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Injection mold commonly used six kinds of mold materials

• 2025-06-18

The choice of steel not only affects the service life of the mold, but also affects the cost of opening the mold. Some characteristic plastic products may also require the use of specific materials. Because, open the injection mold, the choice of material is particularly important. The following is the introduction of the characteristics and applicable products of several commonly used mold materials.

What are the commonly used mold steel?

1. P20 steel

P20 steel is a pre-hardened die steel, the domestic brand is 3Cr2Mo, widely used in the manufacture of low complexity, small and medium batch injection mold.

Core Features

1. Pre-hard state

The factory has been treated with quenching and tempering, pre-hardened to 30-35 HRC, can be directly processed without secondary heat treatment. Uniform hardness distribution, suitable for high precision machining.

2. Processing performance

Good machinability, suitable for CNC milling, electric discharge machining (EDM), etc. Medium polishing, up to #2000-#4000 mesh.

3. Wear resistance and toughness

Medium abrasion resistance, suitable for ordinary engineering plastics. Good toughness, can withstand the impact load of small and medium-sized mold.

4. Corrosion resistance

Corrosion resistance in general, long-term contact with corrosive plastics (such as PVC, flame retardant materials) easy to rust, the need for surface chrome plating or nitriding treatment.

Applicable Scenarios

1. Type of plastic

Suitable for the manufacture of ordinary engineering plastic products, such as ABS, PP, PE, PS, PC, etc. Not suitable for glass fiber reinforced plastics (easy to wear mold), highly corrosive plastics (such as PVC surface treatment).

2. Product type

It is suitable for the production of products with low requirements for mirror gloss or simple texture, such as daily necessities (bottle caps, toy shells, etc.), home appliance parts, automotive interior parts, etc.

3. Product output

The life of injection molds made of P20 steel is about 100000-300000 molds. Within this range, the output is determined by the number of cavities, use and maintenance of the mold cavity.

Precautions

1, to avoid the use of chlorine, fluorine and other corrosive components of the plastic, unless the surface treatment.

2, long-term storage should be coated with anti-rust oil to prevent corrosion caused by environmental moisture.

3. Complex molds can be partially inserted (such as P20 for cavity and steel with higher hardness for core).

2. 718H steel

718H steel corresponds to an improved and upgraded version of P20 steel. The domestic brand is Cr2NiMo 3, which belongs to pre-hardened die steel. The purity, uniformity and comprehensive performance are optimized by adding nickel (Ni) elements, and it is suitable for manufacturing high-precision and long-life medium and large injection molds.

Core Features

1. Pre-hard state

The factory hardness is 35-40 HRC, the hardness distribution is more uniform, and the deformation resistance is stronger. It can be processed directly to avoid the size fluctuation caused by heat treatment.

2. Processing performance

Excellent machinability, suitable for CNC machining and electrical discharge machining (EDM) of complex structures. Polishing is better than P20, up to #6000-#8000 mesh, close to the mirror effect of NAK80.

3. Wear resistance and toughness

Significantly improved wear resistance, suitable for glass fiber, mineral-filled engineering plastics. High toughness, good fatigue resistance, suitable for multi-cavity mold or large mold.

4. Corrosion resistance

Better than P20, but weaker than stainless steel (such as S136), long-term contact with corrosive plastics still need surface treatment (such as chrome plating).

Applicable Scenarios

1. Type of plastic

It is suitable for high-demand engineering plastic products, such as PA (nylon) glass fiber (GF), PBT, PC/ABS, POM and other reinforced plastics. Transparent plastics, such as PC, PMMA (acrylic), etc., require higher surface finish products.

2. Product type

Precision electronic components (such as connectors, housings), automotive functional parts (lampshades, dashboards), high-gloss panels for home appliances, etc. Mould with complex structure or thin wall (good fatigue resistance).

3. Product output

The service life is 30-500000 die, and the service life is about 30% longer than that of P20.

Precautions

1, containing glass fiber plastic mold recommended regular inspection cavity wear, timely polishing repair.

2, avoid long-term exposure to humid environment, storage should be coated with anti-rust oil.

For highly transparent plastics (such as optical grade PC), it is recommended to combine mold temperature control (50-80°C) to optimize surface quality.

3. NAK80 steel

NAK80 steel is a pre-hardened mirror mold steel designed for high-gloss, high-precision injection molds. Its core advantage is that it can achieve high hardness without heat treatment and excellent polishing performance. It is the preferred material for manufacturing transparent parts and high-gloss surface products.

Core Features

1. Pre-hard state

The factory hardness is 40-42 HRC, which can be processed directly to avoid heat treatment deformation. Excellent hardness uniformity, suitable for complex precision molds.

2. Mirror polishing

Polishing can reach #10000-#15000 mesh, which is the top level in the industry and has a surface roughness (Ra)≤ 0.01 μm. It is suitable for optical-grade transparent parts (such as lenses and light guide plates) or high-gloss appearance parts (such as automobile chrome-plated decorative strips).

3. Wear resistance and corrosion resistance

The wear resistance is better than P20 and 718H, but weaker than S136 stainless steel. Medium corrosion resistance, long-term contact with corrosive plastics need surface treatment (such as nickel plating).

4. Processing performance

Good machinability, but high hardness, need to use carbide tools. After electric discharge machining (EDM), the surface is easy to form a hardened layer, which needs fine polishing.

Applicable Scenarios

1. Type of plastic

Suitable for high transparent/high gloss plastic products, such as PC, PMMA (acrylic), COP, transparent ABS, etc. Not applicable to plastics containing corrosive components (such as PVC, flame retardants).

2. Product type

Optical components (camera lens, light guide plate), cosmetic packaging (bottle cap, powder container), car high-gloss grille/interior parts. Mould with complex surface texture (bite flower, imitation leather pattern).

3. Product output

The service life of the mold is about 500000-1 million molds, which is suitable for mass production of products.

Precautions

1, avoid the use of sulfur, chlorine release agent to prevent corrosion of the mold surface.

2, long-term storage should be coated with anti-rust oil, especially in high humidity environment.

3. When transparent plastic injection molding, the mold temperature is recommended to be controlled at 80-120 ℃ to reduce welding lines and improve gloss.

4. steel H13

H13 steel is a kind of hot work die steel, the domestic grade is 4 Cr5MoSiV1, specially designed for high temperature working environment, its core advantage is excellent heat resistance and thermal fatigue resistance, suitable for long time to withstand high temperature cyclic stress mold.

Core Features

1. Hardness and toughness

After heat treatment, the hardness can reach 48-52 HRC (quenching and tempering). High toughness, impact resistance is better than ordinary tool steel, suitable for high stress mold structure.

2. High temperature resistance

Good thermal fatigue resistance, can work at 500-600 ℃ for a long time, short-term tolerance up to 650 ℃, not easy to crack under alternating hot and cold conditions, suitable for rapid cycle production, such as hot runner molds.

3. Wear resistance and corrosion resistance

The wear resistance is medium and can be improved by surface treatment (such as nitriding). Corrosion resistance in general, long-term contact with corrosive media need chrome plating.

4. Processing performance

The hardness in the annealed state is about 180-220 HB, which is easy to cut. When precision machining is required after quenching, electric discharge (EDM) or grinding processes are recommend used.

Applicable Scenarios

1. Type of plastic

Suitable for high temperature engineering plastic products, such as PEEK, PEI, LCP (liquid crystal polymer), PPS, etc., as well as glass fiber reinforced plastic products, such as PA GF, PBT GF (high wear resistance cavity).

2. Product type

Thick-walled or fast-cycle products, such as car hoods, battery housings, and home appliance housings (such as microwave oven frames), require rapid demoulding. Engineering parts with high dimensional accuracy requirements, such as electronic connectors, 5G radomes (LCP materials), medical devices (such as surgical tool handles, PEEK materials).

3. Scale of production

It is suitable for long-life requirements of more than one million mold times, especially under high temperature and high pressure conditions.

5. steel S136

S136 steel is a kind of high chromium stainless steel die steel, the domestic brand is 4Cr13, known for its excellent corrosion resistance and excellent polishing, specially designed for high cleanliness, high gloss and corrosive plastic injection mold design, especially suitable for medical, food packaging and other harsh scenes.

Core Features

1. Hardness and wear resistance

The hardness after heat treatment can reach 48-52 HRC (quenching and tempering). Medium wear resistance, can be improved by nitriding or PVD coating (such as contact glass fiber reinforced plastic).

2. Corrosion resistance

The high chromium content (13.6%) gives it extremely strong corrosion resistance and long-term exposure to corrosive media such as PVC, flame retardants, and acidic plastics. Rust resistance far exceeds that of ordinary die steel (such as P20, 718H), and no additional coating is required in humid environments.

3. Polishing

Polishing can reach #8000-#12000 mesh, surface roughness (Ra)≤ 0.015 μm, close to the mirror effect of NAK80. Suitable for transparent plastics (such as PC, PMMA) and medical grade high clean products.

4. Processing performance

Annealed state hardness of about 215-235 HB, good machinability, but need to avoid sticking knife. Fine polishing is required after electrical discharge machining (EDM) to remove the white layer.

Applicable Scenarios

1. Type of plastic

Corrosive plastic products, such as PVC, halogen-containing flame retardant materials (such as V0 grade ABS), biodegradable plastics (containing acidic components). High transparent/medical grade plastic products, such as PC, PMMA, medical grade PP, PE (such as syringes, vials).

2. Product type

Medical equipment (surgical equipment, dialysis parts), food containers (bottle caps, fresh-keeping boxes), optical lenses, mobile phone lenses, cosmetic packaging (mirror polishing required).

3. Product output

Die life of 500000~1 million mold times, especially in corrosive environment life is far more than ordinary steel.

Precautions

1, medical mold special machine processing, to prevent oil or iron residue, to avoid cross contamination.

2, long-term storage still need to be coated with anti-rust oil, especially in the seashore or high humidity environment.

6. 2344 steel

2344 steel is a chromium-molybdenum-vanadium alloy hot-working die steel with similar characteristics to H13 steel. It is specially designed for high temperature and high pressure working conditions, has excellent thermal fatigue resistance, and is suitable for the harsh production environment of frequent cold and hot cycles.

Core Features

1. Hardness and toughness

After heat treatment, the hardness is 48-52 HRC (quenching and tempering), taking into account high hardness and impact toughness, suitable for complex mold structures (such as thin-walled deep cavities), and reducing the risk of stress cracking.

2. High temperature performance

It can work at 500-600 ℃ for a long time and withstand 650 ℃ for a short time. Excellent thermal fatigue resistance, in alternating hot and cold conditions (such as die-casting mold) anti-cracking ability, significantly extended life.

3. Wear resistance and corrosion resistance

The wear resistance is medium and can be improved by nitriding or coating (such as PVD). Corrosion resistance in general, contact with corrosive plastic surface chrome plating.

4. Processing performance

Annealed hardness 180-220 HB, easy to cut, mill and EDM. When precision machining is required after quenching, grinding or wire cutting process is recommend.

Applicable Scenarios

1. Type of plastic

High temperature engineering plastics, such as PEEK, PEI, LCP, PPS (processing temperature> 300 ℃). Glass fiber reinforced plastics, such as PA66 GF, PBT GF (need high wear cavity).

2. Product type

Auto parts (such as car dashboards, door panels, center consoles, car bumpers, rearview mirror shells), electronic product shells (such as mobile phone shells, computer shells), daily necessities (such as disposable lunch boxes, storage boxes), etc.

3. Product output

Suitable for long life requirements of more than 1 million modes.

Precautions

Check the cavity surface every 50000-100000 times and repair micro cracks or wear in time.

The above several kinds of mold steel, basically has been able to meet most of the plastic products open mold demand.