The microstructure of sub-zero treated Vanadis 6 tool steel has been examined with reference to the same material without the application of sub-zero treatment. Changes in the microstructure were recorded using light microscopy, scanning electron microscopy and transmission electron microscopy. The obtained results infer that the amount of retained austenite decreases with application of sub-zero treatment. The retained austenite is located mainly along the boundaries of martensitic domains. The martensite is refined due to sub-zero treatment. The carbide phases in as-quenched and/or sub-zero treated Vanadis 6 steel can be divided into eutectic phases (MC-carbides), secondary carbides (M7C3-phase) and small globular carbides that were identified as alloyed cementite. Sub-zero treatment refines the carbides and increases their number, particularly the small globular carbides, but it does not alter their nature. It is hypothesised that the amount of small globular carbides is enhanced due to extensive stress state of the material after SZT rather than as a result of “accelerated precipitation rate” that was considered recently as a principal explanation.Keywords: ledeburitic tool steel, sub-zero treatment, microstructure, phase constitution, hardness
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