RU2775855C1 - Method for assessing the quality of strengthening technologies - Google Patents

Abstract

FIELD: hardening technologies quality assessing.

SUBSTANCE: invention is intended for assessing the quality of hardening technologies. The substance of the invention lies in the fact that the number of acoustic emission pulses is loaded and recorded, the state parameter is determined and the value of the diagnostic parameter is calculated with further comparison of the values, while high-frequency acoustic emission sensors are installed on the samples from both sides and the product is smoothly loaded in the elastic deformations area, loading is controlled by the control unit and the values of mechanical stresses are recorded on a personal computer, then the loading is stopped and graphs of the dependence of the number of acoustic emission pulses on mechanical stresses are plotted, then the stage of homogeneous destruction is distinguished, which follows the partial or complete attenuation of the acoustic emission signals and ends with a sharp increase in the acoustic emission signal overlap coefficient, at which the value of the state parameter is determined, expressed in in the form of a concentration-kinetic strength index Y_AE as a parameter of a multilevel model of the time dependence of the number of acoustic emission pulses according to a given formula, then, the allowable value of the slope of the fatigue curve Yr is calculated and compared with the value of the concentration-kinetic strength index Y_AE, if Y_AE/Yr ≤ 1, then the hardening technology is performed qualitatively, and if Y_AE/Yr > 1 - poorly.

EFFECT: improving the accuracy of assessing the quality of hardening technology.

1 cl, 3 dwg

Description

The invention relates to acoustic methods for non-destructive strength testing and is intended to assess the quality of hardening technologies. It can be used to optimize the choice of materials hardening technologies.

A known method for assessing the crack resistance of hardening coated in terms of kinetic indentation and acoustic emission (V.K. Kachanov, I.V. Sokolov, V.M. Matyunin, V.A. Barat, V.V. Bardakov, A.Yu. Marchenkov. Evaluation of the crack resistance of titanium nitride hardening coatings according to the parameters of kinetic indentation and acoustic emission // Izmeritelnaya Tekhnika No. 7, 2017, pp. 41-44). The assessment is made by indexing, that is, by pressing a diamond pyramid into the surface of the product with simultaneous recording of acoustic signals. The amplitude and energy of the acoustic signal are estimated from the results of indentation.

The disadvantage of this method is the ambiguity in the interpretation of the results of registration of acoustic signals. Low noise immunity. Control of only the surface layer. There is a trace of indentation, which cannot be attributed to non-destructive methods.

A known method for assessing the degree of hardening of the surface layer of solid materials (patent RU No. 2475719, publ. 20.02.2013). Strength is evaluated by indenting the indenter into the sample and evaluating the resulting imprint. The angles between the deformed and undeformed material are measured and their ratio is used to judge the degree of hardening.

The disadvantage of this method is the ambiguous relationship between the angular ratio and strength. This method is suitable only for strength control of products homogeneous in terms of mechanical properties in their cross section or for strength control of only the surface layer. These limitations make this method unsuitable for testing the strength of work-hardened and non-uniformly hardened metal products in cross-section with an assessment of hardening and the corresponding strength.

A known method for assessing the quality of the surface layer during cutting and surface plastic deformation using acoustic emission signals (Miroshin I.V. Methods of acoustic emission studies of inherited quality parameters of the surface layer under cutting and surface plastic deformation // Bulletin of the Kuzbass State Technical University No. 3, 2010, pp. 46-49). Quality assessment is performed by recording acoustic emission signals during technological processes such as cutting and plastic deformation. The energy of acoustic signals is used as an informative parameter.

The disadvantage of this method is the low connection of the energy of the acoustic signal with strength and high with noise and interference. The assessment is made only for surface hardening and for the destructive method. An additional disadvantage is the complexity of the cutting and deformation processes.

A known method for assessing surface hardening by reducing the energy parameter of acoustic emission Y (D.L. Merson, M.A. Vagapov. The special role of the surface in deformation processes and acoustic radiation of metals and alloys // Bulletin of TSU, vol. 15, issue 3, 2010, pp. 798-799) using copper as an example. The method is carried out by removing the surface layer with a step of 20 microns until complete removal. After each step, diagnostic loading occurs with registration of acoustic signals.

The disadvantage of this method is the destructive effect on the surface, such an assessment leads to its complete removal. The decrease in the value of the energy parameter occurs due to a change in volume and the influence of the Kaiser effect, which is not related to the strength of the surface itself.

A known method for assessing the strength of products (patent RU No. 2445616, publ. 03/20/2012), adopted as a prototype, which is designed to control the strength of complex metal structures, such as lifting and transport mechanisms, to identify developing and prone to development of defects, and to determine the suitability metal structures for further use. The obtained method differs from the prototype in that in the proposed method it is proposed to single out the stage of homogeneous destruction, which follows a significant or even complete attenuation of the acoustic emission activity in the elastic deformation region, by straightening the graph of the dependence of the number of pulses on time in semi-logarithmic coordinates, to find the parameter values on it state, expressed as a concentration-kinetic strength index Y _AE as a parameter of a multilevel model of the time dependence of the number of acoustic emission pulses, and evaluate the quality of hardening technologies, by comparison with the diagnostic parameter Yr, expressed as the slope of the fatigue curve.

The disadvantage of this method is the need for double loading and exposure under load for a long time, as well as the inaccuracy of calculating the parameter Y _AE due to its determination at the entire stage of loading without taking into account the influence of strength inhomogeneity caused by the influence of strengthening technologies on the structure of the material.

The technical result is to increase the accuracy of assessing the quality of the hardening technology.

The technical result is achieved by the fact that high-frequency acoustic emission sensors are installed on the samples from both sides and smoothly load the product in the area of elastic deformations, the loading is controlled by the control unit and the values of mechanical stresses are recorded on a personal computer, then the loading is stopped and graphs of the dependence of the number of acoustic emission pulses are plotted. from mechanical stresses, then a stage of homogeneous destruction is distinguished, which follows the partial or complete attenuation of acoustic emission signals and ends with a sharp increase in the overlap coefficient of acoustic emission signals, at which the value of the state parameter is determined, expressed as a concentration-kinetic strength index Y _AE as a multilevel parameter models of the time dependence of the number of acoustic emission pulses according to the formula:

Y _AE = dln N _Σ / dσ, where:

dln N _Σ is the difference between the values of the logarithm of the number of acoustic emission pulses at the beginning and at the end of homogeneous destruction,

dσ - difference in mechanical stress values at the beginning and at the end of homogeneous fracture,

then, the allowable value of the slope of the fatigue curve Yr is calculated and compared with the value of the concentration-kinetic strength index Y _AE , if Y _AE / Yr ≤ 1, then the hardening technology is performed qualitatively, and with Y _AE / Yr > 1 - poorly.

The method is illustrated by the following figures:

fig. 1 - functional diagram of the loading device;

fig. 2 - graph for determining the angular coefficient Y _R based on the results of low-cycle tests of fillet weld metal of defect-free welded joints of steel St3sp;

fig. 3 - graph of the dependence of the number of acoustic emission pulses on the mechanical load, where:

1 - sample;

2 - sensors of acoustic emission (AE);

3 - tensile machine;

4 - control unit;

5 - personal computer for recording and controlling the load;

6 - pre-amplifiers of acoustic emission signals;

7 - acoustic emission signal processing unit;

8 - personal computer for registration of acoustic emission signals.

The method is carried out as follows. Samples 1 (figure 1), which were previously exposed to hardening technology, are placed in a tensile machine 3 for static loading with registration of acoustic emission (AE) and load data. High-frequency acoustic emission (AE) sensors 2 are mounted on the samples from both sides. Next, a smooth loading process is performed with a constantly increasing loading rate in the region of elastic deformations in the range from 0 to 300 MPa. In parallel, the values of the number of acoustic emission pulses N _Σ are recorded using acoustic emission equipment, consisting of pre-amplifiers of acoustic emission signals 6, an acoustic emission signal processing unit 7 and recording signals on a personal computer for recording acoustic emission signals 8. Loading is controlled by a control unit 4 with by recording the values of mechanical stresses σ on a personal computer for recording and controlling the load 5. Then the loading is stopped, and plots of the dependence of the number of acoustic emission pulses N _Σ on mechanical stresses σ are plotted in semilogarithmic coordinates. On this graph, the stage of homogeneous destruction is distinguished, which follows the partial or complete attenuation of acoustic emission signals and ends with a sharp increase in the AE signal overlap coefficient. At this stage, the value of the state parameter is determined, expressed as a concentration-kinetic indicator of strength Y _AE as a parameter of a multilevel model of the time dependence of the number of acoustic emission pulses, which is determined by the formula:

Y _AE = dln N _Σ / dσ, where

Y _AE - concentration-kinetic indicator of strength;

dln N _Σ is the difference between the values of the logarithm of the number of acoustic emission pulses at the beginning and at the end of homogeneous destruction;

dσ is the difference between the values of mechanical stresses at the beginning and at the end of uniform destruction.

Next, the allowable value of the value of the diagnostic parameter Yr, expressed by the slope of the material fatigue curve, is calculated. To do this, find a graph of the fatigue curve of defect-free samples for the material under study in the reference data. Next, a linear section is found on the fatigue curve graph, on which the value of N _c is determined - the number of cycles at the beginning and at the end of the linear section, after which the logarithm of the obtained value is calculated. By analogy, the value of σ _a is found, which is the amplitude rated voltage from the external load for a given cycle. The Yr value is found as the ratio of the number of cycles lnN _c to the amplitude rated voltage σ _a (Fig. 2), or is determined by the formula:

Yr = 5.5 / σ _В , where

Yr is the slope of the fatigue curve;

σ _B - endurance limit of the material of the controlled product.

Next, the values of the concentration-kinetic strength index Y _AE and the slope of the fatigue curve Yr are compared as their ratio and a conclusion is made about the quality of the hardening technology. If Y _AE / Yr ≤ 1, then the hardening technology is of high quality. When Y _AE / Yr > 1, the hardening technology is of poor quality, then the optimal type of material hardening technology is selected.

The method is illustrated by the following examples.

Example 1 Samples of St3sp material with welded joints were subjected to ultrasonic impact strengthening technology in the weld zone. Processing was carried out with the following parameters of the ultrasonic sensor: frequency 20.1 kHz, power 200 W. Next, static loading was carried out at a constant rate in the region of elastic deformations with registration of the number of acoustic emission (AE) pulses N _Σ and the values of mechanical stresses σ. The resulting graph of the dependence of the registration of the number of pulses on mechanical stresses for one of the samples is shown in Fig. 3. A section of uniform destruction was distinguished on the graph, which occurred from 16 to 23 seconds of loading, which followed the complete decay of the AE activity. The values of the logarithm of the number of pulses at the beginning of homogeneous destruction lnN _Σ1 = 4.92 and at the end of homogeneous destruction lnN _Σ2 = 5.22 were found on it. Next, the difference between these two values was calculated by the formula dlnN _Σ = lnN _Σ2 - lnN _Σ1 = 5.22 - 4.92 = 0.3. Next, the values of mechanical stresses were found in this interval, where σ ₁ = 184 MPa at the beginning of homogeneous destruction, σ ₂ =282 MPa at the end of homogeneous destruction. The difference was calculated as dσ = σ ₂ -σ ₁ = 282 - 184 = 98 MPa. Next, the value of the state parameter Y _AE was calculated by the formula Y _AE = dlnN / dσ = 0.3 / 98 = 0.003 MP ^-1 . According to the graph of the fatigue curve for a defect-free weld of the material steel 3 (Fig. 2), the allowable value of the slope of the fatigue curve Yr was determined, which is equal to 0.015 MP ^-1 . Next, the value of the ratio of the concentration-kinetic strength index Y _AE and the slope of the fatigue curve Yr was calculated, where Y _AE / Yr = 0.0011 / 0.015 = 0.07. The value of the concentration-kinetic strength index Y _AE and the slope of the fatigue curve Yr were compared. Since 0.07 < 1, it means that the hardening technology is performed qualitatively and can be chosen as a hardening method for welded joints made of steel 3 with appropriate processing parameters.

Example 2. Samples of steel grade 09G2S with welded joints were subjected to hardening technology - vibration treatment. Vibration treatment of welded joints on samples was carried out at a resonant frequency from 24 to 32 Hz, vibration time from 25 to 20 min, and vibration stress from 250 to 400 MPa. Next, static loading was carried out at a constant rate in the region of elastic deformations with registration of the number of acoustic emission (AE) pulses N_Σ and values of mechanical stresses σ. A graph of the dependence of the logarithm of the number of impulses N_Σfrom mechanical stresses σ. A section of uniform destruction was distinguished on the graph, which manifested itself behind the partial attenuation of the AE activity and passed from 22 to 25 seconds of loading. Next, the values of the logarithm of the number of pulses at the beginning of uniform destruction lnN_Σ1 = 4.17 and at the end of uniform fracture lnN_Σ2 = 4.89. Next, the difference between these two values was calculated using the formula dlnN_Σ = lnN_Σ2-lnN_Σ1 = 4.89 - 4.17 = 0.72. Next, the values of mechanical stresses were found in this interval, where σ_one = 215 MPa at the beginning of homogeneous fracture, σ₂ = 275 MPa at the end of homogeneous destruction. The difference was calculated by the formula dσ = σ2 - σ1 = 275 – 215 = 60 MPa. Next, the value of the concentration-kinetic strength index Y was calculated_AE according to the formula Y_AE = dlnN_Σ / dσ = 0.72 / 60 = 0.012 MPa^-one. The value of the slope Yr was found by the formula Yr = 5.5 / σ_AT = 5.5 / 460 = 0.012 MPa^-one, where the endurance limit σ_AT material 09G2S is 460 MPa. Next, the value of the ratio of the concentration-kinetic strength index Y_AE and the slope of the fatigue curve Yr, where Y_AE / Yr = 0.012 / 0.012 = 1. Since 1 = 1, it means that the hardening technology is performed qualitatively, however, it is worth reconsidering the values of the parameters of the impact of this hardening technology on this material, since the ratio of parameters Y_AEto Yr is in the borderline value.

Example 3. Samples of the material steel 5ps with welded joints were subjected to hardening technology - heat treatment. Heat treatment was carried out with the following parameters: mode - high tempering, temperature - 400°C, time - 1 hour, cooling - in air. After preparing the samples, static loading was performed in the region of elastic deformations with constant recording of the number of acoustic emission pulses N _Σ and stresses σ. A plot of the dependence of the logarithm of the number of impulses N _Σ on mechanical stresses σ was plotted. A section of homogeneous destruction was distinguished on the graph, which followed the partial attenuation of activity and passed from 15 to 20 seconds of loading. Next, the values of the logarithm of the number of pulses at the beginning of homogeneous destruction lnN _Σ1 = 4.51 and at the end of homogeneous destruction lnN _Σ2 = 5.72 were found. Next, the difference between these two values was calculated using the formula dlnN _Σ = lnN _Σ2 - lnN _Σ1 = 5.71 - 4.51 = 1.2. Next, the values of mechanical stresses were found in this interval, where σ ₁ = 210 MPa at the beginning of homogeneous destruction, σ ₂ = 280 MPa at the end of homogeneous destruction. The difference was calculated as dσ = σ2 - σ1 = 280 - 210 = 70 MPa. Next, the value of the concentration-kinetic strength index Y _AE was calculated using the formula Y _AE = dlnN _Σ / dσ = 1.2 / 70 = 0.017 MPa ^-1 . The value of the angular coefficient Yr was found by the formula Yr = 5.5 / σ _В = 5.5 / 640 = 0.009 MPa ^-1 , where the endurance limit σ _В of the 5ps material is 640 MPa. Next, the value of the ratio Y _AE /Yr was calculated, where 0.017 / 0.09 = 1.9. Since 1.9 > 1, it means that the hardening technology is of poor quality. It is not recommended to use hardening technology with these parameters for this material.

Thus, using the proposed method, by installing sensors on both sides of the sample, isolating a homogeneous area of destruction following the partial or complete attenuation of acoustic emission activity, and finding the concentration-kinetic strength index Y _AE on it, it is possible to increase the accuracy of assessing the quality of hardening technologies.

Claims (5)

A method for assessing the quality of hardening technologies, including loading and recording the number of acoustic emission pulses, determining the state parameter and calculating the value of the diagnostic parameter with further comparison of the values, characterized in that high-frequency acoustic emission sensors are installed on the samples from both sides and smoothly load the product in the elastic region. deformations, loading is controlled by the control unit and the mechanical stress values are recorded on a personal computer, then the loading is stopped and graphs of the dependence of the number of acoustic emission pulses on mechanical stresses are plotted, then the stage of uniform destruction is isolated, which follows the partial or complete attenuation of the acoustic emission signals and ends with a sharp increase acoustic emission signal overlap coefficient, on which the value of the state parameter is determined, expressed as a concentration-kinetic strength index Y _AE as a parameter of many level model of the time dependence of the number of acoustic emission pulses according to the formula: Y _AE = dln N _Σ / dσ, where: dln N _Σ is the difference between the values of the logarithm of the number of acoustic emission pulses at the beginning and at the end of homogeneous destruction, dσ - difference in mechanical stress values at the beginning and at the end of homogeneous fracture, then, the permissible value of the slope of the fatigue curve Yr is calculated and compared with the value of the concentration-kinetic strength index Y _AE , if Y _AE / Yr ≤ 1, then the hardening technology is performed qualitatively, and with Y _AE / Yr > 1 - poorly.

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