Annealing is a gentle heating up to a specified temperature with or without maintenance at annealing temperature and subsequent cooling down.
The most important types of annealing in molding are stress relieving annealing, soft annealing, normal annealing and re-crystallization annealing.
- stress relieving annealing:
Removing or reducing the residual stresses in materials that occur while non-uniform cooling in casting, rolling, forging, welding, or hardening.
The work piece is heated gently up to 550-650 ° C. After a few hours at this temperature, the work piece cools down slightly.
At high temperatures, offset yield strength of steel decreases. Therefore, atoms can be released from the compulsory state of affairs and reduce internal stresses. Of course, there is no structural change in this case.
Forms before machining, parts – forging or – casting and welding components.
- Soft annealing:
The hardened steel evolves as much as possible into a soft structural condition.
Hyper otoktoid steels are heated up to 720-680 Celsius degree and hypo-octoid steels up to 730-750 Celsius degree. Depending on the size of the work piece, it remains at this temperature for several hours and then cools slowly in the furnace. The softening effect can be achieved by an oscillatory annealing and very close to the top or bottom line of the PSK.
Long cementite sheets are deformed into round grain beads thus the work piece is easily chipped.
With soft annealing, you can prepare steel tools for hardening. If the hardened parts should be machined, first the annealing will be soft. The proper structure for shaping is created by soft annealing.
- Normal annealing:
With normal annealing, the uniform structure and fine grain are formed with rounded beads.
First, the work piece is slowly heated to around 600 ° C and then warmed up to 50 ° C above the GSK line. The work piece is kept for a period of time at this temperature so that the entire cross-section reaches this temperature (about 20 minutes for a diameter of 50 mm). Cooling is done in dwelling air.
With normal ablation, the structure is completely rebuilt. The fine grain structure is created. Coarse grains are undesirable because they make the steel brittle.
Non-uniform structure and coarse grains of forging, welding, rolling, traction and casting are normalized, that is, with normal annealing, structure becomes uniform and fine grain. The coarse grain structure is produced in a long-term annealing or annealing at high temperature. Normal annealing re-grains the structure.
- recrystallization annealing:
The deformed structure in cold deformation must revert to the original state by recrystallization annealing. The work piece of cold-formed has increased tensile strength and reduced relative length. After annealing, it can be deformed again.
Depending on the degree of deformation, it is kept for several hours at a temperature of 550-650 Celsius degrees. In degrees of deformation, low temperatures are sufficient.
Long-grain seeds (stretched) Cold deformation causes internal stresses. In this annealing, the atoms free themselves from the compulsory condition and make non-stressed crystals.
Annealing at low temperatures does not result in the development of the desired structure.
Annealing at high temperatures results in the grinding of seeds. At high temperatures, the surface of the work piece flake. In addition, at the surface of the work piece, carbon is burnt, which can’t be hardened. Long-term annealing at high temperatures leads to carbon burning. This so-called “burnt” steel has low mechanical properties, is impossible to hardened and completely unused.