Forging Alloy Steel 3140

Chemical Analysis
C Carbon
.38 – .43
Mn Manganese
.7 – .9
P Phosphorus
S Sulfur
Si Silicon
.2 – .35
Ni Nickel
1.1 – 1.4 max
Cr Chromium
0.55 – 0.75

General Characteristics of AISI 3140

Alloy steel 3140 is a nickel-chromium low-alloy steel. The alloy has good hardenability, and good strength and toughness properties.

Alloy AISI 3140 was designed to withstand high temperature exposure and severe corrosive conditions. The alloy is not embrittled by long exposure to high temperatures, thanks to the nickel, chromium and aluminium contents that together form a protective and adherent oxide film.


This alloy finds its uses in applications where strength and toughness are prime requirements. The alloy finds many uses in the auto industry as forged crankshafts, gear shafts and connecting rods, and in the aircraft industry as landing gear.

Forging AISI 3140

This alloy is forged at a start temperature of around 2200ºF (1205ºC) and could be forged down to approximately 1700ºF(925ºC.) The alloy may be slow cooled after forging, or transferred to a furnace held at a temperature approximating the forging finishing temperature, soaked then air cooled.

Heat Treatment

Annealing: For optimum machinabilty of this alloy, a microstructure consisting of coarse lamellar pearlite to coarse spheroidite is considered to be optimum. Such a structure can be obtained by austenitizing at 1525ºF (830ºC), furnace cooling to 1350ºF (730ºC) then to 1200ºF (650º) at 20ºF/hr. An alternative is an iso-anneal at 1225ºF (660ºC)

Normalizing: 1600ºF (870ºC) and air cool.

Hardening: The alloy will be austenitized at around 1500 – 1550ºF (815 – 845ºC) and oil or water quenched depending upon section size and intricacy.

Tempering: to desired hardness, using temperatures based on past experience, following water or oil quench.

Machinability: This grade of alloy is readily machined following suitable heat treatment.

Weldability: This steel may be welded by normal fusion methods, but prior to hardening and tempering. Pre heat and post heat are recommended.

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