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

(1) Surface welding (or spray welding) of hard alloy on the sphere can achieve a hardness of over 40HRC. The process of surface welding of hard alloy on the sphere is complex, with low production efficiency, and large area welding can easily cause deformation of the parts. Currently, there is relatively little use of surface hardening technology on the sphere.

(2) The surface of the 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 relatively 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 exceed 427 ℃. In addition, the bonding strength of the chrome plating layer is low, and the coating is prone to detachment.

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

(4) The HVOF process on the surface of a sphere can achieve a maximum hardness of 70-75HRC, high aggregate strength, and a thickness of 0.3-0.4mm. HVOF is the main process for hardening the surface of a sphere. High viscosity fluids in thermal power plants, petrochemical systems, and coal chemical industries; This hardening process is mostly used in mixed fluids with dust and solid particles, as well as highly corrosive fluid media. Supersonic spraying process is a process method in which oxygen fuel combustion generates high-speed airflow to accelerate the impact of powder particles on the surface of the workpiece, forming a dense surface coating. During the impact process, due to the fast particle velocity (500-750m/s) and low particle temperature (-3000 ℃), a coating with high bonding strength, low porosity, and low oxide content can be obtained after impacting the surface of the workpiece. The characteristic of HVOF is that the velocity of alloy powder particles exceeds the speed of sound, even 2-3 times that of sound, and the airflow velocity is 4 times that of sound. HVOF is a new processing technology, with a spraying thickness of 0.3-0.4ram. The coating is mechanically bonded to the workpiece, with high bonding strength (77MPa) and low coating porosity (<1%). This process has a low heating temperature for the workpiece (<93 ℃), and the workpiece does not deform, allowing for cold spraying. When spraying, the powder particle velocity is high (1370m/s), there is no heat affected zone, the composition and structure of the workpiece remain unchanged, the coating hardness is high, and it can be machined. Spray welding is a surface thermal spraying treatment process for metal materials. It heats the powder (metal powder, alloy powder, ceramic powder can all be) to a molten or highly plastic state through a heat source, and then sprays it onto the surface of the pre treated workpiece by air flow, forming a coating (welding) layer that is firmly bonded to the surface of the workpiece (substrate). In the hardening process of spray welding and overlay welding, both the hard alloy and the substrate have a melting process, and there is a hot melt zone at the junction of the hard alloy and the substrate. In order to fully achieve the performance of the spray welding or overlay welding hard alloy layer and avoid welding the hot melt zone as a metal contact surface after processing, it is recommended that the thickness of the spray welding or overlay welding hard alloy should be greater than 3mm.