What Kind Of Stainless Do We Use?

Stainless steel is not just an alloy of iron, carbon and chromium, but also includes manganese and in certain classes, nickel and molybdenum as well. Despite its nefarious reputation, the layer that corrosion forms isn’t necessarily harmful. When aluminum corrodes, the resulting layer of aluminum oxide protects it from being further exposed to oxygen molecules and therefore prevents further corrosion! The same is true of chromium.

Stainless steel
Stainless steel

We can purchase and work with any commercially available grade of stainless steel . For most of our common work we use four main types:

Type 303
Because of its relatively high sulfur content, this stainless steel is softer and therefore is used for most CNC machining work. It is non-magnetic and does not accept heat treatment, so the hardness is not affected by the heat induced via the machining process (work hardening). However, the additional sulfur makes it a little less corrosion-resistant than type 304.

Type 304
Higher corrosion resistance than type 303, it is also harder and tougher. It is a bit more difficult to work (machine) than type 303, but it also makes a stronger finished part. This is the most common type of stainless steel used in manufacturing.

Type 316L
A specialty stainless steel with a low carbon content but more molybdenum. This makes it even more corrosion-resistant than type 304. And because it is low in carbon, it does not carburize or give off heavy fumes when welded. This is often used for marine applications where saltwater might damage other steels. Because it doesn’t produce fumes when welded it’s ideal for metal 3D printing.

Type S136
An especially high purity of stainless steel. It is used mostly for plastic injection mold tools when the molded part needs to be an optically clear plastic lens, because the steel takes a very high polish.

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