High-strength low-alloy (HSLA) steels are widely used in structural and pressure vessel fabrication for their excellent strength-to-weight ratio. However, notch toughness in the heat-affected zone (HAZ) often becomes the limiting factor for qualification, especially in thick sections above 25 mm.
Per the Welding in the World journal, the key microstructural zones controlling toughness are the intercritical and fine-grained HAZ. Coarse-grained HAZ, formed at peak temperatures above 1200°C, is the most susceptible to low Charpy values due to large prior austenite grain size and brittle transformation products like martensite-austenite (M-A) constituents.
Optimization strategies include:
• Controlling heat input between 1.0 and 2.5 kJ/mm to limit grain growth.
• Using low-hydrogen consumables (H5 or lower) to reduce hydrogen-assisted degradation.
• Applying interpass temperatures of 150-200°C to promote acicular ferrite formation.
A practical approach from ISO 15614-1 Annex A allows engineering critical assessment to extend qualified thickness ranges without retesting, provided toughness data supports the extension. This can save weeks in project schedules.
What heat input range do you typically target for HSLA steels in your shop?