Ultra-fine (α+ θ) duplex structure formed by cold rolling and annealing of pearlite

Abstract

The ferrite (α)+cementite (θ) microduplex structure formed by heavy cold rolling and annealing of pearlite was studied in an Fe-1.4Cr-1.0C (mass%) alloy. Cold-rolled pearlite structure is inhomogeneous consisting of three components; (1) irregularly bent lamellae (IBL), (2) coarse lamellae with shear band (CLS) and (3) fine lamellae (FL) as was previously reported by the present authors. Misorientation in α is large in the IBL and near the shear band in the CLS. As rolling reduction increases, the proportion of FL increases. By annealing at 973 K after heavy cold rolling, the (α+θ) microduplex structure with α and θ grain sizes less than 0.5 μm is formed. This structure consists of a coarse grain region (d α∼0.4 μm) containing high-angle α boundaries and a fine grain region (d α∼0.2 μm) with low-angle α boundaries by inheriting local orientation distribution in the deformed α structure. The coarse grain region is formed at the deformed region where local misorientation in α is large essentially by recovery under pinning by θ particles. As the annealing is prolonged, the fraction of the coarse grain region increases. The cold-rolled and annealed pearlite exhibits a wide range of strength-ductility balance. © 2005 ISIJ.