Effect of Nb on Microstructure Evolution in Cold Rolled Dual-Phase Steels:Interaction of Recovery, Recrystallization and Phase Transformations

摘要

The effects of Nb addition, individually and in combination with Ti, were evaluated over a range of coiling temperatures. Coiling temperature influences the ratio of soluble and precipitated Nb in the hot rolled steel containing 0.08 % C and 2.2 % Mn. Nb bearing precipitates can co-precipitate on TiN and impact the microstructure and mechanical properties of the steel after annealing treatment. Microstructure characterization revealed that recovery and recrystallization processes preceded austenite formation. The effects of Nb on austenite formation in cold rolled steels during heating and isothermal holding and on austenite decomposition during subsequent cooling were investigated using dilatometry. The addition of Nb retarded ferrite recrystallization starting temperature, but had no significant effect on the starting temperature of austenite formation during heating. The Nb addition also accelerated austenite formation once the transformation started, and was beneficial for the formation of a finer and homogeneous microstructure.