The exhaust valve is made of:

The exhaust valve is typically made of a very special steel primarily because this material can withstand the extreme temperatures and stresses encountered in a high-performance engine environment. Exhaust valves are subject to significant thermal loads, as they are positioned in the path of exhaust gases, which can reach very high temperatures.

Using a special steel alloy ensures that the valve retains its structural integrity while exhibiting the necessary resistance to wear and thermal fatigue. These alloys often contain elements like chromium and nickel, which enhance heat resistance and strength, making them suitable for engine applications where durability is crucial. The design of exhaust valves is focused on performance, as they must maintain a tight seal to prevent leaks and operate effectively under varying thermal and mechanical conditions.

In contrast, while aluminum offers lightweight properties, it is not suitable for exhaust valves due to its lower melting point and lesser wear resistance compared to specialized steel. Standard steel alloys may not provide the required performance characteristics for high-temperature applications. Lastly, plastic composites lack the necessary strength and heat resistance to function effectively as exhaust valves in engine environments.