Dongfeng ball valve will have problems such as low elasticity and fracture after being used for a long time. What are the methods to prolong the service life of ball valves?
1、 Shot peening
Shot peening is one of the widely used methods to improve the surface quality of ball valves. The ball valve is required to have high surface quality. Surface defects such as scratches, folds, oxidation and decarburization will cause fatigue fracture sources in the stress concentration areas of the ball valve during operation. If small steel shot is used to blast the surface of the ball valve at high speed, shot peening can improve the surface quality of the ball valve, improve the surface strength, and the surface is in a state of compressive stress, thus improving the fatigue strength and service life of the ball valve.
2、 Isothermal quenching of ball valve
The ball valve with small diameter or sufficient hardenability can be austempered, which can not only reduce the change of center, but also improve the strength and toughness. After isothermal quenching, it is better to conduct another tempering to improve the elasticity limit. The tempering temperature is the same as that of isothermal quenching.
3、 Thermomechanical treatment
Thermomechanical treatment is the combination of deformation strengthening and heat treatment strengthening to further improve the strength and toughness of steel. Thermomechanical treatment can be divided into high temperature, medium temperature and low temperature. High temperature thermomechanical treatment refers to quenching immediately after deformation in a stable austenite state, or it can be combined with forging or hot rolling, that is, quenching immediately after hot forming.
4、 Relaxation treatment of ball valve
The ball valve works under external force for a long time, which will produce slight permanent (plastic) deformation due to stress relaxation. Especially for the ball valve working at high temperature, the stress relaxation phenomenon is more serious at high temperature, which will reduce the accuracy of the ball valve. This is not allowed for general precision ball valves. Therefore, this type of ball valve should be relaxed after quenching and tempering.