Steel 4718-A (Solution annealed)
Temper · default condition
AISI/SAE 4718 · UNS G47180
Softest, most machinable condition — the standard stock form for gear blanks that will be carburized.
Values for the A condition
Other 4718 tempers and conditions
4718 is listed in 6 conditions; see the grade overview at 4718.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefaultThis page Solution annealed | Softest, most machinable condition — the standard stock form for gear blanks that will be carburized. | 400 | 585 | 27 | 170 HB | — |
Hot rolled | Mill-supplied as-rolled bar for parts that will be normalized or carburized after rough machining. | 460 | 700 | 22 | 207 HB | — |
Normalized | Uniform fine-grain structure for dimensional stability and consistent case depth before carburizing. | 480 | 725 | 22 | 217 HB | — |
Cold drawn | Cold-drawn bar for close size tolerance and better as-machined finish on small shafts and pins. | 640 | 760 | 15 | 229 HB | — |
direct quenched and tempered (through hardened core) | Through-hardened condition for shafts and non-carburized parts needing high core strength with good toughness. | 830 | 1,000 | 17 | 32 HRC | — |
Carburized, quenched & tempered | The service condition for gears and races: hard wear-resistant case with compressive residual stress over a tough alloy core. | 1,000 | 1,250 | 12 | 60 HRC | — |
What is 4718-A?
4718-A is 4718 in the A temper — softest, most machinable condition — the standard stock form for gear blanks that will be carburized. 4718-A has a yield strength of 400 MPa (58 ksi) and a tensile strength of 585 MPa (84.8 ksi) — weaker than 60% of steel grades. Elongation at break is 27% and the elastic modulus is 205 GPa (29.7 Msi). 4718-A has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F).
Advantages
- Ductile — tolerates forming and impact — 27%, better than 86% of steel grades
Limitations
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
4718-A properties
Typical room-temperature values for 4718-A; 12 are specific to this condition. Other listed values are 4718 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
4718-A has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical13
4718-A has a yield strength of 400 MPa (58 ksi) and a tensile strength of 585 MPa (84.8 ksi) — weaker than 60% of steel grades. Elongation at break is 27% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4718-A is rated for continuous service to 200°C (392 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
4718-A conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 4718-A takes about 32 MJ of energy and emits 2.3 kg of CO₂ — more than 70% of steel grades. Typical recycled content is 30%.
Manufacturability7
4718-A's machinability is good (55/100, better than 62% of steel grades); weldability fair (45/100); formability good (55/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 4718-A
Is 4718 easy to machine?
Machine in the annealed or normalized state (≈65 % of 1212) with carbide tooling and generous coolant; leave grinding stock because carburizing causes distortion.
Can 4718 be welded?
Weldable with low-hydrogen consumables but requires 200–300 °C preheat and immediate temper; avoid welding on carburized surfaces.
Can 4718 be formed, bent or molded?
Hot forge 1150–1200 °C and normalize afterwards; cold forming is limited to mild bending/upsetting in the annealed condition.
What surface finishes work on 4718?
Case surfaces are typically hard-ground or honed; uncarburized areas take black oxide, manganese phosphate, zinc or nickel plating (bake to avoid hydrogen embrittlement).
4718 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 | 0.16 – 0.21 | 0.19 |
| Mn | 0.7 – 0.9 | 0.8 |
| Si | 0.15 – 0.35 | 0.25 |
| Ni | 0.9 – 1.2 | 1.05 |
| Cr | 0.35 – 0.55 | 0.45 |
| Mo | 0.3 – 0.4 | 0.35 |
| P | ≤ 0.04 | — |
| S | ≤ 0.04 | — |
| Fe | balance | — |
4718-A — frequently asked
What is 4718-A used for?
4718-A is typically used for heavy-duty gears, pinions and carburized power-transmission shafts. In short: ni-Cr-Mo carburizing grade; alloy-rich 8620 alternative; fatigue-resistant gear steel.
What is the yield strength of 4718-A?
4718-A has a typical yield strength of 400 MPa (58 ksi) and a tensile strength of 585 MPa (84.8 ksi) — weaker than 60% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is 4718-A easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machine in the annealed or normalized state (≈65 % of 1212) with carbide tooling and generous coolant; leave grinding stock because carburizing causes distortion.
Can 4718-A be welded?
With care — weldability is rated fair (45/100). Weldable with low-hydrogen consumables but requires 200–300 °C preheat and immediate temper; avoid welding on carburized surfaces.
What surface finishes work on 4718-A?
Case surfaces are typically hard-ground or honed; uncarburized areas take black oxide, manganese phosphate, zinc or nickel plating (bake to avoid hydrogen embrittlement).
Can 4718-A be formed, bent or molded?
Hot forge 1150–1200 °C and normalize afterwards; cold forming is limited to mild bending/upsetting in the annealed condition.
What is the maximum service temperature of 4718-A?
4718-A is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 4718-A and 4718-CD?
A is the default condition — softest, most machinable condition — the standard stock form for gear blanks that will be carburized. CD: cold-drawn bar for close size tolerance and better as-machined finish on small shafts and pins. Yield strength is 400 MPa in A versus 640 MPa in CD.
Sources
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- SAE J1268 — Hardenability Bands for Carburizing Steels (4718H) — SAE International (2019)
- ASTM A29/A29M — General Requirements for 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.4A — Steel Heat Treating Fundamentals and Processes (carburizing) — ASM International (2013)
- 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.