The recommended heat treatment temperature is less than 240℃.

When performing heat treatment after spring processing, more attention must be paid to the heat treatment temperature for galvanized steel wire than stainless or nickel-plated steel wire.

In the case of our galvanized wire, the iron content in the surface steel starts to be thermally diffused (alloyed) into the galvanized layer at 250℃. When the diffusion layer reaches the plated surface, it changes color tone and gloss of the plated surface.

Therefore, if you do not want to change the color tone and gloss of galvanized material, it is recommended to perform heat treatment at a temperature of 240℃ or less, considering variations in furnace temperature distribution.

If the temperature is 240℃ or less, the color tone and gloss before heat treatment are maintained regardless of heat treatment duration.

What happens if the heat treatment temperature is set to 250℃?

When the heat treatment temperature exceeds 250℃, it causes iron to start to be thermally diffused into the galvanized layer, increases temperature, decreases the gloss of the plated surface as time elapses, and changes the color tone, resulting in color shading.

However, corrosion resistance of the plated material improves in proportion to thermal diffusion.

In the temperature range from 250–280℃, the plated surface is placed in the most unstable state in terms of color tone and gloss. Therefore, it is recommended to test the sample in advance.

When the temperature exceeds 280℃, the galvanized material becomes mat and turns black, whereas the corrosion resistance improves about 2.3 times compared with the condition before the heat treatment is performed.

The Maximum Heat Treatment Temperature Allowed

Even when heat treatment is performed to the plated film of “Mac Wire” at 350℃ for 10 minutes, there is no decline in corrosion resistance or damage to the plated film.

However, the plated surface turns black and mat.

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