To understand the process of annealing, we first need to understand the Ductile and brittle behaviour of metals.
Ductility: Ductility is the ability of the metal to be stretched into a wire without breaking when tension is applied in it.
Brittleness: Brittleness is the opposite of ductility.
So when a piece of metal is stretched, how soon it break defines if the metal is brittle or ductile.
But why this is important in shipping ? A ship at sea is subjected to lot of stress. If a ship is made of brittle material, the material will brake (or develop cracks) under this stress.
Annealing is a process where we heat a metal to a certain temperature or color and then allow it to cool down naturally. This makes the metal more ductile and soft, which means that the metal can be cut/shaped easily and also the metal will not break easily.