Ironmaking fundamentals – Composition of pig iron: The impure iron (pig iron) tapped from a blast furnace typically contains approximately what percentage of carbon by mass?

Introduction / Context:
Pig iron is the high-carbon iron product from the blast furnace, serving as a feedstock for steelmaking (basic oxygen furnace) or for cast iron production. Knowing its carbon level helps distinguish it from steel and cast irons and explains its brittleness and low ductility.

Given Data / Assumptions:

• Pig iron is the as-tapped product from a blast furnace using iron ore, coke, and fluxes.
• Contains carbon and impurities such as silicon, manganese, phosphorus, and sulfur.
• We seek the typical carbon percentage.

Concept / Approach:
Pig iron generally contains around 3–4.5% carbon. This high carbon content originates from the coke and the reducing atmosphere present in the furnace. The product is brittle and not malleable; subsequent refining lowers carbon to produce steels or retains high carbon with silicon for cast irons.

Step-by-Step Solution:
Recall typical composition band: C ≈ 3–4.5% for pig iron.Among the given options, 4% best matches the standard range.Conclude that ≈4% is the representative choice.

Verification / Alternative check:
Standard metallurgy texts show pig iron with high carbon plus silicon and other elements. Steel grades typically have much lower carbon (≤2%), distinguishing pig iron from steel by carbon level alone.

Why Other Options Are Wrong:

• 0.2%: corresponds to low-carbon (mild) steel, not pig iron.
• 2%: upper bound for steel/cast steel; too low for pig iron.
• 8%: unrealistically high; pig iron rarely exceeds ~4.5% C.

Common Pitfalls:
Confusing pig iron with cast irons; although both have high carbon, cast irons are engineered alloys often with silicon control and intended properties, while pig iron is the raw product from smelting.

Final Answer:
4%