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HaiGang Yunyi
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Tianjin Haigang Steel Coil
Service first, quality assured. More dedicated and focused on crafting even better boards.
31
2021
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Why does hot-dip galvanized steel appear gray?
After hot-dip galvanizing, the surface color of the steel strip is indeed less bright than that of steel strips that have undergone phosphating treatment—there’s a noticeable difference. Once the steel strip has been hot-dip galvanized, its surface becomes matte. Since each person’s eyes have different sensitivities to light, we can only discuss, in general terms, what color hot-dip galvanized steel strips typically exhibit, under what conditions their color appears brighter, and in what natural environments their color tends to look darker.
First of all, whether the color of hot-dip galvanized strip steel is dull gray or lacks luster depends on several factors. The primary factor is the quality of the zinc raw material. Generally speaking, it’s perfectly normal for hot-dip galvanized strip steel to have a dark-gray hue. However, if the steel appears exceptionally dull and gray—almost black—then that’s unusual. Although hot-dip galvanized strip steel has a matte finish, it shouldn’t completely lack any trace of gloss. If the surface looks so dim and lifeless that it’s simply unacceptable, you should first suspect the quality of the zinc raw material. The zinc we use for hot-dip galvanizing must have a zinc content of at least 99.99% to meet the national standard specifications. Moreover, there are strict limits on how often zinc can be reused. After a batch of zinc is melted in the bath and used to galvanize a certain amount of strip steel, the remaining zinc blocks must be replenished. This is precisely regulated: if you keep using the same zinc blocks indefinitely without replacing them, the molten zinc in the bath will gradually deplete. To cut costs, some operators might instead add other metallic materials or even scrap zinc residues from previous galvanizing processes—materials that aren’t technically compliant with the standards. In such cases, the strip steel produced will undoubtedly have an especially dull and grayish appearance. If this kind of dullness is caused by such substandard practices, then it’s clearly a product quality issue.
Hot-dip galvanized strip steel color
As everyone often mentions, the color differences among hot-dip galvanized steel strips arise under the same material specifications—meaning you should only compare steel strips of the same grade. It’s not appropriate to compare, for instance, an 8.8-grade hot-dip galvanized steel strip with a 4.8-grade one and then claim there’s a significant color difference. Indeed, due to differences in raw materials, some degree of color variation is inevitable. In my view, the second point I mentioned—that certain color variations are within acceptable limits—is entirely justified.
Generally speaking, hot-dip galvanized strip steel of grade 10.9 tends to have a brighter color. This is due to differences in the raw materials and varying thermal environments they are exposed to. Temperature changes play a crucial role in determining the color: at the same temperature of 600°C, the raw material used for grade 10.9 strip steel has a higher temperature resistance. Consequently, at 600°C, the temperature appears relatively lower, and under these lower-temperature conditions, the color appears brighter.
As for the 8.8-grade hot-dip galvanized strip steel, its color is the most neutral. This is because at a temperature of 600°C, the properties of 8.8-grade strip steel undergo significant reintegration. Consequently, the color of 8.8-grade hot-dip galvanized strip steel tends to be neither bright nor dark—it appears as a perfectly normal matte finish. So which grade of hot-dip galvanized strip steel would appear relatively gray? Naturally, it’s the 4.8-grade hot-dip galvanized strip steel. Due to the nature of its raw material, 4.8-grade strip steel has not undergone heat treatment, and its surface hardness is relatively low. When placed in a molten bath at 600°C, its resistance differs from that of 8.8-grade strip steel, resulting in different transformations. Under the same environmental conditions, the color of 4.8-grade hot-dip galvanized strip steel will appear somewhat darker and grayer—this is entirely normal and does not indicate any product quality issue.
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We primarily produce various products including galvanized strip steel, pickled strip steel, and cold-rolled strip steel. These products are widely used in industries such as construction, mechanical manufacturing, automotive, and household appliances.
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