What metal is best for die casting molds? (Material analysis)

When making die casting molds, the questions of "what material to use for the mold" and "what material to use for the product" are two different issues.
The ideal mold material must be like an "ironclad burger," able to withstand the erosion of high-temperature liquids and not crack during frequent cycles of heating and cooling.

The following are some of the most commonly used metal materials in the industry:

1. The "skeleton" of the mold itself: Hot work tool steel

This is the core material for making die casting molds. Because the molten metal is scorching hot during die casting, ordinary steel would soften upon contact.
H13 steel (most commonly used): This is the "all-rounder" in the mold industry. It not only has high hardness, but most importantly, it is very heat-resistant. Even after repeated exposure to high-temperature molten metal, it is not prone to cracking (called thermal fatigue in the industry). It is the preferred choice for making aluminum alloy and magnesium alloy molds.
Improved high-grade steel: For molds that require extremely high performance and need to produce hundreds of thousands of products continuously, better performing steel is used. These materials have fewer impurities and greater toughness, allowing the mold to last longer.

2. "Tailoring" materials for different products

The choice of steel for the mold largely depends on what metal you are pouring into it:
When casting aluminum alloys: Aluminum has a high melting point, which is more damaging to the mold. High-strength hot work steel that has undergone rigorous heat treatment must be used.
When casting zinc alloys: Zinc has a relatively low melting point, like boiling a frog slowly, so the damage to the mold is not as great. Therefore, when making die casting molds for zinc alloys, the range of steel choices can be slightly wider, and the mold life is usually much longer than that of aluminum alloy molds.
When casting copper alloys: The temperature of molten copper is very high, and ordinary steel is difficult to withstand for a long time. In this case, some expensive special alloys or materials with special surface hardening treatments may even be needed.

3. "Supporting" materials for mold accessories

A complete die casting mold is not just two large steel plates; it also contains many parts:
Mold base (outer shell): This does not need to directly contact the high-temperature molten metal, so ordinary medium-carbon steel is usually sufficient, which saves costs. Push rods and guide posts: These are parts that experience frequent movement and friction, so they are usually made of alloy steel with excellent wear resistance, and their surfaces are made very smooth.
Cooling water pipes: To cool the mold quickly, copper pipes are embedded inside or holes are drilled in the steel to utilize water circulation to dissipate heat.

4. Why can't ordinary iron be used?

Many people ask, can't we use cast iron or ordinary steel that can be found everywhere on the roadside? The answer is: absolutely not.
Ordinary iron will "flake": After being heated, the surface will quickly oxidize and peel, resulting in parts with a pitted surface.
Ordinary iron will deform: Under the clamping pressure of several hundred tons, ordinary iron will be squeezed and deformed like clay, causing the mold to not close properly and the molten metal to spray out uncontrollably.