Heat Treatment of Stainless Steels:
Stainless steels, as other steels, react to heat treatments over broad range. They are subjected to one or more of the given heat treatments.
This relieving treatment eliminates undesirable residual tensile stresses such are induced in the material like consequence of mechanical working.
Stainless steels stress relieving is carried out via heating it to 370oC and after that cooling at a low rate. This treatment also decreases susceptibility to corrosion. Though, resistance against corrosion cracking is enhanced by stress relieving at 770oC.
As ferritic stainless steels are prone to form patches of transformation products mostly after welding this is subjected to annealing treatment. The treatment is carried out via heating ferritic steel to 770oC and then cooling it in furnace or air. Such treatment will stress relieve and homogenized the structure.
Such treatment is illustrates to austenitic stainless steel. Whilst this steel is heated to 1000oC to 1120oC the austenite proceeds as a powerful solvent for chromium carbide and makes a homogenous structure. Homogenous structure is retained via quenching heated steel in water, air or oil depending upon the thickness of the section. Air is suitable quenching media for thin sections. The procedure is also concerns to as quench annealing.
Hardening and Tempering
Such treatment extremely same to one for plain carbon steel but simply meant as martensitic stainless steel. The steel is heated to a temperature of 950 to 1050oC and quenched in oil or air resulting in hard marteniste formation. The quenched steel is tempered in between 100 and 700oC depending on the needed hardness.
This is individual treatment for austenitic steel's stabilized grade. The steel is heated to 870 to 900oC and held for 2 to 4 hours. This is after that quenched in, oil or air water that causes precipitation of columbium or titanium carbide. These carbides do not allow precipitation of chromium carbide during service life.
Post Weld Treatment
The welding induces unneeded residual stresses and decrease corrosion resistance. Stress annealing, solution or relieving annealing are the treatments recommended for weldments before putting them to utilize. Weld decay is a usual welding defect in stainless steel such is reasoned by precipitation of carbide of chromium in the weld area and HAZ. The consequence of this precipitation is great susceptibility to intercrystalline cracking while a corrosive media comes in contacts.