Method for detecting the thickness of the iron oxide scale of a girder steel

Abstract

This invention discloses a method for detecting the thickness of iron oxide scale on main beam steel, comprising the following steps: First, processing the sample; second, applying a layer of casting adhesive with a thickness of 1.8-2.2 mm around the test surface of the cut sample and air-drying it; third, using phenolic resin for hot mounting; fourth, metallographic polishing; and fifth, microscopic observation and detection. A 1000X bright-field test is performed, measuring 3-10 points and taking the average value. The purpose of this invention is to provide a method for detecting the thickness of iron oxide scale on main beam steel, which is simple to prepare, fast to detect, yields relatively complete iron oxide scale, and provides accurate data.

Description

Technical Field

[0001] This invention relates to the field of metal material testing, and in particular to a method for testing the thickness of iron oxide scale on main beam steel. Background Technology

[0002] Currently, the domestic steel market is facing increasingly fierce competition and severe product homogenization. Surface quality of steel products is a crucial indicator that manufacturers and users constantly strive for. The iron oxide scale formed during the rolling process of beam steel, while eliminating initial surface defects through oxidation, also leaves a large amount of residual iron oxide scale on the surface of the rolled steel, affecting subsequent processing and use. Therefore, studying the structure and thickness of the iron oxide scale is an important parameter for evaluating the surface quality of beam steel and formulating rolling processes.

[0003] Because iron oxide scale is brittle and easily breaks off, preserving its integrity during sample preparation is a key factor limiting the measurement of iron oxide scale thickness. Traditional metallographic sample preparation methods struggle to preserve the edges; the external forces applied during coarse grinding, fine grinding, and polishing further weaken the fragile iron oxide scale, significantly reducing or eliminating the area of ​​iron oxide scale observable under a microscope, posing considerable challenges for testing personnel. A literature review found no reports on iron oxide scale sample preparation methods. Summary of the Invention

[0004] The purpose of this invention is to provide a method for detecting the thickness of iron oxide scale on main beam steel. The method is simple to prepare, fast to detect, and produces relatively complete iron oxide scale with accurate data.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a method for detecting the thickness of iron oxide scale on main beam steel, comprising the following steps:

[0007] The first step is to process the sample. Processing requirements: the sample edges should be flat, burr-free, and free of grinding. Before cutting, it can be wrapped with A4 paper to reduce the shedding of iron oxide scale caused by machining, or laser cutting can be used.

[0008] The second step is to apply a layer of casting adhesive with a thickness of 1.8-2.2mm around the test surface of the cut sample, air dry for 20-30 hours or put it in a box-type drying oven at a temperature of 250-350℃ for 30-70 seconds, and then dry it with cold air after water cooling.

[0009] The third step involves using phenolic resin thermal mounting to mount two samples at once, with the main testing surfaces of the two samples placed together. The mounting temperature is 120℃, the pressure is 300 bar, and the heating and holding time is 5 minutes, followed by medium-speed cooling for 5 minutes.

[0010] The fourth step is metallographic polishing. The mounted sample is roughly ground to a depth of 1mm to ensure that the mounting material and casting adhesive on the sample surface are completely removed. Then, it is ground flat on 320#, 600#, and 1000# metallographic sandpaper in sequence, grinding in one direction with the grinding marks between each sandpaper perpendicular to each other. The sample is then polished using a pressure-sensitive adhesive woolen polishing cloth with 4-6µm metallographic polishing agent evenly sprayed on it. Water is sprayed while polishing. The polishing machine speed is 140-160 rpm, and the polishing time is 4-6 minutes, until the sample surface is bright and free of scratches.

[0011] Step 5: Microscopic observation and testing. Use a 1000X microscope to perform a bright field test, measuring 3-10 points and taking the average value.

[0012] Furthermore, in the first step, the size of the test sample is 20*25mm.

[0013] Furthermore, in the second step, a 2mm thick layer of casting adhesive is applied around the test surface of the cut sample, and it is air-dried for 24 hours or placed in a box-type drying oven at 300℃ for 50 seconds, then cooled with water and dried with cold air.

[0014] Furthermore, in the third step, more attention is paid to the thickness of the iron oxide scale on the upper surface. The upper surfaces of the two samples are placed together, inside the middle, so that the lower surface is on the outside.

[0015] Furthermore, in the fourth step, the grinding is performed back and forth in one direction to prevent the iron oxide scale from falling off.

[0016] Furthermore, in the fourth step, a pressure-sensitive adhesive woolen polishing cloth with 5µm metallographic polishing agent evenly sprayed is used to polish the sample. Water is sprayed while polishing. The polishing machine speed is 150 rpm and the polishing time is 5 minutes until the sample surface is bright and free of scratches.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0018] This invention provides a method for detecting the thickness of iron oxide scale on main beam steel. The iron oxide scale obtained by using this method is more complete, with more areas available for detection, and the results are closer to the true value. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings.

[0020] Figure 1 This is a schematic diagram of the sample to be tested after applying casting adhesive.

[0021] Figure 2 It is the inlaid sample;

[0022] Figure 3 These are images showing the thickness of iron oxide scale.

[0023] Figure 4 It is a sample after ultrasonic oscillation;

[0024] Figure 5 It involves the testing of iron oxide scale thickness and energy dispersive spectroscopy analysis. Detailed Implementation

[0025] Example:

[0026] The user requested the measurement of iron oxide scale thickness on a 6mm thick beam steel sample. To obtain the most complete iron oxide scale possible and reduce the measurement error, the testing process is as follows: Step 1: Process the sample. The sample size is 20*25 (mm). Processing requirements: The sample edges must be flat, burr-free, and free of grinding. Before cutting, it can be wrapped with A4 paper to reduce iron oxide scale shedding during machining, or laser cutting can be used. Step 2: Apply a layer of casting adhesive approximately 2mm thick around the test surface of the cut sample. Figure 1 As shown, air dry for 24 hours or dry in a box-type drying oven at 300℃ for 50 seconds, then water-cool and air-dry. The third step involves phenolic resin hot mounting. Two samples are mounted at a time, with the main testing surfaces of the two samples close together (for example, if more attention is paid to the thickness of the iron oxide scale on the upper surface, place the upper surfaces of the two samples together, inside the middle, so that the lower surface is on the outside). Mounting temperature: 120℃, pressure: 300 bar, heating and holding for 5 minutes, medium-speed cooling for 5 minutes. The finished mounting appearance is as shown. Figure 2 As shown. Step 4, metallographic polishing. Roughly grind the mounted sample to a depth of approximately 1mm, ensuring complete removal of the mounting material and casting adhesive from the sample surface. Then, grind it smooth on 320#, 600#, and 1000# metallographic sandpaper in sequence, grinding in one direction (avoid back-and-forth grinding to prevent iron oxide scale from peeling off). The grinding marks between each sandpaper pass should be perpendicular to each other. Use a pressure-sensitive adhesive woolen polishing cloth evenly coated with 5µm metallographic polishing agent for polishing. Spray water while polishing. The polishing machine speed is 150 rpm, and the polishing time is approximately 5 minutes, until the sample surface is bright and scratch-free. Step 5, microscopic observation and testing. Use a 1000X microscope for bright-field testing, measuring 3-10 points and taking the average value. The image of the iron oxide scale thickness acquired under the microscope is shown below. Figure 3 As shown.

[0027] To verify the accuracy and scientific validity of the results, scanning electron microscopy and energy dispersive spectroscopy were used to detect the thickness of the iron oxide scale. The experimental steps are as follows: First, the thickness of the iron oxide scale was measured. Figure 2 The embedded sample was placed in anhydrous ethanol and ultrasonically vibrated for 10-30 minutes. After vibration, many cracks appeared on the surface of the embedded material (phenolic resin), such as... Figure 4As shown, the sample is easily removed by gently tapping it with a hammer, minimizing damage to the integrity of the iron oxide scale thickness. The second step involves placing the sample into a scanning electron microscope (SEM), evacuating the microscope, and setting parameters such as detection voltage, probe current, working distance, and magnification. Focusing is then performed, and brightness, contrast, and astigmatism correction are adjusted until a clear image of the iron oxide scale thickness is obtained. Energy dispersive spectroscopy (EDS) is then used for qualitative and quantitative analysis of the iron oxide scale. Figure 5 As shown.

[0028] The results obtained by metallurgical microscopy were verified by scanning electron microscopy and are scientifically reliable. A selection of the results is shown in Table 1.

[0029] Table 1. Results of iron oxide scale thickness

[0030]

[0031]

[0032] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for detecting the thickness of iron oxide scale on main beam steel, characterized in that: Includes the following steps: The first step is to process the sample. Processing requirements: the sample edges should be flat, burr-free, and free of grinding. Before cutting, it can be wrapped with A4 paper to reduce the shedding of iron oxide scale caused by machining, or laser cutting can be used. The second step is to apply a layer of casting adhesive with a thickness of 1.8-2.2mm around the test surface of the cut sample, air dry for 20-30 hours or put it in a box-type drying oven at a temperature of 250-350℃ for 30-70 seconds, and then dry it with cold air after water cooling. The third step involves using phenolic resin thermal mounting to mount two samples at once, with the main testing surfaces of the two samples placed together. The mounting temperature is 120℃, the pressure is 300 bar, and the heating and holding time is 5 minutes, followed by medium-speed cooling for 5 minutes. The fourth step is metallographic polishing. The mounted sample is roughly ground to a depth of 1mm to ensure that the mounting material and casting adhesive on the sample surface are completely removed. Then, it is ground flat on 320#, 600#, and 1000# metallographic sandpaper in sequence, grinding in one direction with the grinding marks between each sandpaper perpendicular to each other. The sample is then polished using a pressure-sensitive adhesive woolen polishing cloth with 4-6µm metallographic polishing agent evenly sprayed on it. Water is sprayed while polishing. The polishing machine speed is 140-160 rpm, and the polishing time is 4-6 minutes, until the sample surface is bright and free of scratches. The fifth step is to observe and test under a microscope. Use a 1000X microscope to perform a bright field test, measure 3-10 points, and take the average value.

2. The method for detecting the thickness of iron oxide scale on main beam steel according to claim 1, characterized in that: In the first step, the test sample size is 20*25mm.

3. The method for detecting the thickness of iron oxide scale on main beam steel according to claim 1, characterized in that: In the second step, apply a 2mm thick layer of casting adhesive around the test surface of the cut sample, air dry for 24 hours or place it in a box-type drying oven at 300℃ for 50 seconds, and then dry it with cold air after water cooling.

4. The method for detecting the thickness of iron oxide scale on main beam steel according to claim 1, characterized in that: In the third step, more attention is paid to the thickness of the iron oxide scale on the upper surface. The upper surfaces of the two samples are placed together, inside the middle, so that the lower surface is on the outside.

5. The method for detecting the thickness of iron oxide scale on main beam steel according to claim 1, characterized in that: In the fourth step, the iron oxide scale is ground back and forth in one direction to prevent it from falling off.

6. The method for detecting the thickness of iron oxide scale on main beam steel according to claim 1, characterized in that: In the fourth step, a pressure-sensitive adhesive woolen polishing cloth with 5µm metallographic polishing agent evenly sprayed is used to polish the sample. Water is sprayed while polishing. The polishing machine speed is 150 rpm and the polishing time is 5 minutes until the sample surface is bright and free of scratches.

Images