Ultra-fine (.ALPHA.+.THETA.) 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 973K 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 (dα∼0.4 μm) containing high-angle α boundaries and a fine grain region (dα∼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.