CN106950130B - Method for predicting austenite content of TRIP type high-strength steel after fatigue fracture - Google Patents
Method for predicting austenite content of TRIP type high-strength steel after fatigue fracture Download PDFInfo
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- CN106950130B CN106950130B CN201710267536.3A CN201710267536A CN106950130B CN 106950130 B CN106950130 B CN 106950130B CN 201710267536 A CN201710267536 A CN 201710267536A CN 106950130 B CN106950130 B CN 106950130B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/32—Investigating strength properties of solid materials by application of mechanical stress by applying repeated or pulsating forces
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/20—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by using diffraction of the radiation by the materials, e.g. for investigating crystal structure; by using scattering of the radiation by the materials, e.g. for investigating non-crystalline materials; by using reflection of the radiation by the materials
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
- G01N2203/0073—Fatigue
Abstract
The invention discloses a method for predicting the austenite content of TRIP type high-strength steel after fatigue fracture, which comprises the following steps of firstly measuring the initial residual austenite volume fraction of a plate; then loading cyclic loads with different stress amplitudes on the plate until the sample is broken or the number of cycles exceeds one million times; fitting based on test data to obtain an expression of the residual austenite content of the attachment of the fracture of the sample after the TRIP type high-strength steel is fractured under the action of cyclic loads with different stress amplitudes; based on the expression, the residual austenite content of the TRIP type high-strength steel after fatigue fracture at different stress amplitudes can be accurately predicted by giving the stress amplitude. The method is simple, accurate, low in cost and easy to implement, accurately predicts the residual austenite content of the TRIP type high-strength steel plate after fatigue fracture with different stress amplitudes, provides basis for predicting the service life and the performance of the plate, and accordingly accelerates popularization of the TRIP type high-strength steel.
Description
Technical Field
The invention relates to the field of metal material performance, in particular to a method for predicting austenite content of TRIP type high-strength steel after fatigue fracture.
Background
The light weight of the automobile is a main way for energy conservation and emission reduction of the automobile, and is paid attention today when the energy crisis and the environmental problem are increasingly prominent. Transformation-induced plasticity (TRIP) steel, which is a representative of advanced high-strength steel, has an internal retained austenite that undergoes martensitic Transformation under stress/strain to improve the overall plasticity and hardening capacity of the material, thereby obtaining a very high product of strength and elongation. This makes TRIP steel an excellent choice of materials for automotive structural members, particularly safety members, such as B-pillars, door bumpers, and the like.
Fatigue fracture is one of main failure modes of automobile body parts, and the application and popularization of advanced TRIP type high-strength steel on an automobile body must meet the requirement of fatigue performance. Because a certain content of residual austenite is transformed along with the applied stress and strain in the TRIP type high-strength steel, the martensite phase transformation of the residual austenite under the action of cyclic load can obviously influence the service life and the performance of the material in the service process of the TRIP type high-strength steel material. Therefore, the method has important significance for applying the TRIP type high-strength steel and analyzing the failure mechanism of the TRIP type high-strength steel in predicting the residual austenite content of the sample after fatigue fracture quantitatively, quickly and accurately.
The transformation law of the retained austenite of the TRIP-type high-strength steel material under the action of cyclic load is obviously different from that under unidirectional static load, and the transformation law of the retained austenite obtained based on unidirectional static load loading in the traditional method cannot be used for predicting the content of the retained austenite in the TRIP-type high-strength steel under the action of cyclic load. Accurate prediction of austenite content in TRIP type high-strength steel after fatigue fracture under cyclic loading action requires a new method based on cyclic loading.
Disclosure of Invention
In view of the above technical problems, the present invention aims to provide a method for predicting the austenite content of a TRIP type high-strength steel after fatigue fracture. The prediction method is accurate, rapid and easy to implement, can accurately predict the content of the residual austenite in the plate material after the load fatigue fracture with different stress amplitudes, and provides a basis for accurately estimating the fatigue life and the performance of the TRIP type high-strength steel material, thereby accelerating the popularization of the TRIP type high-strength steel.
In order to realize the purpose, the invention is realized according to the following technical scheme:
a method for predicting the austenite content of TRIP type high-strength steel after fatigue fracture comprises the following steps:
step S1: preparing a TRIP type high-strength steel plate fatigue sample, and measuring the initial residual austenite volume fraction of the plate;
step S2: carrying out fatigue failure tests on the plate under the action of cyclic loads with different stress amplitudes, applying the cyclic loads with different stress amplitudes to the sample at room temperature until the fatigue failure or the cyclic times of the sample are higher than 100 ten thousand, stopping the tests, taking down the sample, and measuring the content of the residual austenite at the fracture center point of 10 mm;
step S3: according to the results of limited experiments, fitting the relation that the content of the residual austenite in the sample changes along with the change of the maximum stress after the fatigue fracture, and establishing an expression of the content of the residual austenite near the fatigue fracture along with the change of the stress amplitude:
wherein S isbCritical maximum stress, determined by limited experiments; below this critical stress, the volume fraction of austenite remains at f, no matter how many cyclesγf(means)The method can be obtained by averaging the experiment results for a limited number of times; above this critical stress, the volume fraction of austenite is according to fγfIs calculated by the expression of (a);
step S4: and (3) quantitatively predicting the content of the residual austenite near the fatigue fracture of the TRIP type high-strength steel plate material by combining the expression of the content of the residual austenite near the fatigue fracture, which is obtained in the steps and changes along with the stress amplitude.
Further, the step S1 of measuring the initial volume fraction of retained austenite of the plate material adopts an X-ray diffraction method.
Further, the fatigue fracture test described in step S2 is a test in which the test is stopped by applying a cyclic load to the sample until the sample fails in fatigue or the number of cycles is more than 100 ten thousand.
Compared with the prior art, the invention has the following beneficial effects:
the method considers the influence of the cyclic loads with different stress amplitudes on the phase change of the retained austenite, and can accurately and quickly predict the content of the retained austenite in the plate material after the cyclic load action fatigue fracture through the prediction formula provided by the invention, thereby reducing the time cost and the economic cost.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a schematic diagram of the method of predicting the austenite content of a TRIP-type high-strength steel after fatigue fracture according to the present invention;
FIG. 2 shows the residual austenite content of QP980 steel after fatigue fracture under cyclic loads with different stress amplitudes.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention.
FIG. 1 is a schematic diagram of the method of predicting the austenite content of a TRIP-type high-strength steel after fatigue fracture according to the present invention; as shown in fig. 1, the prediction method of the present invention includes the following steps:
a method for predicting the austenite content of TRIP type high-strength steel after fatigue fracture comprises the following steps:
step S1: preparing a TRIP type high-strength steel plate fatigue sample, and measuring the initial residual austenite volume fraction of the plate;
step S2: carrying out fatigue failure tests on the plate under the action of cyclic loads with different stress amplitudes, applying the cyclic loads with different stress amplitudes to the sample at room temperature until the fatigue failure or the cyclic times of the sample are higher than 100 ten thousand, stopping the tests, taking down the sample, and measuring the content of the residual austenite at the fracture center point of 10 mm;
step S3: according to the results of limited experiments, fitting the relation that the content of the residual austenite in the sample changes along with the change of the maximum stress after the fatigue fracture, and establishing an expression of the content of the residual austenite near the fatigue fracture along with the change of the stress amplitude:
wherein S isbCritical maximum stress, determined by limited experiments; below this critical stress, the volume fraction of austenite remains at f, no matter how many cyclesγf(means)The method can be obtained by averaging the experiment results for a limited number of times; above this critical stress, the volume fraction of austenite is according to fγfIs calculated by the expression of (a);
step S4: and (3) quantitatively predicting the content of the residual austenite near the fatigue fracture of the TRIP type high-strength steel plate material by combining the expression of the content of the residual austenite near the fatigue fracture, which is obtained in the steps and changes along with the stress amplitude.
Wherein, the volume fraction of the initial retained austenite of the measured plate in the step S1 adopts an X-ray diffraction method.
In the fatigue fracture test in step S2, the test is stopped until the sample is subjected to fatigue fracture or the number of cycles is greater than 100 ten thousand by applying a cyclic load to the sample.
Implementation mode one
The method selects QP980 steel, predicts the residual austenite content of the QP980 steel after fatigue fracture under the action of different stress amplitude cyclic loads, and comprises the following steps:
1. in the example, a QP980 plate material with the thickness of 1.2mm is taken as an example, a plurality of QP980 steel plate fatigue samples are prepared, and the volume fraction of the retained austenite of the original state sample measured by an X-ray diffraction method is fY0＝10.68％；
2. The stress ratio R was 0.1 and the maximum stress S was applied to the test piecemaxA cyclic load of 960MPa, 750MPa, 630MPa, respectively, i.e. the stress amplitude SaRespectively 432MPa, 337.5MPa and 283.5MPa, stopping the test until the fatigue failure or the cycle number of the sample is higher than 100 ten thousand, taking off the sample, and measuring the volume fraction of 10mm of residual austenite near the fracture of the sample;
3. according to the data of the content of the retained austenite after the fatigue fracture, which is obtained in the step 2, along with the change of the stress amplitude, as shown in fig. 2, it can be found that when the maximum stress of the cyclic load is less than 840MPa, S can be set according to the experimental datab840MPa, where the stress amplitude is less than 378MPa, the volume fraction of retained austenite remains fluctuating within a very small range, which can be considered as a constant, independent of the maximum stress or of the change in the stress amplitude, and is taken as the average of the retained austenite contents measured at several different stress levels: establishing retained austenite under the action of different maximum stress cyclic loadsExpression of volume fraction:
4. when the maximum stress of the cyclic load is more than 840MPa, the volume fraction of retained austenite decreases with the increase of the maximum stress or the stress amplitude, and the relationship between the two can be described by the following formula:
fγf＝fγf(means)-k(Smax-840)m
in the formula, k and m are constants, the volume fraction of the retained austenite of the central point of the final fatigue fracture sample under the action of cyclic loads with different stress amplitudes is measured, and k is obtained by fitting, wherein k is 2.5508 multiplied by 10-8，m＝2.96。
5. In summary of the experimental data of the volume fraction of retained austenite and the maximum stress in the final fatigue fracture sample in steps 3 and 4, the relationship is fitted with a piecewise function:
and (4) accurately and quickly calculating the residual austenite content of the QP980 steel plate after fatigue fracture under the action of cyclic loads with different stress amplitudes according to the finally obtained piecewise function expression.
Although the invention has been described in detail above with reference to a general description and specific examples, it will be apparent to one skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.
Claims (2)
1. A method for predicting the austenite content of TRIP type high-strength steel after fatigue fracture is characterized by comprising the following steps:
step S1: preparing a TRIP type high-strength steel plate fatigue sample, and measuring the initial residual austenite volume fraction of the plate;
step S2: carrying out fatigue failure tests on the plate under the action of cyclic loads with different stress amplitudes, applying the cyclic loads with different stress amplitudes to the sample at room temperature until the fatigue failure or the cyclic times of the sample are higher than 100 ten thousand, stopping the tests, taking down the sample, and measuring the content of the residual austenite at the fracture center point of 10 mm;
step S3: according to the results of limited experiments, fitting the relation that the content of the residual austenite in the sample changes along with the change of the maximum stress after the fatigue fracture, and establishing an expression of the content of the residual austenite near the fatigue fracture along with the change of the stress amplitude:
wherein S isbCritical maximum stress, determined by limited experiments; below this critical stress, the volume fraction of austenite remains at f, no matter how many cyclesγf(means)The method can be obtained by averaging the experiment results for a limited number of times; above this critical stress, the volume fraction of austenite is according to fγfIs calculated by the expression ofγf(i)Represents the volume fraction of austenite at the ith time, i represents the number of times of test results, k represents a first constant, and n represents a second constant;
step S4: and (4) quantitatively predicting the content of the residual austenite near the fatigue fracture of the TRIP type high-strength steel plate material by combining the expression of the content of the residual austenite near the fatigue fracture obtained in the previous step along with the change of the stress amplitude.
2. The method for predicting the austenite content of the TRIP-type high-strength steel after the fatigue fracture according to claim 1,
and in the step S1, the original residual austenite volume fraction of the plate is measured by adopting an X-ray diffraction method.
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| JP2011237221A (en) * | 2010-05-07 | 2011-11-24 | Ihi Corp | Stress state estimation method for austenitic stainless steel |
| CN102680388A (en) * | 2011-03-09 | 2012-09-19 | 宝山钢铁股份有限公司 | Method for measuring volume distribution of retained austenite in transformation induced plasticity (TRIP) steel stamped part |
| CN103323471A (en) * | 2013-05-14 | 2013-09-25 | 青岛理工大学 | Quantitative prediction method of retained austenite transformation in incremental forming process of TRIP steel plate material |
| CN103776977A (en) * | 2014-01-22 | 2014-05-07 | 上海交通大学 | Method for forecasting retained austenite change of Q&P steel after transformation under different temperatures |
| CN104281774A (en) * | 2014-09-02 | 2015-01-14 | 上海交通大学 | Method for predicting residue austenite content in Q&P steel after single-direction stretching at different strain rates |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2011237221A (en) * | 2010-05-07 | 2011-11-24 | Ihi Corp | Stress state estimation method for austenitic stainless steel |
| CN102680388A (en) * | 2011-03-09 | 2012-09-19 | 宝山钢铁股份有限公司 | Method for measuring volume distribution of retained austenite in transformation induced plasticity (TRIP) steel stamped part |
| CN103323471A (en) * | 2013-05-14 | 2013-09-25 | 青岛理工大学 | Quantitative prediction method of retained austenite transformation in incremental forming process of TRIP steel plate material |
| CN103776977A (en) * | 2014-01-22 | 2014-05-07 | 上海交通大学 | Method for forecasting retained austenite change of Q&P steel after transformation under different temperatures |
| CN104281774A (en) * | 2014-09-02 | 2015-01-14 | 上海交通大学 | Method for predicting residue austenite content in Q&P steel after single-direction stretching at different strain rates |
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