Engineering Materials MCQ Questions & Answers | Mechanical Engineering

The machinability of steel is improved by adding Sulphur, lead and phosphorus

Nodular cast iron is produced by adding magnesium to the molten cast iron.

When manganese is added to aluminum, its strength is increased slightly through solution strengthening and its strain hardening is also improved

The copper provides substantial increases in strength and facilitates precipitation hardening.
The introduction of copper to aluminum can also reduce ductility and corrosion resistance.

Addition of lead and bismuth to aluminium results in Improving machinability

addition of silicon is for ease of casting.
Silicon is good in metallic alloys used for casting.
This is because it increases the fluidity of the melt, reduces the melting temperature, decreases the contraction associated with solidification and is very cheap as a raw material

* Carbon's Role: The primary factor determining steel hardness is the amount of carbon it contains. More carbon generally leads to higher hardness.

* Why Not the Others?
* Percentage of alloying elements: Alloying elements (like chromium, nickel, etc.) can increase hardness, but their influence is secondary to carbon. They mostly affect other properties like corrosion resistance or strength.
* Heat treatment employed: Heat treatment (like quenching, tempering) significantly alters hardness, but it primarily works by changing the microstructure of the steel, which is influenced by the carbon content. A steel with low carbon will not achieve very high hardness even with aggressive heat treatment.
* Shape of carbides and their distribution in iron: Carbides (compounds of iron and carbon) are important, and their shape and distribution certainly affect hardness. But, the amount of carbon available to form these carbides is the fundamental control.

In summary, while other factors play a role, the percentage of carbon is the most important and direct determinant of steel hardness.

Beryllium bronze contains 97.75% copper and 2.25% beryllium

Aluminium bronze contains 10% aluminium and 90% copper

The ultimate tensile strength and yield strength of most of the metals, when temperature falls from 0 to 100°C will Increase