4340 steel is a high-strength alloy steel known for its excellent toughness, wear resistance, and good fatigue strength. Here are key properties of 4340 steel:
Chemical Composition:
Carbon (C): 0.38-0.43%
Chromium (Cr): 0.7-0.9%
Manganese (Mn): 0.6-0.8%
Phosphorus (P): 0.035% max
Sulfur (S): 0.04% max
Silicon (Si): 0.15-0.35%
Nickel (Ni): 1.65-2.0%
Molybdenum (Mo): 0.2-0.3%
Heat Treatment:
Typically supplied in a heat-treated and tempered condition.
Heat treatment involves quenching and tempering to achieve the desired combination of hardness and toughness.
Mechanical Properties:
Tensile Strength: Typically in the range of 745-1000 MPa.
Yield Strength: Generally around 470 MPa.
Hardness: After heat treatment, the hardness is typically in the range of 22-32 HRC (Rockwell Hardness).
Machinability:
Machinable in the annealed condition.
After heat treatment, machining becomes more challenging due to increased hardness.
Weldability:
Fair weldability, but precautions are necessary to avoid cracking during welding.
Preheating and post-weld heat treatment are recommended for certain applications.
Fatigue Resistance:
Excellent fatigue strength, making it suitable for components subjected to cyclic loading.
Applications:
Commonly used in applications requiring high strength and toughness, such as aircraft landing gear, crankshafts, connecting rods, and other critical components in the aerospace and automotive industries.
Temperatures:
4340 steel can be used in elevated temperature environments, and it maintains its mechanical properties at moderately high temperatures.
Corrosion Resistance:
While not a stainless steel, it has good corrosion resistance in most environments. However, it may be susceptible to corrosion under harsh conditions.