Introduction
The heat treatment given to a particular grade of steel by the steelmaker/
supplier should be shown on the material test certificate and may be
referred to as the supply condition.
Welding inspectors may need to refer to material test certificates and it is
appropriate that they be familiar with the terminology that is used and have
some understanding of the principles of some of the most commonly applied
heat treatments.
Welded joints may need to be subjected to heat treatment after welding
(PWHT) and the tasks of monitoring the thermal cycle and checking the heat
treatment records are often delegated to welding inspectors.
2 Heat Treatment of Steel
The main supply conditions for weldable steels are:
As rolled, hot rolled, hot finished
Plate is hot rolled to finished size and allowed to air cool; the temperature at
which rolling finishes may vary from plate to plate and so strength and
toughness properties vary and are not optimised;
Applied to
Relatively thin, lower strength C-steel
Thermo-mechanical controlled processing (TMCP), control-rolled,
thermo-mechanically rolled
Steel plate given precisely controlled thickness reductions during hot rolling
within carefully controlled temperature ranges; final rolling temperature is
also carefully controlled;
Applied to
Relatively thin, high strength low alloy steels (HSLA) and for some steels
with good toughness at low temperatures, eg, cryogenic steels
Normalised
After working the steel (rolling or forging) to size, it is heated to ~900°C and
then allowed to cool in air to ambient temperature; this optimises strength
and toughness and gives uniform properties from item to item for a
particular grade of steel;
Applied to
C-Mn steels and some low alloy steels