What improvements can be made in steel by heat treatment?

Improvements made in the steel by heat treatment is:

Hardness: Using the heat treatment method low carbon steel irons cannot be hardened. If the cast iron cooled rapidly it will form white iron. This white iron is hard and also very brittle. If the cast iron cooled slowly then it will form gray iron. This gray iron is soft and brittle.

Tempering: It is used to reduce the brittleness and produce some physical properties in the steel.  It will also soften the iron. It is conducted at the temperature lower than the critical point. The minimum time required for the tempering process is one hour.

Annealing: It will produce fine grained, ductile and soft metal without any internal stresses and strains. Steel is at its lower strength in annealed state. It is the opposite procedure of hardening. It is done by heating the metal above its critical point. The heated metal is then soaked for one hour and the slowly cooled in the furnace.