What do the different product grades of sintered NdFeB mean?

NdFeB strong magnetic grades are in contact with friends in the magnetics-related industries every day, so what is behind these complex grades? What are the differences between different grades of NdFeB magnets? How to choose the appropriate NdFeB magnetic material by grade? Today I will give you a systematic explanation.

Magnetic Characteristics of Sintered NdFeB Magnets

Grade Remanence  Coercive Force  Intrinsic Coercive force  Max Energy Product  Max Working Temp.
Br Hcb Hci (BH) max
KG T KOe KA/m KOe KA/m MGOe KJ/m °F
N35 11.4-11.8 1.18-1.28 ≥ 10.8 ≥ 836 ≥ 12 ≥ 955 33-36 263-287 80 176
N38 11.8-12.3 1.18-1.28 ≥ 10.8 ≥ 860 ≥ 12 ≥ 955 36-39 287-310 80 176
N40 12.7-12.9 1.27-1.29 ≥ 11.0 ≥ 876 ≥ 12 ≥ 955 38-41 303-326 80 176
N42 12.9-13.3 1.29-1.33 ≥ 10.5 ≥ 836 ≥ 12 ≥ 955 40-43 318-342 80 176
N45 13.3-13.8 1.33-1.38 ≥ 9.5 ≥ 756 ≥ 12 ≥ 955 43-46 342-366 80 176
N48 13.8-14.2 1.38-1.42 ≥ 10.5 ≥ 835 ≥ 12 ≥ 955 46-49 366-390 80 176
N50 13.8-14.5 1.38-1.45 ≥ 10.5 ≥ 835 ≥ 11 ≥ 955 47-51 374-406 80 176
N52 14.3-14.8 1.43-1.48 ≥ 10.8 ≥ 860 ≥ 11 ≥ 876 50-53 398-422 80 176
33M 11.4-11.8 1.14-1.18 ≥ 10.3 ≥ 820 ≥ 14 ≥ 1114 31-33 247-263 100 212
35M 11.8-12.3 1.18-1.23 ≥ 10.8 ≥ 860 ≥ 14 ≥ 1114 33-36 263-287 100 212
38M 12.3-12.7 1.23-1.27 ≥ 11.0 ≥ 876 ≥ 14 ≥ 1114 38-41 303-326 100 212
40M 12.7-12.9 1.27-1.29 ≥ 11.4 ≥ 907 ≥ 14 ≥ 1114 38-41 303-326 100 212
42M 12.8-13.2 1.28-1.32 ≥ 11.6 ≥ 923 ≥ 14 ≥1114 40-43 318-342 100 212
45M 13.2-13.8 1.32-1.38 ≥ 11.8 ≥ 939 ≥ 14 ≥ 1114 43-46 342-366 100 212
48M 13.6-14.0 1.36-1.40 ≥ 11.8 ≥ 939 ≥ 14 ≥ 1114 46-49 366-390 100 212
50M 14.0-14.5 1.40-1.45 ≥ 13.0 ≥ 1033 ≥ 14 ≥ 1114 48-51 382-406 100 212
30H 10.8-11.4 1.08-1.14 ≥ 10.2 ≥ 812 ≥ 17 ≥ 1353 28-31 223-247 120 248
33H 11.4-11.8 1.14-1.18 ≥ 10.6 ≥ 844 ≥ 17 ≥ 1353 31-33 247-263 120 248
35H 11.8-12.3 1.18-1.28 ≥ 11.0 ≥ 876 ≥ 17 ≥ 1353 33-36 263-287 120 248
38H 12.3-12.7 1.23-1.27 ≥ 11.2 ≥ 890 ≥ 17 ≥ 1353 36-39 287-310 120 248
40H 12.7-12.9 1.27-1.29 ≥ 11.5 ≥ 915 ≥ 17 ≥ 1353 38-41 303-326 120 248
42H 12.8-13.2 1.28-1.32 ≥ 12.0 ≥ 955 ≥ 17 ≥ 1353 40-43 318-342 120 248
45H 13.2-13.5 1.32-1.38 ≥ 12.0 ≥ 955 ≥ 17 ≥ 1353 42-46 335-366 120 248
46H 13.3-13.8 1.33-1.38 ≥ 12.2 ≥ 972 ≥ 16 ≥ 1274 44-47 350-374 120 248
48H 13.6-14.3 1.36-1.43 ≥ 12.5 ≥ 995 ≥ 16 ≥ 1274 46-49 366-390 120 248
30SH 10.8-11.4 1.081.14 ≥ 10.0 ≥ 796 ≥ 20 ≥ 1672 28-31 223-247 150 302
33SH 11.4-11.8 1.14-1.18 ≥ 10.5 ≥ 836 ≥ 20 ≥ 1672 31-34 247-276 150 302
35SH 11.8-12.3 1.18-1.23 ≥ 11.0 ≥ 876 ≥ 20 ≥ 1672 33-36 263-287 150 302
38SH 12.3-12.7 1.23-1.27 ≥ 11.4 ≥ 907 ≥ 20 ≥ 1972 36-39 287-310 150 302
40SH 12.5-12.8 1.25-1.28 ≥ 11.8 ≥ 939 ≥ 20 ≥ 1972 38-41 302-326 150 302
42SH 12.8-13.2 1.28-1.32 ≥ 11.8 ≥ 939 ≥ 20 ≥ 1672 40-43 320-343 150 302
45SH 13.2-13.8 1.32-1.38 ≥ 12.6 ≥ 1003 ≥ 20 ≥ 1592 43-46 342-366 150 302
30UH 10.8-11.4 1.08-1.14 ≥ 10.2 ≥ 812 ≥ 25 ≥ 1990 28-31 223-247 180 356
33UH 11.3-11.7 1.13-1.17 ≥ 10.7 ≥ 852 ≥ 25 ≥ 1990 31-33 247-263 180 356
35UH 11.7-12.1 1.17-1.21 ≥ 10.7 ≥ 852 ≥ 25 ≥ 1990 33-36 263-287 180 356
38UH 12.1-12.5 1.21-1.25 ≥ 11.4 ≥ 907 ≥ 25 ≥ 1990 36-39 287-310 180 356
40UH 12.5-12.8 1.25-1.28 ≥ 11.4 ≥ 907 ≥ 25 ≥ 1990 38-41 302-326 180 356
28EH 10.5-10.8 1.05-1.08 ≥ 9.5 ≥ 756 ≥ 30 ≥ 2388 26-29 207-231 200 392
30EH 10.8-11.4 1.08-1.14 ≥ 9.5 ≥ 756 ≥ 30 ≥ 2388 28-31 223-241 200 292
33EH 11.3-11.7 1.13-1.17 ≥ 10.2 ≥ 812 ≥ 30 ≥ 2388 31-33 247-263 200 392
35EH 11.7-12.1 1.17-1.21 ≥ 10.2 ≥ 812 ≥ 30 ≥ 2388 33-36 263-287 200 392
38EH 12.1-12.5 1.21-1.25 ≥ 11.4 ≥ 907 ≥ 30 ≥ 2388 36-39 287-310 200 392
30AH 10.8-11.3 1.08-1.13 ≥ 10.2 ≥ 812 ≥ 35 ≥ 2785 28-32 223-255 220 428
33AH 11.2-11.7 1.12-1.17 ≥ 10.2 ≥ 812 ≥ 35 ≥ 2785 31-34 247-271 220 428

First, the common sintered NdFeB grades can be divided into seven categories: N, M, H, SH, UH, EH and TH. Except for the N type, every other type will appear at the end of the product brand. For example, N38M is M series, N38TH is TH series, and if there is no letter after “N38”, then it is N series. (Of course, there are some uncommon and higher-performance grades in the back.

Secondly, there are four main indicators for measuring the performance of sintered NdFeB products.

  • Br remanence: the unit is Tesla (T) and Gauss (Gs), 1Gs = 0.0001T. It refers to the magnetic induction intensity of a sintered neodymium iron boron magnet when a magnet is magnetized by an external magnetic field in a closed circuit environment until the technology is saturated and then the external magnetic field is cancelled. In layman’s terms, it can be temporarily understood as the magnetic force of the magnet after magnetization.
  • Hcb Coercivity: The unit is Oersted (Oe) or Ampere/meter (A/m), 1A/m=(4π/1000)Oe, 1 Oe=(1000/4π) A/m. When the magnet is magnetized in the reverse direction, the value of the reverse magnetic field strength required to reduce the magnetic induction intensity to zero is called the magnetic coercive force. But at this time, the magnetization of the magnet is not zero, but the applied reverse magnetic field and the magnetization of the magnet cancel each other out. At this time, if the external magnetic field is removed, the magnet still has certain magnetic properties.
  • Hcj Intrinsic coercivity: The strength of the reverse magnetic field required to reduce the magnetization of the magnet to zero. We call it the intrinsic coercive force. Its unit of measurement is the same as the coercive force. The classification of magnetic grades is based on their intrinsic coercivity. Low coercivity N, medium coercivity M, high coercivity H, ultra-high coercivity UH, extremely high coercivity EH, highest coercivity TH. The intrinsic coercivity of NdFeB magnets will decrease as the temperature rises. Therefore, when choosing to use NdFeB magnets, you must choose the grade that suits us. The next issue will be further introduction
  • (BH)max Maximum magnetic energy product: represents the magnetic energy density established in the space between the two magnetic poles of the magnet, that is, the static magnetic energy per unit volume of the air gap, which is the maximum value of the product of B and H, and its size directly indicates the performance of the magnet . The numbers in the magnetic grades represent the theoretical maximum energy product of the product.

Again, we can see that there are two measurement units for each performance index. This is because they use different unit systems— SI system and CGS system, that is, the international system of units and the Gaussian system of units, which are like length units. The difference between “m” and “li”. There is a certain conversion relationship between the International System of Units and the Gaussian System of Units, but it is more complicated, so we won’t introduce it.
Finally, it is not difficult to find that the performance of sintered NdFeB products under each brand is not a unique fixed value, but a numerical range. The performance ranges of products from different manufacturers are not completely the same. You should pay special attention to whether the performance of the supplier’s products can meet your requirements when purchasing.

Thermal Characteristics of Sintered NdFeB Magnets

Neodymium Material Type Maximum Operating Temp Curie Temp
N 176°F (80°C) 590°F (310°C)
M 212°F (100°C) 644°F (340°C)
H 248°F (120°C) 644°F (340°C)
SH 302°F (150°C) 644°F (340°C)
UH 356°F (180°C) 662°F (350°C)
EH 392°F (200°C) 662°F (350°C)
AH 428°F (220°C) 662°F (350°C)

Physical and Mechanical Characteristics of Sintered NdFeB Magnets

Density 7.4-7.5 g/cm3
Compression Strength 950 MPa (137,800 psi)
Tensile Strength 80 MPa (11,600 psi)
Vickers Hardness (Hv) 560-600
Young’s Modulus 160 GPa (23,200 ksi)
Recoil Permeability 1.05 μrec
Electrical Resistivity (ρ) 160 μ-ohm-cm
Heat Capacity 350-500 J/(kg.°C)
Thermal Expansion Coefficient (0 to 100°C) 5.2 x 10-6 /°C
parallel to magnetization direction
Thermal Expansion Coefficient (0 to 100°C) -0.8 x 10-6 /°C
Perpendicular to magnetization direction

Plating Characteristics of Sintered NdFeB Magnets

Plating Type Overall Thickness Salt Spray Test Pressure Cooker Test
NiCuNi (Nickel Copper Nickel) 15-21 μm 24 hours 48 hours
NiCu + Black Nickel 15-21 μm 24 hours 48 hours
NiCuNi + Epoxy 20-28 μm 48 hours 72 hours
NiCuNi + Gold 16-23 μm 36 hours 72 hours
NiCuNi + Silver 16-23 μm 24 hours 48 hours
Zinc 7-15 μm 12 hours 24 hours

Each individual layer of Nickel and Copper are 5-7 μm thick. The Gold and Silver plating layers are 1-2 μm thick. Test results shown to allow comparison between plating options. Performance in your application under your specific test conditions may vary. Salt Spray testing conducted with a 5% NaCl solution, at 35°C. Pressure Cooker Test (PCT) conducted at 2 atm, 120°C at 100% RH.

Measurement Systems of Sintered NdFeB Magnets

Unit cgs System SI System English System
Length (L) centimeter (cm) meter (m) inch (in)
Flux (ø) Maxwell Weber (Wb) Maxwell
Flux Density (B) Gauss (G) Tesla (T) lines/in2
Magnetizing Force (H) Oersted (Oe) Ampere turns/m (At/m) Ampere turns/in (At/in)
Magnetomotive Force (mmf or F) Gilbert (Gb) Ampere turn (At) Ampere turn (At)

Conversion Between Systems of Sintered NdFeB Magnets

CGS System to SI system
1 Oe = 79.62 At/m
10,000 G = 1 T
1 Gb = 0.79577 At
1 Maxwell = 1 Line = 10-8 Wb
1 G = 0.155 lines/in2

How to distinguish between sintered NdFeB magnet and bonded NdFeB magnet?

Neodymium magnet is the industry name for neodymium iron boron powerful magnets. Its chemical formula is Nd2Fe14B. It is a man-made powerful magnet and has the strongest magnetic force so far. The material grades of NdFeB magnets are N25-N52EH; the shapes can be processed into different shapes according to specific requirements, including round, diamond, square, perforated, magnetic tile, racetrack, convex, concave, trapezoidal or Semicircle etc.
How to distinguish bonded NdFeB and sintered NdFeB? In fact, both of these magnetic materials belong to NdFeB. The difference between these two types of magnets is based on their production process. The bonded neodymium iron boron magnet is actually formed by injection molding, while the sintered neodymium iron boron magnet is formed by evacuation and then high-temperature heating and pressing.
The bonded neodymium iron boron magnet is formed by injection molding, so it contains an adhesive, the density of which is generally only about 75% of theoretical. The sintered NdFeB magnet is heated at a high temperature through a complicated process. Therefore, the bonded NdFeB magnet is attenuated by about 25% compared to the sintered NdFeB magnet.
Sintered NdFeB is an anisotropic magnet produced by powder sintering. Generally, only a blank can be produced after sintering, and then through mechanical processing (such as wire cutting, slicing, grinding, etc.) to become magnets of various shapes. Sintered NdFeB is a hard and brittle material that is difficult to process. It has high loss during processing, high cost, poor dimensional accuracy, poor corrosion resistance, and the surface needs to be electroplated. But the advantage is that it has higher performance, and it has achieved N52H at present.
In summary, the magnetic properties of bonded NdFeB magnets are only about 6% of that of sintered. At present, the energy product of sintered NdFeB magnets can reach above N52H, while the bonded magnets are generally below 10T, and the best is only 12M. The performance of the magnetic powder used in the bonded magnet is generally 15T, and the bonded magnet is only 10.5T at most. Therefore, sintered NdFeB is generally used in a wider range than bonded NdFeB.

Source: China Permanent Magnet Manufacturer – www.ymagnet.com

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