How does the cold-rolled process affect the mechanical properties of SPA-H weathering steel plate?

 

Cold rolling induces room-temperature work hardening via plastic deformation, causing grain distortion and dislocation accumulation in the steel matrix. This raises the yield strength by 20–30% (to 415–450 MPa) and tensile strength by 15–25% (to 550–600 MPa); Brinell hardness also increases by 15–25% (to 210–270 HBW), enhancing surface wear and scratch resistance.

 

The work-hardened microstructure drastically impairs plastic deformation capacity: elongation at break drops from the hot-rolled ≥20% to ≤15% for cold-rolled SPA-H. The steel loses the ability for tight-radius bending, deep stamping and complex shaping, only suitable for flat processing or gentle, large-radius bending without cracking.

 

Cold rolling has little impact on ambient-temperature toughness but causes a minor decline in low-temperature toughness (sub-zero environments). The steel's resistance to low-temperature impact and brittle fracture is reduced, though this change is negligible for most normal outdoor atmospheric applications of cold-rolled SPA-H (1.6–6 mm gauges).

 

Uneven plastic deformation during cold rolling introduces significant internal residual stress in the steel plate, which is trapped in the matrix without high-temperature annealing. This stress may cause slight warpage or deformation during subsequent cutting, welding or secondary processing if not properly relieved by low-temperature stress relief treatment.

 

The cold-rolled process does not bring substantive improvement or reduction to the fatigue strength of SPA-H. The steel's resistance to cyclic load fatigue remains consistent with hot-rolled SPA-H, as fatigue performance is mainly determined by the base alloy composition rather than cold working-induced physical structure changes.