10.5 PREHEATING

It may be important for the welding engineer and inspector to understand the
hardenability of the steel as it can be an indirect indicator of weldability.
Hardenability relates to the amount of martensite that forms during the
heating and cooling cycles of welding. This is most evident in the base metal
heat affected zone. Significant amounts of martensite formation in the HAZ
can lead to delayed hydrogen cracking or a loss in ductility and toughness.
Certain steels with high hardenability will form when they are cooled in air.
While other steels with low hardenability require much faster cooling rates for
form martensite. Knowing the hardenability will help the engineer or inspector
determine if pre-heat or postweld heat treatment are required or if a controlled
cooling practice may be acceptable to produce a serviceable weld and
acceptable properties in the HAZ.
Key Note: Hardenability affects weldability due to martensite formations at
weld/HAZ which leads to HIC, loss of ductility and toughness.