Method for evaluating eutectoid structure of oxide scale of hot-rolled plate

Abstract

The invention belongs to the technical field of metal material surface scale evaluation, and particularly discloses a method for evaluating a hot-rolled plate scale eutectoid structure, which comprises the following steps: (1) sample preparation: putting a hot-rolled plate into a vacuum coating machine, and carrying out sputter coating on the surface of the hot-rolled plate; cutting one part as a sample, curing and inlaying the sample by using normal-temperature oxidation resin, and then grinding and polishing the cross section of the sample until the surface of the sample is bright and free of scratches; (2) chemical corrosion: putting the prepared sample into a corrosive liquid for chemical corrosion, wherein the corrosive liquid is prepared from hydrochloric acid, ammonium persulfate and absolute ethyl alcohol; after chemical corrosion is completed, the sample is washed clean with absolute ethyl alcohol and blow-dried; and (3) quantitative evaluation with a scanning electron microscope: observing with the scanning electron microscope, and performing quantitative measurement. According to the method provided by the invention, the complete oxide scale can be obtained, and the eutectoid structure of the oxide scale can be clearly displayed and measured and evaluated.

Description

Technical Field

[0001] The invention belongs to the technical field of evaluating iron oxide scale on the surface of metal materials, and in particular relates to a method for evaluating the eutectoid structure of iron oxide scale on a hot-rolled plate. Background Art

[0002] When hot-rolled plates are oxidized at high temperatures, an oxide scale composed of Fe203, Fe3O4 and FeO will form on the surface. After coiling, as the temperature of the strip decreases, under a suitable oxygen concentration environment, the FeO in the oxide scale will form a lamellar Fe3O4 / α-Fe structure after a eutectic phase transformation. The different structural compositions of the oxide scale will result in different resistance to plastic deformation, hardness and strength of the oxide scale. These changes directly affect subsequent deep processing, such as the impact on pickling efficiency and the problem of oxide scale peeling during bending deformation. Therefore, how to accurately characterize the morphology, structure and phase composition of the oxide scale, so as to achieve precise control of the oxide scale structure, is of great significance to meeting the requirements of downstream users.

[0003] The commonly used methods for characterizing the microstructure of iron oxide scale on the surface of steel are to observe the surface integrity of the iron oxide scale, measure the total thickness of the iron oxide scale, measure the thickness of each layer of Fe203, Fe3O4, eutectoid Fe3O4 / α-Fe and FeO in the iron oxide scale, and calculate the proportion of each layer of Fe203, Fe3O4, eutectoid Fe3O4 / α-Fe and FeO. The eutectoid Fe3O4 / α-Fe is a lamellar structure composed of α-Fe and Fe3O4. The spacing of this lamellar structure leads to different toughness of the iron oxide scale. The smaller the lamellar spacing, the better the toughness. At present, there is no special evaluation method for the eutectoid Fe3O4 / α-Fe lamellar structure, and the commonly used hydrochloric acid and ethanol can only corrode the iron oxide scale. If the steel structure needs to be observed, secondary corrosion is required. In addition, the iron oxide scale formed on the surface of hot-rolled steel is relatively loose, fragile and easy to fall off. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for evaluating the eutectoid structure of hot-rolled iron scale, which can obtain complete iron scale, clearly display the eutectoid structure of the iron scale and perform measurement and evaluation.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for evaluating the eutectoid structure of hot-rolled plate oxide scale comprises the following steps: (1) Sample preparation: Place the hot-rolled plate in a vacuum coating machine and perform sputtering coating on its surface; cut a portion as a sample, solidify it with room temperature oxidized resin and mount it, then grind and polish the cross section of the sample until the surface of the sample is bright and scratch-free; (2) Chemical corrosion: The prepared sample is placed in a corrosion solution for chemical corrosion. The corrosion solution is prepared from hydrochloric acid, ammonium persulfate and anhydrous ethanol. After the chemical corrosion is completed, the sample is rinsed with anhydrous ethanol and blown dry. (3) Quantitative evaluation using scanning electron microscopy: Observation and quantitative measurement are performed using a scanning electron microscope.

[0006] Furthermore, in the etching solution of step (2) of the present invention, the volume concentration of hydrochloric acid is 1-2%, the volume concentration of ammonium persulfate is 5-10%, and the rest is anhydrous ethanol, and the etching time is 15-25s.

[0007] Furthermore, the quantitative evaluation by scanning electron microscopy in step (3) of the present invention is as follows: the eutectoid Fe3O4 / α-Fe lamellae spacing is measured using a backscattering mode; the specific measurement method is as follows: a straight line with a length value is measured in a direction perpendicular to the eutectoid Fe3O4 / α-Fe lamellae, the number of single α-Fe bars in the eutectoid Fe3O4 / α-Fe is counted from one end of the straight line to the other end of the straight line, the total number of bars is recorded, and the eutectoid Fe3O4 / α-Fe lamellae spacing is obtained by dividing the length of the straight line by the total number of bars; each sample is measured and calculated three times, and the arithmetic average of the three lamellae spacings is the eutectoid Fe3O4 / α-Fe lamellae spacing of the sample, and the lamellae spacing average value is accurate to 1 nm.

[0008] Furthermore, in the quantitative evaluation by scanning electron microscopy in step (3) of the present invention, the magnification of the observation field is 5000 to 50000 times.

[0009] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: The method of the present invention can obtain a complete iron oxide scale, and can clearly display the eutectoid organizational structure of the iron oxide scale and the microstructure of the steel matrix through one corrosion, and can accurately measure the spacing size of the eutectoid Fe3O4 / α-Fe lamella structure, so as to accurately evaluate the eutectoid Fe3O4 / α-Fe lamella structure.

[0010] The present invention uses sputtering coating before inlaying to form a relatively dense foreign metal layer on the outermost layer, which can effectively protect the loose iron oxide scale. In addition, after coating, the edge of the sample can also obtain good conductivity, and a better image can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is the scanning electron microscope backscattering image of Example 1; Figure 2 This is a scanning electron microscope backscattering photograph measurement diagram of Example 1; Figure 3 This is a scanning electron microscope backscattering photograph measurement diagram of Example 2; Figure 4This is a scanning electron microscope backscattering photograph measurement diagram of Example 3. DETAILED DESCRIPTION

[0012] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Example 1

[0013] A method for evaluating the eutectoid structure of hot-rolled plate oxide scale comprises the following steps: (1) Sample preparation: Prepare a piece of 65Mn hot-rolled steel plate and place it in a vacuum coating machine for sputtering coating on its surface; cut a 15 mm × 20 mm sample by wire cutting, solidify it with room temperature oxidized resin and mount it, then grind and polish the cross section of the sample until the surface of the sample is bright and scratch-free; (2) Chemical corrosion: Place the prepared sample in a corrosion solution for 25 seconds. The corrosion solution is prepared from hydrochloric acid, ammonium persulfate and anhydrous ethanol, wherein the volume concentration of hydrochloric acid is 1%, the volume concentration of ammonium persulfate is 5%, and the rest is ethanol. After the chemical corrosion is completed, rinse the sample with anhydrous ethanol and blow dry it with a hair dryer. (3) Quantitative evaluation by scanning electron microscopy: The scanning electron microscope was used in backscattering mode, with a voltage of 15 kV and a working distance of 8.2 mm. The backscattering results of the scanning electron microscope with a field of view magnified 5000 times are shown in Figure 1 ,from Figure 1 In this figure, not only can the iron oxide scale structure and the eutectoid lamellae be clearly seen, but also the organizational structure of the matrix can be seen. The backscattering observation field of the scanning electron microscope was magnified 10,000 times, and then the eutectoid Fe3O4 / α-Fe lamella spacing was measured and calculated. The measurement diagram is shown in Figure 1. Figure 2 The specific calculation method is as follows: First, measure the first straight line in the direction perpendicular to the eutectoid Fe3O4 / α-Fe lamella, with a length of 2.469um. Count the number of elemental α-Fe in the eutectoid Fe3O4 / α-Fe from one end of the first straight line to the other end of the straight line, a total of 16 lines. Divide the length of the straight line 2.469um by the number of lines 16 to obtain the interlamellar spacing of the first eutectoid Fe3O4 / α-Fe, which is 154 nm. Then measure the interlamellar spacing of the second and third eutectoid Fe3O4 / α-Fe in turn according to the above method.

[0014] The length of the second straight line is 2.223um, and the number of single-element α-Fe within this straight line length is 12. Dividing the length of the straight line 2.223um by the number of lines 12, we can get the interlamellar spacing of the second eutectoid Fe3O4 / α-Fe, which is 185 nm.

[0015] The length of the third straight line is 2.342um, and the number of single-element α-Fe within this straight line length is 17. Dividing the length of the straight line 2.342um by the number of lines 17, we can get the interlamellar spacing of the third eutectoid Fe3O4α-Fe, which is 138 nm.

[0016] The arithmetic mean of the three interlamellar spacings is (154+185+138)÷3=159 nm. The eutectoid Fe3O4 / α-Fe interlamellar spacing of this sample is 159 nm. Example 2

[0017] A method for evaluating the eutectoid structure of hot-rolled plate oxide scale comprises the following steps: (1) Sample preparation: Prepare a piece of DC04 hot-rolled steel plate and place it in a vacuum coating machine for sputtering coating on its surface; cut a 15 mm × 15 mm sample by wire cutting, solidify it with room temperature oxidized resin and mount it, then grind and polish the cross section of the sample until the surface of the sample is bright and scratch-free; (2) Chemical corrosion: Place the prepared sample in a corrosion solution for 20 seconds. The corrosion solution is prepared from hydrochloric acid, ammonium persulfate and anhydrous ethanol, wherein the volume concentration of hydrochloric acid is 2%, the volume concentration of ammonium persulfate is 8%, and the rest is ethanol. After the chemical corrosion is completed, rinse the sample with anhydrous ethanol and blow dry it with a hair dryer. (3) Quantitative evaluation by scanning electron microscopy: The scanning electron microscope was used in backscattering mode, with a voltage of 15 kV and a working distance of 8.2 mm. The observation field was magnified 10,000 times, and then the interlamellar spacing of the eutectoid Fe3O4 / α-Fe was measured and calculated. The measurement diagram is shown in the figure below. Figure 3 The specific calculation method is as follows: First, measure the first straight line in the direction perpendicular to the eutectoid Fe3O4 / α-Fe lamella, with a length of 2.553um. Count the number of elemental α-Fe in the eutectoid Fe3O4 / α-Fe from one end of the first straight line to the other end of the straight line, a total of 13 lines. Divide the length of the straight line 2.553um by 13 to obtain the interlamellar spacing of the first eutectoid Fe3O4 / α-Fe, which is 196 nm. Then measure the interlamellar spacing of the second and third eutectoid Fe3O4 / α-Fe in turn according to the above method.

[0018] The length of the second straight line is 2.392um, and the number of single-element α-Fe within this straight line is 15. Dividing the length of the straight line 2.392um by the number of lines 15, we can get the interlamellar spacing of the second eutectoid Fe3O4 / α-Fe, which is 159 nm.

[0019] The length of the third straight line is 3.218um, and the number of single-element α-Fe within this straight line length is 18. Dividing the length of the straight line 3.218um by the number of lines 18, we can get the interlamellar spacing of the third eutectoid Fe3O4α-Fe, which is 179 nm.

[0020] The arithmetic mean of the three interlamellar spacings is (196+159+179)÷3=178 nm. The eutectic Fe3O4 / α-Fe interlamellar spacing of this sample is 178 nm. Example 3

[0021] A method for evaluating the eutectoid structure of hot-rolled plate oxide scale comprises the following steps: (1) Sample preparation: Prepare a piece of 45# steel hot-rolled steel plate and place it in a vacuum coating machine for sputter coating on its surface; cut a 20 mm × 20 mm sample by wire cutting, solidify it with room temperature oxidized resin and mount it, then grind and polish the cross section of the sample until the surface of the sample is bright and scratch-free; (2) Chemical corrosion: Place the prepared sample in a corrosion solution for 15 seconds. The corrosion solution is prepared from hydrochloric acid, ammonium persulfate and anhydrous ethanol, wherein the volume concentration of hydrochloric acid is 2%, the volume concentration of ammonium persulfate is 10%, and the rest is ethanol. After the chemical corrosion is completed, rinse the sample with anhydrous ethanol and blow dry it with a hair dryer. (3) Quantitative evaluation by scanning electron microscopy: The scanning electron microscope was used in backscattering mode, with a voltage of 15 kV and a working distance of 8.5 mm. The observation field was magnified 20,000 times, and then the interlamellar spacing of the eutectoid Fe3O4 / α-Fe was measured and calculated. The measurement diagram is shown in the figure below. Figure 4 The specific calculation method is as follows: First, measure the first straight line in the direction perpendicular to the eutectoid Fe3O4 / α-Fe lamella, with a length of 1.846um. Count the number of elemental α-Fe in the eutectoid Fe3O4 / α-Fe from one end of the first straight line to the other end of the straight line, a total of 11 lines. Divide the length of the straight line 1.846um by the number of lines 11 to obtain the interlamellar spacing of the first eutectoid Fe3O4 / α-Fe, which is 168nm. Then measure the interlamellar spacing of the second and third eutectoid Fe3O4 / α-Fe in turn according to the above method.

[0022] The length of the second straight line is 1.761um, and the number of single-element α-Fe lines within this straight line is 10. Dividing the length of the straight line 1.761um by the number of lines 10, we can get the interlamellar spacing of the second eutectoid Fe3O4 / α-Fe, which is 176 nm.

[0023] The length of the third straight line is 2.096um, and the number of single-element α-Fe within this straight line is 10. Dividing the length of the straight line 2.096um by the number of lines 10, we can get the interlamellar spacing of the third eutectoid Fe3O4α-Fe as 210 nm.

[0024] The arithmetic mean of the three interlamellar spacings is (168+176+210)÷3=185 nm. The eutectic Fe3O4 / α-Fe interlamellar spacing of this sample is 185 nm.

Claims

1. A method for evaluating the eutectoid structure of hot-rolled sheet oxide scale, characterized in that: The method comprises sample preparation, chemical etching and quantitative evaluation by scanning electron microscope; wherein the etching solution used for the chemical etching is prepared from hydrochloric acid, ammonium persulfate and anhydrous ethanol.

2. A method for evaluating the eutectoid structure of hot-rolled sheet oxide scale according to claim 1, characterized in that: The volume concentration of hydrochloric acid in the etching solution is 1-2%, the volume concentration of ammonium persulfate is 5-10%, and the rest is anhydrous ethanol.

3. A method for evaluating the eutectoid structure of hot-rolled sheet oxide scale according to claim 1, characterized in that: The corrosion time of the chemical corrosion is 15-25s.

4. The method for evaluating the eutectoid structure of hot-rolled sheet oxide scale according to claim 1, characterized in that: After the chemical etching is completed, the sample is rinsed with anhydrous ethanol and blown dry.

5. The method for evaluating the eutectoid structure of hot rolled sheet oxide scale according to claim 1, characterized in that: The specific operation of the sample preparation is: putting the hot-rolled plate into a vacuum coating machine and sputtering coating the surface thereof; cutting a part as a sample, curing and embedding it with room temperature oxidizing resin, and then grinding and polishing the cross section thereof until the surface of the sample is bright and scratch-free.

6. A method for evaluating the eutectoid structure of hot-rolled sheet oxide scale according to claim 1, characterized in that: The scanning electron microscope quantitative evaluation: the backscattering mode is used to measure the interlamellar spacing of the eutectoid Fe3O4 / α-Fe. The specific measurement method is as follows: a straight line with a length value is measured in the direction perpendicular to the eutectoid Fe3O4 / α-Fe lamellae, and the number of elemental α-Fe in the eutectoid Fe3O4 / α-Fe is counted from one end of the straight line to the other end of the straight line, and the total number of bars is recorded. The length of the straight line is divided by the total number of bars to obtain the interlamellar spacing of the eutectoid Fe3O4 / α-Fe.

7. A method for evaluating the eutectoid structure of hot-rolled sheet oxide scale according to claim 6, characterized in that: The quantitative evaluation by scanning electron microscopy: Each sample is measured and calculated three times, and the arithmetic mean of the three interlamellar spacings is the eutectoid Fe3O4 / α-Fe interlamellar spacing of the sample.

8. A method for evaluating the eutectoid structure of hot-rolled sheet oxide scale according to claim 6, characterized in that: The quantitative evaluation under the scanning electron microscope: the observation field magnification is 5000 to 50000 times.

Images