Unlike other types of materials, or at least to a more significant degree than other materials, metal and alloys will change in internal structure during the working process. Different types of processes, including forming, rolling and machining can create stress internally within the steel.
Without the process of stress relieving steel, the internal structural changes in the steel can result in significant issues. These may include cracking or distortion of the part that causes it to twist, warp or bend. It is also very likely that the part will have a shorter life cycle due to these issues, plus it is more likely to fail when under load or during use in any given application.
The Process
The stress relieving steel is not complicated, but it has to be completed precisely and correctly to achieve the desired results. The process includes heating the worked or formed steel in an oven or furnace to a specific time at a temperature that is just below the lower critical temperature. This is also called the lower transformational temperature.
The heated steel, at the precise temperature, for a specified amount of time. The time becomes an important factor as this will allow uniform heating through of the part to ensure the process is applied to the entirety of the part.
After this process, the steel part and component is air cooled. In addition, it is important to the stress relieving steel to cool in still air, not in moving air. The natural cooling process allows the internal molecular structure of the steel to align, relieving the stress and improving the integrity of the part.