Correlation Between Secondary Precipitation and Tensile Ductility of High-Speed Steels
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The aim of this study is to evaluate the effect of secondary carbide precipitation on strain hardening and tensile ductility of high-speed steels and to develop a novel pathway for ductility enhancement by engineering the annealing microstructure. The results demonstrate a strong correlation between secondary precipitation and austenitization. With decreasing austenitization temperature, secondary carbides exhibit a transformation from a rod-shaped Cr-rich M23C6 type to a granular Mo-rich M6C one, corresponding to a transition of the underlying eutectoid decomposition mechanism from a cooperative growth mode to a divorced eutectoid manner. Highly dispersed rod-shaped M23C6 precipitates contribute to an enhanced tensile strength but lead to a degraded work hardening rate in the late deformation stage and, therefore, a lower total elongation. In contrast, granular M6C precipitates exhibit an excellent capacity of accumulating dislocations and enhancing the work hardening rate especially at a high strain, which enables a significant increase of ductility. It is suggested that granular M6C precipitates embedded in fine ferritic grains with lean dislocations is a desirable annealing microstructure to produce a more ductile high-speed steel.
The authors gratefully acknowledge the support from the National Natural Science Foundation of China (Project Nos. 51301038, 51371050, and 51201031), Key Research Program of Jiangsu Province (Project No. BE2016154), and Fundamental Research Funds for the Central Universities.
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