A method for the determination and characterization of the content of non-metallic inclusions in CB2 cast steel

Abstract

The present invention discloses a method for determining and characterizing the content of non-metallic inclusions in CB2 cast steel, comprising the following steps: intercepting the middle position of the cast steel body to be inspected or its attached cast test block as a sample, and processing the sample until the surface is smooth; observing the sample with an optical microscope, selecting a representative field of view, and taking a metallographic photograph; using Image software to perform statistical measurement on the non-metallic inclusions in each field of view to identify the type of non-metallic inclusions, obtain the characteristic values ​​of various types of non-metallic inclusions, and obtain the level of each non-metallic inclusion according to the level calculation formula; using Image software to calculate the area fraction of non-metallic inclusions; using the type, level and area fraction of non-metallic inclusions to jointly characterize the content distribution state of non-metallic inclusions in CB2 cast steel. The method can realize the measurement and characterization of non-metallic inclusions in CB2 cast steel, and provide technical support for the study of the influence of non-metallic inclusions on the service life of cast steel.

Description

Technical Field

[0001] The present invention relates to the technical field of steel quality evaluation, and in particular to a method for determining and characterizing the content of non-metallic inclusions in CB2 cast steel. Background Art

[0002] CB2 cast steel has excellent high temperature strength and oxidation resistance. It is a high temperature resistant material widely used in 620℃ high efficiency supercritical unit steam turbines. It is mainly used in the manufacture of key components such as high temperature main steam valves and turbine inner cylinders of 620℃ high efficiency steam turbines.

[0003] CB2 steel castings are supplied in the normalizing + tempering state, and their product performance is closely related to smelting, casting and final heat treatment, among which the smelting level directly affects the content of non-metallic inclusions in the steel. A large number of studies have found that there are various types and shapes of non-metallic inclusions in CB2 cast steel, especially some larger spherical, dendritic and irregular inclusions. The determination and characterization methods of the content of non-metallic inclusions in steel based on existing standards cannot clearly reflect the actual shape, size and content of non-metallic inclusions in CB2 cast steel, which causes large deviations for engineering and technical personnel, and thus has an adverse effect on the quality control of CB2 steel castings, and cannot effectively evaluate and analyze the manufacturing quality of CB2 steel castings. At the same time, since CB2 steel castings work in a high-temperature and high-pressure steam environment for a long time, the presence of non-metallic inclusions has an adverse effect on their high-temperature strength and durability. Especially under vibration conditions, when subjected to external forces, microcracks are easily generated on the interface between large hard non-metallic inclusions and the matrix, which seriously affects the service life of CB2 steel castings. Therefore, in order to ensure the product manufacturing quality, long-term operation safety and service life of CB2 steel castings, it is of great technical significance to measure and characterize the content of non-metallic inclusions in CB2 steel castings. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a method for determining and characterizing the content of non-metallic inclusions in CB2 cast steel, which can realize the measurement and characterization of non-metallic inclusions in CB2 cast steel, and further provide technical support for the study of the influence of non-metallic inclusions on the service life of cast steel.

[0005] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0006] A method for determining and characterizing the content of non-metallic inclusions in CB2 cast steel comprises the following steps:

[0007] (1) Preparation of test specimens: Cut the middle of the steel casting to be tested or its attached test block as the test specimen, and process the specimen until the surface is smooth for later use;

[0008] (2) Observe the specimen: Observe the specimen using an optical microscope, select representative fields of view, and take metallographic photos.

[0009] (3) Statistically measure the non-metallic inclusions in each field of view using Image software to identify the types of non-metallic inclusions, obtain the characteristic values of various non-metallic inclusions, and calculate the grades of each non-metallic inclusion according to the corresponding grade calculation formula for each type of non-metallic inclusion.

[0010] (4) Use image software to calculate the area fraction of each type of non-metallic inclusion respectively.

[0011] (5) Characterize the content distribution state of non-metallic inclusions in CB2 cast steel jointly using the type, grade, and area fraction of non-metallic inclusions.

[0012] Furthermore, the dimensions of the specimen in step (1) are: length 20 - 23 mm, width 20 - 23 mm, thickness 15 - 18 mm, which is suitable for holding by hand.

[0013] Furthermore, in step (1), the specimen is ground with sandpaper and then polished, and then cleaned with alcohol and dried to obtain a specimen with a smooth surface; during the grinding process, pay attention to avoiding the shedding of inclusions, and avoid generating drag tails during the polishing process to avoid affecting subsequent measurements.

[0014] Furthermore, the magnification of the optical microscope in step (2) is 100 times or 200 times, preferably 100 times.

[0015] Furthermore, in step (3), the types of non-metallic inclusions are identified with reference to the descriptions of various non-metallic inclusions.

[0016] Even further, the types of non-metallic inclusions include Q-type spherical composite inclusions, Y-type dendritic composite inclusions, and D-type inclusions; the D-type inclusions among them are small-sized hard inclusions in the shape of dots with a size below 15 μm.

[0017] Even further, the calculation formula for the grade i corresponding to each type of non-metallic inclusion is as follows:

[0018] For Q-type spherical composite inclusions: lg(i) = [0.904lg(d) - 1.345], where d is the diameter of the inclusion in μm.

[0019] For Y-type dendritic composite inclusions: lg(i) = [0.81lg(L) - 1.82], where L is the length of the inclusion in μm.

[0020] D-type hard spot inclusions with a size below 15μm: lg(i) = [1.15lg(n) - 1.664], where n is the number of inclusions in each field of view.

[0021] Furthermore, the calculation process for the grade of Q-type spherical composite inclusions is as follows: First, substitute the diameter of a single inclusion of this type into the formula to calculate the grade of a single inclusion of this type, and then sum up the grades of inclusions of this type in a single field of view to obtain the total grade of Q-type spherical composite inclusions in a single field of view.

[0022] The calculation process for the grade of Y-type dendritic composite inclusions: First, sum up the lengths of single inclusions of this type in the field of view to obtain the total length L of inclusions of this type in a single field of view, and then substitute L into the formula to calculate the grade of Y-type dendritic composite inclusions.

[0023] The calculation process for the grade of D-type inclusions is to substitute the total number n of D-type inclusions in a single field of view into the formula to calculate the grade of D-type inclusions.

[0024] Furthermore, in step (4), the image software is used to calculate the area fractions of Q-type and Y-type non-metallic inclusions respectively.

[0025] Furthermore, in step (5), when characterizing, indicate the source of the specimen, which is the body of the cast steel part or the attached casting test block.

[0026] Advantages of the present invention:

[0027] The method of the present invention is aimed at the situation of complex inclusion shapes, relatively large sizes, and relatively large quantities in CB2 cast steel. It can quickly identify the inclusion types, refine the grades, use both grades and area fractions for characterization, accurately represent the types, grades, and contents of non-metallic inclusions, evaluate the size of inclusions, clearly reflect the distribution of non-metallic inclusions in CB2 cast steel; the method of the present invention is simple to operate, the measurement results are comprehensive and accurate, the characterization results are clear, it can accurately reflect the smelting level of the steel, and the obtained measurement and characterization results are of great significance for controlling the product performance, and can provide technical support for the research on the influence of non-metallic inclusions on the service life of CB2 cast steel parts. Description of the drawings

[0028] Figures 1 to 4 It is a polished-state photo of four representative fields of view of the CB2 cast steel specimen in the embodiment of the present invention. Detailed implementation manners

[0029] The following elaborates on the preferred embodiments of the present invention in conjunction with the drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0030] The present invention provides a method for determining and characterizing the content of non-metallic inclusions in CB2 cast steel, comprising the following steps:

[0031] (1) Sample preparation: Cut the middle of the steel casting to be tested or its attached test block as the sample. The sample size is: length 20-23mm, width 20-23mm, thickness 15-18mm, suitable for hand-held. Grind the sample with sandpaper, then polish it, clean it with alcohol and blow it dry. During the grinding process, pay attention to avoid the fall of inclusions, and during the polishing process, avoid tailing to avoid affecting subsequent measurements.

[0032] (2) Observation of the sample: Use an optical microscope to observe the overall condition of the sample, select a representative field of view, and collect metallographic photographs of multiple representative fields of view at a magnification of 100 or 200 times; the magnification of the optical microscope should be based on the actual situation so that the type of inclusions can be identified, preferably 100 times.

[0033] (3) The non-metallic inclusions in the metallographic photographs of each field of view are statistically measured using Image software to identify the types of non-metallic inclusions, obtain the characteristic values ​​of each type of non-metallic inclusions, and obtain the level of each non-metallic inclusion according to the level calculation formula corresponding to each type of non-metallic inclusion; the specific process is as follows:

[0034] a) Identify the type of non-metallic inclusions according to the description of each type of non-metallic inclusions. During the identification process, a large multiple can be used for further judgment and identification; the descriptions of each type of non-metallic inclusions are as follows:

[0035] Q-type spherical composite inclusions: black-gray spherical, mainly aluminum, calcium, magnesium / silicon oxides and their composite phase inclusions;

[0036] Y-type dendritic composite inclusions: dendritic oxides and irregularly shaped nitrides and their composite phase inclusions;

[0037] D-type inclusions, some small-sized inclusions with a size of less than 15 μm;

[0038] b) Use image software to measure and calculate the characteristic values ​​of various non-metallic inclusions. The characteristic values ​​of various non-metallic inclusions are as follows:

[0039] Q-type spherical composite inclusions, the characteristic value is the diameter d of this type of inclusion, expressed in μm;

[0040] The characteristic value of Y-type dendritic composite inclusions is the length l of this type of inclusion, expressed in μm:

[0041] D-type inclusions, the characteristic value is the total number of D-type inclusions n in a single field of view;

[0042] c) Calculate the grade i of each type of non-metallic inclusion according to the corresponding grade calculation formula. The calculation formulas are as follows:

[0043] For Q-type spherical composite inclusions: lg(i) = [0.904lg(d) - 1.345]; when calculating, first substitute the diameter d of a single inclusion of this type 1 into the formula to calculate the grade i of a single inclusion of this type 1 , and sum up the grades of inclusions of this type in a single field of view to obtain the total grade i of inclusions of this type in a single field of view (i = i 1 + i 2 + i 3 …);

[0044] For Y-type dendritic composite inclusions: lg(i) = [0.81lg(L) - 1.82]. First, sum up the lengths l 1 , l 2 , l 3 ……… of a single inclusion of this type in the field of view to obtain the total length L of inclusions of this type in a single field of view (L = l 1 + l 2 + l 3 ……), and then substitute L into the formula to calculate the grade i of inclusions of this type;

[0045] For D-type hard inclusions with a diameter of less than 15μm: lg(i) = [1.15lg(n) - 1.664]. Substitute the total number n of D-type inclusions in a single field of view into the formula to calculate the grade i of inclusions of this type;

[0046] (4) Use image software to calculate the area fraction of each type of non-metallic inclusion, mainly the area fraction of Q-type spherical composite inclusions and Y-type dendritic composite inclusions; this area fraction refers to the ratio of the area of a certain type of inclusion in a metallographic photo of a single field of view to the area of the entire metallographic photo.

[0047] (5) Characterization of the content of non-metallic inclusions: Use the type, grade, and area fraction of non-metallic inclusions to jointly represent the content distribution state of non-metallic inclusions in CB2 cast steel; when characterizing, it is required to indicate the source of the specimen (attached casting test block or the body of the cast steel part).

[0048] Example

[0049] With reference to the accompanying drawings, the specific embodiments of the present invention will be further described in detail through specific examples. The sample materials in the following examples are all CB2 cast steel, with the supply state being normalized and tempered, and the chemical composition (wt%) being: (C: 0.14, Si: 0.28, Mn: 0.9, Cr: 9.36, Ni: 0.18, Mo: 1.44, V: 0.18, N: 0.021, Nb: 0.057, Co: 0.92, B: 0.0091, Al: 0.0018, Sn: 0.0020, Cu: 0.022, As: 0.006, Ti: 0.0014, P: 0.0094, S: 0.0069).

[0050] (1) Preparation of specimens

[0051] In this embodiment, the specimens are taken from attached cast blocks, and metallographic blocks with a length of 20 mm, a width of 20 mm, and a thickness of 15 mm are intercepted. After grinding, polishing, cleaning with alcohol, and drying.

[0052] (2) Observation of specimens and collection of metallographic photos

[0053] An optical microscope is used to observe the non-metallic inclusions at different positions of the specimens to determine the distribution of non-metallic inclusions, and metallographic photos of multiple representative fields of view are collected; the magnification of the optical microscope is 100 times.

[0054] (3) For the metallographic photos of the representative fields of view as Figure 1 shown, identify the types of non-metallic inclusions according to the descriptions of various non-metallic inclusions; as Figure 1 shown, there are Q-type spherical composite inclusions, Y-type dendritic composite inclusions, and D-type inclusions;

[0055] Through statistical measurement with image software, the lengths of the Y-type dendritic composite inclusions are l 1 = 88.23 μm, l 2 = 41.17 μm, l 3 = 35.2 μm, l 4 = 71.7 μm; by summing l 1 , l 2 , l 3 , l 4 to obtain the total length L of this type of inclusion as 236.3 μm, substituting the total length L into the level calculation formula for this type of inclusion: lg(i) = [0.81lg(L) - 1.82], the level of this type of inclusion is obtained as 1.3;

[0056] Through statistical measurement with image software, the diameters of the Q-type spherical composite inclusions are d 1 = 44.7 μm, d2 = 49.4 μm, d 3 = 25.88 μm, d 4 = 23.5 μm; Substitute d 1 , d 2 , d 3 , d 4 into the grade calculation formula for Q-type inclusions: lg(i) = [0.904lg(d) - 1.345], and obtain i 1 = 1.40, i 2 = 1.53, i 3 = 0.85, i 4 = 0.78; Sum i 1 , i 2 , i 3 , i 4 to get the total grade i of Q-type inclusions = 4.5;

[0057] By using image software to count, the number of D-type inclusions n = 58. Substitute n into the grade calculation formula for D-type inclusions: lg(i) = [1.15lg(n) - 1.664], and obtain the grade i of D-type inclusions = 2.3;

[0058] (4) By using image software to measure respectively, the area fraction of Y-type dendritic composite inclusions is 7.4%, and the area fraction of Q-type dendritic composite inclusions is 14.9%.

[0059] (5) Characterization of non-metallic inclusion content: Use the inclusion type, grade and area fraction to jointly characterize as "Y-type, 1.3 grade, 7.4%; Q-type, 4.5 grade, 14.9%; D-type, 2.3 grade".

[0060] Repeat the above steps (3), (4) and (5) respectively for Figure 2 , Figure 3 and Figure 4 shown in the metallographic photos of representative fields of view to measure and characterize the non-metallic inclusion content. Figure 2 The non-metallic inclusion content in Figure 3 is characterized as "Y-type, 1.1 grade, 4.5%; D-type, 1 grade"; Figure 4 The non-metallic inclusion content in

[0061] The above are only embodiments of the present invention, and thus do not limit the patent scope of the present invention. Any modifications or equivalent transformations made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for determining and characterizing the content of non-metallic inclusions in CB2 cast steel, It is characterized in that The steps include: (1) Preparation of test specimens: Cut the middle of the steel casting to be tested or its attached test block as the test specimen, and process the specimen until the surface is smooth for later use; (2) Observe the sample: Use an optical microscope to observe the sample, select a representative field of view, and take metallographic photographs; (3) The non-metallic inclusions in each field of view are statistically measured using Image software to identify the type of non-metallic inclusions, obtain the characteristic values ​​of each type of non-metallic inclusions, and obtain the level of each non-metallic inclusion according to the level calculation formula corresponding to each type of non-metallic inclusion; (4) Use image software to calculate the area fraction of each type of non-metallic inclusions; (5) The content distribution of non-metallic inclusions in CB2 cast steel is characterized by the type, grade and area fraction of non-metallic inclusions; In step (3), the type of non-metallic inclusions is identified by referring to the description of each type of non-metallic inclusions; The types of non-metallic inclusions include Q-type spherical composite inclusions, Y-type dendritic composite inclusions, and D-type inclusions; among which D-type inclusions are small-sized hard inclusions with a size of less than 15μm. The level i is calculated according to the level calculation formula corresponding to each type of non-metallic inclusion. The calculation formula is as follows: Q-type spherical composite inclusions: lg(i) = [0.904lg(d)-1.345], d is the inclusion diameter, unit: μm; Y-type dendritic composite inclusions: lg(i) = [0.81lg(L)-1.82], L is the inclusion length, unit: μm; Type D point-shaped hard inclusions with a size of less than 15 μm: lg(i) = [1.15lg(n)-1.664], where n is the number of inclusions in each field of view; The calculation process of the grade of Q-type spherical composite inclusions is as follows: first, the diameter of a single such inclusion is substituted into the formula to calculate the grade of a single such inclusion, and then the grades of such inclusions in a single field of view are summed to obtain the total grade of Q-type spherical composite inclusions in a single field of view; The level calculation process of Y-type dendritic composite inclusions: first, sum up the lengths of single inclusions of this type in the field of view to get the total length L of this type of inclusion in a single field of view, and then substitute L into the formula to calculate the level of Y-type dendritic composite inclusions; The process of calculating the level of type D inclusions is to substitute the total number n of type D inclusions in a single field of view into the formula to calculate the level of type D inclusions.

2. The method for determining and characterizing the content of non-metallic inclusions in CB2 cast steel according to claim 1, It is characterized in that The sample size in step (1) is: length 20-23 mm, width 20-23 mm, thickness 15-18 mm.

3. The method for determining and characterizing the content of non-metallic inclusions in CB2 cast steel according to claim 1, Features: In step (1), the sample is ground with sandpaper and then polished, and then cleaned with alcohol and blown dry to obtain a sample with a smooth surface.

4. A method for the determination and characterization of the content of non-metallic inclusions in CB2 cast steel according to claim 1, characterized in that: The magnification of the optical microscope in step (2) is 100 times or 200 times.

5. A method for the determination and characterization of the content of non-metallic inclusions in CB2 cast steel according to claim 1, characterized in that: In step (4), the image software is used to calculate the area fractions of Q-type and Y-type non-metallic inclusions respectively.

6. A method for the determination and characterization of the content of non-metallic inclusions in CB2 cast steel according to claim 1, characterized in that: In step (5), the source of the specimen is noted during the characterization.

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