Saturation magnetization

Overview

Saturation magnetization is a characteristic of ferromagnetic materials. Ferromagnetic materials are magnetized under the action of an external magnetic field. At the beginning, with the gradual increase in the intensity of the external magnetic field, the magnetization of the material also continues to increase; when the external magnetic field increases to a certain strength, the magnetization of the material stops increasing and remains at a constant level. At a stable value, the substance has reached a state of saturation magnetization at this time. This stable magnetization value is called the saturation magnetization of the substance. Different types of ferromagnetic materials have different saturation magnetization values.

Measuring method

There are many methods for measuring Ms. Two methods are introduced here.

The first is to determine the Ms value by measuring the magnetic flux inside or around the sample based on electromagnetic induction. The general relationship between the magnetic induction intensity B, the magnetic field intensity change H and the magnetization intensity M in the magnetic medium is

B=μ₀(H+M)

When the sample is magnetized to a saturated state, there is

B=_μ0(Hm+Ms)

The second method is to pass the test sample in The magnitude of the force in the gradient magnetic field is used to measure the Ms value. For example, the commonly used balance method and ring scale method belong to this category.

Unit of measurement

The SI unit system is A/m.

Application

(1) Good single correspondence relationship between Ms value and alloy carbon content

The Ms variable is within the measurement sensitivity range, which can make the alloy The carbon content measurement accuracy is 0.01%, and it is a non-destructive test, the method is simple and fast.

(2) Correspondence between the Ms value and the internal microstructure of the alloy and its internal relationship with the flexural strength of the alloy

The flexural strength of the alloy mainly depends on the internal microstructure of the alloy Structure, under the condition of Aoo level, the value of Ms has a good corresponding relationship with it. Therefore, it is feasible to use the Ms value to characterize the flexural strength of the alloy. Compared with the commonly used metallographic analysis and physical property analysis methods, its outstanding advantage is that it can quantitatively indicate the changes in the internal microstructure of the alloy.

(3) Ms value is a reliable physical quantity for testing alloy η phase

Usually, when metallographic analysis is used to determine the amount of η phase, it can only be qualitative analysis without quantitative analysis. Concept. In actual production, there is an urgent need to quantitatively analyze the amount of η phase in order to accurately grasp the properties of the alloy. Experiments have proved that the MS value is an accurate physical quantity for quantitatively testing the alloy eta phase. Because when the dry content of the alloy is constant, the change of the Ms value is mainly determined by two factors. First, due to the difference in the t content of carbon in the alloy, the solubility of tungsten atoms and carbon atoms in the alloy in the binder phase drill is different, resulting in varying degrees of changes in the magnetization mechanism, and corresponding changes in the Ms phase. This is a gradual process. Second, because the carbon content of the alloy is much lower than the stoichiometric value (or the atmosphere in the furnace is a decarburization atmosphere), a non-magnetic η phase appears in the alloy, which has no effect on the magnetization activity, so a large amount of drilling becomes In addition to non-magnetic materials, the value of Ms decreased significantly, and the decrease range reached 40-50% of the maximum value of Ms. Therefore, according to the measured corresponding relationship between the different Ms values ​​and the knife, the amount of η phase can be quantitatively characterized.

(4) The Ms value is an important parameter to accurately determine that the alloy is close to the reasonable carbon content

When the alloy carbon content is close to the theoretical carbon content, Ms gradually increases, and when the alloy carbon content fluctuates When the value is 0.01%, the Ms value corresponds to a variable of about 0.0022T. When the alloy is close to the saturated carbon content, the Ms value reaches the saturation value (but it is difficult to reach the saturation value completely, because there is always a trace of tungsten dissolved in the binder phase drill). Therefore, for different grades of alloys, it can be controlled in the high-carbon zone or low-carbon zone according to performance requirements. And this can be selected by the displayed Ms value.

Conclusion

(1) The saturation magnetization Ms value of cemented carbide has a good unity correspondence relationship with the carbon content of the alloy. When the change of alloy carbon content is 0.01%, the corresponding variable of Ms is about 0.0022T. The relationship between alloy carbon content and Ms can be used to determine the alloy carbon content with an accuracy of 0.01%.

(2) The Ms value has a good corresponding relationship with the internal microstructure of the alloy. When the alloy is in the γ+WC two-phase zone, the γ+WC + η carbon-poor zone, and the γ+WC+C carbon-rich zone, different Ms values ​​can be present. The maximum Ms value of the alloy in the two-phase region indicates that the alloy has achieved the best performance. In the Aoo state, the Ms value can fully reflect the flexural strength of the alloy.

(3) The Ms value is an accurate physical quantity for testing the weight percentage of the alloy eta phase. When the alloy carbon content is lower than the stoichiometric amount, η phase appears, and the Ms value decreases by 40-50% of the maximum value. By accurately formulating the relationship curve between the Ms value and the eta phase content, the alloy Ms value can be determined and the percentage of the alloy eta phase content can be determined.

(4) The Ms value is a reliable physical quantity that accurately indicates that the alloy is close to the theoretical carbon content high-carbon zone or low-carbon zone. According to the WC-Co state diagram, the width of the two-phase zone of the alloy with different Co content is 0.17~0.42%, and the change of Ms is 0.030~0.080T, so even if the carbon content of the alloy changes within 0.01%, the Ms value can be tracked. Instructions.