Annealing aims: to reduce the hardness to facilitate machining; to cause recrystallization of steel to repair the structure or improve the mechanical properties; to relieve internal stresses.
Distinguish high annealing (diffusion), complete, incomplete, low temp. Kind of annealing is prescribed depending on the steel grade and the part shape.
Normalizing — heating steel above the critical point AC3 by 30...50°C, exposure at this temperature and subsequent air cooling. Duration of exposure depends on the steel grade, the configuration and dimensions of the part.
After normalization, the steel becomes, compared to the annealing, higher hardness and more fine grain, as well as the best combination of mechanical properties.
Normalization is used to align the structural heterogeneity, improving the machinability of low alloy steels and for the preparation of the structure to subsequent heat treatment. The normalization is subjected to low and medium carbon structural steels and some low alloy steel. Normalization is mandatory for stress-relief and improvement of plastic properties of welded joints.
Annealing — heating steel to above the AC3 point 20...30°C, exposure at this temperature and subsequent fast cooling (in water, oil, emulsion, molten salts and alkalis).
Hardened steel has maximum strength, minimum ductility and high internal stress. Hardening (in conjunction with the release) is used to obtain the relevant mechanical and physical properties, to improve the corrosion properties and the homogeneity of the structure (stainless steel). Distinguish between complete, incomplete, isothermal, step, light, and surface hardening.
Vacation — pre-heating hardened steel below the critical point AC1, shutter speed and subsequent air cooling. The purpose of vacation is to transform the unsustainable structure of the hardening — martensite more stable. In issue change of physico-mechanical properties of steel and partially reduced internal stress. Distinguish between high, medium, low and multiple vacation.
Aging — heating hardened steel to a certain temperature with a long exposure. Aging used to stabilize the size, removing casting strains and to obtain the desired properties from heat-resistant steels. Welded structure during aging is heated to 160 to 200°C and incubated for 16 to 18 h.