P20 Steel Properties and Heat Treatment for Plastic Molds

Imagine a precision plastic product - what kind of mold is required to transform design blueprints into the final form? The choice of mold steel directly determines product accuracy, lifespan and production efficiency. Among various mold steel materials, DIN 1.2311 (P20) has emerged as a star material in plastic mold manufacturing due to its excellent comprehensive properties. This article provides an in-depth examination of DIN 1.2311 (P20) plastic mold steel, covering its characteristics, applications and heat treatment processes.

DIN 1.2311, commonly known as P20, is a pre-hardened alloy tool steel renowned for its good machinability, polishing characteristics and weldability. Even in hardened and tempered condition (approximately 300HB Brinell hardness), it maintains excellent workability. With its smooth surface finish, this steel is a popular choice for machined plastic molds and die-casting molds.

DIN 1.2311 is typically supplied in pre-hardened condition, allowing direct machining without additional heat treatment. In this state, the steel offers good wear resistance. For applications requiring higher surface hardness, such as compression plastic molds, carburizing treatment can be performed.

To further enhance machinability, a high-sulfur variant of DIN 1.2311 is available in the market. This modified version significantly reduces cutting resistance and extends tool life while maintaining original performance characteristics.

• Excellent Machinability: Even in pre-hardened state, DIN 1.2311 remains easy to cut, drill and mill, reducing mold manufacturing difficulty and costs.
• Superior Polishability: With proper polishing, mirror-like surface finishes can be achieved, meeting high surface quality requirements for plastic products.
• Good Weldability: The steel's welding characteristics facilitate mold repairs and modifications, extending service life.
• Pre-hardened Supply Condition: Typically supplied at 240-280 BHN, eliminating heat treatment requirements and shortening mold production cycles.
• Uniform Hardness Distribution: Maintains consistent hardness across large cross-sections, ensuring stable mold performance.
• Good Wear Resistance: The pre-hardened condition provides sufficient wear resistance for most plastic mold applications.

The typical chemical composition of DIN 1.2311 includes:

• Carbon (C): 0.35 - 0.45%
• Silicon (Si): 0.20 - 0.40%
• Manganese (Mn): 1.30 - 1.60%
• Chromium (Cr): 1.80 - 2.10%
• Molybdenum (Mo): 0.15 - 0.25%
• Sulfur (S): ≤ 0.03% (standard), 0.05-0.10% (free-cutting variant)
• Phosphorus (P): ≤ 0.03%

Due to its outstanding properties, DIN 1.2311 (P20) is widely used in various plastic mold manufacturing applications including:

• Injection molds for plastic products such as automotive components, household appliances and electronic product housings
• Die-casting molds for non-ferrous metal products like zinc and aluminum alloy castings
• Extrusion molds for plastic profiles including pipes and special-shaped materials
• Mold bases providing structural support and rigidity
• Mold cores determining product shape and dimensions
• Pressure plates and backing plates for mold support and fixation
• Shoe lasts for footwear manufacturing
• High-pressure die-casting molds
• Receiver sleeves connecting molds to injection machines

While typically supplied pre-hardened, additional heat treatments may be required for specific applications:

• Carburizing: For higher surface hardness, heat in carburizing medium at 871-899°C (1600-1650°F), followed by quenching at 816-871°C (1500-1600°F) with 15-minute holding time and oil quenching.
• Quenching: Uniform heating to 820-840°C followed by oil cooling.
• Forging: Slow heating for uniform temperature distribution. Start forging at 1050°C, never below 930°C, followed by slow cooling.
• Stabilization: For stress relief before finishing, heat to 460-500°C with sufficient holding time followed by air cooling.
• Annealing: Uniform heating to 770-790°C with sufficient holding time followed by slow furnace cooling.
• Tempering: Uniform heating to tempering temperature with minimum 1 hour holding time per 25mm thickness followed by air cooling.

DIN 1.2311 can be welded using conventional methods. Proper cleaning of welding areas and selection of appropriate electrodes and techniques are essential. Post-weld tempering is recommended to relieve stresses and improve joint performance.

When selecting DIN 1.2311 (P20), consider:

• Plastic product type and performance requirements
• Mold size and complexity
• Production volume
• Budget constraints

DIN 1.2311 offers excellent machinability, polishability and weldability in pre-hardened condition, making it a versatile choice for plastic mold manufacturing. Understanding its properties and treatment options enables optimal material selection for enhanced mold performance and longevity, ultimately improving plastic product quality and production efficiency.