Key Takeaways
- ◆N42H is rated to 120 C continuous; N42SH is rated to 150 C. Both deliver 40-42 MGOe (BHmax), so the energy product and Br are nearly identical at room temperature.
- ◆The difference is intrinsic coercivity: N42H has Hcj >= 17 kOe at 20 C; N42SH has Hcj >= 20 kOe. That 3 kOe gap translates to roughly 30 C of additional thermal margin before the irreversible demagnetization knee enters the working region.
- ◆At 120 C, N42H retains approximately 10.6 kOe of coercivity. At 150 C, N42SH retains approximately 11.7 kOe. Both are tight against typical IPM load lines, which is why motor designers add 20-30 C of margin above worst-case operating temperature.
- ◆N42SH costs roughly 10-15% more than N42H due to higher Dy or Tb content. GBD-treated N48H can match N42SH coercivity at comparable or lower cost while delivering higher Br.
- ◆EV traction motors almost always specify SH or higher because locked-rotor events push magnet temperature well above the continuous rating. Humanoid actuators often use H grades for low-torque joints and SH for hips and shoulders.
Overview
N42H and N42SH are the two most commonly specified NdFeB grades for motors that operate above room temperature but below the extreme end of the thermal envelope. They share the same nominal energy product (40-42 MGOe) and similar remanence (approximately 1.28-1.32 T at 20 C). The only meaningful difference is coercivity, which determines how much thermal abuse the magnet can survive before it loses flux permanently. Choosing between them is a straightforward engineering tradeoff: how hot does your magnet actually get, and how much margin do you need against transient thermal events?
Side-by-Side Comparison
| Criterion | N42H | N42SH |
|---|---|---|
| BHmax (energy product) | 40-42 MGOe | 40-42 MGOe |
| Remanence (Br) at 20 C | 1.28-1.32 T | 1.28-1.32 T |
| Intrinsic coercivity (Hcj) at 20 C | >= 17 kOe | ✓>= 20 kOe |
| Max continuous operating temperature | 120 C | ✓150 C |
| Hcj retained at rated temperature | ~10.6 kOe at 120 C | ✓~11.7 kOe at 150 C |
| Dy/Tb content (weight %) | ✓1-3% | 3-6% |
| Cost per kg (relative) | ✓Baseline | +10-15% |
| Availability and lead time | Broadly available, 4-6 weeks | Broadly available, 4-6 weeks |
Green tick indicates the better option for the criterion. Winner assignment reflects typical engineering practice; your application may weight criteria differently.
When N42H Is the Right Choice
- •Motor operates below 110 C continuously with no stall-risk scenarios (e.g., industrial servos with liquid cooling and soft current limits)
- •Application is cost-sensitive and the 10-15% savings per kg of magnet matters at production volumes
- •GBD post-processing is available from your supplier, allowing N42H (or N48H) to be boosted to SH-level coercivity without the Br penalty
- •Operating environment has low demagnetizing field exposure (high permeance coefficient magnetic circuit, no locked-rotor testing requirement)
When N42SH Is the Right Choice
- •Worst-case magnet temperature exceeds 120 C, including transient events like locked-rotor or stall under load
- •Automotive Tier 1 qualification requires survival of a locked-rotor test at rated coolant temperature, which typically drives magnet temperature to 140-160 C
- •Application has no active cooling (air-cooled humanoid actuators, small BLDC motors) and must survive thermal soak
- •Design requires margin against hot-spot uncertainty, manufacturing variation in magnet placement, or degradation over 15+ year service life
- •Customer specification or test standard explicitly requires SH-grade minimum (common in EV and wind OEM specs)
Decision Framework
Start with your worst-case magnet temperature, not your average operating temperature. Include transient events: locked-rotor, stall under load, cooling system failure, and hot-climate soak. If that worst case stays below 100 C with margin, N42H is the right grade and the 10-15% cost savings is real money at volume. If it reaches 120-140 C or if locked-rotor testing is part of your qualification, N42SH is the safer specification. The gray zone is 100-120 C, where N42H technically works but has thin margin. In that zone, consider GBD-treated N48H: it matches N42SH coercivity while delivering higher Br (approximately 1.36 T vs 1.30 T), giving you both thermal margin and torque density. The price sits between N42H and N42SH. For any application above 150 C, both grades are undersized and you should be looking at UH or EH families.
Related NdFeB Grades
N42
80°CHigh-performance sintered NdFeB grade widely used in compact motors, generators, and precision actuators.
N42H
120°CWorkhorse high-temperature NdFeB grade for automotive motors, pumps, and industrial drives up to 120°C.
N42SH
150°CWorkhorse SH-grade NdFeB for 150°C traction motors, robotics actuators, and high-duty servo drives.
N42UH
180°CHigh-performance UH-grade NdFeB for the most demanding traction, aerospace, and industrial motor applications.
N42EH
200°CHighest commercial EH-grade NdFeB — the upper limit of 200°C NdFeB in production today.
Related Applications
EV Motors
High-performance NdFeB magnets for electric vehicle traction motors, auxiliary drives, and e-axle systems — with the temperature stability and flux density required for continuous high-torque service.
Robotics
Radial multi-pole rings, joint-motor magnets, and high-torque servo-motor assemblies for humanoid robots, collaborative robots, and industrial robotic systems.
Industrial Automation
NdFeB magnets for stepper motors, servo drives, linear actuators, magnetic couplings, and factory automation equipment across European and North American manufacturing.
Frequently Asked Questions
Can I use N42H in an EV traction motor?
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It depends on the thermal design. Liquid-cooled IPM motors with well-designed rotor cooling can keep magnet temperatures below 120 C during normal operation, which is within N42H range. However, most automotive OEMs require survival of a locked-rotor test that pushes magnet temperatures to 140-160 C for several seconds. N42H will likely demagnetize irreversibly during that test. For this reason, most EV traction motors specify SH as the minimum grade family.
Is N42SH always better than N42H?
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N42SH has higher coercivity and can survive higher temperatures, but it is not universally better. If your application never exceeds 100 C, N42H delivers the same magnetic performance at 10-15% lower cost. Over-specifying SH when H is sufficient wastes money without improving motor performance. The higher Dy/Tb content in SH grades also makes the supply chain more sensitive to rare earth price swings.
What does GBD do to these grades?
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Grain boundary diffusion deposits a thin layer of Dy or Tb at the grain boundaries without bulk-substituting throughout the grain. Applied to N42H (or better, N48H), GBD can boost Hcj by 5-8 kOe, pushing it into N42SH territory. The advantage is that Br drops only 0.02-0.04 T instead of the 0.10-0.15 T penalty of conventional full substitution. GBD-treated N48H typically costs 5-10% less than conventional N42SH while delivering higher remanence.
How do I specify the right grade in an RFQ?
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State your worst-case operating temperature (including transients), the demagnetizing field at the worst load point (or provide the motor geometry so the supplier can calculate it), and the minimum Br you need at operating temperature. A good supplier will recommend the grade and can provide B-H curves at your specific operating temperature. Avoid specifying grade by name without thermal context, as the right grade depends on your magnetic circuit, not just temperature alone.
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