P20 tool steel is a widely used type of tool steel, primarily known as a low-carbon mold steel. It is categorized as a plastic mold steel designed for machined cavities. The AISI (American Iron and Steel Institute) designation for P20 is UNS T51620. P20 is most frequently used for plastic dies and molds. It can also be applied to zinc die-casting dies and holder blocks. A key characteristic of P20 tool steel is that it is typically purchased and supplied in a prehardened condition. P20 material is equivalent to China GB 3Cr2Mo, Germany DIN 1.2311, Sweden ASSAB 618, and ISO 35CrMo2.

1. Application

• Plastic Molds and Dies.
• Die-Casting Dies (for low-melting alloys)
• Hot Extrusion (specifically for Aluminum and Magnesium)

2. Chemical composition

3. P20 Steel Properties¹

• Pre-hardened hardness: 32 HRC.
• Hardness of P20 filler wire: 40 HRC.
• Yield Strength: 950 MPa after prehardening.
• Elastic Modulus: 210 GPa (30 × 10^6 psi) at room temperature. This decreases to about 185 GPa (27 × 10^6 psi) at 260 °C (500 °F) and to about 150 GPa (22 × 10^6 psi) at 540 °C (1000 °F).
• Poisson’s Ratio: 0.287.
• Machinability:  Good machinability. It is readily machined in its pre-hardened condition. Machinability can be further improved by adding sulfur to the P20 grade. Machining before final P20 tool steel heat treatment results in better machinability.
• Polishability: Excellent polishability. Higher hardness (e.g., 40 HRC) can improve polished quality.
• Dimensional Stability: Good dimensional stability. It has fewer dimensional changes on hardening compared to water-hardening steel grades.
• Toughness: Medium to high toughness. Carburized P20 material provides good toughness. If higher toughness than P20 is needed (e.g., for large dies subject to severe shock), we suggest P4 and P6 mold steels.
• Wear Resistance: It has low to medium wear resistance in its general condition. Wear resistance is improved by carburizing.
• Weldability: Medium weldability. 
• Other Processing: P20 material is also suitable for photo-etching (texturing) and Electrical Discharge Machining (EDM).

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4. Heat Treatment

P20 steel is commonly supplied in a pre-hardened state, with a hardness of 28-40 HRC. It can be directly machined into complex mold cavities and put into use without further high-temperature heat treating. The pre-hardened state helps to avoid deformation and dimensional changes that may occur during subsequent heat treatment.

Although P20 material is always used directly in a pre-hardened state, its surface properties can be enhanced through further heat treatment (particularly carburizing) to meet specific application requirements, such as plastic molding.

4.1 Carburization

For plastic molding applications, P20 material is frequently carburized and then hardened after the mold impression has been machined. The as-quenched surface hardness of carburized P20 molds can reach up to 65 HRC, with the core hardness typically around 45 HRC. Case depths can be controlled, generally varying from 0.030 inches for smaller molds to 0.065 inches for large molds. We would like to remind you that the resistance of carburized P20 material to softening during tempering is relatively low, similar to that of plain carbon steel.

The carburizing temperature should NOT exceed 870°C (1600°F). Exceeding this temperature will adversely affect its polishing performance. For instance, carburizing at 845°C (1550°F) resulted in a surface hardness of 65.6 HRC and a case depth of 0.36 mm, whereas at 900°C (1650°F), the surface hardness was slightly lower at 62.5 HRC with a case depth of 0.41 mm.

Carburized P20 steel has a good combination of wear resistance, toughness, and polishability.

4.2 Preheating

We strongly recommend preheating P20 tool steel to a temperature of 1200°F (650°C).

The purpose of preheating is to precondition the molecules within the part for transformation and to relieve stresses caused by machining. It also helps to equalize heat within the part, allowing stresses to dissipate before the metal becomes too soft at higher temperatures.

4.3 Hardening (Austenitizing)

The hardening temperature is 1525°F (830°C). The soaking time is 45–60 minutes per inch of thickness. For parts under 1 inch in thickness, we recommend a minimum soaking time of 45–60 minutes. [For information about austenite, please refer to the explanation of austenite on Wikipedia.]

4.4 Quenching

Material P20 steel is oil quenched. Oil quenching from a relatively low temperature results in less dimensional change compared to water-hardening steels. After quenching, parts should be cooled to a minimum of 150°F (66°C) if air-hardened, or 150-200°F (66-93°C) if liquid-quenched, and then tempered immediately.

4.5 Tempering 

P20 tool steel usually requires double tempering. The standard tempering temperature is 400°F (205°C).

For a P20 steel that has been oil quenched from 845°C (1550°F) and tempered for 2 hours at 205°C (400°F), the resulting hardness is 36-38 HRC, with a tensile strength of 1310 MPa, a yield strength of 1172 MPa, 13% elongation, and 51% reduction of area. If the as-quenched microstructure is bainitic, the hardness after tempering may be 4 HRC lower than standard tempering diagrams.

4.6 Forging²

P20 should be slowly preheated to 815°C (1500°F). The forging temperature is 1065 to 1230°C (1950 to 2250°F). For larger sections or when heavy and rapid reductions are planned, it is advisable to use the higher end of this temperature range. For smaller sections or lighter reductions, the lower end of the range is more suitable. Do NOT forge P20 below 815 °C (1500 °F). 

After forging, the steel is cooled slowly by cooling it inside the furnace or burying it in heat-insulating media such as lime, mica, or diatomaceous earth.

5. P20 Steel Technical Data Sheet

Experimental Conditions: Carbon: 0.30% Manganese: 0.75% Silicon: 0.50% Chromium: 1.65% Molybdenum: 0.40%

Hardness Reference After Quenching and Tempering

Hardness Reference After Carburizing and Tempering

6. Supply forms and dimensions

The P20 tool steel we supply is available in various shapes, including round bars, sheet plates, slabs, flat bars, square bars, and blocks. The dimensions of the flat bar range from: width 20–600 mm × thickness 20–400 mm × length 1,000–5,500 mm. The dimensions of the round bar range from a diameter of 20–400 mm × a length of 1,000–5,500 mm. The block dimensions are obtained by cutting the flat bar.

UT testing: Sep 1921-84 D/d, E/e. 

Surface Treatment: original black, peeled, machined/turned, polished, grounded, or milled surface finishes.

Inventory Status: We do not maintain a stock. We arrange production based on customer orders.

Delivery time: Electric Arc Furnace (EAF) materials are 30-45 days.