Q1: Which of the following alloying elements when added in steel does not improve its lachinability ?

ANS:C - Copper

Copper is sometimes added as an alloying element to steel to enhance certain properties, but it generally does not improve machinability. Here's an explanation of the effects of adding copper to steel:

1. Strength and Corrosion Resistance: Copper can improve the strength and corrosion resistance of steel when added in small amounts. It forms solid solution strengthening with iron, which increases the overall strength of the steel. Additionally, copper contributes to the formation of protective oxide layers on the surface of the steel, enhancing its corrosion resistance.
2. Hardness: Copper tends to increase the hardness of steel, which can be beneficial for certain applications where hardness is desired. However, increased hardness can also lead to reduced machinability, as harder materials are generally more difficult to machine.
3. Machinability: While copper itself doesn't directly improve machinability, its presence can have an impact on machinability depending on the steel composition and processing conditions. In some cases, copper may form hard particles or precipitates within the steel matrix, which can make machining more challenging. However, the effect of copper on machinability can vary depending on other alloying elements present, the steel's microstructure, and machining parameters.

Overall, while copper can offer benefits such as increased strength and corrosion resistance when added to steel, its effect on machinability may not be straightforward. In some cases, the presence of copper may actually reduce machinability due to increased hardness or the formation of hard precipitates. Therefore, careful consideration is needed when adding copper to steel alloys to ensure that the desired balance of properties is achieved.