Steel 4320 · heat-treated state
Steel 4320 Carburized
Properties of the Carburized condition, compared with the other 4320 tempers.
The intended service condition: hard wear/contact-fatigue-resistant case over a tough Ni-Mo core for gears and bearing races.
What is 4320 Carburized?
4320 Carburized is 4320 heat treated to Carburized — the intended service condition: hard wear/contact-fatigue-resistant case over a tough Ni-Mo core for gears and bearing races. 4320 Carburized has a yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,200 MPa (174 ksi) — stronger than 92% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi). 4320 Carburized has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). HR is the default condition FabDigit quotes; Carburized is available on request or by drawing note.
Advantages
- High strength — 1,000 MPa (145 ksi), better than 92% of steel grades
Limitations
- Difficult to machine — 10/100, worse than 100% of steel grades
- Limited formability — 3/100, worse than 100% of steel grades
- Difficult to weld — 10/100, worse than 99% of steel grades
- Limited service temperature — 180°C (356 °F), worse than 98% of steel grades
- Limited ductility — 12%, worse than 84% of steel grades
4320 Carburized properties
Typical room-temperature values for 4320 Carburized — 13 properties are specific to this condition; the rest are grade-level values shared by every 4320 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
4320 Carburized has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical13
4320 Carburized has a yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,200 MPa (174 ksi) — stronger than 92% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4320 Carburized is rated for continuous service to 180°C (356 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 11.7 µm/m·K (6.5 µin/in·°F).
Electrical2
4320 Carburized has an electrical resistivity of 2.2×10⁻⁷ Ω·m.
Chemical & Environmental3
Corrosion resistance is not recommended (11/100), worse than 73% of steel grades.
Sustainability4
Producing a kilogram of 4320 Carburized takes about 31 MJ of energy and emits 2.3 kg of CO₂ — more than 64% of steel grades. Typical recycled content is 30%.
Manufacturability7
4320 Carburized's machinability is not recommended (10/100, worse than 100% of steel grades); weldability not recommended (10/100); formability not recommended (3/100).
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 4320 tempers and conditions
4320 is also supplied in 6 other conditions. The full side-by-side table is on the 4320 overview.
- HRDefaultStandard stock form for carburizing-grade bar that will be machined and then heat treated.415 MPa yield · 187 HB
- CarburizedThe intended service condition: hard wear/contact-fatigue-resistant case over a tough Ni-Mo core for gears and bearing races.1,000 MPa yield · 60 HRC
- Q&TDirect-hardened condition for shafts and non-carburized parts needing high core strength with good toughness.900 MPa yield · 34 HRC
- CDChoose for close-tolerance, bright-surface bar that needs minimal turning before carburizing.620 MPa yield · 217 HB
- CRThin strip/sheet form for stamped, carburized parts needing good surface and tight thickness.550 MPa yield · 207 HB
- NormalizedRefines grain and homogenizes forgings/bar before carburizing; best pre-heat-treat condition for dimensional stability.464 MPa yield · 21 HRC
- AnnealedSoftest condition; pick it for heavy machining, deep hobbing or cold forming before carburizing.425 MPa yield · 163 HB
Working with 4320 Carburized
Is 4320 easy to machine?
Machine in the annealed or normalized condition with carbide tooling and rigid setups; leave grind stock because carburize-quench distorts, and finish-grind the case.
Can 4320 be welded?
Restricted weldability — preheat 200–300 °C, use low-hydrogen Ni-Mo filler and PWHT; never weld after carburizing.
Can 4320 be formed, bent or molded?
Cold-form only in the annealed state and with generous radii; hot forge 1150–1200 °C, finish above 900 °C and normalize afterwards.
What surface finishes work on 4320?
No anodizing; protect with oil, black oxide, manganese phosphate, or zinc/zinc-nickel plating with post-plate bake to avoid hydrogen embrittlement.
4320 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| C | 0.17 – 0.22 | 0.2 |
| Mn | 0.45 – 0.65 | 0.55 |
| Si | 0.15 – 0.35 | 0.25 |
| Ni | 1.65 – 2 | 1.82 |
| Cr | 0.4 – 0.6 | 0.5 |
| Mo | 0.2 – 0.3 | 0.25 |
| P | ≤ 0.04 | — |
| Smax; 4320H/E-grades tighter | ≤ 0.04 | — |
| Fe | balance | — |
4320 Carburized — frequently asked
What is 4320 Carburized used for?
4320 Carburized is typically used for gears, pins and shafts. In short: carburizing Ni-Cr-Mo bar.
What is the yield strength of 4320 Carburized?
4320 Carburized has a typical yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,200 MPa (174 ksi) — stronger than 92% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is 4320 Carburized easy to machine?
Not especially — machinability is rated not recommended (10/100, worse than 100% of steel grades). Machine in the annealed or normalized condition with carbide tooling and rigid setups; leave grind stock because carburize-quench distorts, and finish-grind the case.
Can 4320 Carburized be welded?
Not readily — weldability is rated not recommended (10/100). Restricted weldability — preheat 200–300 °C, use low-hydrogen Ni-Mo filler and PWHT; never weld after carburizing.
What surface finishes work on 4320 Carburized?
No anodizing; protect with oil, black oxide, manganese phosphate, or zinc/zinc-nickel plating with post-plate bake to avoid hydrogen embrittlement.
Can 4320 Carburized be formed, bent or molded?
Cold-form only in the annealed state and with generous radii; hot forge 1150–1200 °C, finish above 900 °C and normalize afterwards.
What is the maximum service temperature of 4320 Carburized?
4320 Carburized is rated for continuous use to about 180°C (356 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 4320-HR and 4320-CD?
HR is the default condition — standard stock form for carburizing-grade bar that will be machined and then heat treated. CD: choose for close-tolerance, bright-surface bar that needs minimal turning before carburizing. Yield strength is 415 MPa in HR versus 620 MPa in CD.
Can FabDigit make parts in 4320 Carburized?
Yes — 4320 Carburized is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating (carburizing of Ni-Cr-Mo steels) — ASM International (1991)
- GB/T 3077 (20CrNi2Mo) — SAC (2015)
- JIS G 4053 (SNCM420) — JSA (2016)
- Mysteel / SMM alloy bar and nickel price references — Mysteel, SMM (2025)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.