CN111879226A - A furnace roll life evaluation method based on on-site metallography and roll surface deformation - Google Patents

Abstract

The invention relates to a furnace roll life evaluation method based on on-site metallography and roll surface deformation, including determining the metallographic structure with the tendency of creeping holes to connect into cracks or the occurrence of cracks as the metallographic scrapping standard, based on the furnace roll The metallographic structure of the furnace is subjected to creep damage analysis to judge whether it meets the metallographic scrap standard; the threshold value L ₀ is determined as the deformation failure standard, and whether it is directly continued to be used is judged based on the deformation L of the furnace roll; according to the deformation of the furnace roll L, establish the original hearth roll model or the repaired hearth roll model; S4, based on the corresponding metallographic creep material parameters of the hearth roll, simulate and obtain the life prediction result of the hearth roll based on the metallographic and roll surface deformation. According to the furnace roll life evaluation method of the present invention, based on on-site metallographic inspection and furnace roll deformation detection, the relationship between the microstructure change and performance caused by the furnace roll creep damage and the furnace roll surface deformation in actual production are fully considered. relationship between quantity and service life.

Description

A furnace roll life evaluation method based on on-site metallography and roll surface deformation

technical field

The invention relates to a life evaluation method of in-service furnace rolls, and more particularly to a furnace roll life evaluation method based on on-site metallography and roll surface deformation.

Background technique

Furnace roll is an important part for conveying steel strip in continuous annealing furnace, and the surface state of its roll surface directly affects the quality of strip steel produced. Furnace rolls need to rotate under the action of thermal load and billet load with a temperature above 800 °C, and at the same time, they are subject to mechanical damage (collision, wear, etc.) of the heated billet, and the operating conditions are harsh, so SCH22 (ZG40Cr25Ni20) austenite resistant Hot steel is used as furnace roll material. The design life of this kind of furnace roll is generally up to 100,000 hours. However, due to the long-term operation of the furnace roll in the harsh operating environment of high temperature and high pressure, the microstructure of the furnace roll is degraded, resulting in deformation of the roll surface, and the quality of the rolled steel strip is not good. Therefore, the regular life evaluation and failure detection of the in-service furnace rolls are of great significance to the normal operation of the annealing furnace.

The damage mechanism of the furnace roll is mainly creep damage. The creep damage will cause the embrittlement of the furnace roll material, the aggregation and coarsening of carbides in the microstructure of the material, the precipitation of σ phase, and the elongation and impact energy will decrease significantly after high temperature and normal temperature fracture. Therefore, the roll surface of the furnace roll is deformed, resulting in uneven surface of the rolled steel strip, resulting in economic losses in factory production.

The furnace roll life evaluation method given in the prior art mainly adopts the parameter extrapolation method or the reference furnace tube metallographic evaluation method to evaluate the creep damage of the furnace roll, while the operating environment and failure mode of the furnace roll in actual production are different from those of the furnace roll. Different tubes, the deformation of the furnace roll is the main basis for judging the failure of the furnace roll. Therefore, there is no standard and effective method for evaluating the life of in-service furnace rolls.

On-site metallographic testing technology is one of the important non-destructive testing methods for material deterioration of high-temperature components, and is mainly used for high-temperature damage and creep damage assessment of components. Traditional methods usually qualitatively evaluate the damage degree of materials based on the carbide morphology in the metallographic phase and the microstructure characteristics of materials such as creep holes or cracks, and based on the experience of the inspectors. There is no method for evaluating the metallographic evaluation of the furnace roll in the prior art. The metallographic evaluation of the furnace roll is mainly carried out by referring to the metallographic evaluation method of the furnace tube. In the judgment process, it is necessary to subjectively distinguish the creep damage. , and the failure mode and operating environment of the furnace roll are not exactly the same as the furnace tube, so it is necessary to propose a more standard furnace roll life evaluation method.

SUMMARY OF THE INVENTION

In order to more accurately and conveniently evaluate the damage state and life of the in-service furnace rolls, the present invention provides a furnace roll life evaluation method based on on-site metallography and roll surface deformation classification.

The method for evaluating the life of a furnace roll based on on-site metallography and roll surface deformation according to the present invention includes the following steps: S1, determining the metallographic structure with the tendency of creeping holes to connect into cracks or the appearance of cracks as the metallographic scrapping standard , based on the metallographic structure of the furnace roll, perform creep damage analysis to determine whether it meets the metallographic scrap standard; S2, determine the threshold L ₀ as the deformation failure standard, and judge whether it is directly continued to be used based on the deformation amount L of the furnace roll ; S3, establish the original furnace roll model or the repaired furnace roll model according to the deformation amount L of the furnace roll; S4, simulate the furnace roll based on the metallographic and roll surface deformation based on the corresponding metallographic creep material parameters of the furnace roll Roll life prediction results.

Preferably, step S1 includes: if the metallographic structure analysis of the furnace roll shows a tendency of creeping holes to connect into cracks or the appearance of cracks, it is determined that the furnace roll has reached the scrapping standard, its life is exhausted, and it needs to be scrapped; if the furnace roll The metallographic structure analysis shows that there is no tendency for cracks or no cracks appear, then it is judged that the furnace roll has not reached the scrapping standard, the service life has not been exhausted, and it can continue to be used.

Preferably, step S1 includes: performing on-site metallographic detection on the furnace roll, obtaining metallographic structure picture information, and performing creep damage analysis based on the metallographic structure picture information.

Preferably, grinding and polishing the outer surface at the middle position of the furnace roll in the shutdown state, and then performing on-site metallographic inspection of the film to obtain n groups of metallographic structure picture information P(1)...P of the furnace roll at the middle position (n).

Preferably, n is 5. It should be understood that the purpose of the n groups of metallographic structure pictures is that due to creep damage of the material, some metallographic pictures may not show damage characteristics, so multiple groups of pictures are taken for comprehensive analysis. Therefore, the value of n here is only used as an example to clarify the number of samples.

Preferably, step S2 includes: if the deformation amount L of the hearth roll is less than the threshold value L ₀ , determining that the deformation amount of the hearth roll is classified as A grade, and the roll surface deformation degree is small, and it can continue to be used; if the deformation amount L of the hearth roll is greater than Threshold L ₀ , it is judged that the deformation of the furnace roll is classified as B grade, the roll surface has been seriously deformed, the quality of the steel strip at the rolling site is not good, and the furnace roll cannot be used continuously or after repairing.

Preferably, step S2 includes: rotating the furnace roll frame on the lathe, measuring the deformation of the roll surface with a dial indicator or a dial indicator, to obtain the roll surface deformation of the furnace roll along the warp, and taking the roll surface deformation of the furnace roll The maximum value is the deformation amount L of the furnace roll.

Preferably, step S3 includes: if the degree of deformation of the furnace rolls is grade A and the furnace rolls can continue to be used, establishing an original furnace roll model; if the level of deformation of the furnace rolls is grade B, the furnace rolls cannot continue to be used or are used after repairing. , the model of the repaired furnace roll is established.

The finite element constitutive equation is selected from Kachanov-Rabotnov damage equation (K-R equation for short).

为材料K-R方程参数，通过拟合单轴蠕变试验数据获得。Among them: ε _c is the creep strain, σ is the initial stress value, D is the damage variable, t is the running time of the furnace roll, A, B, n, v,

are the KR equation parameters of the material, obtained by fitting the uniaxial creep test data.

Preferably, step S4 includes: according to the obtained metallographic structure of the material and the service temperature of the furnace roll, the K-R equation parameters of the material are selected from the K-R equation parameters of the material corresponding to the existing metallographic structures. According to the temperature of the furnace roll, the initial stress field and the K-R equation parameters of the material, the finite element simulation is carried out, and the residual life prediction result of the furnace roll is obtained.

According to the furnace roll life evaluation method based on on-site metallography and roll surface deformation of the present invention, the metallography is used as the rejection standard, the deformation is used as the classification standard, and the finite element simulation method is used to obtain the residual life result of the furnace roll. Specifically, The K-R equation parameters at the corresponding temperature are determined based on the results of on-site metallographic inspection and the corresponding furnace roll model is established based on the detection of the deformation of the furnace roll. According to the service temperature and stress of the furnace roll, the finite element simulation method is used to obtain the furnace roll. The remaining life result of the lifetime. The furnace roll life evaluation method based on on-site metallography and finite element simulation of roll surface deformation classification according to the present invention is a non-destructive non-destructive testing method, which does not require pipe cutting, nor does it need to perform a permanent test again. The evaluation technology has low difficulty, high efficiency, and low cost, which is convenient for on-site implementation. According to the furnace roll life evaluation method based on on-site metallography and roll surface deformation of the present invention, the safety management of the furnace rolls can be realized, and the poor quality of the steel strip rolled by the furnace rolls can be avoided, so the production loss can be greatly reduced, and the guarantee economic benefits.

Description of drawings

1 is a typical metallographic structure picture of the furnace roll life evaluation method based on on-site metallography and roll surface deformation according to the present invention;

FIG. 2 is a picture of the metallographic structure of Example 1. FIG.

Detailed ways

Below in conjunction with the accompanying drawings, preferred embodiments of the present invention are given and described in detail.

The evaluation method according to a preferred embodiment of the present invention includes determining that the metallographic structure has a tendency of creeping holes to connect into cracks or the occurrence of cracks as the metallographic rejection standard, and performing creep damage analysis based on the metallographic structure of the furnace roll to Determine whether it meets the metallographic scrapping standard. Specifically, grinding and polishing the outer surface of the furnace roller at the intermediate position X in the shutdown state, and then performing on-site metallographic inspection of the film to obtain n groups of metallographic structure picture information P(1) of the furnace roller at the intermediate position X ...P(n), the typical metallographic structure information is shown in Figure 1. The metallographic structure picture information P(1)...P(n) is analyzed. According to the typical metallographic characteristics, if the metallographic structure has creep hole connections If there is a tendency to crack or there are cracks, it is judged that the furnace roll has reached the scrapping standard, and its life is exhausted, and it needs to be scrapped; if there is no trend of cracking or no cracking, it is judged that the furnace roll has not reached the scrapping standard, and its life has not been reached. Exhausted, can continue to use.

The evaluation method according to a preferred embodiment of the present invention includes determining the threshold value L ₀ as the deformation amount failure criterion, and judging whether it is directly continued to be used based on the deformation amount L of the furnace roll. Specifically, the furnace roll frame is rotated on the lathe, and the deformation of the roll surface is measured with a dial indicator or a dial indicator to obtain the roll surface deformation of the furnace roll along the warp line, taking the maximum value of the roll surface deformation of the furnace roll, is the deformation amount L of the furnace roll. If L<L ₀ , the classification D of the deformation amount of the furnace roll is judged to be grade A, and the degree of deformation of the roll surface is small, and it can continue to be used; if L ≥ L ₀ , the classification of the deformation amount of the furnace roll is judged. D is grade B, the roll surface has been seriously deformed, and the quality of the steel strip at the rolling site is not good, so it cannot be used or repaired and then used again.

The evaluation method according to a preferred embodiment of the present invention includes establishing a hearth roll creep model in combination with the roll surface deformation of the hearth roll. Specifically, if the degree of deformation of the furnace roll is grade A, and it can be used directly, the original furnace roll model is established; if the grade of deformation of the furnace roll is grade B, which cannot be used continuously or after repairing, a certain cutting model is established. Thickness, repaired furnace roll model. The finite element constitutive equation selects the K-R damage equation, which is expressed as:

为材料K-R方程参数，通过拟合单轴蠕变试验数据获得。Among them: ε _c is the creep strain, σ is the initial stress value, D is the damage variable, t is the running time of the furnace roll, A, B, n, v,

are the KR equation parameters of the material, obtained by fitting the uniaxial creep test data.

The evaluation method according to a preferred embodiment of the present invention includes performing finite element simulation life evaluation on the furnace roller according to the temperature section of the furnace roller, the initial stress and the parameters of the KR equation of the obtained material. In this step, for the convenience of calculation, the following assumptions are made: the heat transfer process is regarded as steady-state heat conduction, and the friction between the strip steel and the furnace roll is ignored. Specifically, the finite element simulation temperature is the actual temperature of the furnace roll, and the initial stress includes the furnace roll's own weight, strip tension, strip gravity and temperature stress. The material KR equation parameters are based on the service temperature of the furnace roll and the metallographic structure of the furnace roll. selected from the existing parameters. According to the service temperature of the furnace roll, the initial stress state and the selected material KR equation parameters, the finite element simulation is carried out, and the time required for the roll surface deformation L of the furnace roll model to reach the failure deformation amount L ₀ is obtained as the remaining life of the furnace roll.

Example 1

The rolls evaluated were rolls that had been in service for 10 years. The furnace roll is SCH22 centrifugally cast austenitic stainless steel with a total length of 2000mm and a service temperature of approximately 825°C. First, the evaluated furnace rolls were tested, and the outer surface of the furnace rolls in the middle position was selected to be ground, polished and corroded, and then the film was tested. The typical metallographic structure picture information P(1)...P(5) magnified by 500 times is obtained by testing to obtain 5 groups of this position (that is, 5 positions are selected to ensure that the damage characteristics of the material can be observed), and the typical metallographic structure picture information P( i) As shown in Figure 2. The metallographic analysis of P(1)...P(5) was carried out, and the metallographic diagram was observed to find that the carbides at the metallographic grain boundary of the furnace roller were severely coarsened and the σ phase (black phase) was precipitated in large quantities, and there was a tendency for creep holes to connect to form cracks. It is judged that the life of the furnace roll is exhausted and needs to be scrapped.

Rotate the furnace roll stand on the lathe, measure the deformation of the roll surface with a dial indicator or a dial gauge, and obtain the roll surface deformation of the furnace roll along the warp line. Take the maximum value of the roll surface deformation of the furnace roll, which is the deformation of the furnace roll. Quantity L. The maximum value of the deformation amount of the furnace roll is selected as the deformation amount L of the furnace roll, L=0.9 mm. The deformation amount of the furnace roll L ≥ the failure deformation amount of the furnace roll L ₀ (this value is determined by measuring the deformation amount of the failed furnace roll), so it is determined that the deformation amount of the furnace roll is classified as grade B, which cannot be used continuously or after repair.

According to the degree of deformation of the furnace roll, it is classified as grade B, and a model of the furnace roll after cutting to a certain thickness and repaired is established; according to the metallographic evaluation of the furnace roll, it can be seen that the furnace roll has reached the scrap standard, and the material corresponding to the failed metallographic phase at a temperature of 825 °C is selected. KR equation parameters, the specific parameters are shown in Table 1. According to the service temperature, the initial stress state and the parameters of the material KR equation, the finite element simulation is carried out. The simulation results show that under its service temperature and service stress field, the time for the deformation L of the furnace roll surface to reach the failure deformation L ₀ is extremely short, which can no longer meet the production requirements, and its metallographic structure has reached the scrapping standard. Exhausted and need to be scrapped.

Table 1

In fact, during the continuous use of the furnace roll, the roll surface of the furnace roll has been deformed, resulting in the unevenness of the belt at the rolling site, which shows the correctness and reliability of the present invention.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Various changes can be made to the above-mentioned embodiments of the present invention. That is, all simple and equivalent changes and modifications made according to the claims and descriptions of the present invention fall into the protection scope of the claims of the present invention. What is not described in detail in the present invention is conventional technical content.

Claims (10)

1. a furnace roll life evaluation method based on on-site metallography and roll surface deformation, is characterized in that, this furnace roll life evaluation method comprises the following steps: S1, the metallographic structure has the tendency of creeping holes to connect into cracks or the appearance of cracks is determined as the metallographic scrapping standard, and the creep damage analysis is carried out based on the metallographic structure of the furnace roll to judge whether it meets the metallographic scrapping standard; S2, the threshold value L ₀ is determined as the failure standard of the deformation amount, and whether it is directly continued to be used is judged based on the deformation amount L of the furnace roll; S3, according to the deformation amount L of the hearth roll, establish the original hearth roll model or the repaired hearth roll model. S4, based on the creep material parameters of the hearth roll corresponding to the metallographic phase, the life prediction result of the hearth roll based on the metallographic phase and the deformation of the roll surface is obtained by simulation. 2. The method for evaluating the life of a furnace roll according to claim 1, wherein step S1 comprises: if the metallographic structure analysis of the furnace roll shows that there is a tendency that creep holes are connected into cracks or cracks appear, then determining the furnace roll If the roll reaches the scrapping standard and its life is exhausted, it needs to be scrapped; if the metallographic structure analysis of the furnace roll shows that there is no tendency for cracks or no cracks appear, it is determined that the furnace roll does not meet the scrapping standard and its life is not exhausted, and it can continue. use. 3. The furnace roll life evaluation method according to claim 1, wherein step S1 comprises: performing on-site metallographic detection on the furnace roll, obtaining metallographic structure picture information, and performing creep based on the metallographic structure picture information Damage Analysis. 4. The furnace roll life evaluation method according to claim 3 is characterized in that, grinding and polishing the outer surface at the middle position of the furnace roll in the shutdown state, and then performing on-site coating metallographic detection to obtain the middle position. N groups of metallographic structure picture information P(1)...P(n) of the furnace roll. 5 . The furnace roll life evaluation method according to claim 4 , wherein n is 5. 6 . 6. The method for evaluating the life of the furnace roll according to claim 1, wherein step S2 comprises: if the deformation amount L of the furnace roll is less than the threshold value L ₀ , then judging that the deformation amount D of the furnace roll is graded A, and the roll surface If the degree of deformation is small, it can continue to be used; if the deformation amount L of the furnace roll is greater than the threshold value L ₀ , it is judged that the deformation amount D of the furnace roll is grade B, the roll surface of the furnace roll has been seriously deformed, and the steel strip at the rolling position The quality is not good enough to continue to be used or repaired for further use. 7. The method for evaluating the life of a furnace roll according to claim 6, wherein step S2 comprises: rotating the furnace roll frame on a lathe, measuring the deformation of the roll surface with a dial indicator or a dial indicator, and obtaining along the warp Method For the deformation of the roll surface of the furnace roll, the maximum value of the deformation of the roll surface of the furnace roll is taken as the deformation amount L of the furnace roll. 8 . The method for evaluating the life of the hearth roll according to claim 1 , wherein step S3 comprises: establishing an original hearth roll model or a repaired hearth roll model for the measured deformation L of the hearth roll. 9 . 9. The furnace roll life assessment method according to claim 8, wherein the finite element model selects Kachanov-Rabotnov damage constitutive equation (K-R equation for short), which is:

Among them: ε _c is the creep strain, σ is the initial stress value, D is the damage variable, t is the running time of the furnace roll, A, B, n, v,

are the KR equation material parameters, obtained by fitting the uniaxial creep test data. 10. The method for evaluating the life of a furnace roll according to claim 1, wherein step S4 comprises: according to the obtained metallographic structure information of the furnace roll and the service temperature of the furnace roll, the material K-R equation parameters are obtained from the existing metallographic structure. The corresponding furnace roll material K-R equation parameters are selected. According to the temperature section of the furnace roll, the initial stress field and the parameters of the material K-R equation, the life prediction results of the furnace roll under the corresponding metallographic and the deformation of the furnace roll are obtained by simulation.

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