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Carbide precipitation, coarsening and hardness variations have been investigated for a quenched and tempered Dievar steel by SEM, TEM, STEM, HRTEM, XRD and Rockwell hardness testing. The carbide precipitation sequence has been ascertained as: M8C7 + bainitic/auto-tempered carbides → M8C7 + M2C + M7C3 → M8C7+ M7C3 +M23C6 → M8C7 + M7C3 + M23C6 + M6C. Boundary carbides coarsen obviously faster than matrix ones. Hardness variations originating from the carbide evolution have been qualified. A fine-dispersion of M2C carbides leads to a high hardness tempered at 550°C, whereas the hardness drops drastically for tempering at 600/650°C predominately due to the dissolution of unstable M2C and the coarsening of carbides.

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