Steel 718 · heat-treated state · default condition
Steel 718 Prehard
Properties of the Prehard condition, compared with the other 718 tempers.
Standard stock condition: machine the cavity directly, no heat treatment or size-change risk.
What is 718 Prehard?
718 Prehard is 718 heat treated to Prehard — standard stock condition: machine the cavity directly, no heat treatment or size-change risk. 718 Prehard has a yield strength of 880 MPa (128 ksi) and a tensile strength of 1,030 MPa (149 ksi) — stronger than 90% of steel grades. Elongation at break is 14% and the elastic modulus is 205 GPa (29.7 Msi). 718 Prehard has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,420°C (2,588 °F).
Advantages
- Polishes to a fine finish — 80/100, better than 97% of steel grades
- High strength — 880 MPa (128 ksi), better than 90% of steel grades
Limitations
- Limited formability — 15/100, worse than 87% of steel grades
- Poor heat conductor — 32 W/m·K (18.5 BTU/hr·ft·°F), worse than 82% of steel grades
- Limited ductility — 14%, worse than 75% of steel grades
718 Prehard properties
Typical room-temperature values for 718 Prehard — 12 properties are specific to this condition; the rest are grade-level values shared by every 718 temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
718 Prehard has a density of 7.8 g/cm³ (0.282 lb/in³), lighter than 87% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
718 Prehard has a yield strength of 880 MPa (128 ksi) and a tensile strength of 1,030 MPa (149 ksi) — stronger than 90% of steel grades. Elongation at break is 14% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
718 Prehard is rated for continuous service to 400°C (752 °F). It conducts heat at 32 W/m·K (18.5 BTU/hr·ft·°F), worse than 82% of steel grades. Thermal expansion is 12.6 µm/m·K (7 µin/in·°F).
Electrical2
718 Prehard has an electrical resistivity of 2.2×10⁻⁷ Ω·m.
Chemical & Environmental2
Corrosion resistance is poor (15/100), better than 75% of steel grades.
Sustainability4
Producing a kilogram of 718 Prehard 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
718 Prehard's machinability is good (55/100, better than 62% of steel grades); weldability fair (45/100); formability poor (15/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 718 tempers and conditions
718 is also supplied in 5 other conditions. The full side-by-side table is on the 718 overview.
- PrehardDefaultStandard stock condition: machine the cavity directly, no heat treatment or size-change risk.880 MPa yield · 32 HRC
- Q&T-40Used only on small inserts/cores that are re-austenitized (~850 °C, oil) and low-tempered for extra strength; expect distortion and lower toughness.1,150 MPa yield · 41 HRC
- NitridedPost-machining surface treatment for wear and gas-erosion resistance on slides, gates and glass-filled-resin cavities.1,030 MPa tensile
- Prehard-HChoose when the mould runs abrasive filled resins or needs better cavity wear/dent resistance while still machinable prehard.1,000 MPa yield · 36 HRC
- Prehard-SPick for optical/high-gloss cavities and photo-etched textures where inclusion streaks and polish defects are unacceptable.880 MPa yield · 32 HRC
- AnnealedPick when you intend to rough-machine deep cavities and then quench-and-temper or carburize/nitride yourself.450 MPa yield · 215 HB
Working with 718 Prehard
Is 718 easy to machine?
Machines predictably at 30–34 HRC with coated carbide (≈120–180 m/min milling, rigid setups); use positive geometry and adequate coolant to avoid work-hardened glaze in deep pockets.
Can 718 be welded?
Repair-weldable with matching or low-alloy Ni filler: preheat/interpass 250–325 °C, slow cool, then temper ~30 °C below the original tempering temperature to restore hardness match.
Can 718 be formed, bent or molded?
Supplied as prehard blocks/plate — not a cold-forming product; hot work at 850–1100 °C with slow cooling if reforging is required.
What surface finishes work on 718?
Excellent mirror-polish and photo-etch response; protect with hard chrome, EN Ni-P or nitriding for wear and rust resistance, and keep cooling channels inhibited.
718 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 | 0.35 – 0.45 | 0.4 |
| Si | 0.2 – 0.4 | 0.3 |
| Mn | 1.3 – 1.6 | 1.45 |
| Cr | 1.8 – 2.1 | 1.95 |
| Mo | 0.15 – 0.25 | 0.2 |
| NiNi addition over P20 for through-hardening of thick blocks | 0.9 – 1.2 | 1.05 |
| P | ≤ 0.03 | — |
| Smax; some grades add S ~0.05–0.10 for free-machining | ≤ 0.03 | — |
| Fe | balance | — |
718 Prehard — frequently asked
What is 718 Prehard used for?
718 Prehard is typically used for large injection mould cavity and core plates, mould bases and bolster plates, mould inserts, blow mould bodies, die-casting die holders and textured cosmetic cavities for automotive interior parts. In short: workhorse mold-base plate.
What is the yield strength of 718 Prehard?
718 Prehard has a typical yield strength of 880 MPa (128 ksi) and a tensile strength of 1,030 MPa (149 ksi) — stronger than 90% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is 718 Prehard easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machines predictably at 30–34 HRC with coated carbide (≈120–180 m/min milling, rigid setups); use positive geometry and adequate coolant to avoid work-hardened glaze in deep pockets.
Can 718 Prehard be welded?
With care — weldability is rated fair (45/100). Repair-weldable with matching or low-alloy Ni filler: preheat/interpass 250–325 °C, slow cool, then temper ~30 °C below the original tempering temperature to restore hardness match.
What surface finishes work on 718 Prehard?
Excellent mirror-polish and photo-etch response; protect with hard chrome, EN Ni-P or nitriding for wear and rust resistance, and keep cooling channels inhibited.
Can 718 Prehard be formed, bent or molded?
Supplied as prehard blocks/plate — not a cold-forming product; hot work at 850–1100 °C with slow cooling if reforging is required.
What is the maximum service temperature of 718 Prehard?
718 Prehard is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in 718 Prehard?
Yes — 718 Prehard is available for CNC machining with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- DIN EN ISO 4957 — Tool steels (40CrMnNiMo8-6-4 / 1.2738) — ISO/DIN (2018)
- Uddeholm Impax Supreme (P20+Ni prehardened mould steel) — Uddeholm/ASSAB (2020)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels — ASM International (1990)
- ASM Specialty Handbook: Tool Materials — ASM International (1995)
- GB/T 1299 — Tool and die steels (3Cr2MnNiMo) — SAC (2014)
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.