Steel 718 · hardness band
Steel 718 Prehard-H
Properties of the Prehard-H condition, compared with the other 718 tempers.
Choose when the mould runs abrasive filled resins or needs better cavity wear/dent resistance while still machinable prehard.
What is 718 Prehard-H?
718 Prehard-H is 718 heat treated to Prehard-H — choose when the mould runs abrasive filled resins or needs better cavity wear/dent resistance while still machinable prehard. 718 Prehard-H has a yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,180 MPa (171 ksi) — stronger than 92% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi). 718 Prehard-H 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). Prehard is the default condition FabDigit quotes; Prehard-H is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 83/100, better than 98% of steel grades
- High strength — 1,000 MPa (145 ksi), better than 92% of steel grades
Limitations
- Limited formability — 15/100, worse than 87% of steel grades
- Limited ductility — 12%, worse than 84% of steel grades
- Poor heat conductor — 32 W/m·K (18.5 BTU/hr·ft·°F), worse than 82% of steel grades
718 Prehard-H properties
Typical room-temperature values for 718 Prehard-H — 10 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-H 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-H has a yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,180 MPa (171 ksi) — stronger than 92% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
718 Prehard-H 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-H 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-H 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-H's machinability is fair (48/100, worse than 57% of steel grades); weldability fair (40/100); formability poor (15/100).
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-H
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-H — frequently asked
What is 718 Prehard-H used for?
718 Prehard-H 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-H?
718 Prehard-H has a typical yield strength of 1,000 MPa (145 ksi) and a tensile strength of 1,180 MPa (171 ksi) — stronger than 92% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is 718 Prehard-H easy to machine?
Reasonably — machinability is rated fair (48/100, worse than 57% 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-H be welded?
With care — weldability is rated fair (40/100). 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-H?
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-H 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-H?
718 Prehard-H 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-H?
Yes — 718 Prehard-H 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.