1.What are the characteristics of cold rolling process?
Multi-pass rolling, extremely high dimensional accuracy
Room temperature rolling: hot-rolled steel plates are rolled at room temperature (no reheating is required), and the thickness tolerance of the steel plates is controlled within ±0.01mm through micron-level adjustment of the mill roll gap, which is far higher than the ±0.1mm accuracy of hot-rolled plates.
Directional optimization of mechanical properties
Work hardening: During the cold rolling process, the grains of the steel plates are elongated, and the strength and hardness are significantly improved (such as the yield strength from 235MPa of hot-rolled plates to more than 300MPa), but the elongation decreases, and annealing treatment (such as continuous annealing furnace) is required to restore plasticity and achieve "strength and toughness balance".
High surface quality cleanliness
Degreasing and cleaning: Before rolling, the oxide scale and oil stains on the surface of the hot-rolled plate are removed by alkaline solution or electrolytic cleaning to ensure the adhesion of the subsequent galvanized layer;
2.What are the characteristics of galvanizing process?
The coating has various attachment modes, strong bonding force, customizable coating composition, and functional surface post-treatment.
3.What does it mean that the coating composition can be customized?
Pure zinc coating (Z): standard anti-corrosion, low cost, suitable for most environments;
Zinc-aluminum coating (ZA/ZAL): contains 5% aluminum, the aluminum element forms a dense aluminum oxide film, the salt spray resistance test can reach more than 1000 hours (pure zinc layer Z275 is about 500 hours), suitable for coastal and high humidity areas;
Zinc-iron alloy coating (GA): annealed immediately after galvanizing to form a Fe-Zn alloy layer, the surface is silver-gray, the weldability is excellent (less spatter in resistance welding), and the paint adhesion is increased by 30%, commonly used for automobile bodies.
4.What is the core competitiveness of cold-rolled galvanizing process?
The production process of cold-rolled galvanized steel is centered on high-precision rolling, strong bonding coating, functional surface treatment and intelligent continuous production. It not only achieves the dual improvement of "corrosion protection + mechanical properties", but also meets the diversified material needs of high-end manufacturing through customized coating design (such as zinc-aluminum, zinc-iron alloy) and surface treatment. These process characteristics make it the "core basic material" of industries such as automobiles and home appliances, and occupy an important position in the global supply chain.
5.What is the core difference with hot-rolled galvanized steel?
Thickness range: cold-rolled galvanized steel 0.3-3.0mm; hot-rolled galvanized steel 2.0-6.0mm.
Surface quality: cold-rolled galvanized steel is smooth and scale-free and can be directly painted; hot-rolled galvanized steel has a rough surface and requires secondary grinding.
Forming performance: cold-rolled galvanized steel has an elongation of ≥30%, which is suitable for deep drawing and complex stamping; hot-rolled galvanized steel has an elongation of ≈25%, which is only suitable for simple bending.
Application scenarios: cold-rolled galvanized steel is used in automobiles, home appliances, and precision components; hot-rolled galvanized steel is used in low-end scenarios such as building steel bars and scaffolding.
Production cost: high for cold-rolled galvanized steel (more cold rolling and annealing processes); low for hot-rolled galvanized steel.