Method for predicting three-point bending fatigue life of cold work die steel based on subsurface carbide size

Abstract

The invention discloses a cold work die steel three-point bending fatigue life prediction method based on the subsurface carbide size, which comprises the following steps: carrying out a three-point bending fatigue test on a cold work die steel sample, and analyzing a fatigue fracture to obtain a subsurface carbide size parameter; calculating a stress intensity factor based on the stress amplitude and a subsurface carbide size parameter; and constructing a fatigue life prediction formula, and predicting the three-point bending fatigue life of the cold work die steel by combining the stress intensity factor. According to the method, the stress intensity factor is introduced, the external stress amplitude and the subsurface carbide size are coupled, the stress concentration effect is quantified, the explicit relation with the fatigue life is established, and the cycle index is directly predicted. A scanning electron microscope and an energy scattering spectrum are combined to optimize model parameters, and fisheye morphology fracture is accurately predicted; only a three-point bending test and SEM analysis are needed, the process is simplified, the cost is reduced, the prediction precision is improved, and the engineering applicability is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of fatigue performance evaluation of metal materials, and in particular relates to a method for predicting the three-point bending fatigue life of cold-working die steel based on the size of subsurface carbides. Background Art

[0002] Fatigue failure of cold working die steel is one of the main reasons for premature mold damage, which will lead to reduced production efficiency, increased maintenance costs and fluctuations in product quality. Existing fatigue life prediction technologies are mainly divided into two categories:

[0003] (1) Based on the model of inclusion / carbide size (such as Murakami model), the inclusions / carbides in the material are observed by metallographic microscope (OM) or scanning electron microscope (SEM), and the equivalent size of the largest defect (such as the square root of the projected area) is used. ) as the key parameter, and substitute into the empirical formula (such as ) to predict fatigue limit. Although this method is simple and direct, it does not consider the interaction between carbides and the matrix and the dynamic influence of stress amplitude, especially the harmfulness of large-sized carbides in the subsurface layer.

[0004] (2) Fracture mechanics combined with microstructure model, the crack growth rate (dα / dN) was measured by fatigue testing machine, the morphology of the crack path was observed by SEM, and the internal structure and size parameters of the carbide were observed by TEM (transmission electron microscope), the interaction between the crack path and the carbide was analyzed, and the carbide size parameters were introduced into the modified Paris formula (dα / dN=C(ΔK-ΔK th ) m , where ΔK th Although these methods can reflect the effects of microstructure, they require complex crack growth tests. Furthermore, existing models are mostly targeted at surface defects and lack a quantitative description of the fracture mechanism of the "fisheye" morphology caused by subsurface carbides.

[0005] In summary, the existing cold working die steel fatigue life prediction technology has the following main problems:

[0006] The existing Murakami-type model only uses the maximum defect size ) to estimate fatigue limit, but no relationship between carbide size and actual cycle life (N f ), especially the lack of explicit mathematical relations for stress amplitude (Δσ a ) and carbide size Quantitative description of synergy.

[0007] Although existing fracture mechanics models (such as the modified Paris formula) can reflect the hindering effect of carbides in the crack propagation stage, they have not established a dedicated model for the "fisheye" morphology fracture (FGA characteristic area) caused by large carbides in the subsurface layer.

[0008] The existing technology does not distinguish between M7C3 type carbides (rich in Fe / Cr) and M 23 The differential effects of C6 carbides (containing Si / S / Mn) on fatigue properties lead to prediction deviations. Summary of the Invention

[0009] In order to solve the above technical problems, the present invention proposes a method for predicting the three-point bending fatigue life of cold working die steel based on the size of subsurface carbides to solve the problems existing in the above-mentioned prior art.

[0010] To achieve the above objectives, the present invention provides a method for predicting the three-point bending fatigue life of cold-working die steel based on the size of subsurface carbides, comprising:

[0011] Three-point bending fatigue tests were performed on cold-working die steel specimens, and the subsurface carbide size parameters were obtained by analyzing the fatigue fracture surfaces.

[0012] Calculate the stress intensity factor based on the stress amplitude and subsurface carbide size parameters;

[0013] A fatigue life prediction formula is constructed and combined with the stress intensity factor to realize the three-point bending fatigue life prediction of cold working die steel.

[0014] Optionally, the conditions of the three-point bending fatigue test are: loading frequency 80 Hz, stress ratio R=0.1, and constant amplitude sinusoidal load.

[0015] Optionally, a scanning electron microscope is used to observe the fatigue fracture, and the projection area of ​​the subsurface carbide at the position of the crack source region is measured, and the size parameters of the subsurface carbide are obtained based on the projection area.

[0016] Optionally, the stress amplitude is coupled with the subsurface carbide size parameter to quantify the local stress concentration effect and obtain the calculation formula of the stress intensity factor, which is expressed as follows:

[0017]

[0018] Where Δσ a is the stress amplitude, A carbide is the projected area of ​​subsurface carbides, ΔK carbide is the stress intensity factor.

[0019] Optionally, the relationship between the stress intensity factor and fatigue life is fitted by using test data from a three-point bending fatigue test to obtain the fatigue life prediction formula as follows:

[0020]

[0021] Where N f is the number of cycles to failure, Δσ a is the stress amplitude, A carbide is the projected area of ​​subsurface carbides.

[0022] Optionally, it also includes: analyzing the composition of carbides in the crack source area through energy dispersion spectroscopy to determine the type of carbides, adjusting the parameters in the calculation formula of the stress intensity factor according to the carbide type; and updating the fatigue life prediction formula according to the adjusted stress intensity factor calculation formula.

[0023] The present invention also provides a computer device comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-mentioned method for predicting the fatigue life of cold-working die steel three-point bending based on the size of subsurface carbides.

[0024] The present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the above-mentioned method for predicting the fatigue life of cold-working die steel three-point bending based on the size of subsurface carbides.

[0025] The present invention also provides a computer program product, comprising a computer program, which, when executed by a processor, implements the steps of the above-mentioned method for predicting the fatigue life of cold-working die steel three-point bending based on the size of subsurface carbides.

[0026] Compared with the prior art, the present invention has the following advantages and technical effects:

[0027] The present invention proposes a stress intensity factor, which is the external stress amplitude (Δσ a) is coupled with the carbide size as a single mechanical parameter. The subsurface carbide is used as a stress concentration source, and its size directly affects the local stress field intensity. The stress intensity factor quantifies this effect, thereby establishing an explicit relationship with fatigue life. For the first time, it is possible to directly predict the number of cycles through carbide size, rather than just estimating the fatigue limit, solving the technical problem that the existing model cannot quantitatively correlate carbide size with fatigue life. The stress intensity factor captures the principle of this microscopic damage process through carbide size parameters, allowing the model to accurately predict the fracture of subsurface carbides characterized by a "fisheye" morphology (FGA area), solving the problem that the special damage mechanism of subsurface carbides has not been considered. In addition, the present invention utilizes only conventional three-point bending tests and SEM fracture analysis, without the need for complex crack extension tests, and integrates macroscopic stress and microstructural characteristics through stress intensity factors, thereby simplifying the prediction process, reducing prediction costs, and improving accuracy, solving the problem of insufficient engineering applicability of existing fatigue life prediction methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0029] Figure 1 This is a flow chart of a method for predicting the three-point bending fatigue life of cold-working die steel based on the subsurface carbide size according to an embodiment of the present invention;

[0030] Figure 2 Schematic diagram of a three-point bending high cycle fatigue specimen according to an embodiment of the present invention;

[0031] Figure 3 SN curve of three-point bending of HYC1MOD steel according to an embodiment of the present invention;

[0032] Figure 4 is a graph showing the relationship between fatigue failure life and carbide size under the same stress amplitude in an embodiment of the present invention;

[0033] Figure 5 Statistical diagram of fatigue source data and EDS analysis diagram of carbide at location A according to an embodiment of the present invention. (a) is the statistical diagram of fatigue source data, and (b) is the EDS analysis diagram of carbide at location A.

[0034] Figure 6 The stress intensity factor K and fatigue life N in the embodiment of the present invention are f The relationship curve between

[0035] Figure 7 A comparison diagram of fatigue life prediction simulation values ​​and actual values ​​according to an embodiment of the present invention;

[0036] Figure 8TEM diagrams of the interaction mechanism between dislocations and carbides in an embodiment of the present invention, wherein (a) is a schematic diagram of the obstruction of dislocations by long carbides, and (b) is a schematic diagram of the obstruction of dislocations by spherical carbides;

[0037] Figure 9 Schematic diagram of the crack propagation path and carbide interaction in an embodiment of the present invention, wherein (a) is the macroscopic morphology of the secondary crack; (b) is the enlarged view of frame 1; (c) is the enlarged view of frame 2; and (d) is the microscopic morphology of the secondary crack. DETAILED DESCRIPTION

[0038] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0039] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0040] Example 1

[0041] like Figure 1 As shown, this embodiment provides a method for predicting the three-point bending fatigue life of cold-working die steel based on the size of subsurface carbides, including:

[0042] Three-point bending fatigue tests were performed on cold-working die steel specimens, and the subsurface carbide size parameters were obtained by analyzing the fatigue fracture surfaces.

[0043] The conditions of the three-point bending fatigue test are: loading frequency 80 Hz, stress ratio R = 0.1, and constant amplitude sinusoidal load.

[0044] The fatigue fracture was observed by scanning electron microscopy, and the projection area of ​​the subsurface carbides at the crack source region was measured. The size parameters of the subsurface carbides were obtained based on the projection area.

[0045] Specifically, the fatigue fracture was observed by SEM and the square root of the projected area of ​​carbides in the crack source area was measured. Its purpose is to quantify the stress concentration effect of carbides.

[0046] Calculate the stress intensity factor based on the stress amplitude and subsurface carbide size parameters;

[0047] The stress amplitude is coupled with the subsurface carbide size parameters to quantify the local stress concentration effect and obtain the calculation formula of the stress intensity factor, which is expressed as follows:

[0048]

[0049] Where Δσ a is the stress amplitude, A carbide is the projected area of ​​subsurface carbides, ΔK carbide is the stress intensity factor.

[0050] Specifically, the stress intensity factor ΔK is introduced carbide ,propose The stress amplitude (Δσ a ) and carbide size Coupled to quantify the stress concentration effect of subsurface carbides.

[0051] A fatigue life prediction formula is constructed and combined with the stress intensity factor to realize the three-point bending fatigue life prediction of cold working die steel.

[0052] The fatigue life prediction formula is obtained by fitting the relationship between the stress intensity factor and fatigue life through the test data of the three-point bending fatigue test, as follows:

[0053]

[0054] Where N f is the number of cycles to failure, Δσ a is the stress amplitude, A carbide is the projected area of ​​subsurface carbides.

[0055] Specifically, ΔK is fitted based on experimental data. carbide with lgN f Relationship: ΔK carbide =3.26-0.15lgN f , the fatigue life prediction formula is derived, which is directly related to ΔK carbide With N f , to achieve quantitative prediction, see Figure 6 shown.

[0056] The method also includes: analyzing the composition of carbides in the crack source area through energy dispersion spectroscopy to determine the type of carbides, adjusting the parameters in the calculation formula of the stress intensity factor according to the carbide type; and updating the fatigue life prediction formula according to the adjusted calculation formula of the stress intensity factor.

[0057] For example, targeted modeling of M7C3 carbides was performed, the composition of crack source carbides (mainly Fe / Cr) was confirmed by EDS, and the model parameters were optimized to improve the applicability to cold working die steel.

[0058] Example 1: High stress amplitude (Δσ a =550MPa) and large carbide size

[0059] Step 1: Specimen preparation and fatigue test;

[0060] Material: HYC1MOD cold work die steel, quenched at 1055℃, deep cooled at -190℃, and tempered twice at 525℃.

[0061] Sample processing: Prepare three-point bending specimens according to GBT 232-2010 standard (size see Figure 2 ), span L = 30mm.

[0062] Fatigue test: Loading on QB-100 testing machine, Δσ a =550MPa, R=0.1, frequency 80Hz, record the number of failure cycles N f =1.2×10 5 times (test results see Figure 3 , Δσ a With N f relationship curve).

[0063] Step 2: Fracture analysis and carbide size measurement;

[0064] SEM observation: The fatigue source area is a large carbide in the subsurface layer ( Figure 5 ), measure its projected area

[0065] EDS confirmed: carbide composition is Fe-65.2%, Cr-28.5%, V-4.3% (M7C3 type, Figure 5 ).

[0066] Step 3: Lifespan prediction and verification;

[0067] Calculate ΔK carbide :

[0068] Predicted lifespan: (N f =1.2×10 5 Second-rate);

[0069] Results: The predicted value and the actual value (1.2×10 5 The error is 0%.

[0070] Example 2: Moderate stress amplitude (Δσ a =500MPa) and carbide size

[0071] Step 1: Test conditions: Δσ a =500MPa, other parameters are the same as in Example 1, the measured N f =5×10 5 Second-rate.

[0072] Step 2: Fracture analysis: The crack source is the subsurface carbide. (A carbide =225μm 2 ), the relationship between its size and fatigue life is shown in Figure 4 .

[0073] Step 3: Lifespan prediction;

[0074]

[0075] (N f =1.35×10 5 Second-rate);

[0076] Result: Predicted value 1.35×10 5 times, the actual value is 5.0×10 5 Second, the error is caused by the irregular shape of the carbide, such as Figure 6 shown.

[0077] This embodiment proposes a stress intensity factor The applied stress amplitude (Δσ a ) and carbide size The invention of coupling as a single mechanical parameter uses the subsurface carbide as a stress concentration source, whose size directly affects the local stress field intensity, ΔK carbide This effect was quantified, allowing an explicit relationship to fatigue life to be established, enabling the first direct prediction of the number of cycles (N) from carbide size. f ), rather than just estimating the fatigue limit, which solves the technical problem that the existing model cannot quantitatively correlate carbide size and fatigue life. Combined with TEM observation (see Figure 8 ), revealing the dislocation accumulation mechanism caused by the carbide-matrix incoherent interface and correlating it to ΔK carbide model, where large carbides hinder dislocation motion, causing stress concentration and microcrack initiation (see Figure 9 ), ΔK carbide pass The parameters capture the principle of this microscopic damage process, enabling the model to accurately predict the fracture of subsurface carbides characterized by a "fisheye" morphology (FGA area) (accounting for 86.4%), solving the problem that the special damage mechanism of subsurface carbides has not been considered. In addition, the present invention uses only conventional three-point bending tests (80Hz, R=0.1) and SEM fracture analysis, without the need for complex crack growth tests, to predict the fracture dynamics of subsurface carbides by ΔK. carbide Integrate macro stress and microstructure characteristics, simplify the prediction process, reduce the prediction cost by more than 50%, and improve the accuracy (error <10%, Figure 7 ), which solves the technical problem of insufficient engineering applicability of existing fatigue life prediction methods.

[0078] This embodiment also provides a computer device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-mentioned method for predicting the fatigue life of cold-working die steel three-point bending based on the subsurface carbide size.

[0079] This embodiment also provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the steps of the above-mentioned method for predicting the fatigue life of cold-working die steel three-point bending based on the subsurface carbide size are implemented.

[0080] This embodiment also provides a computer program product, including a computer program, which, when executed by a processor, implements the steps of the above-mentioned method for predicting the fatigue life of cold-working die steel three-point bending based on the size of subsurface carbides.

[0081] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for predicting the fatigue life of cold-working die steel in three-point bending based on the size of subsurface carbides, characterized in that: The following steps are involved: Three-point bending fatigue tests were performed on cold-working die steel specimens, and the subsurface carbide size parameters were obtained by analyzing the fatigue fracture surfaces. Calculate the stress intensity factor based on the stress amplitude and subsurface carbide size parameters; A fatigue life prediction formula is constructed and combined with the stress intensity factor to realize the three-point bending fatigue life prediction of cold working die steel.

2. The method for predicting the three-point bending fatigue life of cold-working die steel based on the subsurface carbide size according to claim 1, characterized in that: The conditions of the three-point bending fatigue test are: loading frequency 80 Hz, stress ratio R=0.1, and constant amplitude sinusoidal load.

3. The method for predicting the three-point bending fatigue life of cold-working die steel based on the size of subsurface carbides according to claim 1, characterized in that: The fatigue fracture was observed by scanning electron microscopy, and the projection area of ​​the subsurface carbides at the crack source region was measured. The size parameters of the subsurface carbides were obtained based on the projection area.

4. The method for predicting the three-point bending fatigue life of cold-working die steel based on the subsurface carbide size according to claim 1, characterized in that: The stress amplitude is coupled with the subsurface carbide size parameters to quantify the local stress concentration effect and obtain the calculation formula of the stress intensity factor, which is expressed as follows: Where Δσ a is the stress amplitude, A carbide is the projected area of ​​subsurface carbides, ΔK carbide is the stress intensity factor.

5. The method for predicting the three-point bending fatigue life of cold-working die steel based on the subsurface carbide size according to claim 1, characterized in that: The fatigue life prediction formula is obtained by fitting the relationship between the stress intensity factor and fatigue life through the test data of the three-point bending fatigue test, as follows: Where N f is the number of cycles to failure, Δσ a is the stress amplitude, A carbide is the projected area of ​​subsurface carbides.

6. The method for predicting the three-point bending fatigue life of cold-working die steel based on the size of subsurface carbides according to claim 1, characterized in that: Also includes: The composition of carbides in the crack source area is analyzed by energy dispersive spectroscopy to determine the type of carbides, and the parameters in the calculation formula of the stress intensity factor are adjusted according to the carbide type; And according to the calculation formula of the adjusted stress intensity factor, the fatigue life prediction formula is updated.

7. A computer device comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the method for predicting the fatigue life of cold-working die steel three-point bending based on the size of subsurface carbides according to any one of claims 1 to 6.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for predicting the three-point bending fatigue life of cold-working die steel based on the subsurface carbide size according to any one of claims 1 to 6 are realized.

9. A computer program product comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method for predicting the three-point bending fatigue life of cold-working die steel based on the subsurface carbide size according to any one of claims 1 to 6 are realized.

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