Acta Metallurgica Sinica (English Letters) ›› 2017, Vol. 30 ›› Issue (3): 238-237.DOI: 10.1007/s40195-016-0496-9

Special Issue: 2017年钢铁材料专辑

• Orginal Article • Previous Articles     Next Articles

Correlations of Ni Contents, Formation of Reversed Austenite and Toughness for Ni-Containing Cryogenic Steels

Meng Wang1(),Zhen-Yu Liu1(),Cheng-Gang Li1   

  1. 1 State Key Laboratory of Rolling and Automation,Northeastern University, Shenyang 110819, China
  • Received:2016-10-08 Online:2017-03-16 Published:2017-05-16

Abstract:

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 low-temperature 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.

Key words: Ni-containing cryogenic steel, Microstructure, Reversed austenite, Impact toughness, Crack propagation