Rails for heavy traffic and sharp curves — which alloy steel is preferred for superior wear resistance and toughness? Select the most appropriate material.

Introduction / Context:
Railway rails experience intense contact stresses, impact loads, and abrasive wear, especially under heavy traffic and on sharp curves where wheel–rail contact is severe. This question checks your knowledge of alloy selection for rails, emphasizing wear resistance, work-hardening behavior, and toughness that together extend rail life and reduce maintenance on demanding track segments.

Given Data / Assumptions:

• Operating environment involves heavy axle loads and tight curvature.
• Key properties required: high wear resistance, impact toughness, and resistance to surface fatigue.
• Standard alloy families considered: nickel steels, chromium steels, manganese steels, and vanadium steels.

Concept / Approach:
Manganese steel (notably Hadfield steel with ~12–14% Mn and high carbon) is renowned for exceptional work-hardening. Under impact and abrasion, its surface hardens significantly while retaining a tough, ductile core. This behavior is advantageous in high-stress track components. While plain carbon rails with modest Mn additions are common, high-manganese steels are classically preferred where wear and impact are extreme (e.g., sharp curves, crossings, and switches).

Step-by-Step Solution:

Verification / Alternative check:
Field practice often specifies manganese steel for components exposed to repeated impact and abrasive wear. Historical and modern rail metallurgy both recognize the unique work-hardening of high-Mn steels in demanding zones (e.g., crossings, guard rails, tight curves).

Why Other Options Are Wrong:

• Nickel steel: Adds toughness but lacks the distinctive work-hardening response of high-Mn steel.
• Chrome steel: Increases hardness; can be brittle if not balanced; not the classical choice for severe curve wear.
• Vanadium steel: Useful for grain refinement; not the standard for curve wear resistance.

Common Pitfalls:
Assuming the highest hardness always means best rails; without toughness and work-hardening, rails may crack under impact and thermal cycles on curves.

Final Answer:
Manganese steel