Why is it important to me?
As a car enthusiast, I've always admired the internal combustion engines and how does it work. What mesmerised me the most is the poppet valve and how it can withstand corrosion, fatigue, and the heat that comes from the small explosions in each cylinder.
A poppet valve was found by James Watts back in 1770s. He used it for his steam engine.
A Poppet valve is a system that consists of valve seat and the valve itself. The valve seat is mainly made of Stellite, and the valve is made of stainless steel.
Stainless Steel is a steel that is alloyed with chromium to make it more resistant to corrosion and fatigue. That's why it is used in the valve. There is some grades for stainless steel. Stainless steel has over 150 grades, and it starts from 300 to around 2300 SAE grade. SAE grade is a numbering system for different alloys. It takes into consideration different elements that is alloyed into steel. For example, carbon steel.
Stainless Steel price ranges from $0.75 to $2.00. The thermal expansion also varies. It starts from 9.9-17.3 * 10^6 (m/(m k)). Stainless Steel also has a Young's modulus, Tensile strength, and Yield strength of 180 GPa, 860 MPa, 502 MPa respectively.
References: http://www.scrapsmetalprices.com http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html http://www.engineeringtoolbox.com/young-modulus-d_417.html https://en.wikipedia.org/wiki/SAE_steel_grades