Steel classification by carbon content — name at 0.8% C A plain carbon steel containing approximately 0.8% carbon is known as:

Introduction / Context:
Steel nomenclature often references the eutectoid composition, near which austenite transforms into a lamellar mixture of ferrite and cementite upon slow cooling. Identifying this composition is central to understanding pearlite formation and heat treatment behavior.

Given Data / Assumptions:

• Eutectoid composition in plain carbon steel is about 0.8% carbon (sometimes cited as 0.77% depending on source).
• Terminology: hypo-eutectoid < 0.8% C; eutectoid ≈ 0.8% C; hyper-eutectoid > 0.8% C.

Concept / Approach:
At the eutectoid composition, austenite decomposes isothermally at the eutectoid temperature to form 100% pearlite in equilibrium transformation. This composition is therefore called eutectoid steel. Below it, proeutectoid ferrite forms in addition to pearlite; above it, proeutectoid cementite forms.

Step-by-Step Solution:
Recognize 0.8% C as the eutectoid point in plain carbon steel.Assign the correct classification: eutectoid steel.Rule out hypo- and hyper-eutectoid by their definitions relative to 0.8% C.

Verification / Alternative check:
Standard Fe–C diagrams and materials texts consistently cite the eutectoid composition near 0.8% C, reinforcing the term eutectoid steel for that carbon level.

Why Other Options Are Wrong:

• Hyper-eutectoid: refers to carbon content greater than 0.8% C.
• Hypo-eutectoid: refers to carbon content less than 0.8% C.
• Eutectic steel: eutectic applies to the cast-iron range near 4.3% C, not steels at 0.8% C.

Common Pitfalls:
Mixing up eutectic with eutectoid terminology; the former describes liquid to two solid transformation in cast irons, the latter describes solid-state transformation in steels.

Final Answer:
eutectoid steel