1. Vibratory Stress Relief (VSR): Non-Thermal, Mechanical Stress Reduction
Process details:
Attach electromagnetic or mechanical vibrators to the welded component, then tune the vibration frequency to match the material's natural resonance (typically 10–200 Hz).
Run the vibration for 30–120 minutes, depending on component size. The resonance causes internal stress to redistribute by mobilizing dislocations in the steel's crystal structure, reducing peak stress levels.
Effectiveness: Reduces residual stress by 30–50% (compared to 60–80% with annealing). It does not impact SMA570W's weathering performance, as no heat is applied to alter alloying element distribution.
Applicability: Ideal for small/complex components (e.g., thin-walled brackets, precision structural parts) or on-site repairs where transporting large assemblies to annealing facilities is unfeasible. It also avoids thermal distortion-critical for components with tight dimensional tolerances.
2. Low-Temperature Tempering: Supplementary Thermal Relief
Process details:
Heat the welded component to a low temperature of 180–220°C (far below the 550–600°C range for annealing) and hold for 2–4 hours.
Cool the component slowly in air (no strict rate control needed, unlike annealing).
Effectiveness: Reduces residual stress by 20–35% and primarily improves HAZ toughness by refining small, brittle microstructures (e.g., martensite) formed during welding. It does not soften the base metal or dilute weathering elements (Cu, Cr), so patina formation remains unaffected.
Applicability: Best for thin plates (<20mm) or components used in cold environments (below 0°C), where maintaining low-temperature toughness is critical. It is also used to "touch up" stress relief after VSR, further reducing remaining stress.
3. Shot Peening: Surface Stress Modification
Process details:
Blast the weld surface and HAZ with small, high-velocity metal shots (typically steel or stainless steel, 0.2–1.0mm in diameter) at a pressure of 0.2–0.6 MPa.
The impact of the shots creates tiny plastic deformations on the surface, converting tensile residual stress (which promotes cracking and corrosion) into compressive stress.
Effectiveness: Focuses on surface and near-surface stress (up to 0.5mm deep), reducing these stresses by 40–60%. The compressive stress layer also slows down the initiation of corrosion pits, indirectly supporting patina stability.
Applicability: Used as a supplementary method for welds exposed to cyclic loads (e.g., bridge joints) or harsh environments (e.g., coastal areas). It cannot replace annealing for thick components (where internal stress dominates) but works well alongside VSR or low-temperature tempering.
