The Influence of Microstructure on the Bendability of Direct Quenched Wear Resistant Steel

The influence of chemical composition and processing parameters on the microstructure and bendability of three thermomechanically rolled and direct-quenched wear resistant steel plates is studied. Overall, the bendability of the steels is good, but there are exceptions that are given special attention. The prior austenite condition and final microstructure is evaluated with respect to subsurface hardness and bendability. The possible effect of inclusions on bendability is taken into account. Away from the surfaces, the samples consisted mainly of auto-tempered martensite. Lowering the finishing rolling temperature (FRT) increased the total rolling reduction below the recrystallization temperature leading to pancaking of austenite and the formation of increasing fractions of polygonal ferrite (PF) and bainite near the plate surface together with an increased intensity of the shear texture component {112}. Strength increased with increasing austenite pancaking provided the microstructure remained mostly martensitic. A homogeneous, largely martensitic microstructure extending across the plate thickness seemed to ensure good bendability. Microstructures that are inhomogeneous with respect to the hardness of the microconstituents, or highly ferritic, or microstructures with an intense {112} shear texture component combined with elongated martensite-austenite (MA) plates in the subsurface layers resulted in the largest minimum useable bending radii.