The system used for metal numbers that classifying metals and their alloys is found in specifications and drawings. In this system, metal class, the principal alloying agent, and the average carbon content percentage are detailed.
With the proliferation of the types of metals, there is an equal growth in how metals are classified. Welders, Brazers, solderers and metallurgists should be familiar with four metal number classification schemes:
- AISI (American Iron and Steel Institute): for steel classification
- ASME (Society of Mechanical Engineers): oversees fittings, pipes and pressure vessels
- SAE (Society of Automobile Engineers (SAE): automobile metals
- API (American Petroleum Institute): Gas and oil industry
- ASTM (American Society for Testing and Materials): classification of 12,000 metals
- AA (Aluminum Association): for aluminum stock
- U.S. Military (MIL): for federal government projects
- CSA (Canadian Standards Association): if operating in Canada vs. the U.S.
Iron Metal Numbers, Designations and Codes
Cast iron is available in six general types:
- alloyed iron
- white iron
- malleable iron
- compacted graphite iron (CGI)
- ductile iron
- gray iron
Iron is also alloyed use many types of elements including copper, molybdenum, chromium and nickel. Iron standard specification and metal characteristics from ASTM and SAE are in the table below:
Iron Specification Codes and Characteristics
Standard Designation System for Steel Numbers
Numbers designate different chemical compositions. A four-digit number series identifies alloying and carbon steels according to the types and classes are shown in the table below. Over time the system has been modified, using five digits to designate certain types of steel alloys.
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*There is always a high level of chromium in stainless steels, along with nickel and possibly molybdenum and other materials. Stainless steels use a three-digit number beginning with a 2,3,4 or 5.
Metal numbers often have a two letter prefix.
- (C) indicates basic open-hearth carbon steels
- (E) indicates electric furnace carbon and alloy steels
- (H) is sometimes used as a suffix to describe steel that is manufactured to meet hardenability standards
The first two digits represent the principal steel alloys such as chrome-molybdenum, nickel-chromium, and manganese.
The last digits describe the middle of the carbon content range as a percent. As an example, the numbers .21 represents a range of .18% to .23% carbon. In some cases, the system doesn’t follow this rule, and some carbon ranges then relate to the amount of chromium, phosphorous, sulfur, manganese and other materials.
The system designates the approximate steel carbon range, the manufacturing process used to produce the steel and the major elements in steel. The table below shows the complete designation system.
For example, a nickel steel with about 3% nickel and .40% carbon is represented by the metal number 2340. For nickel-chrome-molybdenum with .40% carbon is represented by the number 4340.
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Metal Number Specifications for Steel
The ever-growing quality requirements for steel specifications and the variety of chemical compositions have resulted in several thousand combinations of chemical elements being specified to meet individual demands of steel product purchasers.
S.A.E. Steel Specifications
The S.A.E. (Society of Automotive Engineers) has a nomenclature for identifying various chemical compositions which symbolize certain standards as to heat treating, carburizing and machining. The American Iron and Steel Institute has developed new standards with restricted carbon ranges and combinations of other elements which are now being used by the steel industry when manufacturing steel bars. The Society of Automotive Engineers has revised most of their specifications to match those set up by the American Iron and Steel Institute.
Prefix Letters
- No prefix for basin open-hearth alloy steel
- (B) Indicates Bessemer carbon acid
- (C) Indicates basic open-hearth carbon steel
- (E) Indicates electric furnace steel
Number Designations
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Stainless Steel Codes and Groups
Austenitic Stainless Steel
Most welding applications use austenitic stainless steel. Types include chromium nickel steel where chromium is >17% and >7% nickel (there are exceptions to this rule.)
*Values that are single indicates the maximum % unless it is stated differently. Unless notes, other elements of all alloys listed include a maximum content of 2.0% MN, 1.0% Si, .045% P and .03% S, The balance if Fe.
Ferritic Stainless Steel
Ferritic stainless steel includes AISI 400 series metals. This type of stainless steel contains 14% to 27% chromium with no nickel content.
* Single values indicate the maximum % unless it is noted otherwise. Unless noted, other alloy elements of the metals listed have a maximum content level of 2.0% Mn, 1.0% Si, .045% P and .030% S. Any balance is Fe.
Martinistic Stainless Steel
Martinistic stainless steel includes iron-chromium alloys that are desired, can be heat treated to improve hardness.
*Single values indicate the maximum % unless noted. + unless indicated, other elements of listed alloys include the maximum content of 1.0% Mn, 1.0% Si, .040% P and .303% S. the balance is Fe.
Duplex Stainless Steel
In duplex stainless steel, it has a 50% austenite and 50% ferrite microstructure. It was manufactured to give welders a corrosion resistant, higher strength option as an alternative to 300 series austenitic stainless products.
Duplex Stainless Steel Composition
Standard Designation System for Aluminum Alloys and Aluminum
Aluminum castings have no standard metal numbers classification system. Aluminum alloys and wrought aluminum use a standard schema for four-digit numbering.
Aluminum Metal Numbers or Classifications indicate the Use of Alloys such as Zinc, Magnesium, Silicon, Manganese, and Copper.
The first digit represents the major alloying.
The second digit classifies any alloy modifications (a zero indicates it is the original alloy).
The last two digits only identify the various aluminum alloys that are commonly used for commercial applications, with the exception of the 1XXX class. In the 1XXX class, the last two digits indicate the aluminum content above 99 percent, in hundredths of one
For example, the number 1017, uses the 1 to denote a minimum aluminum composition of 99%; the 0 indicates it is the original composition, and the 17 indicates the hundredths of one percent of aluminum above the 99% composition minimum. In this example, the aluminum content is 99.17
In the metal numbers 3217, the 3 indicates a manganese aluminum alloy; the 2 indicates the second modification of this particular alloy, and the 17 indicates a commonly used commercial
The various classes of aluminum and aluminum alloys are identified by numbers as shown in the table below.
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Standard Designation System for Magnesium Alloys and Magnesium
Magnesium alloys and wrought magnesium are identified by a combination of numbers and letters. Letters denote the alloys in the magnesium alloy (see table below). Numbers, which may follow the letters, indicate the percentage of magnesium alloy elements. At times, there could be an additional letter following the percentage designators which shows the alloy modifications. As an illustration, the letter A equals 1; B equals 2, and C equates to 3.
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For example, in the number AZ93C:
- A stands for aluminum
- Z stands for zinc
- 9 indicates there is 9% aluminum in the alloy
- 3 indicates there is 3% zinc in the alloy
- The third change to the alloy is represented by a C. The first digit, 9 is always the percentage of the first letter, A or aluminum in this example. The second digit is the percentage of the second letter, which is 3% Zinc (see table below).
Per ASTM B275 Magnesium Alloys (abridged)
A dash can be used to add a temper indicator to the magnesium designation. Aluminum uses the same temper designations.
Magnesium Alloys Classifications are Needed in Industries such as Automotive to Aerospace
Standard Designation System for Copper Alloys and Copper
There are over 300 types of copper alloy and wrought copper available. The Copper Development Association has established a numbers naming system comprised of alloy metal numbers is utilized in the United States and Canada. It is used to identify and group as opposed to classifying different copper alloys and coppers. The approach has been updated to that it is consistent with the numbering method developed by UNS. UNS is managed by the ASTM and SAE. The system encompasses all commercially sold alloys and metals. UNS designations consist of the prefix C, followed by a space, three digits, another space, and, two zeros (five-digit codes).
The table below groups copper alloys by similar names which commonly include constituent alloys. Even within groups, differences in metal composition could result in welding issues. Consider this more of an exception, but still only use this data as a guideline.
Copper Tempers
Copper alloys are described by tempers. Tempers refer to metallurgical conditions such as casting methods and heat treatment (see ASTM B 601).
Standard Temper Designations for Copper and Casting Alloys
(Based on ASTM B 601)
Copper Casting Alloys Standard Temper Designations (ASTM B 601)
Copper UNS Metal Numbers and Classifications
Copper alloys are assigned UNS numbers C800000 to C99999. There are 8 families grouped within 18 related classifications. These include:
- Coppers (C80100-C81200): Minimum copper content of 99.3%
- Brasses (C83300-C87900): Copper alloys with zinc as the main alloying element
- Red and Semi-Red Brasses, Unleaded and Leaded (C8330-C84800)
- Yellow Brasses (C85200-C85800)
- High Strength and Leaded High Strength Yellow Brasses (C86100-C86800)
- Silicon Bronzes/Brasses (C87300-C87900)
- Nickel-Tin Bronzes (C94700-C94900)
- Nickel-Silvers (C97300-C97800)
- Aluminum Bronzes (C95200-C95800)
- Copper-Nickel Alloys (C96200-C96900)
- Leaded Coppers (C98200-C98840)
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Standard Designation System for Titanium
There is no recognized standard metal numbers designation system for titanium alloys and titanium. These compositions are designated by using the chemical symbol for titanium, Ti, followed by the percentage number(s) and the chemical symbols(s) of the alloying element(s). For example, Ti-5 A1-2.5 Sn would indicate that 5% aluminum and 2-1/2% tin alloying elements are present in the titanium metal.
Brochures
Metal Uses, Classification and Codes
by Army Institute for Professional Development
Steel Classification Codes(AISI, SAE, ASME, CSA)
by Air Liquide
Iron Specifications and Characteristics
by Engineered Casting Solutions
Copper and Copper Alloys Specifications, Properties and Selection Guide
by Non-ferrous Founders’ Society, Copper Development Association
References
“standard metal designations, Plasma Welding, welding …” aircraftplasma.com. N.p., n.d. Web. 24 Feb. 2017
“Metallurgy Matters: Carbon content, steel classifications …” thefabricator.com. N.p., n.d. Web. 24 Feb. 2017