Key findings include:
• HAZ softening is most pronounced in the subcritical zone (tempered region), where peak temperatures are below Ac1.
• The softened zone width increases with heat input; keeping heat input below 1.5 kJ/mm is recommended for typical TMCP grades.
• Matching filler metal with slightly lower strength can sometimes reduce strain concentration at the softened region.
For welding coordinators, this means re-evaluating WPS parameters for TMCP steels. Standard prequalification may not capture HAZ softening. The IIW recommends additional hardness traverses and cross-weld tensile tests to verify joint performance.
How does your current WPS address HAZ softening in TMCP steels?
Source: Welding in the World, 2025