Block Moulds

This step is essential in heat treatment as it helps mold resist thermal shocks. During operations, die-casting molds experience thermal shocks from rapid changes that can result in cracking and deformation. During preheating, mold engineers heat the molds to operating temperatures before molding begins. This process prevents premature failure. Preheating also extends the mold's life and ensures dimensional stability during molding operations.
After the molding process, mold engineers undergo post-heating in controlled cooling conditions. The process reduces the formation of internal stresses that can lead to warping.

This process is critical in die-casting molds. It is similar to annealing in metals, but it occurs at relatively lower temperatures in this case. Also, in die-casting molds, stress relieving aims to relax built-up stress rather than soften the mold materials.

This process helps to harden the mold steel's surface without affecting the mold materials' internal surface. Nitriding leads to improved wear resistance and increases the mold's life span.
Nitriding involves heating the mold in a nitrogen-rich environment. In this process, nitrogen diffuses to the steel surface to create a hard nitride surface.
The process goal is akin to quenching. However, the temperatures for nitriding are 500-550C, relatively lower than quenching temperature. While quenching takes slow time, nitriding requires a relatively longer time, several hours.

This process occurs in a vacuum to avoid oxidation and mold surface contamination. Oxidation can lead to poor surface finish and weaken the mold. Vacuum heat treatment is similar to other metal heat treatments, including annealing. The difference is that it occurs in a vacuum.