CN114577587A - Method for judging reheat crack sensitivity of coarse crystal region - Google Patents

Method for judging reheat crack sensitivity of coarse crystal region Download PDF

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CN114577587A
CN114577587A CN202210278933.1A CN202210278933A CN114577587A CN 114577587 A CN114577587 A CN 114577587A CN 202210278933 A CN202210278933 A CN 202210278933A CN 114577587 A CN114577587 A CN 114577587A
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resistant steel
evaluating
creep
low
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张磊
王艳松
刘福广
米紫昊
王德瑞
李启国
巴特尔
韩天鹏
杨二娟
袁树斌
罗树林
杨兰
雷俊龙
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Xian Thermal Power Research Institute Co Ltd
Huaneng Yimin Coal and Electricity Co Ltd
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Xian Thermal Power Research Institute Co Ltd
Huaneng Yimin Coal and Electricity Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/44—Sample treatment involving radiation, e.g. heat
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • G01N1/42—Low-temperature sample treatment, e.g. cryofixation
    • 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
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • 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
    • G01N2203/0001—Type of application of the stress
    • G01N2203/0003—Steady
    • 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
    • G01N2203/0014—Type of force applied
    • G01N2203/0016—Tensile or compressive
    • G01N2203/0019—Compressive
    • 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
    • G01N2203/006—Crack, flaws, fracture or rupture
    • G01N2203/0062—Crack or flaws
    • 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
    • G01N2203/0071—Creep
    • 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
    • G01N2203/0075—Strain-stress relations or elastic constants

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Abstract

The invention discloses a method for judging the sensitivity of reheat cracks in a coarse crystal region, and belongs to the technical field of welding evaluation. The method comprises the steps of firstly carrying out a thermal simulation experiment on a low-alloy heat-resistant steel sample according to the actual thermal cycle process of low-alloy heat-resistant steel welding to obtain a sample with a coarse crystal area structure, then carrying out a creep experiment on the sample, applying preset stress on the sample under the conditions of constant temperature and constant strain until the sample is fractured, calculating a creep strain value according to a stress relaxation curve in the experiment process, and finally establishing a relation between creep strain and section shrinkage rate by combining evaluation indexes of a short-time creep fracture test to further establish an evaluation criterion for evaluating the reheat crack sensitivity of the low-alloy heat-resistant steel welding coarse crystal area. The method solves the problems that the sectional area of the sample is measured inaccurately after the evaluation experiment of the reheat crack sensitivity of the coarse crystal area of the low-alloy heat-resistant steel is interrupted, so that the calculation error of the reduction of area is large, and the evaluation of the reheat crack sensitivity of the coarse crystal area is inaccurate.

Description

Method for judging reheat crack sensitivity of coarse crystal region
Technical Field
The invention belongs to the technical field of welded joint evaluation, and particularly relates to a method for evaluating the sensitivity of reheat cracks in a coarse crystal region.
Background
Alloy steel with the total mass fraction of alloy elements below 5 percent is generally called low-alloy heat-resistant steel, and the alloy system comprises the following components: C-Mo, C-Cr-Mo-V-Nb, C-Mo-V, C-Cr-Mo-V, C-Mn-Mo-V, C-Mn-Ni-Mo, and C-Cr-Mo-W-V-Ti-B, etc. With the successive appearance of low-alloy Mo steel, Cr-Mo steel and Cr-Mo-V steel in recent years, low-alloy heat-resistant steel has been widely used in the fields of boilers, pressure vessels, chemical equipment and the like due to its excellent weldability, corrosion resistance, wear resistance and formability. Nevertheless, the precipitation-strengthened, low-alloy, heat-resistant steel welded joint has a significant tendency to reheat cracking during long-term use at high temperatures and pressures, and is mainly generated in the coarse grain region of the heat-affected zone. Therefore, there is an urgent need for a method suitable for evaluating the reheat crack sensitivity of the coarse crystal region.
At present, the experimental methods related to the evaluation of the reheat crack sensitivity of the low-alloy heat-resistant steel welded joint comprise a bolt type reheat crack test, an H-shaped constraint test and a simulated coarse-grain-region short-time creep rupture test. The shape and size of a test piece used in the bolt type reheating crack test and a test device are the same as those of the bolt test of the cold crack, and only one electric furnace for heating is arranged at the position where the bolt is welded. The bolt type reheat crack test is a stress release test under a constant-load tensile condition, can be used for obtaining stable quantitative data, is mainly used for researching the influence rule of various components or various parameters on reheat crack sensitivity, and has the defect that the production practice cannot be approached. The H-shaped constraint test is a test method for detecting weld heat cracks and reheat cracks. The design of the test piece has a certain gap, and the restraint degree can be changed by changing the size of the gap, so that the test piece is a self-restraint type test piece. It can be seen that the H-constraint test is mainly directed to the detection of weld heat cracks and reheat cracks, and is not good at evaluating the susceptibility to reheat cracks in the heat affected zone. The short-time creep rupture test of the simulated coarse crystal region comprises two parts of preparation of the simulated coarse crystal region and high-temperature constant strain rate stretching. When the sample is subjected to the calculation of the reduction of area, the calculation result of the reduction of area is inaccurate and often influences the evaluation result of the reheat crack sensitivity of the material.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a method for evaluating the reheat crack sensitivity of a coarse crystal area, and solves the problems that the sectional area of a sample is measured inaccurately after the evaluation experiment of the reheat crack sensitivity of the coarse crystal area of low-alloy heat-resistant steel is interrupted, so that the calculation error of the reduction of area is large, and the evaluation of the reheat crack sensitivity of the coarse crystal area is inaccurate.
The invention is realized by the following technical scheme:
a method for judging reheat crack sensitivity of a coarse crystal region comprises the following steps:
s1: machining a low-alloy heat-resistant steel sample required by a thermal simulation experiment;
s2: setting thermal simulation experiment parameters according to the actual thermal cycle process of low-alloy heat-resistant steel welding, and carrying out thermal simulation experiment on a low-alloy heat-resistant steel sample to obtain a sample with a coarse crystal area structure;
s3: heating the sample obtained in the step S2 to an experimental temperature on a creep testing machine under the condition of no external load and preserving heat;
s4: applying preset stress to the sample obtained in the step S3 under the conditions of constant temperature and constant strain until the sample is broken, and calculating a creep strain value according to a stress relaxation curve in the experimental process;
s5: and establishing a relation between creep strain and reduction of area by combining evaluation indexes of a short-time creep rupture test, and further establishing an evaluation criterion for evaluating the reheat crack sensitivity of the low-alloy heat-resistant steel welding coarse crystal area.
Preferably, in S1, the surface temperature of the low-alloy heat-resistant steel sample is controlled to be less than or equal to 100 ℃ in the whole process of machining.
Preferably, in S1, the low alloy heat resistant steel test piece is a bar-like test piece.
Preferably, in S2, the thermal simulation experiment parameters include a heating rate, a peak temperature, and a cooling rate.
Preferably, in S2, the thermal simulation experiment uses thermocouple to measure the thermal cycle of the characteristic point of the temperature field or uses finite element simulation to obtain the temperature field of the welding process.
Preferably, in S3, the experimental temperature depends on the service environment of the low-alloy heat-resistant steel.
Further preferably, the heating time is 2min, the experiment temperature is 500-750 ℃, and the heat preservation time is 10 min.
Preferably, in S4, the temperature and strain of the sample are not changed during the experiment, the stress is changed with time, and the curve of the change of the stress with time is recorded as the stress relaxation curve.
Preferably, in S4, the creep strain value is calculated according to the following formula:
Figure BDA0003557304270000031
in the formula, epsiloncIs creep strain; e is the modulus of elasticity;
Figure BDA0003557304270000032
is the creep stress rate of change.
Preferably, in S5, for the test result of the same sample, the creep strain is calculated by using the data recorded in the creep test process, and the reduction of area of the sample is calculated by using the cross-sectional areas of the fracture position before and after the fracture of the sample, so as to establish the relationship between the creep strain and the reduction of area of the sample.
Compared with the prior art, the invention has the following beneficial technical effects:
the invention discloses a method for evaluating the reheat crack sensitivity of a coarse crystal area, which is based on the combination of experimental measurement and numerical calculation, establishes the relationship between creep strain and reduction of area by calculating creep strain amount and combining with evaluation indexes of a short-time creep rupture test, and further establishes an evaluation criterion for evaluating the reheat crack sensitivity of the low-alloy heat-resistant steel welding coarse crystal area. The creep strain and the reduction of area are performance indexes reflecting the plastic deformation capacity of the coarse crystal area sample under the condition of high temperature external load, the measurement of the reduction of area of the sample is greatly influenced by human factors, and the creep strain is measured by an instrument, so that the accuracy is high. Meanwhile, the method does not depend on the experience and skill level of an operator, and solves the problems that the sectional area of the sample is measured inaccurately after the evaluation experiment of the reheat crack sensitivity of the coarse crystal area of the low-alloy heat-resistant steel is interrupted, the calculation error of the reduction of area is large, and the evaluation of the reheat crack sensitivity of the coarse crystal area is inaccurate.
Further, in S1, the surface temperature of the low-alloy heat-resistant steel sample is controlled to be less than or equal to 100 ℃ in the whole machining process, so that the phenomenon that the surface structure of the sample is subjected to phase change due to overhigh surface temperature of the sample in the machining process, and the adverse effect on the performance of the sample is avoided.
Drawings
FIG. 1 is a schematic flow chart of the method of the present invention.
Detailed Description
The present invention will now be described in further detail with reference to the attached drawings, which are illustrative, but not limiting, of the present invention.
Referring to fig. 1, the method for evaluating the reheat crack sensitivity of the coarse grain region of the present invention includes:
firstly, a technician samples along a steel pipe or a steel bar longitudinally in a machining mode, the total length of a processed bar-shaped sample is 150mm, the length of a test segment is 10mm, the diameter of the test segment is phi 6mm, a clamping segment is M10mm, a transition angle is 45 degrees, the surface temperature of the sample in the machining process is not more than 100 ℃, and the surface of the processed sample is smooth and has no burrs;
secondly, calculating welding heat input Q ═ eta UI/v and measuring or finite element simulation heat cycle of the coarse crystal area of the actual joint according to actual welding parameters of the low-alloy heat-resistant steel, and setting corresponding heating speed, peak temperature and cooling speed on a thermal simulation testing machine according to the heat cycle so that a sample simulates the heating process in welding and finally obtains a sample of the coarse crystal area structure of the low-alloy heat-resistant steel;
thirdly, a sample of the coarse crystal region structure of the low-alloy heat-resistant steel is arranged on a creep testing machine, the sample is heated to a testing temperature (500-750 ℃) within 2min under the condition of no external load, the specific testing temperature is determined according to the actual service condition, and then the temperature is kept for 10 min;
fourthly, applying certain stress on the sample under the conditions of constant temperature and constant strain until the sample is broken, and recording a stress relaxation curve in the experimental process;
fifthly, calculating a creep strain value according to the curve data of stress relaxation
Figure BDA0003557304270000041
And sixthly, establishing a relation between creep strain and reduction of area by combining the evaluation indexes of the short-time creep rupture test shown in the table 1, and further establishing an evaluation criterion for evaluating the reheat crack sensitivity of the low-alloy heat-resistant steel in the welding coarse crystal area.
TABLE 1
Figure BDA0003557304270000051
The invention is further illustrated below in a specific embodiment:
in this embodiment, 15Cr1Mo1V low-alloy heat-resistant steel was selected as a study object, and a machining method was used to machine a thermal simulation sample having a length of 150mm, an experimental section length of 10mm, a test section diameter of 6mm, and clamping sections of M10mm and 10 mm. The heat affected zone of manual arc welding was simulated with thermal simulated heating rate, peak temperature and cooling rate settings according to a welding voltage of 20V, a welding speed of 20m/h, welding currents of 110A, 120A, 130A, 140A and 150A, respectively, and corresponding heat inputs of 2.77kJ/cm, 3.02kJ/cm, 3.28kJ/cm, 3.53kJ/cm and 3.78kJ/cm, respectively (see Table 2). Creep tests were performed on the obtained test specimens, and creep strain was calculated from the test results as shown in table 3. The relationship between critical creep strain and reduction of area under the 5 welding heat inputs is obtained by combining the evaluation indexes of the short-time creep rupture test, and is shown in table 3, and further the creep strain evaluation standard for evaluating the reheat crack sensitivity of the coarse grain region of the heat affected zone of the low-alloy heat-resistant steel is obtained and is shown in table 4.
TABLE 2
Figure BDA0003557304270000052
TABLE 3
Figure BDA0003557304270000053
Figure BDA0003557304270000061
TABLE 4
Figure BDA0003557304270000062
It should be noted that the above description is only a part of the embodiments of the present invention, and equivalent changes made to the system described in the present invention are included in the protection scope of the present invention. Persons skilled in the art to which this invention pertains may substitute similar alternatives for the specific embodiments described, all without departing from the scope of the invention as defined by the claims.

Claims (10)

1. A method for judging reheat crack sensitivity of a coarse crystal region is characterized by comprising the following steps:
s1: machining a low-alloy heat-resistant steel sample required by a thermal simulation experiment;
s2: setting thermal simulation experiment parameters according to the actual thermal cycle process of low-alloy heat-resistant steel welding, and carrying out thermal simulation experiment on a low-alloy heat-resistant steel sample to obtain a sample with a coarse crystal area structure;
s3: heating the sample obtained in the step S2 to an experimental temperature on a creep testing machine under the condition of no external load and preserving heat;
s4: applying preset stress to the sample obtained in the step S3 under the conditions of constant temperature and constant strain until the sample is broken, and calculating a creep strain value according to a stress relaxation curve in the experimental process;
s5: and establishing a relation between creep strain and reduction of area by combining evaluation indexes of a short-time creep rupture test, and further establishing an evaluation criterion for evaluating the reheat crack sensitivity of the low-alloy heat-resistant steel welding coarse crystal area.
2. The method for evaluating the sensitivity of the reheat cracking of the coarse crystalline region according to claim 1, wherein the surface temperature of the low alloy heat resistant steel sample is controlled to 100 ℃ or less throughout the machining in S1.
3. The method for evaluating the reheat crack sensitivity of the coarse grain region according to claim 1, wherein in S1, the low alloy heat resistant steel sample is a bar-shaped sample.
4. The method for evaluating the reheat crack sensitivity of the coarse grain region according to claim 1, wherein in S2, the thermal simulation experiment parameters include a heating rate, a peak temperature and a cooling rate.
5. The method for evaluating the reheat crack sensitivity of the coarse grain region according to claim 1, wherein in S2, the thermal simulation experiment adopts thermocouple heat cycle measurement on the temperature field characteristic point or utilizes a finite element simulation method to obtain the temperature field of the welding process.
6. The method for evaluating the reheat crack sensitivity of the coarse grain region according to claim 1, wherein in S3, the experimental temperature is determined according to the service environment of the low alloy heat resistant steel.
7. The method for evaluating the reheat crack sensitivity of the coarse crystal region according to claim 6, wherein the heating time is 2min, the experimental temperature is 500-750 ℃, and the holding time is 10 min.
8. The method for evaluating the sensitivity of the reheat crack of the coarse crystalline region as claimed in claim 1, wherein in S4, the temperature and the strain of the sample are unchanged during the experiment, the stress is changed with time, and the curve of the change of the stress with time is recorded as the stress relaxation curve.
9. The method for evaluating the reheat crack sensitivity of the coarse grain region according to claim 1, wherein in S4, the creep strain value is calculated according to the following formula:
Figure FDA0003557304260000021
in the formula, epsiloncIs creep strain; e is the modulus of elasticity;
Figure FDA0003557304260000022
is the creep stress rate of change.
10. The method for evaluating the reheat crack sensitivity of the coarse grain region according to claim 1, wherein in S5, the relationship between creep strain and reduction of area of the sample is established by calculating creep strain using data recorded in a creep test process for the test result of the same sample, and calculating the reduction of area of the sample using the cross-sectional areas of fracture positions before and after the sample is fractured.
CN202210278933.1A 2022-03-21 2022-03-21 Method for judging reheat crack sensitivity of coarse crystal region Pending CN114577587A (en)

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