Abstract
Microstructural characterization and electron diffraction crystal structure determinations have been carried out on the tool steel M2. Detailed examination using optical microscopy and thin-film and replica transmission electron microscopy substantiate preliminary findings.2,3 Namely, that laser melted material has a two-phase σ-ferrite/austenite matrix containing a dispersion of fine M2C carbides together with a smaller amount of M23C6 carbides. Subsequent heat treatment at 560 and 1230°C increases the hardness (to a maximum value of ∼1100 VHN) by carbide precipitation. In material heat treated at 560°C there is a preponderance of M23C6 carbides together with a small amount of M2C carbides. In contrast, the effect of heat treatment at 1230°C is to produce material containing only MC1-x type carbides with diameters in the range from 20 nm to ∼1 µm.
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