A differential temperature release-thermal conductivity detection method for ferrous alloy powder nitrides

Abstract

The application discloses a differential temperature release-thermal conductivity detection method of ferrous alloy powder nitride, and belongs to the technical field of metallurgical analysis. The application reduces the detection cost without using nickel capsules, forms stable flaky samples, is convenient to put into and will not be adsorbed on the container wall due to electrostatic action, finds suitable detection conditions, realizes the differential temperature release-thermal conductivity detection method and a special composite flux, realizes selective release of different forms of nitride through program temperature control, realizes component quantitative calculation in combination with software calculation, realizes the tabletting sample preparation scheme of powder sample without nickel capsule wrapping through pre-prepared sample processing, reduces the detection cost, eliminates the interference of nickel capsules and solves the problem of no nickel capsules.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical analysis technology, specifically relating to a differential temperature release-thermal conductivity detection method for ferroalloy powder nitrides. Background Technology

[0002] Ferroalloys (such as ferromanganese, ferrochrome, ferrosilicon, and ferrovanadium) are indispensable additives in steelmaking, and their nitrogen content directly affects the strength, toughness, and processing performance of steel. With the development of high-nitrogen steel, heat-resistant steel, and powder metallurgy materials, the differences in the contribution of different forms of nitrides to the final product performance have received increasing attention.

[0003] Currently, the inert gas melting-thermal conductivity method is the mainstream method for determining nitrogen content in the industry. my country's current standard GB / T20124-2006, "Determination of Nitrogen Content in Iron and Steel - Inert Gas Melting Thermal Conductivity Method (Conventional Method)," specifies the determination of nitrogen content in iron and steel with a mass fraction of 0.002%~0.6%. The metallurgical industry standard YB / T 4528-2016, "Determination of Nitrogen Content in Ferrochrome Nitride and High-Nitrogen Ferrochrome - Inert Gas Melting Thermal Conductivity Method," is applicable to the determination of total nitrogen content in ferrochrome nitride (2.00%~7.00%) and high-nitrogen ferrochrome (>7.00%~12.00%), while YB / T 4529-2016, "Determination of Nitrogen Content in Ferromanganese Nitride - Inert Gas Melting Thermal Conductivity Method," is applicable to the determination of total nitrogen content in ferromanganese nitride (2.00%~9.00%). However, the above methods can only provide the total nitrogen content and cannot distinguish between different forms of nitrides, making it difficult to meet the needs of refined analysis of nitrogen occurrence state in the research and development of new materials.

[0004] Therefore, based on the differences in pyrolysis release temperatures of different nitrides, an increasing number of researchers are focusing on temperature-programmed methods for determining nitrogen content in metals and powders. However, existing research faces the following technical bottlenecks: Current research on temperature-programmed methods all employs nickel-encapsulated powder samples. For example, the study on determining nitrogen content in alloy powders using pulse-heated inert gas melting-thermal conductivity method utilizes nickel encapsulation. However, the nickel-encapsulated sample itself contains trace amounts of nitrogen, and its own nitrogen release can interfere with the pyrolysis absorption of the sample peaks, especially under precise temperature-programmed conditions, where this interference is more pronounced.

[0005] Meanwhile, the release peaks of different nitrides in the sample often overlap and are indistinguishable. There is still a lack of systematic solutions, including the optimization and control of the heating program parameters and the identification and calculation methods of overlapping peaks. In particular, there is no mature solution for the programmed heating mode.

[0006] Therefore, developing a method that can identify and quantify different forms of nitrides in ferroalloys while reducing detection costs has become an important issue that urgently needs to be addressed. Summary of the Invention

[0007] Therefore, the purpose of this invention is to provide a differential temperature release-thermal conductivity detection method for iron alloy powder nitrides to solve the problems in the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a differential temperature release-thermal conductivity detection method for ferroalloy powder nitrides, comprising the following steps: S1: Grind the sample to a particle size ≤200 mesh, then dry it at 100-110℃ for 1.5-2.5h, and cool it for later use; S2: Mix the sample with the composite flux at a mass ratio of (6-8):(3-5) evenly, and press the mixed powder into a thin sheet; S3: The thin section was tested using a nitrogen and oxygen analyzer after blank correction to obtain the test results; The detection employs a three-stage heating method: starting at room temperature, the first stage involves increasing the initial power and holding for 15-30 seconds; the second stage involves increasing the initial power to the final power of the first peak and holding at a constant temperature for 60-120 seconds; and the third stage involves increasing the power from the beginning of the second peak to the final power of the second peak and holding for 60-100 seconds. The first and second peaks are the peaks of the power-nitrogen release curve for the sample pre-detection. S4: Process the test results; after subtracting the baseline, calculate the separation, attribution determination, and content.

[0009] The drying process in S1 is carried out in an oven to remove adsorbed moisture, and the product is then placed in a desiccator at room temperature for later use.

[0010] In S2, the sample and the composite flux are thoroughly mixed in a grinding container.

[0011] In S3, the initial power is 1500W.

[0012] Based on the above technical solution, the composite flux in S2 is further formed by uniformly mixing nickel powder and tin powder in a mass ratio of (3-5):1.

[0013] Based on the above technical solution, further, the purity of nickel powder is ≥99.9% and the particle size is ≤150 mesh; the purity of tin powder is ≥99.5% and the particle size is ≤200 mesh.

[0014] Based on the above technical solution, further, in S2, pressing is carried out using a tablet pressing mold, with a pressure of 30-45t and a holding time of 20-30s. The sheet is a circular sheet with a diameter of 5-8mm and a thickness of 1-2mm.

[0015] Among them, the circular thin sheet is compact and not easily broken, and does not need to be wrapped in a nickel pouch.

[0016] The preliminary detection process involves identifying the release temperature range of nitrides. Different alloy samples require a preliminary detection to roughly determine the release power of different nitrogen forms. This helps to better separate the peaks of different nitrides, facilitating subsequent detection and calculations. The preliminary detection process is as follows: 1. Take 0.040g of the iron alloy powder sample to be tested, mix it with 0.020g of composite flux, compress it into a tablet, and test it on the instrument. Use a nitrogen and oxygen analyzer (the laboratory uses a Horiba EMGA-830 nitrogen and oxygen analyzer; the specific instrument is not required) for testing. Use high-purity helium (99.999%) as the carrier gas, with a flow rate of 250mL / min, a degassing power of 5000W, and a degassing time of 20 seconds.

[0017] 2. Use a manual stepped heating method: Start at 2000W, increasing the temperature in 500W increments, holding each power point at a constant temperature for 40-60 seconds, until reaching 5500W. Record the nitrogen release at each power point. If individual peaks show splitting or crossing, it indicates that the heating step is too large. Further refine the step, selecting 200W increments, and shorten the holding time as needed based on the tailing of each peak.

[0018] The specific power selection and isothermal time are determined based on the "power-nitrogen release" curve. Identify two peaks on the curve: the first peak (medium temperature zone) with its initial power, peak power, and final power; and the second peak (high temperature zone) with its initial power, peak power, and final power. The difference in power at the valley between the two peaks indicates how close the peaks are.

[0019] Based on the preliminary test results, set the temperature ramp parameters for the formal test: First stage (purge): Reduce to 1500W for 15-30s to remove nitrogen from non-sample components. Second stage (intermediate-temperature release): Increase from 1500W to the power at the end of the first peak, then hold at that power for 60-100s to allow the first nitride to release. Transition step: Hold at the valley region for 20-30s to observe the tailing of the first peak and ensure complete peak separation. Third stage (high-temperature release): Increase from the power at the beginning of the second peak to the power at the end of the second peak for 60-100s to allow the second nitride to release.

[0020] The process includes on-machine testing and data export: The instrument is used for testing under the temperature rise conditions set in step two. The instrument records the nitrogen signal intensity at each time point throughout the process. After the test, the raw data is exported to the computer.

[0021] Based on the above technical solution, further, the blank correction in S3 is to take the same mass of composite flux, press it into a sheet under the same conditions, and measure the blank value under the same conditions as the detection conditions, repeating the measurement 3-5 times; take the average value of the blank value with stable value as the blank correction value.

[0022] The specific number of repeated measurements is determined based on whether the blank value is stable; three sets of blank values ​​with stable values ​​are selected.

[0023] Based on the above technical solution, the nitrogen and oxygen analyzer further has an analysis power of 2000-5500W and adopts a pulse heating mode; a degassing power of 4500-5000W and a degassing time of 15-25s; an analysis time of 50-70s; and a carrier gas of high-purity helium with a purity ≥99.999% and a flow rate of 200-300mL / min.

[0024] Based on the above technical solution, further, in S4, the baseline subtraction specifically removes the background drift of the curve, allowing the peak to start from the zero line.

[0025] Based on the above technical solution, the separation degree is further calculated in S4 using the following formula: Rs = 2 × (t2 - t1) / (w1 + w2); In the formula: t1 and t2 are the peak times of the two peaks, and w1 and w2 are the base widths of the two peaks; When Rs≥1.5, the area of ​​the integral is used to calculate the content; If Rs < 1.0, the overlapping peaks are split into two separate peaks and their areas are calculated separately.

[0026] Among them, Rs≥1.5 means that they can be separated and the area can be directly integrated; Rs<1.0 means that the two peaks are overlapping and cannot be separated, and mathematical methods are needed to separate the overlapping peaks into two separate peaks and then calculate the area separately.

[0027] Based on the above technical solution, the attribution determination in S4 further includes thermodynamic property determination, standard substance spectrum comparison, chemical composition cross-validation, and peak shape auxiliary verification.

[0028] The data processing also includes marking the peaks on the curve and recording the start time, end time, and peak area of ​​each peak.

[0029] The attribution determination involves comparing the power-nitrogen release curve obtained from the pre-detection study to determine the wattage corresponding to each peak. This helps identify whether the peak belongs to a mid-temperature or high-temperature nitride. Additionally, the symmetry of the peak shape and the compatibility of the sample composition with the desired nitride are considered. A comprehensive assessment is then made. Specific determinations are as follows: Thermodynamic property determination: Based on the chemical composition and thermodynamic data of the iron alloy to be tested, the possible types of nitrides and their theoretical decomposition temperature ranges are predicted.

[0030] For manganese iron nitride, Mn2N usually decomposes at a relatively low temperature (about 700-900℃, corresponding to a power of about 2500-3000W) to form the first release peak; MnN is thermodynamically metastable and decomposes at a relatively high temperature (above about 1000℃, corresponding to a power of about 4000-4500W) to form the second release peak.

[0031] For ferrochrome nitride, the main nitrides are CrN and Cr2N, with a decomposition temperature range of 700-1100℃ (corresponding to a power of about 2500-4000W). Since the two temperatures are close, they usually merge to form a single release peak.

[0032] For vanadium-nitrogen alloys, the main phase is VN, which has an extremely high decomposition temperature (>1500℃, corresponding to a power of >4500W). Therefore, it is released in a concentrated manner under the high-temperature pulse heating conditions in the third stage, forming a distinct single peak.

[0033] Standard substance spectrum comparison: By detecting standard substances of known phases (such as pure phase VN, CrN, etc.), a standard release spectrum is established. The peak positions and peak shapes of the sample spectrum are compared with those of the standard spectrum to find the one with the highest degree of matching.

[0034] Cross-validation of chemical composition: When theoretical predictions and comparisons with standards cannot definitively determine the nature of the sample, a comprehensive judgment should be made by considering the chemical composition of the sample. For example, if two peaks with similar properties are detected in a vanadium-nitrogen alloy sample, one may be assigned to VN, while the other, based on its composition, can be inferred to be V2N or a carbonitride.

[0035] Peak shape verification: The symmetry factor of a peak (between 0.8 and 1.2) usually represents a pure nitride phase. If the peak shape is severely tailed or elongated, it suggests the possible overlap of multiple phases or an abnormal release process, requiring comprehensive identification using the methods described above.

[0036] By employing the aforementioned multi-principle cross-judgment, we ensure that the attribution of each release peak has sufficient scientific basis. When the conclusions of multiple principles conflict, the comparison with standard substances shall be the final basis.

[0037] Based on the above technical solution, further, the calculated content in S4 is obtained by substituting the peak area into the calibration curve formula to calculate the respective contents of nitrides in the medium temperature zone and nitrides in the high temperature zone; the respective contents of nitrides in the medium temperature zone and nitrides in the high temperature zone are compared with the total nitrogen of the instrument, and the deviation is ≤5%.

[0038] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention eliminates the need for a nickel bladder, reducing testing costs. It allows the sample to form a stable, thin sheet, facilitating its placement and preventing it from adhering to the container wall due to electrostatic effects. By finding suitable testing conditions, a differential temperature release-thermal conductivity detection method and a dedicated composite flux are implemented. Selective release of different nitride morphologies is achieved through programmed temperature control, and quantitative component calculations are performed using software. Pre-preparation of powder samples eliminates nickel bladder-free tableting, reducing testing costs and removing interference from the nickel bladder, thus solving the problem of not having a nickel bladder.

[0039] 2. This invention addresses the limitations of existing inert gas melting-thermal conductivity methods, which can only determine total nitrogen content. It achieves selective release of nitrides with different thermal stabilizations through programmed temperature control and realizes quantitative component analysis by combining overlapping peak decoupling algorithm, thus filling the gap in industry standards for nitride speciation analysis.

[0040] 3. The "premixed tablet" pre-preparation sample treatment method of the present invention is to directly mix nickel powder and tin powder as composite flux with the sample, which not only plays a role in binding and shaping, but also plays a role in fluxing during melting. Finally, the flux particles and iron alloy particles are tightly bonded by high pressure, which solves the technical problem of uneven melting of powder sample and the problem that powder sample cannot be put into the hopper without nickel bladder.

[0041] 4. The three-stage refined temperature control program of this invention consists of a first stage as a low-temperature purification zone, a second stage as a medium-temperature constant power zone, and a third stage as a high-temperature pulse zone. Each stage has specific temperature control requirements and switching criteria, forming a complete differential temperature release process system. In particular, the automatic identification and correction of peak tail drag is incorporated into the program, significantly reducing the impact of peak tail drag on quantitative results.

[0042] 5. The method of the present invention is not only applicable to ferromanganese alloys, but can also be extended to the determination of nitrogen content in various ferroalloy powders such as ferrochrome, ferrosilicon, and ferrovanadium, and has good adaptability. Attached Figure Description

[0043] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0044] Figure 1 This is a schematic diagram of the detection process of the present invention. Detailed Implementation

[0045] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0046] Example 1 Detection of nitrides in manganese nitride iron standard samples. The detection procedure is as follows: Figure 1 As shown.

[0047] A standard sample of manganese nitride iron (total nitrogen standard value 4.50%) was taken, and the sample was prepared according to S2 and pre-tested according to S3. The results are as follows: First peak: starting 2200W, peak 2800W, ending 3400W; Second peak: starting 4000W, peak 4400W, ending 4800W; The valley was between 3600-3800W, with a valley difference of 200W.

[0048] Set the program heating parameters as follows: First stage: 1500W, hold for 30 seconds; Second stage: increase from 1500W to 3400W and hold for 120 seconds; Transition stage: 3600W, hold for 45 seconds; Third stage: increase from 4000W to 4800W and hold for 90 seconds.

[0049] After testing, the data was processed. The separation degree between the two peaks was Rs=0.95. After mathematical calculation, according to step seven, the first peak (medium temperature region) was identified as Mn2N or Mn4N, with a content of 3.00%; the second peak (high temperature region) was identified as MnN, with a content of 1.49%. The total nitrogen content was 4.49%, and the relative standard deviation (6 parallel tests) was 0.56%.

[0050] Example 2 Detection of nitrides in standard ferrochrome nitride samples.

[0051] A standard sample of ferrochromium nitride (total nitrogen 6.00%) was taken, and the procedure was the same as in Example 1. Pre-detection showed the first peak started at 2400W, peaked at 3000W, and ended at 3600W; the second peak started at 4200W, peaked at 4600W, and ended at 5000W. The programmed temperature rise parameters were set as follows: first stage, 1500W held for 30s; second stage, increased to 3600W and held for 120s; transition step, 3800W held for 45s; third stage, increased from 4200W to 5000W and heated for 90s. The total nitrogen content was found to be 5.98%, 4.20% in the mid-temperature range, and 1.78% in the high-temperature range, with a relative standard deviation of 0.67%.

[0052] Example 3 Tests on samples with different nitrogen contents.

[0053] Standard samples with total nitrogen contents of 2.50%, 4.50%, 6.50%, and 8.50% were tested according to the method in Example 1. The test results are shown in Table 1 below. The results show that this method is applicable in the nitrogen content range of 2.50-8.50%.

[0054] Table 1: Detection of samples with different nitrogen contents.

[0055]

[0056] Example 4 Detection of nitrides in vanadium-nitrogen alloy samples.

[0057] A standard vanadium-nitrogen alloy sample (total nitrogen 14.50%) was taken. Preliminary measurements showed the first peak starting at 3000 W, peaking at 3200 W, and ending at 3600 W; the second peak starting at 5000 W, peaking at 5200 W, and ending at 5500 W. Parameters were adjusted: the second stage involved heating to 3600 W and holding at that temperature for 200 seconds; the third stage involved pulse heating from 5000 W to 5500 W for 90 seconds. The total nitrogen content was measured at 14.48%, with 12.08% in the mid-temperature range and 2.40% in the high-temperature range, with a relative standard deviation of 0.36%.

[0058] Example 5 Comparison of different composite flux ratios.

[0059] The same batch of manganese nitride iron samples were tested using composite fluxes with different ratios. The test results are shown in Table 2 below.

[0060] Table 2: Comparison of different composite flux ratios.

[0061]

[0062] The results showed that a nickel-tin ratio of 4:1 was the optimal ratio.

[0063] Example 6 Examples of pre-detection are shown in Table 3.

[0064] Table 3: Pre-detection examples.

[0065]

[0066] The table shows that the first peak starts at 2200 W, reaches a peak of 2800 W, and ends at 3400 W; the second peak starts at 4000 W, reaches a peak of 4400 W, and ends at 4800 W; the range from 3400 W to 4000 W is in the low nitrogen release range, with relatively good separation and relatively low peak overlap.

[0067] Comparative Example 1 Conventional constant power method (nickel-encapsulated).

[0068] Using the same batch of manganese ferronitride, without programmed temperature rise, constant power heating (5000W for 60s) was used, and the sample was wrapped in a nickel bladder. The total nitrogen was measured to be 4.48%, but the content of nitrides in the medium-temperature and high-temperature regions could not be distinguished.

[0069] Comparative Example 2 The temperature was programmed, but the sample was encased in a nickel bladder.

[0070] The sample was encased in a nickel bladder and pressed into a pellet without flux using a programmed temperature rise method. The total nitrogen content was measured at 4.47%, which is essentially the same as the result obtained by the invented method, proving the feasibility of the invented method.

[0071] Comparative Example 3 Direct powder addition, without tableting or adding flux.

[0072] The powder was poured directly into the crucible without pressing or adding flux. The measurement was performed under programmed temperature conditions. The sample was difficult to insert due to static electricity, and the sample contaminated the instrument. The total nitrogen was only measured at 2.85-3.42%, far below the standard value of 4.50%, with an RSD > 12%.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A differential temperature release-thermal conductivity detection method for ferroalloy powder nitrides, characterized in that, Includes the following steps: S1: Grind the sample to a particle size ≤200 mesh, then dry it at 100-110℃ for 1.5-2.5h, and cool it for later use; S2: Mix the sample with the composite flux at a mass ratio of (6-8):(3-5) evenly, and press the mixed powder into a thin sheet; S3: The thin section was tested using a nitrogen and oxygen analyzer after blank correction to obtain the test results; The test uses a three-stage heating method; with room temperature as the initial temperature, the first stage is the initial power, held for 15-30 seconds. In the second stage, the initial power is increased to the power at the end of the first peak, and the temperature is maintained for 60-120 seconds. In the third stage, the power is increased from the starting power of the second peak to the power at the end of the second peak, and the temperature is maintained for 60-100 seconds. The first and second peaks are the peaks of the power-nitrogen release curve of the sample pre-detection. S4: Process the test results; after subtracting the baseline, calculate the separation, attribution determination, and content.

2. The differential temperature release-thermal conductivity detection method for ferroalloy powder nitrides according to claim 1, characterized in that, The composite flux in S2 is made by uniformly mixing nickel powder and tin powder in a mass ratio of (3-5):

1.

3. The differential temperature release-thermal conductivity detection method for ferroalloy powder nitrides according to claim 2, characterized in that, Nickel powder has a purity of ≥99.9% and a particle size of ≤150 mesh; tin powder has a purity of ≥99.5% and a particle size of ≤200 mesh.

4. The differential temperature release-thermal conductivity detection method for ferroalloy powder nitrides according to claim 1, characterized in that, In S2, pressing is performed using a tableting mold with a pressure of 30-45t and a holding time of 20-30s. The sheet is a circular sheet with a diameter of 5-8mm and a thickness of 1-2mm.

5. The differential temperature release-thermal conductivity detection method for ferroalloy powder nitrides according to claim 1, characterized in that, The blank correction in S3 involves taking the same mass of composite flux, pressing it into tablets under the same conditions, and measuring the blank value under the same conditions as the test conditions. This measurement is repeated 3-5 times. The average value of the stable blank values ​​is taken as the blank correction value.

6. The differential temperature release-thermal conductivity detection method for ferroalloy powder nitrides according to claim 1, characterized in that, The nitrogen and oxygen analyzer has an analysis power of 2000-5500W and uses pulse heating mode; the degassing power is 4500-5000W and the degassing time is 15-25s; the analysis time is 50-70s; the carrier gas is high-purity helium with a purity ≥99.999% and a flow rate of 200-300mL / min.

7. The differential temperature release-thermal conductivity detection method for ferroalloy powder nitrides according to claim 1, characterized in that, In S4, the baseline subtraction function specifically removes the background drift of the curve, allowing the peak to start from the zero line.

8. The differential temperature release-thermal conductivity detection method for ferroalloy powder nitrides according to claim 1, characterized in that, The separation degree is calculated in S4 using the following formula: Rs = 2 × (t2 - t1) / (w1 + w2); In the formula: t1 and t2 are the peak times of the two peaks, and w1 and w2 are the base widths of the two peaks; When Rs≥1.5, the area of ​​the integral is used to calculate the content; If Rs < 1.0, the overlapping peaks are split into two separate peaks and their areas are calculated separately.

9. The differential temperature release-thermal conductivity detection method for ferroalloy powder nitrides according to claim 1, characterized in that, The attribution determination in S4 includes thermodynamic property determination, standard substance spectrum comparison, chemical composition cross-validation, and peak shape auxiliary verification.

10. The differential temperature release-thermal conductivity detection method for ferroalloy powder nitrides according to claim 1, characterized in that, The calculated content in S4 is obtained by substituting the peak area into the calibration curve formula to calculate the content of nitrides in the medium-temperature zone and the high-temperature zone. The content of nitrides in the medium-temperature zone and the high-temperature zone is compared with the total nitrogen of the instrument, and the deviation is ≤5%.

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