The stainless steel means that the material will not get rust or corrosion. It is very important for valve industry, especially when handling the corrosion fluid. The most used stainless steel in valve industry is as following;

In order to understand why this kind of material have this property, we need to look into chemical elements are added to find the answer.

There are three basic chemical elements inside the stainless steel:

• Chromium(Cr); used for high corrosion resistant
• Nickel （Ni）: Typically increase the tensile strength, toughness and elastic limit.
• Molybdenum (Mo): in High temperature carbon steel, it is used to increase the mechanical strength and protecting material not getting soft in high temperature environment. But in stainless steel material, it is used to enhance their corrosion resistant ability.

For the chart above, we learn that the CF3M and CF8M, the M is means the steel contains the Molybdenum elements. In this principle, the CF8M has better corrosion resistant ability than CF8; CF3M is better than CF3;

Then we have the questions, how to compare the CF8M and CF3M, because both material have the molybdenum element, then which one have better performance in corrosion resistance?

The main difference between CF8M and CF3M is the CF8M has more carbon elements(0.08%) while CF3M has less(0.03%)。We can not delete the carbon element from the stainless steel, since without the carbon element, the steel would become soft. But while with more carbon elements, the steel would get rusty quickly.

Then we get the conclusion as following:

• More carbon element means better mechanical strength while weaker corrosion resistant ability
• Less carbon element means better corrosion resistant ability while weaker mechanical strength.