Mechanical Characteristics Of Stainless Steel

Mechanical characteristics

Austenitic stainless steel has the lowest yield point of all steels. Therefore from the consideration of mechanical properties, austenitic stainless steels are not the best material for valve stem, because to ensure a certain strength, the diameter of the valve stem should be increased. The yield point cannot be increased by heat treatment, but can be obtained by cold forming.

magnetic performance

Due to the wide application of austenitic stainless steel, many of us have false impression that all stainless steel has no magnetic. For austenitic stainless steel, this can be understood as non-magnetic, because it is true that the forged steels have no magnetic after quenched, but SS304 will be somewhat magnetic after cold forming. For casting stainless steel, if the material is 100 percent Austenitic stainless steel, then it is no magnetic. 

Low carbon type stainless steel

The corrosion resistance of austenitic stainless steel comes from the oxidation chrome protective layer formed on metal surface. If the material is heated to a high temperature of 450 degree to 900 degree , the structure of the material will change, and carbide will form along the edge of the crystal. In this way, the protective layer of magnesium oxide cannot be formed on the edge of the crystal, which decreases the corrosion resistance. This corrosion is called "intergranular corrosion".

As a result, 304L stainless steel and 316L stainless steel were developed to combat this corrosion. Both 304L stainless steel and 316L stainless steel have lower carbon content, so there will be no carbonization problem, and the "Intergranular corrosion" will not occur.

It should be noticed that the sensitivity between higher intergranular corrosion does not mean that low carbon materials are easier to corrosion. In a high chloride environment, this sensitivity is higher.

Please note that this phenomenon is due to high temperature (450 degree -9000c), and usually soldering is the direct reason to reach such high temperature. For soft seat butterfly valve, since we do not proceed welding on the valve plate, it doesn't make much sense to use low carbon stainless steel, while most specs will require also 304L stainless steel or 316L stainless steel.

Why does stainless steel also rust?

Why does stainless steel also rust? When brown rust spots appear on the surface of stainless steel pipes, people were amazed: "Stainless steel is not rusted, the rusted one is not stainless steel, it may be some problems with the steel", while it is just false conception of stainless steel, because stainless steel is also rusted under specific circumstances.