What is Mold Steel?
Mold steel is a type of tool steel, one that has been manufactured specifically for being utilized in demanding manufacturing processes such as die casting, injection molding, and stamping. Unlike regular structure steel, mold steel is manufactured to withstand extreme pressures through numerous cycles of heat, friction, and corrosion without deforming or failing. Mold steel is the foundation of mass fabrication and directly affects the durability, dimensional accuracy, and cost efficiency of the finished product.
The choice of the right mold steel is not merely a material choice but a function of strategy. The correct mold steel will determine the longevity of the tool as well as the consistency of the parts that it helps produce. Good quality mold steel will allow for consistent results. In all cases where the company or agency is attempting to machine part using turning milling drilling machining manufacturers or divide to make millions of parts of plastic moldings, the process becomes consistent.
Materials Used for Mold Steel: The Common Grades
Mold steels can be divided into categories that reflect their main usage – cold working, hot working and plastic molding steels. Each of the categories is represented by different grades that are appropriate for various working environments.
The major grades are:
P20: This grade is made from high strength steel that is prehardened. It is popular for large molds where extreme wear resistance is not required. It has good machinability and toughness, thus offering a good value for medium productions.
NAK80: A type of prehardened steel that can be polished and which has an even hardness. It is used for producing surfaces for applications such as transparent parts and decoration of automobiles.
S136 (SUS420): A corrosion-resistant stainless steel grade. It is essential for plastic materials that contain corrosive additives (e.g. PVC and flame retardants). It can prevent mold cavity rust and pitting.
Hot Work Mold Steels
These grades are used in molds responsible for high temperatures and thermal cycling.
H13 (SKD61): The major standard for hot-working applications offering good hardness, high temperature stability and thermal fatigue resistance needed for die casting of aluminum and plastic gears.
Cold Work Mold Steels
These molds are often used in stamping and cold working because of the need for wear resistance at normal temperatures.Types of Mold Steels Based on Their Application.
There are different grades of mold steels as per their application in either cold work, hot work, or plastic mold steels. Every category has its specific grades that are optimized for different conditions.
Plastic Mold Steels
Plastic mold steels are used in injection molding of plastics that are known as thermoplastics and thermosets. Plastic mold steels comprise grades like:
P20: A pre-hardened steel that is a general-purpose mold steel used in the making of bigger mold openly.
NAK80: A pre-hardened mold steel that is used for creating a polished surface with uniform hardness.
S136 (SUS420): A stainless steel made of corrosion resistant grade that is significant while molding caustic plastic like PVC resin, flame retardants, etc.
Cold Work Mold Steels
Cold work steel molds are there for activities like stamping and cold forging.Steel for Mold Manufacturing: The Different Types of Grades
Mold steel is classified based on whether the application is cold work, hot work, or plastic mold steels. Each type of mold steel will have specific types of grades suitable for specific purposes.
Mold Steels for Plastic
Mold steels are utilized in the manufacturing of thermoplastics and thermosets by means of injection molding. The most common grades include the following:
P20 mold steel is general-purpose pre-hardened steel. It is popularly utilized in manufacturing larger molds due to the good balance of machinability and toughness it offers to medium-volume production.
A common grade is also NAK80 pre-hardened steel that is characterized with superior polishability and uniform hardness. This grade is used for offering high-gloss surfaces to mold products like automotive components and other transparent parts.
S136 grade or SUS420 which is used to make highly corrosion resistant stainless steels is of critical importance when injecting plastics with corrosive additives like PVC and flame retardants to help avoid rust and pitting in the cavity of the mold.
Mold Steels for Hot Work
Mold steels of the hot work type are designed for withstanding high temperatures and thermal cycling; die casting and hot forging application falls under this category.
The industry standard for working with hot work mold steel is H13 that has good hardness, heat resistant capabilities, and thermal fatigue resistance.
Mold steels for cold work offer high wear resistance at room temperatures and are used for stamping and cold forging processes.D2 (SKD11) is able to withstand tough usage and it is principally used to produce stamping dies.
Processing technology
The raw material for preparing mold steel has its own processing method as well as heating treatment needed to obtain the desired mechanical properties concerning hardness, toughness, and dimensional stability.
In modern industries, almost all manufacturers apply CNC machining and sheet metal fabrication methods during the preparatory process but it is heating treatment that brings out the most benefit of the steel.
Heating Treatment Process
Mold steel performance has to do with its microstructure which is determined by heat treatment operations.
1. Quenching: This process requires heating the steel material to specific temperatures (i.e., 900-1030°C) and then cooling it quickly either by forcing cold air or through oil. As a result, martensite or very hard and brittle microstructure is created.
2. Tempering: After quenching, the next step to be undertaken is tempering at lower temperatures (i.e., 500-630°C). This process helps to reduce brittleness and remove internal stresses in the steel.
To guarantee uniform characteristics throughout the profile of the die, it is often necessary to apply advanced composing processes.
Surface Treatment
The main treatment required to protect the outer surface of the mold against wear, corrosion, heat, and friction.
- Nitriding: This process is made with the help of chemical heating and the nitrogen diffusing into the surface of the steel that creates a layer resistant to wearing.
- Arc ion plating: The process requires the application of a thick layer of high-strength ceramic material such as TiAlN onto the mold surface. Studies have demonstrated that coatings made of TiAlN on SKD61 prevent soldering.
- Laser-clad coatings: This process includes creating a strong layer of high-performance alloy on the steel surface in order to restore dimensions and create a layer resistant to wear.
Conclusion
The mold steel acts silently in facilitating mass production. An engineer who is involved in mass production should have a profound knowledge of the material so as to choose between P20 or H13 mold steel.
Post time: Sep-12-2026