2. Heat treatment incidents and remedies

2.1 Tapestries

Tapping is the cracking of metal due to thermal stress: it can appear on heating (cracking inside the part) or cooling (cracking on the part skin).

Tapping on heating mainly concerns martensitic stainless steels, particularly those with a high carbon content. The following precautions can be taken (all aimed at limiting the core-skin thermal gradient):

• place in a cold oven;

• limit the rate of temperature rise (for example, do not exceed 300°C/h);

• perform a landing during ascent (particularly at 600°C or before passing the Ac ₁ transformation point);

• for...