Metallurgy for permanent magnets Which alloying addition most effectively increases residual magnetism (remanence) in steels used for making permanent magnets?

Introduction / Context:
Permanent magnet steels require high remanence (residual magnetism) and high coercivity. Alloying elements can dramatically influence the magnetic domain structure and anisotropy, thereby altering magnetic performance.

Given Data / Assumptions:

• Base material: magnet steels or magnet alloys.
• Target property: higher residual magnetism (remanence) after magnetization.
• Consider common alloying additions: Cr, Ni, W, Co.

Concept / Approach:
Cobalt is well known for enhancing saturation magnetization and magnetic anisotropy. Classical permanent magnet materials (e.g., Alnico family) include significant cobalt, which raises remanence and energy product. Chromium typically improves corrosion resistance; nickel improves toughness and austenite stability; tungsten contributes to high-temperature strength but is not primary for maximizing remanence.

Step-by-Step Solution:
Identify element with strongest positive effect on remanence → cobalt.Relate to industrial magnet alloys (e.g., Alnico: Al–Ni–Co) where cobalt content is key to magnetic strength.Confirm others do not primarily increase residual magnetism compared to cobalt.

Verification / Alternative check:
Magnetic materials datasheets show increased Br (remanence) with cobalt content in many hard-magnetic alloys.

Why Other Options Are Wrong:

• Chromium: mainly corrosion and oxidation resistance; minor magnetic effect.
• Nickel: stabilizes austenite and used in soft magnets, but not the most effective for raising remanence in steels.
• Tungsten: improves hot strength/hardness rather than remanence.

Common Pitfalls:

• Confusing soft magnetic alloying (for transformers) with hard magnets (for remanence).

Final Answer:
Cobalt