Introduction

P20 steel, also known as 1.2311 or 3Cr2Mo, is a high-quality mold steel characterized by its excellent toughness, good polishability, and consistent hardness. It is supplied in a pre-hardened condition, typically in the range of 28-32 HRC, thus eliminating the need for heat treatment prior to mold manufacturing. P20 is widely used for plastic injection molds, compression molds, die-casting dies for zinc, and other tooling applications requiring superior performance, durability, and machining efficiency.

Due to its balanced composition of chromium and molybdenum, P20 offers an ideal combination of strength, wear resistance, and machinability, making it a preferred choice across toolmaking and mold manufacturing industries worldwide.

Properties of P20 Steel:

  • Pre-hardened Condition: Supplied in the hardened and tempered condition, typically between 28–32 HRC.
  • Good Machinability: Easy to machine with excellent surface finish capability.
  • Toughness: High impact resistance and toughness to withstand heavy mechanical stresses.
  • Uniform Hardness: Throughout the cross-section, ensuring consistent mechanical properties.
  • Good Polishing and Texturing: Suitable for applications requiring mirror finishes or intricate mold texturing.
  • Moderate Wear Resistance: Enhanced by its chromium content.
  • Dimensional Stability: Minimal distortion during machining and service life.
  • Heat Treatment Compatibility: Can be nitrided or carburized for enhanced surface hardness.

Uses/Applications:

P20 is predominantly used in the following industries:

  • Plastic Injection Molds: Core and cavity materials for mold bases and inserts.
  • Compression Molds: Especially for thermoplastics and thermosetting materials.
  • Die Casting Dies: Particularly for zinc, magnesium, and light aluminum die casting.
  • Blow Molding Dies: For producing hollow plastic parts like bottles and containers.
  • Plastic Extrusion Dies: In tooling applications where excellent polish and surface finish are required.
  • Machine Components: Shafts, gears, and structural components subjected to moderate stresses.

Chemical Composition:

Element Content (%)
Carbon (C) 0.28 – 0.40
Manganese (Mn) 0.60 – 1.00
Silicon (Si) 0.20 – 0.80
Chromium (Cr) 1.40 – 2.00
Molybdenum (Mo) 0.30 – 0.55
Sulfur (S) ≤ 0.005
Phosphorus (P) ≤ 0.025

Mechanical Properties:

Property Typical Value
Hardness (As-supplied) 28–32 HRC
Tensile Strength ~1000 MPa
Yield Strength ~800 MPa
Elongation at Break ~15%
Impact Toughness High

These properties contribute to the material’s ability to withstand repeated loading, stress, and surface wear during service.

This balanced chemistry provides excellent toughness, moderate wear resistance, and good hardenability.

Physical Properties:

Property Value
Density 7.85 g/cm³
Modulus of Elasticity 205 GPa
Thermal Conductivity ~29.5 W/m·K (at 20°C)
Coefficient of Thermal Expansion 12.3 x10⁻⁶/°C (20-100°C)
Specific Heat Capacity 460 J/kg·K

Forging:

  • Forging Temperature Range: 1100°C to 870°C.
  • Cooling: After forging, the material should be cooled slowly in a furnace or dry lime to prevent cracking.
  • Note: Overheating should be avoided to maintain structural integrity.

Proper forging practices ensure the retention of material toughness and minimize defects.

P20’s physical properties make it suitable for tooling exposed to moderate thermal and mechanical stresses.

Heat Treatment:

Although P20 is supplied in a pre-hardened condition, it can undergo surface hardening to enhance wear resistance:

  • Annealing: Heat at 760–790°C, followed by slow furnace cooling to improve machinability.
  • Stress Relieving: After rough machining, heat to ~600°C, hold for 1–2 hours, then cool slowly to minimize residual stresses.
  • Nitriding: Can be nitrided to a surface hardness of up to 65–70 HRC for improved wear resistance without affecting core properties.

Heat treatment enhances the performance of P20 molds under extended service conditions.

Machinability:

P20 offers excellent machinability, rated approximately 75% compared to free-machining steels:

  • Suitable for high-speed machining.
  • Good surface finishes achievable with conventional and CNC machining.
  • Pre-hardened condition allows direct mold making without prior hardening steps.
  • Coolant usage is recommended to avoid heat buildup during machining.

Efficient machinability ensures reduced production time and cost.

Dimensional Tolerances:

P20 Bright Bars and Plates are available in precise tolerances, typically:

  • Bars: h9/h11 tolerance class depending on the finish.
  • Plates: Thickness tolerances of ±0.3 mm are common.
  • Special Profiles: Custom sizes and precision cuts are available upon request.

Accurate tolerances ensure reduced machining time and improved final product quality.

Corrosion Resistance:

  • P20 is not inherently corrosion-resistant.
  • For applications exposed to moisture or corrosive environments, surface coatings (e.g., hard chrome plating or nitriding) are recommended.
  • Routine maintenance, storage in dry conditions, and protective coatings prolong tool life.

Weldability:

  • Good weldability when proper procedures are followed.
  • Preheat to ~250°C before welding to avoid cracking.
  • Post-weld heat treatment (stress relieving at ~600°C) is recommended to maintain structural integrity.
  • Suitable filler materials include low-carbon consumables for matching base hardness.

Proper welding practices ensure tool longevity and strength.

Available Form:

P20 Steel is available in various standard forms, including:

  • Rounds: Bright Bars, Forged Bars
  • Flats: Rolled and Precision Ground Flats
  • Plates: Mold plates, Die plates
  • Blocks: For large mold bases and tool construction
  • Custom Profiles: As per application requirements

A wide range of forms and sizes ensures adaptability for diverse applications.

Conclusion:

P20 Steel is a reliable and versatile mold/tool steel offering an excellent balance of toughness, polishability, machinability, and wear resistance. Its pre-hardened supply condition saves time and cost in mold manufacturing, while its consistent mechanical properties ensure durability in demanding tooling applications. Although it lacks intrinsic corrosion resistance, appropriate surface treatments can extend its service life significantly.

With wide availability in various forms and outstanding mechanical and physical characteristics, P20 remains a preferred choice for mold makers and tool engineers worldwide. Proper machining, heat treatment, and maintenance practices can maximize the performance and longevity of P20 Steel in production environments.

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