SAE International, as a standards organization, maintains several alloy numbering systems,
one of which, for steel grades, is the SAE steel grades system.
In the 1930s and 1940s the American Iron and Steel Institute and SAE were both involved
in efforts to standardize such a numbering system for steels. These efforts were similar
and overlapped significantly. For several decades the systems were united into a joint
system designated the AISI/SAE steel grades. In 1995 the AISI turned over future maintenance
of the system to SAE because the AISI never wrote any of the specifications.
Today steel quotes and certifications commonly make reference to both SAE and AISI, not always
with precise differentiation. For example, in the alloy/grade field, a cert might say
"4140", "AISI 4140", or "SAE 4140", and in most light-industrial applications any of
the above is accepted as adequate, and considered equivalent, for the job at hand, as long as
the specific specification called out by the designer is certified to on the certificate.
The alloy number is simply a general classifier, whereas it is the specification itself that
narrows down the steel to a very specific standard.
The SAE steel grade system's correspondence to other alloy numbering systems, such as
the ASTM-SAE unified numbering system, can be seen in cross-referencing tables.
The AISI system used a letter prefix to denote the steelmaking process. The prefix "C" denoted
open-hearth furnace, electric arc furnace or basic oxygen furnace, while "E" denotes
electric arc furnace steel. A letter "L" within the grade name indicates lead as an added
ingredient; for example, 12L14 is a common grade that is 1214 with lead added for machinability.
Carbon and alloy steel
Carbon steels and alloy steels are designated by a four digit number, where the first digit
indicates the main alloying element(s), the second digit indicates the secondary alloying
element(s), and the last two digits indicate the amount of carbon, in hundredths of a percent
by weight. For example, a 1060 steel is a plain-carbon steel containing 0.60 wt% C.
An "H" suffix can be added to any designation to denote hardenability is a major requirement.
The chemical requirements are loosened but hardness values defined for various distances
on a Jominy test. Stainless steel
Type 102—austenitic general purpose stainless steel working for furniture
200 Series—austenitic chromium-nickel-manganese alloys
Type 201—austenitic that is hardenable through cold working
Type 202—austenitic general purpose stainless steel
300 Series—austenitic chromium-nickel alloys Type 301—highly ductile, for formed products.
Also hardens rapidly during mechanical working. Good weldability. Better wear resistance and
fatigue strength than 304. Type 302—same corrosion resistance as 304,
with slightly higher strength due to additional carbon.
Type 303—free machining version of 304 via addition of sulfur and phosphorus. Also referred
to as "A1" in accordance with ISO 3506. Type 304—the most common grade; the classic
18/8 stainless steel. Outside of the US it is commonly known as "A2 stainless steel",
in accordance with ISO 3506. Type 304L—same as the 304 grade but lower
carbon content to increase weldability. Is slightly weaker than 304.
Type 304LN—same as 304L, but also nitrogen is added to obtain a much higher yield and
tensile strength than 304L. Type 308—used as the filler metal when welding
304. Type 309—better temperature resistance than
304, also sometimes used as filler metal when welding dissimilar steels, along with inconel.
Type 316—the second most common grade; for food and surgical stainless steel uses; alloy
addition of molybdenum prevents specific forms of corrosion. It is also known as marine grade
stainless steel due to its increased resistance to chloride corrosion compared to type 304.
316 is often used for building nuclear reprocessing plants.
Type 316L—is an extra low carbon grade of 316, generally used in stainless steel watches
and marine applications, as well exclusively in the fabrication of reactor pressure vessels
for boiling water reactors, due to its high resistance to corrosion. Also referred to
as "A4" in accordance with ISO 3506. Type 316Ti—variant of type 316 that includes
titanium for heat resistance. It is used in flexible chimney liners.
Type 321—similar to 304 but lower risk of weld decay due to addition of titanium. See
also 347 with addition of niobium for desensitization during welding.
400 Series—ferritic and martensitic chromium alloys
Type 405—ferritic for welding applications Type 408—heat-resistant; poor corrosion
resistance; 11% chromium, 8% nickel. Type 409—cheapest type; used for automobile
exhausts; ferritic. Type 410—martensitic. Wear-resistant, but
less corrosion-resistant. Type 416—easy to machine due to additional
sulfur Type 420—Cutlery Grade martensitic; similar
to the Brearley's original rustless steel. Excellent polishability.
Type 430—decorative, e.g., for automotive trim; ferritic. Good formability, but with
reduced temperature and corrosion resistance. Type 439—ferritic grade, a higher grade
version of 409 used for catalytic converter exhaust sections. Increased chromium for improved
high temperature corrosion/oxidation resistance. Type 440—a higher grade of cutlery steel,
with more carbon, allowing for much better edge retention when properly heat-treated.
It can be hardened to approximately Rockwell 58 hardness, making it one of the hardest
stainless steels. Due to its toughness and relatively low cost, most display-only and
replica swords or knives are made of 440 stainless. Available in four grades: 440A, 440B, 440C,
and the uncommon 440F. 440A, having the least amount of carbon in it, is the most stain-resistant;
440C, having the most, is the strongest and is usually considered more desirable in knifemaking
than 440A, except for diving or other salt-water applications.
Type 446—For elevated temperature service
500 Series—heat-resisting chromium alloys 600 Series—originally created for proprietary
alloys, which are no longer given SAE grade numbers601 through 604: Martensitic low-alloy
steels. 610 through 613: Martensitic secondary hardening
steels. 614 through 619: Martensitic chromium steels.
630 through 635: Semiaustenitic and martensitic precipitation hardening stainless steels.
Type 630 is most common PH stainless, better known as 17-4; 17% chromium, 4% nickel.
650 through 653: Austenitic steels strengthened by hot/cold work.
660 through 665: Austenitic superalloys; all grades except alloy 661 are strengthened by
second-phase precipitation.
High-strength low-alloy steel
See also ASTM International
Steel grades Unified numbering system
References Notes
Bibliography Degarmo, E. Paul; Black, J T.; Kohser, Ronald
A.. Materials and Processes in Manufacturing. Wiley. ISBN 0-471-65653-4.
Jeffus, Larry F.. Welding: Principles and Applications. Cengage Learning. ISBN 1-4018-1046-2.
Oberg, E.; et al.. Machinery's Handbook. Industrial Press Inc.
Cobb, Harold. "The Naming and Numbering of Stainless Steels". Advanced Materials & Processes:
39–44.