Two electrical steel grades with similar thickness or core-loss ratings can still behave differently as the magnetizing field increases, particularly near the knee and saturation regions.

A B-H curve shows these differences by plotting the material's magnetic response as the applied field changes.

Key Points

B-H curves show magnetization behavior, not total core loss.
Grade comparison should be made at the same B or H value.
Knee and saturation behavior matter when comparing grades.

What Does an Electrical Steel B-H Curve Show?

A B-H curve plots magnetic field strength (H) against the resulting magnetic flux density (B). In simple terms, it shows how the material responds as the applied magnetizing field increases.

The shape of the curve helps engineers evaluate several aspects of magnetic behavior, including how easily the steel can be magnetized, how its permeability changes, and where the material begins to approach saturation.

When comparing electrical steel grades, the curve can also reveal differences that are not obvious from thickness or nominal core-loss values alone.

Understanding the Axes: H and B

The horizontal axis represents magnetic field strength (H), usually expressed in amperes per meter (A/m). It describes the magnetizing field applied to the material and is related to the magnetomotive force produced by the winding and the magnetic path in the device.

The vertical axis represents magnetic flux density (B), measured in tesla (T). It describes the magnetic flux established in the material in response to the applied magnetic field.

How to Read the Main Regions of a B-H Curve

1790042077579-Main Regions of an Electrical Steel B-H Curve.webp

Electrical steel B-H curve showing the initial magnetization, lower-field, knee and saturation regions

Initial magnetization curve: Starting from a demagnetized state, the curve shows how B increases as H is gradually increased.
Lower-field region: At relatively low field strength, B increases rapidly with H. The slope of the curve in this region reflects how easily the material can be magnetized.
Knee region: As B increases, the curve begins to flatten. Progressively more H is required to obtain further increases in B.
Saturation region: Beyond the knee, large increases in H produce only relatively small increases in B. Operating close to this region can substantially increase the magnetizing requirement.

B-H Curve vs Hysteresis Loop: They Are Not the Same Thing

The terms B-H curve and hysteresis loop are sometimes used loosely, but they do not always refer to the same plot.

A magnetization B-H curve typically shows how B rises with H toward saturation. A hysteresis loop shows the full cyclic response of the material as the magnetic field is increased, reduced, and reversed.

1790042086579-B-H Curve vs Hysteresis Loop.webp

Comparison of an electrical steel B-H magnetization curve and hysteresis loop showing permeability, remanence and coercivity

Data	What It Mainly Shows
Magnetization B-H curve	Permeability, knee region, saturation behavior
Hysteresis loop	Remanence, coercivity, hysteresis energy
Core-loss data	Total measured loss under specified B, frequency, and test conditions

What the Hysteresis Loop Tells You

Remanence

Remanence (Br) is the magnetic flux density that remains when H returns to zero after the material has been magnetized.

Coercivity

Coercive field (Hc) is the reverse magnetic field required to reduce B back to zero.

What Does the Hysteresis Loop Area Mean?

In AC magnetic applications such as motors and transformers, the material passes repeatedly through magnetization and demagnetization cycles. Plotting B against H over a full cycle produces a hysteresis loop.

The area enclosed by the hysteresis loop represents magnetic energy dissipated per unit volume during one magnetization cycle.

For AC magnetic-core applications, a relatively narrow hysteresis loop is generally desirable because it indicates lower hysteresis energy per cycle.

How to Compare Two Electrical Steel Grades Using B-H Data

The practical value of a B-H curve becomes clearer when two electrical steel grades are compared at the same operating point.

Example: Comparing Two Grades at 1.5 T

Consider two hypothetical electrical steel grades evaluated at a target magnetic flux density of 1.5 T.

Grade	Magnetic Flux Density (B)	Required Magnetic Field Strength (H)
Grade A	1.5 T	200 A/m
Grade B	1.5 T	350 A/m

The values above are illustrative and are used only to explain how B-H curves are compared.

At 1.5 T, Grade A requires a lower magnetic field strength than Grade B. This indicates that Grade A is more easily magnetized around this operating point.

What the Lower H Value Means

At the same B value, a lower required H generally corresponds to higher permeability at that operating point, meaning less magnetizing field is needed to reach the target flux density.

This does not translate directly into lower winding current or higher motor efficiency, because the complete magnetic circuit also affects those outcomes.

B-H Curve vs Core Loss: Why You Need Both

A B-H curve and core-loss data describe different aspects of electrical steel performance.

The B-H curve shows how easily the material can be magnetized and how it behaves as it approaches saturation. Core-loss data, usually expressed in W/kg, show the energy dissipated under specified test conditions.

Two grades can therefore show similar core-loss values but different magnetization behavior, or similar B-H behavior but different core losses.

At higher frequencies, frequency-specific core-loss data become increasingly important because a standard B-H curve does not show total AC loss.

Property	B-H Curve	Core-Loss Data
Magnetization behavior	✓	—
Permeability	✓	—
Knee / saturation behavior	✓	—
Loss in W/kg	—	✓
Frequency-specific total loss	—	✓
Flux-density-specific loss	—	✓

B-H behavior and core-loss values should therefore be treated as separate, complementary data.

Why Finished-Core B-H Behavior May Differ

Cutting, punching, and welding can introduce stress that changes the magnetic behavior of electrical steel. Permeability may decrease near the affected areas, so the B-H curve measured on a standard specimen may not exactly represent the finished core.

Depending on the grade and manufacturing process, stress-relief annealing may recover part of this degradation.

1790042080408-Finished-Core B-H Behavior After Electrical Steel Processing.webp

Electrical steel punching and finished core showing how manufacturing stress can affect B-H behavior

Other Factors Affecting Finished-Core Behavior

In addition to cutting and punching stress, stacking pressure, interlocking, welding, air gaps, and heat treatment can also affect the magnetic behavior of the finished core. The impact depends on the steel grade, lamination geometry, and manufacturing process.

Comparing B-H Data From Different Suppliers

B-H curves should only be compared when the test conditions are reasonably similar.

Check the:

grade and thickness
B or H range used for the curve
test method or standard
specimen orientation, where relevant

A curve that appears steeper or reaches a higher B value is not necessarily better if the underlying test conditions are different.

Conclusion

When comparing grades, the most useful question is not simply which curve looks better, but how easily each material can reach the magnetic flux density required by the design under comparable test conditions.

FAQ

What does a B-H curve tell you about electrical steel?

A B-H curve shows how magnetic flux density changes with applied magnetic field strength. It is commonly used to evaluate magnetization behavior, permeability, the knee region, and saturation.

Is a steeper B-H curve always better?

Not necessarily. A steeper curve generally indicates that a higher B can be reached with less H over that region, but that does not make it the better grade for every application.

Does a B-H curve show core loss?

Not directly. A magnetization B-H curve describes magnetic response, while total core loss is normally measured separately in W/kg under specified flux-density and frequency conditions.

What is the difference between a B-H curve and a hysteresis loop?

A magnetization B-H curve typically shows how B increases with H toward saturation. A hysteresis loop shows the full cyclic magnetic response and includes remanence, coercivity, and hysteresis energy.

What does the knee point of a B-H curve mean?

The knee is the region where the curve begins to flatten. Beyond this region, increasingly large changes in H produce smaller increases in B as the material approaches magnetic saturation.

Why can finished-core performance differ from datasheet B-H data?

Cutting, punching, welding, assembly stress, heat treatment, and operating conditions can alter magnetic behavior. Datasheet curves are therefore reference material data rather than a complete prediction of the finished component.

Electrical Steel B-H Curve Explained: How to Read and Compare Grades

How to Compare Electrical Steel Grades Across IEC, EN, ASTM, JIS and GB/T Standards

How to Read Electrical Steel Core Loss Test Conditions: P1.5/50 vs P1.7/50

Electrical Steel Grade vs. Actual Core Loss: What Should Buyers Specify?

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