1. Core PWHT Type: Stress Relieving Annealing (Primary Choice)
Temperature range: 550–620°C (critical to avoid exceeding 650°C, as higher temps can reduce the steel's yield strength and disrupt corrosion-resistant oxide film formation).
Heating/cooling rate: ≤200°C/h for plates thicker than 25mm (slower rates prevent thermal stress); cool to ≤300°C in the furnace, then air-cool to room temperature.
Holding time: 1–2 hours per 25mm of plate thickness (e.g., 2 hours for 50mm-thick steel, ensuring full stress relief).
2. Key Exceptions: When PWHT May Be Omitted
Plate thickness ≤16mm (lower 拘束 and residual stress, low cracking risk).
Welding uses low-hydrogen processes (e.g., gas metal arc welding/GMAW with low-hydrogen wires, submerged arc welding/SAW) and pre-weld preheating (80–120°C).
The welded structure is for non-critical service (no long-term exposure to cyclic loads or harsh corrosion environments like marine/industrial atmospheres).
3. Critical Precautions to Avoid Damage
Pre-clean welds: Remove slag, spatter, and oil before PWHT-contaminants can cause discoloration or local corrosion during heating.
Avoid overheating: Never exceed 620°C; overheating will reduce SMA570W's tensile strength (from ~670MPa to <600MPa) and weaken its weather resistance.
Protect after PWHT: After air-cooling, lightly grind the weld surface if oxide scales form-this ensures the weather-resistant alloy elements (Cu, Cr) can react with air to form a stable protective film.
