Key Properties to Consider When Selecting Mold Steel
Mold material selection is a critical part of the overall mold manufacturing process. The selected mold steel should meet three basic principles: it must satisfy the working requirements of the mold, meet the processing and manufacturing requirements, and remain economically practical for the intended application.
1. Wear resistance
When the workpiece or molten material deforms and flows inside the mold cavity, it slides along the cavity surface and creates continuous friction. This friction can gradually wear the mold surface and eventually lead to mold failure. For this reason, wear resistance is one of the most basic and important properties of mold steel.
Hardness is one of the main factors affecting wear resistance. In general, the higher the hardness of the mold component, the lower the wear and the better the wear resistance. Wear resistance is also influenced by the type, quantity, shape, size, and distribution of carbides in the steel.
2. Strength and toughness
Most molds operate under demanding working conditions, and some are exposed to significant impact loads during use. If the material does not have sufficient toughness, brittle fracture may occur during operation. To prevent sudden cracking or breakage, mold materials must have both high strength and good toughness.
The toughness of mold steel depends mainly on factors such as carbon content, grain size, and microstructure.
3. Fatigue fracture resistance
During repeated production cycles, molds are subjected to long-term cyclic stress, which may eventually cause fatigue fracture. Common forms include repeated impact fatigue, tensile fatigue, contact fatigue, and bending fatigue. The fatigue resistance of a mold depends mainly on its strength, toughness, hardness, and the amount of non-metallic inclusions present in the material.
4. High-temperature performance
When the working temperature of a mold becomes too high, its hardness and strength may decrease, leading to early wear, plastic deformation, or premature failure. Therefore, mold materials should have strong temper resistance and good high-temperature stability so they can maintain sufficient hardness and strength during operation.
5. Resistance to thermal fatigue
Some molds are repeatedly heated and cooled during production. This constant thermal cycling causes alternating tensile and compressive stress on the cavity surface, which may lead to surface cracking, chipping, and spalling. These defects increase friction, interfere with normal forming, and reduce dimensional accuracy. Thermal fatigue is one of the main failure modes in hot-work molds, so good resistance to thermal fatigue is essential.
6. Corrosion resistance
Some molds, especially plastic molds, may be exposed to corrosive gases released during processing. For example, certain plastics containing chlorine or fluorine may release aggressive substances such as HCl or HF during heating. These gases can corrode the mold cavity surface, increase surface roughness, and accelerate wear. In such cases, corrosion resistance becomes an important factor in mold material selection.
In summary, proper mold steel selection should consider wear resistance, toughness, fatigue resistance, thermal stability, thermal fatigue resistance, and corrosion resistance, while also balancing process requirements and cost. Choosing the right material helps improve mold life, maintain product quality, and reduce long-term production risk.