for SPA-H steel plates as per JIS G 3125; the default is hot-rolled (as-rolled, AR) or controlled-rolled (TMCP) for hot-rolled plates, and cold-rolled (CR) for thin strips. Annealing is a custom option, not the norm.
◎Standard Delivery States for SPA-H Steel Plates
Hot-rolled SPA-H plates
as-rolled (AR)thermo-mechanical control process (TMCP). In the as-rolled state, the steel undergoes rolling above the recrystallization temperature and then natural cooling, forming a stable ferrite-pearlite microstructure. This state ensures balanced mechanical properties (yield strength >= 235 MPa, elongation >= 22%) that meet the basic requirements of outdoor structural applications, such as guide signs, guardrails, and containers. The TMCP state, achieved through controlled rolling and cooling, further refines the grain size and enhances strength and toughness without additional heat treatment. Both as-rolled and TMCP states are cost-effective and do not involve annealing, making them the default choices for most industrial orders.
Cold-rolled SPA-H strips/plates
cold-rolled (CR) without annealing. Cold rolling is performed at room temperature using hot-rolled SPA-H as the base material, which causes plastic deformation and work hardening of the steel. This process improves the surface finish and dimensional accuracy of the steel plate but increases hardness while slightly reducing ductility. The cold-rolled state is suitable for applications requiring thin gauge (0.3–3 mm) and precise shaping, such as decorative panels and small precision components.
Annealing becomes an optional process only when customers have specific performance or processing requirements. Common annealing types for SPA-H steel plates include:
: Heating the steel to 850–900℃, holding it for a sufficient time, and then cooling slowly. This eliminates work hardening from cold rolling, softens the material, and restores ductility, making it easier for subsequent bending, stamping, or welding processes.
: A low-temperature annealing (550–650℃) applied to cold-rolled SPA-H to relieve internal stress without significantly reducing strength, which is suitable for components that need to maintain a balance between hardness and formability.
It should be noted that requesting an annealing treatment will increase production costs and extend the delivery lead time, as it adds an extra heat treatment step to the production process. Therefore, it must be clearly specified in the purchase contract.
For general outdoor load-bearing structures (e.g., large guide signs, steel structure components), the standard as-rolled or TMCP hot-rolled SPA-H is sufficient and does not require annealing.
For cold-rolled SPA-H used in precision processing (e.g., decorative sign panels that need complex bending), annealing should be specified to improve formability and avoid cracking during processing.
The annealing state will affect the patina formation speed of SPA-H steel: annealed surfaces are cleaner and more uniform, which helps to form a consistent protective patina faster in outdoor environments.
