Introduction to the SAE-AISI Designation SystemAbstract: The SAE system uses a basic four-digit system to designate the chemical composition of carbon and alloy steels. The first digit (1), of this designation indicates a carbon steel; i.e., carbon steels comprise 1xxx groups in the SAE-AISI system and are subdivided into four categories due to the variance in certain fundamental properties among them. For many years, certain grades of carbon and alloy steels have been designated by a four-digit AISI/SAE numerical index system that identified the grades according to standard chemical compositions. Since the American Iron and Steel Institute (AISI) ceased writing material specifications, the relationship between AISI and grade designations has been discontinued. From point of edition of the 1995 Iron and Steel Society (ISS) Strip Steel Manual, the four-digit designations are referred to solely as SAE Designations. The SAE system uses a basic four-digit system to designate the chemical composition of carbon and alloy steels. The simplest system for designation of steel is schematically shown in Figure 1.

Figure 1: Schematic Representation of AISI/SAE Steel Designation SystemFigure 1 demonstrates that the SAE-AISI system uses a four-digit number to designate a carbon and alloy steel and refers to its specific chemical composition. It is worth noting however, that there are also certain types of alloy steels that are designated by five digits (51XXX; 52XXX). The first digit (1), of this designation indicates a carbon steel; i.e., carbon steels comprise 1xxx groups in the SAE-AISI system and are subdivided into four categories due to the variance in certain fundamental properties among them. Thus the plain carbon steels are comprised within the 10xx series (containing 1.00% Mn maximum); resulfurized carbon steels within the 11xx series; resulfurized and rephosphorized carbon steels within the 12xx series; and non-resulfurized high-manganeze (up-to 1.65%) carbon steels which are produced for applications requiring good machinability are comprised within the 15xx series. The SAE-AISI system then classifies all other alloy steels using the same four digit index as follows:2 - Nickel steels;3 - Nickel-chromium steels;4 - Molybdenum steels;5 - Chromium steels;6 - Chromium-vanadium steels;7 - Tungsten-chromium steels;9 - Silicon-manganese steels. The second digit of the series indicates the concentration of the major element in percentiles (1 equals 1%). The last two digits of the series indicate the carbon concentration to 0.01%. Example:SAE 5130 indicates a chromium steel alloy, containing 1% of chromium and 0.30% of carbon. Table 1 shows the SAE/AISI steel Numbering designation system Additional letters added between the second and third digits include B when boron is added (between 0.0005 and 0.003%) for enhanced hardenability, and L when lead is added (between 0.15 and 0.35%) for enhanced machinability. The prefix M is used to designate merchant quality steel (the least restrictive quality descriptor for hot-rolled steel bars used in noncritical parts of structures and machinery). The prefix E (electric-furnace steel) and the suffix H (hardenability requirements) are mainly applicable to alloy steels. The full series of classification groups is shown in Table 2-4. Table 1: The SAE/AISI steel numbering designation system Carbon steels10XXPlain carbon, Mn 1.00% max

11XXResulfurized free machining

12XXResulfurized/rephosphorized free machining

15XXPlain carbon, Mn 1.00-1.65%

Manganese steels13XXMn 1.75%

Nickel steels23XXNi 3.50%

25XXNi 5.00%

Nickel-chromium steels31XXNi 1.25%, Cr 0.65-0.80%

32XXNi 1.75%, Cr 1.07%

33XXNi 3.50%, Cr 1.50-1.57%

34XXNi 3.00%, Cr 0.77%

Molybdenum steels40XXMo 0.20-0.25%

44XXMo 0.40-0.52%

Chromium-molybdenum steels41XXCr 0.50-0.95%, Mo 0.12-0.30%

Nickel-chromium-molybdenum steels43XXNi 1.82%, Cr 0.50-0.80%, Mo 0.25%

47XXNi 1.05%, Cr 0.45%, Mo 0.20-0.35%

Nickel-molybdenum steels46XXNi 0.85-1.82%, Mo 0.20-0.25%

48XXNi 3.50%, Mo 0.25%

Chromium steels50XXCr 0.27-0.65%

51XXCr 0.80-1.05%

50XXXCr 0.50%, C 1.00% min

51XXXCr 1.02%, C 1.00% min

52XXXCr 1.45%, C 1.00% min

Chromium-vanadium steels61XXCr 0.60-0.95%, V 0.10-0.015%

Tungsten-chromium steels72XXW 1.75%, Cr 0.75%

Nickel-chromium-molybdenum steels81XXNi 0.30%, Cr 0.40%, Mo 0.12%

86XXNi 0.55%, Cr 0.50%, Mo 0.20%

87XXNi 0.55%, Cr 0.50%, Mo 0.25%

88XXNi 0.55%, Cr 0.50%, Mo 0.35%

Silicon-manganese steels92XXSi 1.40-2.00%, Mn 0.65-0.85%, Cr 0-0.65%

Nickel-chromium-molybdenum steels93XXNi 3.25%, Cr 1.20%, Mo 0.12%

94XXNi 0.45%, Cr 0.40%, Mo 0.12%

97XXNi 0.55%, Cr 0.20%, Mo 0.20%

98XXNi 1.00%, Cr 0.80%, Mo 0.25%

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 (AISI) 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.[1]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 (for example, "4140 bar per ASTM-A108" or "4140 bar per AMS 6349") 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 (UNS), can be seen in cross-referencing tables (including the ones given below).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.[2][3] 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 steelMain articles: Carbon steel and Alloy steelCarbon 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 (basis points) by weight. For example, a 1060 steel is a plain-carbon steel containing 0.60 wt% C.[4]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.[3]Major classifications of steel[2]

SAE designationType

1xxxCarbon steels

2xxxNickel steels

3xxxNickel-chromium steels

4xxxMolybdenum steels

5xxxChromium steels

6xxxChromium-vanadium steels

7xxxTungsten steels

8xxxNickel-chromium-molybdenum steels

9xxxSilicon-manganese steels

Carbon and alloy steel grades[5]

SAE designationType

Carbon steels

10xxPlain carbon (Mn 1.00% max.)

11xxResulfurized

12xxResulfurized and rephosphorized

15xxPlain carbon (Mn 1.001.65%)

Manganese steels

13xxMn 1.75%

Nickel steels

23xxNi 3.50%

25xxNi 5.00%

Nickel-chromium steels

31xxNi 1.25%; Cr 0.65%, or 0.80%

32xxNi 1.25%; Cr 1.07%

33xxNi 3.50%; Cr 1.50%, or 1.57%

34xxNi 3.00%; Cr 0.77%

Molybdenum steels

40xxMo 0.20%, 0.25%, or Mo 0.25% and S 0.042%[1]

44xxMo 0.40%, or 0.52%

Chromium-molybdenum (chromoly) steels

41xxCr 0.50%, 0.80%, or 0.95%; Mo 0.12%, 0.20%, 0.25%, or 0.30%

Nickel-chromium-molybdenum steels

43xxNi 1.82%; Cr 0.500.80%; Mo 0.25%

43BVxxNi 1.82%; Cr 0.50%; Mo 0.12%, or 0.35%; V 0.03% min

47xxNi 1.05%; Cr 0.45%; Mo 0.20%, or 0.35%

81xxNi 0.30%; Cr 0.40%; Mo 0.12%

81BxxNi 0.30%; Cr 0.45%; Mo 0.12%; and added boron[1]

86xxNi 0.55%; Cr 0.50%; Mo 0.20%

87xxNi 0.55%; Cr 0.50%; Mo 0.25%

88xxNi 0.55%; Cr 0.50%; Mo 0.35%

93xxNi 3.25%; Cr 1.20%; Mo 0.12%

94xxNi 0.45%; Cr 0.40%; Mo 0.12%

97xxNi 0.55%; Cr 0.20%; Mo 0.20%

98xxNi 1.00%; Cr 0.80%; Mo 0.25%

Nickel-molybdenum steels

46xxNi 0.85%, or 1.82%; Mo 0.20%, or 0.25%

48xxNi 3.50%; Mo 0.25%

Chromium steels

50xxCr 0.27%, 0.40%, 0.50%, or 0.65%

50xxxCr 0.50%; C 1.00% min

50BxxCr 0.28%, or 0.50%; and added boron[1]

51xxCr 0.80%, 0.87%, 0.92%, 1.00%, or 1.05%

51xxxCr 1.02%; C 1.00% min.

51BxxCr 0.80%; and added boron[1]

52xxxCr 1.45%; C 1.00% min.

Chromium-vanadium steels

61xxCr 0.60%, 0.80%, 0.95%; V 0.10%, or 0.15% min.

Tungsten-chromium steels

72xxW 1.75%; Cr 0.75%

Silicon-manganese steels

92xxSi 1.40%, or 2.00%; Mn 0.65%, 0.82%, or 0.85%; Cr 0.00%, or 0.65%

High-strength low-alloy steels

9xxVarious SAE grades

xxBxxBoron steels

xxLxxLeaded steels

Stainless steelMain article: Stainless steel Type 102austenitic general purpose stainless steel working for furniture 200 Seriesaustenitic chromium-nickel-manganese alloys Type 201austenitic that is hardenable through cold working Type 202austenitic general purpose stainless steel 300 Seriesaustenitic chromium-nickel alloys Type 301highly ductile, for formed products. Also hardens rapidly during mechanical working. Good weldability. Better wear resistance and fatigue strength than 304. Type 302same corrosion resistance as 304, with slightly higher strength due to additional carbon. Type 303free machining version of 304 via addition of sulfur and phosphorus. Also referred to as "A1" in accordance with ISO 3506.[6] Type 304the most common grade; the classic 18/8 (18% chromium, 8% nickel) stainless steel. Outside of the US it is commonly known as "A2 stainless steel", in accordance with ISO 3506 (not to be confused with A2 tool steel).[6] Type 304Lsame as the 304 grade but lower carbon content to increase weldability. Is slightly weaker than 304. Type 304LNsame as 304L, but also nitrogen is added to obtain a much higher yield and tensile strength than 304L. Type 308used as the filler metal when welding 304. Type 309better temperature resistance than 304, also sometimes used as filler metal when welding dissimilar steels, along with inconel. Type 316the second most common grade (after 304); 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 316Lis 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.[6] Type 316Tivariant of type 316 that includes titanium for heat resistance. It is used in flexible chimney liners. Type 321similar 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 Seriesferritic and martensitic chromium alloys Type 405ferritic for welding applications Type 408heat-resistant; poor corrosion resistance; 11% chromium, 8% nickel. Type 409cheapest type; used for automobile exhausts; ferritic (iron/chromium only). Type 410martensitic (high-strength iron/chromium). Wear-resistant, but less corrosion-resistant. Type 416easy to machine due to additional sulfur Type 420Cutlery Grade martensitic; similar to the Brearley's original rustless steel. Excellent polishability. Type 430decorative, e.g., for automotive trim; ferritic. Good formability, but with reduced temperature and corrosion resistance. Type 439ferritic grade, a higher grade version of 409 used for catalytic converter exhaust sections. Increased chromium for improved high temperature corrosion/oxidation resistance. Type 440a 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: Type 440Ahas the least amount of carbon making this the most stain-resistant. Type 440Bslightly more carbon than 440A. Type 440Chas the greatest amount of carbon of the Type 440 variants. Strongest and considered more desirable in knifemaking than the Type 440A variant[citation needed], except for diving or other salt-water applications. This variant is also more readily available than other variants of Type 440.[7] Type 440Fa free-machining variant. Contains the same high carbon content as Type 440C. Type 446For elevated temperature service 500 Seriesheat-resisting chromium alloys 600 Seriesoriginally created for proprietary alloys, which are no longer given SAE grade numbers[8] 601 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.Stainless steel designations[9]

SAE designationUNS designation% Cr% Ni% C% Mn% Si% P% S% NOther

Austenitic

201S2010016183.55.50.155.57.50.750.060.030.25-

202S202001719460.157.510.00.750.060.030.25-

205S2050016.51811.750.120.251415.50.750.060.030.320.40-

254[10]S3125420180.02 max----0.206 Mo; 0.75 Cu; "Super austenitic"; All values nominal

301S301001618680.1520.750.0450.03--

302S3020017198100.1520.750.0450.030.1-

302BS3021517198100.1522.03.00.0450.03--

303S3030017198100.15210.20.15 min-Mo 0.60 (optional)

303SeS3032317198100.15210.20.06-0.15 Se min

304S304001820810.500.0820.750.0450.030.1-

304LS3040318208120.0320.750.0450.030.1-

304CuS3043017198100.0820.750.0450.03-34 Cu

304NS304511820810.500.0820.750.0450.030.100.16-

305S30500171910.50130.1220.750.0450.03--

308S30800192110120.08210.0450.03--

309S30900222412150.2210.0450.03--

309SS30908222412150.08210.0450.03--

310S31000242619220.2521.50.0450.03--

310SS31008242619220.0821.50.0450.03--

314S31400232619220.2521.53.00.0450.03--

316S31600161810140.0820.750.0450.030.102.03.0 Mo

316LS31603161810140.0320.750.0450.030.102.03.0 Mo

316FS31620161810140.08210.20.10 min-1.752.50 Mo

316NS31651161810140.0820.750.0450.030.100.162.03.0 Mo

317S31700182011150.0820.750.0450.030.10 max3.04.0 Mo

317LS31703182011150.0320.750.0450.030.10 max3.04.0 Mo

321S3210017199120.0820.750.0450.030.10 maxTi 5(C+N) min, 0.70 max

329S3290023282.550.0820.750.040.03-12 Mo

330N08330172034370.0820.751.500.040.03--

347S3470017199130.0820.750.0450.030-Nb + Ta, 10 x C min, 1 max

348S3480017199130.0820.750.0450.030-Nb + Ta, 10 x C min, 1 max, but 0.10 Ta max; 0.20 Ca

384S38400151717190.08210.0450.03--

SAE designationUNS designation% Cr% Ni% C% Mn% Si% P% S% NOther

Ferritic

405S4050011.514.5-0.08110.040.03-0.10.3 Al, 0.60 max

409S4090010.511.750.050.08110.0450.03-Ti 6 x (C + N) [11]

429S4290014160.750.12110.040.03--

430S4300016180.750.12110.040.03--

430FS430201618-0.121.2510.060.15 min-0.60 Mo (optional)

430FSeS430231618-0.121.2510.060.06-0.15 Se min

434S434001618-0.12110.040.03-0.751.25 Mo

436S436001618-0.12110.040.03-0.751.25 Mo; Nb+Ta 5 x C min, 0.70 max

442S442001823-0.2110.040.03--

446S4460023270.250.21.510.040.03--

SAE designationUNS designation% Cr% Ni% C% Mn% Si% P% S% NOther

Martensitic

403S4030011.513.00.600.1510.50.040.03--

410S4100011.513.50.750.15110.040.03--

414S4140011.513.51.252.500.15110.040.03--

416S416001214-0.151.2510.060.15 min-0.060 Mo (optional)

416SeS416231214-0.151.2510.060.06-0.15 Se min

420S420001214-0.15 min110.040.03--

420FS420201214-0.15 min1.2510.060.15 min-0.60 Mo max (optional)

422S4220011.012.50.501.00.200.250.51.00.50.0250.025-0.901.25 Mo; 0.200.30 V; 0.901.25 W

431S4162315171.252.500.2110.040.03--

440AS440021618-0.600.75110.040.03-0.75 Mo

440BS440031618-0.750.95110.040.03-0.75 Mo

440CS440041618-0.951.20110.040.03-0.75 Mo

SAE designationUNS designation% Cr% Ni% C% Mn% Si% P% S% NOther

Heat resisting

501S5010046-0.10 min110.040.03-0.400.65 Mo

502S5020046-0.1110.040.03-0.400.65 Mo

Martensitic precipitation hardening

630S1740015-173-50.07110.040.03-Cu 3-5, Ta 0.15-0.45 [12]