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How to choose the right mold steel for your project?

There are many different kinds of steel that can be used to build plastic injection molds. When choosing the mold steel, we always need to consider steel cost, steel hardness, the lifetime of steel, surface finish, and the plastic materials.

What is mold steel?

Plastic mold steel is characterized by good dimensional stability during heating, good polishability, high impact strength, and good wear characteristics. Within the general class of mold steel, different grades will deliver better polishability or improved machinability.

Classification of mold steel

Alloy tool steel and non-alloy tool steel

Tool steel can basically be divided into alloy steel and non-alloy steel. If the amount of alloy components is very small (the mass of most components is less than 0.10% some are even less), which is usually called non-alloy steel. The difference between alloy steel and non-alloy tool steels is that alloy steels have a much higher hardness and can withstand higher loads in the injection molding process and prolong the service life. At the same time, it can also withstand higher operating temperatures.

The alloy composition in alloy tool steel can be adjusted according to the required performance of the steel. Some alloy elements are added to the tool steel. Common ones are chromium, vanadium, manganese, molybdenum, nickel, tungsten, cobalt.

The carbon content of non-alloy tool steel is generally higher usually between 0.5% and 1.5%. Although the carbon content of stainless steel is usually less than 0.1%.

Cold work tool steel and hot work tool steel

The difference between cold-worked and hot-worked steels only exists in alloy mold steels. Apart from some other differences, the main difference between cold-worked and hot-worked steel is heat resistance. Cold work steel is suitable just for up to 200 ° C, while hot work steel can withstand twice the working temperature (up to 400 ° C). For higher temperatures, only high-speed steel (up to 600 ° C) is used.

10 kinds of commonly used mold steel for the plastic injection mold manufacturing


P20 material is one of the most commonly used plastic mold steels, with a hardness between 28 ~ 32HRC, which can be eroded by electricity and has good polishing. It is often used in plastic toy molds and is suitable for PP and PE plastics.


718H material is pre-hardened plastic mold steel without hardening and tempering treatment. It is often used in long-life plastic injection molds, such as home appliance parts and computer housing molds. The working life is longer than P20 steel and has good polishing. It is widely used in plastic injection mold, blow molds, and extrusion molds and is suitable for the production of plastics such as PS, PE, PP, and ABS.


Pre-hardened plastic mold steel, the hardness can reach 32 ~ 43HRC. This kind of material does not need heat treatment and has good polishing and machinability, erosion-resistance. It is often used to make products with high appearance requirements. Such as ear thermometer shell, TV filter plate, cosmetic case, etc., suitable for plastic products such as ABS, GPPS, PS, PC, and AS.


The hardness of NAK55 is between 37 ~ 43HRC, no heat treatment, high hardness, good wear resistance and pressure resistance, uniform hardness and good machinability, suitable for high-precision mold processing, commonly used in manufacturing high-precision mirror molds, such as cameras, Makeup instruments or transparent cover, etc. suitable for injection mold materials such as PMMA, PC and PS.


S136 steel has a hardness between 290 ~ 300HB, has excellent corrosion resistance, polishing, and machinability, no need for heat treatment. It is suitable for making molds used in weak acids and humid environments, especially for high-volume transparent plastic parts, such as CDs and optical instruments. It is preferred to manufacture transparent products of PVC, PP, EP, PC, PMMA, and other materials.


420SS steel is stainless steel with high hardness, good polishing, and corrosion resistance. The hardness is 30-33HRC. Its corrosion resistance and strength are far more than other materials. Commonly used for corrosive materials, suitable for mass production molds.


H13 material contains tungsten and has higher temperature resistance. It is suitable for die-casting alloy mold materials, such as aluminum, magnesium, zinc, and copper alloy die-casting mold, and is often used for knife tools.


1.2344 is a tool steel grade standardized for hot working. The main feature of this grade is the combination of alloying elements of chromium, molybdenum, and vanadium, Cr-Mo-V, which provides high wear resistance to thermal shock. It is well known for its great strength, and heat resistance. It is heavily used for die casting in the cold heading field. The presence of high vanadium in DIN 1.2344 can handle the abrasion at both low and high temperatures. It always provides a uniform and high level of machinability. This tool steel is mostly used for aluminum, magnesium and Zinc die casting.


8407 material is alloy tool steel with chromium, molybdenum, and vanadium. It is better than the general H13 material and has good fatigue strength and thermal stress fatigue performance. It is often used in die casting molds, forging molds, and extrusion molds.


S7 material is composed of chromium-molybdenum alloy, which has high impact resistance and toughness, good processing and heat treatment performance, and is suitable for molds such as knife dies and punches.

The last & free solution

After reading this article, hope that you can choose the right mold steel for your project. If you still can’t make the decision yourself, please contact us for help, and it is absolutely free.

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