Why Galvanized Steel Sheet Offers Better Corrosion Resistance

In the field of metal materials, galvanized steel sheet and cold rolled steel sheet are two widely used but distinct products. Cold rolled steel sheet represents the basic form of rolled steel, while galvanized steel sheet is an upgraded product created through surface treatment of cold rolled steel sheet.

Fundamental Differences in Manufacturing Process

(1) Cold Rolled Steel Sheet: Basic Processing by Rolling

Cold rolled steel sheet production uses hot rolled steel sheet as raw material. Through multiple passes of rolling at room temperature (rolling temperature < recrystallization temperature, typically between room temperature and 100℃), thickness reduction and performance enhancement are achieved. The core processes include:

Rolling Process: Hot rolled slab (thickness 3–8 mm) is rolled by cold rolling mill to 0.15–3.0 mm. The number of passes depends on target thickness (thin specifications require 5–8 passes). Each pass reduces thickness by 15%–30%. Through plastic deformation, the grains are refined and strength improved.

Annealing Treatment: After cold rolling, the steel sheet experiences reduced plasticity due to work hardening. Continuous annealing (temperature 700–800℃) is required to restore plasticity, allowing different hardness states to be achieved (soft, half-hard, hard).

Finishing Process: Includes leveling (improving flatness, controlling roughness Ra0.5–2.0 μm), trimming (ensuring dimensional accuracy), etc., ultimately producing smooth surface and precise dimensions.

The key of cold rolling is to achieve densification and performance adjustment of steel through mechanical force, without changing material composition via chemical or thermal treatments. It is the "basic raw material" for steel deep processing.

(2) Galvanized Steel Sheet: Corrosion-Resistant Upgrade by Surface Treatment

Galvanized steel sheet mainly uses cold rolled steel sheet as its substrate (over 90%), and the galvanizing process provides corrosion resistance. The core processes are divided into hot-dip galvanizing and electro-galvanizing:

Hot-Dip Galvanizing: The substrate undergoes degreasing, pickling, and then immersion in molten zinc at 450–460℃, forming a zinc-iron alloy layer (thickness 5–15 μm) plus a pure zinc layer (total coating 50–275 g/m²). The zinc layer metallurgically bonds with the substrate, achieving adhesion strength above 80 N/cm.

Electro-Galvanizing: In a zinc-ion electrolyte, electrolysis deposits a pure zinc layer (5–50 g/m²) on the substrate surface. The zinc layer is physically bonded with adhesion strength of 30–50 N/cm, producing a smoother surface (Ra0.1–0.5 μm).

The essence of galvanizing is forming a zinc layer on cold rolled steel sheet, transforming "basic steel" into "corrosion-resistant steel." The galvanizing process involves 3–5 additional surface treatment steps compared to cold rolled steel sheet.

Relationship Between Galvanized Steel and Cold Rolled Steel

Galvanized steel sheet and cold rolled steel sheet are not substitutes, but products at different stages of the steel processing chain. Cold rolled steel sheet is the "basic version," offering diverse performance options. Galvanized steel sheet is the "upgraded version," specifically solving corrosion issues. Understanding their process differences, performance characteristics, and cost implications is key to precise selection in industrial applications, ensuring both product performance and cost control while maximizing material value.

Since its establishment in 2008, GNEE STEEL has specialized in the international trade of cold-rolled galvanized steel products. Our stable quality and professional service have earned the trust of customers in over 160 countries worldwide. Our cold-rolled galvanized steel products, including galvanized steel sheets, galvanized steel coils, cold-rolled steel coils, and cold-rolled steel sheets, are widely used in construction, automotive manufacturing, home appliances, and electrical equipment.