Final answer:
Precipitation hardening and hardening of steel by quenching and tempering are two heat treatment procedures with different microstructures and changes in mechanical properties.
Step-by-step explanation:
Precipitation hardening and the hardening of steel by quenching and tempering are two different heat treatment procedures that result in different microstructures and changes in mechanical properties.
With precipitation hardening, the alloy is heated to a high temperature and then cooled rapidly, followed by aging at a lower temperature. During aging, small particles precipitate out of the solid solution, creating a harder and stronger microstructure. The mechanical properties, such as hardness and strength, increase during this process.
On the other hand, the hardening of steel by quenching and tempering involves heating the steel to a high temperature, followed by rapid cooling (quenching) to form a hard, brittle microstructure. Then, the quenched steel is reheated to a temperature below the transformation range and held there to allow for the formation of a desired microstructure (tempering). This process improves the toughness and ductility of the steel while retaining some hardness.