[caleb-charles]

it’s important to know – at least- this kind of information. 1) grade of stainless steel ( i.e. martensitic or PH martensitic )- 2) autogenous welding or welding by filler 3) which kind of filler 4) kind of welding and its geometry . These are minimum info in order to understand which kind o PWHT have to be applied.
Considering that there is a dilution in FZ between a carbon steel such as S355 and martensitic SS or PH , HAZ could cause some risk of stress cracks due to martensitc or retained austenit tranformation . This could involved not only the kind of PWHT but -in addition- the choice of NDT method in terms of UT and MT parameters. Therefore, more info about welding process could be useful in order to give you some suggestion