Heat-affected zone, the band of base metal beside the fusion line that got hot enough to change its microstructure and properties without melting. In steels it can harden and become crack-prone near the fusion line, or soften in quenched-and-tempered and precipitation-hardened alloys. It shows as a distinct band in a macro etch, and procedure qualifications often require HAZ hardness and Charpy tests.
HAZ hardness hit 280 HV, that's over the 250 limit for sour service, we need PWHT.
Also heard as
- heat-affected zone
- heat affected zone
Related terms
Preheat
Heating base metal before welding to slow cooling and drive off moisture, preventing hydrogen cracks.
Heat input
Energy delivered to a weld per unit length, calculated from amps, volts and travel speed.
PWHT
Postweld heat treatment: heating a finished weld to relieve stress and temper the heat-affected zone.
Hydrogen cracking
Delayed cracking in steel welds caused by hydrogen, hard microstructure and stress acting together.