3 Stages of Heat Treatment of Metal Stamping Die

All typical processes applied on metals generate heat, no matter cutting or welding, heating the metal at any time would change the metallurgical structure and properties. Inversely, it’s possible to use heat treatment to restore metals to the original form. Heat treatment is the process of heating the metal without letting it reach its molten or melting stage, and then cooling the metal under a controlled way to choose requested mechanical properties. Heat treatment is used to either make metal stronger, more malleable, more ductile or more resistant to abrasion. Hardening a metal may make it brittle, but softening a metal may reduce its strength. While improving some properties, it may worsen others so it might depend on the metal’s end-use.

All heat treatments include heating and cooling metals, but it has 3 main differences in process: heating temperatures, cooling rates, and quenching types, used to achieve properties requested. To heat treat the metal, it needs the proper equipment in order to closely control all factors around heating, cooling and quenching. There are three stages of heat treatment, details shown as follows.

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1. Heating Stage

During the heating stage, the foremost purpose is to make sure the metal heats uniformly, such as even heating by heating slowly. If heating the metal unevenly, one section might expand faster than another, causing a distorted or cracked section of the metal. Following factors may be helpful for selecting the heating rate:

1>the size and cross-section of the metal

2>the condition of the metal

3>the heat conductivity of the metal

2. Soaking Stage

The aim of the soaking stage is to remain the metal at the appropriate temperature until the requested internal structure takes the shape. The soaking time is the time to keep the metal at the appropriate temperature. The chemical analysis and mass of the metal have some very important influences on determining the correct length of the soaking period. For uneven cross-sections, you could decide the soaking time by using the largest section. It’s important and necessary to heat the metal slowly to below the temperature where the structure would change, and then hold it until the temperature consistent throughout the metal. After preheating, it would be much more quick to heat the temperature to the final temperature needed. Parts with more complicated designs might request more times of preheating in case of warping.

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3. Cooling Stage

During the cooling stage, there are many different methods to cool the metal back to the room temperature, depending on the type of the metal, which might need a cooling medium, such as a gas, liquid, solid or the combination. The cooling rate depends upon the metal itself and the medium of cooling. The choices made in cooling are important elements in the desired properties of the metal.

Quenching is when rapidly cooling the metal in air, water, brine, oil or other kinds of medium. Normally, quenching is related to hardening since most kinds of hardened metals are cooled fast with quenching, but it’s not always right that quenching or other rapid cooling results in hardening, such as, using water quenching to anneal copper, but other metals hardening with slow cooling. Not all kinds of metals are needed quenching, for quenching could crack or warp some metals. Generally speaking, water or brine could be used to cool the metal rapidly, while oil mixtures are better for a slower cooling, for example, using water to harden carbon steel, oil to harden alloy steels, and water to quench nonferrous metals. However, the rate and medium of cooling chosen must fit the metal.