Method for obtaining high temperature creep parameters of iron-nickel based alloy

Abstract

The present application relates to the technical fields of high temperature creep test, in particular to a method for obtaining high temperature creep parameters of iron-nickel based alloy, which mainly determines the creep strain model of iron-nickel based alloy, obtains the creep strain rate calculation formula from the creep strain model, implements two creep tests of target test material under two different creep stresses at target temperature, respectively obtains the creep curves corresponding to creep time and creep strain, selects two creep times at the first stage and the second stage of the two creep curves respectively, obtains the creep strain and creep strain rate under the creep stress corresponding to the two creep times respectively, substitutes into the creep strain model and the creep strain rate calculation formula, and calculates the variable parameters of the creep strain model. The evaluation process of the creep model is greatly simplified, the required number of creep tests and test time are reduced, and the test cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-temperature creep test, in particular to a method for obtaining high-temperature creep parameters of iron-nickel-based alloy. BACKGROUND

[0002] For advanced ultra-supercritical generating units with high parameters and large capacity, the design service temperature is higher than 650℃, which puts forward higher requirements for the high-temperature performance of the materials of the unit components. The materials produce slow and continuous plastic deformation, i.e. creep phenomenon, under long-term operation of the equipment and components at high temperature, and the creep may cause excessive deformation and damage defects of the materials, which is the main form of high-temperature structural damage. Therefore, it is particularly important to examine and evaluate the creep performance of the iron-nickel-based alloy used.

[0003] The creep curve is generally divided into three stages, the first stage is the initial creep with a large creep rate decreasing to a small one, the second stage is the stable stage with a constant minimum creep rate, and the third stage is the accelerated creep with an increasing creep rate. The iron-nickel-based alloy has a Fe (iron) content ranging from 35% to 45% and a weight percentage of Ni (nickel) + Cr (chromium) greater than 50%, and has excellent microstructure stability and good high-temperature creep endurance, and the creep curve of the iron-nickel-based alloy has obvious first and second stages, i.e. the first two stages of the creep curve are the main stages of the service of the iron-nickel-based alloy.

[0004] At present, there are many theories describing the creep phenomenon and creep law, and researchers have proposed more than one hundred creep constitutive models from microstructure and macroscopic phenomenology, such as the widely used Norton, Bailey, Dorn, Garofalo and theta projection models. The variable parameters of most creep models are redundant, the data processing process is complicated, and a large number of creep tests at different temperatures and different loads are required, which has a long test cycle and high economic cost. SUMMARY

[0005] In view of the above defects of the prior art, the technical problem to be solved by the present application is to provide a method for obtaining high-temperature creep parameters of iron-nickel-based alloy, which can simplify the creep model evaluation process and reduce the number, time and cost of required creep tests.

[0006] In order to solve the above technical problems, the present application adopts the following technical solutions:

[0007] The present application provides a method for obtaining high-temperature creep parameters of iron-nickel-based alloy, which comprises the following steps in sequence:

[0008] Step S1, determining the creep strain model of the iron-nickel-based alloy as follows:

[0009]

[0010] In formula (1), ε is the creep strain, σ is the creep stress, t is the creep time, A1 is the first stress coefficient, m1 is the first stress index, A2 is the second stress coefficient, m2 is the second stress index, and n is the initial creep time index.

[0011] The derivative of formula (1) is obtained as follows: The calculation formula of the creep strain rate is as follows:

[0012]

[0013] Step S2, two creep tests of the target test material under two different creep stresses σ1 and σ2 at the target temperature are performed, and two creep curves corresponding to the creep time t and the creep strain ε are obtained, respectively.

[0014] Step S3, the creep time t I is selected in the first stage of the two creep curves, and the creep strain and the creep strain rate corresponding to the creep time t I under the creep stress σ1 are ε I1 and The creep strain and the creep strain rate corresponding to the creep time t I under the creep stress σ2 are ε I2 and

[0015] Step S4, the creep time t II is selected in the second stage of the two creep curves, and the creep strain and the creep strain rate corresponding to the creep time t II under the creep stress σ1 are ε II1 and The creep strain and the creep strain rate corresponding to the creep time t II under the creep stress σ2 are ε II2 and

[0016] Step S5, σ1, σ2, t I , t II , ε I1 , ε I2 , ε II1 , ε II2 and are substituted into formula (1) and formula (2), and m1, n, A1, m2 and A2 are obtained by calculation.

[0017] Preferably, in step S2 , the difference between the two creep stresses σ1 and σ2 does not exceed 10% of the larger value of the two creep stresses σ1 and σ2 .

[0018] Preferably, in step S2, the target temperature is 600°C-750°C.

[0019] Preferably, in step S2, the target test material is an iron-nickel based alloy having an iron content of 35%-45% and a sum of the weight percentages of nickel and chromium greater than 50%.

[0020] Preferably, the creep time t selected in step S3 is I and the creep time t selected in step S4 II Make t I The corresponding creep strain rate is greater than t II The corresponding creep strain rate, and the initial creep time index n satisfies: 0 <n<1。

[0021] Preferably, in step S5, the first stress index m1 is calculated as follows:

[0022] t I ,σ1, σ2, Substituting into formula (2) we get:

[0023]

[0024]

[0025] t I ,σ1,ε I1 ,σ2,ε I2 Substituting into formula (1) we get:

[0026]

[0027]

[0028] By substituting equation (3-1) - equation (4-1), we can get:

[0029]

[0030] By substituting equation (3-2) - equation (4-2), we can get:

[0031]

[0032] Dividing equation (5) by equation (6) yields:

[0033]

[0034] Taking the logarithm of both sides of formula (7), we can get the calculation formula of m1 as follows:

[0035]

[0036] Preferably, in step S5, the calculation method of the initial creep time index n is:

[0037] Substitute t II , σ1, into equation (2) to obtain:

[0038]

[0039] Make equation (3-1) to equation (9) to obtain:

[0040]

[0041] Substitute t II , σ1, ε II1 into equation (1) to obtain:

[0042]

[0043] Make equation (4-1) to equation (11) to obtain:

[0044]

[0045] Divide equation (10) by equation (12) to obtain the calculation formula of n:

[0046]

[0047] Preferably, in step S5, the calculation method of the first stress coefficient A1 is:

[0048] From equation (10), we obtain:

[0049]

[0050] Substitute the calculation formula of m1 and n into equation (14) to obtain the calculation formula of A1.

[0051] Preferably, in step S5, the calculation method of the second stress index m2 is:

[0052] Substitute t II , σ2, into equation (2) to obtain:

[0053]

[0054] From equation (9) and equation (15), we obtain:

[0055]

[0056] Take the logarithm of both sides of equation (16) to obtain:

[0057]

[0058] Substitute the calculation formula of m1, n and A1 into formula (17), to obtain the calculation formula of m2.

[0059] Preferably, in step S5, the calculation method of the second stress coefficient A2 is:

[0060] From formula (9):

[0061]

[0062] Substitute the calculation formula of m1, n, A1 and m2 into formula (18), to obtain the calculation formula of A2.

[0063] Compared with the prior art, the present application has significant progress:

[0064] The method for obtaining the high-temperature creep parameters of the iron-nickel-based alloy of the present application obtains five variable parameters of the creep strain model through the creep curves of two different creep stresses σ1 and σ2 at the target temperature, greatly simplifies the evaluation process of the creep model, reduces the number and time of required creep tests, and lowers the test cost. BRIEF DESCRIPTION OF DRAWINGS

[0065] Figure 1 is a schematic diagram of two creep curves in the method for obtaining the high-temperature creep parameters of the iron-nickel-based alloy of the embodiment of the present application.

[0066] Figure 2 is a schematic diagram of the comparison results of the creep strain model curve obtained by the method for obtaining the high-temperature creep parameters of the iron-nickel-based alloy of the embodiment of the present application and the creep data fitting curve obtained by the prior art multi-sample and multi-test method. DETAILED DESCRIPTION

[0067] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings. These embodiments are only used to illustrate the present application, and are not limiting to the present application.

[0068] In the description of the present application, it should be noted that the orientations or positional relationships indicated by the terms “center”, “longitudinal”, “transverse”, “upper”, “lower”, “front”, “rear”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer” and the like are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms “first” and “second” are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0069] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0070] In addition, in the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0071] As Figure 1 shown, an embodiment of the method for obtaining high-temperature creep parameters of iron-nickel-based alloy of the present application. The method for obtaining high-temperature creep parameters of iron-nickel-based alloy of the embodiment comprises the following steps in turn.

[0072] Step S1, according to the main stages of iron-nickel-based alloy service are the first stage and the second stage of the creep curve, the creep strain model of the iron-nickel-based alloy is determined as:

[0073]

[0074] In formula (1), ε is the creep strain, σ is the creep stress, t is the creep time, A1 is the first stress coefficient, m1 is the first stress index, A2 is the second stress coefficient, m2 is the second stress index, and n is the initial creep time index.

[0075] It should be noted that the relationship formula of creep strain ε and creep stress σ, creep time t represented by formula (1) is a creep strain model that can be obtained by those skilled in the art, wherein the first stress coefficient A1, the first stress index m1, the second stress coefficient A2, the second stress index m2 and the initial creep time index n are five variable parameters of the creep strain model.

[0076] The derivative of formula (1) is obtained, and the calculation formula of the creep strain rate is:

[0077]

[0078] Step S2, two creep tests of the target test material under two different creep stresses σ1, σ2 at the target temperature are carried out, and the creep curves corresponding to the creep time t and the creep strain ε are obtained respectively, as Figure 1As shown, in this embodiment, σ1>σ2. In order to make the two creep curves have the same time in the same creep stage, preferably, the difference between the two creep stresses σ1, σ2 does not exceed 10% of the larger value of the two creep stresses σ1, σ2. In this embodiment, the target test material is preferably an iron-nickel-based alloy with an iron content of 35%-45% and a weight percentage of nickel and chromium greater than 50%, the target temperature is preferably 600-750°C, and the twice creep test method is preferably a standard creep test method.

[0079] Step S3, selecting a creep time t I on the first stage of the two creep curves I The corresponding creep strain and creep strain rate are ε I1 and The creep curve under the creep stress σ2 corresponds to the creep time t I The corresponding creep strain and creep strain rate are ε I2 and

[0080] Step S4, selecting a creep time t II on the second stage of the two creep curves II The corresponding creep strain and creep strain rate are ε II1 and The creep curve under the creep stress σ2 corresponds to the creep time t II The corresponding creep strain and creep strain rate are ε II2 and

[0081] Step S5, substituting σ1, σ2, t I , t II , ε I1 , ε I2 , ε II1 , ε II2 and into formula (1) and formula (2) to obtain m1, n, A1, m2 and A2 by calculation.

[0082] In this embodiment, preferably, in step S5, the calculation method of the first stress index m1 is:

[0083] Substituting t I , σ1, σ2, into formula (2) gives:

[0084]

[0085]

[0086] Substitute t I , σ1, ε I1 , σ2, ε I2 into formula (1), we get:

[0087]

[0088]

[0089] Make formula (3-1) to formula (4-1):

[0090]

[0091] Make formula (3-2) to formula (4-2):

[0092]

[0093] Divide formula (5) by formula (6), we get:

[0094]

[0095] Take the logarithm of both sides of formula (7), and we get the calculation formula of m1:

[0096]

[0097] Substitute σ1, σ2, t I , ε I1 , ε I2 , into formula (8), and we can calculate the value of m1.

[0098] Further, in step S5, the calculation method of the initial creep time index n is:

[0099] Substitute t II , σ1, into formula (2), we get:

[0100]

[0101] Make formula (3-1) to formula (9):

[0102]

[0103] Substitute t II , σ1, ε II1 into formula (1), we get:

[0104]

[0105] The formula (4-1) to formula (11) are obtained:

[0106]

[0107] The formula (10) is divided by the formula (12), and the calculation formula of n is obtained:

[0108]

[0109] The value of t I , t II , ε I1 , ε II1 , is substituted into the formula (13), and the value of n is calculated.

[0110] Further, in the step S5, the calculation method of the first stress coefficient A1 is:

[0111] The formula (10) is obtained:

[0112]

[0113] The calculation formula of m1 and n is substituted into the formula (14), and the calculation formula of A1 is obtained. The value of t I , t II , σ1, and the value of m1 and n are substituted into the formula (14), and the value of A1 is calculated.

[0114] Further, in the step S5, the calculation method of the second stress index m2 is:

[0115] The formula (2) is obtained by substituting t II , σ2, into the formula (2):

[0116]

[0117] The formula (9) and the formula (15) are obtained:

[0118]

[0119] The logarithm of both sides of the formula (16) is taken, and the formula (17) is obtained:

[0120]

[0121] The calculation formula of m1, n and A1 is substituted into the formula (17), and the calculation formula of m2 is obtained. The value of t II , σ1, σ2, and the value of m1, n and A1 are substituted into the formula (17), and the value of m2 is calculated.

[0122] Further, in step S5, the calculation method of the second stress coefficient A2 is:

[0123] From equation (9), we have:

[0124]

[0125] Substitute the calculation formula of m1, n, A1 and m2 into equation (18) to obtain the calculation formula of A2. Substitute the values of t II , σ1, and m1, n, A1, m2 into equation (18) to calculate the value of A2.

[0126] Thus, the values of the five variable parameters m1, n, A1, m2 and A2 in the creep strain model equation (1) are obtained. Substitute the values of m1, n, A1, m2 and A2 into equation (1) to obtain the creep strain model of the iron-nickel-based alloy.

[0127] In this embodiment, preferably, the creep time t I selected in step S3 is greater than the creep time t II selected in step S4, i.e.: I The corresponding creep strain rate is greater than the creep strain rate corresponding to t II , i.e.: And the initial creep time index n satisfies: 0 < n < 1.

[0128] The method for obtaining high-temperature creep parameters of an iron-nickel-based alloy of this embodiment obtains the five variable parameters of the creep strain model through the creep curves of two different creep stresses σ1, σ2 at the target temperature, greatly simplifies the evaluation process of the creep model, reduces the number of required creep tests and test time, and reduces test costs.

[0129] Taking a specific example, two standard creep samples of the target test material iron-nickel-based alloy HT700 are processed, and creep tests are respectively performed according to the standard creep test method. The target test temperature is 700°C, the creep stresses are σ1=200MPa and σ2=180MPa, and two creep curves corresponding to the creep time t and the creep strain ε are obtained. According to the steps S3-S5 of the method for obtaining high-temperature creep parameters of an iron-nickel-based alloy of this embodiment, the values of the five variable parameters m1, n, A1, m2 and A2 in the creep strain model equation (1) in step S1 are calculated, and finally the creep strain model of the target test material iron-nickel-based alloy HT700 at 700°C is obtained as follows: ε=(9.238E-10)σ 3.24 t 0.03 +(5.414E-25)σ 8.775 t.

[0130] In order to verify the method for obtaining the high-temperature creep parameters of the iron-nickel-based alloy in the embodiment, the multi-sample and multi-test method in the prior art is used to perform creep tests on four samples of the iron-nickel-based alloy HT700 under different stresses at 700 DEG C, and test data and fitting curves of the stable creep strain rate and the creep stress are obtained, as shown in FIG. 6. The creep strain model curve of the target test material, the iron-nickel-based alloy HT700, at 700 DEG C obtained by the method for obtaining the high-temperature creep parameters of the iron-nickel-based alloy in the embodiment has a very high coincidence degree with the creep data fitting curve of the iron-nickel-based alloy HT700 at 700 DEG C obtained by the multi-sample and multi-test method in the prior art, which verifies the effectiveness of the method for obtaining the high-temperature creep parameters of the iron-nickel-based alloy in the embodiment. Figure 2

[0131] The above description is only preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, some improvements and replacements can be made without departing from the technical principles of the present application, and these improvements and replacements should also be considered as the protection scope of the present application.​

Claims

1. A method for obtaining high-temperature creep parameters of an iron-nickel based alloy, characterized in that: The following steps are included in sequence: Step S1: Determine the creep strain model of the iron-nickel based alloy as follows: In formula (1), ε is the creep strain, σ is the creep stress, t is the creep time, A1 is the first stress coefficient, m1 is the first stress exponent, A2 is the second stress coefficient, m2 is the second stress exponent, and n is the initial creep time exponent; Taking the derivative of equation (1), we can get the creep strain rate: The calculation formula is: Step S2, performing two creep tests on the target test material at a target temperature with two different creep stresses σ1 and σ2, and obtaining creep curves corresponding to creep time t and creep strain ε, respectively; Step S3: Select creep time t in the first stage of the two creep curves. I , obtain the creep curve under creep stress σ1 at creep time t I The corresponding creep strain and creep strain rate are ε I1 and The creep curve under creep stress σ2 at creep time t I The corresponding creep strain and creep strain rate are ε I2 and Step S4: Select creep time t in phase II of the two creep curves. II , obtain the creep curve under creep stress σ1 at creep time t II The corresponding creep strain and creep strain rate are ε II1 and The creep curve under creep stress σ2 at creep time t II The corresponding creep strain and creep strain rate are ε II2 and Step S5: σ1, σ2, t I , t II , ε I1 、 ε I2 、 ε II1 、 ε II2 and Substituting into equations (1) and (2), m1, n, A1, m2, and A2 are obtained by calculation.

2. The method for obtaining high temperature creep parameters of an iron-nickel based alloy according to claim 1, characterized in that: In step S2, the difference between the two creep stresses σ1 and σ2 does not exceed 10% of the larger value of the two creep stresses σ1 and σ2.

3. The method for obtaining high temperature creep parameters of an iron-nickel based alloy according to claim 1, characterized in that: In step S2, the target temperature is 600°C-750°C.

4. The method for obtaining high temperature creep parameters of an iron-nickel based alloy according to claim 1, characterized in that: In step S2, the target test material is an iron-nickel based alloy having an iron content of 35%-45% and a sum of the weight percentages of nickel and chromium greater than 50%.

5. The method for obtaining high temperature creep parameters of an iron-nickel based alloy according to claim 1, characterized in that: The creep time t selected in step S3 I and the creep time t selected in step S4 II Make t I The corresponding creep strain rate is greater than t II The corresponding creep strain rate, and the initial creep time index n satisfies: 0 <n<1。 6. The method for obtaining high temperature creep parameters of an iron-nickel based alloy according to claim 1, characterized in that: In step S5, the first stress index m1 is calculated as follows: t I ,σ1, σ2, Substituting into formula (2) we get: t I ,σ1,ε I1 ,σ2,ε I2 Substituting into formula (1) we get: By substituting equation (3-1) - equation (4-1), we can get: By substituting equation (3-2) - equation (4-2), we can get: Dividing equation (5) by equation (6) yields: Taking the logarithm of both sides of formula (7), we can get the calculation formula of m1 as follows:

7. The method for obtaining high temperature creep parameters of an iron-nickel based alloy according to claim 6, characterized in that: In step S5, the calculation method of the initial creep time index n is: t II ,σ1, Substituting into formula (2) we get: By using equation (3-1) - equation (9), we can get: t II ,σ1,ε II1 Substituting into formula (1) we get: By using equation (4-1) - equation (11), we can get: Dividing formula (10) by formula (12) yields the following formula for n:

8. The method for obtaining high temperature creep parameters of an iron-nickel based alloy according to claim 7, characterized in that: In step S5, the calculation method of the first stress coefficient A1 is: From formula (10), we can get: Substituting the calculation formulas of m1 and n into formula (14), we can obtain the calculation formula of A1.

9. The method for obtaining high temperature creep parameters of an iron-nickel based alloy according to claim 8, characterized in that: In step S5, the second stress index m2 is calculated as follows: t II ,σ2, Substituting into formula (2) we get: From formula (9) and formula (15), we can get: Taking the logarithm of both sides of formula (16), we get: Substituting the calculation formulas of m1, n, and A1 into formula (17), we can obtain the calculation formula of m2.

10. The method for obtaining high temperature creep parameters of an iron-nickel based alloy according to claim 9, characterized in that: In step S5, the second stress coefficient A2 is calculated as follows: From formula (9), we can get: Substituting the calculation formulas of m1, n, A1 and m2 into formula (18), we can obtain the calculation formula of A2.

Images