Hot Deformation Of Hypereutectoid Steels

The hot working of hypereutectoid steel is traditionally difficult because of the presence of carbides, but judicious processing enhances the hot ductility. In stable austenite, the dissolved C reduces flow stress and facilitates dynamic recrystallization (DRX), but imposes an upper temperature limit due to grain boundary burning. In alloy steels, strength is increased and workability reduced by undissolved carbides and by metallic solute. In the intercritical domain (plain C), Fe3C tends to form along the austenite grain boundaries inhibiting DRX and inducing cracks. When deformation is imposed continually during cooling, however, the Fe,C is dispersed and is able to deform. An increase in the volume fraction of alloy carbides on cooling (notably in tool steels) reduces workability markedly. Constitutive equations for flow stress are assessed.