A method for analyzing oxygen content of 300 series stainless steel samples

Abstract

The application discloses a method for analyzing oxygen content of 300 series stainless steel sample, and belongs to the technical field of metallurgical analysis, and solves the technical problem of insufficient precision and accuracy of spectral analysis of oxygen content in steel, and comprises the following steps: S1, using a milling machine to prepare a standard sample for spectral analysis of oxygen content of stainless steel; S2, determining analysis conditions; S3, performing intensity absorption on the standard sample prepared in step S1 under the specific intensity analysis conditions set in step S2, and performing interference correction by using chromium, nickel, molybdenum, phosphorus and sulfur elements; then, taking Fe14 and Fe4N as internal standards to make a regression curve equation, and taking the average of the oxygen content concentration of the standard sample obtained by the regression curve as the final oxygen content of the stainless steel sample. The application has wide applicability, simple and convenient operation, no environmental pollution, can realize real-time analysis of online samples of stainless steel smelting, and is consistent with the analysis results of mechanical processing method and chemical corrosion method, and greatly shortens the time required for the complete sample preparation and analysis process.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical analysis technology, specifically relating to a method for analyzing the oxygen content of 300 series stainless steel samples. Background Technology

[0002] Oxygen is a harmful gaseous element in steel. It readily forms oxide inclusions, which, distributed along grain boundaries, isolate the matrix, leading to a decrease in the steel's tensile and impact mechanical properties, and even hot brittleness at high temperatures. Excessive oxygen content in steel increases oxide and macroscopic inclusions, severely affecting the steel's purity. Generally, lower oxygen content is better in steelmaking. Gas removal is an essential step in steel refining. Therefore, accurately controlling the content of harmful gases is crucial for ensuring steel quality, especially in the research and development of new steel grades. Accurately measuring the oxygen content in steel is of great significance for improving process control, enhancing steel properties, and improving steel quality.

[0003] Currently, the determination of oxygen content in steel typically employs mechanical processing and chemical etching methods. The mechanical processing method involves machining the sample into a rod-shaped specimen with a diameter of 5 mm and a length of 40 mm. Before analysis, the surface is sanded with sandpaper; for irregular specimens, a file or grinding wheel is used. The sanded sample is then cut into granules, cleaned with organic reagents, and measured on an oxygen and nitrogen analyzer. For columnar, barrel-shaped specimens, or granular samples where surface sanding is not possible, the chemical etching method is used. First, the sample is cut into thin slices with a thickness of 4 mm–5 mm, then punched into granular samples of approximately 1 gram. These granules are boiled in hydrochloric acid, cleaned with organic solvents, and then measured on an oxygen and nitrogen analyzer. Both mechanical processing and chemical etching methods are technically demanding, cumbersome, time-consuming, and costly, while also causing significant environmental pollution. Furthermore, due to the lengthy analysis process, these methods are often performed after steelmaking, resulting in delayed guidance for steelmaking process control and failing to effectively guide smelting process control, thus limiting the full potential of oxygen content analysis in steel.

[0004] Spark discharge atomic emission spectrometry (SDA) has been widely used for the analysis of various steel smelting samples before the furnace. Its popularity stems from its simple sample preparation, fast analysis speed, and high accuracy. With advancements in science and materials technology, SDA can now be used to analyze oxygen content in steel. This method significantly simplifies sample preparation and analysis procedures, reduces pollutant emissions, and enables real-time monitoring of oxygen content in samples during the smelting process, greatly improving the efficiency of oxygen content analysis. Current literature reports that spectrometry can analyze oxygen levels above 0.01% in steel. If spectrometry can be used to analyze low oxygen content in stainless steel, it will provide crucial reference for process control in stainless steel or high-quality steel smelting, guiding real-time adjustment of process parameters and objectively evaluating steel quality. Summary of the Invention

[0005] The main objective of this invention is to overcome the shortcomings of the prior art, solve the technical problem that the precision and accuracy of spectroscopic analysis of oxygen content in steel cannot meet the requirements, and provide a method for analyzing the oxygen content of 300 series stainless steel samples.

[0006] The design concept of this invention is as follows: After polishing the surface of a stainless steel sample, under specific spectral analysis conditions, based on a series of standard samples, a spectroscopic analysis curve is established by analyzing the relationship between the intensity and concentration of characteristic spectral lines emitted by oxygen in the standard samples. The accuracy of the analysis curve is ensured by correcting for high and low scale drift in the sample settings. The intensity of oxygen in the sample is measured using a spectrometer, and the oxygen content in the sample is calculated based on the corresponding relationship of the analysis curves. This invention establishes a spectroscopic analysis method for oxygen content from the aspects of sample preparation, determination of analytical conditions, and verification of method precision and accuracy, thus realizing the spectroscopic analysis of oxygen content in stainless steel samples.

[0007] To solve the above problems, the technical solution of the present invention is as follows:

[0008] A method for analyzing the oxygen content of 300 series stainless steel samples includes the following steps:

[0009] S1. Prepare standard samples for oxygen content analysis of stainless steel by spectroscopic method using a milling machine;

[0010] Samples for spectroscopic analysis are typically prepared using equipment such as grinding wheels, abrasive belts, or milling machines. This experiment investigated three commonly used sample preparation devices. AISI 304 stainless steel samples with an oxygen content of 0.0023% were prepared using grinding wheels, abrasive belts, and milling machines. Six points on the prepared sample surface were analyzed, and the results are shown in Table 1.

[0011] Table 1. Effects of three commonly used sample preparation devices on oxygen content analysis in steel ( / %)

[0012] Analysis points / sample preparation equipment grinding wheel Sand belt Milling machine 1 0.0125 0.0034 0.0021 2 0.0147 0.0028 0.0023 3 0.0238 0.0036 0.0019 4 0.0296 0.0047 0.0022 5 0.0132 0.0032 0.0023 6 0.0251 0.0042 0.0022 average value 0.0198 0.0037 0.0022 Standard deviation 0.00725 0.00069 0.00015 Relative standard deviation 36.5976 18.9616 6.9487

[0013] The results in Table 1 show that: when samples were prepared using a grinding wheel, the analytical results were high but inconsistent and could not represent the oxygen content in the samples; when samples were prepared using a sanding belt, the analytical results were generally high and the analytical precision was poor; when samples were prepared using a milling machine, the analytical precision and accuracy were the best. Therefore, milling machine sample preparation should be used for oxygen content analysis, and grinding wheel sample preparation cannot be used for oxygen content analysis.

[0014] Standard samples used for the spectroscopic analysis of oxygen content in stainless steel must meet the basic requirements for spectroscopic analysis samples, such as sample size requirements, clean and uncontaminated sample surface, and sample temperature.

[0015] S2. Determination of analysis conditions:

[0016] 1) Use specific strength analysis;

[0017] 2) Investigation of Fe internal standard elements in different spectral lines: The average value was taken with Fe14 and Fe4N as internal standards;

[0018] 3) Use time-resolved spectroscopy;

[0019] 4) Order of element integration: Perform oxygen element integration analysis first;

[0020] 5) The spectral argon blowing time is 6 seconds;

[0021] 6) The spectral pre-integration time is 6 seconds;

[0022] 7) The spectral integration time is 4 seconds;

[0023] 8) The static flow rate of the spectrum is 1.5 L / min;

[0024] 9) Use a two-stage argon purification system;

[0025] 10) Excitation points must not overlap;

[0026] 11) The electrode should be cleaned with a steel brush 2 to 3 times after each excitation point;

[0027] 12) The lens should be used for 1 to 5 weeks.

[0028] 13) Replace the sealing ring of the excitation platform monthly;

[0029] 14) The sample placement time should not exceed 30 minutes;

[0030] 15) Chamfering of sample edges;

[0031] S3. The stainless steel oxygen content spectroscopic analysis standard sample prepared in step S1 is subjected to intensity absorption under the specific intensity analysis conditions set in step S2, and interference correction is performed using chromium, nickel, molybdenum, phosphorus, and sulfur elements; then, regression curve equations are constructed using Fe14 and Fe4N as internal standards, respectively. The average oxygen content concentration of the standard sample obtained from the regression curve is taken as the final oxygen content of the stainless steel sample, and the calculation formula is as follows:

[0032] C = [(A 21 ×I1 2 +A 11 ×I1+A 01 )+(A 22 ×I2 2 +A 12 ×I2+A 02 )] / 2;

[0033] In the formula:

[0034] C: Concentration of the sample to be tested;

[0035] I1: The strength of the sample to be tested, with Fe4N as the internal standard;

[0036] A 21 A 11 A 01 : Using Fe4N as an internal standard, the coefficients of the regression curve equation;

[0037] I2: The strength of the sample to be tested, with Fe14 as an internal standard;

[0038] A 22 A 12 A 02 : Using Fe14 as an internal standard, the coefficients of the regression curve equation.

[0039] This invention determines the optimal conditions for spectral analysis of oxygen content samples according to the commonly used sample methods in spectral analysis, and the results are shown in Table 2.

[0040] Table 2. Conditions to be met for oxygen content sample analysis.

[0041]

[0042]

[0043] This invention performs specific intensity analysis under the analytical conditions shown in Table 2, and plots analytical curves of standard samples using Fe4N (273nm) and Fe14 (157nm) as internal standards, respectively. The method of calculating sample content using the average of the specific intensity regression equation is called "spectral dual internal standard analysis method".

[0044] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0045] 1. The analytical results of this invention are consistent with those of mechanical processing and chemical etching methods, and significantly shorten the time required for the complete sample preparation and analysis process;

[0046] 2. This invention only requires surface polishing of the sample before analysis using a spectrometer. It is widely applicable, simple and convenient to operate, and causes no environmental pollution. Furthermore, it enables real-time analysis of online stainless steel smelting samples. Therefore, this invention guides and promotes the improvement of stainless steel smelting technology and is particularly suitable for the analysis of online samples from furnace-front stainless steel smelting. Attached Figure Description

[0047] Figure 1 This is a flowchart illustrating the operation process of the present invention. Detailed Implementation

[0048] The following is combined with Figure 1 The present invention will be further described in detail with reference to the embodiments.

[0049] A method for analyzing the oxygen content of 300 series stainless steel samples includes the following steps:

[0050] 1. Standard Sample:

[0051] Thirty-eight international standard samples of the 300 series with a content range of 0.0003% to 0.011% were collected. Among them, samples 5#, 9#, 12#, 15#, 22#, 27#, 32# and 36# were used to verify the accuracy of the method. The 38 standard samples used in the test are listed in Table 3.

[0052] Table 3 List of Standard Samples for Oxygen Content

[0053]

[0054]

[0055] 2. Preparation of standard samples:

[0056] The surface of the standard sample was prepared using a milling machine, and the prepared sample was immediately subjected to strength analysis.

[0057] 3. Spectral analysis conditions:

[0058] Set the analytical conditions of the spectrometer according to the analytical requirements and conditions shown in Table 2, and then perform intensity analysis of the standard sample.

[0059] 4. Analysis curve establishment:

[0060] Intensities analyzed using Fe4N (273nm) and Fe14 (157nm) as internal standards were subjected to curve regression. Interference corrections were performed using chromium, nickel, molybdenum, phosphorus, and sulfur. After curve regression, the O element content was added, and the calculation formula was reported.

[0061] C = [(A 21 *I1 2 +A 11 *I1+A 01 )+(A 22 *I2 2 +A 12 *I2+A 02 )] / 2

[0062] In the formula:

[0063] C: Concentration of the sample to be tested;

[0064] I1: The strength of the sample to be tested, with Fe4N as the internal standard;

[0065] I2: The strength of the sample to be tested, with Fe14 as the internal standard.

[0066] 5. Validation of the precision and accuracy of the method

[0067] (1) Precision verification of the method

[0068] A precision verification experiment was conducted on the method for analyzing oxygen content by spectrometry. Three samples were selected: the internal control standard AISI304, the production sample, and the international standard. Six points were excited on the sample surface, and the mean, standard deviation, and relative standard deviation were calculated. The results are shown in Table 3.

[0069] Table 4 Precision verification of the spectral analysis method for oxygen content samples

[0070]

[0071] The results show that the method has good precision and can meet the analytical requirements.

[0072] (2) Verification of the accuracy of the method

[0073] Accuracy verification experiments were conducted on the method of spectroscopic analysis of oxygen content. Seven international standards and 15 production samples were selected. The average value was taken at 2-3 points on the sample surface. The analytical values ​​of the international standards were compared with the standard values, and the average values ​​of the production samples were compared with the gas analysis results of the oxygen and nitrogen analyzer. The results are shown in Table 4.

[0074] Table 5. Accuracy verification of the spectral analysis method for oxygen content samples.

[0075]

[0076] The results showed that the deviation between the spectral analysis value and the gas analysis value of the 300 series stainless steel sample was within 0.0007%, and the accuracy of the method met the analytical requirements.

[0077] (3) Detection limit analysis of the method

[0078] The limit of detection (LOD) for the spectroscopic analysis of oxygen content was determined. A standard sample BS 184A with an oxygen content of 0.0003% was selected. Eleven points on the sample surface were analyzed, and the average value of the eleven points was calculated to be 0.0009%, with a standard deviation of 0.00045%. The LOD of the sample was calculated as 0.0015% based on three times the standard deviation. Therefore, the LOD of the sample was determined to be 0.0015%.

[0079] 6. Preparation and analysis of routine samples

[0080] Routine production samples were prepared using the same procedure as standard samples. The prepared samples were then analyzed on a spectrometer. Before analysis, waste samples were used for at least five excitation and degassing points on the spectrometer. A control sample with a content of 0.0023% was then selected for control calibration. After calibration, a retrospective analysis was performed. The deviation between the retrospective analysis result and the control sample standard value was 0.0002%, meeting the calibration analysis requirements. The sample was then directly analyzed. The average value of two excitation points on the sample surface was taken, showing a result of 0.0035%. The analysis result of 0.0035% was directly reported after analysis, thus completing the oxygen content analysis of the stainless steel sample.

[0081] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for analyzing the oxygen content of 300 series stainless steel samples, characterized in that... Includes the following steps: S1. Prepare standard samples for oxygen content analysis of stainless steel by spectroscopic method using a milling machine; S2. Determination of analysis conditions: 1) Use specific strength analysis; 2) Investigation of Fe internal standard elements in different spectral lines: The average value was taken using Fe14 and Fe4N as internal standards; 3) Use time-resolved spectroscopy; 4) Order of element integration: Perform oxygen element integration analysis first; 5) The spectral argon blowing time is 6 seconds; 6) The spectral pre-integration time is 6 seconds; 7) The spectral integration time is 4 seconds; 8) The static flow rate of the spectrum is 1.5 L / min; 9) Use a two-stage argon purification system; 10) Excitation points must not overlap; 11) The electrode should be cleaned with a steel brush 2 to 3 times after each excitation point; 12) The lens should be used every 1 to 5 weeks. 13) Replace the sealing ring of the excitation platform monthly; 14) The sample placement time should not exceed 30 minutes; 15) Chamfering of sample edges; S3. The stainless steel oxygen content spectroscopic analysis standard sample prepared in step S1 is subjected to intensity absorption under the specific intensity analysis conditions set in step S2, and interference correction is performed using chromium, nickel, molybdenum, phosphorus, and sulfur elements; then, regression curve equations are constructed using Fe14 and Fe4N as internal standards, respectively. The average oxygen content concentration of the standard sample obtained from the regression curve is taken as the final oxygen content of the stainless steel sample, and the calculation formula is as follows: C = [(A 21 × I1 2 + A 11 × I1 + A 01 )+(A 22 × I2 2 + A 12 ×I2 + A 02 )] / 2; In the formula: C: Concentration of the sample to be tested; I1: The strength of the sample to be tested, with Fe4N as the internal standard; A 21 A 11 A 01 : Using Fe4N as an internal standard, the coefficients of the regression curve equation; I2: The strength of the sample to be tested, with Fe14 as an internal standard; A 22 A 12 A 02 : Using Fe14 as an internal standard, the coefficients of the regression curve equation.

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