designation and classification of steels

7/29/2019 Designation and Classification of Steels

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Designation and Classification of Steels

Designations of Steels

The American Iron and Steel Institute (AISI) and Society of Automotive Engineers (SAE) provide

designation systems (Table 13-1) that use a four- or five-digit number. The first two numbers refer to the

major alloying elements present, and the last two or three numbers refer to the percentage of carbon. An

AISI 1040 steel is a plain-carbon steel with 0.40% C. An SAE 10120 steel is a plain-carbon steel

containing 1.20% C. An AISI 4340 steel is an alloy steel containing 0.40% C. Note that the American

Society for Testing of Materials (ASTM) has a different way of classifying steels. The ASTM has a list of

specifications that describe steels suitable for different applications.

Classification of Steels

Steels can be classified based on their composition or the way they have been processed.

Carbon steels contain up to @2% carbon.

These steels may also contain other elements, such as Si (maximum 0.6%), copper (up to

0.6%), and Mn (up to 1.65%).


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Decarburized steels contain less than 0.005% C.

Ultra-low carbon steels contain a maximum of 0.03% carbon.

They also contain very low levels of other elements such as Si and Mn.

Low-carbon steels contain 0.04 to 0.15% carbon.

These lowcarbon steels are used for making car bodies and hundreds of other applications.

Mild steel contains 0.15 to 0.3% carbon.

This steel is used in buildings, bridges, piping, etc.

Medium-carbon steels contain 0.3 to 0.6% carbon.

These are used in making machinery, tractors, mining equipment, etc.

High-carbon steels contain above 0.6% carbon.

These are used in making springs, railroad car wheels, and the like.

Note that cast irons are Fe-C alloys containing about 2 to 4% carbon.

Alloy steels are compositions that contain more significant levels of alloying elements.

They improve the hardenability of steels.

The AISI defines alloy steels as steels that exceed in one or more of these elements: >1.65% Mn, 0.6% Si, 0.6% Cu.

The total carbon content is up to 1%


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and the total alloying elements content is below 5%.

A material is also an alloy steel if a definite concentration of alloying elements, such as Ni, Cr, Mo, Ti, etc., is specified

These steels are used for making tools (hammers, chisels, etc.) and also in making parts

such as axles, shafts, and gears.

Certain specialty steels may consist of higher levels of sulfur (>0.1%) or lead (@0.150.35%) to provide machinability.

These, however, can not be welded easily..

Recently, researchers have developed green steel in which lead, an environmental toxin, was replaced with tin (Sn) and/or antimony (Sb).

Steels can also be classified based on theirprocessing. For example, the term concast steels refers to continuously cast steels.

Galvanized steels have a zinc coating for corrosion resistance.

Similarly, tinplated steel is used to make corrosion-resistant tin cans and other products.

o Tin is deposited using electroplatinga process known as continuous web

electrodeposition.

E-steels are steels that are melted using an electric furnace,

while B-steels contain a small (0.0005 to 0.003%), yet significant, concentration of boron.

Recently, a germresistant coated stainless steel has been developed. Some biomedical products, such as cardiovascular stents, also make use of stainless steel

coated with heprin, a chemical that makes the stents(device for keeping bodily tubes open: an

open tubular structure of stainless steel or plastic that is inserted into an artery or another bodily

tube to keep it from becoming blocked by disease) more biocompatible.

Website: astm.org and steel.org


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AISI steel grades (American Iron & Steel Institute) are becoming increasingly popular in the UK, primarily dueto their use in the oil and gas industry. We hold a comprehensive range of stock in AISI material and AISIequivalent specifications. Of AISI steel grades available the majority are as carbon steels and alloysteels. AISI carbon steels and alloy steels are usually given a four digit number, the first two digits indicate thealloying element in the AISI specification and the last two digits indicate the amount of carbon in thespecification. AISI materials grades are shown in the table below, as to how the four digit number indicates thetype it refers to.

Carbon Steel 10XX Plain carbon steel , Mn 1.00% max11XX Resulphurised free cutting12XX Resulphurised - Rephosphorised free cutting15XX Plain carbon steel, Mn 1.00-1.65%

Manganese Steel 13XX Mn 1.75%Nickel Steel 23XX Ni 3.50%

25XX Ni. 5.00%Nickel Chromium Steel 31XX Ni 1.25%, Cr 0.65-0.80%

32XX Ni 1.75%, Cr 1.07%33XX Ni 3.50%, Cr 1.50-1.57%34XX Ni 3.00%, Cr 0.77%

Molybdenum Steel 40XX Mo 0.20-0.25%44XX Mo 0.40-0.52%

Chromium Molybdenum Steel 41XX Cr 0.50-0.95%, Mo 0.12-0.30%Nickel Chromium Molybdenum Steel 43XX Ni 1.82%, Cr 0.50-0.80%, Mo 0.25%

47XX Ni 1.82%, Cr 0.50-0.80%, Mo 0.25%Nickel Molybdenum Steel 46XX Ni 1.05%, Cr 0.45%, Mo 0.20-0.35%

48XX Ni 0.85-1.82%, Mo 0.20-0.25%Chromium Steel 50XX Ni 3.50%, Mo 0.25%

51XX Cr 0.27-0.65%50XXX Cr 0.80-1.05%51XXX Cr 0.50% C 1.00% min52XXX Cr 1.02%, C 1.00% minCr 1.45%, C 1.00%

Chromium Vanadium Steel 61XX Cr 0.60-0.95%, V 0.10-0.15%Tungsten Chromium Steel 72XX W 1.75%, Cr 0.75%

Nickel Chromium Molybdenum Steel 81XX Ni 0.30%, Cr 0.40%, Mo 0.12%86XX Ni 0.55%, Cr 0.50%, Mo 0.20%87XX Ni 0.55%, Cr 0.50%, Mo 0.25%88XX Ni 0.55% Cr 0.50% Mo 0.35%

Silicon Manganese Steel 92XX Si 1.40-2.00%, Mn 0.65-0.85% Cr 0.65%Nickel Chromium Molybdenum Steel 93XX Ni 3.25%, Cr 1.20%, Mo 0.12%

94XX Ni 0.45%, Cr 0.40%, Mo 0.12%97XX Ni 0.55%, Cr 0.20%, Mo 0.20%98XX Ni 1.00%, Cr 0.80%, Mo 0.25%

It is possible that AISI grades are quoted as SAE grades and it is often that AISI/SAE have the samesteel identification number. The AISI range of steel specifications also includes stainless steels which are3 digit numbers starting with either a 2, 3, 4, or 5. The most popular of these being the 300 seriesaustenitic stainless grades, followed by the 400 series martensitic grades. Also stocked are AISIequivalent grades of tool steel and high speed steel. AISI tool steel and high speed steel specificationsare usually designated with a letter followed by 1 or 2 digits.

designation and classification of steels

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