Plastic Mould Steels (also called P20 steels, mould tool steels, or mold steels) are specially engineered steels used for manufacturing plastic injection molds, blow molds, extrusion dies, and compression molds. These steels are designed to offer excellent machinability, polishability, toughness, and dimensional stability, ensuring long mold life and high-quality plastic components.

Plastic mould steels are formulated to resist:

1. high injection pressures

2. repeated thermal cycles

3. surface wear and abrasion

4. corrosion (in some grades)

They come in both through-hardened and pre-hardened conditions.

Common Grades of Plastic Mould Steels

1. Pre-Hardened Plastic Mould Steels

Used for general-purpose molds; supplied ready-to-machine.

a. 1.2311 / P20

b. 1.2738 (P20+Ni)

c. VR 400 ESR

d. VR 300

Features:

a. Easy machining

b. Good toughness

c. Moderate hardness (28–34 HRC)

d. Used for medium production volume molds

2. Hardened & Tempered Plastic Mould Steels

Used for high-wear, long-life molding applications.

a. 1.2083 (Stainless mould steel)

b. 1.2085

c. 1.2083 ESR

d. VR Stainless

Features:

a. 48–52 HRC after hardening

b. Excellent wear resistance

c. High polishability (ideal for transparent molds)

d.Superior corrosion resistance

Commonly used for:

a. Transparent plastic moulds (PC, PMMA, Acrylic)

b. Food-grade and medical-grade moulds

c. PVC and corrosive polymers

3. High-Performance ESR (Electro-Slag Remelted) Mould Steels

Ultra-clean steels with excellent polishing and machining properties.

a. 1.2738 ESR

b. 1.2083 ESR

c. VR 16 HH ESR

Features:

a. Very high purity

b. Excellent mirror polish

c. High hardness uniformity

d. Ideal for high-end molds, lenses, optical parts

Key Properties of Plastic Mould Steels

1. High machinability (reduces machining cost and time)

2. Excellent polishability for mirror-finish molds

3. Dimensional stability during heat treatment

4. High toughness to withstand injection pressures

5. Wear and corrosion resistance (grade-dependent)

6. Long tool life in industrial mold applications

Typical Applications

1. Injection moulds for plastic parts

2. Blow moulds

3. Compression and transfer moulds

4. Plastic dies and cavities

5. Automotive moulds

6. Household and electronics moulds

7. Transparent product moulds (for high polish steels)