Stain steel

Pickling is usually only known from wood - where it is used to deeply change the wood color while maintaining the grain of the wood at the same time. What steel pickling means and where it is used is explained in this article.

Pickling in steel

Unlike wood, steel pickling does not enhance color or color. It is used as a fundamental process step in the production of rolled steel strip.

tinder

Hot rolling produces a so-called burn-off on the surface of the steel, also called tinder in technical language. These are s Fe3O4, small platelets of iron oxide. They are formed by oxidation of the steel surface at high temperatures, when oxygen or other oxidizing gases act on the surface. A stain removes this burnup from the surface.

mordant

Stripping takes place in baths of hydrochloric acid or of sulfuric acid. Technically, the bands are either pulled individually through such a bath, and then rolled up again, or they are welded into a complete band and completely pulled through the bathroom.

Sulfuric acid bath in the steelworks

If sulfuric acid is used to remove the scale, the strip must first be mechanically preprocessed. Sulfuric acid is usually used directly only in steel mills, because the coke used there also supplies the required sulfuric acid. In all other cases hydrochloric acid is usually used.

neutralization

After the action of acid, the surface must then be neutralized again. After extensive rinsing with water, the strips are then immersed in sodium hydroxide to neutralize the acid residues.

Problem hydrochloric acid

As with derusting with hydrochloric acid, hydrochloric acid treatments pose a risk for subsequent corrosion resistance. After treatment with hydrochloric acid, steel surfaces tend to be more corrosive than before treatment. The surface can also become more brittle than it was before. This is done by incorporating hydrogen into the metal lattice of the surface - this acts like a material fatigue. This damage is called in the jargon also "hydrogen embrittlement".

Tips & Tricks

Hydrochloric acid can also be used as a fast-acting agent for rust removal from steel surfaces. However, the same risks apply as with pickling in steelworks. In addition, you should always keep an eye on the potential health risk of using hydrochloric acid.

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