At present, the commonly used hardening processes for the surface of metal hard sealed ball valves mainly include the following:

(1) The surface of the sphere is welded (or sprayed) with hard alloy, with a hardness of over 40HRC. The process of surfacing hard alloy on the surface of the sphere is complex, with low production efficiency, and large-scale surfacing can easily cause deformation of the parts. At present, this process is rarely used.

(2) The surface of the ball sphere is plated with hard chromium, with a hardness of 60-65HRC and a thickness of 0.07-0.10ram. The chromium plating layer has high hardness, wear resistance, corrosion resistance, and can maintain surface brightness for a long time. The process is relatively simple and the cost is low. However, the hardness of the hard chromium coating will rapidly decrease as the temperature increases due to the release of internal stress, and its working temperature cannot be higher than 427 ℃. In addition, the bonding force of the chromium plating layer is low, and the coating is prone to detachment.

(3) The surface of the sphere is plasma nitrided, with a surface hardness of 60-65HRC and a nitrided layer thickness of 0.20-0.40mm. The plasma nitriding hardening process cannot be used in fields such as strong chemical corrosion due to its poor corrosion resistance.