1. Process Annealing (Most Common)
Temperature: 650–750°C (subcritical annealing, below austenitization ~850°C)
Hold Time: 1–2 minutes per mm of thickness (minimum 30 mins for thin gauges <3 mm)
Cooling: Furnace cooling (slow) or air cooling (for low-formability requirements)
Typical Example: 6 mm cold-rolled SPA-H → 680°C + 6–12 mins hold + furnace cool
2. Full Annealing
Temperature: 780–850°C (near/critical austenitization, for full grain recrystallization)
Hold Time: 2–3 minutes per mm of thickness (minimum 1 hour for thick gauges >25 mm)
Cooling: Slow furnace cooling (≤50°C/hour) to room temperature (avoids re-hardening)
Typical Example: 20 mm cold-rolled SPA-H → 820°C + 40–60 mins hold + slow furnace cool
3. Key Universal Rules
Heating Rate: ≤150°C/hour for thick gauges (>25 mm) to prevent thermal stress/cracking; no strict limit for thin gauges (<10 mm).
Uniformity: Ensure the entire SPA-H workpiece reaches the target temperature (critical for consistent property changes).
Post-Annealing: No additional treatment needed-surface preparation (grinding/sandblasting) only for patina uniformity in outdoor applications.
