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What is Ferrous alloy?
- May 22, 2018 -

Ferrous Alloys

The most commonly used industrial materials are ferrous metals, that is, those metals that consist mostly of iron (Fe).

Steel is an iron-based alloy containing typically less than 1% carbon, where iron frequently contains 2% or more carbon. Iron and steel are widely available, strong, cheap, and can be shaped by casting.  Their mechanical properties can be improved by heat treating and, in the case of steels, by working (i.e. rolling or forging). Stainless steels were developed to resist corrosion and generally contain 12% or more chromium, and may contain nickel in any amount up to or even exceeding the chromium content based upon the mechanical properties desired and application.

There are several types of stainless steel. When considering these alloys for use in a corrosive environment, the most widely used method for initial selection is to compare PREn ratings (pitting resistance equivalent number) across materials.  This is calculated using the weight % of key alloying elements present in any particular grade of stainless steel. The formula is:

                                                                PREn = % Cr + (3.3 x % Mo) + (16 x % N)

Obviously, alloys containing the highest amounts of chromium, molybdenum and nitrogen are considered to possess better resistance to pitting corrosion. This may be accompanied by a corresponding increase in tensile and yield strengths.

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