ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Regular Article
Influence of Deformation Temperature on γ-α Phase Transformation in Nb–Ti Microalloyed Steel during Continuous Cooling
Jun ChenFan LiZhen Yu LiuShuai TangGuo Dong Wang
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2013 Volume 53 Issue 6 Pages 1070-1075

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Abstract

The dynamic continuous-cooling-transformation (CCT) diagrams of Nb–Ti microalloyed steel for four different deformation temperatures of 850, 900, 950 and 975°C were plotted by means of a combined method of dilatometry and metallography. The influence of deformation temperature on continuous cooling transformation behavior and transformation microstructure was elucidated. The reason that the polygonal ferrite transformation field is shifted to the right and moved down as the deformation temperature is increased and the progress of transformation for lowest continuous cooling rate of 0.5°C/s was obviously retarded at the lowest deformation temperature of 850°C was discussed in details based on transformation kinetics and strain-induced precipitation kinetics, respectively. Moreover, the polygonal ferrite grain size for lowest continuous cooling rate of 0.5°C/s can be significantly refined from approx. 15.4 μm to 9.4 μm as the deformation temperature is reduced from 975°C to 850°C. In addition, the empirical equation to calculate γ-α phase transformation start temperature was established, and the calculated Ar3 temperatures are in good agreement with measured ones.

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© 2013 by The Iron and Steel Institute of Japan
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