There are very specific reasons for choosing to use heat treatment on stainless steels of different alloys. In general, annealing stainless steel is performed to relieve stress within the metal and to increase corrosion resistance and ductility that may have been decreased during the fabrication process.
Stainless steel annealing can also be used to increase the hardness of the stainless steel to be able to create a more durable component or part. Through annealing the surface of stainless steel is able to withstand wear and tear, to last longer and to withstand higher levels of mechanical stress.
When annealing stainless steel, there are different processes that can be used. The basic annealing process is used to recrystallize austenitic stainless steels that have become work-hardened. This can be used to treat welded areas of stainless steel to remove the stress in the grain created through those processes.
The components have to be completely clean before this process. This means the removal of any surface debris, oxidation or any type of chemical residues, grease or oil.
The temperatures used in stainless steel annealing will depend on the grain size of the steel. Most stainless steels will be annealed at a temperature higher than 1040 degrees Celsius. The temperature is maintained for only a very short interval and then cooling is completed.
The temperature for the annealing process has to be carefully maintained. It is critical to have the capacity to bring the stainless up to the desired temperature quickly and not slowly. It is also important to maintain a precise temperature throughout the heating cycle.
In the process of annealing stainless steel, it is essential to maintain the right atmosphere. The presence of oxygen in the annealing environment can cause instant oxidation of the surface. For this reason, pure atmospheres of hydrogen are required to not only provide a perfect surface but also to maximize the strength of the braze and the future corrosion resistant abilities of the stainless.
Cooling also has to be very carefully managed with stainless steel. The most important stage in the cooling cycle is called the transformation stage, and this requires active and rapid cooling to allow correct grain formation.