Semi-quantitative evaluation method for cross wedge rolling center hole defect

Abstract

The invention relates to the field of metal part rolling defect evaluation, in particular to a semi-quantitative evaluation method for cross wedge rolling center hole defects. The method sequentially comprises a sample cutting step, a grinding step, a testing step and an analysis step, the test step of the sample comprises a test step of an original material and a test step of rolled piece sampling; the defect sensitivity coefficient is calculated by adopting the linear swelling amount, so that the defect degree of the hole in the central part of the cross wedge rolled piece is semi-quantitatively evaluated, and the defects that only qualitative results can be obtained and manual evaluation errors are large in a traditional complete sectioning detection method, an ultrasonic and radiographic flaw detection method, an industrial CT flaw detection method and the like are overcome; the method can semi-quantitatively compare the influence degree of process parameters on the hole defects in the center of the cross wedge rolling piece, overcomes the defects of a traditional method, and has important reference significance for improving the cross wedge rolling process. The method has the advantages that the method is simple and easy to implement, the problem that the detection result in the prior art can only be qualitatively and visually compared and cannot be quantified is solved, and a data basis is provided for improving the cross wedge rolling process.

Description

Technical Field

[0001] The invention relates to the field of metal parts rolling defect evaluation, in particular to a semi-quantitative evaluation method for a hole defect in the core of a wedge cross rolling process. Background Art

[0002] Holes in the center of wedge cross rolling are a common processing defect that can have a serious impact on material properties and the use of parts. Holes in the center can reduce the density of the material, resulting in a significant decrease in its mechanical properties. When subjected to external forces, stress concentration is easily generated at the holes, which can cause cracks to expand and eventually lead to material breakage, greatly shortening the service life of the parts. In addition, holes in the center can also affect the electrical and thermal conductivity of the material. In certain application environments, such as conductive devices or high-temperature components, this defect can have fatal consequences. Therefore, controlling and eliminating holes in the center of wedge cross rolling is crucial to improving product quality and safety.

[0003] The detection of holes in the center of wedge cross rolling is a key link to ensure the quality of wedge cross rolling products. At present, the complete sectioning detection of rolled pieces is a total loss detection method, which can only be verified by post-test. Ultrasonic testing is one of the commonly used methods. Its principle is to use the reflection, refraction and other phenomena when ultrasonic waves propagate in the material and encounter defects such as holes. The existence and size of the holes are judged by analyzing the received ultrasonic signals. This method has the advantages of high detection accuracy and strong penetration. However, this method is suitable for the evaluation of the limit size of holes, and cannot quantitatively describe the overall situation of the hole defects in the center of the rolled piece. In addition, radiographic detection is also an effective means. Holes are detected by image analysis after the rays penetrate the material. This method can intuitively display the location and shape of defects, but the cost is high and there is a certain radiation risk, and quantitative evaluation cannot be achieved. With the development of technology, industrial CT detection has gradually been applied to the internal defect detection of complex components, which can accurately present the three-dimensional structure of local holes, but the equipment is expensive and the detection is time-consuming. In the current actual production, the appropriate detection method can be selected according to the product characteristics and detection requirements. However, there is a lack of specific quantitative standards for the hole defects in the center of wedge cross rolling, and it is impossible to compare the sizes and distribution characteristics of different hole defects accordingly. Therefore, traditional complete sectioning detection methods, ultrasonic and radiographic flaw detection methods, industrial CT flaw detection methods, etc. can only obtain qualitative results, and manual assessment has large errors. Summary of the invention

[0004] The purpose of the present invention is to propose a semi-quantitative evaluation method for the hole defect in the center of wedge cross rolling in response to the problems existing in the above-mentioned prior art, which can semi-quantitatively compare the influence of process parameters on the hole defect in the center of wedge cross rolling and make up for the shortcomings of traditional methods.

[0005] A semi-quantitative evaluation method for a hole defect in the core of a wedge cross rolling mill comprises a sample cutting step, a grinding step, a sample testing step and a sample analysis step in sequence;

[0006] The test steps of the sample include the test steps of the original material and the test steps of the rolled piece sampling;

[0007] First, the testing steps of the original materials:

[0008] The thermal expansion curve of the sample taken from the original material was tested by using a dilatometer to obtain the thermal expansion curve from room temperature to T max The linear expansion of the material within the temperature range L0; calibrate the characteristic values ​​L of the linear expansion from 1 to n at a temperature interval of 50℃ or 100℃ i ; Then carry out the test step of rolling stock sampling;

[0009] Second, the test steps for rolling sampling:

[0010] Under the same test conditions as the original material, the thermal expansion curve of the sample taken from the wedge cross-rolled piece was tested using a dilatometer to obtain the thermal expansion curve from room temperature to T max The linear expansion of the material within the temperature range L w ; Calibrate the characteristic values ​​L of several linear expansions from 1 to n at a temperature interval of 50℃ or 100℃ j ;

[0011] Third, the analysis and calculation steps: C = (L j -L i ) / L i Defined as the defect sensitivity coefficient, the average defect sensitivity coefficient C of the 50℃ or 100℃ temperature interval corresponding to 1 to n is obtained avg , that is, C avg =(C1+C2+……+Cn) / n; according to the average value of defect sensitivity coefficient C avg From large to small values, the hole defects in the center of wedge cross rolling tend to be more serious.

[0012] In the cutting step, samples required for thermal expansion testing are cut along the axial direction of the original material and the cross-wedge rolled piece.

[0013] In the cutting step, the sample is a round rod sample, a thin plate sample or a square end surface sample.

[0014] In the grinding step, the cut sample is ground and polished on the end face and the circumferential surface according to the dilatometer test requirements.

[0015] The test step also includes a preparation step before the test step; in the preparation step, the thermal expansion instrument is debugged and protective gas is introduced into the sample chamber.

[0016] During the test steps, high-purity nitrogen gas with a pressure of 0.05 MPa was always introduced.

[0017] The linear expansion of a material is one of its intrinsic properties. There is a difference in thermal expansion between continuous dense materials and discontinuous and non-dense materials. Using this property, a semi-quantitative evaluation can be performed on samples with different core hole defects. It should be noted that the reason why a complete quantitative evaluation cannot be achieved is that the distribution of core hole defects has a discrete characteristic and cannot be evaluated solely based on the linear expansion, a single directional physical characterization.

[0018] The advantages and beneficial effects of the present invention are:

[0019] Compared with the traditional complete sectioning detection method, ultrasonic and radiographic flaw detection method, industrial CT flaw detection method, etc., which can only obtain qualitative results, can only be compared intuitively and have large errors in human evaluation, the method of the present invention can achieve semi-quantitative evaluation of the hole defects in the center of the wedge cross-rolled piece.

[0020] The method of the invention provides a data basis for improving the wedge cross-rolling process of metal parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flow chart for implementing the semi-quantitative evaluation method of the hole defect in the center of wedge cross rolling;

[0022] Figure 2 These are pictures of the core cross-section samples of the rolled piece obtained under three wedge cross rolling process conditions. DETAILED DESCRIPTION

[0023] In the present invention, the original material of the GH2132 sample and the rolled products obtained under three wedge cross rolling process conditions are selected as evaluation objects.

[0024] Next, we will combine Figure 1 and Figure 2 The present invention is further illustrated by the following embodiments.

[0025] The semi-quantitative evaluation method of the hole defect in the core of the wedge cross rolling of the present embodiment includes the steps of cutting and grinding the sample, and is characterized in that it also includes the steps of testing and analyzing the sample; the testing step of the sample includes the steps of testing the original material, the steps of testing the sample sample, and the steps of testing the sample sample.

[0026] First, samples were cut from the original material of GH2132 and the rolled products obtained under the three wedge cross rolling process conditions. Round bar test specimen. The three wedge cross rolling process conditions are: initial billet diameter 30 mm, rolled piece diameter 13.5 mm, rolling speed 400 mm / s, and rolling temperatures 1000 °C, 1050 °C, and 1100 °C, respectively.

[0027] First, the testing steps of the original materials:

[0028] The thermal expansion curve of the sample taken from the original material was tested using a dilatometer to obtain the linear expansion L0 of the material in the range of room temperature to 800°C; 8 characteristic values ​​of the linear expansion L were calibrated at a temperature interval of 100°C. i ; Then carry out the test step of rolling stock sampling;

[0029] Table 1 Linear expansion of original materials

[0030]

[0031]

[0032] Second, the test steps for rolling sampling:

[0033] Under the same test conditions as the original material, the thermal expansion curves of the samples taken from the three wedge cross-rolled parts were tested using a dilatometer to obtain the linear expansion L of the material in the range of room temperature to 800°C. w ; Calibrate 8 characteristic values ​​of linear expansion L at a temperature interval of 100°C j ;

[0034] Table 2 Linear expansion of rolled parts processed by three wedge cross rolling processes

[0035]

[0036] Third, the analysis and calculation steps: C = (L j -L i ) / L i Defined as the defect sensitivity coefficient, the average defect sensitivity coefficient C of 8 corresponding 100℃ temperature intervals is obtained avg ; That is C avg =(C1+C2+……+C8) / 8. According to the average defect sensitivity coefficient C avg From large to small values, the hole defects in the center of wedge cross rolling tend to be more serious.

[0037] Table 3 Defect sensitivity coefficients of rolled products processed by three wedge cross rolling processes

[0038]

[0039]

[0040] The results in Table 3 show that the hole defect in the center of the wedge cross rolling changes with the rolling temperature. Among them, the hole defect in the center of the wedge cross rolling with a rolling temperature of 1100℃ is the most serious, followed by the wedge cross rolling with a rolling temperature of 1050℃, and the hole defect in the center of the wedge cross rolling with a rolling temperature of 1000℃ is the least obvious.

[0041] Figure 2 The images of the core cross-section samples of the rolled pieces obtained under the three wedge cross rolling process conditions are also consistent with the above analysis and calculation results.

[0042] The description of the above embodiments is only used to help understand the core idea of ​​the present invention; at the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation of the present invention.

Claims

1. A semi-quantitative evaluation method for the hole defect in the center of wedge cross rolling, characterized by: The method includes the steps of cutting and polishing the sample, and also includes the steps of testing and analyzing the sample; The test steps of the sample include the test steps of the original material and the test steps of the rolled piece sampling; First, the testing steps of the original materials: The thermal expansion curve of the sample taken from the original material was tested by using a dilatometer to obtain the thermal expansion curve from room temperature to T max The linear expansion of the material within the temperature range L0; calibrate the characteristic values ​​L of the linear expansion from 1 to n at a temperature interval of 50℃ or 100℃ i ; Then carry out the test step of rolling stock sampling; Second, the test steps for rolling sampling: Under the same test conditions as the original material, the thermal expansion curve of the sample taken from the wedge cross-rolled piece was tested using a dilatometer to obtain the thermal expansion curve from room temperature to T max The linear expansion of the material within the temperature range L w ; Calibrate the characteristic values ​​L of several linear expansions from 1 to n at a temperature interval of 50℃ or 100℃ j ; Third, the analysis and calculation steps: C = (L j -L i ) / L i Defined as the defect sensitivity coefficient, the average defect sensitivity coefficient C of the 50℃ or 100℃ temperature interval corresponding to 1 to n is obtained avg , that is, C avg =(C1+C2+……+Cn) / n; according to the average value of defect sensitivity coefficient C avg From large to small values, the hole defects in the center of wedge cross rolling tend to be more serious.

2. The semi-quantitative evaluation method for the hole defect in the center of cross wedge rolling according to claim 1 is characterized in that: In the cutting step, samples required for thermal expansion testing are cut along the axial direction of the original material and the cross-wedge rolled piece.

3. The semi-quantitative evaluation method for the hole defect in the center of cross wedge rolling according to claim 2 is characterized in that: In the cutting step, the sample is a round rod sample, a thin plate sample or a square end surface sample.

4. The semi-quantitative evaluation method for the hole defect in the center of cross wedge rolling according to claim 3 is characterized by: In the grinding step, the cut sample is ground and polished on the end face and the circumferential surface according to the dilatometer test requirements.

5. The semi-quantitative evaluation method for the hole defect in the center of cross wedge rolling according to claim 1 is characterized in that: The test step also includes a preparation step before the test step; in the preparation step, the thermal expansion instrument is debugged and protective gas is introduced into the sample chamber.

6. The semi-quantitative evaluation method for the hole defect in the center of cross wedge rolling according to claim 1 is characterized in that: During the test steps, high-purity nitrogen gas with a pressure of 0.05 MPa was always introduced.

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