1.2311 is a German standard pre-hardened plastic mold steel, specified under DIN (Deutsches Institut für Normung) standards. Belonging to the nickel-chromium-molybdenum alloy system, it is renowned for its excellent machinability, uniform pre-hardened hardness, and good toughness, making it a go-to material for medium-sized plastic injection molds and precision components. Its pre-hardened state eliminates the need for post-machining heat treatment, streamlining production processes. Below is a detailed overview:
Chemical Composition
The chemical composition of 1.2311 is carefully balanced to optimize pre-hardened performance and machinability:
Element Content Range Role
Carbon (C) 0.35–0.45% Provides a foundation for hardness and wear resistance; balanced to maintain toughness.
Chromium (Cr) 1.70–2.10% Enhances hardenability, corrosion resistance, and wear resistance; improves microstructure stability.
Molybdenum (Mo) 0.25–0.35% Boosts hardenability and high-temperature strength; reduces tempering brittleness.
Nickel (Ni) 0.90–1.20% Improves toughness, impact resistance, and polishability; refines grain structure.
Manganese (Mn) 1.40–1.70% Enhances hardenability and strength; aids in deoxidation.
Silicon (Si) 0.20–0.40% Aids deoxidation and improves mechanical properties.
Phosphorus (P) ≤0.030% Minimized to avoid embrittlement and machining defects.
Sulfur (S) ≤0.030% Controlled to ensure good toughness and surface quality.
Key Properties
1.2311 tool steel is engineered to meet the demands of efficient mold manufacturing and reliable performance:
1. Pre-Hardened Convenience
Delivered in a pre-hardened state with a uniform hardness of 28–32 HRC (or 32–36 HRC in some variants), eliminating the need for post-machining heat treatment. This reduces production time, minimizes distortion risks, and allows immediate use after machining.
2. Excellent Machinability
In its pre-hardened form, it exhibits superior machinability compared to many other mold steels, enabling precise cutting, milling, and drilling of complex mold cavities, cores, and details. This is critical for reducing manufacturing costs and lead times.
3. Good Toughness and Impact Resistance
The nickel content enhances toughness, making it resistant to cracking under injection pressure or mechanical stress—ideal for medium-sized molds or components with thin walls.
4. Dimensional Stability
Maintains stable dimensions during machining and service, ensuring tight tolerances in finished molds. This is essential for producing consistent plastic parts with high precision.
5. Moderate Wear Resistance
Its alloy composition provides sufficient wear resistance for general plastic molding applications, ensuring long service life in high-volume production of non-abrasive plastics.
Physical Properties
Density: ~7.85 g/cm³
Melting Point: ~1430–1480°C
Thermal Expansion Coefficient: ~11.0×10⁻⁶/K (at 20–100°C)
Thermal Conductivity: ~30 W/(m·K) (at room temperature)
Mechanical Properties (Pre-Hardened State)
Property Typical Value
Hardness 28–32 HRC (standard) or 32–36 HRC (high-hardness variant)
Tensile Strength (Rm) ~850–1000 MPa
Yield Strength (Rp0.2) ~750–900 MPa
Elongation (A) ~15–20%
Impact Toughness (Charpy V-notch) ≥30 J/cm² (at room temperature)
Heat Treatment
1.2311 is primarily used in its pre-hardened state, but optional treatments may be applied for specific needs:
1. Stress Relieving
Purpose: Reduce internal stresses after heavy machining to prevent distortion or cracking during service.
Process: Heat to 550–600°C, hold for 2–4 hours, then air cool.
Result: Maintains pre-hardened hardness while stabilizing dimensions.
2. Annealing
Purpose: Soften the steel for complex machining (rarely needed due to pre-hardened convenience).
Process: Heat to 820–850°C, hold for 2–4 hours, then furnace cool slowly (≤50°C/hour) to below 500°C before air cooling.
Result: Hardness ≤230 HBW, improving machinability for intricate designs.
Application Fields
1.2311 tool steel is widely used in medium-sized plastic mold manufacturing and precision components:
Plastic Injection Molds: Ideal for medium-sized molds producing consumer goods, electronic housings, automotive parts, and household appliances, where machinability and toughness are prioritized.
Blow Molding Dies: Suitable for molds used in blow molding of plastic bottles, containers, and hollow parts.
Compression Molds: Applied in compression molding of thermosetting plastics, leveraging its dimensional stability.
Precision Components: Used for non-corrosive mechanical parts requiring good machinability and moderate strength.
Comparison with Similar Steels
Feature 1.2311 Tool Steel 1.2738 Tool Steel (German) P20 Tool Steel (American)
Hardness (HRC) 28–36 (pre-hardened) 30–40 (pre-hardened) 28–32 (pre-hardened)
Toughness Good High Good
Machinability Excellent Good Very Good
Polishability Good Excellent Good
Best For Medium-sized plastic molds Large, complex molds General plastic molds
Summary
1.2311 tool steel is a versatile and cost-effective choice for medium-sized plastic molds, offering the perfect blend of pre-hardened convenience, machinability, and toughness. Its ability to streamline production by eliminating post-machining heat treatment, combined with reliable performance in high-volume molding, makes it a staple in the plastic manufacturing industry. Whether for consumer goods or automotive components, 1.2311 delivers efficiency and quality in medium-scale mold applications.