What are the core elements of selecting mold steel materials?
2025-12-11 14:13
The selection of mold steel is a critical step in mold manufacturing, directly impacting the service life, production efficiency, and manufacturing costs of the mold. The selection process should focus on two core dimensions—"working conditions" and "process performance"—while also comprehensively considering the specific application scenarios of the mold to ensure the material meets functional requirements and facilitates machining and manufacturing. The following sections detail the key points of material selection, covering working conditions, process performance, structural factors, design considerations, and material optimization methods.
1. Working conditions determine material performance
The working environment of molds is complex and variable, requiring materials to possess the following properties to meet these challenges:
Wear resistance: Molds are prone to wear under high-pressure friction, and high-hardness materials can significantly reduce wear and extend service life. For instance, plastic molds must resist corrosion from gases released by chlorine and fluorine elements, requiring a balance between hardness and corrosion resistance in material selection.
Strength and toughness: Molds often bear impact loads, requiring a balance between strength and toughness to prevent brittle fracture. Material toughness depends on carbon content, grain size, and microstructure. For instance, hot-forging molds need high toughness to resist crack propagation under rapid cooling and heating conditions.
Fatigue Fracture Performance: Under cyclic stress, molds are prone to fatigue fractures. The fatigue resistance is closely related to material strength, toughness, and hardness, which can be improved through optimized composition and heat treatment processes.
High-Temperature Performance: Working in high-temperature environments can lead to a decrease in material hardness and strength, resulting in premature failure. Hot work die steel must possess high tempering stability, such as H13 steel, which maintains stable performance at elevated temperatures.
Resistance to thermal fatigue: Repeated heating and cooling can cause surface cracking and spalling of molds. Thermal fatigue resistance is a core performance metric for hot work molds, which can be improved through the optimization of material metallurgical properties.
Corrosion Resistance: Chemical erosion can exacerbate surface roughness on molds. For instance, plastic molds must resist corrosive gases released by chlorine and fluorine elements, necessitating the selection of materials with corrosion-resistant alloying elements.
2. Process Performance Affects Manufacturing Efficiency
Mold manufacturing involves multiple processes such as forging, cutting, and heat treatment, where the material's processability is crucial
Forgeability: The material must be easy to forge, with low deformation resistance and a wide forging temperature range to reduce the tendency for forging cracks and cold cracks. For instance, large mold materials require good forgeability to simplify processing.
Machinability: Materials that are easy to cut can reduce processing costs and improve surface quality. Modern mold steels enhance machinability by adding elements such as sulfur and lead while avoiding the adverse effects of impurities on mechanical properties.
Hardenability: After quenching, the material must achieve the required hardness to ensure wear resistance. Hardenability is influenced by carbon content and alloying elements, and must be precisely controlled through heat treatment processes.
Hardness: During quenching, the material must achieve uniform hardening depth to prevent uneven cross-sectional properties. Materials with good hardenability are suitable for large, complex molds, reducing the risk of deformation.
Oxidation and decarburization sensitivity: The material must be resistant to oxidation and decarburization during heat treatment to maintain surface quality. High-purity materials enhance resistance to these sensitivities through processes such as electroslag remelting.
Quenching deformation and cracking tendency: After heat treatment, the material exhibits minimal deformation and resistance to cracking, which is particularly crucial for high-precision molds. Optimizing the quenching process and material composition can effectively mitigate these risks.
3. Structural Factors and Design Considerations
The structure and design of the mold directly influence material selection
Mold dimensions: Large molds require materials with good hardenability and minimal deformation to ensure uniform cross-sectional performance. For example, hot forging molds need highly hardenable materials to maintain overall strength under high temperature and pressure.
Shape Complexity: Molds with complex shapes are prone to stress concentration, requiring the use of high-performance alloy materials. For simple-shaped molds, cost-effective carbon tool steel can be selected to reduce expenses.
Precision Requirements: High-precision molds require materials with minimal deformation during processing, and material selection must consider dimensional stability after heat treatment. Precision molds often use high-purity materials to minimize machining errors.
Production Batch: Tends to favor high-wear-resistant, long-lasting materials for mass production, such as FCS steel, which significantly enhances the lifespan in aluminum alloy die casting, making it suitable for large-scale production scenarios.
4. Material Optimization Methods
To enhance mold performance, the following optimization techniques can be employed:
Strengthening Technology: Increasing the quantity of lath martensite through heat treatment enhances strength and toughness. Lower bainite structure exhibits high strength and toughness, effectively reducing mold deformation.
Surface hardening techniques, such as nitriding and PVD coating, can enhance the wear and corrosion resistance of mold surfaces. DIEVAR steel significantly improves its resistance to thermal fatigue through surface treatment.
5. Affordability
Material selection should balance performance and cost to avoid overdesign. For instance, large mold bodies can be made from low-cost carbon steel, while critical components use high-performance materials to optimize overall costs.
1. Working conditions determine material performance
The working environment of molds is complex and variable, requiring materials to possess the following properties to meet these challenges:
Wear resistance: Molds are prone to wear under high-pressure friction, and high-hardness materials can significantly reduce wear and extend service life. For instance, plastic molds must resist corrosion from gases released by chlorine and fluorine elements, requiring a balance between hardness and corrosion resistance in material selection.
Strength and toughness: Molds often bear impact loads, requiring a balance between strength and toughness to prevent brittle fracture. Material toughness depends on carbon content, grain size, and microstructure. For instance, hot-forging molds need high toughness to resist crack propagation under rapid cooling and heating conditions.
Fatigue Fracture Performance: Under cyclic stress, molds are prone to fatigue fractures. The fatigue resistance is closely related to material strength, toughness, and hardness, which can be improved through optimized composition and heat treatment processes.
High-Temperature Performance: Working in high-temperature environments can lead to a decrease in material hardness and strength, resulting in premature failure. Hot work die steel must possess high tempering stability, such as H13 steel, which maintains stable performance at elevated temperatures.
Resistance to thermal fatigue: Repeated heating and cooling can cause surface cracking and spalling of molds. Thermal fatigue resistance is a core performance metric for hot work molds, which can be improved through the optimization of material metallurgical properties.
Corrosion Resistance: Chemical erosion can exacerbate surface roughness on molds. For instance, plastic molds must resist corrosive gases released by chlorine and fluorine elements, necessitating the selection of materials with corrosion-resistant alloying elements.
2. Process Performance Affects Manufacturing Efficiency
Mold manufacturing involves multiple processes such as forging, cutting, and heat treatment, where the material's processability is crucial
Forgeability: The material must be easy to forge, with low deformation resistance and a wide forging temperature range to reduce the tendency for forging cracks and cold cracks. For instance, large mold materials require good forgeability to simplify processing.
Machinability: Materials that are easy to cut can reduce processing costs and improve surface quality. Modern mold steels enhance machinability by adding elements such as sulfur and lead while avoiding the adverse effects of impurities on mechanical properties.
Hardenability: After quenching, the material must achieve the required hardness to ensure wear resistance. Hardenability is influenced by carbon content and alloying elements, and must be precisely controlled through heat treatment processes.
Hardness: During quenching, the material must achieve uniform hardening depth to prevent uneven cross-sectional properties. Materials with good hardenability are suitable for large, complex molds, reducing the risk of deformation.
Oxidation and decarburization sensitivity: The material must be resistant to oxidation and decarburization during heat treatment to maintain surface quality. High-purity materials enhance resistance to these sensitivities through processes such as electroslag remelting.
Quenching deformation and cracking tendency: After heat treatment, the material exhibits minimal deformation and resistance to cracking, which is particularly crucial for high-precision molds. Optimizing the quenching process and material composition can effectively mitigate these risks.
3. Structural Factors and Design Considerations
The structure and design of the mold directly influence material selection
Mold dimensions: Large molds require materials with good hardenability and minimal deformation to ensure uniform cross-sectional performance. For example, hot forging molds need highly hardenable materials to maintain overall strength under high temperature and pressure.
Shape Complexity: Molds with complex shapes are prone to stress concentration, requiring the use of high-performance alloy materials. For simple-shaped molds, cost-effective carbon tool steel can be selected to reduce expenses.
Precision Requirements: High-precision molds require materials with minimal deformation during processing, and material selection must consider dimensional stability after heat treatment. Precision molds often use high-purity materials to minimize machining errors.
Production Batch: Tends to favor high-wear-resistant, long-lasting materials for mass production, such as FCS steel, which significantly enhances the lifespan in aluminum alloy die casting, making it suitable for large-scale production scenarios.
4. Material Optimization Methods
To enhance mold performance, the following optimization techniques can be employed:
Strengthening Technology: Increasing the quantity of lath martensite through heat treatment enhances strength and toughness. Lower bainite structure exhibits high strength and toughness, effectively reducing mold deformation.
Surface hardening techniques, such as nitriding and PVD coating, can enhance the wear and corrosion resistance of mold surfaces. DIEVAR steel significantly improves its resistance to thermal fatigue through surface treatment.
5. Affordability
Material selection should balance performance and cost to avoid overdesign. For instance, large mold bodies can be made from low-cost carbon steel, while critical components use high-performance materials to optimize overall costs.
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