The percentage of carbon in cast iron varies from

Understanding the Definition of Cast Iron

The distinction between steel and cast iron is fundamentally defined by their carbon content. This dividing line is a critical concept in metallurgy.

Iron-Carbon Alloys:
• Steel is an iron-carbon alloy with a carbon content generally up to 2.1%.
• Cast Iron is an iron-carbon alloy with a carbon content above 2.1%, typically ranging up to about 4.5%.

Detailed Analysis of the Options

Let's evaluate each range based on the standard definitions of ferrous metals.

(d) 1.7 to 4.5

Why it's the best answer: This range is the broadest and most inclusive for what is considered cast iron. While the technical definition starts at 2.1% carbon, some older or broader classifications start the range slightly lower (around 1.7%). The upper limit of ~4.5% is correct, as this is near the saturation point of carbon in iron. This option is the only one that correctly covers the high-carbon nature of cast iron.

(a) 0.1 to 0.5

What it describes: This range covers low to medium carbon steel. Mild steel, the most common structural steel, falls squarely in this category.

(b) 0.5 to 1

What it describes: This range covers medium to high carbon steel. These steels are used for tools and springs that require high strength and hardness.

(c) 1 to 1.7

What it describes: This range covers very high carbon steel. These are specialized steels used for applications requiring extreme hardness and wear resistance.

Study Tips for Carbon Content

The 2% Dividing Line: The simplest way to remember is that steel is *below* ~2% carbon, and cast iron is *above* ~2% carbon.
Visualize the Spectrum: Picture a line of carbon content:
- Low Carbon Steel (Mild Steel)
- Medium Carbon Steel
- High Carbon Steel
- --- The 2% Wall ---
- Cast Iron
- Pig Iron (Highest Carbon)
Cast Iron = High Carbon: Always associate cast iron with a high percentage of carbon, which gives it its characteristic hardness and brittleness.