Terminology of Hard Alloy(2)

Decarbonization 

After sintering the cemented carbide, the carbon content is insufficient.

When the product is decarbonized, the tissue changes from WC-Co to W2CCo2 or W3CCo3. The ideal carbon content of tungsten carbide in cemented carbide (WC) is 6.13% by weight. When the carbon content is too low, there will be a pronounced carbon-deficient structure in the product. Decarburization greatly reduces the strength of tungsten carbide cement and makes it more brittle.

Carburization

It refers to the excess carbon content after sintering the cemented carbide. The ideal carbon content of tungsten carbide in cemented carbide (WC) is 6.13% by weight. When the carbon content is too high, a pronounced carburized structure will appear in the product. There will be a significant excess of free carbon in the product. Free carbon greatly reduces the strength and wear resistance of tungsten carbide. C-type pores in phase-detection indicate the degree of carburization.

Coercivity

Coercive force is the residual magnetic force measured by magnetizing the magnetic material in a cemented carbide to a saturated state and then demagnetizing it. There is a direct relationship between the average particle size of the cemented carbide phase and the coercivity. The finer the average particle size of the magnetized phase, the higher the coercivity value.

Magnetic saturation

Cobalt (Co) is magnetic, while tungsten carbide (WC), titanium carbide (TiC), and tantalum carbide (TaC) are non-magnetic. Therefore, by first measuring the magnetic saturation value of cobalt in a material and then comparing it with the corresponding value of a pure cobalt sample, since the magnetic saturation is affected by alloying elements, the alloying level of the cobalt-bound phase can be obtained. Any changes in the binder phase can be measured. Since carbon plays an important role in composition control, this method can be used to determine deviations from ideal carbon content. Lower magnetic saturation values indicate low carbon content and potential for decarburization. High magnetic saturation values indicate the presence of free carbon and carburization.

Cobalt Pool

After sintering the metallic cobalt (Co) binder and tungsten carbide, excess cobalt may be formed, which is a phenomenon known as "cobalt pooling". This is mainly because during the HIP (Pressure Sintering) process, the sintering temperature is too low and the material forms insufficient density, or the pores are filled with cobalt. Determine the size of the cobalt pool by comparing metallographic photographs. The presence of a cobalt pool in cemented carbide affects the wear resistance and strength of the material.

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