1. Increased Yield & Tensile Strength
Hot-rolled baseline: SPA-H has a minimum yield strength of 345 MPa and minimum tensile strength of 480 MPa (per JIS G 3125).
Cold-rolled change: Yield strength increases by 20–30% (to ~415–450 MPa), and tensile strength rises by 15–25% (to ~550–600 MPa).
Reason: Plastic deformation during cold rolling compresses and elongates the steel's grains, creating internal stress that resists further deformation-boosting load-bearing capacity for thin, precision components.
2. Elevated Hardness
Hot-rolled baseline: Brinell hardness (HBW) ranges from 180–220.
Cold-rolled change: Hardness increases by 15–25% (to ~210–270 HBW).
Practical effect: The harder surface resists scratching, abrasion, and minor impacts-beneficial for applications like smooth-faced sign panels or industrial equipment casings.
3. Reduced Ductility & Elongation at Break
Hot-rolled baseline: Minimum elongation at break is ≥20% (for thickness ≤16 mm).
Cold-rolled change: Elongation drops significantly to ≤15% (a 25–30% reduction).
Practical effect: Cold-rolled SPA-H loses formability; it cannot withstand sharp bends, deep curves, or complex 3D shaping without cracking, limiting use to flat or gently formed parts.
4. Improved Dimensional Precision & Flatness
Hot-rolled baseline: Thickness tolerance is relatively wide (±0.5 mm for medium gauges), with minor warping or unevenness from high-temperature rolling.
Cold-rolled change: Thickness tolerance tightens to ±0.05–0.1 mm (for thin gauges 0.5–6 mm), and flatness is drastically improved with no warping.
Practical effect: Critical for precision applications requiring tight fits, such as laser-cut sign letters, electrical enclosures, or automotive trim parts.
5. Unchanged Ambient-Temperature Toughness
Cold rolling does not significantly reduce the steel's toughness (resistance to fracture) at room temperature.
Caveat: Toughness may decrease slightly at sub-zero temperatures, but this is rarely a concern for SPA-H's typical outdoor applications.
