ASTM Hot Rolled 4320 Round Alloy Steel Bars Diameter 3-1000mm Hight Strength 20CrMnMoH Flat Steel Bar Factory
ASTM 4320 Alloy Steel Bar
ASTM 4320 (AISI 4320) is a classic nickel-chromium-molybdenum alloy carburizing steel (UNS G43200). It is well-known for its excellent combination of high hardenability, high core toughness, and high surface hardness after heat treatment. It is widely used in key mechanical parts requiring high strength, impact resistance, and wear resistance.
1. Basic Information
Standard: ASTM A29/A29M, SAE 4320
Type: Low-carbon alloy structural steel / carburizing steel
Approximate Chinese Grade: G20CrNi2MoA (GB/T 3077)
Common Shapes: Round bar, forging, square bar, wire rod
2. Chemical Composition (wt%)
| Element |
C |
Si |
Mn |
P |
S |
Cr |
Ni |
Mo |
Fe |
| Range |
0.17~0.22 |
0.15~0.35 |
0.45~0.65 |
≤0.035 |
≤0.040 |
0.40~0.60 |
1.65~2.00 |
0.20~0.30 |
Balance |
3. Key Properties
Hard surface with tough core: Low carbon ensures high core toughness (impact resistance). After carburizing and quenching, surface hardness can reach HRC 60~64, with excellent wear and contact fatigue resistance.
High hardenability: High nickel (~1.8%) combined with chromium and molybdenum enables uniform high strength and toughness even in large-section parts.
Excellent toughness: Especially good low-temperature toughness, strong resistance to impact and overload fracture.
Workability: Good forgeability and machinability; weldability is fair (preheating before welding and post-weld heat treatment recommended).
4. Typical Mechanical Properties
| Condition |
Tensile Strength (MPa) |
Yield Strength (MPa) |
Elongation δ5 (%) |
Reduction of Area (%) |
Hardness (HB) |
| Annealed |
~580 |
~425 |
≥29 |
~58 |
~163 |
| Carburized + quenched + tempered |
≥980 |
≥785 |
≥13 |
≥45 |
Surface HRC 60+ |
5. Recommended Heat Treatment
Annealing: 800~850°C holding, slow cooling → softening for improved machinability
Normalizing: 880~920°C air cooling → grain refinement
Carburizing: 900~930°C (carbon potential 0.8~1.2%C)
Quenching: 820~850°C oil quenching
Tempering: 150~200°C low-temperature tempering → stress relief while maintaining high hardness
6. Main Applications (Round Bar)
Automotive / Construction Machinery: Transmission gears, differential gears, planetary gears, half shafts, spline shafts, bearing rings
General Machinery: Heavy-duty shafts, cams, bolts, wear-resistant pins, high-strength fasteners
Aerospace / Rail Transit: Key transmission components, bearings, high-strength structural parts
7. Round Bar Supply Conditions
Black bar: Hot rolled / forged round bar with mill scale
Bright bar: Cold drawn, peeled, polished; high dimensional accuracy and smooth surface
Diameter range: Generally φ8mm ~ φ300mm+
8. Comparison with Similar Grades
4320 vs 8620: 4320 has higher nickel content, offering better toughness and hardenability than 8620, making it more suitable for heavy-duty, large-size, high-impact applications.
4320 vs 20CrNiMo: The Chinese grade 20CrNiMo has lower nickel, with overall performance slightly lower than 4320.
Q1: Why choose us?
A: Our company, as an internationally experienced and professionalsupplier, has been engaged in steel business for more than ten years. Wecan provide a variety of steel products with high quality to our clients.
Q2: Can you provide OEM/ODM service?
A: Yes. Please feel free to contact us for more details
Q3:What is your terms of payment?
A: 100% T/T advance.
30% T/T and balance against copy of documents.
30% T/T advance, balance L/C at sight.
Q4: Can we visit your factory?
A: Warmly welcome. Once we have your schedule, we will arrange theprofessional sales team to follow up your case.
Q5: Can you provide sample?
A: Yes. Sample is free for regular sizes, but the buyer needs to pay freightcost.
Q6: How long is your delivery time?
A: Regular lead time is 15 to 30 days after receiving deposit.
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