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L 10

British Standards and ASTM standard specification on

iron/steel

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Classifications Steels can be classified by a variety of different systems

depending on: The composition, such as carbon, low-alloy or stainless steel.

The manufacturing methods, such as open hearth, basic oxygen process, or electric furnace methods.

The finishing method, such as hot rolling or cold rolling The product form, such as bar plate, sheet, strip, tubing or

structural shape The deoxidation practice, such as killed, semi-killed,

capped or rimmed steel The microstructure, such as ferritic, pearlitic and

martensitic The required strength level, as specified in ASTM standards The heat treatment, such as annealing, quenching and

tempering, and thermo mechanical processing Quality descriptors, such as forging quality and

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Classifications

►Steel is classified according to the alloying elements it contains.► Carbon is the most important element; therefore all steels are classified according to carbon content. ► Plain carbon steels contain primarily iron & carbon, and they are classified as10XX steels. ► The first two digits refer to plain carbon steel. ► The third & fourth digits refer to the carbon content in hundredths of a percent. ► Thus, a 1035 steel is a plain carbon steel with 0.35 % carbon. ► There are varying amounts of other materials in carbon steel, but their content is so small that they do no affect physical properties.11/8/2011

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Alloy steels• Alloy steels are classified by the society of Automotive

Engineers (SAE) & by the American Iron & Steel Institute (AISI). • Some of the designations accepted by them as standard are

shown in table 3.3. • Often as many as 5 or more alloying elements may be present,

& it is impractical to describe the alloy correctly by a simple numbering system.

• Steels may be more broadly classified as followsA. Carbon steel

1. Low carbon - less than 0.30 %2. Medium carbon - 0.30% to 0.70 %3. High carbon – 0.70 % to 2.0% (Normally the upper limit is 1.40 %)

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Classification Number Range of Number

A. Carbon Steel

Carbon steel SAE- AISI 1XXX

Plain carbon 10XX 1006-1095Free Machining (resulfurized) 11XX 1108-1151

Resulfurized, rephosphorized 12XX 1211-1214

B. Alloy Steels

Manganese (1.5%to2.0%) 13XX 1320-1340

Molybdenum 4XXX

C-Mo (0.25%Mo) 40XX 4024-4068

Cr-Mo(0.70%Cr, 0.15%Mo) 41XX 4130-4150

Ni-Cr-Mo (1.8% Ni, 0.65 % Cr) 43XX 4317-4340

Ni-Mo (1.75 %) 46XX 4608-4640

Ni-Cr (0.45 % Ni, 0.2 % Mo) 47XX

Ni-Mo (3.5 %Ni, 0.25 %Mo) 48XX 4812-4820

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Table3.3Classification of steel

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Table3.3Classification of steel

Classification Number Range of Number

Chromium 5XXX

0.5% Cr 50XX

1.0% Cr 51XX 5120-5152

1.5% Cr 52XXX 52095-52101

Corrosion heat resistant 514XX (AISI 400 series)

Chromium-Vanadium 6XXX

1 % Cr, 0.12 %V 61XX 6120-6152

Silicon Manganese

0.85 % Mn, 2 %Si 92XX 9255-9262

Tripple Alloy Steels

0.55 % Ni, 0.50 % Cr, 0.020 % Mo 85XX 8615-8660

0.55 % Ni, 0.50 % Cr, 0.25 % Mo 87XX 8720-8750

3.25 % Ni, 1.20 % Cr, 0.12 % Mo 93XX 9310-9317

0.45 %Ni, 0.40 % Cr, 0.12 % Mo 94XX 9437-9445

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Table3.3Classification of steel

Classification Number Range of Number

0.45 % Ni, 0.15 % Cr, 0.20 % Mo 97XX 9747-9763

1.0 % Ni, 0.80 % Cr, 0.25 % Mo 98XX 9840-9850

Boron (~0.005 % Mo) XXBXX

Boron is denoted by addition of B. Boron-Vanadium is denoted by addition of BV. Example: 14BXX, 50BXX, 80BXX, 43 BV14. The letters appearing before the no indicate the following: A, Alloy basic open hearth: B, carbon-acid Bessemer; C, carbon basic open hearth; D, carbon acid open hearth; E, electric furnaceStainless and heat resisting steels:2XX Chromium- Nickel-Manganese types3XX Chromium- Nickel types4XX Straight Chromium types5XX Low Chromium typesAll stainless steels are produced in electric furnace

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Classification Contd

B. Alloy Steel1.low alloys-special alloying elements totaling less than 8.0 %2. High alloys- special alloying elements totaling more than 8.0 %

Low carbon steel is used for wire, structural shapes, and screw machine parts such as screws, & bolts. Medium carbon steels are used for rails, axles, gears, and parts requiring high strength & moderate to great hardness. High carbon steels find use in cutting tools such as knives, drills, taps, and for abrasion َم�ل ع کا ِھسنے گresisting properties.

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Classification ContdThe Society of Automotive Engineers (SAE) has established standards for specific analysis of steels. In the 10XX series, the first digit indicates a plain carbon steel. The second digit indicates a modification in the alloys. 10XX means that it is a plain carbon steel where the second digit (zero ) indicates that there is no modification in the alloys. The last two digits denote the carbon content in points. For example SAE 1040 is a carbon steel where 40 points represent 0.40 % Carbon content. Alloy steels are indicated by 2XXX, 3XXX, 4XXX, etc.. The American Iron and Steel Institute (AISI) in cooperation with the Society of Automotive Engineers (SAE) revised the percentages of the alloys to be used in the making of steel, retained the numbering system, and added letter prefixes to indicate the method used in steel making. The letter prefixes are:

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Classification of Steels

A = alloy, basic open hearthB = carbon, acid BessemerC = carbon, basic open hearthD = carbon, acid open hearthE = electric furnaceIf the prefix is omitted, the steel is assumed to be open hearth. Example: AISI C1050 indicates a plain carbon, basic-open hearth steel that has 0.50 % Carbon content.Another letter is the harden ability or H-value. Example: 4340HGeneral representation of steels:12/6/2011

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Classification Contd

• Red Hardness: This property , also called hot-hardness, is related to the resistance of the steel to the softening effect of heat. It is reflected to some extent in the resistance of the material to tempering.

• Hardenability: This property determines the depth and distribution of hardness induced by quenching.

• Hot-shortness: Brittleness at high temperatures is called hot-shortness which is usually caused by sulfur. When sulfur is present, iron and sulfur form iron sulfide (FeS) that is usually concentrated at the grain boundaries and melts at temperatures below the melting point of steel.

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Classification Contd• Due to the melting of iron sulfide, the cohesion

between the grains is destroyed, allowing cracks to develop. This occurs when the steel is forged or rolled at elevated temperatures. In the presence of manganese, sulfur tends to form manganese sulfide (MnS) which prevents hot-shortness.

• Cold-shortness: Large quantities of phosphorus (in excess of 0.12%P) reduces the ductility, thereby increasing the tendency of the steel to crack when cold worked. This brittle condition at temperatures below the recrystallization temperature is called cold-shortness.

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