(a) Define the meaning of the term alloy, stating why they are used.
An alloy is a mixture of two or more metals, or a metal combined with one or more nonmetals. Alloys are used because they often have properties that are superior to those of the pure metals that make them up. For example, alloys can be stronger, harder, more corrosion-resistant, or more conductive than pure metals.
Here are some specific examples of why alloys are used:
- Steel is an alloy of iron and carbon. It is much stronger than pure iron, making it an ideal material for construction, bridges, and tools.
- Brass is an alloy of copper and zinc. It is more resistant to corrosion than pure copper, making it a good material for plumbing fixtures and musical instruments.
- Solder is an alloy of tin and lead. It has a low melting point, making it easy to use for joining metals together.
(b) Describe the changes in the mechanical properties of steel with increasing amounts of carbon.
As the amount of carbon in steel increases, its strength and hardness also increase. However, its ductility and toughness decrease. This means that high-carbon steel is strong and hard, but it is also brittle and more likely to crack. Low-carbon steel is less strong and hard, but it is more ductile and tough, making it more resistant to breaking.
The amount of carbon in steel is typically expressed as a percentage. For example, mild steel has a carbon content of about 0.2%, while high-carbon steel has a carbon content of about 1%.
(c) List six common alloying elements used in the production of steel.
Six common alloying elements used in the production of steel are:
- Carbon: Increases strength and hardness, but decreases ductility and toughness.
- Manganese: Increases strength, hardenability, and resistance to wear and tear.
- Silicon: Increases strength, hardenability, and resistance to oxidation.
- Chromium: Increases strength, hardenability, and resistance to corrosion.
- Nickel: Increases strength, toughness, and ductility at low temperatures.
- Molybdenum: Increases strength, hardenability, and resistance to creep (deformation under stress at high temperatures).