Post-Welded Heat Treatment

Ordinary, annealing is used to relieve internal stresses in the steel casting and forgings. Those in welded structure cannot be removed through an ordinary (phase) annealing.

This is because in an ordinary operation, i.e on heating at temperatures of about 850C, the elastic properties of steel are decreased in such a degree that the welded structure may distort under the load produced by its own weight.

For this reason welded structures are generally not subjected to ordinary annealing.


To relieve internal stresses in welded structure a special annealing operation is applied, cinsisting of heating at temperatures sufficient for local plastic deformation to occur under the effect of internal stresses which, takes place at temperatures from 500 to 600C.

Annealing of welded structures for releasing of internal stresses is conducted as follow.
1. Slow heating at a rate of 100 to 150C per hour up to a temperature of 600 to 650C.

2. Holding at that temperature for a period of time determined on the basis of the following calculation. A period of 3 and 4 minutes for the each millimeter of the maximum thickness of steel sheets the welded structure is compose of.

3. Cooling at the rate of 50 to 100C per hour to a temperature of at least 300C. The slow cooling is necessary to prevent the setting up of new internal stresses on cooling, which inevitably develop if the steel is cooled rapidly because this always progresses non-uniformly. There are many cases recorded where the cracks have developed in annealed welded structure simply because they have been non-uniformly cooled.

From HEAT TREATMENT OF METAL (B.Zakarov).