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#087 Fundamentals of Steel Materials for Dies (6) Steel Materials Used in Dies (High Speed Tool Steels)

Category : Die Materials
July22, 2011

High speed tool steels are frequently abbreviated in Japanese as "Hice". The symbol for these materials is SKH.
High speed tool steels can be based on Tungsten (W) or on Molybdenum (Mo). These are specified in JIS G 4403.

About 18% of tungsten is added in tungsten-based high speed tool steels, and they do not contain any molybdenum. These steels come in the types of SKH2, SKH3, SKH4, and SKH10. Since steels of this series have high wear resistance, they are used very frequently in cutting tools, etc.
About 5% of molybdenum and about 6% of tungsten are added in molybdenum - based high speed tool steels. These steels come in the nine types of SKH51 to SKH59.
Since steels of this series have a high toughness, they are ideally suitable for press dies that are subject to shock. SKH51 (old symbol SKH9) is the type used most frequently.

The tempered hardness of high speed steels is more than 63 HRC. The tempered hardness of the die steel SKD11 is about 62 HRC. High speed steel is used very frequently for small diameter punches, etc., in which case the wear resistance and toughness of die steels are somewhat insufficient.

Powdered high speed tool steel

Similar to the method of manufacturing ordinary tool steel, high speed tool steel is manufactured by solidifying molten material.
A uniform and fine structure of powdered high speed tool steel is prepared by first finely powdering the molten material, and solidifying that powder. By doing this, the wear resistance, toughness, and fatigue resistance all are increased. A sintered hardness of about 64 to 70 HRC is obtained.
These steels are used when using high speed die steels are not satisfactory. JIS has standardized powdered high speed tool steel in SKH40 (molybdenum based). A large number of manufacturers use originally developed steels.

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