American Iron and Steel Institute Designations

The first two digits of the AISI number series indicates the primary alloying element in the alloy steel as follows:

The letter “E” prefixed before the number indicates that the alloy was electric furnace pro­cessed. All other alloys were either open hearth processed, or processed by the basic oxygen method, or it may be electric furnace processed with no adjustments made in the phosphorus and sulfur limits. The last two digits indicate the mid-carbon range contained within the alloy. Example: 4140 indicates the mid-carbon range of this alloy is .40%. If there is a five number series, the last three digits indicate the mid-carbon range Example: 52100 indicate the mid-carbon range of this alloy is 1.00%.

E4130 Aircraft Quality Sheet and Plate 

Type 4130 is an electric-furnace processed, chromium-molybdenum aircraft quality alloy used primarily for welding or where moderate tensile strength is a requirement. The careful processing it undergoes completely eliminates the possibility of seams, grooves, pitting or blistering. It also undergoes diligent inspection and rolling to insure its freedom from lamination and tears. It is available in the normalized or annealed condition, and maybe pickled and oiled.

E4130 Aircraft Quality Bars

4130 is an electric-furnace, through-hardening, chromium-molybdenum alloy processed to meet the rigid standards of the aircraft industry and vacuum degassed to conform to the magnetic particle inspection standards of AMS-2301. Its excellent weldability, formability and temperate hardenability predispose this alloy to a wide range of applications. Normalizing without liquid quenching increases its strength sufficiently for most uses; however, it may be heat treated for greater strength. It may be nitrited for maximum wear and abrasion resistance.

E4140 Aircraft Quality Bars

4140 is an electric furnace processed, through-hardening alloy processed to meet the rigid standards of the aircraft industry and vacuum degassed to conform to the magnetic particle inspection standards of AMS-2301. It contains .95% chromium and approximately .20% molybdenum. It has good fatigue, impact and abrasion resistance, and an extremely wide range of strength and toughness, obtainable by variations in heat treatments. In the fully hardened condition, it has outstanding tensile strength. It has a high fatigue and tensile ratio. 4140 may be successfully nitrited for maximum wear and abrasion resistance. It is remarkably well suited for use in extremely elevated temperatures.

E4340 Aircraft Quality Bars

E4340 is a highly alloyed, electric-furnace processed; vacuum degassed grade, which conforms to the rigid aircraft standards of AMS-2301. It contains approximately 0.8% chromium, 1.8% nickel, and 25% molybdenum. The combination of these elements assures deep and uniform hardness when heat-treated, particularly when oil quenched. It possesses exceptional ductility and toughness and remarkably high fatigue strength, snaking E4340 the steel to use for highly stressed parts operating under heavy-duty conditions. It also maintains its excellent strength and hardness while functioning under extremely elevated temperatures.

E8740 Aircraft Quality Bars

8740 is an electric-furnace processed, chromium-nickel alloy containing approximately .25% molybdenum. It is primarily an oil hardening steel designed to provide excellent shock resistance and outstanding hardenability. It is a very tough alloy, especially free from temper brittleness.

E9310 Aircraft Quality Bars

Type 9310 is a vacuum degassed, carburizing steel containing approximately 1.25% chro­mium, 3.25% nickel, and .12% molybdenum. This alloy is suitable for heavy sectioned components because of its high hardenability and fatigue resistance, and because of its high core strength and hardness offering a narrow hardness range between light and heavy sec­tions. It offers excellent ductility and toughness, and may be used without carburizing. Most applications of 9310 do call for use in the carburized state, which increases its wear and abra­sion resistance to a high degree. It passes the most rigid magnetic particle inspections.

E52100 Bearing Quality Bars

552100 is an electric-furnace processed, vacuum degassed alloy containing approximately 1.5% chromium and 1.0% carbon. In order to maximize machinability and because of the high carbon content, 552100 may be spheroidize annealed. It is primarily a bearing steel possessing excellent resistance to wear and abrasion, medium toughness, and high strength in compression. It is a moderately deep hardening alloy with low softening resistance to elevated temperatures.