Die Casting Die Component Materials and Hardness

How the two lists are organised

A die casting die is not one steel. The cavity that sees the molten metal, the block that carries it and the parts that push metal into it each work at a different temperature and under a different load, so each is specified on its own. The two tables below follow the way a die shop orders the material, as a component with the grade and the hardness it should be at.

The first table covers the die itself, the cavity inserts and the holder blocks. The second covers the injection side, the parts the molten metal passes through on the way into the cavity. In the second table the metal being cast is listed for every row, because that decides how hard the part is specified and whether it is nitrided as well as hardened.

Cavity inserts and holder blocks

Typical material and hardness by component

Source, Table 1, Recommended Materials for Die Components of Tool Materials for Molds and Dies, Application and Performance, edited by G. Krauss and H. Nordberg.

The hardness given is the level the part is put into service at, not a heat treatment instruction. H20, H21 and H22 are tungsten hot work grades, listed for copper castings because copper is poured hotter than zinc or aluminium. The holder block is a support part rather than a working surface, which is why it is only prehardened.

Injection components, sprue to plunger

Typical material and condition by component

Source, Table 2, Typical Materials for Injection Components of the same book.

The metal being cast is listed for every row because the aluminium side of a die runs hotter than the zinc side and the specification changes with it. The plunger tip is the one component not specified in tool steel, and the beryllium copper is chosen so heat leaves the tip rather than for wear resistance.

What the two lists show a die shop

One grade carries most of the page. H13 appears in the cavity for aluminium, magnesium and long-run zinc castings, and every injection component except the plunger tip is H13 as well. The reason is the same in both places. H13 holds its hardness at the temperature the casting is poured at, resists thermal fatigue, and takes a nitrided case, so a single grade covers the parts that touch molten metal.

The hardness figures are deliberately not uniform. The sprue spreader and sprue bushing are listed at 42 to 46 HRC, softer than the 46 to 48 HRC specified for the nozzle, shot sleeve and shot pad, and those three are nitrided on top of the hardened core. Nitriding puts a hard surface on a part whose core is still tough, which is what a shot sleeve needs because it also has to slide and take wear along its length.

The plunger tip is the one part not specified in tool steel. Beryllium copper at 38 to 42 HRC is used for its thermal conductivity, so heat is drawn away from the tip instead of building up in it. Where the moving parts of a die run against each other, the same chapter lists the measures that keep wear down. They are the use of dissimilar hardnesses on contacting parts, nitriding one or both surfaces, the use of dissimilar materials where the incoming metal does not touch the moving part, a lubricant held on the contacting faces, shallow notching or dimpling of the slide or gib so it retains the lubricant, maintenance of the correct fit between wearing surfaces, and smoothly polished faces on both members.

Two points are worth settling before the list is used to order material. The first is that the cavity material follows the metal being cast rather than the size of the die, so a shop running zinc and aluminium on the same press will hold two insert stocks, P20 prehardened for the zinc work and H13 for the aluminium work. The second is that hardness alone does not carry the specification on the injection side. The source asks for the steel type, the chemistry, the microstructure and the physical test results to be stated for H13 die inserts, and for the heat treatment specification to state the process, the austenitizing temperature, the time at temperature, the quenching rate, the number of tempers and the final hardness. An order placed on hardness by itself leaves all of that open.

Figures are reproduced from the published tables and are a reference summary only. They describe the materials and hardnesses the trade normally works with rather than a specification for a particular die, so confirm against the material test certificate or contact Aobo Steel before ordering.

Related reference data

Grade pages for the materials named above are on H13 tool steel, P20 tool steel and H21 tool steel. For the dies these components go into, see tool steel for die casting dies and inserts and die casting cores and inserts selection. Nitriding practice is on the tool steel nitriding guide, and a wider list of tool types with the material normally used for each is on tool and die materials by tool type.

Source: Tool Materials for Molds and Dies, Application and Performance (G. Krauss and H. Nordberg, eds.).