Selecting the right hardness for the ball and seat in a ball valve is crucial to avoid immediate failure.

The metal sliding contact surface should exhibit a certain degree of hardness difference. Otherwise, it may seize. In practical applications, the hardness difference between the valve ball and the valve seat is typically 5 to 10 HRC. This allows the ball valve to have a longer service life. Due to the intricate processing of the sphere and high processing costs, to safeguard the sphere from damage and wear, it is generally chosen to have a higher hardness than the valve seat surface.

There are two popular combinations for the contact surfaces of valve balls and seats:

1) The valve ball has a hardness of 55HRC and the seat has a hardness of 45HRC. The valve ball can be coated with STL20 alloy and the seat can be welded with STL12 alloy. This is commonly used for metal-sealed ball valves and meets standard wear requirements.

2) The valve ball has a hardness of 68HRC and the seat has a hardness of 58HRC. The valve ball can be coated with tungsten carbide and the seat can be coated with STL20 alloy. This is widely used in the coal chemical industry due to its high wear resistance and long service life.