Alloy Groups in the SAE Numbering System

AISI/SAE Designation	Steel Type	Key Characteristics/Alloying Elements
10xx	Plain carbon steel	No significant alloying element except carbon and manganese; less than 1.0% manganese. Also called nonresulfurized.
11xx	Free-cutting steel	Resulfurized. Sulfur content (typically 0.10%) improves machinability.
12xx	Free-cutting steel	Resulfurized and rephosphorized. Presence of increased sulfur and phosphorus improves machinability and surface finish.
12Lxx	Free-cutting steel	Lead added to 12xx steel further improves machinability.
13xx	Manganese steel	Nonresulfurized. Presence of approximately 1.75% manganese increases hardenability.
15xx	Carbon steel	Nonresulfurized; greater than 1.0% manganese.
23xx	Nickel steel	Nominally 3.5% nickel.
25xx	Nickel steel	Nominally 5.0% nickel.
31xx	Nickel-chromium steel	Nominally 1.25% Ni; 0.65% Cr.
33xx	Nickel-chromium steel	Nominally 3.5% Ni; 1.5% Cr.
40xx	Molybdenum steel	0.25% Mo.
41xx	Chromium-molybdenum steel	0.95% Cr; 0.2% Mo.
43xx	Nickel-chromium-molybdenum steel	1.8% Ni; 0.5% or 0.8% Cr; 0.25% Mo.
44xx	Molybdenum steel	0.5% Mo.
46xx	Nickel-molybdenum steel	1.8% Ni; 0.25% Mo.
48xx	Nickel-molybdenum steel	3.5% Ni; 0.25% Mo.
5xxx	Chromium steel	0.4% Cr.
51xx	Chromium steel	Nominally 0.8% Cr.
51100	Chromium steel	Nominally 1.0% Cr; bearing steel, 1.0% C.
52100	Chromium steel	Nominally 1.45% Cr; bearing steel, 1.0% C.
61xx	Chromium-vanadium steel	0.50–1.10% Cr; 0.15% V.
86xx	Nickel-chromium-molybdenum steel	0.55% Ni; 0.5% Cr; 0.20% Mo.
87xx	Nickel-chromium-molybdenum steel	0.55% Ni; 0.5% Cr; 0.25% Mo.
92xx	Silicon steel	2.0% silicon.
93xx	Nickel-chromium-molybdenum steel	3.25% Ni; 1.2% Cr; 0.12% Mo.

Uses of Some Steels

SAE Number	Applications
1015	Formed sheet-metal parts; machined parts (may be carburized)
1030	General-purpose, bar-shaped parts, levers, links, keys
1040	Shafts, gears
1080	Springs; agricultural equipment parts subjected to abrasion (rake teeth, disks, plowshares, mower teeth)
1112	Screw machine parts
4140	Gears, shafts, forgings
4340	Gears, shafts, parts requiring good through-hardening
4640	Gears, shafts, cams
5150	Heavy-duty shafts, springs, gears
6150	Gears, forgings, shafts, springs
8650	Gears, shafts
9260	Springs