1. Effect on Hot-Rolled SPA-H Plates (As-Rolled/TMCP State)
●Reduce strength slightly: Annealing promotes grain growth and eliminates internal stress, leading to a 5–10% decrease in yield strength and tensile strength (e.g., yield strength may drop from 345 MPa to 310–330 MPa).
●Improve ductility marginally: Elongation may increase by 1–2%, but this change is negligible because the as-rolled state already meets the minimum elongation requirement (15–22%).
●Enhance toughness: Charpy V-notch impact energy at room temperature can rise from ≥27 J to ≥35–40 J, which is useful for low-temperature applications (e.g., cold regions).
2. Effect on Cold-Rolled SPA-H Plates (Cold-Rolled State)
●Restore ductility and formability: Full annealing (heating to 850–900°C, holding, then slow cooling) eliminates work hardening, recrystallizes the deformed grains, and raises elongation back to 22–25%. This makes the plate suitable for precision processing like stamping or complex bending.
●Reduce strength to baseline levels: Yield strength decreases from 420–450 MPa (cold-rolled state) back to 335–345 MPa, matching the hot-rolled state's strength.
●Improve surface quality: Annealing removes rolling marks and internal stress, resulting in a more uniform surface that benefits subsequent patina formation.
