A lot of steel is "killed" whether it's required for your application or not. Some checking with suppliers or mills may confirm that your regular steel is okay.
If not required by the plate specifications, normalized is a hefty extra cost, and you won't usually buy normalized plate unintentionally.
Agents added (silicon or aluminium) to killed steel aim to prevent gas evolution during the solidification phase in order to get more chemical homogeneity and reduction of segregations.
Normalizing aims to remove the internal stress, which could potentially lead to deformation or failure, throughout a thermal treatment (heating above austenitic temperature and then air cooling).
I am probably wrong but I thought the austenitization process followed by a soaking phase and then by an air cooling phase always removed internal stresses (besides the improvement of both toughness and tensile strength, throughout cementite and carbides solubilisation to get a finer and more homogenous microstructure).
I have seen some plate come out pretty warped after normalizing. Roll flattening will only add to the internal stress.
Normalizing is performed to refine the grain size of carbon and low alloy steels, primarily with a view to improving the low temperature fracture toughness, but it also improves other basic mechanical properties. Any other effects, whether desirable or not, are incidental to the procedure.
So normalising refines grain size and general properties of the steel. And releiving of stress is is just a possible by-product of the normalising process???
Is Post weld heat treatment opposite? With postweld heat treatment on a weld, the purpose is to relieve residual stress and a by-product is to atleast partially normalise the heat affected zone???
Normalizing results in a more uniform grain structure (it can result in a finer grain structure) and improved mechanical properties. As a by-product of normalizing, residual stress can be removed.
PWHT is a thermal treatment to accomplish two things; reduce residual stresses from welding and temper the weld heat affected zone. There are two types of PWHT; a reheat treatment (like normalizing, or annealing, or a quench and temper) or a subcritical PWHT. The subcritical PWHT is only performed to avoid altering the original base metal properties.
No, you do NOT normalize the weld heat affected zone from a subcritical PWHT, unless you perform a separate normalizing heat treatment.
