Metal in-situ analyzer sample preparation method

Abstract

The invention relates to a metal in-situ analyzer sample preparation method, which comprises the operation methods of sawing machine rough machining, acid corrosion, acid removal and mineral oil removal, and comprises the following steps: taking a sample from a continuous casting billet to be subjected to segregation detection by using a sawing machine; corroding the sample by hot acid: putting the sample corroded by hydrochloric acid into boiling water for cleaning; performing oil coating treatment on the observation surface of the sample; putting the surface-oiled sample into a vacuum sintering furnace, and heating the sample; naturally cooling, and putting into a sealing bag for processing; the surface of the sample is machined through a milling machine, the feed amount of a milling cutter is 2-3 mm, and machining is completed at a time. According to the method, the mineral oil in the defects is thoroughly removed through rough machining of the sawing machine, acid corrosion, acid removal, mineral oil removal and other operations, and the accuracy of metal in-situ analysis is guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of physical and chemical sample preparation, and particularly relates to a method for preparing a sample for a metal in-situ analyzer. Background Art

[0002] Segregation is a common defect in continuous casting billets, mainly manifested as the non-uniform distribution of solute elements inside the continuous casting billets. When serious segregation defects occur in continuous casting billets, it is difficult to eliminate their adverse effects on the properties of the final steel plate even through subsequent controlled rolling and controlled cooling processes. The traditional segregation detection method is to take samples by fixed-point drilling. Since the sampling points are discontinuous and the analysis result is the average content of elements within the sampling range, the analysis result fluctuates greatly, and both the accuracy and reproducibility are not very satisfactory. Another traditional method is the acid etching rating method, but this method has the following important disadvantages: (1) After corrosion, the segregation is likely to deviate from the actual level, resulting in inaccurate rating; (2) For some steel grades that are difficult to corrode, it is difficult to make a correct rating for segregation; (3) The rating method has a large human factor, so the rating result is not objective enough.

[0003] Currently, using a metal in-situ analyzer to evaluate the segregation of casting billets has gradually become the mainstream method. Using this analysis method, the segregation of continuous casting billets can be quantitatively expressed, with good repeatability, and the segregation characteristics and laws can be characterized in the ways of points, lines, and surfaces. Through one scanning result, multi-element quantitative segregation results can be obtained, with accurate results, and fewer analysis samples, reducing the detection time and cost. However, the sample preparation level has a great impact on the analysis result when using a metal in-situ analyzer for detection. As is well known, there will inevitably be defects such as porosity, shrinkage cavities, and microcracks inside the casting billet. Since the casting billet sample processing process avoids the influence of high-temperature processing on the structure of the casting billet, usually, the flame cutting method is not adopted, but the sawing machine processing method is used to cut the casting billet. When using the sawing machine for processing, cutting fluid is inevitably used, and it is very difficult to remove the cutting fluid that penetrates into the defects such as porosity, shrinkage cavities, and microcracks inside the casting billet. Especially after sawing machine processing, many small defect surfaces will be closed by metal, and in this case, it is even more difficult to remove the residual cutting fluid inside the defects. The residual cutting fluid will have a great impact on the analysis result, and the result seriously deviates from the actual segregation degree of the casting billet. This is mainly because the main component of the cutting fluid is mineral oil, and the temperature of the electric spark excited during the scanning of the in-situ analyzer is as high as several thousand degrees. Under such high-temperature conditions, there is a large amount of carbon in the decomposition products of the residual mineral oil. At this time, the metal in-situ analysis result will show that the carbon content at the defect is very high, which is seriously inconsistent with the actual situation. In addition, since there are also a large amount of gases in the high-temperature decomposition products of mineral oil, this gas will affect the discharge, and it can be found in the actual detection process that there will also be a situation of poor excitation in the area near the defect, which also seriously affects the accuracy of the analysis result.

[0004] Patent "Analysis Method for Element Distribution Law in High-Manganese Steel" (Application No.: 202210032131.2, Publication No.: CN114563400A). This invention discloses an analysis method for the element distribution law in high-manganese steel. The invention adopts a rapid cooling method for the specimen after heat treatment, effectively avoiding the precipitation of pearlite and large-sized carbides during the cooling process. The distribution law of elements in high-manganese steel is analyzed and studied by using the metal in-situ analysis method. Before conducting the metal in-situ analysis, the specimen cooled to room temperature is polished on the detection surface with 60-mesh sandpaper, and then the metal in-situ analyzer is used to conduct segregation detection and analysis on the detection surface, thereby obtaining a two-dimensional contour map of the content of each element in the specimen.

[0005] Patent "Quantitative Analysis Method for Composition Segregation of Spring Steel Slab" (Application No.: 201510582105.7, Publication No.: CN105203732A). This invention discloses a quantitative analysis method for composition segregation of spring steel slab, including the following steps: 1) Transversely intercept a rough sample of the spring steel slab; 2) Transversely intercept a slab with a certain thickness as a macro sample, and further saw it into an observation sample; 3) Process the observation surface; 4) Select a chemical element, and conduct a two-dimensional surface scan on the observation surface through a metal in-situ analyzer to obtain the distribution map of the selected element in the scanning area. In the technical solution of this invention, the method adopted when processing the metal in-situ analysis specimen is: First, cut the specimen to be observed from the slab by sawing, and then conduct secondary finishing on the observation surface. The processing method of the observation surface is milling and grinding, and the surface roughness of the processed observation surface is not greater than 0.8 μm.

[0006] As described above, the traditional method for processing metal in-situ analysis specimens mainly cuts out an analysis sample of appropriate size with a sawing machine first, and then conducts simple milling and grinding on the observation surface, and then uses a metal in-situ analyzer to analyze the element segregation situation. This method for preparing samples cannot avoid the problem that the residual mineral oil in the slab defects interferes with the analysis. Therefore, in order to ensure the accuracy of the results of the metal in-situ analyzer, a suitable specimen preparation method must be developed. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for preparing specimens for a metal in-situ analyzer. Since the traditional method for processing metal in-situ analysis specimens mainly cuts out an analysis sample of appropriate size with a sawing machine first, and then conducts simple milling and grinding on the observation surface. This method for preparing samples cannot avoid the problem that the residual mineral oil in the slab defects interferes with the analysis. Therefore, in order to ensure the accuracy of the results of the metal in-situ analyzer, the present invention develops a suitable specimen preparation method. Through rough machining with a sawing machine, and then operations such as acid pickling corrosion, acid removal, and mineral oil removal, the mineral oil in the defects is completely removed, ensuring the accuracy of the metal in-situ analysis.

[0008] To achieve the above purpose, the present invention is realized by adopting the following technical solutions:

[0009] A method for preparing a sample for a metal in-situ analyzer, including the operating methods of rough machining by a sawing machine, acid pickling corrosion, acid removal, and mineral oil removal, thoroughly removing the mineral oil in the defects to ensure the accuracy of metal in-situ analysis; the specific method is as follows:

[0010] 1) Use a sawing machine to take a sample from the continuous casting billet to be segregated and detected. The length and width of the sample are 20 - 180 mm, and the thickness is 10 - 15 mm; the surface roughness of the sample on the observation surface after machining is not greater than 0.5 mm;

[0011] 2) Thermal acid pickling corrosion of the sample: Since the surface of the sample processed by the sawing machine is very rough, some micro-cracks, porosity, and shrinkage cavity defects on the surface will be sealed, and the metal covering the defects on the surface must be removed by acid etching. Hydrochloric acid is used for corrosion, the concentration of hydrochloric acid is 10% - 18%, the temperature of hydrochloric acid is controlled between 50 - 85 °C, and the pickling time is controlled between 20 - 30 min;

[0012] 3) Put the sample corroded by hydrochloric acid into boiling water, with the observation surface of the sample facing up. The water is deionized water, and the water surface is 10 - 20 cm higher than the observation surface of the sample. The sample is soaked in boiling water for 20 - 30 min; after taking out the sample, change the water again and put the sample into boiling water again, repeating the above operation once;

[0013] 4) Take out the sample from boiling water and immediately apply oil to the observation surface of the sample with a brush or spray gun to avoid oxidation inside the defects. The oil can be one or several of mineral oil, animal oil, or vegetable oil;

[0014] 5) Put the sample with oil applied on the surface into a vacuum sintering furnace. When the vacuum degree reaches below 10 Pa, start heating the sample. The heating temperature is 240 - 350 °C, the heating and holding time is 30 - 40 min, and the heating rate is 1 - 10 °C / min;

[0015] 6) After the heating and holding are completed, stop heating the vacuum sintering furnace. The vacuum sintering furnace enters the natural cooling state. When the vacuum sintering furnace naturally cools to below 40 °C, an analysis sample with mineral oil removed is obtained and put into a sealed bag for further processing;

[0016] 7) Machine the observation surface of the sample. Use a milling machine to machine the surface of the sample. Cutting fluid is not allowed during the machining process. The feed rate of the milling cutter is 2 - 3 mm, and the machining is completed in one pass. The surface roughness of the observation surface of the sample after machining is not greater than 50 μm. The machined sample is put into a sealed bag for detecting the composition segregation by a metal in-situ analyzer.

[0017] Step 3) The specimen is placed in boiling water. Due to the fluidity of boiling water, it can better remove the hydrochloric acid inside the defect. The observation surface of the specimen faces upward. To prevent the opening of the defect from contacting the bottom of the container when the observation surface faces downward, which is not conducive to the removal of hydrochloric acid in the defect by water, deionized water can be used to avoid the influence of residual calcium, magnesium and other elements in the water on the segregation detection results inside the defect. In step 5), heating the specimen starts when the vacuum reaches below 10 Pa to prevent combustion reaction when the temperature reaches the flash point of the mineral oil due to the high oxygen content in the furnace. When the combustion is incomplete, carbon will be produced in the combustion products. Once carbon remains in the defect, it will be very difficult to remove in the next step. The heating temperature is 240 - 350 °C to ensure the full volatilization and removal of the mineral oil under vacuum conditions. The heating rate is 1 - 10 °C / min to prevent the expansion of defects such as cracks caused by too fast heating rate. In step 7), cutting fluid is not allowed during the milling process of the specimen. Usually, cutting fluid is required for cooling during milling. However, once cutting fluid is used, the defect area of the specimen will be contaminated again. Since the surface of the specimen is relatively flat during the rough machining by the sawing machine in the early stage, when the feed amount of the milling cutter is 2 - 3 mm, a machining surface that can meet the requirements of the metal in-situ analyzer can be milled out at one time. Therefore, even without cutting fluid, the damage to the milling cutter is not significant.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] A method for preparing a specimen for a metal in-situ analyzer according to the present invention avoids the drawback of easy residual mineral oil in the defect of the traditional specimen preparation method. Through rough machining by a sawing machine and then operations such as acid pickling corrosion, acid removal, and mineral oil removal, the mineral oil in the defect is completely removed, ensuring the accuracy of metal in-situ analysis. Due to no influence of mineral oil in the defect, the electric spark excited during the scanning of the metal in-situ analyzer will not cause the decomposition of the mineral oil, and thus will not lead to a very high carbon content at the defect and poor excitation in the area near the defect. The accuracy of the analysis results of the metal in-situ analyzer is ensured. Description of the Drawings

[0020] Figure 1 It is the metal in-situ analysis result of Example 1 of the present invention.

[0021] Figure 2 It is the metal in-situ analysis result of Example 2 of the present invention.

[0022] Figure 3 It is the metal in-situ analysis result of Comparative Example 1.

[0023] Figure 4 It is the metal in-situ analysis result of Comparative Example 2. Detailed Embodiments

[0024] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further explains the specific implementation manners of the present invention in combination with embodiments. The following embodiments are used to specifically illustrate the content of the present invention. These embodiments are only general descriptions of the content of the present invention and do not limit the content of the present invention.

[0025] Embodiment 1:

[0026] 1) Use a sawing machine to take a sample from the continuous casting billet to be subjected to segregation detection. The dimensions are: length 160 mm, width 50 mm, and thickness 12 mm; the surface roughness of the processed observation surface is 0.45 mm.

[0027] 2) Thermally acid-etch the sample. Hydrochloric acid is used for the corrosion, the concentration of hydrochloric acid is 12%, the temperature of hydrochloric acid is controlled at 55 °C, and the pickling time is controlled at 22 min.

[0028] 3) Put the sample corroded by hydrochloric acid into boiling water, with the observation surface of the sample facing up. The water is deionized water, and the water surface is 11 cm higher than the observation surface of the sample. The sample is soaked in boiling water for 25 min. After taking out the sample, change the water again and put the sample into boiling water once more. Repeat the above operation 1 time.

[0029] 4) Take out the sample from boiling water and immediately coat the observation surface of the sample with oil using a brush. Vegetable oil is selected as the oil.

[0030] 5) Put the sample with the surface coated with oil into a vacuum sintering furnace. When the vacuum degree reaches 8 Pa, start heating the sample. The heating temperature is 245 °C, the heating and holding time is 35 min, and the heating rate is 2 °C / min.

[0031] 6) After the heating and holding are completed, stop heating the vacuum sintering furnace, and the vacuum sintering furnace enters the natural cooling state. When the vacuum sintering furnace naturally cools to 35 °C, an analysis sample with mineral oil removed is obtained and put into a sealed bag for further processing.

[0032] 7) Machine the observation surface of the sample. Use a milling machine to machine the surface of the sample. Cutting fluid is not allowed during the machining process.

[0033] The feed rate of the milling cutter is 2.2 mm, and the machining is completed in one pass. The surface roughness of the processed observation surface is 45 μm. The processed sample is put into a sealed bag for detecting the composition segregation by a metal in-situ analyzer.

[0034] The detection results of the metal in-situ analyzer are shown in Figure 1, the redder the color in the figure, the higher the carbon element content, and the bluer the color, the lower the carbon element content. Since the right - hand side area in the figure is a loose shrinkage cavity, the in - situ metal analysis results show that the carbon element content there is very low, which is consistent with the actual situation of the sample, indicating that the analysis results are accurate. It can be seen that the analysis sample prepared by the technology of the present invention effectively removes the influence of mineral oil during the sample processing, and there will be no phenomenon that the carbon content at the shrinkage cavity increases significantly due to the carbonization of mineral oil during the sample excitation process.

[0035] Example 2:

[0036] 1) Use a sawing machine to take a sample from the continuous casting billet to be detected for segregation. The dimensions are: length 120 mm, width 80 mm, and thickness 14 mm; the surface roughness of the processed observation surface is 0.4 mm.

[0037] 2) Thermally acid - corrode the sample. The acid used is hydrochloric acid with a concentration of 15%, the temperature of hydrochloric acid is controlled at 65 °C, and the pickling time is controlled at 25 min.

[0038] 3) Put the sample corroded by hydrochloric acid into boiling water with the observation surface of the sample facing up. The water is deionized water, and the water surface is 15 cm higher than the observation surface of the sample. The sample is soaked in boiling water for 28 min. After taking out the sample, change the water again and put the sample into boiling water once more, repeating the above operation 1 time.

[0039] 4) Take out the sample from boiling water and immediately apply oil to the observation surface of the sample using a spray gun. The oil selected is mineral oil.

[0040] 5) Put the sample with oil on the surface into a vacuum sintering furnace. When the vacuum degree reaches 5 Pa, start heating the sample. The heating temperature is 300 °C, the heating and holding time is 38 min, and the heating rate is 5 °C / min.

[0041] 6) After the heating and holding is completed, stop heating the vacuum sintering furnace, and the vacuum sintering furnace enters the natural cooling state. When the vacuum sintering furnace cools naturally to 28 °C, an analysis sample without mineral oil is obtained and put into a sealed bag for further processing.

[0042] 7) Process the observation surface of the sample. Use a milling machine to process the surface of the sample. Cutting fluid is not allowed during the processing.

[0043] The feed rate of the milling cutter is 2.8 mm, and the processing is completed in one pass. The surface roughness of the processed observation surface is 48 μm. The processed sample is put into a sealed bag for detecting the composition segregation by a metal in - situ analyzer.

[0044] The detection results of the metal in - situ analyzer are shown in Figure 2, the redder the color in the figure, the higher the carbon element content, and the bluer the color, the lower the carbon element content. Since the central area in the figure is a loose shrinkage cavity, the in-situ metal analysis results show that the carbon element content here is very low, which is consistent with the actual situation of the sample, indicating that the analysis results are accurate. It can be seen that the analysis sample prepared by the technology of the present invention effectively removes the influence of mineral oil during the sample processing, and the carbon content at the shrinkage cavity will not increase significantly due to the carbonization of mineral oil during the sample excitation process.

[0045] Comparative Example 1:

[0046] Take a comparative example analysis sample from the same cross-section of the continuous casting billet as in Example 1. The comparative example sample is processed in a conventional manner. After being processed by a sawing machine, the detection surface is processed by a milling machine, and then the element segregation situation is detected by an in-situ metal analyzer, as Figure 3 shown: Obvious carbon segregation occurs at the shrinkage cavity on the right side of the sample. The redder the color in the figure, the higher the carbon element content, and the bluer the color, the lower the carbon element content. Obviously, the result does not conform to the actual situation. The area with the highest carbon element content in the figure is actually a loose hole. This is mainly because the conventional sample processing method cannot effectively remove the residual mineral oil inside the defect. During the sample excitation process, the mineral oil is carbonized under the action of high temperature, resulting in a very high carbon element content shown in the analysis result at the shrinkage cavity, with a large deviation.

[0047] Comparative Example 2:

[0048] Take a comparative example analysis sample from the same cross-section of the continuous casting billet as in Example 2. The comparative example sample is processed in a conventional manner. After being processed by a sawing machine, the detection surface is processed by a milling machine, and then the element segregation situation is detected by an in-situ metal analyzer, as Figure 4 shown: Obvious carbon segregation occurs at the central shrinkage cavity of the sample. The redder the color in the figure, the higher the carbon element content, and the bluer the color, the lower the carbon element content. Obviously, the result does not conform to the actual situation. The area with the highest carbon element content in the figure is actually a loose hole. This is mainly because the conventional sample processing method cannot effectively remove the residual mineral oil inside the defect. During the sample excitation process, the mineral oil is carbonized under the action of high temperature, resulting in a very high carbon element content shown in the analysis result at the shrinkage cavity, with a large deviation.

Claims

1. A method for preparing a sample for a metal in-situ analyzer, characterized in that: It includes the operation methods of sawing machine rough processing, acid corrosion, acid removal and mineral oil removal; the specific methods are as follows: 1) Use a sawing machine to take samples from the continuous casting billet to be tested for segregation. The surface roughness of the sample on the observation surface after processing shall not exceed 0.5mm; 2) Hot acid corrosion of the sample: hydrochloric acid is used for corrosion, the concentration of hydrochloric acid is 10% to 18%, the temperature of hydrochloric acid is controlled between 50 and 85°C, and the pickling time is controlled between 20 and 30 minutes; 3) Place the sample corroded by hydrochloric acid in boiling water, with the observation side facing up, and soak the sample in boiling water for 20 to 30 minutes; after taking out the sample, replace the water, and place the sample in boiling water again, and repeat the above operation once; 4) Take out the sample from the boiling water and immediately apply oil to the observation surface of the sample with a brush or spray gun; 5) Place the surface oiled sample in a vacuum sintering furnace, and start heating the sample when the vacuum degree reaches below 10Pa. The heating temperature is 240-350℃, the heating and holding time is 30-40min, and the heating rate is 1-10℃ / min; 6) After the heating and heat preservation is completed, the vacuum sintering furnace enters a natural cooling state. When the vacuum sintering furnace is naturally cooled to below 40°C, the mineral oil removal analysis sample is obtained and placed in a sealed bag for processing; 7) Sample observation surface processing: The sample surface is processed by a milling machine. Cutting fluid is not allowed during the processing. The feed amount of the milling cutter is 2 to 3 mm. The processing is completed in one time. The processed sample is placed in a sealed bag to be tested for component segregation by a metal in-situ analyzer.

2. A metal in-situ analyzer sample preparation method according to claim 1, characterized in that: The length and width of the sample are 20 to 180 mm, and the thickness is 10 to 15 mm.

3. A metal in-situ analyzer sample preparation method according to claim 1, characterized in that: The water used in step 3) is deionized water.

4. A method for preparing a metal in-situ analyzer sample according to claim 1 or 3, characterized in that: In the step 3), the water surface is 10 to 20 cm higher than the surface of the sample to be observed.

5. The method for preparing a sample for a metal in-situ analyzer according to claim 1, characterized in that: The oil in step 4) is one or more of mineral oil, animal oil or vegetable oil.

6. The method for preparing a sample for a metal in-situ analyzer according to claim 1, characterized in that: The surface roughness of the observed surface of the sample after processing in the step 7) is not greater than 50 μm.

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