Q1: Addition of __________ to steel does not help in improving its machinability.

ANS:B - silicon

Addition of silicon to steel does not help in improving its machinability. Explanation:

1. Sulphur: The addition of sulphur to steel can improve its machinability by forming manganese sulphide inclusions, which act as chip breakers during machining. These inclusions help to reduce the friction between the cutting tool and the workpiece, resulting in improved surface finish and reduced tool wear.
2. Lead: The addition of lead to steel can also improve its machinability by forming lead particles that act as lubricants during machining. These lead particles help to reduce friction and heat generation during cutting, resulting in smoother cuts and longer tool life.
3. Phosphorus: The addition of phosphorus to steel can improve its machinability to some extent by forming phosphide inclusions, which help to break up the chips during machining. However, excessive phosphorus content can lead to brittleness and reduced toughness in the steel.
4. Silicon: Silicon is not typically added to steel to improve machinability. While silicon can enhance certain properties of steel, such as strength and hardness, it does not have a significant effect on machinability. In fact, high silicon content can make steel more difficult to machine due to its tendency to form abrasive silicon oxide scales on the surface during machining.