__________ of hard alloy and tool steel is done to make it easily machinable.

ANS:B - Tempering

Tempering is a heat treatment process applied to hardened metals, typically steel, to improve their mechanical properties. After a metal has been hardened through processes like quenching, it becomes very hard but also brittle. Tempering is done to reduce this brittleness while retaining the hardness achieved during hardening. During tempering, the hardened metal is heated to a temperature below its critical point (the point at which it becomes non-magnetic), and then held at that temperature for a specific period of time. The temperature and duration of tempering determine the mechanical properties of the final product. The main purpose of tempering is to:

1. Reduce brittleness: Tempering relieves internal stresses and reduces the brittleness caused by the hardening process, making the metal less prone to cracking or fracturing under impact or sudden loads.
2. Improve toughness: By reducing brittleness, tempering improves the toughness of the metal, allowing it to absorb more energy before deforming or fracturing.
3. Adjust hardness: The temperature and duration of tempering can be adjusted to achieve the desired balance between hardness and toughness for specific applications.