CN114279829A - Method for detecting high-speed tensile curve of quenching distribution steel - Google Patents
Method for detecting high-speed tensile curve of quenching distribution steel Download PDFInfo
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Abstract
The invention discloses a method for detecting a high-speed tensile curve of quenching distribution steel, which comprises the following steps: (1) detecting the tensile property of the quenching steel material to obtain the tensile strength of the material
And maximum force total elongation
(ii) a (2) Pre-stretching a high speed tensile specimen of a material, the elongation of the pre-stretching
In the range of 0.02 to 0.8%
(ii) a (3) After the step (2) of pre-stretchingAnd (3) carrying out a high-speed tensile experiment on the high-speed tensile sample to obtain a high-speed tensile curve of the quenching distribution steel. According to the method, the strain strengthening is obtained by pre-stretching the high-speed tensile sample, then the quenching distribution steel high-speed tensile curve experiment is carried out, the actual strain state of the part is better met, and therefore the finally measured high-speed tensile curve is closer to the actual high-speed tensile property of the part; the method has the characteristics of rapid and accurate detection, and provides a more accurate guiding function for the design of a lightweight structure of the automobile, the optimization of material selection and the improvement of the safety of the automobile body.
Description
Technical Field
The invention belongs to the field of alloy detection, and particularly relates to a method for detecting a high-speed tensile curve of quenching distribution steel.
Background
The light weight of automobiles is a trend in the development of automobiles. Relevant data show that the fuel consumption can be reduced by 6% -8% when the self weight of the automobile is reduced by 10%, namely the light weight of the automobile has double effects of energy saving and environmental protection. The safety of the automobile is directly embodied in the capacity of absorbing impact energy and the protection degree of passengers in the process of automobile body impact, the deformation of materials in the impact process is dynamic response with high strain rate, meanwhile, the materials are processed into parts to generate strain strengthening and have certain influence on the material performance, and particularly, the strain hardening of the materials is considered when a high strain rate test is carried out on quenching distribution steel due to the high strain hardening index of the quenching distribution steel. By researching the influence of strain strengthening on high-speed tensile property, the method has guidance effect on the design of a lightweight structure of an automobile, the optimization of material selection and the improvement of the safety of an automobile body.
The quenching distribution steel is third-generation advanced high-strength steel, and has higher strong plasticity compared with first-generation and second-generation high-strength steel, so that the quenching distribution steel has wide application prospect on automobile bodies. The quenching distribution steel is a mixed structure of ferrite, martensite and retained austenite, wherein a harder martensite matrix has higher strength, the retained austenite belongs to a softer phase and is gradually transformed into martensite in the plastic deformation process, namely, transformation induced plasticity, and the strength of the quenching distribution steel is greatly improved. Therefore, the parts produced by QP steel generate strain through stamping, the strength of the parts is greatly improved, and the influence of the strain on the mechanical property of the material needs to be considered for accurately reflecting the performance of the actual parts.
The high-speed tensile curve is used for representing the mechanical property of the material under dynamic load, and is an important means for systematically researching the correlation between the mechanical property of the material and the deformation behavior and the strain rate. The traditional method for measuring the high-speed tensile curve is to directly use a sample made of raw materials to carry out experiments, respectively measure the samples according to different tensile rates to obtain raw data of material stress and strain under different tensile rates, and finally fit the data into a curve through a proper constitutive model. These hardenings are often ignored in conventional measurement methods because normal high strength steels are less strain strengthened. But the quenching distribution steel has large strain strength, and the 5% strain strengthening can reach 300 MPa. Therefore, in the process of measuring the high-speed tensile curve of the quenching distribution steel, the strain strengthening of the material must be considered, the traditional measuring method cannot meet the requirement, and a new measuring method must be explored.
Disclosure of Invention
The invention aims to provide a method for detecting a high-speed tensile curve of quenching distribution steel, which can better reflect the performance of actual parts.
In order to solve the technical problem, the method provided by the invention comprises the following steps: (1) detecting the tensile property of the quenching steel material to obtain the tensile strength R of the materialmAnd the maximum force total elongation At；
(2) High speed tensile testing of materialsThe sample is subjected to pre-stretching, the elongation of the pre-stretching ebIn the range of 0.02 to 0.8At；
(3) And (3) carrying out a high-speed tensile curve experiment on the high-speed tensile sample pre-stretched in the step (2) to obtain a high-speed tensile curve of the quenching distribution steel.
In the step (1) of the invention, the tensile property is detected at a strain rate of 0.01/s to 1/s.
In the step (2) of the invention, the strain rate of the pre-stretching is 0.01/s-1/s.
In the step (3), a strain strengthening coefficient s and a strain hardening index c of a high-speed tensile curve are obtained by fitting the following constitutive equation (A);
σ＝s*(εp+ln(1+eb))c (A)；
in the formula:
sigma is the true stress in MPa;
εptrue plastic strain, unit 1;
s is the strain hardening coefficient in MPa;
c is the strain hardening index, unit 1.
Adopt the produced beneficial effect of above-mentioned technical scheme to lie in: because the strength phase transformation strengthening is generated in the strain process of the quenching distribution steel, the strength of the part processed by the material is originally higher than the original strength of the material; according to the invention, strain strengthening is obtained by pre-stretching the high-speed tensile sample, and then a quenching distribution steel high-speed tensile curve experiment is carried out, so that the actual strain state of the part is better met, and the finally measured high-speed tensile curve is closer to the actual high-speed tensile property of the part. The invention has the characteristics of rapid and accurate detection, and the obtained curve can more accurately reflect the performance of actual parts, thereby providing more accurate guidance for the design of a lightweight structure of an automobile, the optimization of material selection and the improvement of the safety of an automobile body.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
FIG. 1 is a graph showing the high-speed drawing obtained in example 1 of the present invention.
Detailed Description
The detection method for the quenching distribution steel high-speed tensile curve comprises the following process steps: (1) the method is suitable for quenching distribution steel such as HC600/980QP, HC820/1180QP, HC950/1300QP and the like; firstly, detecting a tensile curve of the quenching distribution steel material at a strain rate of 0.01/s-1/s; obtaining the tensile strength R of the materialmAnd the maximum force total elongation At。
(2) Quenching distribution steel is used as a cold stamping material, and in order to ensure normal forming of stamping, avoid necking phenomenon and ensure certain forming safety margin, the elongation e of pre-stretching is takenbShould not be greater than 0.8At(ii) a Meanwhile, in order to ensure that the part is fully deformed and reduce the resilience, the elongation is usually not less than 0.02; thus the elongation e of the material pre-stretchingbIn the range of 0.02-0.8At. The actual deformation of the part can be combined and is 0.02-0.8AtDetermining the elongation e of the pre-stretching within the rangeb。
(3) And the quenching steel material is divided into steel materials to be manufactured into high-speed tensile samples. Performing unidirectional stretching on the high-speed tensile sample by using a tensile testing machine, and when the equivalent strain of the material reaches the pre-stretched elongation e in the step (2)bThen stopping loading; a pre-stretched sample was obtained. The tensile strain rate should take into account the material strain rate during the actual forming process, and the strain rate is selected from 0.01/s to 1/s.
(4) Carrying out a high-speed tensile curve experiment on the pre-stretched sample; the high-speed tensile curve experiment is to carry out a plurality of high-speed tensile experiments with different speeds, preferably 0.001/s, 0.1/s, 1/s, 10/s, 100/s, 500/s and 1000/s strain rate; obtaining true stress sigma and true plastic strain epsilon of different strain ratespCurve line.
(5) Fitting curves with different speeds by using the following constitutive equation (A) to obtain a high-speed tensile curve;
σ＝s*(εp+ln(1+eb))c (A)；
in the formula:
sigma is the true stress in MPa;
εptrue plastic strain, unit 1;
s is the strain hardening coefficient in MPa; c is the strain hardening index, unit 1;
the values of s, c are obtained by fitting of the constitutive equation (a).
Examples 1 to 6: the detection method of the quenching distribution steel high-speed tensile curve adopts the following specific process.
(1) Tensile properties of the material: detecting the tensile curve of the quenching distribution steel material at the strain rate of 0.01/s-1/s to obtain the yield strength of the material and the tensile strength R of the materialmAnd the maximum force total elongation At. The results of the tests of the examples are shown in Table 1.
Table 1: tensile Property test results
(2) Pre-stretching: the steel material is prepared into a high-speed tensile sample by quenching, and the elongation e of the sample is pre-stretchedbIn the range of 0.02-0.8AtThe pre-stretching is carried out within the range. Examples elongation e of Pre-stretchingbAnd the selected specific elongation ebSee table 2.
Table 2: range of elongation of pre-stretching and elongation
(3) High speed tensile curve experiment: performing high-speed tensile curve experiments on the pre-stretched test sample, and performing high-speed tensile experiments at the speed of 0.001/s, 0.1/s, 1/s, 10/s, 100/s, 500/s and 1000/s; record the true plastic strain ε at each ratepAnd the actual stress sigma data, using example 1 as an example, the resultsSee table 3.
Table 3: example 1 high speed tensile Curve test results
(4) And (3) fitting the curves with different speeds by using the constitutive equation (A) to obtain a high-speed tensile curve. Taking example 1 as an example for illustration, the parameters of the fitting are shown in table 4; the high speed draw curve obtained in example 1 is shown in FIG. 1, which is a graph showing the curves at a rate of 0.001/s, 0.1/s, 1/s, 10/s, 100/s, 500/s and 1000/s, from bottom to top.
Table 4: example 1 parameters of the fitting
| Serial number | Rate of strain | s | c |
| 1 | 0.001/s | 1545.2 | 0.16 |
| 2 | 0.1/s | 1583 | 0.16 |
| 3 | 1/s | 1614.8 | 0.155 |
| 4 | 10/s | 1639.7 | 0.155 |
| 5 | 100/s | 1672.2 | 0.155 |
| 6 | 500/s | 1696.4 | 0.15 |
| 7 | 1000/s | 1776.2 | 0.15 |
(5) Respectively inputting the high-speed tensile property obtained in the embodiment 1 and the high-speed tensile property obtained without pre-stretching as performance data of the material into collision simulation software, calculating crushing displacement and absorption energy in the collision process of the hat-shaped beam, and calculating the error between simulation results of the two and experimental values; according to statistics, when the pre-stretching is not performed, the crushing displacement error of a simulation result and an experimental value is about 6%, and the energy absorption error is about 5%; after the method is adopted for pre-stretching, the crushing displacement error of a simulation result and an experimental value is about 2 percent, and the energy absorption error is about 3 percent; the results of the validation of example 1 are shown in Table 5.
Table 5: example 1 Effect verification
As can be seen from table 5, the high-speed tensile properties obtained in example 1 were used for collision simulation analysis, and the error between the simulation result and the experimental value was lower.
Claims (4)
1. A detection method for a high-speed tensile curve of quenching distribution steel is characterized by comprising the following steps:
(1) detecting the tensile property of the quenching steel material to obtain the tensile strength of the material
And maximum force total elongation
；
(2) Pre-stretching a high speed tensile specimen of a material, the elongation of the pre-stretching
In the range of 0.02 to 0.8%
；
(3) And (3) carrying out a high-speed tensile curve experiment on the high-speed tensile sample pre-stretched in the step (2) to obtain a high-speed tensile curve of the quenching distribution steel.
2. The method for detecting the high-speed tensile curve of the quenched distribution steel according to claim 1, wherein the method comprises the following steps: in the step (1), the tensile property is detected at a strain rate of 0.01/s to 1/s.
3. The method for detecting the high-speed tensile curve of the quenched distribution steel according to claim 1, wherein the method comprises the following steps: in the step (2), the pre-stretching strain rate is 0.01/s-1/s.
4. The method for detecting the high-speed tensile curve of quench distribution steel according to any one of claims 1 to 3, characterized in that: in the step (3), the strain strengthening coefficient of the high-speed tensile curve is obtained by fitting the following constitutive equation (A)
And strain hardening index
；
In the formula:
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115597970A (en) * | 2022-11-17 | 2023-01-13 | 太原科技大学（Cn） | Strain distribution testing method for copper-containing stainless steel sheet |
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