If you’re looking for a pre-hardened mold steel that cuts production time, delivers consistent dimensional stability, and works for high-precision molds—718 Pre Hard is the ideal choice. Widely used in plastic injection and automotive molds, this alloy eliminates the need for post-machining heat treatment, solving common problems like mold warping and delayed project timelines. This guide covers its properties, applications, and manufacturing methods.
What are the key properties of 718 Pre Hard?
718 Pre Hard’s popularity stems from its well-balanced composition and ready-to-use pre-hardened condition. Its properties are tailored for mold-making, combining machinability with durability.
Chemical composition
The elements work together to enhance machinability, toughness, and corrosion resistance.
| Element | Content Range (%) | Key Role |
|---|---|---|
| Carbon (C) | 0.28 – 0.35 | Provides moderate hardness, keeps steel machinable |
| Chromium (Cr) | 1.40 – 1.80 | Boosts corrosion resistance, supports fine grain structure |
| Nickel (Ni) | 3.00 – 3.50 | Key element for toughness, prevents mold cracking under stress |
| Molybdenum (Mo) | 0.30 – 0.50 | Increases high-temperature stability, improves dimensional stability |
| Manganese (Mn) | 0.50 – 0.80 | Improves hardenability, reduces brittleness |
| Silicon (Si) | 0.20 – 0.40 | Enhances strength and oxidation resistance |
| Sulfur (S) | ≤ 0.030 | Minimized to avoid surface defects |
| Phosphorus (P) | ≤ 0.030 | Kept low to prevent brittleness |
Physical properties
These traits determine how 718 Pre Hard behaves during mold manufacturing and use.
- Density: 7.85 g/cm³ – standard for mold steels
- Melting point: 1,450–1,500°C – withstands forging and heat treatment
- Thermal conductivity: 31 W/(m·K) – ensures even cooling in injection molds
- Thermal expansion: 11.8 × 10⁻⁶/°C (20–600°C) – low expansion reduces warping
- Specific heat capacity: 470 J/(kg·K) – reduces injection cycle times
Mechanical properties
As a pre-hardened steel, 718 Pre Hard is supplied ready for machining—no extra heat treatment needed.
| Property | Typical Value |
|---|---|
| Hardness (HRC) | 32 – 36 |
| Tensile strength | ≥ 1,100 MPa |
| Yield strength | ≥ 950 MPa |
| Elongation | ≥ 12% |
| Impact toughness | ≥ 45 J at 20°C |
| Fatigue strength | ~500 MPa (10⁷ cycles) |
A Korean automotive parts manufacturer faced warping with P20 mold steel for dashboards. Post-machining heat treatment caused delays of 2 weeks per mold. Switching to 718 Pre Hard eliminated the problem. Production time per mold dropped from 4 weeks to 2.5 weeks—a 37.5% improvement. Warping was eliminated. Dashboard fitment improved with tolerance accuracy of ±0.05 mm versus ±0.1 mm with P20.
Other key properties
- Corrosion resistance: Good. Chromium protects against rust in workshop environments and mild chemicals.
- Wear resistance: Moderate to good. Suitable for most plastic molds. For high-wear molds, add nitriding.
- Machinability: Excellent. Pre-hardened hardness at 32–36 HRC reduces machining time by 25–30% versus unhardened steels.
- Hardenability: Excellent. Maintains uniform hardness across thick sections up to 100 mm.
- Dimensional stability: Outstanding. Low thermal expansion and pre-hardened state prevent warping.
- Pre-hardened condition: Ready to use. Eliminates post-machining heat treatment, cutting mold production time by 30–40%.
Where is 718 Pre Hard used?
718 Pre Hard’s mix of efficiency, precision, and durability makes it versatile for diverse mold types.
Plastic injection molds
Used for smartphone casings, automotive interior components like dashboard vents, and medical device housings. A Chinese plastic manufacturer used 718 Pre Hard for smartphone case molds—production time dropped by 35% versus unhardened steel.
Automotive molds
Used for exterior parts like grille inserts and under-hood components like sensor housings. A German automotive supplier used 718 Pre Hard for sensor molds—mold life increased from 150,000 to 300,000 parts.
Consumer product molds
Used for cosmetic containers, kitchenware like high-gloss plastic bowls, and toys. A French cosmetic brand used 718 Pre Hard for lipstick tube molds—customer complaints about surface flaws dropped to zero.
Optical and medical device molds
Used for optical components like plastic lenses and medical devices like syringe barrels. A U.S. medical manufacturer used 718 Pre Hard for syringe molds—part tolerance accuracy improved by 20%.
How is 718 Pre Hard manufactured?
Turning 718 Pre Hard into high-quality molds is streamlined thanks to its pre-hardened state.
Melting and forging
- Melting: Raw materials melt in an electric arc furnace at 1,550–1,650°C. Strict control ensures uniform element distribution.
- Casting: Molten steel pours into ingot molds or continuous casters. Slow cooling prevents internal defects.
- Forging: Slabs heat to 1,100–1,200°C and press into mold blanks. Forging improves toughness and eliminates voids.
Pre-hardening heat treatment
This is the key step that makes 718 Pre Hard ready for use.
| Process | Temperature | Result |
|---|---|---|
| Annealing | 800–850°C, slow cool | Softens steel for initial processing |
| Quenching | 880–920°C, oil cool | Hardens to HRC 40–45 |
| Tempering | 580–620°C, 2–3 hours | Sets final hardness at HRC 32–36 |
Machining and finishing
- Machining: Mold blanks are milled, drilled, and turned into cavities using CNC machines. Carbide tools achieve tight tolerances of ±0.001 mm.
- Polishing: Fine grain structure allows mirror finishes as smooth as Ra ≤ 0.01 μm with diamond paste.
- Surface treatment: Optional nitriding creates a hard surface layer at HRC 60–65 for high-cycle molds. Electroplating adds corrosion resistance for medical or food-contact molds.
How does 718 Pre Hard compare to other mold materials?
Understanding how 718 Pre Hard stacks up helps with material selection for high-precision molds.
| Material | Hardness (HRC) | Machinability | Dimensional Stability | Pre-hardened? | Cost vs. 718 Pre Hard | Best For |
|---|---|---|---|---|---|---|
| 718 Pre Hard | 32–36 | Excellent | Outstanding | Yes | 100% | High-precision molds, fast production |
| P20 | 28–32 | Excellent | Good | Yes | 70% | General plastic molds, lower precision |
| S136 stainless | 30–32 | Fair | Very good | No | 180% | Corrosion-prone molds like PVC |
| 7075 aluminum | 15–18 | Excellent | Poor | No | 80% | Prototype molds, low-volume |
| 1045 carbon | 18–22 | Excellent | Poor | No | 40% | Low-cost, low-precision molds |
Key takeaways:
- 718 Pre Hard offers better dimensional stability than P20, reducing warping and scrap rates
- It’s more machinable than stainless steel, cutting production time
- It’s far more reliable than aluminum for high-volume production molds
Conclusion
718 Pre Hard mold steel delivers excellent machinability, dimensional stability, and ready-to-use convenience for high-precision mold applications. Its pre-hardened state eliminates post-machining heat treatment, cutting production time by 30–40%. For plastic injection molds, automotive components, and consumer products where quality and speed matter, it offers reliable performance with consistent results.
FAQ
Can 718 Pre Hard be used for die casting molds like aluminum or zinc?
Yes, but add a nitrided surface layer at HRC 60–65 to boost wear resistance. 718 Pre Hard’s toughness handles die casting pressure, but the coating prevents premature wear from molten metal flow.
Is 718 Pre Hard suitable for molds needing mirror finishes like cosmetic containers?
Absolutely. Its fine grain structure and low sulfur content allow mirror finishes as smooth as Ra ≤ 0.01 μm with diamond paste polishing. It’s a top choice for consumer product molds requiring premium aesthetics.
How does 718 Pre Hard’s cost compare to P20, and is it worth the extra expense?
718 Pre Hard costs about 30% more than P20. For high-precision or high-volume molds, it’s worth the investment. It eliminates heat treatment costs, reduces warping with lower scrap rates, and lasts 50–100% longer, saving money in the long run.
What hardness range works best for 718 Pre Hard molds?
The pre-hardened range of 32–36 HRC balances wear resistance and machinability. For applications needing extra wear resistance, nitriding adds a surface hardness of 60–65 HRC while maintaining core toughness.
Does 718 Pre Hard require special machining tools?
Standard carbide tools work well. Its pre-hardened state at 32–36 HRC is soft enough for efficient machining but hard enough to maintain precision. Use sharp tools and appropriate cutting speeds for best results.
Discuss Your Projects with Yigu Rapid Prototyping
At Yigu Rapid Prototyping, we supply 718 Pre Hard mold steel for automotive, consumer product, and medical molds. Our material is ready to machine with consistent hardness and dimensional stability. We offer custom CNC machining, polishing, and nitriding services. Contact us to discuss your next high-precision mold project.