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Classification of steels and cast irons

Classification of steels by composition

Carbon steels

Designation system:

American Iron and Steel Institute (AISI) together with Society of Automotive Engineers (SAE) have established four-digit (with additional letter prefixes) designation system:


First digit 1 indicates carbon steel (2-9 are used for alloy steels);

Second digit indicates modification of the steel.

0 - Plain carbon, non-modified

1 - Resulfurized

2 - Resulfurized and rephosphorized

5 - Non-resulfurized, Mn over 1.0%

Last two digits indicate carbon concentration in 0.01%.

Example: SAE 1030 means non modified carbon steel, containing 0.30% of carbon.

A letter prefix before the four-digit number indicates the steel making technology:

A - Alloy, basic open hearth

B - Carbon, acid Bessemer

C - Carbon, basic open hearth

D - Carbon, acid open hearth

E - Electric furnace

Example: AISI B1020 means non modified carbon steel, produced in acid Bessemer and containing 0.20% of carbon.

Alloy steels

  • Low alloy steels (alloying elements ⇐ 8%);
  • High alloy steels (alloying elements > 8%).

According to the four-digit classification SAE-AISI system:

First digit indicates the class of the alloy steel:

2- Nickel steels;

3- Nickel-chromium steels;

4- Molybdenum steels;

5- Chromium steels;

6- Chromium-vanadium steels;

7- Tungsten-chromium steels;

9- Silicon-manganese steels.

Second digit indicates concentration of the major element in percents (1 means 1%).

Last two digits indicate carbon concentration in 0,01%.

Example: SAE 5130 means alloy chromium steel, containing 1% of chromium and 0.30% of carbon.

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Classification of steels by application

Classification of cast irons

  • Malleable cast irons - cast irons, produced by heat treatment of white cast irons and consisting of ferrite and particles of free graphite.
  • Nodular (ductile) cast irons - grey cast iron in which Graphite particles are modified by magnesium added to the melt before casting. Nodular cast iron consists of spheroid nodular graphite particles in ferrite or pearlite matrix.

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classification_of_steels_and_cast_irons.txt · Last modified: 2012/06/01 by dmitri_kopeliovich
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