Steel 718H
718H is a Ni-modified P20-type low-alloy plastic mould steel (close to DIN 1.2738 in the higher-hardness 'HH' condition), supplied pre-hardened and tempered so that large cavities can be cut straight from plate with no further heat treatment or distortion risk.
Values for the Prehard condition
718H tempers and conditions
718H is supplied in 3 conditions, soft to hard. Prehard is the default FabDigit quotes; the values on this page are for it.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
soft-annealed condition (≈ 200–235 HB) | Choose when the block will be rough-machined soft and then through-hardened/tempered in-house or after weld repair. | 480 | 760 | 20 | 220 HB | — |
PrehardDefault Pre-hardened | Default stock condition: machine cavities and mould bases directly, no heat treatment or distortion afterwards. | 900 | 1,080 | 13 | 32 HRC | — |
prehardened core plus gas/plasma nitrided case (~0.1–0.3 mm) | Pick for glass-filled or abrasive resins and for wear faces where core toughness must stay unchanged. | 900 | 1,080 | 10 | 32 HRC | 7.8 % IACS |
What is 718H?
718H is a Ni-modified P20-type low-alloy plastic mould steel (close to DIN 1.2738 in the higher-hardness 'HH' condition), supplied pre-hardened and tempered so that large cavities can be cut straight from plate with no further heat treatment or distortion risk. The ~1 % Ni addition gives uniform through-hardness in thick sections and good polish/texturing response, which is why it dominates medium-to-large injection mould bases in China. Limits are modest hot hardness (soften above ~ tempering temperature), no corrosion resistance (needs Cr plating or nitriding for PVC/flame-retardant resins), and poor weldability unless preheated with matched Ni-alloyed filler. 718H 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). 718H 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).
What is 718H used for?
- Injection mould cavities and cores
- Mould inserts
- Large mould bases and bolsters
- Blow mould bodies
- Die-cast trim and holder blocks
- Structural foam and thick-wall tooling
- Slides and wear blocks in mould assemblies
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 95% 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 properties
Typical room-temperature values for 718H-Prehard; bars are the position among steel grades.
Physical3
718H 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 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 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 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 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'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.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. 718H is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 718H
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.
Manufacturability
The process limits FabDigit applies to 718H. Every 718H part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Better48 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
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 |
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.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
How much does 718H cost?
718H is a standard-cost steel ($$), cheaper than about 59% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
718H — frequently asked
What is 718H used for?
718H is typically used for injection mould cavities and cores, mould inserts, large mould bases and bolsters, blow mould bodies, die-cast trim and holder blocks and structural foam and thick-wall tooling. In short: standard prehard mold steel.
What is the yield strength of 718H?
718H has a typical yield strength of 900 MPa (131 ksi) and a tensile strength of 1,080 MPa (157 ksi) — stronger than 90% of steel grades. Strength varies by condition: see the 3 listed tempers.
Is 718H easy to machine?
Reasonably — machinability is rated fair (48/100, worse than 57% of steel grades). Machines predictably at ~28–34 HRC with coated carbide (P20-type data, ~60 % of AISI 1212); use rigid setups and stress-relieve at 550 °C after heavy roughing to avoid cavity movement.
Can 718H be welded?
With care — weldability is rated fair (40/100). Weldable only with 250–325 °C preheat, Ni-alloyed mould-repair filler and slow post-weld temper 25–50 °C below the original tempering temperature; hydrogen control is essential.
What surface finishes work on 718H?
Takes fine EDM texturing and mirror polish (low-S/vacuum-degassed melts best); protect with hard chrome, electroless nickel or nitriding for corrosive resins and long-term storage.
Can 718H be formed, bent or molded?
Supplied prehardened for machining, not for cold forming; hot working 1100–850 °C followed by slow cooling and annealing if reforged.
What is the maximum service temperature of 718H?
718H is rated for continuous use to about 450°C (842 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does 718H cost?
718H is a standard-cost steel ($$), cheaper than about 59% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in 718H?
Yes — 718H is available for CNC machining; every part is priced by an engineer rather than instantly. 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; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.