Influence of secondary carbides precipitation and transformation on the secondary hardening of laser melted high chromium steel |
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Authors: | Yong Wang Mei Yan Li Bin Han Tao Han Yi Yuan Cheng |
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Affiliation: | (1) College of Electromechanical Engineering, China University of Petroleum, 271 Bei’er Road, Dongying, 257061, Shandong, China; |
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Abstract: | The influence of secondary carbides precipitation and transformation on the secondary hardening of laser melted high chromium
steels was analyzed by means of scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The
microstructure of laser melted high chromium steel is composed of austenite with supersaturated carbon and alloy elements
and granular interdendritic carbides of type M23C6. Secondary hardening of the laser melted layer begins at 450 °C after tempering, and the hardness reaches a peak of 672HV
at 560 °C and then decreases gradually. After tempering at 560 °C, a large amount of lamellar martensite was formed in the
laser melted layer with a small quantity of thin lamellar M3C cementite due to the martensitic decomposition. The stripy carbides precipitating at the grain boundaries were determined
to be complex hexagonal M7C3 carbides and face centered cubic M23C6 carbides. In addition, the granular M23C6 carbides and fine rod-like shaped M7C3 carbides coexisted within the dendrites. As a result, the combined effects of martensitic transformation, ultrafine carbide
precipitations, and dislocation strengthening result in the secondary hardening of the laser melted layer when the samples
were tempered at 560 °C. |
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