Morphology and Formation Mechanism of Bainite Carbide of High Carbon Chromium-Molybdenum Steel

The morphology and formation mechanism of bainite carbide of 9Cr2Mo and GCr15 steels were studied by metallographic microscope and QUANTA-400 environmental scanning electron microscope after they were austenitized and then quenched at moderate temperature respectively.The results show that upper bainite of 9Cr2Mo and GCr15 steels is feathery and the upper bainite carbide is lamellar or clavate.The upper bainite carbide is distributed between the subunits of bainite ferrites and nearly parallel to the axis of bainite ferrites.Lower bainite of 9Cr2Mo and GCr15 steels is bamboo leaf-like and the lower bainite carbide is shred-like or fibred.The lower bainite carbide is distributed between the bainite ferrites,furthermore,the angles between lower bainite carbonide and the principal axis of the lower bainite ferrites are unequal.Bainitie carbide nucleates at the phase interface of γ/α and grows towards austenite and the subunits of bainite ferrites,which is diffusion transformation in the atom heat activation transition mode.