| In this paper,the Nb-microalloyed CFB/M multiphase steel is tested.Using the thermal expansion apparatus,continuous cooling transformation curve of the CFB/M multiphase steel and Nb-microalloyed CFB/M multiphase steel was determined with different state of Nb.The microstructures of the transformation products of the cooled austenite in the different cooling rate were observed by scanning electron microscope. The effect of the NbC precipitation in austenite and ferrite on the prior austenite grain size is also analyzed.The experiment results will provide guidance to optimize the microstructures of the Nb-microalloyed CFB/M multiphase steel.It has been confirmed that NbC particle rises the transformation temperature of proeutectoid ferrite and bainite, while Nb as solute atoms in austenite makes the transformation temperature of proeutectoid ferrite and bainite decreased.In both condition Nb element decreases the amount of proeutectoid ferrite.The prior austenite grain refinement is effected by the precipitation NbC in austenite within the range from 870 to 930℃and in martenite with tempering at 650℃.The action of NbC precipitation with phase transformation cause finer austenite grain.Nb-microalloyed CFB/M multiphase steel can obtain CFB/M microstructure in a wide cooling rate range.
|
PDF Full Text Request