Alloy Additions — Do Sulphur, Lead, and Phosphorus Increase Steel Hardness? State whether the statement “Hardness of steel is increased by adding sulphur, lead and phosphorus” is correct in general engineering practice.

Introduction / Context:Minor additions like sulphur (S), lead (Pb), and phosphorus (P) are often used in specific steels, but their main roles differ from classic hardness-raising alloying elements such as carbon, chromium, or molybdenum. Understanding what each element does prevents design and processing mistakes.

Given Data / Assumptions:

• The statement claims a general increase in hardness due to S, Pb, and P.
• We consider typical low-to-medium carbon steels used for machining and structural purposes.
• Heat treatment state is not specially optimized for hardness.

Concept / Approach:S and Pb are primarily added to improve machinability. Sulphur combines with manganese to form MnS inclusions that break chips and reduce built-up edge; lead acts as a solid lubricant in free-machining steels. Phosphorus can raise strength and yield slightly via solution strengthening, but it severely reduces toughness and ductility; it is often kept low except in rephosphorised sheet grades. None of these elements is deliberately added mainly to raise hardness; carbon content, quenchability, and carbide-forming alloying elements control hardness far more effectively.

Step-by-Step Solution:Assess roles: S/Pb → machinability; P → strength increase with embrittlement risk.Connect to hardness: marginal or adverse effects on overall hardness; not a primary hardening strategy.Conclude the general claim is false.

Verification / Alternative check:Handbooks show free-machining steels have similar base hardness to comparable carbon steels unless heat-treated; improvements are in machinability, not inherent hardness.

Why Other Options Are Wrong:“Yes” overstates their influence; S and Pb especially do not raise hardness.Conditions like “only for tool steels” or “only after quench” misattribute effects; tool steel hardness depends on C and carbide formers (Cr, Mo, V, W).

Common Pitfalls:Confusing machinability improvements with hardness gains; they are distinct metrics.

Final Answer:No