Grain Refinement of Co-Cr-Mo-C Through Plastic Deformation Followed by Reversion of Lamellar Eutectoid Structure
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Small plastic straining was combined with a two-step heat treatment to obtain grain refinement of the Co-28Cr-6Mo-0.33C alloy. The solution-treated specimens were furnace cooled to room temperature, obtaining partially transformed pearlite at grain boundaries. Afterward, the specimens were compressed up to 10% of engineering strain, followed by aging at 850 °C that contributed to the decomposition of the austenite phase into a lamellar eutectoid structure (α + M23C6). The full lamellar structure was then reverse-treated at temperatures from 1000 to 1237 °C, where the austenite phase was stable. The reversion treatment led to the nucleation of a fine-grained austenitic structure (with average size of 48.23 ± 21.30 μm—i.e., about 1/10 of its initial average size) at the lamellar eutectoid structure. Compression tests carried out on reverse-transformed samples showed better mechanical properties compared to those of the samples tested before reversing transformation.
KeywordsCo-Cr-Mo alloys grain refinement heating microstructure mechanical behaviors
This work was fully sponsored by Metal Forming laboratory of Amirkabir University of Technology and Laboratory of Net Shape Forming of Padova University. The authors thank engineer Reza Bahrami for assisting in use of the facilities of Metal Forming laboratory of Amirkabir University of Technology.
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