Stainless steels

DESCRIPTION

The term Stainless Steel is used for the materials that are resistant to the atmospheric effects, corrosive materials and high temperatures, containing essentially iron, chromium, nickel and carbon. When alone, the iron contained in the stainless steel by about 75%, is not resistant to the external effects, but when alloyed with chromium and or chromium-nickel at various proportions, it gains the property of not rusting
The chromium incorporated in the steel forms an oxide layer on the surface of the steel when it comes in contact with the air. The protection of this rust-proofing layer increases with the luster of the surface.

CLASSIFICATION

The stainless steels are grouped under three main categories according to their structure:
- Ferritic
- Austenitic, and
- Martensitic steels.

Ferritic steels:
This type of steels are essentially iron and chromium alloys,
The anti-magnetic austenitic group in included in the AISI standard as Group 300. A material with suitable properties for almost any application may be selected out that group containing a large variety of types. The types with wide applications areas are 304 309, 310 and 316

Martensitic steels:
The steels of this type essentially contain chromium not less than 11.5%. High carbon content (15-20%) in the structure is the most prominent characteristic of the group. Based on the foregoing, they can be hardened by tempering as opposed to the previous two groups.

The Martensitic steels are magnetic and are used mostly in the places open to corrosion and requiring tempering resistance in particular (pump shafts, valves etc.). The widest used varieties are 410 and 420.