Heat treating metals and annealing them will change the properties of the metal and make them harder, more durable, or sometimes more flexible. The process is not new, but the way it is used in the modern world has changed significantly, and metallurgists have more tools available to fine-tune the molecular properties of the material.
Heat Treating Metal
Different metals have different internal structures that affect the material. Steal is stronger than copper, for instance, but does not have the same flexibility. The steel can be very soft and wear fast unless it is heated to a specific temperature and then cooled in a controlled manner. The cooling, also known as the quench, is critical and can completely change the properties of the steel even though it was heated to the same temperature.
Annealing the steel or other metal typically involves heating the material and holding it at that temperature before slowly bring the temperature down in stages. If the annealing process is correct, the material will have the perfect inner structure and properties you need. Sometimes a small variation in the process can change the properties enough that the annealing process must be started again.
Heat treating metal to make it harder and stronger on the outside, and then annealing it to soften the inside to reduce the possibility of the metal shattering is very common. A metallurgist will develop the steps for the heat treat and annealing process over time, but if you need something done quickly, they will often have the best idea of a starting point based on other metals and projects they have worked on.
When working with a material to heat treat it, you need to heat it to a specific point, then quench the metal in water or oil to get the desired hardness. Annealing often takes more time because the quench is typically much slower.
In many cases, the material cools in stages over hours or even days in the annealing oven. Once the temperature is low enough, the oven is opened and the metal allowed to cool the rest of the way naturally. Once the annealing is complete, the metal item can be sampled and tested on a matching that checks the hardness on a scale called the Rockwell hardness scale.
The testing can determine if the metal is too hard or not hard enough, and can check the part in many different areas. In some cases, the item is sectioned with a bandsaw so that the metallurgist can look at the internal structure with a microscope and fine-tune changes with the annealing recipe to ensure the structure is perfect for the material's use.