TEM characterization of HY-80 steel microstructures after small plastic strains

Abstract

A systematic TEM characterization of HY-80 steel microstructures resulting from various thermomechanical treatments has been completed. The as-received material—50 mm thick plate—was water quenched and tempered. These quenched and tempered materials were given 0.03, 0.063 and 0.075 plastic strain by tensile loading in the long transverse direction. TEM thin foil examination revealed various microconstituents in the as-quenched as well as in the quenched and tempered materials. The microconstituents were typically highly dislocated lath martensite (lath width ⋍ 0.2 μm) with carbide in it, autotempered martensite, typical tempered bainite/martensite duplex structure, and three distinct types of bainite distinguished by the morphology of cementite precipitation within the ferrite laths. It was also found that the shape and size of the precipitated carbide/cementite particles were different in the various microconstituents. Small plastic strains produced tangling of dislocations around the precipitated cementite and tempered carbide/cementite particles within the ferrite laths and/or at the interface boundaries. The microconstituents in the as-received as well as in the prestrained materials are characterized.