Steel 4320 · supply condition · default condition
Steel 4320-HR
Properties of the HR condition, compared with the other 4320 tempers.
Standard stock form for carburizing-grade bar that will be machined and then heat treated.
What is 4320-HR?
4320-HR is 4320 supplied in the HR condition — standard stock form for carburizing-grade bar that will be machined and then heat treated. 4320-HR has a yield strength of 415 MPa (60.2 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 55% of steel grades. Elongation at break is 22% and the elastic modulus is 205 GPa (29.7 Msi). 4320-HR 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).
4320-HR properties
Typical room-temperature values for 4320-HR — 11 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-HR 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-HR has a yield strength of 415 MPa (60.2 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 55% of steel grades. Elongation at break is 22% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4320-HR is rated for continuous service to 350°C (662 °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-HR 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-HR 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-HR's machinability is fair (50/100, worse than 53% of steel grades); weldability fair (40/100); formability fair (45/100).
Common Calculations5
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-HR
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-HR — frequently asked
What is 4320-HR used for?
4320-HR is typically used for gears, pins and shafts. In short: carburizing Ni-Cr-Mo bar.
What is the yield strength of 4320-HR?
4320-HR has a typical yield strength of 415 MPa (60.2 ksi) and a tensile strength of 640 MPa (92.8 ksi) — weaker than 55% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is 4320-HR easy to machine?
Reasonably — machinability is rated fair (50/100, worse than 53% 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-HR be welded?
With care — weldability is rated fair (40/100). Restricted weldability — preheat 200–300 °C, use low-hydrogen Ni-Mo filler and PWHT; never weld after carburizing.
What surface finishes work on 4320-HR?
No anodizing; protect with oil, black oxide, manganese phosphate, or zinc/zinc-nickel plating with post-plate bake to avoid hydrogen embrittlement.
Can 4320-HR 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-HR?
4320-HR is rated for continuous use to about 350°C (662 °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-HR?
Yes — 4320-HR 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.