Here's an overview of how heat treatment affects these properties:

1. Hardness: Heat treatment is used to increase the hardness of the mold. This is achieved by altering the microstructure of the material. For example, in a process called hardening, the mold material is heated to a certain temperature and then quenched (usually in oil or water) to rapidly cool it. This sudden cooling transforms the molecular structure, resulting in a harder and more brittle material.

2. Toughness/Durability: While hardness is desirable to resist wear and tear, it can make the material brittle. So, to counter this brittleness and increase the mold's toughness, the mold undergoes a process called tempering. In this process, the mold is reheated to a lower temperature and then cooled slowly. This increases its toughness, ensuring that the mold has a balanced hardness-toughness property suitable for prolonged use.

3. Stress Relief: Heat treatment can also help in relieving internal stresses generated in the material during machining. Releasing these stresses prevents the mold from warping or cracking, thus improving its durability and lifespan.

4. Wear Resistance: Proper heat treatment can improve the wear resistance of the mold material, which is especially critical in molds used for mass production where the mold experiences constant friction.

In conclusion, heat treatment plays a crucial role in influencing the mold cavity's properties and performance, making it an indispensable step in mold manufacturing. Customizing the heat treatment process parameters (like temperature, cooling method, etc.), one can achieve the desired hardness, durability, and other properties for the mold material.