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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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