Steel 4320 Carburized
Heat-treated state
AISI/SAE 4320 · UNS G43200 · JIS SNCM420
The intended service condition: hard wear/contact-fatigue-resistant case over a tough Ni-Mo core for gears and bearing races.
Values for the Carburized condition
Other 4320 tempers and conditions
4320 is listed in 7 conditions; see the grade overview at 4320.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
HRDefault Hot rolled | Standard stock form for carburizing-grade bar that will be machined and then heat treated. | 415 | 640 | 22 | 187 HB | — |
full anneal ~840–870 °C, furnace cool | Softest condition; pick it for heavy machining, deep hobbing or cold forming before carburizing. | 425 | 580 | 29 | 163 HB | — |
~895 °C, air cool | Refines grain and homogenizes forgings/bar before carburizing; best pre-heat-treat condition for dimensional stability. | 464 | 793 | 21 | 21 HRC | — |
Cold rolled | Thin strip/sheet form for stamped, carburized parts needing good surface and tight thickness. | 550 | 700 | 12 | 15 HRC | 7.8 % IACS |
Cold drawn | Choose for close-tolerance, bright-surface bar that needs minimal turning before carburizing. | 620 | 745 | 15 | 217 HB | — |
Quenched and tempered | Direct-hardened condition for shafts and non-carburized parts needing high core strength with good toughness. | 900 | 1,080 | 15 | 34 HRC | — |
CarburizedThis page case 58–62 HRC, core ~30–40 HRC | The intended service condition: hard wear/contact-fatigue-resistant case over a tough Ni-Mo core for gears and bearing races. | 1,000 | 1,200 | 12 | 60 HRC | — |
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 99% of steel grades
- Difficult to weld — 10/100, worse than 99% of steel grades
- Limited formability — 3/100, 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 are specific to this condition. Other listed values are 4320 reference data and may not represent this condition. Bars are the position among steel grades.
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 99% of steel grades); weldability not recommended (10/100); formability not recommended (3/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
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 99% 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; every part is priced by an engineer rather than instantly. 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.