AISI / Alloy Steel 3145

Chemical Analysis
C% Carbon
0.43 – 0.48
Mn% Manganese
0.70 – 0.90
P% Phosphorus
0.040 max
S% Sulfur
0.040 max
Si% Silicon
0.20 – 0.35
Ni% Nickel
1.10 – 1.40
Cr% Chromium
0.70 – 0.90

General characteristics of Alloy Steel 3145

Alloy steel 3145 is a nickel-chromium low-alloy steel. The alloy has good hardenability, and good strength and toughness properties. It has somewhat better hardenability than does alloy 3140 due to the slightly higher chromium content, plus a higher as-quenched hardness.


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


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 1300ºF (705ºC) then to 1190ºF (645ºC) 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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