Journal
JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY
Volume 45, Issue -, Pages 1-14Publisher
JOURNAL MATER SCI TECHNOL
DOI: 10.1016/j.jmst.2019.03.012
Keywords
Low alloy Cr-Mo-V steel; Rare earth; Microstructure; Impact toughness; Granular bainite; Martensite-austenite constituents
Funding
- National Natural Science Foundation of China [U1708252]
- Youth Innovation Promotion Association, Chinese Academy of Sciences [2013126]
- Innovation Foundation of Graduate School of Institute of Metals Research, Chinese Academy of Sciences, China
- Liao Ning Revitalization Talents Program [XLYC 1807022]
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The effects of rare earth (RE) on the microstructure and impact toughness of low alloy Cr-Mo-V bainitic steels have been investigated where the steels have RE content of 0 to 0.048 wt.%. The results indicate that the normalized microstructures of the steels are typical granular bainite (GB) composed primarily of bainitic ferrite and martensite and/or austenite (M-A) constituents. The M-A constituents are transformed into ferrite and carbides and/or agglomerated carbides after tempering at 700 degrees C for 4 h. The addition of RE decreases the onset temperature of bainitic transformation and results in the formation of finer bainitic ferrite, and reduces the amount of carbon-rich M-A constituents. For the normalized and tempered samples, the ductile-to-brittle transition temperature (DBTT) decreases with increasing RE content to a critical value of 0.012 wt.%. Lower DBTT and higher upper shelf energy are attributed to the decreased effective grain size and lower amount of coarse agglomerated carbides from the decomposition of massive M-A constituents. However, the addition of RE in excess of 0.012 wt.% leads to a substantial increase in the volume fraction of large-sized inclusions, which are extremely detrimental to the impact toughness. (C) 2020 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.
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