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Control of the phase composition and magnetic properties of products made of austenitic-ferritic and austenitic-martensitic steels

https://doi.org/10.38013/2542-0542-2020-3-45-53

Abstract

This article describes the results of studies aimed at investigating the correlation of magnetic properties and phase composition of samples from austenitic steels of various grades. In addition, the work describes devices, which are successfully employed at the Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences for non-destructive testing of the magnetic properties and phase composition of austenitic steels and alloys in various industries of the Russian Federation. These devices enable determination of the quality of various materials, both in laboratory and operating conditions.

For citation:


Rigmant M.B., Korkh M.K. Control of the phase composition and magnetic properties of products made of austenitic-ferritic and austenitic-martensitic steels. Journal of «Almaz – Antey» Air and Space Defence Corporation. 2020;(3):45-53. https://doi.org/10.38013/2542-0542-2020-3-45-53

Over a long period of time, the Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences has been performing re­search aimed at the development of methods and tools for the in-process control of phase compo­sition and measurement of magnetic properties of products made of austenitic steels and alloys [1][2][3][4][5][6][7]. The production and performance characte­ristics of these products, including heat resistance, high temperature strength, corrosion resistance, plasticity, magnetic properties, etc., are largely determined by the phase composition of their ma­terial. As a rule, besides the main austenite phase, steel usually requires ferrite phase (2-12 %), the presence of which ensures strength and other properties at both low and high temperatures. The amount of ferrite phase is strictly regulated for different grades of austenitic steels.

Besides the main paramagnetic austenite phase (γ-phase) and additional ferrite phase (α-phase) present during the products manufac­ture and operation, when plastic deformations af­fect the same, deformation martensite (α'-phase) may form in the steel material. Due to their fer­romagnetic properties, ferrite and deformation martensite significantly affect mechanical and strength properties of austenitic steels, determine the steel capacity to resist aggressive media, there­fore, the control of phase composition is a pri­mary objective that needs to be addressed during the manufacture and operation of parts and structures made of austenitic steels.

A method widely used for these purposes is magnetic saturation, which implies determi­nation of the content of ferromagnetic inclu­sions in a material by the value of its saturation magnetization (JS, A/cm). However, practical implementation of magnetic saturation meth­od requires application of large-sized expen­sive equipment for the creation of high-in- tensity magnetic fields (HS ≥ 5000 A/cm), which makes this method more suitable for the laboratory conditions, and makes its application difficult in the conditions of pro­duction, where fast non-destructive testing of a large number of finished products is re­quired. Therefore, an urgent task is to deter­mine the correlation of other magnetic pa­rameters (besides JS) with the percentage of ferromagnetic phases in the studied steels, since, in the future, these parameters will be used as a design and production basis for the new instruments for measuring phase compo­sition of austenitic steels.

The first part of this paper describes the results of studying the correlation between the magnetic parameters of minor hysteresis loops and the percentage of either α- or α'-phase in the two-phase (austenitic-ferritic or austenitic- martensitic) samples [8]. The samples were made of austenitic and austenitic-ferritic steels of different grades. One ingot was cut into two to four samples with the square section of 8×8 mm and length of 100 mm. A total of 6 austenitic-ferritic sets and 1 austenitic-mar- tensitic set of samples was obtained. Steel grades used to produce the austenitic-ferritic samples are listed in Table 1.

Table 1

Steel grades of austenitic-ferritic samples

Set No.

1

2

3

4

5

6

Steel grade

0Kh17N7GT

08Kh20N9S2BTYu

12Kh21N5T

12Kh25N5TMFL

03Kh22N6M2

0Kh32N8

Austenitic-martensitic samples were made of austenitic steel of grade 05Kh18N11, not con­taining ferromagnetic phases in the initial state (before the deformation). Rolling deformation of steel at room temperature promoted a defor­mation martensite phase formation in the steel structure. The percentage of ferrite (F %, %) and deformation martensite (M %, %) in the samples was determined by the value of their saturation magnetization. Data on the percentage of fer­romagnetic phases in the samples are given in Tables 2-4.

Table 2

Percentage of ferrite in the samples from sets No. 1, 2, 3

Set No. 1

Set No. 2

Set No. 3

Sample No.

F%, %

Sample No.

F%, %

Sample No.

F%, %

1-1

1.36

2-1

6.88

3-1

13.0

1-2

1.58

2-2

5.45

1-3

1.41

2-3

6.68

3-2

13.0

1-4

1.82

2-4

5.56

average F%

1.54

average F%

6.14

average F%

13.0

 

Table 3

Percentage of ferrite in the samples from sets No. 4, 5, 6

Set No. 4

Set No. 5

Set No. 6

Sample No.

F%, %

Sample No.

F%, %

Sample No.

F%, %

4-1

20.1

5-1

40.6

6-1

61.3

4-2

22.6

5-2

42.0

6-2

58.8

4-3

20.6

5-3

39.4

6-3

61.8

4-4

22.2

5-4

41.4

6-4

60.0

average F%

21.4

average F%

40.85

average F%

60.5

 

Table 4

Percentage of deformation martensite in the samples made of steel 05Kh18N11

Sample No.

M1

М2

М3

М4

M %, %

2.50

7.45

12.5

18

Using RemagrafC-500Magnet-Physik instru­ment, magnetization (J, A/cm) of each sample was measured in three magnetic field ranges (Н, A/cm): -300...300; -450...450; -600...600 A/cm. For the graphical representation of obtained re­sults in the form of magnetic hysteresis loops and further mathematical processing of data, specialized mathematical software packages were used. Figure 1 shows an example of loops plotted in three field ranges for austenitic-ferritic sample No. 4-1 (ferrite content - 20.1 %).

Fig. 1. Example of measured hysteresis loops for sample No. 4-1 in fields: а) –300…300 A/cm; b) –450…450 A/cm; c) –600…600 A/cm

We also plotted the dependencies of dif­ferential magnetic susceptibility on the magnetic field - Xdif(H). Examples of dependencies Xdif(H) obtained for sample No. 4-1 in three field ranges are shown in Figure 2.

Fig. 2. Dependencies χdif(H) for sample No. 4-1 in fields: а) –250…250 A/cm; b) –400…400 A/cm; c) –550…550 A/cm

Magnetic parameters were determined for all studied samples based on magnetic hysteresis loops and curves χdif(H): coercive force – Нс, residual magnetization – Jr, maximum magnetization – Jmax, maximum differential magnetic susceptibility – χDmax, curve area χdif(H) – Sχdif. Further studies have shown that each of listed parameters correlate to the percentage of α- or α'-phase in the sample to a greater or lesser extent. Then, we plotted the dependencies of parameters Нс, Jr, Jmax, χDmax, Sχdif on the percentage of ferromagnetic phases in the samples. The best correlation to the percentage of α- or α'-phase was shown by parameters Jmax, χDmax, Sχdif, which is illustrated below in Figures 3–8. For the purposes
of plotting the dependencies in these figures, we used the values of magnetic parameters measured on the magnetic hysteresis loops and magnetic susceptibility curves plotted in the magnetic field range of –300…300 A/cm. In the magnetic field ranges of –450…450 and –600…600 A/cm, the nature of the dependencies remained unchanged.

Fig. 3. Dependencies Jmax(F%) of austenitic-ferritic samples plotted based on average values of Jmax and F%

 

Fig. 4. Dependencies Jmax(M %) of austenitic-martensitic samples

 

Fig. 5. Dependencies Sχdif(F%) of austenitic-ferritic samples plotted based on average values of Sχdif and F%

 

Fig. 6. Dependencies Sχdif(M%) of austenitic-martensitic samples

 

Fig. 7. Dependencies χDmax(F%) of austenitic-ferritic samples plotted based on average values of Sχdif and F%

 

Fig. 8. Dependencies χDmax(M %) of austenitic-martensitic samples

Since the number of austenitic-ferritic sam­ples is quite high, when plotting the graphs, we used the average values of the percentage of ferrite phase and the studied magnetic parameter within one set of austenitic-ferritic samples in order to facilitate representation of the obtained results in Figures 3, 5 and 7.

Thus, based on the above dependencies, in order to control the percentage of ferromagnetic phase components in austenitic steel, a number of other magnetic parameters can be used in ad­dition to the saturation magnetization. This will allow us to avoid the use of large-sized equip­ment necessary to control value Js and proceed to the development of small-sized portable devices that allow for non-destructive testing of magnetic parameters in low-stress fields (as compared to Hs).

Devices for non-destructive testing of phase composition and magnetic properties of steels

Definition of magnetic permeability of low-magnetic austenitic steels. Magnetic per­meability of paramagnetic materials and allied austenitic steels is usually measured on ballistic- type units or magnetic scales. For the study pur­poses, samples are made in the form of tiny pre­molds or plates and placed between the poles of an electromagnet. Magnetic susceptibility or permeability of the examined material is deter­mined by the forces of dragging the sample into the interpolar space with a known magnetic field gradient. Disadvantages of the method include the impossibility of its industrial application for finished products. Other methods of magnetic per­meability control include the method of passing the examined material through differential coils with a high number of measurement turns (as ap­plied in the airports). In the presence of metallic inclusions, audio- and video-alarms are triggered. The disadvantage of this method consists in the absence of required large magnetic fields at this type of control, as well as purely qualitative na­ture of the method.

some domestic enterprises use foreign de­vices based on the same principles as the Russian ferrite meters. First of all, they include Feritscope MP30 and Feritscope МРЗОЕ-S (Germany) that feature functions of measuring relative magnetic permeability using induction method. The measu­ring section of the sensor is designed in the form of a hemisphere, which allows for magnetic field concentration to magnetic fields of the order of 102-103 A/cm. This significantly increases the sensitivity and accuracy of measurements. How­ever, single-point magnetization with a hemi­spherical transducer reduces the control area. The disadvantage of this method also consists in the small depth of object’s magnetization.

Based on the long-term experience [9][10][11][12], the Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences has proposed and introduced into production the device “Mag­netic Permeability Meter for Austenitic Steels - IMPAS” (current name - “FerroKOMPAS”), shown in Figure 9.

Fig. 9. Magnetic Permeability Meter for Austenitic Steels “FerroKOMPAS”

Device “FerroKOMPAS” is designed for local measurement of relative magnetic permea­bility μ (magnetic susceptibility χ = μ - 1) of prod­ucts made of austenitic steels. Magnetic permea­bility is measured based on the strength of stray magnetic field of a magnetized material and using attachable Hall-effect sensor, fixed in the centre of a local permanent magnet (Fig. 10).

Fig. 10. Process functional diagram of sensor of IMPAS series devices (“FerroKOMPAS”): 1 – permanent magnet; 2 – Hall-effect sensor; 3 – examined item (EI); 4 – area
inside EI magnetized with permanent magnet

Since sensor design excludes the influence of the permanent magnet field on the measurement result, only the stray field (Hpac) of the magne­tized section affects the Hall-effect sensor. The stray field of the controlled magnetized section is expressly related to the value of magnetic perme­ability μ (or susceptibility χ = μ - 1) through the following expression:

Formula (1) is also valid for low-magnetic materials, when μ < 1.05 and (μ - 1)/ (μ + 1) ~ χ / 2. Then (1) will be as follows:

Нраc = const · χ.                                                      (2)

It is evident that changes in the susceptibil­ity from χ = 0.001 to χ = 0.002 (i. e., by only one thousandth) instantly increase the value of stray field Hpac twice, which makes the method pro­posed by the authors sensitive to low values of magnetic susceptibility (permeability).

Device “FerroKOMPAS” (IMPAS series), developed by the Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences, employing flux-gate meters or Hall-effect sensors as magnetosensitive transducers, allows for local non-destructive testing of magnetic permeability in the range of 1.001 ≤ μ ≤ 1 .200, thus determining the presence of ferromagnetic inclusions in par­amagnetic material at a level of their content of 0.01-1 %. This modification of the device, besides digital indicator, features a built-in ADC, which allows for transfer of measurement results to a PC for their subsequent storage and processing.

Determination of the phase composition of austenitic and austenitic-ferritic steels. Besides the devices designed to control magnetic perme­ability of low-magnetic chromium-nickel steels with a ferromagnetic phase content of less than 1 %, the Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences has developed and successfully introduced the devices to control phase composition of austenitic-ferritic and austenitic-martensitic steels. Figure 11 shows device “Ferrite meter FKh-3 IFM” that is designed to control the percentage of ferrite in austenitic steels in the range of 0.1-20 and 20-80 % (general range). Figure 12 shows device IMDS-1 (Meter of deformation martensite in steel), which, besides ferrite phase content, can measure the percentage of deformation martensite in chromium-nickel steels and alloys.

Fig. 11. Device “Ferrite meter FKh-3 IFM”

 

Fig. 12. Device “IMDS-1”

Similar to device “FerroKOMPAS”, primary transducers of these devices include a permanent magnet and magnetosensitive elements that record and measure stray fields of a magnetized section of the examined item. The primary transducer is an attachable sensor that allows for performance of measurements both on samples and on the sur­face of finished products in the laboratory, work­shop and field conditions without removing pro­ducts and items from service.

The devices presented in this paper have been introduced at more than 20 large Russian en­terprises of the oil and gas industry, shipbuilding, chemical engineering, as well as at enterprises related to the aerospace industry: in FSUE A. A. Bochvar Central Scientific Research Insti­tute and JSC Ural Production Enterprise Vector (UPP Vector).

Conclusion

  1. Based on studying the magnetic proper­ties of austenitic-ferritic and austenitic-martensitic steels, we have established the correlations between phase composition and certain magnetic parameters, such as coercive force, residual mag­netization, maximum magnetization, area under dependence Xdif(H), and maximum of dependence Xdif(H). It has been shown that all studied para­meters correlate with phase composition and can be used to control the content of ferrite phase or deformation martensite phase in two-phase chro- mium-nickel steels at specific-cycle magnetiza­tion reversal.
  2. This paper considers device “FerroKOM- PAS” that is designed for non-destructive testing of magnetic permeability of materials of parts and mechanisms at a level of μ ≤ 1.01, which is criti­cal for products with strict requirements to lowmagnetic state stability.
  3. Devices “FKh-3 IFM” and “IMDS-1” have been presented; these devices can be used for the express non-destructive testing of phase com­position of chromium-nickel steels, containing ferrite and deformation martensite, besides the main austenite phase.

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About the Authors

M. B. Rigmant
M.N. Mikheev Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences
Russian Federation

Rigmant Mikhail Borisovich – Cand. Sci. (Phys.-Math.), Senior Researcher, M. N. Mikheev IMP Ural Branch RAS; specialist in the field of non-destructive testing; head of a number of projects for the development and manufacture of new devices for assessing the electrical and magnetic properties, as well as the phase composition of products from austenitic steels, introduced at industrial facilities of the Russian Federation. Research interests: control of the structure and phase composition of steels and alloys, development of new devices and measuring instruments for non-destructive testing and technical diagnostics.

Ekaterinburg



M. K. Korkh
M.N. Mikheev Institute of Metal Physics, Ural Branch of the Russian Academy of Sciences
Russian Federation

Korkh Mikhail Konstantinovich – Cand. Sci. (Engineering), Senior Researcher. Research interests: control of the structure and phase composition of steels and alloys, development of new devices and measuring instruments for non-destructive testing and technical diagnostics.

Ekaterinburg



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For citation:


Rigmant M.B., Korkh M.K. Control of the phase composition and magnetic properties of products made of austenitic-ferritic and austenitic-martensitic steels. Journal of «Almaz – Antey» Air and Space Defence Corporation. 2020;(3):45-53. https://doi.org/10.38013/2542-0542-2020-3-45-53

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