SANS-characterized influence of degree of rolling reduction on the microstructure of Ti-containing cold-work tool steel

The influence of rolling reduction on the microstructural variations in Ti-containing tool steel was investigated. The microstructures, including the prior-austenite grain structure and primary/secondary carbides, were characterized using optical and electron microscopy; the carbides were quantitatively analyzed by small-angle neutron scattering data collected from macro-samples. In parallel with refining the primary carbides, increases in the degree of rolling reduction significantly changes the precipitation kinetics of the secondary MC and M₂₃C₆ (M = metallic element) carbides, and thus their mechanical properties, especially the hardness to toughness balance throughout the aging. The improvement of this balance is attributed to the refinement of the prior-austenite grain structure, as well as the retardation of M₂₃C₆ precipitation. The reaction kinetics of the precipitation reactions were analyzed by the reduced heat of reaction observed in a calorimetry experiment. - Highlights: • Microstructural analysis including PAG structure and primary/secondary carbides was performed using SANS technique. • Increase in degree of rolling reduction refined not only PAGs, but also primary and secondary carbides. • Hardness-to-toughness ratio was significantly influenced by hot-rolling process.