Hardening of ball valve components using ion-chemical heat treatment
Shut-off valves are present in all pipeline systems of industrial facilities, technical objects for domestic use (heating, gas, water supply, sewage, etc.), and make up at least 80% of the total number of products used in the pipeline.
Shut-off valves regulate the flow of the working medium to ensure the specified parameters of the technological process - this includes closing, opening, changing the direction, and speed of the movement of gas or liquid.
The most commonly used shut-off elements are valves. In particular, ball valves are widely used, whose advantage lies in the simplicity of the design and minimal time to block the flow of the working medium. The component responsible for closing or regulating the cross-section of the flow channel is made in the form of a ball or a ball plug with a hole. These products are made from structural or stainless steels, titanium, bronze, and other materials.
A feature of ball valves is their relatively small size compared to similarly purposed pipeline fittings. This type of valve is installed in places where the use of gate valves is impossible due to limited space.
Such products are often operated under harsh conditions. The valves handle aggressive media – acids, cracking products, etc.; petroleum products with CO2 and H2S; internal parts may be subjected to deformation due to strong flow pressure. Therefore, to extend the service life of these valves, they must undergo surface hardening.
Ion chemical-thermal treatment (ICT) is one of the advanced and innovative methods of hardening products. Vacuum hardening methods achieve the best characteristics of the hardened surface, improving wear and galling resistance, resistance to erosive and cavitation wear, as well as intergranular corrosion for all steels and alloys. The warranty life and operational reliability of hardened products are increased many times, as confirmed by production tests.
This article presents the results of production tests by the company "Ion Technologies" on the hardening of the working surfaces of the shut-off mechanisms of ball valves. The developed ICT technology allows ball valve manufacturers to quickly set up production of wear-resistant products that meet modern requirements.
The main materials for making ball valves are stainless steels (12X18H10T, 14X17H2, 08X17H13M2T, 10X17H13M2T), titanium alloys, and others.
Ion Chemical-Thermal Treatment of Stainless Steel Parts
| Parts before hardening | ICT hardening process | Parts after hardening |
  |   |  Distribution of microhardness by the depth of the nitrided layer  |
After ICT, surface hardness measurements of ball plugs and other hardened parts were made using a portable ultrasonic hardness tester TKM-459C.
Characteristics of the Nitrided Layer in Steels 12X18H10T, 14X17H2
| Steel Grades Parameters | 12X18H10T | 14X17H2 |
| Surface Hardness HV 10, kgf | 935 - 1015 | 975 - 1015 |
| Surface Hardness HV 5, kgf | 775 - 825 | 810 - 825 |
| Case Depth, mm | 0.4 - 0.45 | 0.38 - 0.43 |
Characteristics of the Nitrided Layer of VT-3 Titanium Alloy Parts
| Parameters of Titanium Alloy | VT-3 |
| Surface Microhardness HV 0.1, kgf | 875 - 955 |
| Layer Depth by Microstructure hm, µm | 10 - 15 |
| Layer Depth by Microhardness hc, µm | 70 |
| Brittleness on the VIAM Scale | Grade I, not brittle |
| Nitrided Layer Microstructure |  |
| Microhardness Distribution by the Depth of the Nitrided Layer |  |
The ICT technology improves the operational characteristics of products. It ensures dimensional and finishing accuracy for future design requirements, while eliminating additional mechanical and grinding operations and/or honing, which significantly reduces costs and increases production rates.
Material published with the consent of LLC "Ion Technologies"