1. Stress Relief Annealing (Primary and Most Effective Method)
Process details:
Heat the entire welded assembly uniformly to a temperature range of 550–600°C (critical to avoid exceeding 620°C, which could degrade the base metal's strength).
Maintain this temperature for 1–2 hours per 25mm of plate thickness (e.g., 4 hours for 50mm-thick sections) to allow sufficient diffusion of internal stresses.
Cool slowly at a controlled rate of ≤50°C/hour until the component reaches 300°C, followed by air cooling. Rapid cooling is prohibited as it reintroduces stress and risks cracking.
Applicability: Mandatory for load-bearing parts (e.g., bridge girders, pressure vessel shells) with thickness >20mm, or joints subjected to dynamic loads (e.g., seismic activity) or harsh environments (coastal salt spray).
2. Low-Temperature Tempering (Supplementary for Thick Plates)
Process details:
Heat the welded component to 180–220°C and hold for 2 hours.
This mild temperature avoids softening the base metal but helps reduce microstructural inhomogeneity in the HAZ, enhancing toughness without compromising strength.
Applicability: Particularly useful for plates >30mm thick or components used in cold regions (below 0°C), where maintaining low-temperature toughness is critical.
3. Vibratory Stress Relief (Non-Thermal Alternative for Specific Cases)
Process details:
Attach vibrators to the welded component and apply vibrations at frequencies matching the material's natural resonance (typically 10–200 Hz) for 30–120 minutes.
The vibrations redistribute internal stresses by encouraging dislocations in the microstructure, reducing peak stress levels.
Applicability: Suitable for small, complex components or parts where high-temperature annealing could cause distortion (e.g., thin-walled structures or precision fabrications). It is less effective than annealing (reducing stress by ~30–50%) but avoids thermal-related risks like HAZ softening.
