CN109541013B - Ferromagnetic alloy steel dislocation density detection method - Google Patents
Ferromagnetic alloy steel dislocation density detection method Download PDFInfo
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- CN109541013B CN109541013B CN201811397804.4A CN201811397804A CN109541013B CN 109541013 B CN109541013 B CN 109541013B CN 201811397804 A CN201811397804 A CN 201811397804A CN 109541013 B CN109541013 B CN 109541013B
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- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
- G01N27/725—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables by using magneto-acoustical effects or the Barkhausen effect
Abstract
The invention relates to a dislocation density detection method for ferromagnetic alloy steel. The magnetic Barkhausen noise method is adopted to detect the dislocation density of the ferromagnetic alloy steel, the detection process is convenient and rapid, the requirement on the surface quality of a sample is low, the detection result precision is high, and quantitative nondestructive evaluation can be carried out on the dislocation densities of different degrees in the ferromagnetic alloy steel.
Description
Technical Field
The invention relates to a dislocation density detection method for ferromagnetic alloy steel. More particularly, the invention relates to a method for quantitatively and nondestructively detecting the dislocation density of ferromagnetic alloy steel by adopting a magnetic Barkhausen noise method.
Background
The steel is a metal material which is widely applied in production and life, and the mechanical property of the steel determines the quality and the application of the steel. Dislocation is a defect difficult to avoid in steel, has important influence on the mechanical property of the steel, and four modes of fine grain strengthening, precipitation strengthening, solid solution strengthening and deformation strengthening are provided for researching the strengthening of the steel in materials science.
There are currently five main methods for evaluating dislocation density: pitting, transmission electron microscopy, X-ray diffraction, positron emission tomography, three-dimensional atom probe microscopy, the most commonly used of which are transmission electron microscopy and X-ray diffraction. The transmission electron microscope observation method is difficult to prepare samples, has a small observation range and is only suitable for samples with low dislocation density and low deformation, and the X-ray diffraction method is simpler in sample preparation, accurate in measurement result and wide in application compared with the sample preparation method.
In the plastic deformation process of the steel, the dislocation density is greatly increased, the larger the plastic deformation degree is, the larger the dislocation density in the crystal is, the more serious the lattice distortion is, and the wider the X-ray diffraction peak is. The W-H method is a method commonly used for measuring the dislocation density by X-ray diffraction. The W-H method considers that the broadening δ of the diffraction peak can be expressed by the following formula
Wherein delta c Represents the half-height width, delta, of the sample to be measured b Indicates the full width at half maximum of the standard sample.
The diffraction peak broadening δ and the average effective microstrain ∈ have the following relationship:
where α =0.9, d is the crystal grain size, λ is the X-ray wavelength, θ is the position of the diffraction peak, and ∈ represents the average effective microstrain.
ε has the following relationship to the dislocation density ρ:
in the formula, b is the Berth vector of dislocation in iron, and the value is 0.248nm.
In the formula (2)
And
having a linear relationship with an intercept of
The slope is epsilon. Drawing
And
the slope ε can be obtained from the linear relationship, and the value of the dislocation density can be obtained by taking the value of ε into formula (3).
Although the X-ray diffraction method is a very common method for measuring dislocation density, the method has high requirements on sample preparation, and complicated sample preparation and detection processes, and is not suitable for on-line detection of large samples. In practical engineering application, by detecting the dislocation density of the component, the using and stress conditions of the material can be known, even the service life of the material can be predicted, and the method has great application value, so that new requirements on a nondestructive online detection method are provided from the engineering application angle. The magnetic Barkhausen noise nondestructive detection method has low requirements on the surface of a sample, has the characteristics of quick and convenient detection process and the like, and has unique advantages in laboratory detection, on-line detection and in-service detection. However, there is no report on quantitative study of the dislocation density of ferromagnetic materials using magnetic barkhausen noise technology. Theoretically, the larger the dislocation density of the material is, the stronger the barrier effect of the dislocation on the magnetic domain motion is, the smaller the amplitude of the generated magnetic Barkhausen noise signal is, and the detection of the dislocation density by adopting the magnetic Barkhausen noise technology is feasible. Based on the method, the invention provides a method for quantitatively detecting the dislocation density of the ferromagnetic material by adopting a magnetic Barkhausen noise technology.
Disclosure of Invention
The invention aims to provide a method for quantitatively and nondestructively detecting the dislocation density of ferromagnetic alloy steel by adopting a magnetic Barkhausen noise method, which can quantitatively and nondestructively evaluate the dislocation densities of different degrees in the ferromagnetic alloy steel. The reason why the dislocation density is measured by the magnetic barkhausen method is that the dislocation density has a hindrance effect on the magnetic barkhausen noise signal. The greater the dislocation density, the lower the mobility of the magnetic domains and the smaller the magnetic barkhausen noise signal, and vice versa. Since the magnetic barkhausen noise signal is very sensitive to the variation of the dislocation density, the evaluation of the dislocation density using the magnetic barkhausen noise signal has high accuracy.
The dislocation density detection method of the ferromagnetic alloy steel comprises the following steps:
(1) Preparing a group of test pieces with the same specification by using the same ferromagnetic alloy steel material;
(2) Carrying out tensile plastic deformation of the group of test pieces with the same specification to different degrees to obtain test pieces with different dislocation densities;
(3) Demagnetizing each test piece by a magnetic method;
(4) Measuring the root mean square value RMS of the magnetic Barkhausen noise signal of each test piece in the step (3) by adopting a magnetic Barkhausen noise testing device;
(5) Measuring the dislocation density of each test piece in the step (3) by adopting an X-ray diffraction method;
(6) Establishing a standard curve of the dislocation density and the root mean square of the material according to the steps (4) and (5), and determining a fitting function;
(7) Demagnetizing the tested piece by a magnetic method;
(8) Measuring the root mean square of the test piece in the step (7) by adopting a magnetic Barkhausen noise testing device;
(9) And (5) comparing the root mean square value obtained in the step (8) with a standard curve to obtain the predicted dislocation density of the tested piece.
The method can be used for quantitatively and nondestructively detecting the dislocation density of the ferromagnetic alloy steel, has the advantages of convenient and quick detection process, low requirement on the surface quality of a sample and high detection result precision, can realize quantitative detection of the dislocation density of a ferromagnetic test piece, and has good application prospect.
In a preferred embodiment, the magnetic method described in step (3) refers to placing the material in an alternating magnetic field that saturates the material and then gradually reducing the magnetic field until the material reaches a magnetically neutral state.
In a preferred embodiment, the root mean square RMS is a statistical calculation of the pulse amplitude for which the magnetic barkhausen noise signal pulse strength is greater than zero, and is formulated as
Wherein, f (x) is the pulse amplitude value of MBN signal pulse intensity greater than zero, b represents the maximum value of the sampling point count in all f (x) pulse signals, a represents the minimum value of the sampling point count in all f (x) pulse signals, and b-a represents the number of the sampling point counts corresponding to all f (x) pulse signals.
In a preferred embodiment, the X-ray diffraction method described in step (5) for measuring the dislocation density of each test piece is based on Williamson-Hall (W-H) analysis.
In a preferred embodiment, step (6) employs an exponential function y = a + bc x And (5) establishing a standard curve, and determining values a, b and c according to the root mean square value measured in the step (4) and the dislocation density measured in the step (5).
In a preferred embodiment, step (9) is to calculate the predicted dislocation density by substituting the root mean square value obtained in step (8) into the fitting function determined in step (6).
The magnetic Barkhausen noise technology is a new electromagnetic nondestructive testing method and is mainly used for testing the content of a second phase in a ferromagnetic material, the thickness of a carburized layer, the hardness, the plastic deformation, the stress and the like at present. The magnetic Barkhausen noise is caused by discontinuous motion generated by magnetic domains which are hindered by dislocation, grain boundary, second phase and other defects in the microstructure of the material in the magnetization process of the ferromagnetic material, so the magnetic Barkhausen noise is very sensitive to the structural change of the material, and the magnetic Barkhausen noise nondestructive detection technology has high sensitivity. Upon detection, a complete test signal includes an ambient noise signal and a Magnetic Barkhausen Noise (MBN) signal, where the magnetic barkhausen noise signal is composed of a number of pulse signals. The pulse signals have different intensities, so that the whole magnetic Barkhausen noise signal is in a spindle shape with a large middle and small two ends, and the pulse signals with the intensity larger than zero and the intensity smaller than zero have symmetry. For convenience, the magnetic barkhausen noise signal is quantitatively described using Root Mean Square (RMS).
Root mean square RMS is a statistical calculation of the pulse amplitude for MBN signals with pulse intensities greater than zero, and is formulated as
Wherein f (x) is the pulse amplitude value of MBN signal whose pulse intensity is greater than zero, b represents the maximum value of the sampling point count in all f (x) pulse signals, a represents the minimum value of the sampling point count in all f (x) pulse signals, and b-a represents the sampling corresponding to all f (x) pulse signalsAnd counting the number of sampling points. Root Mean Square (RMS) is used as the magnetic barkhausen noise parameter.
Drawings
FIG. 1 shows tensile specimens of different degrees of plastic deformation in example 1;
FIG. 2 shows the average effective microstrain of each sample measured by the W-H method in example 1;
FIG. 3 shows the standard RMS curve for the dislocation density in example 1.
Fig. 4 is a schematic diagram of a magnetic barkhausen noise signal.
Detailed Description
The principles and features of this invention will be described hereinafter with reference to the accompanying drawings, which illustrate embodiments of the invention and are not intended to limit the scope of the invention, which is defined solely by the claims appended hereto.
Example 1
The test procedure according to the method of the invention is as follows:
(1) 45 steel was used to prepare 9 tensile specimens of the same size.
(2) The 7 samples underwent different degrees of tensile deformation, with deformation amounts of 1%,4%,8%,12%,14%,16%,18%, respectively (see fig. 1); 1 sample is used as an original sample; and (3) subjecting 1 verification sample to random tensile deformation, controlling the deformation degree within the total elongation range, and using the method for verification.
(3) All samples were demagnetized by magnetic methods.
(4) Dislocation densities of 7 tensile-deformed specimens were measured using the W-H method (see fig. 2).
(5) The RMS values of 7 tensile deformation specimens were measured using the magnetic barkhausen noise method.
(6) Standard curves for dislocation density and RMS were established. Taking the dislocation density value obtained in the step (4) as a vertical coordinate, taking the root mean square value obtained in the step (5) as a horizontal coordinate, and adopting an exponential function y = a + bc x Fitting each data point to obtain a fitting function y =0.14+20.33 + 0.0014 x The corresponding fitted curve is shown in FIG. 3, which is the dislocation densityAnd a standard curve of root mean square.
(7) And (5) demagnetizing the test piece by adopting a magnetic method.
(8) The RMS value of the test piece was determined to be 0.374 using the magnetic Barkhausen method.
(9) Substituting the root mean square value in the step (8) into the fitting function in the step (6) to obtain the predicted dislocation density value of 1.90 multiplied by 10 18 /m 2 。
Dislocation density of the verification sample measured by the W-H method is 1.85 multiplied by 10 18 /m 2 Compared with the predicted value of the magnetic Barkhausen noise method, the error is about 2.7 percent.
Although the present invention has been described in terms of the preferred embodiment, it is not intended that the invention be limited to the embodiment. Any equivalent changes or modifications made without departing from the spirit and scope of the present invention are also within the protection scope of the present invention. The scope of the invention should therefore be determined with reference to the appended claims.
Claims (4)
1. A dislocation density detection method for ferromagnetic alloy steel is characterized by comprising the following steps:
the method comprises the following steps:
(1) Preparing a group of test pieces with the same specification by using the same ferromagnetic alloy steel material;
(2) Carrying out tensile plastic deformation of the group of test pieces with the same specification to different degrees to obtain test pieces with different dislocation densities;
(3) Demagnetizing each test piece by a magnetic method;
(4) Measuring the root mean square value RMS of the magnetic Barkhausen noise signal of each test piece in the step (3) by adopting a magnetic Barkhausen noise testing device;
(5) Measuring the dislocation density of each test piece in the step (3) by adopting an X-ray diffraction method;
(6) Establishing a standard curve of the dislocation density and the root mean square of the material according to the root mean square value measured in the step (4) and the dislocation density value measured in the step (5), and determining a fitting function;
(7) Demagnetizing the tested piece by a magnetic method;
(8) Measuring the root mean square value of the test piece in the step (7) by adopting a magnetic Barkhausen noise testing device;
(9) Comparing the root mean square value obtained in the step (8) with a standard curve to obtain the predicted dislocation density of the tested piece;
the root mean square value RMS is a statistical calculation value of the pulse amplitude value of the magnetic Barkhausen noise signal with the pulse intensity larger than zero; formula for calculation
Wherein f (x) is the pulse amplitude value of the magnetic Barkhausen noise signal with the pulse intensity larger than zero, b represents the maximum value of the counting of the sampling points in all the f (x) pulse signals, a represents the minimum value of the counting of the sampling points in all the f (x) pulse signals, and b-a represents the counting number of the sampling points corresponding to all the f (x) pulse signals;
step (6) adopts an exponential function y = a + bc x And (4) establishing a standard curve, wherein the values of a, b and c are determined according to the root mean square value measured in the step (4) and the dislocation density value measured in the step (5).
2. The method of claim 1, wherein: the magnetic method described in the steps (3) and (7) means that the material is placed in an alternating magnetic field which can make the material saturated, and then the magnetic field intensity is gradually reduced until the material reaches a magnetic neutral state.
3. The method of claim 1, wherein: the measurement of the dislocation density of each test piece by the X-ray diffraction method described in the step (5) is based on the Williamson-Hall (W-H) analysis method.
4. The method of claim 1, wherein: and (9) substituting the root mean square value obtained in the step (8) into the fitting function determined in the step (6) to calculate and obtain the predicted dislocation density.
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