Carbon & Alloy Steels Technical Information

Basics of...Carbon & Alloy Steels

Carbon and alloy steels are the most basic and most frequently used steels. They normally have small amounts of carbon and alloying elements. Carbon steels are frequently used as is, without heat treatment of any kind, but can be case hardened. Addition of lead or sulfur improves machinability but is detrimental to weldability, heat treatability and formability. Steel parts that require no special properties or heat treatment often are madeof this type of steel. Alloy steels have additional alloying elements and carbon added to improve the mechanical properties and hardenability. The alloying elements allow the steel to form carbon or alloy carbides that improve wear and/or toughness when heat treated.

Alloying Elements

Carbon: Carbon is present in all steels and provides hardenability. Strength and hardness increase with increased carbon content. Ductility and weldability decrease as carbon increases.
Manganese: Contributes to strength and hardness but to a lesser extent than carbon.
Phosphorus: High phosphorus decreases ductility and toughness so it is usually kept below a certain level.
Sulfur: Sulfur decreases ductility, weldability, toughness and surface quality but is used in some steels to improve machinability. Levels of sulfur are usually specified as a maximum value.
Silicon: Improves strength and hardness but decreases machinability and formability.
Nickel: Greatly increases low temperature toughness and somewhat improves hardenability.
Chromium: Greatly improves hardenability and is a strong carbide former. Chrome improves resistance to wear and abrasion and also adds to corrosion and heat resistance.
Molybdenum: Adds to hardenability and control of hardenability of steel. Molybdenum forms stable carbides and increased tensile and creep strength at high temperatures.
Vanadium: Enhances hardenability and forms stable carbides

Material Type and Description

Type	Description
Carbon Steels
1018	Low carbon cold finished bar useful as a general purpose steel. 1018 can be carburized for a hard surface and has good weldability and bendability. Used for machine parts, structural parts, gears, cams, worms, pinions.
1045	1045 cold drawn is a medium carbon steel used when greater strength is desired than 1018. Used for shafts, machine parts, bolts, gears, pinions. Due to the higher carbon 1045 does not weld well unless special procedures are followed. Responds to heat treatment. Hardness in the heat treated condition depends on heat treat process and temperatures.
12L14	The addition of .15/.35 % lead and sulfur makes this among the easiest to machine steels. Used for machine parts, shafts, bushings, couplings, hydraulic fittings. Not weldable or hardenable.
1215	A free machining, resulfurized and rephosphorized, non-leaded steel. Machines to a smooth bright finish. Used for machine parts, shafts, bushings. Poor weldability due to sulfur content. Not normally heat treated.
Alloy Steels
4140	General purpose alloy steel suitable for gears, machine parts, cams, short run dies, spindles, bolts, zinc die cast dies, low cost molds and other components requiring an elevated tensile strength. Better wear resistance than carbon steels.
8620	8620 is a nickel-chromium-molybdenum alloy steel. It is recommended that the steel be hardened by carburization which gives it a tough core and hard, wear resistant surface. Nickel provides good toughness while the chrome and molybdenum increase through hardness and wear resistance. Uses include machine parts as gears, crankshafts, shafts, gear rings. 8620 has good machinability before carburizing.

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