Materials and corrosion — Which of the following treatments does NOT prevent corrosion of metals?

Introduction:
Corrosion prevention relies on surface treatments, material selection, and electrochemical control. Some heat treatments enhance mechanical properties but do not inherently protect against electrochemical attack. Distinguishing these methods is crucial when specifying protection for service environments.

Given Data / Assumptions:

• We consider common corrosion-mitigation strategies versus purely mechanical-property heat treatments.
• Surface diffusion coatings (chromising, aluminising) and alloying can improve corrosion resistance.
• Tempering is a heat treatment to adjust hardness/toughness after quenching.

Concept / Approach:

Tempering reduces residual stresses and modifies microstructure (e.g., tempered martensite) but does not provide a protective chemical barrier or change corrosion potential significantly. In contrast, chromising and aluminising form protective diffusion layers (Cr-rich or Al-rich) that oxidize to stable films. Alloying (e.g., Cr in stainless steels) increases passivation. Electrochemical methods like cathodic protection alter corrosion currents to suppress metal dissolution.

Step-by-Step Solution:

Verification / Alternative check:

Metallurgy handbooks show corrosion resistance changes primarily with alloy composition, surface treatments, and environment—not with tempering temperature alone.

Why Other Options Are Wrong:

B/C form protective intermetallic/diffusion layers. D tailors composition for passivity (e.g., stainless steels). E directly prevents corrosion via impressed current/ sacrificial anodes.

Common Pitfalls:

Assuming higher hardness automatically improves corrosion resistance; often it does not and may worsen stress-corrosion susceptibility.

Final Answer:

tempering