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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: M 8 C 7 + bainitic/auto-tempered carbides → M 8 C 7 + M 2 C + M 7 C 3 → M 8 C 7 + M 7 C 3 +M 23 C 6 → M 8 C 7 + M 7 C 3 + M 23 C 6 + M 6 C. Boundary carbides coarsen obviously faster than matrix ones. Hardness variations originating from the carbide evolution have been qualified. A fine-dispersion of M 2 C 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 M 2 C and the coarsening of carbides.
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Xie et al. (2022) studied this question.
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