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

ANS:B - silicon

Silicon is often added to steel for various reasons, but it doesn't significantly improve machinability. Instead, it primarily affects other properties of the steel. Here's how silicon influences steel:

1. Deoxidization: Silicon is commonly used as a deoxidizer in the steelmaking process. During steel production, impurities such as oxygen can adversely affect the steel's properties. Silicon reacts with oxygen to form silica (SiO2), which floats to the surface of the molten steel and can be easily removed. This helps in producing cleaner steel with fewer impurities.
2. Strength and Hardenability: Silicon can enhance the strength and hardenability of steel. It forms solid solution strengthening with iron, contributing to increased strength and hardness. This property is particularly important in certain applications where high strength and hardness are required, such as in automotive components and machinery parts.
3. Heat Resistance: Silicon improves the heat resistance of steel. It helps in maintaining the structural integrity of steel at elevated temperatures, making it suitable for applications involving high temperatures, such as in furnace components and engine parts.
4. Magnetic Properties: Silicon can influence the magnetic properties of steel. Silicon steel, also known as electrical steel, contains high levels of silicon and is used in electrical transformers and motors due to its low core loss and high magnetic permeability.

While silicon has these beneficial effects on steel, it does not significantly affect machinability. Machinability primarily depends on factors such as the composition, microstructure, and mechanical properties of the steel, as well as the machining conditions and tools used. Other elements, such as lead or sulphur, are more commonly associated with improving machinability by forming free-machining steels.