Which material is molten impure iron from a blast furnace used for moulds, with good compressive strength but brittle, and used for brake discs, machine bases, vices, manhole covers, and engine blocks?

• A. High-speed steel
• B. Cast iron
• C. Copper
• D. Aluminium alloys

Answer: (B)

Cast iron, produced by melting pig iron from a blast furnace and allowing it to solidify in molds, has a distinctive combination: high compressive strength and good wear resistance, yet it is brittle under tension. This brittleness comes from its graphite-rich microstructure, which interrupts the continuity of the iron and makes crack propagation easy when pulled or bent, even though it can withstand heavy loads pressed together. The material also casts very well, filling complex shapes and producing good surface finishes, which is why it’s widely used for heavy components like brake discs, engine blocks, manhole covers, machine bases, and vices. Other metals such as high-speed steel are designed for cutting tools, while copper and aluminium alloys are generally too soft or lack the necessary wear resistance for these applications.