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 pain points like mold warping or delayed project timelines. In this guide, we’ll break down its key properties, real-world applications, manufacturing steps, and how it compares to other materials—so you can build high-quality molds faster and more cost-effectively.
1. Material Properties of 718 Pre Hard Mold Steel
718 Pre Hard’s popularity stems from its well-balanced composition and ready-to-use pre-hardened condition. Let’s explore its properties in detail:
1.1 Chemical Composition
The elements in 718 Pre Hard work together to enhance machinability, toughness, and corrosion resistance—tailored for mold-making. Below is its typical composition (per industry standards):
| Element | Content Range (%) | Key Role |
|---|---|---|
| Carbon (C) | 0.28 – 0.35 | Provides moderate hardness (critical for pre-hardened use) while keeping the steel machinable. |
| Manganese (Mn) | 0.50 – 0.80 | Improves hardenability and reduces brittleness during heat treatment. |
| Silicon (Si) | 0.20 – 0.40 | Enhances strength and resistance to oxidation in mild environments. |
| Chromium (Cr) | 1.40 – 1.80 | Boosts corrosion resistance and wear resistance; supports fine grain structure for polishability. |
| Nickel (Ni) | 3.00 – 3.50 | A key element for toughness and ductility—prevents mold cracking under stress. |
| Molybdenum (Mo) | 0.30 – 0.50 | Increases high-temperature stability (useful for plastic injection molds); improves dimensional stability. |
| Sulfur (S) | ≤ 0.030 | Minimized to avoid surface defects (e.g., pits) in molds. |
| Phosphorus (P) | ≤ 0.030 | Kept low to prevent brittleness, especially in cold or high-stress conditions. |
1.2 Physical Properties
These properties determine how 718 Pre Hard behaves during mold manufacturing and use—such as heat transfer and shape retention. All values are measured at room temperature unless noted:
- Density: 7.85 g/cm³ (consistent with most mold steels, making it easy to calculate mold weight).
- Melting Point: 1450 – 1500 °C (high enough to withstand forging and pre-hardening heat treatment).
- Thermal Conductivity: 31 W/(m·K) (good heat transfer, ensuring plastic parts cool evenly in injection molds).
- Coefficient of Thermal Expansion: 11.8 × 10⁻⁶/°C (from 20 to 600 °C; low expansion reduces mold warping during production).
- Specific Heat Capacity: 470 J/(kg·K) (efficient at absorbing and releasing heat, reducing plastic injection cycle times).
1.3 Mechanical Properties
As a pre-hardened steel, 718 Pre Hard is supplied ready for machining—no extra heat treatment needed. Below are its typical mechanical properties (in pre-hardened state):
| Property | Typical Value | Test Standard | Why It Matters |
|---|---|---|---|
| Hardness (HRC) | 32 – 36 | ASTM E18 | Balanced hardness—hard enough for mold durability, soft enough for easy machining and polishing. |
| Tensile Strength | ≥ 1100 MPa | ASTM A370 | Handles the pressure of plastic injection without deformation. |
| Yield Strength | ≥ 950 MPa | ASTM A370 | Resists permanent damage, keeping molds dimensionally stable for thousands of cycles. |
| Elongation | ≥ 12% | ASTM A370 | Good ductility, reducing the risk of cracking during mold clamping or polishing. |
| Impact Toughness (Charpy V-notch) | ≥ 45 J (at 20 °C) | ASTM A370 | Excellent toughness—prevents mold failure from sudden impacts (e.g., part jams). |
| Fatigue Strength | ~500 MPa (10⁷ cycles) | ASTM E466 | Resists wear from repeated use (key for high-cycle packaging molds or consumer product molds). |
1.4 Other Properties
- Corrosion Resistance: Good. Chromium content protects against rust in workshop environments and mild chemical exposure (e.g., plastic additives or mold release agents).
- Wear Resistance: Moderate to Good. Suitable for most plastic and die casting applications; for high-wear molds, add a surface coating like nitriding.
- Machinability: Excellent. Its pre-hardened hardness (HRC 32–36) and fine grain structure make it easy to mill, drill, and turn—reducing machining time by 25–30% vs. unhardened steels.
- Hardenability: Excellent. It maintains uniform hardness across thick sections (up to 100 mm), so large molds (e.g., automotive molds for bumpers) have consistent performance.
- Dimensional Stability: Outstanding. Low thermal expansion and pre-hardened state prevent mold warping—critical for optical molds or precision consumer product molds.
- Pre-hardened Condition: Ready to use. Eliminates post-machining heat treatment, cutting mold production time by 30–40%.
2. Applications of 718 Pre Hard Mold Steel
718 Pre Hard’s mix of efficiency, precision, and durability makes it versatile for diverse mold types. Here are its most common uses, with real examples:
2.1 Plastic Injection Molds
- Examples: Molds for making plastic parts like smartphone casings, automotive interior components (e.g., dashboard vents), or medical device housings.
- Why it works: Pre-hardened state speeds up production, while dimensional stability ensures part consistency. A Chinese plastic manufacturer used 718 Pre Hard for smartphone case molds—production time dropped by 35% vs. using unhardened steel.
2.2 Automotive Molds
- Examples: Molds for automotive exterior parts (e.g., grille inserts) or under-hood components (e.g., sensor housings).
- Why it works: Toughness handles the stress of high-volume production, and corrosion resistance stands up to workshop chemicals. A German automotive supplier used 718 Pre Hard for sensor molds—mold life increased from 150,000 to 300,000 parts.
2.3 Consumer Product Molds
- Examples: Molds for cosmetic containers, kitchenware (e.g., high-gloss plastic bowls), or toys.
- Why it works: Machinability lets you create complex shapes, while polishability delivers premium surface finishes. A French cosmetic brand used 718 Pre Hard for lipstick tube molds—customer complaints about surface flaws fell to zero.
2.4 Optical and Medical Device Molds
- Examples: Molds for optical components (e.g., plastic lenses) or medical devices (e.g., syringe barrels).
- Why it works: Dimensional stability ensures precision, and corrosion resistance meets medical hygiene standards. A U.S. medical manufacturer used 718 Pre Hard for syringe molds—part tolerance accuracy improved by 20%.
3. Manufacturing Techniques for 718 Pre Hard Mold Steel
Turning 718 Pre Hard into high-quality molds is streamlined thanks to its pre-hardened state. Here’s a step-by-step breakdown:
- Melting: Raw materials (iron, nickel, chromium, etc.) are melted in an electric arc furnace (EAF) at 1550–1650 °C. Strict control ensures uniform element distribution (critical for consistent hardness).
- Casting: Molten steel is poured into ingot molds or continuous casters to form slabs. Slow cooling (50–100 °C/hour) prevents internal defects and refines grain structure.
- Forging: Slabs are heated to 1100–1200 °C and pressed/hammered into mold blanks (e.g., 600x600x300 mm for large injection molds). Forging improves toughness and eliminates voids.
- Pre-hardening Heat Treatment:
- Annealing: Heat to 800–850 °C, hold 2–4 hours, cool slowly. Softens steel for initial processing.
- Quenching: Heat to 880–920 °C, hold 1–2 hours, quench in oil. Hardens steel to HRC 40–45.
- Tempering: Reheat to 580–620 °C, hold 2–3 hours, cool. Sets final pre-hardened hardness (HRC 32–36).
- Machining: Mold blanks are milled, drilled, or turned into mold cavities using CNC machines. Carbide tools are recommended for tight tolerances (±0.001 mm).
- Polishing: Molds are polished to the desired finish—from matte (for functional parts) to mirror (for consumer products). 718 Pre Hard’s fine grain structure lets it achieve Ra ≤ 0.01 μm with diamond paste.
- Surface Treatment (Optional):
- Nitriding: Creates a hard surface layer (HRC 60–65) to boost wear resistance for high-cycle molds.
- Electroplating: Adds a chrome or nickel coating to improve corrosion resistance (ideal for medical or food-contact molds).
4. Case Study: 718 Pre Hard in Automotive Dashboard Mold
A Korean automotive parts manufacturer faced a problem: their P20 mold steel dashboards required post-machining heat treatment, which caused warping and delayed production by 2 weeks per mold. They switched to 718 Pre Hard, and here’s what happened:
- Process: Mold blanks (pre-hardened to HRC 34) were CNC-machined to dashboard geometry, polished to Ra 0.8 μm, and nitrided for extra wear resistance.
- Results:
- Production time per mold dropped from 4 weeks to 2.5 weeks (37.5% improvement) — no post-heat treatment needed.
- Warping eliminated (718 Pre Hard’s dimensional stability kept mold shape consistent).
- Dashboard quality improved: fewer fitment issues (tolerance accuracy ±0.05 mm vs. ±0.1 mm with P20).
- Why it works: 718 Pre Hard’s pre-hardened state skipped heat treatment, while its nickel and molybdenum content prevented warping—solving both timeline and quality issues.
5. 718 Pre Hard vs. Other Mold Materials
How does 718 Pre Hard compare to common alternatives for mold-making? Let’s evaluate key properties:
| Material | Hardness (HRC) | Machinability | Dimensional Stability | Pre-hardened? | Cost (vs. 718 Pre Hard) | Best For |
|---|---|---|---|---|---|---|
| 718 Pre Hard Mold Steel | 32 – 36 | Excellent | Outstanding | Yes | 100% | High-precision molds, fast production |
| P20 Pre-hardened Steel | 28 – 32 | Excellent | Good | Yes | 70% | General plastic molds (lower precision) |
| Stainless Mold Steel (S136) | 30 – 32 | Fair | Very Good | No | 180% | Corrosion-prone molds (e.g., PVC) |
| Aluminum Mold Materials (7075) | 15 – 18 | Excellent | Poor | No | 80% | Prototype molds (low-volume) |
| Carbon Steel (1045) | 18 – 22 | Excellent | Poor | No | 40% | Low-cost, low-precision molds |
Key takeaway: 718 Pre Hard offers the best balance of precision, speed, and durability for high-volume, high-quality molds. It’s more dimensionally stable than P20, more machinable than stainless steel, and far more reliable than aluminum for production molds.
Yigu Technology’s View on 718 Pre Hard Mold Steel
At Yigu Technology, 718 Pre Hard is our go-to for clients needing fast, high-precision mold production—like automotive and consumer product manufacturers. Its pre-hardened state cuts lead times by 30–40%, while its dimensional stability ensures consistent part quality. We often recommend it for complex molds, as its machinability lets us create intricate geometries without warping. For clients needing extra wear resistance, we pair it with nitriding to extend mold life. 718 Pre Hard isn’t just a material—it’s a way to streamline production and deliver molds that meet the strictest standards.
FAQ About 718 Pre Hard Mold Steel
1. Can 718 Pre Hard be used for die casting molds (e.g., aluminum or zinc)?
Yes, but we recommend adding a nitrided surface layer (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.
2. Is 718 Pre Hard suitable for molds that need mirror finishes (e.g., cosmetic containers)?
Absolutely. 718 Pre Hard’s fine grain structure and low sulfur content let it achieve mirror finishes (Ra ≤ 0.01 μm) with diamond paste polishing. It’s a top choice for consumer product molds requiring premium aesthetics.
3. 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, but it’s worth it for high-precision or high-volume molds. It eliminates heat treatment costs, reduces warping (lower scrap rates), and lasts 50–100% longer—saving money in the long run.
