ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
Mechanical Properties
Hydrogen Embrittlement and Local Characterization at Crack Initiation Associated with Phase Transformation of High-strength Steel Containing Retained Austenite
Taku NagaseTakuya ItoYoshiro NishimuraHiroshi SuzukiKenichi Takai
Author information
JOURNALS OPEN ACCESS FULL-TEXT HTML

Volume 58 (2018) Issue 2 Pages 349-358

Details
Full Text-HTML Download PDF (3098K) Email to author Contact us
Abstract

States of hydrogen present in high-strength steels for use as bearing steel SUJ2 and hydrogen embrittlement susceptibility were examined using thermal desorption analysis (TDA) and tensile tests. SUJ2 specimens containing the retained austenite phase (γR) in the martensitic phase exhibited three hydrogen desorption peaks in the TDA profile. Two of the peaks desorbed at higher temperatures decreased with a decreasing amount of γR, indicating they corresponded to desorption associated with γR. Fracture strength in the presence of hydrogen increased with a decreasing amount of γR and with an increasing strain rate. For the specimens containing γR and hydrogen, a flat facet at the crack initiation site and a quasi-cleavage (QC) fracture in the initial crack propagation area were observed on the fracture surface. Local characterization using electron back-scattered diffraction (EBSD) revealed that the flat facet on the fracture surface corresponded not to γR but to strain-induced martensite. In addition, the facet was on the {112} plane of martensite, which is the slip plane or deformation twin plane of body-centered-cubic metals. The reason for high hydrogen embrittlement susceptibility of the specimens containing γR was attributed to the strain-induced phase transformation at the crack initiation site of the flat facet and in the initial crack propagation area of the QC fracture. Furthermore, the strain rate dependency of hydrogen embrittlement susceptibility is presumably ascribable to local plastic deformation, i.e., the interaction between dislocations and hydrogen.

Crack initiation and propagation areas of SUJ2 specimen with hydrogen after a tensile test at a strain rate of 2×10−6s−1 at 30°C. (a) Image of crack initiation on the fracture surface observed by SEM. (b) IPF map of the flat facet at the crack initiation site on the fracture surface analyzed by EBSD. The flat facet is on the {112} plane of martensite which is the slip plane in the bcc lattice. (c) IPF map of a cross section near the flat facet at the crack initiation site analyzed by EBSD. The flat facet is on the {112} plane of martensite, which is the slip plane in the bcc lattice. (d) Phase map of a cross section near the flat facet at the crack initiation site analyzed by EBSD. The phase of the flat facet and surrounding area is not retained austenite but martensite. (Online version in color.) Fullsize Image
Information related to the author
© 2018 by The Iron and Steel Institute of Japan
Previous article Next article

Altmetrics
Recently visited articles
feedback
Top