8 What is sensitization the reason of this phenomenon and it

8. What is sensitization, the reason of this phenomenon and its effect on the free energy of the material?

Solution

Sensitization is the loss of alloy integrity.

Sensitization occurs during welding or annealing after cold-working.

Sensitization happens when SS Steel is heated at temperatures between 425C – 815C.

Sensitization is a phenomenon induces during welding and there are prevention and control measures to avoid or reduce this occurrence during manufacturing.

To identify chromium depletion, there is a requirement of a specialized micro structural study of the welded material.

Sensitization causes inter granular corrosion

Carbide precipitation removes Cr to <12% (Sometimes ~ 5%) – passive film is lost

M23C6 must not form, to prevent sensitization – use stabilized or L grades

N delays sensitization kinetics

The occurrence of sensitization is mostly due to the following combinations

Material composition used for exhaust assembly

Welding process used

Filler wire/electrode used

Thickness of the job

Multi layer or single layer weld

Cooling time between welding passes