AISI 4340 alloy steel is a high performance medium carbon alloy steel with high strength, good toughness and wear resistance. It is widely used in fields where high mechanical properties and good fatigue resistance. ‌‌

Chemical composition and mechanical properties

The main chemical components of AISI 4340 alloy steel include carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), chromium (Cr), nickel (Ni) 

and molybdenum (Mo). Its typical chemical composition is as follows:

Carbon (C) : 0.38%~0.43%

Silicon (Si) : 0.15%~0.35%

Manganese (Mn) : 0.60%~0.80%

Phosphorus (P) : ≤0.035%

Sulfur (S) : ≤0.040%

Chromium (Cr) : 0.70%~0.90%

Nickel (Ni) : 1.65%~2.00%

Molybdenum (Mo) : 0.20%~0.30%

Its typical mechanical properties are as follows:

Tensile strength (Rm) : ≥1100 MPa

Yield strength (ReL) : ≥900 MPa

Elongation (A) : ≥10%

Section shrinkage (Z) : ≥50%

Impact power (KV2) : ≥47 J (-20°C)

Hardness (HRC) : usually in the range of 28~34 HRC ‌

Heat treatment process

AISI 4340 alloy steel's heat treatment process includes quenching and tempering:quenching ‌ : the temperature is 820°C~870°C, and the holding time is 

determined according to the thickness and shape of the parts, usually for 1 hour every 25 mm thickness. Cooling methods are usually oil or water cooling, 

oil cooling is suitable for large or complex parts, water cooling is suitable for small or simple parts.

‌tempering ‌ : The temperature is 500°C~650°C, the holding time depends on the thickness and shape of the part, usually 1~2 hours. The cooling method is 

usually air cooling or furnace cooling ‌

Application field

AISI 4340 alloy steel is widely used in the following fields due to its excellent comprehensive properties:

1.Automobile industry ‌ : engine connecting rod, crankshaft, piston pin, transmission gear, drive shaft and so on.

‌2.Mechanical engineering ‌ : large machinery shaft, gear, connecting rod, bolt, hydraulic cylinder piston rod, hydraulic valve body, etc.

‌3. Aerospace ‌ Parts, fasteners, etc. of aircraft engines.

‌4. Oil and gas ‌ : drill rods, sucker rods, valves, etc.

‌5. Railway transport ‌ : axle, gear, bogie par

We can provide all kinds of round bars, steel plates, round/square tubes and coils, please feel free to contact with us if you have any needs, our email address is sales1@bolaishengsh.com.