What are the differences between hot-dip galvanized steel and cold-dip galvanized steel?

In the regular trading of galvanized steel sheets, cold-rolled sheets are the primary type, while hot-rolled sheets are relatively rare. So, what are the differences between galvanized products made from hot-rolled and cold-rolled sheets? Let's briefly explain from the following aspects:

1. Cost: Because hot-rolled sheets undergo one less process than cold-rolled sheets, their production cost is lower. This is mainly due to the annealing cost and the cost of cold rolling; other processes are similar.

2. Quality and Performance: Hot-rolled sheets only undergo pickling and annealing to remove surface impurities, resulting in a rougher surface and better zinc layer adhesion. The coating thickness tends to be 140/140 g/m². However, the dimensional accuracy of hot-rolled sheets is not as high as that of cold-rolled sheets, and the zinc layer thickness is not uniform due to the predominantly thick zinc layer. Mechanical properties are not significantly different, and some properties are even better than cold-rolled sheets.

3. Application Areas: Because hot-rolled galvanized sheets have lower dimensional accuracy and surface quality than cold-rolled sheets, but are thicker, they are often used in structural components with lower surface finish requirements but higher strength and thickness requirements. Applications include automotive interior structural components and parts, such as those for household appliances like washing machines and refrigerators; automotive chassis structural components; bus bodies and roofs; highway guardrails; and cold-formed steel sections.

Hot-rolled galvanized steel sheets are used in various applications because of their low cost and increasing thickness and specifications with technological advancements.

4. Grades: Common grades of hot-rolled galvanized steel sheets in China include DD51D+ZHD340LAD+ZHR340LAHR420LAHR550LA, etc. Cold-rolled galvanized steel sheets are typically DC51D+ZHC340LAD+ZHC340LA, HC420LA, HC550LA, etc. There are also grades that don't specify whether the base material is hot-rolled or cold-rolled, such as DX51D+Z; these are generally considered to be hot-rolled galvanized steel sheets.