Classification of steels and cast irons

Dr. Dmitri Kopeliovich

• Classification of steels by composition
• Classification of steels by application
• Classification of cast irons

Carbon steels

• Low carbon steels (C < 0.25%);

• Medium carbon steels (C =0.25% to 0.55%);

• High carbon steels (C > 0.55%).

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:

SAE 1XXX

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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Stainless steels:

AISI has established three-digit system for the stainless steels:

2XX series – chromium-nickel-manganese austenitic stainless steels;

3XX series – chromium-nickel austenitic stainless steels;

4XX series – chromium martensitic stainless steels or ferritic stainless steels;

5XX series – low chromium martensitic stainless steels;

Tool and die steels:

Designation system of one-letter in combination with a number is accepted for tool steels.

The letter means:

• W - Water hardened plain carbon tool steels;

• O - Oil hardening cold work alloy steels;

• A - Air hardening cold work alloy steels;

• D -Diffused hardening cold work alloy steels;

• S – Shock resistant low carbon tool steels;

• T – High speed tungsten tool steels;

• M - High speed molybdenum tool steels;

• H – Hot work tool steels;

• P – Plastic mold tool steels.

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• White cast irons - hard and brittle wear resistant cast irons consisting of pearlite and cementite.

• Grey cast irons - cast irons at slow cooling and consisting of ferrite and dispersed graphite flakes.

• 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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• Iron-carbon phase diagram
• Effect of alloying elements on steel properties
• Carbon steels
• Alloy steels
• Tool and die steels
• Stainless steels
• Creep resistant steels
• Cast irons
• Welding stainless steels
• Steel strip processing
• Steel making (introduction)
• Basic Oxygen Furnace (BOF)
• Electric Arc Furnace (EAF)
• Ladle refining
• Deoxidation of steel
• Desulfurization of steel
• Non-metallic inclusions in steel
• Structure of killed steel ingot
• Macrosegregation in steel ingots
• Fabrication of large steel ingots
• Electroslag Remelting

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