Steel 718H · heat-treated state · default condition
Steel 718H Prehard
Properties of the Prehard condition, compared with the other 718H tempers.
Default stock condition: machine cavities and mould bases directly, no heat treatment or distortion afterwards.
What is 718H Prehard?
718H Prehard is 718H heat treated to Prehard — default stock condition: machine cavities and mould bases directly, no heat treatment or distortion afterwards. 718H Prehard has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 90% of steel grades. Elongation at break is 13% and the elastic modulus is 205 GPa (29.7 Msi). 718H 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 — 900 MPa (131 ksi), better than 90% of steel grades
- High service temperature — 450°C (842 °F), better than 86% of steel grades
Limitations
- Limited formability — 10/100, worse than 94% of steel grades
- Poor heat conductor — 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades
- Limited ductility — 13%, worse than 78% of steel grades
718H Prehard properties
Typical room-temperature values for 718H Prehard — 11 properties are specific to this condition; the rest are grade-level values shared by every 718H temper. Each bar shows where the value sits among the steel grades in FabDigit's library — further right is higher.
Physical3
718H 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).
Mechanical15
718H Prehard has a yield strength of 900 MPa (131 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 90% of steel grades. Elongation at break is 13% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
718H Prehard is rated for continuous service to 450°C (842 °F). It conducts heat at 33 W/m·K (19.1 BTU/hr·ft·°F), worse than 80% of steel grades. Thermal expansion is 12.5 µm/m·K (6.94 µin/in·°F).
Electrical2
718H 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 718H Prehard takes about 34 MJ of energy and emits 2.3 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 35%.
Manufacturability6
718H Prehard's machinability is fair (48/100, worse than 57% of steel grades); weldability fair (40/100); formability not recommended (10/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other 718H tempers and conditions
718H is also supplied in 2 other conditions. The full side-by-side table is on the 718H overview.
- PrehardDefaultDefault stock condition: machine cavities and mould bases directly, no heat treatment or distortion afterwards.900 MPa yield · 32 HRC
- NitridedPick for glass-filled or abrasive resins and for wear faces where core toughness must stay unchanged.1,080 MPa tensile
- AnnealedChoose when the block will be rough-machined soft and then through-hardened/tempered in-house or after weld repair.480 MPa yield · 220 HB
Working with 718H Prehard
Is 718H easy to machine?
Machines predictably at ~28–34 HRC with coated carbide (P20-type data, ~60 % of AISI 1212); use rigid setups and stress-relieve at 550 °C after heavy roughing to avoid cavity movement.
Can 718H be welded?
Weldable only with 250–325 °C preheat, Ni-alloyed mould-repair filler and slow post-weld temper 25–50 °C below the original tempering temperature; hydrogen control is essential.
Can 718H be formed, bent or molded?
Supplied prehardened for machining, not for cold forming; hot working 1100–850 °C followed by slow cooling and annealing if reforged.
What surface finishes work on 718H?
Takes fine EDM texturing and mirror polish (low-S/vacuum-degassed melts best); protect with hard chrome, electroless nickel or nitriding for corrosive resins and long-term storage.
718H 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 – 0.42 | 0.38 |
| 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 gives uniform through-hardness in thick plate | 0.9 – 1.2 | 1.05 |
| P | ≤ 0.03 | — |
| Smax; low-S for polishing grades | ≤ 0.03 | — |
| Fe | balance | — |
718H Prehard — frequently asked
What is 718H Prehard used for?
718H Prehard is typically used for injection mould cavities and cores, mould inserts, large mould bases and bolsters, blow mould bodies, die-cast trim and holder blocks and structural foam and thick-wall tooling. In short: standard prehard mold steel.
What is the yield strength of 718H Prehard?
718H Prehard has a typical yield strength of 900 MPa (131 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 90% of steel grades. Strength varies by condition: see the 3 listed tempers.
Is 718H Prehard easy to machine?
Reasonably — machinability is rated fair (48/100, worse than 57% of steel grades). Machines predictably at ~28–34 HRC with coated carbide (P20-type data, ~60 % of AISI 1212); use rigid setups and stress-relieve at 550 °C after heavy roughing to avoid cavity movement.
Can 718H Prehard be welded?
With care — weldability is rated fair (40/100). Weldable only with 250–325 °C preheat, Ni-alloyed mould-repair filler and slow post-weld temper 25–50 °C below the original tempering temperature; hydrogen control is essential.
What surface finishes work on 718H Prehard?
Takes fine EDM texturing and mirror polish (low-S/vacuum-degassed melts best); protect with hard chrome, electroless nickel or nitriding for corrosive resins and long-term storage.
Can 718H Prehard be formed, bent or molded?
Supplied prehardened for machining, not for cold forming; hot working 1100–850 °C followed by slow cooling and annealing if reforged.
What is the maximum service temperature of 718H Prehard?
718H Prehard is rated for continuous use to about 450°C (842 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in 718H Prehard?
Yes — 718H 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 (1.2738 / 40CrMnNiMo8-6-4) — ISO/DIN (2018)
- Prehardened P20+Ni mould steel plate datasheets (718/718H class) — Mould steel producers (2023)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
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.