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다층 FCA 용착금속의 수소취성 저항성 및 확산성 수소 방출 거동
유재석,곽현,이명진,김용덕,강남현,Yoo, Jaeseok,Xian, Guo,Lee, Myungjin,Kim, Yongdeok,Kang, Namhyun 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.6
In this study, constant loading test (CLT) was performed to evaluate the hydrogen embrittlement resistance for multipass FCA weld metals of 600MPa tensile strength grade. The microstructures of weld metal-2 having the smallest carbon equivalent (Ceq=0.37) consisted of grain boundary ferrite and widmanstatten ferrite in the acicular ferrite matrix. The weld metal-1 having the largest Ceq=0.47, showed the microstructures of grain boundary ferrite, widmanstatten ferrite and the large amount of bainite (vol.%=19%) in the acicular ferrite matrix. The weld metal-3 having the Ceq=0.41, which was composed of grain boundary ferrite, widmanstatten ferrite, and the small amount of bainite (vol.%=9%) in the acicular ferrite matrix. Hydrogen desorption spectrometry (TDS) used to analyze the amount of diffusible hydrogen and trapping site for the hydrogen pre-charged specimens electrochemically for 24 hours. With increasing the current density of hydrogen pre-charging, the released amount of diffusible hydrogen was increased. Furthermore, as increasing carbon equivalent of weld metals, the released diffusible hydrogen was increased. The main trapping sites of diffusible hydrogen for the weld metal having a low carbon equivalent (Ceq=0.37) were grain boundaries and those of weld metals having a relatively high carbon equivalent (Ceq: 0.41~0.47) were grain boundaries and dislocation. The fracture time for the hydrogen pre-charged specimens in the constant loading test was decreased as the carbon equivalent increased from 0.37 to 0.47. This result is mainly due to the increment of bainite that is vulnerable to hydrogen embrittlement.
Sourav Kr. Saha,Hyoungjin An(안형진),Byungrok Moon(문병록),Jaeseok Yoo(유재석),Jong Min Park(박종민),Kwang Hee Yun(윤광희),Namhyun Kang(강남현) 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5
The study is devoted towards the investigation of a hydrogen-induced cold cracks (HICC) in welded joints of structural steels. HICC is a well-known phenomenon in structural metals that limit their uses in various valuable applications such as hydrogen transport, marine application, ship building etc. Normally, hydrogen in the weld metal produces hydrogen embrittlement (HE), therefore suppressing the cold crack and HE should be considered. In the present study, multi-pass butt welds were fabricated with low and high heat input conditions (10 kJ/cm and 35 kJ/cm) using various welding fillers having various strength levels as of American Welding Society standard and two base metals (DH36 and S500). HE effects on various specimens were evaluated using the in-situ slow strain rate test (SSRT) and hydrogen permeation test. The HE sensitivity index (HE index) calculated using the SSRT suggests that HE index increased with the strength of welding fillers in low heat input condition. However, reverse phenomenon occurred in high heat input condition. Hydrogen diffusion coefficient (Deff) and reversible hydrogen trap concentration (Crev) calculated using permeation test reflects that Crev increased with the strength level of welding filler. On the other hand, welding specimen fabricated in high heat input condition showed a lower Crev and higher Deff in comparison to the low heat input specimen and thereby decreasing the HE. Microstructure analysis suggests that in low heat input condition, low transformation bainite phase was dominated and vulnerable for HE with increasing strength level of welding filler. On the other hand, high heat input condition produced larger amount of acicular ferrite with increasing strength level and inhibited HE.
Hole Drilling 방법의 열과 표면처리에 의한 잔류응력 계산
유재석,박세만 明知大學校 産業技術硏究所 2008 産業技術硏究所論文集 Vol.27 No.-
Residual stresses deteriorate strength of materials adversely affecting quality of industrial products. A removable or a reduction of the residual stresses is an essential procedure in successful product developments. Effective and convenient methods are necessary for detection and evaluation of the residual stresses. In this investigation Hole Drilling Method is chosen for identification and a quantitative determination of the residual stresses of specimen in different groups under three heat and surface treatment conditions. The specimen in the first group is standard reference specimen without the heat treatment. The ones in the second group is carburized specimen with the surface treatment. In another group specimen is exposed to high frequency electric power to achieve the desired heat treatment condition. The residual stresses of metal alloys are evaluated subsequently with an analysis for the specimens prepared under a variety of heat and surface conditions, revealing complex effects of the treatments on the residual stresses as well as on properties of the materials. The amount of the residual stresses comes in that order of the specimen with the high frequency, with the carburized treatment and the specimen without the heat treatment. The quantitative analysis as well as experience suggests reliable and effective processes to eliminate or reduce the residual stresses. Also, during process of pipe welding a high level of residual stresses is observed to develop and its level increases non-uniformly with a depth into a hole. Based on the experimental results and the analysis, proper treatment conditions can be predicted to reduce or even completely eliminate the residual stresses, leading to an establishment of reliable methods for a control of the residual stresses.