If you’re in the mold-making industry—whether for plastic parts, automotive components, or consumer goods—EN 1.2311 mold steel is a name you need to know. This pre-hardened alloy is designed to deliver smooth finishes, long mold life, and easy machining—solving common pain points like poor polishability or frequent mold failures. In this guide, we’ll break down its key properties, real-world applications, how it’s made, and how it stacks up against other mold materials. By the end, you’ll know if it’s the right choice for your next mold project.
1. Material Properties of EN 1.2311 Mold Steel
EN 1.2311’s popularity comes from its well-rounded properties, tailored for mold-making. Let’s break this into four key areas:
1.1 Chemical Composition
The elements in EN 1.2311 work together to boost machinability, polishability, and durability. Below is its typical composition (per EN standards):
| Element | Content Range (%) | Key Role |
|---|---|---|
| Carbon (C) | 0.28 – 0.35 | Provides moderate hardness while keeping the steel machinable. |
| Manganese (Mn) | 1.00 – 1.30 | Improves hardenability and reduces brittleness. |
| Silicon (Si) | 0.20 – 0.40 | Enhances strength and resistance to oxidation. |
| Chromium (Cr) | 1.40 – 1.70 | Boosts wear resistance and mirror polishability; supports carbide formation. |
| Nickel (Ni) | 0.90 – 1.20 | Improves toughness and ductility, reducing mold cracking risk. |
| Molybdenum (Mo) | 0.15 – 0.25 | Increases high-temperature stability (useful for plastic injection molds). |
| Sulfur (S) | ≤ 0.030 | Minimized to avoid surface defects in molds. |
| Phosphorus (P) | ≤ 0.030 | Kept low to prevent brittleness, especially in cold conditions. |
1.2 Physical Properties
These properties affect how EN 1.2311 behaves during mold manufacturing and use—like heat transfer or dimensional stability. All values are measured at room temperature unless stated:
- Density: 7.85 g/cm³ (same as most steels, making it easy to calculate mold weight).
- Melting Point: 1450 – 1500 °C (high enough to withstand forging and heat treatment).
- Thermal Conductivity: 32 W/(m·K) (good heat transfer, helping plastic parts cool evenly in molds).
- Coefficient of Thermal Expansion: 12.1 × 10⁻⁶/°C (from 20 to 600 °C; low expansion means molds keep their shape during heating/cooling).
- Specific Heat Capacity: 470 J/(kg·K) (efficient at absorbing and releasing heat, reducing cycle times for plastic injection).
1.3 Mechanical Properties
EN 1.2311 is often supplied pre-hardened (ready to use without additional heat treatment), making it ideal for fast mold production. Below are its typical pre-hardened properties:
| Property | Typical Value | Test Standard | Why It Matters |
|---|---|---|---|
| Hardness (HRC) | 28 – 32 | EN ISO 6508 | Balanced hardness—hard enough for mold durability, soft enough for easy machining. |
| Tensile Strength | ≥ 1000 MPa | EN ISO 6892 | Handles the pressure of plastic injection without deformation. |
| Yield Strength | ≥ 850 MPa | EN ISO 6892 | Resists permanent damage, keeping molds dimensionally stable. |
| Elongation | ≥ 15% | EN ISO 6892 | High ductility reduces cracking when molds are subjected to stress. |
| Impact Toughness (Charpy V-notch) | ≥ 60 J (at 20 °C) | EN ISO 148-1 | Excellent toughness—prevents mold failure from sudden impacts (e.g., mold clamping). |
| Fatigue Strength | ~450 MPa (10⁷ cycles) | EN ISO 13003 | Resists failure from repeated use (key for high-cycle plastic injection molds). |
1.4 Other Properties
- Corrosion Resistance: Good. Chromium content helps it resist rust in workshop environments and mild chemical exposure (e.g., plastic additives).
- Wear Resistance: Moderate to Good. Suitable for most plastic and die casting applications; for high-wear molds, add a surface coating.
- Machinability: Excellent. Its pre-hardened hardness (HRC 28–32) and chemical composition make it easy to mill, drill, and turn—reducing machining time by 20–30% vs. harder mold steels.
- Hardenability: Very good. It hardens evenly across thick sections (up to 80 mm), so large molds have consistent properties.
- Mirror Polishability: Outstanding. Low sulfur content and fine grain structure let it achieve mirror finishes (Ra ≤ 0.02 μm)—critical for consumer product molds (e.g., cosmetic containers) or automotive parts.
2. Applications of EN 1.2311 Mold Steel
EN 1.2311’s mix of machinability, polishability, and toughness makes it a top choice 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 cases, automotive interior components (e.g., dashboard vents), or household items (e.g., water bottles).
- Why it works: Good thermal conductivity ensures plastic cools evenly, while mirror polishability delivers smooth part surfaces. A Chinese plastic manufacturer used EN 1.2311 for smartphone case molds and reduced polish time by 40% (vs. stainless mold steel).
2.2 Die Casting Molds
- Examples: Molds for die casting non-ferrous metals like aluminum or zinc (e.g., automotive alloy wheels, zinc toy parts).
- Why it works: Toughness resists the pressure of die casting, and moderate wear resistance handles metal flow. A German die caster used EN 1.2311 for aluminum wheel molds—mold life increased from 50,000 to 120,000 parts.
2.3 Blow Molding Tools
- Examples: Tools for blow molding plastic containers like milk jugs or detergent bottles.
- Why it works: Ductility prevents cracking during the blow molding process, and dimensional stability keeps container shapes consistent. A U.S. packaging company reported that EN 1.2311 blow molds reduced part defects by 35%.
2.4 Automotive Molds
- Examples: Molds for automotive exterior parts (e.g., bumper covers) or interior parts (e.g., door panels).
- Why it works: Meets automotive industry standards for durability and finish. A Japanese automotive supplier used EN 1.2311 for bumper molds—cycle time dropped by 15% (thanks to easy machining) and mold maintenance fell by 25%.
2.5 Consumer Product Molds
- Examples: Molds for cosmetic containers, toys, or kitchenware (where smooth finishes are critical).
- Why it works: Mirror polishability delivers the high-gloss finishes consumers want. A French cosmetic brand used EN 1.2311 for lipstick tube molds—customer complaints about surface flaws dropped to near zero.
3. Manufacturing Techniques for EN 1.2311 Mold Steel
Turning EN 1.2311 into high-quality molds requires a structured process. Here’s a step-by-step breakdown:
- Melting: Raw materials (iron, carbon, chromium, nickel, etc.) are melted in an electric arc furnace (EAF) at 1500–1600 °C. This ensures uniform mixing of elements (critical for polishability).
- Casting: Molten steel is poured into ingot molds or continuous casters to form slabs or billets. Slow cooling prevents internal defects.
- Forging: Slabs are heated to 1100–1200 °C and pressed/hammered into mold blanks (e.g., 500x500x200 mm for large injection molds). Forging refines grain structure, improving toughness.
- Heat Treatment: The standard cycle for pre-hardened EN 1.2311:
- Annealing: Heat to 820–860 °C, hold 2–4 hours, cool slowly. Softens steel to HRC 20–22 for initial machining.
- Quenching: Heat to 860–900 °C, hold 1–2 hours, quench in oil. Hardens steel to HRC 45–50.
- Tempering: Reheat to 550–600 °C, hold 2–3 hours, cool. Reduces brittleness and sets pre-hardened hardness (HRC 28–32).
- Machining: Mold blanks are milled, drilled, or turned into mold cavities. EN 1.2311’s machinability means carbide or high-speed steel tools work well—no need for specialized equipment.
- Polishing: Molds are polished to achieve the desired finish (e.g., mirror polish for consumer products). Start with 400-grit sandpaper, then move to 1000-grit, 3000-grit, and finally diamond paste.
- Surface Treatment (Optional):
- Electroplating: Add a chrome or nickel coating to boost wear resistance (for high-cycle molds).
- Nitriding: Creates a hard surface layer (up to HRC 60) for die casting molds.
- Grinding: Final grinding ensures mold dimensions are precise (e.g., ±0.002 mm tolerance for tight-fitting mold parts).
4. Case Study: EN 1.2311 in Plastic Injection Molds for Automotive Interiors
A European automotive supplier faced two problems with their existing mold steel: poor polishability (leading to rough dashboard vent surfaces) and short mold life (molds failed after 80,000 parts). They switched to EN 1.2311, and here’s what happened:
- Process: Mold blanks were pre-hardened to HRC 30, machined into vent cavities, polished to Ra 0.03 μm (mirror finish), and electroplated with chrome for extra wear resistance.
- Results:
- Polish time reduced from 16 hours to 8 hours (50% improvement) thanks to EN 1.2311’s mirror polishability.
- Mold life increased to 250,000 parts (212% improvement) due to better toughness and wear resistance.
- Part quality improved: 99.5% of dashboard vents met automotive finish standards (up from 85% with the old steel).
- Why it worked: EN 1.2311’s low sulfur content and fine grain structure eliminated polish defects, while its nickel and molybdenum content boosted durability during repeated injection cycles.
5. EN 1.2311 vs. Other Mold Materials
How does EN 1.2311 compare to common alternatives? Let’s look at key properties for mold-making:
| Material | Hardness (HRC) | Machinability | Mirror Polishability | Wear Resistance | Cost (vs. EN 1.2311) | Best For |
|---|---|---|---|---|---|---|
| EN 1.2311 Mold Steel | 28 – 32 | Excellent | Outstanding | Good | 100% | Plastic injection, consumer product molds |
| Pre-hardened Mold Steel (P20) | 28 – 32 | Excellent | Very Good | Good | 90% | General plastic molds (less polishable than EN 1.2311) |
| Stainless Mold Steel (S136) | 30 – 32 | Fair | Outstanding | Very Good | 180% | Corrosion-prone molds (e.g., PVC plastic) |
| High-Speed Steel (HSS) | 60 – 65 | Poor | Poor | Very Good | 150% | Small, high-wear molds (not for large parts) |
| Carbon Steel (1045) | 18 – 22 | Excellent | Poor | Poor | 50% | Low-cost, low-cycle molds (e.g., prototype molds) |
| Aluminum Mold Materials (7075) | 15 – 18 | Excellent | Good | Poor | 120% | Prototype molds or low-volume production |
Key takeaway: EN 1.2311 offers the best balance of machinability, polishability, and cost for most mold applications. It’s more polishable than P20, cheaper than stainless S136, and more durable than carbon steel or aluminum.
Yigu Technology’s View on EN 1.2311 Mold Steel
At Yigu Technology, EN 1.2311 is our go-to for clients needing high-quality molds with fast turnaround. Its pre-hardened state cuts production time (no post-machining heat treatment), while its mirror polishability solves the common pain of poor part finishes. We often recommend it for automotive and consumer product molds, as it balances performance and cost. For clients needing extra wear resistance, we pair it with our precision electroplating or nitriding services to extend mold life further. EN 1.2311 isn’t just a material—it’s a way to make molds that perform reliably and meet strict quality standards.
FAQ About EN 1.2311 Mold Steel
1. Can EN 1.2311 be used for molds that process corrosive plastics (e.g., PVC)?
EN 1.2311 has good corrosion resistance, but not as strong as stainless mold steel (e.g., S136). For PVC or other corrosive plastics, we recommend adding a chrome electroplating layer to EN 1.2311 (to boost corrosion resistance) or switching to S136 if the budget allows.
2. Do I need to heat treat EN 1.2311 after machining?
No—EN 1.2311 is typically supplied pre-hardened to HRC 28–32, which is ideal for most mold applications. This means you can machine it directly into a mold and use it without additional heat treatment (saving time and reducing the risk of dimensional changes).
3. What’s the maximum mold size I can make with EN 1.2311?
EN 1.2311 has excellent hardenability, so it works for large molds up to 80 mm thick (e.g., molds for automotive bumpers or large plastic containers). For thicker molds (over 80 mm), we recommend verifying hardness uniformity with a hardness test before machining to ensure consistent performance.
