Deep Cryogenic Treatment Effect on Tungsten Carbide Materials

First of all, viewed from micro structure, deep cryogenic treatment has no obvious effect on the WC granularity, contiguity, and γ phase mean free path of tungsten carbide materials. Carbide without cryogenic treatment contains only a small amount of brittle η phases, by comparison, after the cryogenic treatment due to carbide long-term exposure to extreme temperatures and η phase increases. There are some experiments found that after deep cryogenic treatment, tungsten carbide has more uniform distribution, the binder Co and hard phase WC combined firmer and the overall wear resistance is significantly improved. Furthermore, the deep cryogenic treatment temperature provides greater two-phase free energy difference (High-temperature phase α-Co (fcc structure) and Low temperature phase Σ-Co (hcp structure)). At such low temperature, the atomic diffusion capacity reduced and formed no-diffusion phase transition process. In the research of deep cryogenic treatment of TW carbide inserts, we can found that the blade without deep cryogenic treatment has both of Σ-Co phase andα-Co phase, while the blade after treatment only hasΣ-Co phase. It indicates that after deep cryogenic treatment, Co of TW has a complete martensitic transformation. Overall, deep cryogenic treatment can promote binder Co transfer fcc structure to hcp structure.

Due to the great difference of the coefficient of thermal expansion and linear expansion coefficient between WC and Co phases of tungsten carbide, tungsten carbide has large thermal stress inside after cooling. And WC phase is subjected to compression stress, Co phase is subjected to tensile stress. By cryogenic treatment can make the carbide obtained two-phase thermal stress relaxation, thereby increasing the strength of carbide cutting tools. In addition, in mechanical properties, carbide cutting tools after deep cryogenic treatment, the hardness has greatly improved (from HRA90 to improve HRA92, HV1764 increased to HV2263.7). While YG6X, YG8, YG10C, YT14 four grades after deep cryogenic treatment, Various grades of alloy coercive force has been significantly improved, significantly lower than the saturation magnetization, has improved hardness, density substantially constant and flexural strength dramatically.

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