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#088 Fundamentals of Steel Materials for Dies (7) Steel Materials Used in Dies (Pre-hardened Steel, Cast Iron, and Others)

Category : Die Materials
July29, 2011

Below we introduce materials including non-steel materials.

(1) Pre-hardened steel

These are mold materials developed for plastic molding and used for dies of presses. These have not been stipulated in JIS standards, and the materials used are those developed under the brand names of the manufacturers. These materials have reasonable hardness and can be machined. The material properties are adjusted to obtain a hardness of about 40 HRC, and precipitation hardened types (see note [*]) are used.
Pre-hardened steel is used frequently for punches and dies for blanking or bending in the case of low volume production. In the case of large volume production, pre-hardened steel is used for punch plates, backing plates, etc. This material is commonly used because it can be machined and is convenient because it can be used as is without heat treatment.

* Precipitation hardening:
This is hardening caused by the precipitation of certain constituents when a supersaturated solid solution is heated to an appropriate temperature.

(2) Flame hardened steel

Flame hardened steel is used for dies for the blanking, drawing, or bending of automobile components. This is a material in which surface hardening can be done easily by flame hardening.
Normally, while it is necessary to harden (total hardening) the die to the necessary hardness after it has been machined, this step can be simplified in the case of flame hardened steel, and although the strength is lower than the steels that require total hardening, it is used widely in the case of some specific applications since the time required for preparing dies can be shortened.

(3) Aluminum bronze

Aluminum bronze is a copper-based alloy. It can withstand high press pressures, has superior wear resistance, and high galling resistance. This material is also called HZ alloy (Hitachi Shipbuilding), AMPCO metal (USA). This is used frequently in the dies for drawing or for forming hard to form materials such as SUS or titanium, etc.

(4) Cast iron

Cast iron is used very frequently for die sets, or the dies forming medium to large sized products, or the dies for drawing, etc.

4-1. Gray cast iron (JIS G 5501)

This is also called ordinary cast iron, has excellent casting properties, and is used frequently for die sets, holders, and punches and dies of medium sized products.
The JIS symbol is FC, and its types have been stipulated from FC100 to FC350 with the number increasing in steps of 50. Among these, FC200, FC250, and FC300 are being used for dies.

4-2. Spherical graphite cast iron (JIS G 5502)

This is also called ductile cast iron, and is used when the strength of gray cast iron is considered insufficient. In gray cast iron, carbon precipitates inside the form of flakes inside a matrix of ferrite or pearlite. In contrast, magnesium has been added to the melt so as to make the precipitated carbon have the shape of spherical nodules. By making the precipitated carbon have a spherical shape, this material has achieved a high strength close to that of steel, and also has excellent ductility, rigidity, and wear resistance.
The JIS symbol is FCD, and its types have been stipulated from FCD350 to FCD800. Among these, FCD450, FCD500, and FCD600 are being used for dies.

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