Hot shortness prevention in steels Which alloying element is most effective at reducing the formation of low-melting iron sulphide (FeS) in steel, thereby preventing hot shortness during hot working?

Introduction / Context:
Hot shortness in steels arises when iron sulphide forms along grain boundaries, melting at hot-working temperatures and causing intergranular cracking. Alloy design can mitigate this by tying up sulphur into benign compounds.

Given Data / Assumptions:

• Trace sulphur is present as an impurity in many steels.
• Prevention approach: form high-melting sulphides that do not wet grain boundaries.
• Standard practices include intentional Mn additions in steelmaking.

Concept / Approach:
Manganese has strong affinity for sulphur, forming manganese sulphide (MnS), which has a much higher melting point than FeS and is non-deleterious at hot-working temperatures. MnS particles are typically dispersed and can be controlled by processing; they prevent FeS films from forming at grain boundaries.

Step-by-Step Solution:
Recognize problem: FeS melts at low temperature and causes hot brittleness.Select solution: add Mn so that S preferentially forms MnS.Result: reduced hot shortness and improved hot workability.Therefore, manganese is the correct alloying element.

Verification / Alternative check:
Steelmaking practice maintains Mn/S ratio above a threshold (often >= 8) to ensure sulphur is bound as MnS rather than FeS.

Why Other Options Are Wrong:
Chromium, nickel, vanadium, and molybdenum offer other benefits (corrosion resistance, hardenability, precipitation strengthening) but are not primary sulphur fixers in standard steels.

Common Pitfalls:
Confusing desulphurisation in the ladle (with fluxes) versus in-solid solution control; Mn addition is a direct metallurgical fix inside the steel matrix.

Final Answer:
manganese