Softening of hardned steel is done by its

ANS:A - normalising

Normalizing is a heat treatment process used to refine the grain structure of steel and improve its mechanical properties, such as strength and toughness. The process involves heating the steel to a specific temperature above its critical temperature and then allowing it to cool in still air. Here's how the normalizing process works:

1. Heating: The steel is heated to a temperature slightly above its critical temperature. The critical temperature is the temperature at which the steel undergoes a phase change, typically the transformation from austenite to ferrite and pearlite. The exact temperature depends on the composition of the steel.
2. Soaking: Once the steel reaches the desired temperature, it is held at that temperature for a specific period of time to ensure that the entire cross-section of the steel reaches the same temperature. This soaking period allows for the austenite phase to fully form throughout the steel.
3. Cooling: After the soaking period, the steel is allowed to cool in still air. The cooling rate during normalizing is slower than that during quenching, which is used in other heat treatment processes such as hardening. This controlled cooling rate helps to refine the grain structure of the steel.

The primary objectives of normalizing are to:

• Refine the grain structure of the steel, making it more uniform and fine-grained.
• Relieve internal stresses that may have been introduced during previous processing steps, such as casting or hot rolling.
• Improve the mechanical properties of the steel, including its strength, toughness, and ductility.

Normalizing is commonly used for a variety of steel products, including structural components, forgings, and castings. It provides a balance of mechanical properties and dimensional stability, making it a valuable heat treatment process in the manufacturing industry.