Machinability of hard alloys & tool steels is improved by

ANS:B - annealing

Annealing is a heat treatment process used to alter the microstructure of a material, typically to make it softer, more ductile, or to relieve internal stresses. It involves heating the material to a specific temperature, holding it at that temperature for a predetermined amount of time, and then slowly cooling it down. The exact temperature and cooling rate depend on the material being annealed and the desired outcome. Here's a breakdown of the annealing process:

1. Heating: The material is heated to a temperature above its critical temperature, which is the temperature at which its internal structure undergoes significant changes. This temperature varies depending on the material but is typically well above room temperature.
2. Soaking: Once the material reaches the desired temperature, it is held at that temperature for a period of time to allow for uniform heating throughout its entire volume. This soaking period ensures that the material's internal structure is fully transformed.
3. Cooling: After the soaking period, the material is slowly cooled down to room temperature. The cooling rate can vary depending on the material and the desired properties. In some cases, the material may be cooled in the furnace along with the furnace, while in other cases, it may be allowed to cool in the air or be quenched in a controlled manner.

The primary purposes of annealing are to:

• Reduce hardness: Annealing softens the material by promoting the formation of a more ductile microstructure, which reduces hardness and increases toughness.
• Relieve internal stresses: Annealing helps to relieve internal stresses that may have built up in the material during previous processing steps, such as casting, forging, or machining.
• Improve machinability: Annealing can improve the machinability of materials by making them softer and more uniform, which reduces tool wear and improves surface finish during machining operations.

Annealing is commonly used in the manufacturing of metals and alloys, including steel, copper, aluminum, and brass, among others. It is a versatile heat treatment process that can be tailored to achieve specific material properties based on the application requirements.