The US mold steel series and selection schemes were initially formed in the 1940s.
American mold industry material analysis
The United States divides mold steel into three categories according to the conditions of mold service. The American Society of Metals Tool Steel Committee lists three types: cold work die steel, hot work die steel and plastic die steel. Among them, the cold work die steel is divided into 12 small categories, hot work die steel 9 small class, plastic mold steel 2 small class. The selection of each subcategory depends on three main factors:
Size and shape complexity
Processed material
Durability requirements or design life
Classification of cold work die steel
Cold work die steel is divided into five groups: W group, O group, A group, D group, S group.
Group W is water-quenched tool steel with 11 steel grades and 7 carbon tool steels with carbon content ranging from 0.7% to 1.3%.
Group O is oil-quenched cold work die steel (commonly known as oil steel). There are 4 steel grades with a carbon content of 0.85-1.55%.
Group A is an air-quenched alloy cold work die steel with 9 steel grades with a carbon content ranging from 0.5 to 2.25%.
Group D, high carbon and high chromium cold work die steel, has 7 steel grades with a carbon content of 0.9%-2.5%.
The S group is an impact-resistant tool steel with 7 steel grades and a carbon content of 0.4-0.6%.
For cold working molds, high speed steel (HSS group) and ultra high speed steel (SHSS group), cobalt based cemented carbide and steel bonded cemented carbide (HA group), powder steel and engineering ceramics (PIM group), carbon tungsten Tool steel (Group F), special purpose tool steel (Group L).
Selection of cold work die steel
The main series of cold work die steel is high-hard cold work, mainly used for molds requiring high compression and wear resistance, and the hardness is higher than HRC60-62. For molds requiring high impact resistance and high toughness, the hardness is lower than HRC60-62, mainly using S and some Class A and the most common quenched and tempered steel, spring steel, hot work die or base steel. For large stamping dies, such as automotive exterior stampings, cast iron is mainly used. Zinc-based alloys or polymer composites that are simple or have a small lifetime.
The application of high speed steel and ultra high speed steel in cold work dies has grown rapidly. Mainly there is a high "compressive strength / hardness" ratio. And the hardness can be selected between HRC60-70.
Powder mold steel has excellent wear life, hardness is not more than HRC60-62, and the application is quite large.
Carbon tool steel still has a certain range of applications in punch or soft material stamping die with a life of 100,000 pieces.
Classification of hot work die steel
American hot work die steel is divided into two categories: hot work die steel and super heat-strength alloy.
Selection of hot work die steel
Because the hot work die works under temperature conditions, the material is required to have thermal strength and heat wear resistance. In order to ensure the life of the mold, the mold should be cooled, and the hot and cold alternate mold will have cracks, that is, thermal fatigue cracks, so the material Also required to have crack resistance and thermal fatigue resistance.
Material selection according to the main series of heat intensity:
Low alloy quenching and tempering die steel (6G, 6F2, 6F3) - medium chromium hot work die steel (H11, H12, H13) - tungsten hot work die steel (H21, H22).
Non-standard hot work die steel: For example, hot forging die is age hardened type 6H4. When H11, H12, and H13 appear to be incapable of satisfying thermal wear resistance, 6H1 and 6H2 can be selected.
When the mold is required to be hot for wear resistance, D2, D4 - M2, M4 - powder steel can be selected. Steel-bonded cemented carbide and cobalt-based cemented carbide have high high-temperature wear resistance, but their thermal fatigue properties (ie, hot and cold anti-fatigue cracks) are poor and cannot be used in quenching and hot conditions.
Classification of plastic mold steel
The United States was the first country to list plastic mold steels in tool steel. It was mainly represented by P and was divided into five categories.
Carburized plastic mold steel: P1, P2, P3, P4, P5, P6. This kind of steel has a very low carbon content, mainly in the early stage of the United States and by extrusion molding. It requires good cold plasticity and high extrusion performance. After surface forming, carburizing and quenching increases surface hardness and has a long service life. The ultra-low carbon of the core minimizes the amount of deformation during quenching.
Tempered plastic mold: P20, P21. At present, the amount of P20 in plastic molds is very large, and has become the main body, and most of them are used in a pre-hard state.
Medium carbon alloy tool steel is used for thermosetting plastic molds. Steel grades have H13, while L12 and S7, O1 and A2 are also used. The characteristics of this category are:
1. It is basically secondary hardened gold steel, and the heat strength is good at 500-600 °C.
2. High chromium content and good atmospheric corrosion.
3, excellent hardenability, suitable for large modules.
Stainless steel is used for plastic molds with high corrosion resistance. The main steel grades are 420, 414L, 440, 416.
The aged steel is subjected to aging treatment to obtain high performance. There are two types, one is P21 low carbon Ni-A1 aged steel; the other is 18Ni maraging steel. The latter is a carbon-free, high-purity, high-toughness material for the aerospace industry. Used in plastic molds where high mechanical properties, dimensional accuracy, smoothness and corrosion resistance are required.
Selection of plastic mold steel
Thin-walled plastic box, when the production batch is less than 100,000 pieces, use P20, P21 pre-hard state (HB250-300), when the corrosion is strong, use 414L.
Ordinary plastic mold with high life, with P6 or P20, hardness after carburizing-quenching is HRC54-58; when plastic parts are not too large, O1 and S7 can be used. Use 420 when corrosive.
The non-high temperature thermosetting mold is used after carburizing and quenching with P6 and P20. Corrosive strength is 420.
High temperature thermosetting plastic molds are made of H13 and S7 or carburized steel P4. These chromium-containing metals have high temper resistance and high temperature oxidation resistance.
American mold industry material analysis
The United States divides mold steel into three categories according to the conditions of mold service. The American Society of Metals Tool Steel Committee lists three types: cold work die steel, hot work die steel and plastic die steel. Among them, the cold work die steel is divided into 12 small categories, hot work die steel 9 small class, plastic mold steel 2 small class. The selection of each subcategory depends on three main factors:
Size and shape complexity
Processed material
Durability requirements or design life
Classification of cold work die steel
Cold work die steel is divided into five groups: W group, O group, A group, D group, S group.
Group W is water-quenched tool steel with 11 steel grades and 7 carbon tool steels with carbon content ranging from 0.7% to 1.3%.
Group O is oil-quenched cold work die steel (commonly known as oil steel). There are 4 steel grades with a carbon content of 0.85-1.55%.
Group A is an air-quenched alloy cold work die steel with 9 steel grades with a carbon content ranging from 0.5 to 2.25%.
Group D, high carbon and high chromium cold work die steel, has 7 steel grades with a carbon content of 0.9%-2.5%.
The S group is an impact-resistant tool steel with 7 steel grades and a carbon content of 0.4-0.6%.
For cold working molds, high speed steel (HSS group) and ultra high speed steel (SHSS group), cobalt based cemented carbide and steel bonded cemented carbide (HA group), powder steel and engineering ceramics (PIM group), carbon tungsten Tool steel (Group F), special purpose tool steel (Group L).
Selection of cold work die steel
The main series of cold work die steel is high-hard cold work, mainly used for molds requiring high compression and wear resistance, and the hardness is higher than HRC60-62. For molds requiring high impact resistance and high toughness, the hardness is lower than HRC60-62, mainly using S and some Class A and the most common quenched and tempered steel, spring steel, hot work die or base steel. For large stamping dies, such as automotive exterior stampings, cast iron is mainly used. Zinc-based alloys or polymer composites that are simple or have a small lifetime.
The application of high speed steel and ultra high speed steel in cold work dies has grown rapidly. Mainly there is a high "compressive strength / hardness" ratio. And the hardness can be selected between HRC60-70.
Powder mold steel has excellent wear life, hardness is not more than HRC60-62, and the application is quite large.
Carbon tool steel still has a certain range of applications in punch or soft material stamping die with a life of 100,000 pieces.
Classification of hot work die steel
American hot work die steel is divided into two categories: hot work die steel and super heat-strength alloy.
Selection of hot work die steel
Because the hot work die works under temperature conditions, the material is required to have thermal strength and heat wear resistance. In order to ensure the life of the mold, the mold should be cooled, and the hot and cold alternate mold will have cracks, that is, thermal fatigue cracks, so the material Also required to have crack resistance and thermal fatigue resistance.
Material selection according to the main series of heat intensity:
Low alloy quenching and tempering die steel (6G, 6F2, 6F3) - medium chromium hot work die steel (H11, H12, H13) - tungsten hot work die steel (H21, H22).
Non-standard hot work die steel: For example, hot forging die is age hardened type 6H4. When H11, H12, and H13 appear to be incapable of satisfying thermal wear resistance, 6H1 and 6H2 can be selected.
When the mold is required to be hot for wear resistance, D2, D4 - M2, M4 - powder steel can be selected. Steel-bonded cemented carbide and cobalt-based cemented carbide have high high-temperature wear resistance, but their thermal fatigue properties (ie, hot and cold anti-fatigue cracks) are poor and cannot be used in quenching and hot conditions.
Classification of plastic mold steel
The United States was the first country to list plastic mold steels in tool steel. It was mainly represented by P and was divided into five categories.
Carburized plastic mold steel: P1, P2, P3, P4, P5, P6. This kind of steel has a very low carbon content, mainly in the early stage of the United States and by extrusion molding. It requires good cold plasticity and high extrusion performance. After surface forming, carburizing and quenching increases surface hardness and has a long service life. The ultra-low carbon of the core minimizes the amount of deformation during quenching.
Tempered plastic mold: P20, P21. At present, the amount of P20 in plastic molds is very large, and has become the main body, and most of them are used in a pre-hard state.
Medium carbon alloy tool steel is used for thermosetting plastic molds. Steel grades have H13, while L12 and S7, O1 and A2 are also used. The characteristics of this category are:
1. It is basically secondary hardened gold steel, and the heat strength is good at 500-600 °C.
2. High chromium content and good atmospheric corrosion.
3, excellent hardenability, suitable for large modules.
Stainless steel is used for plastic molds with high corrosion resistance. The main steel grades are 420, 414L, 440, 416.
The aged steel is subjected to aging treatment to obtain high performance. There are two types, one is P21 low carbon Ni-A1 aged steel; the other is 18Ni maraging steel. The latter is a carbon-free, high-purity, high-toughness material for the aerospace industry. Used in plastic molds where high mechanical properties, dimensional accuracy, smoothness and corrosion resistance are required.
Selection of plastic mold steel
Thin-walled plastic box, when the production batch is less than 100,000 pieces, use P20, P21 pre-hard state (HB250-300), when the corrosion is strong, use 414L.
Ordinary plastic mold with high life, with P6 or P20, hardness after carburizing-quenching is HRC54-58; when plastic parts are not too large, O1 and S7 can be used. Use 420 when corrosive.
The non-high temperature thermosetting mold is used after carburizing and quenching with P6 and P20. Corrosive strength is 420.
High temperature thermosetting plastic molds are made of H13 and S7 or carburized steel P4. These chromium-containing metals have high temper resistance and high temperature oxidation resistance.
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