ASTM A519 Grade Chromoly 4340 Seamless Alloy Steel Tube
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|Outer diameter||83-254 mm|
|Wall thickness||7 to 60 mm|
|Cold drawn tolerance for OD and ID||within ±0.2mm|
|Cold rolled tolerance for OD and ID||within ±0.1mm|
Alloy Steel 4340, also referred to as AISI 4340, is a nickel, chromium, and molybdenum alloy steel. This heat treatable alloy is known for its toughness and high-strength in a heat-treated condition. It is weldable by both fusion and resistance welding, and offers good ductility in the annealed condition. You will find Alloy Steel 4340 used in the aerospace and automotive industries in a number of different structural situations such as:
Aircraft landing gear
Power transmission gears
Power transmission shafts.
Dimensions：Outer diameter: 83-254 mm, Wall thickness: 7 to 60 mm, length: not more than 12 meters.
Tolerance for OD and ID：
Cold drawn: within ±0.2mm
Cold rolled: within ±0.1mm
Tolerance for Wall Thickness：
Hot rolled: within +/-5%,
Cold drawn: within 0.6mm
Process：Hot Rolled, Cold Drawn, Precision Rolled
Delivery Condition：Hot rolled, Cold drawn, Annealed, Normalized, Quenched and tempered.
Surface Condition：Black surface, Rough turned, Peeled.
AISI 4340 Steel Grade Heat Treatment
For pre-hardened steel stress relieving is achieved by heating steel 4340 to between 500 to 550°C. Heat to 600 °C – 650 °C, hold until temperature is uniform throughout the section, soak for 1 hour per 25 mm section, and cool in still air.
A full anneal may be done at 844°C (1550 F) followed by controlled (furnace) cooling at a rate not faster than 10°C (50 F) per hour down to 315°C (600 F). From 315°C 600 F it may be air cooled.
AISI 4340 alloy steel should be in the heat treated or normalized and heat treated condition before tempering. The tempering temperature for depends upon the strength level desired. For strength levels in the 260 – 280 ksi range temper at 232°C (450 F). For strength in the 125 – 200 ksi range temper at 510°C (950 F). And don’t temper the 4340 steels if it is in the 220 – 260 ksi strength range as tempering can result in degradation of impact resistance for this level of strength.
Tempering should be avoided if possible within the range 250 °C – 450 °C due to temper brittleness.
Flame or Induction Hardening
As mentioned above, pre-hardened and tempered 4340 steel bars or plates can be further surface hardened by either the flame or induction hardening methods resulting in a case hardness in excess of Rc 50. AISI 4340 steel parts should be heated as quickly as possible to the austenitic temperature range (830 °C – 860 °C) and required case depth followed by an immediate oil or water quenching, depending upon hardness required, workpiece size/shape and quenching arrangements.
Following quenching to hand warm, tempering at 150°C – 200°C will reduce stresses in the case with minimal effect on its hardness.