WHAT IS THE ANNEALING AND PICKLING PROCESS IN METAL
Updated: Jun 19, 2020
Annealing is a heat treatment process mainly used in metallurgy to increase the ductility and reduce the hardness of a material. This change is caused by the reduction of number of dislocations in the crystal structure of the material that is annealed. A lot of times, annealing is performed after a material has undergone a hardening or a cold working process. Annealing prevents such materials from becoming brittle or increase formability.
Steel, cast iron, certain aluminium types, copper, brass and other materials are known to normally respond to annealing processes.
The three main stages during an annealing process include:
Grain growth stage
There are multiple advantages of annealing, including increased ductility and formability of a material. Firstly, annealing improves the formability of hard, brittle materials that are difficult to bend or press. Annealing can also improve machinability of materials that are highly brittle, by reducing its hardness and the wear of the tools used. Annealing also eliminates residual stresses that can create cracks and other mechanical complications.
Pickling is a metal treatment process used to remove superficial impurities from metal. It involves the use of an acidic solution known as pickle liquor, which contributes to the name.
The main step involved in pickling is the treatment of the target material in acidic solution. The metal is submerged in pickle liquor, which erodes any oxide or other impurities remaining on the surface of the metal.
Newly produced metal often has a layer of impurities on the surface. For example, hot-rolled steel usually develops an oxide layer when developed. The presence of such oxides prevents the steel from obtaining a smooth and clean surface for better appearance and maximum usability. There are numerous ways to remove oxide from steal, but picking is the most commonly used process by manufacturing companies like Diamond Brite Metals, because of its simplicity. During pickling, the acidic pickle liquor reacts with the oxide layer, eating it away, without harming or disturbing the underlying steel.
Although every piece of metal may not contain an oxide layer on its surface, it is very common for some impurities to be present. It is very normal for newly produced metal to contain inorganic compounds like trace metals on its surface, which may thwart its performance. Pickling plays a crucial role in removing all such impurities.