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AISI 4340/JIS SNCM439 Alloy Steel Bar

alloy bar (7)

Size: 16-500mm

Hot rolled or forged

Process: EAF + LF + VD + Forged + Heat Treatment (optional)


AISI 4340/JIS SNCM439 Alloy Steel Bar

4340 alloy steel round bar is a nickel-chromium-molybdenum alloy steel known for its toughness and its ability to attain high strengths in the heat-treated condition. It has very good fatigue resistance.

AISI 4340 alloy steel round bar Similar Grades

  • Standard: GB/AISI/JIS
  • Grade: 40CrNiMoA/4340/SNCM439

AISI 4340 alloy steel round bar Available Size

  • Hot rolled round bar: dia16mm-dia310mm
  • Hot rolled flat bar: thickness5mm-30mm, width50mm-130mm
  • Hot rolled square bar: 16mm*16mm-100mm*100mm
  • Forged steel round bar: dia100mm-dia1500mm
  • Forged flat bar: thickness20mm-400mm, width80mm-1000mm
  • Forged steel block: 100mm*100mm-1000mm*1000mm
  • Cold drawn round bar: dia4mm-dia100mm

Heat Treatment


  • Annealing: AISI 4340 round bar alloy steel is annealed at 844°C (1550°F) followed by cooling the furnace.
  • Tempering: AISI 4340 round bar alloy steel should be in the heat treated or normalized and heat treated condition before tempering. Tempering temperatures depend upon the desired strength level.
  • Hardening: AISI 4340 round bar alloy steel can be hardened by cold working or heat treatment.

Packaging & Delivery

  • Delivery: 30 Days according to your quantity;
  • Transport: By bulk or Containers;
  • Payment terms: L/C, T/T
  • 4340 round bar Hot rolled, black surface / brigth surface with customers’ required heat treatment

Chemical composition (%)
C Si Mn Cr Ni Mo P s
0.37-0.44 0.17-0.37 0.50-0.80 0.60-0.90 1.25-1.65 0.15-0.25 ≤0.035 ≤0.035
0.38-0.43 0.15-0.35 0.60-0.80 0.70-0.90 1.65-2.00 0.20-0.30 ≤0.035 ≤0.040
0.36-0.43 0.15-0.35 0.60-0.90 0.60-1.00 1.60-2.00 0.15-0.30 ≤0.030 ≤0.030


  • Power transmission gears and shafts, aircraft landing gear, and other structural parts.