Introduction of Ni-Cr-based Cemented Carbide for Mechanical Seals

   There are three ways to improve the chemical corrosion resistance of tungsten carbide-based cemented carbides: reducing the content of cobalt in the binder metal; choosing a corrosion-resistant binder metal or alloy to replace cobalt, Such as Ni, Ni-Cr, Ni-Cr-Co, Ni-Mo, Pt alloys, etc.; adding TiC, TaC and other corrosion-resistant carbides to improve the corrosion resistance of the hard phase.

   my country's newly developed YWN8 and W7 belong to nickel-based, nickel-chromium-based cemented carbide, also known as corrosion-resistant cemented carbide.

   Many of the imported mechanical seal cemented carbide rings are corrosion-resistant cemented carbide materials. After analysis and test, the wear-resistant cemented carbide containing low cobalt fine particle WC (Co<1%) can only use hot pressing process due to the small cobalt content. Hot-pressed cemented carbide is not expensive, and products with complex shapes are difficult to form.

   Using Ni instead of Co as the bonding metal can improve the corrosion resistance of the metal, but its strength is 70% to 80% of that of WC+Co, and its hardness is 0.5 to 1HRA lower than that of WC+Co, while WC+Ni- Cr alloy has good corrosion resistance, its strength and hardness are comparable to WC+Co, and it has excellent non-magnetic properties. Practice has proved that when WC/Cr+Ni is 0.015% to 0.15% (wt), the alloy can resist acid and alkali corrosion. W7 cemented carbide belongs to this type of material.

   Through the analysis of the imported cemented carbide sealing ring, it is found that most of its materials contain TaC or TiC. The addition of TaC and TiC can improve various properties of the alloy, especially the addition of TaC can inhibit the growth of carbide grains, enhance the fatigue strength and oxidation resistance of the alloy, and can also improve the thermal shock resistance of the alloy, reduce heat Crack susceptibility, which is very beneficial for sealing rings.