Low-Carbon Steels — Effect of Small Sulphur Additions In low-carbon steels, the presence of small amounts of sulphur primarily improves which property (with typical resulfurised grades)?

Introduction / Context:
Resulfurised free-machining steels are engineered to cut easily, break chips, and reduce tool wear. The role of sulphur (often with manganese) is to form inclusions that act as internal chip-breaking and lubricating sites in the shear zone during machining operations.

Given Data / Assumptions:

• Base chemistry: low carbon steels.
• Small sulphur additions (with adequate manganese to avoid hot shortness).
• Objective: identify the dominant property improvement.

Concept / Approach:
Sulphur combines with manganese to form MnS inclusions. These inclusions encourage chip segmentation and reduce built-up edge, thereby improving machinability. However, sulphur tends to reduce ductility, weldability, and impact toughness, which is why such steels are used primarily where extensive machining is required but high toughness is not critical.

Step-by-Step Solution:
Note inclusion engineering: MnS dispersoids modify chip formation.Relate to process outcome: lower cutting forces and better surface finish at given settings.Conclude machinability gains outweigh other properties, which may decline.

Verification / Alternative check:
Material datasheets list “S-resulfurised” grades (e.g., 12L14, 11XX) with superior machinability ratings versus plain low-carbon steels.

Why Other Options Are Wrong:
Weldability and formability generally deteriorate with sulphur additions.Hardenability is governed mainly by alloying and carbon, not small S additions.Corrosion resistance is not improved by sulphur in low-carbon steels.

Common Pitfalls:
Confusing the effect of lead or sulfur; both are used in free-machining grades but have similar machining benefits with different mechanisms.

Final Answer:
machinability