The material depends on medium, there are different materials for ball valves like cast steel, stainless steel, brass or forged steel. The most popular are stainless steel and brass.
Stainless steel is used for corrosive media, They are often used in high temperatures and many chemicals like seawater, swimming pools,, 304 or 316 are the most common.
Brass material have a pretty large market share, it is widely used in drinking water, gas, oil, air and so on.
