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9РОЗБРАКОВУВАННЯ ТОНКОСТ1ННИХ ЛИСТ1В ОДНШ МАРКИ СТАЛИ Р1ЗНИХ ЗАВОД1В
ВИРОБНИК1В
Горкунов Б.М.
доктор техтчних наук, професор кафедри ¡нформацшно-вимгрювальних технологш i систем На^онального техтчного yHiверситету «Хартвський полiтехнiчний iHcmumym»
Тищенко А.А.
кандидат технiчних наук, доцент кафедри електричних станцт Нацюнального техтчного yнiверситетy «Хартвський полiтехнiчний iнститyт»
Богомаз О.В.
кандидат технiчних наук, доцент кафедри радiоелектронiки На^онального техтчного yнiверситетy «Хартвський полiтехнiчний iнститyт»
Львов С.Г.
кандидат технiчних наук, професор кафедри iнформацiйно-вимiрювальних технологш i систем На^онального техтчного yнiверситетy «Хартвський полiтехнiчний iнститyт»
A66aci Жаббар
Астрант кафедри iнформацiйно-вимiрювальних технологш i систем На^онального техтчного yнiверситетy «Хартвський полiтехнiчний iнститyт»
SORTING THIN-WALL SHEETS OF THE SAME STEEL GRADE VARIOUS MANUFACTURERS
Gorkunov B.
Doctor of technical sciences, professor of the department of Information-measuring technologies and systems, National technical university "Kharkiv polytechnic institute "
Tyshchenko A.
Candidate of technical sciences Associate professor of the department of electric power stations, National technical university "Kharkivpolytechnic institute"
Bogomaz O.
Candidate of technical sciences Associate professor of the department of radio electronics, National technical university "Kharkivpolytechnic institute"
Lvov S.
Candidate of technical sciences, professor of the department of Information-measuring technologies and systems, National technical university "Kharkivpolytechnic institute"
Abbasi Jabbar Postgraduate student of the department of Information-measuring technologies and systems, National technical university "Kharkivpolytechnic institute"
Анотащя
В робот запропонований метод розбраковування сталей по коерцитивно! силг В якосп приладу для вишрювання коерцитивно! сили по намагшченосп виробiв з феромагнггаих сплашв використовувався магнггаий структуроскоп типу КРМ-Ц-К2М. В експериментах дослвджували зразки, яш виготовлеш 3i стат двох плавок в сташ заводсько! поставки, хiмiчний склад яких приблизно однаковий. Подальша обробка результата включала iнтерполяцiю отриманих значень коерцитивно! сили, а також усереднення даних за трьома вимiрами. Вимiрянi параметри залежать як ввд мiсця розташування первинного перетворю вача, так i його орieнтацi!' щодо напрямку прокату. Як видно з результата дослвджень, коефiцieнт варiацi!, обумовлений неоднорвднютю властивостей стали в партi!, в 3 рази бшьше коефiцieнга варiацi!, що характеризуе випадкову похибку вишрювання властивостей проби. Це означае, що при визначенш похибки оцiнки середшх властивостей партл стали, перш за все, необидно враховувати неоднорвднють властивостей.
Abstract
In the work, a method for sorting steels by coercive force is proposed. As a device for measuring the coercive force of the magnetization of products from ferromagnetic alloys, a magnetic structurescope MC-04H-2 was used. In the experiments, samples made of steel of two melting, the chemical composition of which are approximately the same, were investigated. Subsequent processing of the results included interpolation of the obtained values of the coercive force, as well as averaging of data over three measurements. The measured parameters depend both on the location of the primary transducer and its orientation relative to the direction of the steel rolling. The research results show that the coefficient of variation due to the inhomogeneity of the properties of steel in the batch is 3 times greater than the coefficient of variation characterizing the random error in measuring the properties of the sample. It means that when determining the estimation error, the average properties of a batch of steel, it is necessary to take into account the heterogeneity of the material properties.
Ключовi слова: феромагнггаий сплав, коерцитивно! сила, магнггаий структуроскоп.
The scientific heritage No 42 (2019) 59
Keywords: ferromagnetic alloy, coercive force, magnetic structurescope.
A coercimetric method occupies a special place among the known methods of magnetic structuretroscopy in the practice of nondestructive testing of products made of ferromagnetic alloys. [1]. The reason is that the coercive force is one of the most structure-sensitive characteristics of ferromagnetic materials, which include hard alloys. The coercive force (Hc) as a physical characteristic of the magnetic properties of the material is widely used for the functional express control in production of ferromagnetic products, as well as in study of their phase composition, structure and influence of various technological operations on them. The value of the coercive force of a hard alloy is determined by the state of its ferromagnetic component.
Depending on the carbon content in the hard alloy, the amount of molybdenum dissolved in cobalt will be large (with a lack of carbon) or less (with an excess of carbon) and, accordingly, the magnetization will be different.
Depending on carbon content, an amount of dissolved molybdenum in cobalt will be more (in case of carbon deficiency) or less (in case of carbon excess) in the solid alloy, and respectively magnetization will be different. Thus, coercive is an indicator of ferromagnetic materials quality [2, 3].
The coercive force of ferromagnetic materials is significantly affected by heat treatment modes used for improving their mechanical properties. For example, quenched alloys with a high cooling rate have coercive force magnifying by 10-14% relative to its value in the initial state [4, 5].
Technical devices for measuring coercive force of ferromagnetic alloys products must conform to a
number of characteristic features of these products. Such features are relatively small linear dimensions of controlled objects (tens of millimeters), a variety of external shapes, generally irregular configurations, as well as high values of the coercive force (tens of kA/m). Therefore, coercimeters used for nondestructive testing of ferromagnetic materials measure the integral value of the coercive force of a controlled object. Firstly, it is impossible to make local measurements of the coercive force of ferromagnetic products because of practical impossibility of magnetizing to a state of technical saturation and subsequent demagnetization of individual local sections of these products. Secondly, the magnetization and demagnetization of ferromagnetic products are carried out in an open magnetic circuit due to the complexity, and in many cases the impossibility of creating closed magnetic circuit for objects of control of various shapes and sizes. This determines the third feature of coercimeters for monitoring ferromagnetic products, which consists in the fact that they measure the coercive force of the magnetization. In this case, the value of the coercive force can be obtained from the value of the demagnetization coil constant and the current in it at the moment when controlled object reaches the state of zero magnetization [6].
As a device for measuring the coercive force of the magnetization of products from ferromagnetic alloys a magnetic structurescope MC-04H-2 is used [7]. Its physical configuration, the primary converter and control samples with Hc = 4 A/cm and Hc = 33.8 A/cm are shown in Fig. 1.
Fig 1 Physical configuration magnetic structurescope MC-04H-2
Coercimeter is used for non-destructive local quality control of thermal, thermomechanical or chemothermal treatments, determining the hardness and mechanical properties of parts made of ferromagnetic materials in the presence of a correlation between the controlled and measured parameters [8]. The device can be used to sort metals by steel grades and control the surface layers of ferromagnetic materials. An important advantage of the device is that the indicated value depends only on the properties of the metal and is not affected by interfering factors such as the protective coating (paint, film, etc.) up to a thickness of 6 mm on the controlled metal or an equivalent to such a gap, etc. The main technical characteristics are the range of measurement of coercive force from 1.0 to 80.0 A/cm and the measurement error
of coercive force on control samples from 2.5 to 5%. It allows providing automatic measurements of the integral value of the coercive force of products made from ferromagnetic alloys.
The device has a portable design and consists of two units: the unit for magnetic measurements and the unit for electronic transformations. The unit for magnetic measurements is based on the demagnetizing coil of the compensated type in the form of a solenoid with an internal slotted hole. This coil has an expanded homogeneity zone of the magnetic field that it creates. An internal slotted hole allows to place in it a magnetization coil, which is located directly near the controlled product. In this case, the energy of the field of the magnetizing coil is used to the maximum for its magnetization. This combined design of sources of magnetizing and demagnetizing fields has minimum
weight and dimensions for given requirements for the parameters of magnetizing and demagnetizing fields.
The ferroprobe-gradiometer used as an indicator of zero magnetization of the ferromagnetic controlled object during its demagnetization. Indication of this is the magnetic field homogeneity in close proximity to the object during its demagnetization. The ferroprobe-gradiometer consists of two half-elements representing ferroprobes, measuring windings of which are included differentially. In this case, effective suppression of the first harmonic of the field voltage of the ferroprobe is achieved.
The device operates in accordance with the following algorithm. After starting, the device activates the magnetization unit and passes the rectified current through the magnetization coil
A pulsed magnetic field arises in the zone of the controlled object, the intensity of which is sufficient to bring the object to state of technical saturation. After that, the demagnetization unit starts. A gradually increasing current is supplied to the demagnetization winding. It creates the magnetic field in the direction opposite to the magnetizing field. During the demagnetization voltage of ferroprobe-gradiometer is continuously analyzed. Its spectrum contains only odd
harmonics in the absence of an external magnetic field. When a magnetic field created by the control object is exposed to the ferroprobe, even harmonics appear in its voltage spectrum. The voltage of the second harmonic is used as an informative signal. Its phase relative to the voltage of the excitation generator is determined by the polarity of the magnetization of the controlled object. The phase of the second harmonic signal of the output voltage of the ferroprobe-gradiometer is converted to DC voltage, the polarity of which depends on its value relative to the voltage of the excitation generator. DC voltage is used to control the demagnetization process. The second harmonic phase abruptly changes to 180° when the controlled object reaches a state of zero magnetization and DC voltage at which this harmonic is transformed changes its sign. At this moment, the increase in the demagnetization current stops, its value is directly proportional to the coercive force and is measured using an analog-to-digital converter. The measurement result is displayed on the display panel in coercive force units [9].
In the experiments, samples made of steel of two melting from factory supply were investigated. Their chemical composition is given in table 1.
Table 1
The chemical composition of steels, weight %
Melting number C Si Mn P S Cr Mo
1 0,38 0,41 0,484 0,014 0,001 13,56 1,02
2 0,38 0,38 0,51 0,022 0,0012 13,57 0,93
During the experiment, metallography of the crystal structure of materials (Table 1) manufactured at two different factories was carried out. The results are shown in Fig. 2.
Fig 2 - The results of metallography of samples of melting No. 1 a) and melting No. 2 b)
The experimental data represent the dependence of the magnetic properties on the coercive force of sheet steel of various manufacturers on the location of the primary converter of the magnetic structurescope MC-04H-2 and are shown in Fig. 3-10. Coercive force measurements were made at 15 control points, selected to provide a different distance from them to the edges of the steel sheet. Measurements were performed three times for each sheet of steel. Calibration of the device was carried out before each experiment. Subsequent processing of the results included interpolation of the obtained values of the coercive force, as well as averaging of data over three measurements. The measured parameters depend both on the location of the primary converter and its orientation relative to the direction of the steel rolling.
a) b)
Fig 3 The results of experimental research of the sample melting No. 1 with horizontal
a) and vertical b) converter orientation relative to the steel rolling
Horizontal
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a) b)
Fig 4 Interpolation of experimental research of the sample melting No. 1 with horizontal a) and vertical b) converter orientation relative to the steel rolling
a) b)
Fig 5 The results of experimental research with averaging over three measurements of the sample melting No. 1 with horizontal a) and vertical b) converter orientation relative to the steel rolling
a) b)
Fig 6 Interpolation of experimental research with averaging over three measurements of the sample melting No. 1 with horizontal a) and vertical b) converter orientation relative to the steel rolling
a) b)
Fig 7 The results of experimental research of the sample melting No. 2 with horizontal a) and vertical b) converter orientation relative to the steel rolling
a) b)
Fig 8 Interpolation of experimental research of the sample melting No. 2 with horizontal a) and vertical b) converter orientation relative to the steel rolling
a) b)
Fig 9 The results of experimental research, averaged over three measurements, of the sample melting No. 2 with horizontal a) and vertical b) converter orientation relative to the steel rolling
a) b)
Fig 10 Interpolation of experimental research with averaging over three measurements of the sample melting No. 2 with horizontal a) and vertical b) converter orientation relative to the steel rolling
The basis for reliable quality control of ferromagnetic steels by magnetic properties are standards created taking into account the metrological characteristics of steel. The system of metrological characteristics provides reliable quality control of the
batch of steel only with a high homogeneity of its properties in the batch or if the standard has an index of inhomogeneity of the normalized properties.
The lack of the last one does not allow to build a system of metrological assurance of control of
magnetic properties of the steel and, primarily, create the required standard test methods [10].
The paper presents a special case of researching the inhomogeneity of the coercive force Hc inside batches of steel sheet 0.3 mm thick of two manufacturers. During the incoming inspection of steel, the degree of homogeneity may be uncharacteristic of this grade.
Multiple coercive force measurements at separately selected control points were carried out to verify the reliability of the experimental results. As in the experiment described earlier, it was measured with different orientation of the converter relative to the direction of rolled steel sheet. The distribution of the indicated value of the coercimeter for one of the points is shown in Fig. 11 and 12. The coefficient of variation of the instrumental error does not exceed 2%.
a) b)
Fig 11 The distribution of the indicated value of the coercimeter for the sample melting No. 1 with horizontal
a) and vertical b) converter orientation relative to the steel rolling
Horizontal
Vertical
52 54 56
a) b)
Fig 12 The distribution of the indicated value of the coercimeter for the sample melting No. 2 with horizontal a) and vertical b) converter orientation relative to the steel rolling
The research results showed that the standard deviation of the Hc values, which characterizes the degree of structure inhomogeneity in the batch, varies within the range of Hc = 2,5 - 7,0 A/cm. The average value of standard deviation for the totality of the batches is Hcav = 4.62 A / cm with a confidence probability of 0.95. The average value of the coefficient of variation Hc at their nominal average value in the batch Hcav = 61.06 A/cm is cav = 7.6% with the confidence probability of 0.95.
Conclusions.
The research results show that the coefficient of variation due to the inhomogeneity of the properties of steel in the batch is 3 times greater than the coefficient of variation characterizing the random error in measuring the properties of the sample. This means that when determining the error in estimating the average properties of a batch of steel, it is necessary to take into account the heterogeneity of the material properties.
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