1.2738 plastic tool steel is a premium German standard pre-hardened plastic mold steel, belonging to the nickel-chromium-molybdenum alloy system. It is specifically designed for large, complex plastic injection molds requiring high toughness, excellent polishability, and dimensional stability. Renowned for its uniform pre-hardened hardness, 1.2738 eliminates the need for post-machining heat treatment, making it a time-efficient choice for high-precision mold manufacturing. Below is a detailed overview:
Chemical Composition
The typical chemical composition of 1.2738 plastic tool steel is as follows:
Carbon (C): 0.37–0.42% (contributes to hardness and wear resistance)
Silicon (Si): 0.20–0.40% (aids in deoxidation and improves mechanical properties)
Manganese (Mn): 1.30–1.60% (enhances hardenability and strength)
Nickel (Ni): 1.00–1.30% (boosts toughness, impact resistance, and polishability)
Chromium (Cr): 1.80–2.20% (improves corrosion resistance, wear resistance, and hardenability)
Molybdenum (Mo): 0.15–0.25% (enhances high-temperature strength and dimensional stability)
Phosphorus (P): ≤0.030% (minimized to avoid embrittlement)
Sulfur (S): ≤0.015% (controlled to ensure good polishability and toughness)
Key Properties
1.2738 steel is engineered to meet the rigorous demands of large plastic mold applications, with properties optimized for performance and manufacturing efficiency:
Pre-Hardened Convenience
Delivered in a pre-hardened state with a uniform hardness of 30–35 HRC (or 35–40 HRC in some variants), eliminating the need for post-machining heat treatment. This reduces production time, minimizes distortion risks, and ensures immediate readiness for precision finishing.
Excellent Toughness and Impact Resistance
The nickel content enhances toughness, making it highly resistant to cracking under mechanical stress—critical for large or thin-walled mold components subject to high injection pressures.
Superior Polishability
Its low sulfur content and fine, homogeneous microstructure allow it to achieve high-quality surface finishes (up to mirror polish), suitable for plastic parts requiring strict aesthetic standards (e.g., automotive interiors, consumer electronics).
Good Machinability
Despite its pre-hardened state, 1.2738 maintains reasonable machinability, enabling precise 加工 of complex mold cavities, cores, and intricate details.
Dimensional Stability
Exhibits minimal dimensional change during machining and service, ensuring long-term precision in large molds where tight tolerances are critical.
Moderate Corrosion Resistance
Chromium content provides basic resistance to corrosion from non-aggressive plastics and cleaning agents, suitable for most general plastic molding applications.
Physical Properties
Density: ~7.85 g/cm³
Thermal Expansion Coefficient: ~11.0×10⁻⁶/K (at 20–100°C)
Thermal Conductivity: ~30 W/(m·K) (at room temperature)
Melting Point: ~1400–1450°C
Mechanical Properties (Pre-Hardened State)
Hardness: 30–35 HRC (standard) or 35–40 HRC (high-hardness variant)
Tensile Strength (Rm): ~900–1100 MPa
Yield Strength (Rp0.2): ~800–1000 MPa
Elongation (A): ~12–15%
Impact Toughness (Charpy V-notch): ≥40 J/cm² (at room temperature)
Heat Treatment
Unlike many tool steels, 1.2738 is typically used in its pre-hardened state, eliminating the need for quenching and tempering by the end-user. However, optional processes may include:
Stress Relieving
Purpose: Reduce internal stresses after heavy machining to prevent distortion.
Process: Heat to 550–600°C, hold for 2–4 hours, then air cool.
Result: Maintains hardness while stabilizing dimensions.
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 to ≤500°C before air cooling.
Result: Hardness ≤230 HBW.
Application Fields
1.2738 plastic tool steel is widely used in large-scale, high-precision plastic mold manufacturing:
Large Plastic Injection Molds: Ideal for automotive parts (e.g., bumpers, dashboards), household appliances (e.g., refrigerator liners, washing machine components), and industrial containers, where size and complexity demand high toughness.
High-Gloss Surface Molds: Used for molds producing plastic parts requiring a polished finish, such as automotive interior trim, electronic device casings, and cosmetic packaging.
Thin-Walled or Complex Molds: Suitable for molds with intricate geometries or thin sections, where toughness and dimensional stability prevent cracking under injection pressure.
Mass Production Molds: Valued for its wear resistance in high-volume production, ensuring consistent part quality over extended mold life.
Comparison with 1.2316 Steel
Feature 1.2738 Plastic Tool Steel 1.2316 Plastic Tool Steel
Primary Use Large, complex molds (pre-hardened) Corrosion-resistant molds
Hardness 30–40 HRC (pre-hardened) 45–50 HRC (after heat treatment)
Corrosion Resistance Moderate Excellent (high chromium)
Toughness High Good
Best For Large-scale, high-toughness applications Corrosive plastics, medical/food molds
1.2738 steel’s combination of pre-hardened convenience, toughness, and polishability makes it a preferred material for large, complex plastic molds, streamlining production while ensuring reliability in high-stress manufacturing environments.