Method for determining oxygen and nitrogen contents in lanthanum-cerium rare earth steel

Abstract

The present invention provides a method for determining the oxygen and nitrogen contents in lanthanum-cerium rare earth steel. The oxygen and nitrogen contents in lanthanum-cerium rare earth steel are determined by pulse melting-infrared absorption and thermal conductivity methods, and the process is as follows: treating the surface of the sample → debugging the working parameters of the pulse infrared thermal conductivity oxygen-nitrogen-hydrogen analyzer → establishing the standard working curve → determining the sample → retesting and verifying the standard sample; different analysis methods are adopted according to the lanthanum and cerium contents in the rare earth steel. For low rare earth contents, the analysis method for ordinary steel samples is used; for higher rare earth contents, the oxygen and nitrogen contents are simultaneously determined by reducing the analysis power; for samples with high rare earth contents, for the measurement of oxygen content, the bath material method is used for testing; for the measurement of nitrogen content, it can be directly tested. The present invention establishes a method for testing the oxygen and nitrogen contents in lanthanum-cerium rare earth steel, which can solve the problem that the recovery of gas elements is incomplete due to the volatilization of metallic lanthanum and cerium in lanthanum-cerium rare earth steel, thus making it impossible to accurately detect the gas impurity elements.

Description

Technical Field

[0001] The present invention belongs to the field of gas analysis of metal materials, and particularly provides a method for determining the oxygen and nitrogen contents in lanthanum-cerium rare earth steel. Background Art

[0002] Rare earth elements have a very important influence on the microstructure and mechanical properties of steel and alloys. Rare earth has the functions of deep deoxidation and deep desulfurization, can modify and refine inclusions, and can inhibit grain growth, thereby improving the toughness, plasticity, fatigue performance, wear resistance, corrosion resistance and heat resistance of metal materials. The extraction and preparation costs of lanthanum and cerium light rare earths are low. Using lanthanum and cerium light rare earths to improve the quality of steel is an effective way to lead the transformation and upgrading of the steel industry. Due to the poor purity of rare earth metals, which is prominently manifested in the high contents of impurity elements such as oxygen, sulfur and phosphorus, the oxygen content in rare earth metals is often as high as more than 0.1%. Oxygen easily combines with rare earths to form rare earth oxides. When this part of rare earth oxides is added to steel, it will exist in the form of inclusions, thereby reducing the performance of steel, especially wear resistance, heat resistance, corrosion resistance and low-temperature toughness. Therefore, in the process of rare earth steel research and development and production, the control and determination of the oxygen content in rare earth steel are essential important links. Especially for the high demand for the purity of rare earth steel, it inevitably puts forward higher requirements for the accurate determination of the oxygen and nitrogen contents in rare earth steel. Therefore, accurately analyzing the oxygen and nitrogen contents in rare earth steel is of great significance for the production of rare earth steel and related scientific research work.

[0003] The gas analysis principle of metal materials is as follows: The instrument uses high-purity helium as the carrier gas and the pulse electrode furnace heating method to melt the sample at high temperature in a graphite crucible. The oxygen in the sample reacts with the carbon in the high-purity graphite crucible to generate CO and a small amount of CO 2 , and nitrogen is released in the form of N 2 . The mixed gas is carried by the carrier gas and enters the CO infrared detector and the high-concentration CO 2 infrared detector for detection respectively. Then the gas passes through the hot copper oxide catalytic furnace to oxidize CO into CO 2 . The generated CO 2 enters the low-concentration CO 2 infrared cell for detection, and N 2 enters the thermal conductivity detector for detection, so as to obtain the oxygen and nitrogen contents in the sample.

[0004] The rare earth metals commonly added to rare earth steel are mostly lanthanum and cerium metals, and the melting points of lanthanum and cerium metals are low, and they are extremely volatile at high temperatures. When analyzing rare earth steel samples, the samples are melted at high temperatures, and the molten rare earth volatilizes to the furnace wall of the reaction chamber and adheres to it. The rare earth volatilization residue will adsorb the gas to be detected, CO, so that part of the CO cannot reach the detector smoothly, and the detected amount of CO decreases, resulting in the oxygen content finally detected by the equipment being lower than the actual value. Therefore, how to effectively inhibit the volatilization of lanthanum and cerium metals and make the gas completely released and reach the detection system for detection is the key problem for accurately determining the gas content in rare earth steel. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for determining the oxygen and nitrogen content in lanthanum-cerium rare earth steel. The pulse melting-infrared absorption thermal conductivity method is used to determine the oxygen and nitrogen content in lanthanum-cerium rare earth steel, which can solve the problems of instrument pollution, low detection results, and decreased test accuracy caused by rare earth volatilization during the analysis of lanthanum-cerium rare earth steel.

[0006] The technical solution of the present invention is as follows:

[0007] It includes the following steps:

[0008] (1) Pretreat the sample to be analyzed, remove the surface oxide layer of the lanthanum-cerium rare earth steel sample, and clean it with acetone or absolute ethanol and then air-dry it.

[0009] (2) Debug the working parameters of the pulse infrared thermal conductivity oxygen, nitrogen and hydrogen analyzer and set the analysis method.

[0010] (3) According to the analysis method set in step (2), perform a blank analysis.

[0011] (4) Establishment of the standard working curve: Use the single-point method to calibrate the instrument and establish the standard working curve.

[0012] (5) Determine the sample: First, classify the lanthanum and cerium rare earth contents in the sample, and use different analysis methods for rare earth steel with different rare earth content ranges. For rare earth steel samples with low rare earth content, use the conventional steel analysis method for testing; for rare earth steel samples with higher rare earth content, use a low analysis power for testing; for rare earth steel samples with high rare earth content, for the test of the oxygen content in the sample, use the bath material method for testing, and for the test of the nitrogen content in the sample, it can be directly tested.

[0013] Specifically, make the lanthanum-cerium rare earth steel sample into small pieces with a weight of 0.30 g to 0.60 g, clean it with analytical pure acetone or absolute ethanol, and blow it dry with cold air or air-dry it naturally.

[0014] Further, for the rare earth steel samples with low rare earth content in step (5), where the total rare earth content ranges from 10 ppm to 50 ppm, the oxygen and nitrogen contents can be simultaneously measured using conventional steel analysis methods.

[0015] Further, for the rare earth steel samples with relatively high rare earth content in step (5), where the total rare earth content ranges from 50 ppm to 500 ppm, the oxygen and nitrogen contents are simultaneously measured using a relatively low analysis power of 4000 W - 4500 W.

[0016] Further, for the rare earth steel samples with high rare earth content in step (5), where the total rare earth content ranges from 500 ppm to 1000 ppm, the test is carried out using a low analysis power of 4000 W - 4500 W. The test method for oxygen content is as follows: Open the sample loading port of the pulse furnace, place a certain weight of the sample into the loader of the pulse furnace, place the bath metal into the graphite crucible, turn on the pulse furnace, place the crucible on the lower electrode of the pulse furnace, and then the lower electrode rises; After the graphite crucible and the bath metal are degassed, the sample drops into the crucible and is heated to melt; The oxygen in the sample is released in the form of carbon monoxide, carried by the carrier gas into the pulse infrared thermal conductivity oxygen, nitrogen and hydrogen analyzer, and the oxygen content value is obtained through software data processing.

[0017] Specifically, the bath material is a tin cake, and the mass ratio of the tin cake to the sample is in the range of 1:1 - 2:1.

[0018] Further, for the rare earth steel samples with high rare earth content in step (5), where the total rare earth content ranges from 500 ppm to 1000 ppm, the test is carried out using a low analysis power of 4000 W - 4500 W. The test method for nitrogen content is as follows: Open the sample loading port of the pulse furnace, place a certain weight of the sample into the loader of the pulse furnace, directly inject the sample, turn on the pulse furnace, place the crucible on the lower electrode of the pulse furnace, and then the lower electrode rises; After the graphite crucible is degassed, the sample drops into the crucible and is heated to melt; The nitrogen in the sample is released in the form of nitrogen gas, carried by the carrier gas into the pulse infrared thermal conductivity oxygen, nitrogen and hydrogen analyzer, and the nitrogen content value is obtained through software data processing.

[0019] Further, the instrument is calibrated using the single-point method to establish a standard working curve, and the standard sample content range should be greater than or close to the sample content; The working curves for measuring oxygen and nitrogen contents are both drawn using steel standard samples.

[0020] Further, since lanthanum and cerium metals are volatile at high temperatures, and the volatilization of the used tin bath material causes metal condensation in the furnace chamber, after analyzing every 5 samples, the furnace chamber should be cleaned, the upper and lower electrodes should be cleaned with an electrode brush, and the furnace chamber should be wiped with absorbent cotton; After analyzing every 20 samples, the filter cotton in the disc filter should be replaced, and after cleaning, the sample testing can continue.

[0021] The present invention focuses on suppressing and reducing the volatilization pollution of lanthanum and cerium metals in rare earth steel, overcoming the problem that the rare earth volatilization residue adsorbs the measured gas CO, and selects four ideas to solve the volatilization pollution problem of lanthanum and cerium metals in rare earth steel. First, reduce the analysis power, thereby reducing the furnace temperature to reduce the volatilization of lanthanum and cerium metals. Second, select appropriate fluxes or bath materials for rare earth steel with high rare earth content to inhibit the volatilization of rare earth metals and improve the kinetic conditions for gas extraction in the sample. By replacing the relevant filters in a timely manner, the pollution of the furnace chamber and gas path can be reduced. The volatilization amount of lanthanum and cerium rare earth metals in rare earth steel can be reduced by reducing the sample weighing amount. In order to achieve the purpose of inhibiting volatilization, reducing pollution, and enabling the gas to be completely released for detection.

[0022] The advantages and beneficial effects of the present invention are as follows:

[0023] 1. The present invention uses the pulse melting-infrared absorption thermal conductivity method to determine the oxygen and nitrogen contents in lanthanum-cerium rare earth steel. By classifying rare earth steel with different rare earth contents, setting instrument analysis parameters, selecting the optimal analysis power and the optimal sample weighing amount, and selecting the optimal bath material / flux, the volatilization of rare earth metals in rare earth steel is effectively inhibited, and the problem of accurately determining the oxygen and nitrogen contents in rare earth steel is solved.

[0024] 2. The present invention uses tin as the bath metal and uses a pulse melting-infrared absorption thermal conductivity instrument to quantitatively analyze the oxygen content in rare earth steel with high rare earth content. No flux or bath material is required for nitrogen content testing. The oxygen and nitrogen gas elements in rare earth steel with high rare earth content need to be determined separately. And the pollution of the analytical instrument is reduced by cleaning the electrode in a timely manner, regularly replacing the filter cotton and reagents. A quantitative analysis method for the oxygen and nitrogen contents in rare earth steel is established.

[0025] 3. The present invention has low cost, simple operation, easy control, effectively improves the analysis accuracy, has high test accuracy, and the test results are accurate and reliable. Specific implementation mode

[0026] Example 1

[0027] I. Instrument preparation

[0028] The instrument used in the present invention is the ONH836 oxygen, nitrogen and hydrogen analyzer of LECO Corporation. Before analysis, the instrument is preheated and the carrier gas is introduced. The flow rate of the carrier gas is 450 mL / min. The temperature of the inlet air purifier reaches 650 °C, the temperature of the catalyst reaches 650 °C, and the gas is introduced for about 1 hour for analysis. The carrier gas is high-purity helium, and its working pressure is 22 psi; the power gas is ordinary nitrogen, and its working pressure is 40 psi.

[0029] II. Sample preparation

[0030] Remove the surface oxide layer of the sample, cut it into small pieces, weigh 0.3569 g and 0.3301 g respectively, wash with analytical pure acetone, dry with cold air, and put it into the sample box for standby.

[0031] Note: The total content of lanthanum and cerium rare earths in this sample detected in the previous stage is 0.017%.

[0032] III. Analytical method setting

[0033] The heating method adopts the power control mode, the degassing power is 5000 w, the analysis power adopts the constant temperature mode, the analysis power is 4200 w, the shortest analysis time for oxygen is 35 s, the shortest analysis time for nitrogen is 60 s, and the comparator level is 1%.

[0034] IV. Blank and calibration

[0035] According to the analytical method set in step III, conduct 3 blank analyses on the high-purity graphite sleeve crucible, and perform blank deduction after the blank is stable. Use 502-712 (w(O)% = 0.0009, LECO Corporation, USA); use 501-646 (w(N)% = 0.0023, LECO Corporation, USA) standard samples to calibrate the oxygen and nitrogen contents.

[0036] V. Sample analysis

[0037] Simultaneous determination of oxygen and nitrogen contents

[0038] Input the sample number and sample mass in the set analytical method, open the sample loading port, place the weighed samples (0.3569 g, 0.3301 g) in step II into the loader, turn on the pulse furnace, place the crucible on the lower electrode, and then the lower electrode rises. After the crucible is degassed, the sample falls into the crucible, heats and melts, and perform parallel determinations twice according to the same steps, and the instrument software calculates the measurement average value.

[0039] The analysis results of the example are as follows:

[0040] The measured oxygen content in the lanthanum-cerium rare earth steel submitted by a certain laboratory for inspection is 0.0005%, and the nitrogen content is 0.0009%.

[0041] Example 2

[0042] I. Instrument preparation

[0043] The instrument used in the present invention is the ONH836 oxygen-nitrogen-hydrogen analyzer of LECO Corporation. Before analysis, preheat the instrument and introduce the carrier gas, and the carrier gas flow rate is 450 mL / min. Make the temperature of the inlet purifier reach 650 °C, the temperature of the catalyst reach 650 °C, and conduct analysis after ventilating for about 1 hour. The carrier gas is high-purity helium, and its working pressure is 22 psi; the motive gas is ordinary nitrogen, and its working pressure is 40 psi.

[0044] II. Sample Preparation

[0045] Remove the surface oxide layer of the sample, cut it into small pieces, weigh 0.3062 g, 0.3217 g, 0.5425 g, and 0.5649 g respectively, wash with analytical pure acetone, dry with cold air, and place in a sample box for standby.

[0046] Note: The total content of lanthanum and cerium rare earths in this sample detected in the previous stage is 0.083%.

[0047] III. Analytical Method Setting

[0048] The heating method adopts the power control mode, the degassing power is 5000 w, the analytical power adopts the constant temperature mode, the analytical power is 4500 w, the shortest analysis time for oxygen is 35 s, the shortest analysis time for nitrogen is 60 s, and the comparator level is 1%.

[0049] IV. Blank and Calibration

[0050] According to the analytical method set in step III, conduct 3 blank analyses on the high-purity graphite sleeve crucible, and perform blank deduction after the blank is stable. Use 502 - 712 (w(O)% = 0.0009, LECO Corporation, USA); use 501 - 646 (w(N)% = 0.0023, LECO Corporation, USA) standard samples to calibrate the oxygen and nitrogen contents.

[0051] V. Specimen Analysis

[0052] 1. Determination of Oxygen Content

[0053] Input the sample number and sample mass in the set analytical method, open the sample loading port, place the weighed specimens (0.3062 g, 0.3217 g) in step II into the loader, weigh about 0.5 g of Sn bath material and place it in the graphite crucible, open the pulse furnace, place the crucible on the lower electrode, and then the lower electrode rises. After the crucible and bath material are degassed, the specimen drops into the crucible, heats and melts, and perform parallel measurements twice according to the same steps. The instrument software calculates the measurement average value.

[0054] 2. Determination of Nitrogen Content

[0055] Input the sample number and sample mass in the set analytical method, open the sample loading port, place the weighed specimens (0.5425 g, 0.5649 g) in step II into the loader, open the pulse furnace, place the crucible on the lower electrode, and then the lower electrode rises. After the crucible is degassed, the specimen drops into the crucible, heats and melts, and perform parallel measurements twice according to the same steps. The instrument software calculates the measurement average value.

[0056] The analysis results of the examples are as follows:

[0057] The measured oxygen content in the lanthanum-cerium rare earth steel submitted by a certain laboratory is 0.0010% and the nitrogen content is 0.0012%.

[0058] Matters not covered in this invention are well-known technologies.

[0059] The above embodiments are only used to illustrate the technical concept and features of the present invention. The purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and it should not be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for determining the oxygen and nitrogen contents in lanthanum-cerium rare earth steel, characterized in that, it includes the following steps: (1) Pretreat the sample to be analyzed. Remove the surface oxide layer of the lanthanum-cerium rare earth steel sample, wash it with acetone or absolute ethanol, and then air-dry it; (2) Debug the working parameters of the pulse infrared thermal conductivity oxygen, nitrogen and hydrogen analyzer, and set the analysis method; (3) According to the analysis method set in step (2), conduct a blank analysis; (4) Establishment of the standard working curve: Use the single-point method to calibrate the instrument and establish the standard working curve; (5) Determine the sample: First, classify the lanthanum and cerium rare earth contents in the sample, and use different analysis methods for rare earth steels with different rare earth content ranges; for rare earth steel samples with low rare earth content, use the conventional steel analysis method for testing; for rare earth steel samples with relatively high rare earth content, use a low analysis power for testing; for rare earth steel samples with high rare earth content, for the test of the oxygen content in the sample, use the bath material method for testing, and for the test of the nitrogen content in the sample, it can be directly tested; For the rare earth steel samples with low rare earth content mentioned in step (5), the total rare earth content is in the range of 10 ppm to 50 ppm, and the conventional steel analysis method is used to test the oxygen and nitrogen contents; For the rare earth steel samples with relatively high rare earth content mentioned in step (5), the total rare earth content is in the range of 50 ppm to 500 ppm, and a low analysis power of 4000 W to 4500 W is used for simultaneous oxygen and nitrogen testing; For the rare earth steel samples with high rare earth content mentioned in step (5), the total rare earth content is in the range of 500 ppm to 1000 ppm, and a low analysis power of 4000 W to 4500 W is used for testing; The test method for the oxygen content in the sample is as follows: Open the sample loading port of the pulse furnace, place a certain weight of the sample into the loader of the pulse furnace, place the bath material metal into the graphite crucible, open the pulse furnace, place the crucible on the lower electrode of the pulse furnace, and then the lower electrode rises; After the graphite crucible and the bath material are degassed, the sample drops into the crucible and is heated and melted; The oxygen in the sample is released in the form of carbon monoxide and is carried by the carrier gas into the pulse infrared thermal conductivity oxygen, nitrogen and hydrogen analyzer, and the oxygen content value is obtained through software data processing; The test method for the nitrogen content in the sample is as follows: Open the sample loading port of the pulse furnace, place a certain weight of the sample into the loader of the pulse furnace, directly inject the sample, open the pulse furnace, place the crucible on the lower electrode of the pulse furnace, and then the lower electrode rises; After the graphite crucible is degassed, the sample drops into the crucible and is heated and melted; The nitrogen in the sample is released in the form of nitrogen gas and is carried by the carrier gas into the pulse infrared thermal conductivity oxygen, nitrogen and hydrogen analyzer, and the nitrogen content value is obtained through software data processing.

2. The method for determining the oxygen and nitrogen contents in lanthanum-cerium rare earth steel according to claim 1, characterized in that, in step (5), first determine the lanthanum and cerium rare earth contents in the sample and classify them according to the total content of rare earth lanthanum and cerium, and use different analysis methods for rare earth steels with different rare earth content ranges.

3. The method for determining the oxygen and nitrogen contents in lanthanum-cerium rare earth steel according to claim 1 or 2, characterized in that, the bath material is a tin cake, and the mass ratio of the tin cake to the sample is in the range of 1:1 to 2:

1.

4. The method for determining the oxygen and nitrogen contents in the lanthanum-cerium rare earth steel according to claim 1, characterized in that, after analyzing every 5 samples, clean the furnace chamber, clean the upper and lower electrodes with an electrode brush, and wipe the furnace chamber with absorbent cotton; after analyzing every 20 samples, replace the filter cotton in the disc filter, clean it and then continue with the sample testing.