Free-Cutting Steels — Intended Use and Cutting Behavior Which statement best reflects the purpose and application of free-cutting (free-machining) steels?

Introduction / Context:
Free-cutting steels are specially designed to improve machinability by modifying chip formation and reducing built-up edge. They typically contain additions like sulphur, lead, tellurium, or phosphorus (with manganese to control hot shortness) to form inclusions that aid chip breakage and lubrication at the tool–chip interface.

Given Data / Assumptions:

• Standard resulfurised or leaded grades are considered.
• Machining speed and tool life are key performance metrics.
• No requirement that these steels possess superior weldability or toughness.

Concept / Approach:
The hallmark of free-machining steels is productivity in turning, drilling, and tapping. They enable higher cutting speeds and better surface finish with lower tool wear. The phrase “rapid machining is the prime requirement” captures their intended use. They do not literally eliminate cutting forces or tool wear; rather, they improve the overall machining economics.

Step-by-Step Solution:
Identify the alloying strategy: S, Pb, etc., create inclusions that interrupt chips.Relate to practice: higher speeds, cleaner chip control, reduced downtime.Choose the option describing their purpose: rapid machining where productivity is vital.

Verification / Alternative check:
Machinability ratings in handbooks rank free-cutting steels far above plain mild steels for drilling and turning.

Why Other Options Are Wrong:
“Contain carbon in free form”: incorrect; free carbon is not the defining feature.“Require minimum cutting force”: forces may reduce but not to a universal “minimum.”“Can be cut freely (no tool wear)”: exaggeration; tool wear still occurs.“Improve weldability”: often they weld poorly due to S/P/Pb inclusions.

Common Pitfalls:
Confusing free-machining with high-strength structural steels; the goals differ.

Final Answer:
is used where rapid machining is the prime requirement