In any engine, you have something called the intake and exhaust valves. These are like the lungs of the engine that let's air in and exhaust out. Since it is crucial to the engine my very small and fragile, mechanical engineers have to carefully choose the valve's material to ensure it fits its function. A great material that will do the job are steel alloys. It's a mixture of certain elements which will create a material with all the needed characteristics. For valves, it needs to be strong enough to withstand constant rubbing of the engine at hundreds of horsepower. It needs thermal resistance to withstand sizzling hot temperatures. It also needs to be light enough to move faster, thus making the engine more efficient. That is a lot to think about. There are two types of steel alloys used for making valves, which are martensitic steel and austenitic steel. These two have their own uses and vital to know which goes where. Martensitic steel are used in exhaust valves because they are great for high temperatures and are very corrosive resistant, which is perfect for resisting hot toxic gases released through the exhaust and into the environment. Its unique crystalline structure allows them to retain strength at very high temperatures. It is created through tempering, which is heating and cooling the alloys to rearrange its crystalline structure. In the bocharch cars, valves that have these properties are even more important to resist the heat of nitrous. Meanwhile, austenitic steel are used for intake valves. Astonitic steel does not have the thermal and corrosive resistance of martensitic steel as they are constantly cooled by the air and fuel mixture passing through and they are not exposed to corrosive exhaust gases. But what they do have is where resistance. This is important as the lubrication for the valve will get washed by the fuel, so they need to withstand the constant friction that would otherwise wear them down. Some other manufacturing tricks have been used to enhance the properties of these alloys. Some coat them with friction reducing materials to reduce wear. Some would hollow out the stems for valve to reduce weight, then fill them with sodium to increase thermal resistance. All of these may have gone unnoticed, but their functions and properties remain top priority when it comes to performance and safety. So that's all, take a time to take our valves. Next time, start the engine.