Pickling
Pickling is the chemical cleaning of metal surfaces with acid to remove scale, oxides, and heat tint. It restores the original passive layer and corrosion resistance.
Physicochemical mechanism of action
Pickling uses an acid to remove scale, oxides, and heat tint from the metal surface. The acid reacts with these impurities to form a soluble compound that can be easily rinsed off.
Metallurgical relevance & risks in welding
Without pickling, scale and oxides in the weld can lead to cracks and deformation. They also slow down the diffusion of carbon, leading to a fine-cracked martensitic structure. This increases the risk of hot cracking and reduces weld toughness.
Shop practice & action instructions
Use an acid like HCl or H2SO4 at a concentration of 5-10% for pickling. The pickling time is typically 30-60 seconds, depending on the metal and welding method. After pickling, rinse the surface thoroughly to avoid leaving acid residues.