An evaluation method for the protective effect of high temperature anti-oxidation coatings on nickel-based steel

Abstract

A method for evaluating the protective effect of high-temperature anti-oxidation coatings for nickel-based steel comprises the following steps: (1) sample preparation: polishing the nickel-based steel sample with sandpaper, cleaning and removing the surface oil, spraying the coating, and then heating and heat preservation in a heating furnace, and knocking to remove the surface oxide scale after cooling; (2) obtaining metallographic photographs: cutting the sample, grinding and polishing the cross section to prepare the sample, and observing the cross-sectional morphology with a metallographic microscope; (3) analyzing data: comparing the data of different coatings by measuring the thickness of the nickel-rich layer and the decarburized layer to determine the protective effect of the coating; the formula for calculating the burnout rate is as follows: S=(2.25lnA-9.07)*100%, where A is the total thickness value of the nickel-rich layer and the decarburized layer in μm; the formula for calculating the protective effect of the coating is as follows: P=(1-S / 4.52)*100%. The evaluation method can accurately determine the protective effect of different coatings.

Description

Technical Field

[0001] The invention relates to a method for evaluating the protective effect of a coating, and in particular to a method for evaluating the protective effect of a high-temperature anti-oxidation coating on nickel-based steel. Background Art

[0002] In the heating furnace, a layer of iron oxide scale is generated on the surface of nickel-based steel. Nickel is enriched between the iron oxide scale and the matrix to form nickel-rich metal oxide mesh and particles, i.e., the nickel-rich layer. Due to its strong adhesion, it is difficult to remove during the rolling and descaling process, which can easily cause surface quality defects such as pockmarks and pits on the plate. Therefore, before the nickel-based steel enters the heating furnace, the surface needs to be sprayed with high-temperature anti-oxidation coating to prevent the nickel-based steel ingot from oxidizing in the heating furnace, reduce surface quality defects on the plate, and improve the yield rate of the plate. Therefore, the protective effect of the coating plays an important role in the production of nickel-based steel plates.

[0003] At present, the mass loss method is the most common evaluation method for the protective effect of coatings. This method is simple to operate. The sample is weighed before spraying and fired after spraying. After firing, the paint and oxide scale on the surface are removed and weighed. The protective effect of the coating is judged based on the mass loss before and after firing. However, this method has obvious disadvantages. Since nickel-based steel is heated at high temperature, a nickel-rich layer is generated on the surface. The nickel-rich layer is pinned to the surface of the substrate and is difficult to remove, resulting in a large calculation error of the mass loss method, which will directly affect the evaluation of the protective effect of the coating. Summary of the invention

[0004] Purpose of the invention: The present invention aims to provide an evaluation method that can accurately determine the protective effect of high-temperature anti-oxidation coatings on nickel-based steel.

[0005] Technical solution: The method for evaluating the protective effect of high-temperature anti-oxidation coating for nickel-based steel of the present invention comprises the following steps:

[0006] (1) Sample preparation: Use sandpaper to smooth the six surfaces of the nickel-based steel sample, clean and remove the surface oil, spray the paint, and then heat and keep warm in a heating furnace. After cooling, knock to remove the surface oxide scale;

[0007] (2) Obtaining metallographic photographs: cutting the sample, grinding and polishing the cross section, and observing the cross-sectional morphology with a metallographic microscope;

[0008] (3) Data analysis: By measuring the thickness of the nickel-rich layer and the decarburized layer, the data of different coatings are compared to determine the protective effect of the coating. Nickel-based steel will also generate a nickel-rich layer and a decarburized layer under the protection of the coating. The thickness of the two directly reflects the protective effect of the coating. The thinner the nickel-rich layer and the decarburized layer, the better the protective effect of the coating.

[0009] The formula for calculating the burning rate based on the thickness of the nickel-rich layer and the decarburized layer is as follows:

[0010] S=(2.25lnA-9.07)*100%,where A is the total thickness of the nickel-rich layer and the decarburized layer in μm;

[0011] The calculation formula of the coating protection effect is as follows:

[0012] P=(1-S / 4.52)*100%.

[0013] Preferably, the coating in step (1) is a MgO spinel system coating or a SiC-Al2O3 system coating specially used for nickel-based steel; the coating thickness is controlled at 300±15μm, the heating furnace is heated to 1150±10°C, and the holding time is 2-2.5 hours; the cooling method after heating in the heating furnace is water quenching. Preferably, during cooling in step (1), the sample is placed flat on a sample rack, and the sample rack is a hollow structure to reduce the contact area with the sample.

[0014] Preferably, the magnification of the metallographic microscope in step (2) is 100 times, 200 times or 500 times.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the thickness of the nickel-rich layer and the decarburized layer is increased, especially the nickel-rich layer, which is difficult to remove by high-pressure descaling and is pressed into the substrate during the rolling process, which easily causes cracks in the substrate. The present invention proposes a method for evaluating the protective effect of high-temperature anti-oxidation coatings for nickel-based steels. This method can accurately determine the protective effect of the coatings. Nickel-based steels with different nickel contents can be targeted to select coatings, thereby reducing the surface quality defects of the plates caused by oxidation of the ingots and improving the yield rate of the materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a metallographic photograph of the protective effect of MgO spinel system coating;

[0017] Figure 2 Metallographic photograph of the protective effect of SiC-Al2O3 system coating. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0019] Example 1

[0020] (1) Sample preparation: Nickel steel was cut into 40*40*10mm specimens, and the six surfaces were polished with sandpaper to make them smooth. After cleaning and removing the surface oil, MgO spinel system coating was sprayed. For comparative tests, the coating thickness should be controlled at about 300μm. Then the specimen was heated in a furnace at 1150℃ for 2 hours, and the cross-sectional morphology was observed after water quenching and cooling. After the heating furnace was heated to 1150℃, the specimen was placed flat on the specimen rack. The specimen rack was a hollow structure, and the contact area with the specimen should be minimized as much as possible. After water quenching, the adhered oxide scale was removed as much as possible.

[0021] (2) Obtaining metallographic photographs: Use a metallographic microscope to obtain photographs with a magnification of 100 times to obtain cross-sectional metallographic photographs;

[0022] (3) Analyze data: Measure the thickness of the nickel-rich layer and the decarburized layer, and compare the data of different coatings.

[0023] Example 2

[0024] (1) Sample preparation: Nickel steel was cut into 40*40*10 mm specimens, and the six surfaces were polished with sandpaper to make them smooth. After cleaning and removing the surface oil, SiC-Al2O3 system coating was sprayed. For comparative tests, the coating thickness should be controlled at about 300 μm. Then the specimens were heated in a furnace at 1150°C for 2 hours, and the cross-sectional morphology was observed after water quenching.

[0025] (2) Obtaining metallographic photographs: Use a metallographic microscope to obtain photographs with a magnification of 100 times to obtain cross-sectional metallographic photographs;

[0026] (3) Analyze data: Measure the thickness of the nickel-rich layer and the decarburized layer, and compare the data of different coatings.

[0027] like Figure 1 As shown in the figure, the nickel-rich layer thickness of the sprayed MgO spinel system coating is 95μm, the decarburized layer thickness is 110μm, and the total thickness of the two is 205μm. The protective effect of the coating is average; Figure 2 As shown, the nickel-rich layer thickness of the sprayed SiC-Al2O3 system coating is 38μm, the decarburization layer thickness is 76μm, and the total thickness is 114μm. According to the calculation formula of the burnout rate and protective effect, the burnout rate of the MgO spinel system coating is 2.91%, and the protective effect is 36%; the burnout rate of the SiC-Al2O3 system coating is 1.59%, and the protective effect is 65%, indicating that the SiC-Al2O3 system coating has a better protective effect.

Claims

1. A method for evaluating the protective effect of high temperature anti-oxidation coatings for nickel-based steel, characterized in that: The following steps are involved: (1) Sample preparation: The six surfaces of the nickel-based steel sample are polished smooth with sandpaper, the surface oil is cleaned and removed, and then the coating is sprayed, and then heated and kept warm in a heating furnace. After cooling, the surface oxide scale is removed by knocking. The coating is a MgO spinel system high-temperature antioxidant coating or a SiC-Al2O3 system high-temperature antioxidant coating specially used for nickel-based steel; (2) Obtaining metallographic photographs: cutting the sample, grinding and polishing the cross section, and observing the cross-sectional morphology with a metallographic microscope; (3) Data analysis: By measuring the thickness of the nickel-rich layer and the decarburized layer, the data of different coatings are compared to determine the protective effect of the coatings. The formula for calculating the burnout rate based on the thickness of the nickel-rich layer and the decarburized layer is as follows: S=(2.25lnA-9.07)×100%,where A is the total thickness of the nickel-rich layer and the decarburized layer in μm; The calculation formula of the coating protection effect is as follows: P=(1-S / 4.52)×100%.

2. The method for evaluating the protective effect of high temperature anti-oxidation coating for nickel-based steel according to claim 1, characterized in that: The coating thickness in step (1) is 300±15 μm.

3. The method for evaluating the protective effect of high temperature anti-oxidation coating for nickel-based steel according to claim 1, characterized in that: The cooling method in step (1) is water quenching cooling.

4. The method for evaluating the protective effect of high temperature anti-oxidation coating for nickel-based steel according to claim 1, characterized in that: In the step (1), the heating furnace is heated to 1150±10° C. and the heat preservation time is 2-2.5 hours.

5. The method for evaluating the protective effect of high temperature anti-oxidation coating for nickel-based steel according to claim 1, characterized in that: During cooling in step (1), the sample is placed flat on a sample rack, which has a hollow structure to reduce the contact area with the sample.

6. The method for evaluating the protective effect of high temperature anti-oxidation coating for nickel-based steel according to claim 1, characterized in that: The magnification of the metallographic microscope in step (2) is 100 times, 200 times or 500 times.

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