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Korean Journal of Metals and Materials > Volume 56(1); 2018 > Article
Korean Journal of Metals and Materials 2018;56(1): 1-7. doi: https://doi.org/10.3365/KJMM.2018.56.1.1
베이나이트계 X70강 수소가압분위기 인장시험의 수소취성균열 전파
최병학1, 장현수1, 이범규1, 김의수2, 김우식3, 백운봉4, 남승훈4
1강릉원주대학교 신소재금속공학과
2한국교통대학교 안전공학과
3한국가스공사 가스기술연구원
4한국표준과학연구원 에너지소재표준센터
Hydrogen Induced Crack Propagation in Bainitic X70 Steel in Hydrogen Pressured Tensile Test
Byung Hak Choe1, Hyeon Su Jang1, Bum Gyu Lee1, Eui Soo Kim2, Woo Sik Kim3, Un Bong Baek4, Sung Hoon Nam4
1Department of Metal and Materials Engineering, Gangneung-Wonju National University, Gangneung 25457, Republic of Korea
2Department of Safety Engineering, Korea National University of Transportation Chungju 27469, Republic of Korea
3Gas Facility Technology Center, KOGAS Research institute, Daegu 41062, Republic of Korea
4Center for Energy Materials Metallurgy, Korea Research Institute of Standards and Science, Daejeon 34113, Republic of Korea
Correspondence  Byung Hak Choe ,Tel: +82-33-640-2365, Email: cbh@gwnu.ac.kr
Received: 27 March 2017;  Accepted: 28 July 2017.  Published online: 1 January 2018.
ABSTRACT
This study investigated hydrogen induced cracking (HIC) of X70 steel, used for gas pipeline material, with a bainitic microstructure. The effect of hydrogen on the steel was investigated by tensiletesting in a high pressure hydrogen atmosphere, using OM, SEM and TEM analyses. The mechanisms of hydrogen-related cracking were represented as stress-induced hydride formation, hydrogen enhanced localized plasticity and decohesion. While hydrogen-trapped sites increased the HIC susceptibility, a kind of surface corrosion occurred in the tensile tested gauge length, due to the high pressured hydrogen atmosphere. The surface corrosion was composed of HIV (hydrogen induced voids) and HIC occurred by linking of the voids. Typical SOHIC (stress oriented HIC) propagated to the inner areas by linking of planar cracks normal to the primary propagation direction. Carbides at grain and lath boundary of the X70 bainite acted as initiation sites of the voids, followed by cracking without any phase transformation. The relation of hydrogen induced defects and grain boundary carbide is discussed in relation to hydrogen corrosion and safe application in hydrogen system.
Keywords: hydrogen induced crack (HIC), hydrogen induced void (HIV), X70 steel, bainite, grain and lath boundary carbide, hydrogen corrosion
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