Welding and Spot Welding of High-Strength and Advanced High-Strength Steel
Steel families and weldability
High-strength steel (HSS) and advanced high-strength steel (AHSS) include HSLA, dual-phase (DP), TRIP, complex-phase, martensitic, and boron grades. They are not interchangeable. DP and TRIP steels can soften in the heat-affected zone (HAZ); martensitic and boron grades are often restricted to STRSW or rivet-bonding because GMAW heat destroys their strength.
Process selection
Follow the OEM procedure for the exact grade and location. STRSW is common for factory joints; GMAW may be allowed for mild and some HSLA steels but not for UHSS. Use the specified filler, wire size, gas, and weld count. Restore corrosion protection after welding. Do not substitute a continuous weld for a specified stitch or spot pattern.
Worked example
A B-pillar reinforcement is martensitic steel. The OEM procedure says “STRSW only; no MIG.” The correct reasoning: use the approved squeeze welder with the specified tips and force; if the welder cannot reach, use the OEM-approved rivet-bond method. MIG welding because “it looks like steel” is a strength failure, not a shortcut.
Traps
Treating all high-strength steel as mild steel; using a generic weld schedule; skipping the OEM weld-count diagram; grinding welds on AHSS; forgetting seam sealer and anti-corrosion coating.