Effect of alloying elements in low-carbon steels — improved ductility and bendability In ordinary low-carbon steels, which element is most beneficial for promoting ductility and good bending qualities by neutralising hot shortness and refining sulfidic inclusions?

Introduction / Context:
Small additions of alloying elements have outsized effects on the workability and toughness of structural steels. Understanding which elements help or harm ductility guides melt practice and specification of grades for forming and bending operations.

Given Data / Assumptions:

• Ordinary low-carbon steels (approx. 0.05–0.25% C) used for forming.
• Trace sulfur and phosphorus present as residuals.

Concept / Approach:
Manganese combines with sulfur to form manganese sulfide (MnS), which is less harmful than iron sulfide (FeS) that causes hot shortness by forming low-melting films at grain boundaries. By tying up sulfur and promoting cleaner grain boundaries, manganese improves hot workability and bend ductility. In moderate amounts, it also contributes to solid-solution strengthening without severely compromising elongation.

Step-by-Step Solution:

Verification / Alternative check:
Specifications often require Mn:S ratios above a threshold to ensure adequate hot ductility; bend tests and reduction-of-area values improve with adequate manganese for a given sulfur level.

Why Other Options Are Wrong:

• Sulphur: increases hot shortness; harmful to ductility.
• Phosphorus: increases cold shortness and raises ductile-to-brittle transition temperature.
• Silicon: primarily a deoxidiser; increases strength but can reduce ductility at higher levels.
• Chromium: adds hardenability and wear resistance rather than bend ductility in plain low-carbon steels.

Common Pitfalls:
Overlooking inclusion shape control; ignoring that excessive Mn or certain inclusion morphologies can still impair transverse ductility.

Final Answer: