all the original NdFeB magnet patents (both sintered and bonded) have long since expired.
Here’s a clear breakdown
Sintered NdFeB (Sumitomo / Masato Sagawa)
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Key U.S. Patent: US 4,588,439
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Filed: November 26, 1984
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Granted: October 21, 1986
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Patent term: 17 years from the issue date (for pre-1995 U.S. patents)
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Expired: October 21, 2003
Status: Expired worldwide — any company can now manufacture sintered NdFeB magnets using similar basic compositions and processes (as long as they don’t infringe later improvements).
Bonded NdFeB (GM / John J. Croat)
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Key U.S. Patent: US 4,496,395
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Filed: September 30, 1983
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Granted: January 29, 1985
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Expired: January 29, 2002
Status: Also expired.
What Still Might Be Protected
Although the foundational patents (1980s) have expired, later-generation improvements are still under active protection — for example:
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Grain boundary diffusion (Dy/Tb infiltration) for high-temperature coercivity
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Corrosion-resistant coatings and binders
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Nanocrystalline or additive-manufactured NdFeB
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Sintering aids, orientation control, and recycling processes
Those were mainly filed from the 2000s–2020s by companies like Hitachi Metals, Shin-Etsu, VAC (Vacuumschmelze), and Beijing Zhong Ke San Huan.
Summary
| Patent | Inventor | Type | Filed | Expired | Status |
|---|---|---|---|---|---|
| US 4,588,439 | Masato Sagawa (Sumitomo) | Sintered NdFeB | 1984 | 2003 | Expired |
| US 4,496,395 | John J. Croat (GM) | Bonded NdFeB | 1983 | 2002 | Expired |
现在在大美和中国有效的专利：
United States
In the U.S., numerous patents cover various aspects of sintered NdFeB magnets:
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Manufacturing Methods: Innovations in processes for producing high-coercivity sintered NdFeB magnets, including grain-boundary diffusion techniques and the application of heavy rare earth elements.
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Material Enhancements: Development of compositions that improve magnetic properties and resistance to environmental factors.
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Surface Treatments: Methods to enhance corrosion resistance and other surface characteristics of the magnets.
Companies like Hitachi Metals and Proterial hold extensive patent portfolios in this field. For instance, Hitachi Metals is reported to hold over 600 patents worldwide related to sintered NdFeB magnets American Bar Association.
China
China is a major hub for the development and production of sintered NdFeB magnets, with a significant number of patents:
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Innovative Manufacturing Techniques: Patents focusing on grain-boundary diffusion methods and the incorporation of heavy rare earth elements to enhance magnetic properties.
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Material Composition Improvements: Development of new compositions to improve the performance and durability of NdFeB magnets.
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Surface Coatings: Methods to apply coatings that enhance corrosion resistance and other surface properties.
For example, Proterial has emphasized its extensive patent portfolio in sintered NdFeB magnets, indicating a strong presence in the Chinese market proterial.com.
