HEAT TREATMENT OF H13 EQUIVALENT STEELS FOR DIECASTING DIES/MOULDS

H13 and equivalent hot work tool steels are generally used for making diecasting dies/moulds. In order to obtain high quality diecasting dies/moulds, the typical process sequences of heat-treating diecasting dies have been recommended by the North America Die Casting Association (NADCA). With reference to the results obtained by NADCA, an investigation into the H13 equivalent materials available in Asia region was carried out to identify the response of the materials to the NADCA heat treating processes.

Methodology

One cube of DAC (A-50x50x50mm) and 2 cubes of DAC 10 (B-50x50x50mm and C-100x10x100mm) were used for this study. The cubes were heat treated using the Nadcap heat treating procedure for the sample size below 90mm and then test samples were extracted from these cubes at specific locations as specified by NADCA for tensile test, Charpy test and microstructural analysis respectively. Comparisons between these samples were made.

Heat treating process

The heat treating process used is shown in Fig.1. It is in compliance with the processes recommended by NADCA.
        
              Fig.1 Heat treating process for this study

Thermocouple placement

• Surface temperature was measured using a thermocouple placed at the surface (Ts) with 15 ± 3 mm deep.
• The core thermocouple (Tc) placed as close to the centre of mass as possible.
• Thermocouples secured to prevent movement during quenching.
• Thermocouple holes packed with fiber refractory material to prevent direct contact with quenchant.

Test sample extraction

Small samples from specific locations were extracted for testings. Fig.2 shows the diagram where each sample was taken from the cube. The tensile test samples were represented by the green circles, the Charpy impact test samples were shown by the yellow regions and the blue region represented the area where the metallographic specimen was extracted. The red circle in the center was the hole drilled for placement of core thermocouple.

Fig.2 Top view of where the specimens were extracted from a cube

Test results

1) Hardness values of three cubes

2) Charpy test results

It is confirmed that the hardness values and Charpy test results are in compliance with the values specified by Nadca.