Maraging steel is one type of special steel used for the for plastic injection mold.
Usually, when quenching and heat treating special steels, although the solidification is done by sudden cooling from a temperature higher than the A1 transformation point (723°C) after obtaining the martensite structure, considerably large residual stresses remain in the material due to sudden cooling, and also there will be dimensional deformations. The maraging a type of steel in which the steel is hardened without taking such risks.

The following typical types are present maraging steels.

1) SUS630 type
2) Maraging steel
3) Non-magnetic steel

The principles by which the maraging steel becomes hard is that, the steel is supplied in the soft state after processing in a method called solution heat treatment. Next, after the material is machined into the component shapes such as the cavity or the core, etc., it is heated and left to cool. When this is done, a phenomenon called age hardening occurs, and the hardness of the steel increases naturally. In the age hardening process, compositions called intermetallic compounds are precipitated, and this increases the hardness.

Since heat treatment is simpler than quenched and annealed steel, it is also easy to stabilize the dimensions, and maraging steel is a useful item depending on the application.

The appropriate temperature of age hardening depends on the type of steel, and the optimum processing is selected following the respective guidelines.

The features of the different steel materials are given below.

1) SUS630 type

This steel is obtained by modifying the stainless steel SUS 630. A steel material with a hardness in the range of 35 to 40 HRC is supplied, and very often it would already have been age hardened. Its resistance to corrosion is high and is suitable for the die steels of plastics having high corroding property.

2) Maraging steel

The specularity of this steel is very good. This is used very frequently for the cavities of optical components, or lens cavities. This material has both high hardness and high strength, and also has toughness. This steel is used also for thin core pins and long and thin components.

3) Non-magnetic steel

This is a steel does not stick to a magnet and is used for plastic magnets. Since a magnet has a high hardness and wears out the steel, a high hardness is required in the steel. By carrying out solution hardening, the hardness increases and it is possible to obtain a steel having non-magnetic properties.