Mold steel is a material that is used to manufacture the molds, including cold-punching mould, hot forging die, die-casting mold, and more. The mold is the main processing tool for the industry of machinery manufacturing, motor, radiometers and etc. The quality of mold would directly impact the quality of processing technic, the precision and output of products and more. The properties and heat treatment of mold steel would make a huge impact on the quality of mold except for the good design of structural and processing precision. Its grades, specification and quality determine the properties, life and manufacturing period of die.
Many people feel confused about how to select the right steel grade for own mold. The making of mold always been through forging, cutting, processing, heat treatment, test and more. In order to make sure the quality and cost of mould, the material must have great machinability, hardenability, malleability, and more. And there are several things we need to think about it.
The wear resistance of mold steel is the basic and one of the most important. And the hardness is the main factor for wear resistance. In general, high hardness of die with lower loss, that means the wear resistance is good. At the same time, the wear resistance of mold steel is related to its types, amount, shape of the carbide.
There is so high pressure for the working of mould. It has to suffer big impact load. So it must have great strength and toughness to handle such difficult conditions of working. The toughness of it is depending on the carbon content and texture.
During the working, the die under so big pressure always would be fatigue fracture. The strength, toughness, hardness and inclusion quantity of material are the factors of fatigue limit.
When the temperature is high in the working time, the hardness and strength of it would get down, which will cause the mold to get plastic deformation then become useless. So the die steel must have high stability of resistance tempering to make sure the mold has high strength and hardness in the high temperature of working time.
Because plastic has chlorine, fluorine and other elements, the HCI, HF and other etchant gas would come out after the heating and decomposition. That will attack the surface of mould cavity, make the surface become tougher then raise the loss of mold.
Different type of mould steel has different characteristics. The characteristics of common grades of mould steel as below.
SAE D2 has great hardenability and wear resistance. After quenching and polishing, its corrosion resistance will be better. And its heat treatment deformation is small, is a good material for cold work mold with high precision and long life.
It belongs to plastic mould steel. Due to the great machinability and other properties, it is widely used for plastic injection mold cavities and tooling and for die casting dies for zinc.
Mold Steel 718
It has great mechanical property and machinability. With sample processing technic, it is commonly used in the industry of mold.
It has high hardenability and toughness and medium wearing resistance. And the heat treatment deformation is small. By the way, it can be used to make the fittings of the aircraft industry.
|D2||7.7 * 1000kg/m³||1421℃|
|P20||7861 kg/m³||2600 (Deg F)|
|GRADES||ROUND BAR (mm)||PLATE (mm)|
It has three branches, including hot rolled mold steel, cold rolled mold steel and plastic mold steel. They are used for the forging, punching, pressure casting and more. Due to the different mold playing a different role in the production, so we need to make it by the requirements of working to satisfy the needs of hardness, strength, wear resistance, hardenability and more. So that causes the different types of mold steel has different properties.
Cold Rolled Mold Steel
Cold rolled mold includes cold-punching mould, wire-drawing die, cold heading die and more. Cold rolled mold steel always belong to high carbon alloy steel, its carbon content is beyond 0.80%. And chromium is a big alloy element for this steel type, its content is less than 5%. And the common steel type for it is high carbon low alloy steel, high carbon high chromium steel, chrome molybdenum steel and etc.
Hot Rolled Mold Steel
There are several types for hot rolled mold, they are hammer forge, die forging, pressure casting and etc. For example, hot-forging die, press forging die, punching die, hot-extrusion die and more. It must suffer high mechanical stress and the effect of in cold and hot repeatedly, that would make huge thermal stress. So the hot rolled mould steel must have high hardness, strength, red hardness, wear-resistance and toughness.
On the other hand, great high-temperature strength, thermal fatigue stability, thermal conductivity and corrosion resistance are what they need. And it needs to have high hardenability to make sure the mechanical property of hole section is the same. For this type of steel, they commonly are medium carbon alloy steel, the carbon content at the range of 0.30%-0.60%. The common type for it is chromium manganese steel, chrome-nickel steel, chrome-tungsten steel and more.
Plastic Mold Steel
The plastic molds including thermosetting plastics mold and thermoplastic plastics mold. It must have the same properties of mold steel. Besides that, great processing property is what they need. Such as the small heat treatment deformation, good corrosion resistance and polishing performance and more. In general, injection mold and extrusion forming mould can use the hot-rolled mould steel. And if the mold with high wear resistance and strength requirements, cold rolled mold steel also is the good choice.
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