Steel Designation0

8/12/2019 Steel Designation0

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Based on data provided in Tables 11.1(b), 11.2(b), 11.3, and 11.4, Callister 7e .

Steels

Low AlloyHigh Alloy

low carbon


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Nomenclature of Steels

Historically, many methods for identifying alloysby their composition have been developed

The commonly used schemes in this country arethose developed by AISI/SAE and ASTM

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

American Society for Testing and Materials (ASTM)

European countries, Japan, Russia etc.developed their own schemes

In order to avoid confusion, the Universal/UnifiedNumbering System (UNS) was developed


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AISI/SAE Classification of Steels

A four digit description

First two digits identify the alloy type Last two digits indicate the carbon content For example

AISI/SAE 1020 steel is a plain carbon steel (10xx) which has0.20 wt.% carbon (xx20)

Plain carbon steel (10xx) are inexpensive, but have severallimitations including: Poor hardenability because the critical cooling rate is very high Rapid cooling leads to distortion and cracking Poor corrosion resistance

Poor impact resistance at low temperature Alloy steels were developed to address these issues

Alloying changes the eutectoid composition, the eutectoidcarbon content and the critical cooling rate

These alloys are more expensive, but a better combination of

properties is obtained


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AISI/SAE Classification of Steels

UNS uses the AISI/SAE designation with a letter before and a 0 after the 4 digits The letter identifies the alloy group


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Overview of UNS

Axxxxx - Aluminum Alloys Cxxxxx - Copper Alloys, including Brass and Bronze Fxxxxx - Iron, including Ductile Irons and Cast Irons Gxxxxx - Carbon and Alloy Steels Hxxxxx - Steels - AISI H Steels Jxxxxx - Steels - Cast Kxxxxx - Steels, including Maraging, Stainless, HSLA, Iron-Base Superalloys L5xxxx - Lead Alloys, including Babbit Alloys and Solders

M1xxxx - Magnesium Alloys Nxxxxx - Nickel Alloys Rxxxxx - Refractory Alloys

R03xxx - Molybdenum Alloys R04xxx - Niobium (Columbium) Alloys R05xxx - Tantalum Alloys R3xxxx - Cobalt Alloys R5xxxx - Titanium Alloys R6xxxx - Zirconium Alloys

Sxxxxx - Stainless Steels, including Precipitation Hardening and Iron-BasedSuperalloys

Txxxxx - Tool Steels Zxxxxx - Zinc Alloys


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AISI/SAE, ASTM, UNS

ASTM developed a parallel classification, starting witha letter A followed by numbers and other descriptors


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Tool Steels

AISI designation has a letter and a number.The letter describes the application

M (high speed machine tool), H (hot working)The letter describes the heat treatment

A (air hardening), O (oil quenching), W (water quenching)

UNS designation all tool steels start with a T


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Stainless Steels

Excellent corrosion resistance Contain 12 to 30% Chromium

Cr oxidizes easily and forms a thin continuous layer of oxide thatprevents further oxidation of the metal

Cr is a ferrite stabilizer

Austenite is restricted to a smallregion of the phase diagram

Fer r i t i c S t a in l e s s S t ee l s areessentially Fe-Cr Alloys Ferrite phase (bcc structure)Inexpensive, high strength


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Stainless Steels

Austenitic Stainless Steels Nickel is an austenite stabilizer. The addition of both

Cr and Ni results in the austenite ( g , fcc) phase beingretained to room temperature

The austenite phase is very formable (fcc structure)

Ni makes these alloys expensive Martensitic Stainless Steels

Have both Cr and C There is more Cr than in ferritic SS since Cr tends to

form Cr 23 C6, which removes available Cr for corrosionprotection Can be heat treated to high strength


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UNS letter S indicates stainless steel


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