Annealing is used to induce ductility, soften material, relieve internal stresses, refine the structure by making it homogeneous, and improve cold working properties.
This process is performed by substantially heating
the material, generally until glowing, then allowing it to cool (usually, slowly in air).
will be hardened if quickly quenched in water, and must be cooled slowly (in air or furnace) to anneal.
However, copper and brass can be either cooled slowly, or quickly by quenching in water.
You do not need to anneal new washers. They come out of the manufacturing process soft and ductile. You only need to re
-anneal used washers that have been worked.