Roymech engineering encyclopedia

Material Properties of Ferrous Metals & Alloys

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Ferrous Metals and Alloys

Stainless Steels

Stainless steels are steels with a high degree of corrosion resistance and chemical resistance to most a wide range of aggressive chemicals. The corrosion resistance is mainly due to their high chromium content. Stainless steels normally have more than 12% chromium. Stainless steels are classified as Austenitic, Martensitic or Ferritic.

Austenitic Stainless Steels

These are usually alloy containing three main elements Iron, Chromium and Nickel (6% to 22%). These steels cannot be hardened by heat treatment. They retain an austenitic structure at room temperature and are ductile and have good corrosion resistance compared to ferritic stainless steel. They are at risk of intergranular corrosion unless heat treated to modify their chemical composition.

Ferritic Stainless Steel

This steel normally contains 11% to 30% chromium with a carbon content below 0,12%. Other alloying elements are added to improve its corrosion resistance or other characteristics such as machinability. Because of the low carbon content ferritic stainless steels are not normally considered heat treatable. However there is some hardness improvement resulting from quenching from high temperatures. The carbon and nitrogen content of these steels must be maintained at low levels for weldability , ductility and corrosion resistance.

Martensitic Stainless Steels

These steels contain 12% to 17% chromium with 0,1 to 1% Carbon. They can be hardened by heat treatment in the same way as plain carbon steels. Very high hardness values can be obtained for carbon levels approximately 1% using correct heat treatment. Small amounts of other alloying elements may be included to improve corrosion, resistance, strength and roughness.