SPA-H is a Japanese standard (JIS G 3125) weathering steel grade, widely used in outdoor structural components. The core differences between its cold-rolled (CR) and hot-rolled (HR) versions lie in production process, microstructure, performance, and application scenarios, as detailed below:
| Comparison Item | Hot-Rolled SPA-H Steel Plate | Cold-Rolled SPA-H Steel Plate |
|---|---|---|
| Production Process | Rolled above the steel's recrystallization temperature (≈1100–1250°C), then cooled naturally or controlled cooling. | Rolled at room temperature using hot-rolled steel as the base material; cold deformation causes work hardening, often followed by annealing to adjust performance. |
| Thickness Range | Generally 3–150 mm (thicker specifications available). | Generally 0.3–3 mm (thin-gauge plates/strips). |
| Surface Quality | Rough surface; may have oxide scales, rolling marks, or slight warpage. Oxide scales need removal (mechanical/chemical methods) for patina uniformity. | Smooth, clean surface with high dimensional accuracy; no obvious oxide scales; excellent flatness and surface finish. |
| Microstructure & Mechanical Properties | Ferrite-pearlite microstructure, no work hardening; balanced strength and ductility (yield strength ≥235 MPa, elongation ≥22%). | Cold deformation refines grains and induces work hardening; higher strength (yield strength increases by 20–30% compared to hot-rolled) but slightly reduced ductility. Annealed cold-rolled plates can restore ductility while retaining fine-grain strength. |
| Patina Formation | Oxide scales on the surface delay initial patina formation; uniform patina requires pre-treatment (shot blasting/descaling). The thick substrate ensures long-term corrosion resistance for load-bearing structures. | Clean surface promotes fast, uniform patina formation without pre-treatment; suitable for decorative applications requiring consistent appearance. |
| Processing Performance | Good weldability and formability; suitable for bending, cutting, and welding of large components. | High hardness after cold rolling; poor cold bending performance (prone to cracking) if not annealed. Annealed plates have improved formability for precision parts. |
| Application Scenarios | Outdoor load-bearing structures: highway guardrails, containers, guide signs, building frames, and steel bridges. | Thin-gauge decorative or precision components: architectural cladding panels, furniture parts, electronic device shells, and small outdoor signs. |
| Cost | Lower production cost; more economical for large-batch, thick-plate applications. |
