Magnetic materials – cobalt content in cobalt steel for permanent magnets Permanent magnets are made from high carbon steel alloyed with approximately what percentage of cobalt?

Difficulty: Easy

Correct Answer: 35% cobalt

Explanation:


Introduction:
Permanent magnet materials must exhibit high coercivity and good retentivity. Historically, cobalt steels and later AlNiCo and rare-earth magnets have been used for strong permanent magnets. This question targets a classic composition range for cobalt steel magnets used in engineering contexts.


Given Data / Assumptions:

  • Material class: cobalt steel (prior to or alongside AlNiCo developments).
  • High carbon steel is alloyed with cobalt to increase coercivity.
  • We choose the commonly quoted cobalt percentage.


Concept / Approach:

Cobalt addition to high carbon steel significantly improves magnetic hardness (coercive force). Traditional references describe cobalt steels for permanent magnets containing roughly one-third cobalt by weight, i.e., about 35%. This composition yields improved ability to retain magnetization compared with plain carbon steel.


Step-by-Step Solution:

1) Identify the alloy system: cobalt steel based on high carbon steel.2) Recall typical cobalt range used to raise coercivity: around 35% is widely cited.3) Select the option that matches the established figure: 35% cobalt.


Verification / Alternative check:

Classic materials texts list cobalt steels with ~35% cobalt for permanent magnets, preceding the extensive use of AlNiCo and rare-earth magnets. This aligns with the option given.


Why Other Options Are Wrong:

15% / 20%: Lower cobalt content typically does not deliver the same coercivity as the established 35% composition.

45%: Higher than common cobalt steel compositions cited for traditional permanent magnets, impacting cost and properties.


Common Pitfalls:

Confusing cobalt steel compositions with AlNiCo alloys; assuming any cobalt addition is sufficient without considering the established optimum ranges.


Final Answer:

35% cobalt

More Questions from Building Materials

Discussion & Comments

No comments yet. Be the first to comment!
Join Discussion