embrittlement of TRIP steels charged with hydrogen according to varying the current density and the charging time under acid and alkaline electrolyte conditions were tested by small punch test. The results of SP test showed that the degree of hydrogen embrittlement at acid electrolyte condition was more effective factor compared to that of alkaline electrolyte condition. Therefore, all of the charging time and the charging current density were at the condition of acid electrolyte appeared as the main factor of the degree of hydrogen embrittlement in the condition of acid electrolyte. But, it was considered that the charging time compared to the charging current density at the condition of alkaline electrolyte was more effective factor to raise the degree of hydrogen embrittlement.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.87-87
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• 2013

복합조직강의 미세조직제어를 통한 자동차용 고강도 강판재의 개발이 주요 연구과제로 있다. 하지만 고강도화에 따라 수소에 의한 지연파괴의 문제점이 있어, 이를 규명하고 해결하기 위한 많은 연구가 함께 이루어지고 있다. 본 연구에서는 연구, 개발되고 있는 복합조직강 중 DP강과 TRIP강의 수소취성에 미치는 미세조직의 영향을 분석하고, 수소주입조건에 따른 수소취성 및 지연파괴 거동에 대하여 조사하고자 하였다. 이를 위해 음극전기분해법을 이용, 주입수소량을 달리하여 주입수소가 복합조직강의 지연파괴에 미치는 영향을 분석하였다. Hydrogen determinator를 통해 시편 내 수소량을 측정하였고, 소형펀치시험에 의한 기계적물성 변화를 조사하였다. 또한 파단부위의 넓이와 깊이를 비교측정하였고, 파단면을 SEM으로 관찰하여 수소지연파괴 거동을 평가하고자 하였다.

• Journal of the Korean Institute of Gas
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• v.18 no.1
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• pp.61-67
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• 2014

Small punch(SP) tests were performed on high strength Dual Phase(DP) steels in order to evaluate the behavior of hydrogen embrittlement. For this purpose, three different kinds of DP steel specimens were charged with hydrogen by electochemical hydrogen charging experiment. After charging with hydrogen, the amount of charged hydrogen was measured. The measurement results showed that amounts of charged hydrogen were largely dependent on the martensite volume fraction of DP steel. The hydrogen charging time of 25 hrs with current densities of 150 and $200mA/cm^2$ was investigated as saturation condition with hydrogen. The analysis results on the SP energy and height of SP bulbs after SP tests showed that those were decreased as the amount of charged hydrogen increased. Fractographs of SP bulbs were observed a brittle fracture mixed with quasi-cleavage fractures, layered structures and clear facets.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2011.05a
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• pp.193-195
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• 2011

강판재 사용에 있어 수소취성현상은 강판재가 고강도화됨에 따라 그 감수성이 커지는 것으로 알려져 있다. 특히 노출강판재의 경우, 표면으로부터 침투해 들어가는 수소에 의한 수소취화 거동에 대한 연구가 필요하다. 본 연구에서는 고강도 DP강을 시험편으로 하여, 음극전기분해법에 의해 수소를 강제주입시킨 후, DP강 표면하 subsurface zone의 수소취화 거동을 평가하고자 하였다. 미소경도분포 측정결과, 수소주입시간이 증가함에 따라 표면하 subsurface zone의 경도 또한 증가하는 것으로 조사되었다. 이는 수소에 의해 표면하 subsurface zone의 경화가 일어나 DP강의 기계적 특성에 영향을 미친것으로 판단된다. 미소경도분포의 측정결과와 미세조직 관찰결과로부터 수소임계침투깊이를 평가하였고, 이를 통해 DP강내 수소확산에 의한 수소임계침투깊이가 존재함을 확인할 수 있었다.

• Journal of the Korean Institute of Gas
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• v.18 no.5
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• pp.40-46
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• 2014

The hydrogen embrittlement degree of 5 type high strength DP steel charged with hydrogen by electrochemical method was evaluated by small punch test(SP test). After SP test, SP absorbed energy was remarkably decreased from 363 kgf-mm to 209 kgf-mm with increasing hydrogen charging time from 5hr to 50hr at DP5 specimen under the $200mA/cm^2$ current density condition. It was investigated that the decrease of hydrogen charging amount and SP absorbed energy according to the increase of current density and hydrogen charging time had a linear relationship. And it also investigated that the change of bulb height appeared by the SP test was decreased from 1.79mm to 1.59mm with the hydrogen charging conditions. It was supposed that it could be used as indicator of the evaluation of hydrogen embrittlement because of the similar trend of the formal results of SP absorbed energy. From the SEM observation of fracture area by crack in bulb, the morphology of fracture surface according to increasement of the hydrogen charging amount was varied with the cleavage mode.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1992-1996
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• 2007

This study focuses on the hydrogen embrittlement of iron tube for fuel line of PEMFC (Proton Exchange Membrane Fuel Cell). PEMFC is operated by feed of hydrogen as a reactant and steam for proton conductivity of membrane. However, the environment with hydrogen and steam occur the hydrogen-induced degradation in BOP system. When iron tube was exposed to hydrogen and steam condition for 24 hours, the oxide layer on the surface was decreased by reduction. When the ambient temperature was 90$^{\circ}C$ micro cracks were found on the surface than any other temperature. The mechanical strength of iron tube was 3% lower than that of non-experiment tube. Maximum tensile stress was decreased 8%.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.2
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• pp.121-127
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• 2013

Tritium was attracted with high energy source in neutron fusion energy systems. A number of research was performed in tritium storage materials. The Korea was raised storage and delivery systems (SDS) of international thermonuclear experimental reactor (ITER) research. However, bottles of SDS would be important because of stability. The bottles have a welding zone, this zone will be vulnerable to hydrogen embrittlement. This zone have a high thermodynamic energy and heat deterioration. Therefore bottles were studied about hydrogen embrittlement to retain stability. The heat treatment of hydrogen was carried under pressure-composition-temperature (PCT) apparatus because of checking at real time. And then, mechanical properties were evaluated by tensile test and hardness test. In results of this study, hydrogen atmosphere condition is very important by tensile test and kinetics test. The samples were evaluated, that is more weak hydrogen pressure, increasing temperature and time. This results could be useful in SDS bottle designs.

• Journal of the Korean Institute of Gas
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• v.14 no.6
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• pp.38-43
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• 2010

According to the lack of resources and the stringency of environmental regulations, a study of the high strength thin plate sheet steels for automobile have been become an important issue for automobile industry. However, the problem of hydrogen embrittlement of high strength sheet steels was concerned with the degradation of mechanical properties. Therefore, we studied the hydrogen behavior of surface layers of 590MPa DP sheet steels on development using by relationship the microstructure of subsurface and the distribution of micro hardnesses. Hydrogen was charged into the specimens using by the cathodic electrolytic method. The behavors of under surface layers were investigated by the observation of microstructures and the micro vickers hardness test with the amount of hydrogen charging with hydrogen charging conditions.