Millwright Level 1 Practice Exam

What percentage of carbon in a metal is considered the threshold for classifying it as cast iron?

1. 1.0%

2. 1.5%

3. 1.7%

4. 2.0%

The correct answer is: 1.7%

The classification of iron alloys is determined primarily by their carbon content. Specifically, when the carbon content in a metal reaches a certain threshold, it is categorized as cast iron. This threshold is typically recognized to be around 2.0% carbon. When the carbon content is between 2.0% and 4.0%, the metal exhibits properties distinct from those of wrought iron or steel, such as increased castability, fluidity in liquid form, and easier machinability in solid form. In the context of the given choices, the option providing 1.7% carbon does not meet the established threshold for cast iron classification. Although iron with a carbon content of 1.5% is closer, it still falls short of the minimum requirement. Both 1.0% and 1.5% are below the casting threshold. Consequently, the correct choice signifies a deeper understanding of how carbon concentration alters the characteristics of iron alloys, particularly in terms of their workability and application.