https://www.eathu.com/u-flange-type-butterfly-valve.html
1. Grey cast iron: for low-pressure valves with operating temperature between-15~+ 200℃, nominal pressure PN≤1.6MPa.
2. Blackheart malleable cast iron: for medium and low-pressure valves with operating temperature between-15~+ 250℃, nominal pressure PN≤2.5MPa.
3. Ductile iron: for medium and low-pressure valves with operating temperature between-30~+ 350℃, nominal pressure PN≤4.0MPa.
4. Carbon Steel (WCA, WCB, WCC), suitable for medium and high-pressure valves with operating temperatures between-29~+ 425℃,