10.5 PREHEATING

Welding variables, such as heat input, interpass temperature and size of the
weld bead being applied all affect the cooling rate of the base metal HAZ
which in turn affect the amount of martensite formation and hardness. The
cooling rate of the base metal can also be affected by the section size of the
base metal being welded, temperature of the metal eing welded and weld
joint geometry. If the alloying elements which increase hardenability are found
in the base metal HAZ, the cooling rate during welding necessary to produce
a high hardness HAZ are generally lower than for plain carbon steel without
alloying elements.
Welding factors affecting Hardness;
1. Heat input
2. Preheat
3. Interpass temperature
4. Section sizes
5. Weld joint geometry