[1] A solution called pickle liquor, which usually contains acid, is used to remove the surface impurities.
In order to remove the scale the workpiece is dipped into a vat of pickle liquor.
[4] Carbon steels, with an alloy content less than or equal to 6%, are often pickled in hydrochloric or sulfuric acid.
Rust- and acid-resistant chromium-nickel steels are pickled traditionally in a bath of hydrofluoric and nitric acid.
Sheet steel that undergoes acid pickling will oxidize (rust) when exposed to atmospheric conditions of moderately high humidity.
For this reason, a thin film of oil or similar waterproof coating is applied to create a barrier to moisture in the air.
The hydrogen from the acid reacts with the surface and makes it brittle, causing cracks.
Because of its high reactivity with treatable steels, acid concentrations and solution temperatures must be kept under control to ensure desired pickling rates.
eliminating the need to apply the oil coating that serves as a barrier to oxidation for acid-pickled carbon steel.