TY - JOUR
T1 - Factors affecting hydrogen-assisted cracking in a commercial tempered martensitic steel
T2 - Mn segregation, MnS, and the stress state around abnormal cracks
AU - Sasaki, Daisuke
AU - Koyama, Motomichi
AU - Noguchi, Hiroshi
N1 - Publisher Copyright:
© 2015 Elsevier B.V.
PY - 2015/7/9
Y1 - 2015/7/9
N2 - The purpose of this paper is to reveal the dominant factors affecting tensile fracture under a hydrogen gas atmosphere. Tensile tests were conducted in hydrogen gas with circumferentially-notched specimens of a commercial tempered martensitic steel. Two specimens were exposed to hydrogen gas for 48. h before tensile testing; the other two specimens were not pre-charged. Longitudinal cracks along the loading direction and a transverse crack perpendicular to the loading direction were observed on a cross section of the non-charged specimen, but there was only one small crack on a cross section of the pre-charged specimen. Electron back scatter diffraction, energy dispersive X-ray spectrometry and finite element method analyses were applied to clarify the relationships among the longitudinal crack, Mn segregation, microstructures of martensitic steel and hydrogen. As a result, it has been demonstrated that Mn segregation and MnS promote hydrogen-assisted cracking in the tempered martensitic steel, causing the longitudinal cracking which is a mechanically non-preferential direction in homogeneous situations. More specifically, we have shown that the role of the Mn segregation is to promote the hydrogen-enhanced decohesion effect (HEDE), which is particularly important for crack propagation in the present case. These considerations indicate that the presence of Mn is crucially important for hydrogen-assisted cracking associated with hydrogen-enhanced localized plasticity (HELP) as well as HEDE.
AB - The purpose of this paper is to reveal the dominant factors affecting tensile fracture under a hydrogen gas atmosphere. Tensile tests were conducted in hydrogen gas with circumferentially-notched specimens of a commercial tempered martensitic steel. Two specimens were exposed to hydrogen gas for 48. h before tensile testing; the other two specimens were not pre-charged. Longitudinal cracks along the loading direction and a transverse crack perpendicular to the loading direction were observed on a cross section of the non-charged specimen, but there was only one small crack on a cross section of the pre-charged specimen. Electron back scatter diffraction, energy dispersive X-ray spectrometry and finite element method analyses were applied to clarify the relationships among the longitudinal crack, Mn segregation, microstructures of martensitic steel and hydrogen. As a result, it has been demonstrated that Mn segregation and MnS promote hydrogen-assisted cracking in the tempered martensitic steel, causing the longitudinal cracking which is a mechanically non-preferential direction in homogeneous situations. More specifically, we have shown that the role of the Mn segregation is to promote the hydrogen-enhanced decohesion effect (HEDE), which is particularly important for crack propagation in the present case. These considerations indicate that the presence of Mn is crucially important for hydrogen-assisted cracking associated with hydrogen-enhanced localized plasticity (HELP) as well as HEDE.
UR - http://www.scopus.com/inward/record.url?scp=84930946084&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84930946084&partnerID=8YFLogxK
U2 - 10.1016/j.msea.2015.05.083
DO - 10.1016/j.msea.2015.05.083
M3 - Article
AN - SCOPUS:84930946084
SN - 0921-5093
VL - 640
SP - 72
EP - 81
JO - Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing
JF - Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing
ER -