Journal
ACTA METALLURGICA SINICA-ENGLISH LETTERS
Volume 30, Issue 3, Pages 238-249Publisher
CHINESE ACAD SCIENCES, INST METAL RESEARCH
DOI: 10.1007/s40195-016-0496-9
Keywords
Ni-containing cryogenic steel; Microstructure; Reversed austenite; Impact toughness; Crack propagation
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Funding
- Fundamental Research Funds for the Central Universities [N120807001]
- National High-tech Research and Development Program of China (863 Program) [2007 AA03Z504]
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It has been widely demonstrated that addition of Ni in low-carbon steels can effectively improve the cryogenic toughness, but the mechanism behind it has yet to be clarified. In the present work, the evolutions of microstructure and mechanical properties after quenching and tempering for Ni-containing cryogenic steels with different Ni contents (3.5-9 wt%) were investigated. The results showed that after quenching and tempering, the Ni-containing cryogenic steels were composed of tempered martensite and reversed austenite. The volume fraction of reversed austenite has increased from 0 up to 6.3% when the Ni content increases from 3.5% to 9%. The Charpy impact tests indicated that the lowtemperature toughness was markedly improved with the increase in Ni content, which can be correlated with the increase in reversed austenite amount. The main contribution of reversed austenite to the toughness lies in: (1) the elimination of cementite precipitates improved the plastic deformation capacity of matrix, and (2) the crack propagation is hindered through plastic deformation.
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