Method for treating vanadium-nitrogen alloy

Abstract

The invention relates to the technical field of vanadium-nitrogen alloy preparation, and discloses a method for treating a vanadium-nitrogen alloy, which comprises the following five steps: a batch raw material pretreatment process, an atmosphere dynamic adjustment segmented reduction pretreatment process, a catalyst layered addition process, a water vapor assisted segmented nitridation process and a whole-course atmosphere component dynamic proportioning process. According to the method, the technical problems of non-uniform nitridation, low catalytic efficiency, poor raw material fluctuation adaptability and the like in a traditional process are solved, the technical breakthrough that the nitridation uniformity is improved by 60% or above, the nitrogen content deviation is reduced to be within + / -3%, the batch qualification rate is improved to 92-97%, and the atmosphere utilization efficiency is improved by 30% or above is achieved, and the vanadium-nitrogen alloy product quality and the production stability are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of vanadium-nitrogen alloy preparation technology, and more specifically, to a method for processing vanadium-nitrogen alloys. Background Technology

[0002] Vanadium-nitrogen alloys are important steel additives, widely used in the production of high-strength steel, stainless steel, tool steel, and other high-end steel products. Traditional vanadium-nitrogen alloy preparation processes typically involve raw materials such as vanadium pentoxide, graphite, iron powder, and liquid ammonia, followed by crushing, grinding, dry mixing, rolling, extrusion molding, and nitriding sintering to obtain the finished product.

[0003] However, existing technologies have significant technical drawbacks: First, the traditional nitriding process uses a one-time high-concentration ammonia gas introduction method, which leads to rapid nitriding of the surface layer to form a dense layer, hindering the diffusion of ammonia gas into the interior, resulting in a large difference in nitrogen content between the inside and outside of the product, with a nitrogen content deviation typically exceeding ±8%; Second, vanadium pentoxide is not fully reduced during the nitriding process, and the residual high-valence vanadium oxide is difficult to nitrid, affecting product purity and nitriding depth; Third, the catalyst is added using a one-time uniform mixing method, without considering the spatial gradient characteristics of the nitriding process, thus failing to maximize catalytic efficiency; Fourth, the quality of vanadium pentoxide raw materials fluctuates between different batches in industrial production, and the traditional process has poor adaptability to raw material fluctuations, resulting in unstable batch pass rates, typically only 75-85%; Fifth, the atmosphere composition uses a fixed ratio, which cannot be adjusted according to the dynamic changes in raw material characteristics and reaction progress, resulting in low atmosphere utilization efficiency. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides a method for processing vanadium-nitrogen alloys, comprising the following steps: Step 1: Batch-by-batch raw material pretreatment process: Each batch of vanadium pentoxide raw material was evaluated for its characteristics. Differentiated pretreatment was carried out based on the evaluation results of impurity content, particle size, reducing properties and nitriding activity to compensate for and balance the characteristic differences between different batches of raw materials. Step 2, Segmented reduction pretreatment process: Vanadium pentoxide is mixed with graphite and pressed into a blank. First, a weak reduction treatment is carried out at 500-700℃ using a low-concentration reducing gas, and then a strong reduction treatment is carried out at 700-900℃ using a high-concentration reducing gas, forming a valence gradient distribution from the outside to the inside. Step 3, Catalyst layering addition process: The iron powder catalyst was added in two stages: first, coarse iron powder was added to form an outer layer distribution, and second, fine iron powder was added to form an inner layer distribution. Step 4: Steam-assisted segmented nitriding process: The nitriding process is divided into two stages. In the first stage, ammonia with low nitrogen partial pressure and trace amounts of water vapor are used for pre-nitriding at 900-1100℃. In the second stage, ammonia with high nitrogen partial pressure is used for deep nitriding at 1200-1400℃. At the same time, the atmosphere ratio is dynamically adjusted according to the characteristics of the raw materials and the reaction process.

[0005] Preferably, in the batch raw material pretreatment process, the impurity content is detected by X-ray fluorescence spectroscopy, the particle size distribution is determined by laser particle size analyzer, the reducing and nitriding activities are evaluated by small sample tests, and the batches with excessive impurity content are acid washed according to the evaluation results, the grinding time is increased for the batches with excessively coarse particles, and the batches with poor reducing properties are pre-reduced and activated.

[0006] Preferably, in the segmented reduction pretreatment process, the first stage of weak reduction treatment uses CO or H2 with a volume ratio of 15-30% as the reducing gas and is kept at a temperature of 500-700℃ for 2-4 hours; the second stage of strong reduction treatment uses CO or H2 with a volume ratio of 40-70% as the reducing gas and is kept at a temperature of 700-900℃ for 3-6 hours.

[0007] Preferably, in the catalyst layered addition process, the coarse iron powder has a particle size of 100-200 mesh and is added at 8-15% of the billet mass; the fine iron powder has a particle size of 300-500 mesh and is added at 5-12% of the billet mass.

[0008] Preferably, in the steam-assisted segmented nitriding process, the ammonia partial pressure in the pre-nitriding stage is 0.1-0.3 MPa, the water vapor volume fraction is 1.5-2.0%, the temperature is 900-1100℃, and the treatment time is 3-6 hours; the ammonia partial pressure in the deep nitriding stage is 0.5-0.8 MPa, the water vapor volume fraction is 0.5-1.0%, the temperature is 1200-1400℃, and the treatment time is 4-8 hours.

[0009] Preferably, the dynamic adjustment of the atmosphere ratio is based on the evaluation results of the raw material characteristics, and the composition of the outlet gas is monitored by an online gas detector. The ratio of reducing gas, ammonia and water vapor is finely adjusted in real time according to the ammonia conversion rate, hydrogen content and water vapor content.

[0010] Preferably, between steps 2 and 4, a molding process is also included: the mixture is mixed with a binder and then rolled, and then extruded in three stages. The first stage extrusion pressure is 15-25 MPa, the second stage extrusion pressure is 35-50 MPa, and the third stage extrusion pressure is 60-80 MPa.

[0011] Preferably, the water vapor is generated by heating distilled water in an evaporator at a temperature of 110-130°C, and the water vapor flow rate is precisely controlled by a mass flow controller.

[0012] Preferably, the purity of the vanadium pentoxide raw material is ≥98%, the purity of the graphite powder is ≥99%, the purity of the iron powder is ≥99%, and the purity of the ammonia is ≥99.8%.

[0013] Preferably, the nitrogen content is 16-20%, the uniformity deviation of nitrogen content is ≤±3%, the vanadium content is 75-82%, and the product density is 3.8-4.2 g·cm³. -3 .

[0014] The beneficial effects of this invention are as follows: (1) Nitriding uniformity is significantly improved By combining the segmented nitriding process with the synergistic effect of segmented reduction pretreatment, a high degree of uniformity in nitriding between the inner and outer surfaces of vanadium-nitrogen alloys was achieved. The valence gradient formed by segmented reduction matches the process characteristics of segmented nitriding, avoiding the problem of excessively rapid densification of the surface layer caused by traditional one-time nitriding. This allows nitrogen atoms to diffuse uniformly into all areas of the material, significantly improving the uniformity of nitrogen content both inside and outside the product.

[0015] (2) Comprehensive optimization of catalytic efficiency The catalyst layering addition process achieves both spatial and temporal optimization of catalytic activity. The distribution pattern of coarse iron powder in the outer layer and fine iron powder in the inner layer perfectly matches the two-stage characteristics of segmented nitridation, enabling the catalyst to play a continuous and efficient role throughout the nitridation process and avoiding the uneven catalytic efficiency problem caused by traditional uniformly distributed catalysts.

[0016] (3) Nitriding depth and rate are increased simultaneously The steam-assisted nitriding process significantly improves the nitriding effect through the dual action of loosening the material structure and promoting atomic diffusion. The redox cycle of steam creates a rapid channel for nitrogen atom diffusion, while the generated active species increase the nitrogen atom diffusion coefficient, achieving a simultaneous improvement in nitriding depth and nitriding rate.

[0017] (4) Production stability has been greatly improved The batch-by-batch raw material pretreatment process eliminates the impact of differences in the characteristics of different batches of raw materials on product quality, while the dynamic composition of atmosphere further adapts to the dynamic changes in the process. The synergistic effect of the two processes enables the production process to have dual adaptability to raw material fluctuations and process changes, and the production stability is fundamentally improved.

[0018] (5) Resource utilization efficiency has been comprehensively improved The dynamic proportioning process for atmosphere components enables precise supply of atmosphere components, avoiding the waste or shortage problems caused by fixed proportions. Through dual control of pre-adjustment and real-time fine-tuning, all gas components can be fully and effectively utilized, and resource utilization efficiency is comprehensively improved.

[0019] (6) The process synergy effect is prominent. The five process steps form a complete technology chain, with significant synergistic enhancement effects among the steps. Raw material pretreatment provides a stable foundation for subsequent processes, dynamic atmosphere adjustment and segmented reduction pretreatment create optimal conditions for the nitriding process, catalyst stratification and segmented nitriding achieve spatiotemporal matching, steam assistance and segmented nitriding synergistically promote each other, and dynamic proportioning throughout the process optimizes the process. Each technical element promotes and reinforces the other, producing a comprehensive effect far exceeding that of any single technical element.

[0020] This invention overcomes key technical challenges in traditional vanadium-nitrogen alloy preparation processes, such as uneven nitriding, low catalytic efficiency, and poor batch stability. It achieves technical improvements such as reducing the nitrogen content deviation of the product from ±8% to ±3%, increasing the catalytic efficiency by 40-50%, increasing the batch qualification rate from 75-85% to 92-97%, and improving the atmosphere utilization efficiency by more than 30%. It provides a complete and effective technical method for the industrial production of vanadium-nitrogen alloys. Attached Figure Description

[0021] Figure 1 This is a comparison of the radial distribution of nitrogen content in the vanadium-nitrogen alloy of the present invention; Figure 2 This is a comparison of the nitriding uniformity index of the present invention; Figure 3 These are the nitridation kinetic curves for different catalyst addition methods of the present invention; Figure 4 This is the ammonia conversion rate versus time curve of the present invention; Figure 5 This is a radar chart showing the comprehensive evaluation of the catalytic efficiency of this invention; Figure 6 This is a comparison of the nitrogen content stability of 15 batches of the present invention; Figure 7 This is a comparison of the pass rates of 15 batches of this invention; Figure 8 This is a box plot of batch stability for different raw material types according to the present invention; Figure 9 This invention provides a comprehensive evaluation of process capability. Detailed Implementation

[0022] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.

[0023] Example 1 This embodiment proposes a method for processing vanadium-nitrogen alloys, comprising the following steps: Step 1: Batch-by-batch raw material pretreatment process: Each batch of vanadium pentoxide raw material was evaluated for its characteristics. Differentiated pretreatment was carried out based on the evaluation results of impurity content, particle size, reducing properties and nitriding activity to compensate for and balance the characteristic differences between different batches of raw materials. Impurity content was detected by X-ray fluorescence spectroscopy, particle size distribution was determined by laser particle size analyzer, and reducibility and nitriding activity were evaluated by small-sample tests. Based on the evaluation results, batches with excessive impurity content were acid-washed, batches with excessively coarse particles were ground for longer periods, and batches with poor reducibility were pre-reduced and activated.

[0024] Step 2, Segmented reduction pretreatment process: Vanadium pentoxide and graphite are mixed and pressed into a blank. First, a weak reduction treatment is carried out at 600℃ using a low-concentration reducing gas, and then a strong reduction treatment is carried out at 800℃ using a high-concentration reducing gas, forming a valence gradient distribution from the outside to the inside. The first stage of weak reduction treatment uses CO at a volume ratio of 22% as the reducing gas and is held at 600℃ for 3 hours; the second stage of strong reduction treatment uses CO at a volume ratio of 55% as the reducing gas and is held at 800℃ for 4 hours.

[0025] Step 3, Catalyst layering addition process: The iron powder catalyst was added in two stages: first, coarse iron powder was added to form an outer layer distribution, and second, fine iron powder was added to form an inner layer distribution. The coarse iron powder has a particle size of 150 mesh and is added at 12% of the body mass; the fine iron powder has a particle size of 400 mesh and is added at 9% of the body mass.

[0026] Step 4: Steam-assisted segmented nitriding process: The nitriding process is divided into two stages. The first stage uses low nitrogen partial pressure ammonia and trace amounts of water vapor at 1000℃ for pre-nitriding, and the second stage uses high nitrogen partial pressure ammonia at 1300℃ for deep nitriding. At the same time, the atmosphere ratio is dynamically adjusted according to the characteristics of the raw materials and the reaction process. The ammonia partial pressure in the pre-nitriding stage is 0.2 MPa, the water vapor volume fraction is 1.7%, the temperature is 1000℃, and the treatment time is 5 hours; the ammonia partial pressure in the deep nitriding stage is 0.6 MPa, the water vapor volume fraction is 0.7%, the temperature is 1300℃, and the treatment time is 6 hours. Dynamic atmosphere ratio adjustment involves pre-adjusting the atmosphere ratio based on the raw material characteristic assessment results, and monitoring the outlet gas composition through an online gas detector. The ratio of reducing gas, ammonia, and water vapor is then finely adjusted in real time based on the ammonia conversion rate, hydrogen content, and water vapor content.

[0027] Between steps 3 and 4, a molding process is also included: the mixture is mixed with an adhesive and rolled, and then extruded in three stages. The first stage extrusion pressure is 20 MPa, the second stage extrusion pressure is 40 MPa, and the third stage extrusion pressure is 70 MPa.

[0028] Water vapor is generated by heating distilled water in an evaporator at a temperature of 120°C. The water vapor flow rate is precisely controlled by a mass flow controller.

[0029] The purity of the vanadium pentoxide raw material is ≥98%, the purity of the graphite powder is ≥99%, the purity of the iron powder is ≥99%, and the purity of the ammonia is ≥99.8%.

[0030] The vanadium-nitrogen alloy product prepared by the above method has a nitrogen content of 18%, a nitrogen content uniformity deviation of ≤±3%, a vanadium content of 80%, and a product density of 4.0 g·cm³. -3 .

[0031] Example 2 The difference between this embodiment and Embodiment 1 is that: Vanadium pentoxide and graphite are mixed and pressed into a blank. First, a weak reduction treatment is carried out at 500℃ using a low-concentration reducing gas, and then a strong reduction treatment is carried out at 700℃ using a high-concentration reducing gas, forming a valence gradient distribution from the outside to the inside. The first stage of weak reduction treatment uses 15% H2 by volume as the reducing gas and is kept at 500℃ for 2 hours; the second stage of strong reduction treatment uses 40% H2 by volume as the reducing gas and is kept at 700℃ for 3 hours.

[0032] The coarse iron powder has a particle size of 100 mesh and is added at 8% of the body mass; the fine iron powder has a particle size of 300 mesh and is added at 5% of the body mass.

[0033] The nitriding process is divided into two stages. In the first stage, ammonia with low nitrogen partial pressure and trace amounts of water vapor are used for pre-nitriding at 900℃. In the second stage, ammonia with high nitrogen partial pressure is used for deep nitriding at 1200℃. At the same time, the atmosphere ratio is dynamically adjusted according to the characteristics of the raw materials and the reaction process. The ammonia partial pressure in the pre-nitriding stage is 0.1 MPa, the water vapor volume fraction is 1.5%, the temperature is 900℃, and the treatment time is 3 hours; the ammonia partial pressure in the deep nitriding stage is 0.5 MPa, the water vapor volume fraction is 0.5%, the temperature is 1200℃, and the treatment time is 4 hours. Between steps 3 and 4, a molding process is also included: the mixture is mixed with an adhesive and rolled, and then extruded in three stages. The first stage extrusion pressure is 15 MPa, the second stage extrusion pressure is 35 MPa, and the third stage extrusion pressure is 60 MPa.

[0034] Water vapor is generated by heating distilled water in an evaporator at a temperature of 110°C. The water vapor flow rate is precisely controlled by a mass flow controller.

[0035] The vanadium-nitrogen alloy product has a nitrogen content of 16%, a nitrogen content uniformity deviation of ≤±3%, a vanadium content of 75%, and a product density of 3.8 g·cm³. -3 .

[0036] Example 3 The difference between this embodiment and Embodiment 1 is that: Vanadium pentoxide and graphite are mixed and pressed into a blank. First, a weak reduction treatment is carried out at 700℃ using a low-concentration reducing gas, and then a strong reduction treatment is carried out at 900℃ using a high-concentration reducing gas, forming a valence gradient distribution from the outside to the inside. The first stage of weak reduction treatment uses CO2 at a volume ratio of 30% as the reducing gas and is kept at 700℃ for 4 hours; the second stage of strong reduction treatment uses CO at a volume ratio of 40-70% as the reducing gas and is kept at 900℃ for 6 hours.

[0037] The coarse iron powder has a particle size of 200 mesh and is added at 15% of the body mass; the fine iron powder has a particle size of 500 mesh and is added at 12% of the body mass.

[0038] The nitriding process is divided into two stages. In the first stage, ammonia with low nitrogen partial pressure and trace amounts of water vapor are used for pre-nitriding at 1100℃. In the second stage, ammonia with high nitrogen partial pressure is used for deep nitriding at 1400℃. At the same time, the atmosphere ratio is dynamically adjusted according to the characteristics of the raw materials and the reaction process. The ammonia partial pressure in the pre-nitriding stage is 0.3 MPa, the water vapor volume fraction is 2.0%, the temperature is 1100℃, and the treatment time is 6 hours; the ammonia partial pressure in the deep nitriding stage is 0.8 MPa, the water vapor volume fraction is 1.0%, the temperature is 1400℃, and the treatment time is 8 hours. Between steps 3 and 4, a molding process is also included: the mixture is mixed with an adhesive and then rolled, and then extruded in three stages. The first stage extrusion pressure is 25 MPa, the second stage extrusion pressure is 50 MPa, and the third stage extrusion pressure is 80 MPa.

[0039] Water vapor is generated by heating distilled water in an evaporator at a temperature of 130°C. The water vapor flow rate is precisely controlled by a mass flow controller.

[0040] The vanadium-nitrogen alloy product has a nitrogen content of 20%, a nitrogen content uniformity deviation of ≤±3%, a vanadium content of 82%, and a product density of 4.2 g·cm³. -3 .

[0041] Example 4 This embodiment proposes a method for processing vanadium-nitrogen alloys, comprising the following steps: Step 1: Batch-by-batch raw material pretreatment process The specifications for the raw materials used in this step are as follows: Vanadium pentoxide: purity ≥ 98%, V₂O₅ content ≥ 98.5%, moisture ≤ 0.5%; Graphite powder: purity ≥99%, fixed carbon content ≥99%, particle size 100-300 mesh (48-150μm), conforming to GB / T3521-2008 standard; Iron powder: purity ≥99%, Fe content ≥99%, oxygen content ≤0.3%; Reducing gases: CO purity ≥ 99.5% (CAS No.: 630-08-0), or H2 purity ≥ 99.9%; Ammonia: Purity ≥ 99.8%, Moisture ≤ 0.5%; Dilute acid: Hydrochloric acid (HCl) with a concentration of 10-20 wt% is preferred, or sulfuric acid (H2SO4) with a concentration of 5-15 wt% is preferred. Adhesive: Polyvinyl alcohol (PVA), relative molecular mass 12×10 4 -15×10 4 Or sodium carboxymethyl cellulose (CMC-Na), with a dynamic viscosity of 800-1200 mPa·s.

[0042] (1) Raw material characteristic assessment: Multi-dimensional characteristic tests were performed on each batch of vanadium pentoxide raw materials. V₂O₅ content and impurity content were determined by X-ray fluorescence spectrometry (XRF) with a detection accuracy of ±0.1%. Emphasis was placed on detecting alkali metals (total Na and K ≤0.5%), iron (Fe ≤2.0%), and silicon (Si ≤1.0%). Particle size distribution was determined using a Malvern laser particle size analyzer to obtain D0. 50 (Median particle size), D 90 Parameters such as (90% cumulative particle size) require D 50 The specific surface area should be within the range of 20-60 μm, determined by the BET nitrogen adsorption method, and should be 0.5-2.0 m². 2 ·g -1The reducing power was evaluated through a small-sample reduction test: 10g of sample was weighed and reduced in a tube furnace at 500-700℃ with CO or H2 (20% by volume, balance N2) for 60 minutes. The reduction rate was calculated by the weight loss method, and the pass standard was ≥85%. The nitriding activity was evaluated through a small-sample nitriding test: 5g of the reduced sample was weighed and nitrided with NH3 at 900-1100℃ for 4 hours. The nitriding rate was calculated by nitrogen content analysis, and the pass standard was ≥75%.

[0043] (2) Differentiated preprocessing strategy: Based on the characteristic assessment results, targeted pretreatment was implemented for different batches of raw materials. For batches with impurity content exceeding standard values ​​(e.g., alkali metal content >0.5%, iron content >2%), dilute acid immersion treatment was used. The pickling time was determined according to the impurity content (usually 2-6 hours). After pickling, the materials were washed with water until neutral and dried. For batches with excessively coarse particle size (D... 50 For batches with a surface area >50μm, ball milling or air jet milling should be used to increase the grinding time (extending by 50%-100%). For batches with poor reducibility (reduction rate <80%), pre-reduction activation should be carried out in the pretreatment stage, i.e., low concentration of CO or H2 (volume ratio 5-15%) should be introduced at 400-600℃ for 1-3 hours to improve surface activity. For batches with low nitriding activity (nitriding rate <70%), the amount of iron powder catalyst should be increased by 10-30% or nitriding activity promoters (such as calcium fluoride, ammonium chloride, etc., with an addition amount of 0.1-0.5%) should be added during mixing and milling.

[0044] (3) Verification of preprocessing effect: The pretreated raw materials are subjected to characteristic tests again to ensure that the key indicators such as impurity content, particle size, reducibility, and nitriding activity of each batch of raw materials meet the consistency requirements (deviation controlled within ±10%), so as to obtain vanadium pentoxide raw materials with uniform impurity content, consistent particle size, uniform reducibility, and similar nitriding activity.

[0045] Step 2: Segmented reduction pretreatment process (1) First stage of weak reduction processing: The pretreated vanadium pentoxide raw material is mixed with graphite powder (mass ratio of 100:(8-12), preferably 100:10) and then pressed into a blank in a press (pressing pressure 20-40 MPa, preferably 30 MPa, blank density 1.8-2.2 g·cm³). -3 The preferred density is 2.0 g·cm³. -3 The billet is loaded into a box-type reduction furnace, and the heating rate is controlled at 5-10℃ / min. A reducing atmosphere is introduced.

[0046] Adjust the reducing atmosphere ratio based on the raw material characteristic assessment results in step 1: For raw material batches with poor reducing properties (reduction rate <85%), increase the reducing gas concentration to 15-30%; for raw material batches with good reducing properties (reduction rate ≥90%), use the basic ratio. The basic ratio is 15-30% CO or H2 volume ratio (preferably 20% H2, as H2 has stronger reducing properties than CO and is non-toxic), with the remainder being N2 or Ar (preferably N2 as the carrier gas). The gas flow rate is controlled at 0.5-2.0 L / min (preferably 1.2 L / min), and the reduction is carried out at a temperature of 500-700℃ (preferably 600℃) for 2-4 hours (preferably 3 hours). The reduction process is judged by monitoring the CO2 or H2O content at the outlet using an online gas analyzer.

[0047] Characteristics of intermediate products: After the first stage of reduction, the outer layer of the green body (depth 0-2mm) is dark green to black. XRD analysis shows that the content of V2O4 and V2O3 phases accounts for 60-80%, while the content of V2O5 phase decreases to 10-30%. The inner layer (depth >2mm) is orange-yellow to brown, with the content of V2O5 phase still accounting for 50-70%. The weight loss rate of the green body is 8-15%, there are no obvious cracks on the surface, and the mechanical strength is ≥5MPa.

[0048] (2) Second-stage strong reduction treatment: Based on the first-stage reduction, the reduction intensity is increased. For batches of raw materials with poor reducibility, the reduction time is extended to 4.5-6 hours; for batches with high impurity content, the temperature is appropriately reduced to 750℃ to avoid side reactions. The basic conditions are: the reducing gas concentration is increased to a CO or H2 volume ratio of 40-70% (preferably H2 55%), the balance is N2 or Ar (preferably N2), the gas flow rate is increased to 1.0-3.0 L / min (preferably 2.0 L / min), the temperature is raised to 700-900℃ (preferably 800℃), and the holding time is 3-6 hours (preferably 4 hours). A programmed temperature rise method is adopted: the temperature is increased from the first-stage reduction temperature to the second-stage reduction temperature at a rate of 3-8℃ / min.

[0049] Characteristics of intermediate products: After the second stage of reduction, the outer layer (0-3mm depth) of the billet is dark gray to black. XRD analysis shows that the VO phase content is 40-60%, the V2O3 phase content is 25-40%, the V2O4 phase content is 10-25%, and the residual V2O5 phase content is ≤5%. The middle layer (3-6mm depth) is grayish-green, mainly composed of V2O3 and V2O4 phases. The inner layer (>6mm depth) is light green, with V2O4 and V2O5 phases still dominating. The overall weight loss rate is 18-28%, the billet shows no obvious deformation, and the mechanical strength remains at 3-8MPa.

[0050] (3) Formation of reduction gradient: Through two-stage reduction treatment, a clear valence gradient distribution is formed inside the billet, namely, from the outside to the inside, it presents a valence distribution of low-valence vanadium oxides (VO, V2O3) → medium-valence vanadium oxides (V2O4) → high-valence vanadium oxides (V2O5). This valence gradient distribution makes the outer layer vanadium oxides easier to nitrid, while the inner layer vanadium oxides require enhanced nitriding conditions, which corresponds to the low nitrogen partial pressure pre-nitriding and high nitrogen partial pressure deep nitriding in the segmented nitriding process. After reduction, the billet is cooled to room temperature to obtain a pretreated billet with a high degree of reduction in the outer layer and a relatively low degree of reduction in the inner layer.

[0051] Step 3: Catalyst layering addition process (1) First layer addition: The pre-treated billet is crushed to a particle size of 3-8 mm using a jaw crusher, and then ground to 100-200 mesh using a Raymond mill. The crushed raw material is then mixed with graphite powder (purity ≥99%, particle size 100-300 mesh) and coarse iron powder. The coarse iron powder specifications are: particle size 100-200 mesh (75-150 μm, preferably 100 μm), purity ≥99% (preferably electrolytic iron powder, purity 99.5%), apparent density 4.8-5.2 g·cm³. -3 (Preferred 5.0g·cm) -3 The addition amount is 8-15% of the mass of the reduced billet (preferably 12%). A plow-type mixer is used for light mixing: rotor speed 350 rpm (adjustable range 300-500 rpm), mixing time 20 minutes (adjustable range 15-30 minutes), and hopper filling rate 40-60%. During mixing, the machine is stopped every 5 minutes to check the mixing uniformity, and the iron content distribution uniformity is determined by sampling analysis (relative standard deviation RSD ≤ 15%). Under light mixing conditions, due to the high density of coarse iron powder (7.86 g·cm³), the iron content distribution is relatively uniform. -3 Furthermore, due to their large particle size, they preferentially distribute themselves around the particle agglomerates under centrifugal force, forming an outer layer of coarse iron powder concentration gradient.

[0052] (2) Second layer addition: Add fine iron powder to the mixture from the first mixing and milling. The specifications for the fine iron powder are: particle size 300-500 mesh (30-50μm, preferably 40μm), purity ≥99% (preferably carbonyl iron powder, purity 99.8%), and specific surface area 0.8-1.5m². 2 ·g -1 (Preferred size: 1.2m) 2 ·g -1The amount added is 5-12% of the billet mass (preferably 8%). Continue moderate mixing in a plow-type mixer: increase the rotor speed to 450 rpm (adjustable range 400-600 rpm), and the mixing time is 30 minutes (adjustable range 20-40 minutes). The mixing process is divided into two stages: the first 15 minutes of low-speed mixing (300 rpm) to initially disperse the fine iron powder, and the next 15 minutes of high-speed mixing (450 rpm) to fully penetrate the fine iron powder into the particle gaps. Observe the cross-section of the mixture using an optical microscope to verify the stratified distribution effect: the distribution density of coarse iron powder in the outer layer should be 1.5-2.5 times that of the inner layer.

[0053] (3) Catalyst layering and distribution: Through two-stage layering, a spatially stratified catalyst distribution is formed within the mixture: the outer layer has a coarse iron powder concentration of 8-15% (based on billet mass), while the inner layer has a fine iron powder concentration of 5-12% (based on billet mass). This stratified distribution allows the outer layer of coarse iron powder to catalyze the surface nitriding reaction during the low-nitrogen partial pressure pre-nitriding stage (900-1100℃, 0.1-0.3MPa), while the inner layer of fine iron powder catalyzes the deep nitriding reaction during the high-nitrogen partial pressure deep nitriding stage (1200-1400℃, 0.5-0.8MPa). The spatial distribution of the catalyst corresponds to the temperature and pressure conditions of the nitriding process, resulting in a mixture with an outer layer enriched in coarse iron powder and an inner layer filled with fine iron powder.

[0054] Step 4: Molding process (1) Adhesive preparation and addition: Prepare an adhesive solution, preferably with a polyvinyl alcohol (PVA-1799) concentration of 8-12 wt% (preferably 10 wt%) or a sodium carboxymethyl cellulose (CMC-Na) concentration of 6-10 wt%, and maintain the solution temperature at 85-95℃ (preferably 90℃) to ensure complete dissolution. Spray the adhesive solution into the mixture in an atomized manner, with an addition amount of 2-5% (preferably 3.5%) of the dry mixture mass, a spray pressure of 0.2-0.4 MPa (preferably 0.3 MPa), and a spraying time of 5-8 minutes (preferably 6 minutes). Mix and grind for 15-25 minutes at a speed of 200-300 rpm to ensure uniform distribution of the adhesive, and control the moisture content of the mixture at 8-12%.

[0055] (2) Three-stage extrusion molding: Three-stage extrusion molding is performed using a hydraulic extruder. First-stage extrusion: pressure 15-25MPa (preferably 20MPa), holding time 30-60s (preferably 45s), die temperature 40-60℃ (preferably 50℃), to obtain a preliminarily densified preform with a density of 2.2-2.6 g·cm³. -3Second-stage extrusion: pressure 35-50 MPa (preferably 42 MPa), holding time 60-90 s (preferably 75 s), die temperature 50-70℃ (preferably 60℃), further increasing density to 2.8-3.2 g·cm³. -3 Third-stage extrusion: pressure 60-80 MPa (preferably 70 MPa), holding time 90-120 s (preferably 100 s), die temperature 60-80℃ (preferably 70℃), to obtain the final shaped preform with a density of 3.2-3.6 g·cm³. -3 (Preferred density 3.4 g·cm³) -3 The interval between each compression stage is 5-10 minutes to release internal stress.

[0056] Molding quality inspection: The molded blank should be free of cracks and delamination, with dimensional accuracy ±2%, density uniformity (density difference between different parts ≤5%), mechanical strength ≥8MPa (compressive strength test), and moisture content 6-10%. Qualified molded blanks should be immediately loaded into the nitriding furnace to avoid prolonged exposure to air, which could lead to surface oxidation.

[0057] Step 5: Steam-assisted segmented nitriding process (1) Low-NOx partial pressure steam-assisted pre-nitriding stage: The formed blank is loaded into a tubular nitriding furnace (furnace tube inner diameter 80-120mm, heating length 600-1000mm). The atmosphere inside the furnace adopts a multi-point air intake method to ensure uniform airflow distribution. Detailed heating program: room temperature → 300℃ (heating rate 5℃ / min, purpose: to slowly remove residual moisture) → 600℃ (heating rate 3℃ / min, purpose: to activate catalyst surface) → pre-nitriding temperature 900-1100℃ (heating rate 2℃ / min, preferably heated to 1000℃, purpose: to avoid thermal stress causing the blank to crack). During the heating process, N2 protective gas is introduced at a flow rate of 1-2L / min to prevent oxidation. Adjust the atmosphere ratio according to the characteristics of the raw materials: Basic atmosphere composition: ammonia partial pressure 0.1-0.3 MPa (preferably 0.2 MPa), water vapor volume fraction 1.5-2.0% (preferably 1.8%), nitrogen or argon as carrier gas (nitrogen is preferred due to its low cost and good inertness). For raw material batches with low nitriding activity (nitriding rate <75%), the ammonia partial pressure is increased to 0.25-0.3 MPa or the water vapor content is increased to 2.0-2.5%; for raw material batches with high impurity content (total impurities >3%), the proportion of inert gas in the carrier gas is increased to 60-80% to dilute the reactivity.

[0058] Operating conditions: Pre-nitriding temperature 900-1100℃ (preferably 1000℃), processing time 3-6 hours (preferably 4.5 hours), total gas flow rate 2-5L / min (preferably 3.5L / min), furnace pressure maintained at 0.05-0.15MPa positive pressure (preferably 0.10MPa). Detailed description of the steam generation and control system: Distilled water (conductivity <2μS / cm) is used to generate steam through a stainless steel heated evaporator (preferably at 120℃ to ensure full vaporization). The evaporator has built-in temperature sensors (accuracy ±1℃) and pressure sensors (accuracy ±0.01MPa). The steam flow rate is precisely controlled by a mass flow controller (preferably Bronkhorst EL-FLOW type, accuracy ±1%FS). The steam pipeline is heat-traced and insulated (insulation temperature 130℃) to prevent condensation. Key control parameters: Steam generation rate 0.1-0.5kg / h, response time <30s, stability ±2%.

[0059] Characteristics of intermediate products: After pre-nitriding, the outer layer of the green body (depth 0-3mm) has a metallic gray-black color. XRD detection shows that the VN phase content is 40-60% and the residual oxide phase is 30-40%; the surface nitrogen content is 12-15%; a microporous structure is formed on the surface of the green body, with a porosity of 15-25% and an average pore size of 0.5-2.0μm.

[0060] (2) High nitrogen partial pressure steam-assisted deep nitriding stage: The temperature of the nitriding furnace is programmed to rise from the pre-nitriding temperature to the deep nitriding temperature, and the heating rate is controlled at 2-5℃ / min. At the same time, the atmosphere composition is adjusted: the volume fraction of water vapor is reduced to 0.8% (adjustable range 0.5-1.0%), the partial pressure of ammonia is increased to 0.6MPa (adjustable range 0.5-0.8MPa), and the total flow rate is increased to 3-8L / min to enhance mass transfer.

[0061] Operating conditions: Deep nitriding temperature 1200-1400℃ (preferably 1300℃), processing time 4-8 hours (preferably 6 hours), furnace pressure maintained at 0.1-0.3MPa (preferably 0.2MPa). An online gas chromatograph (GC-2030) is used to detect the composition of the outlet gas every 30 minutes, and the changes in the contents of NH3, N2, H2, and H2O are monitored in real time.

[0062] (3) Layered nitriding completion: Through two-stage treatment of low nitrogen partial pressure pre-nitriding and high nitrogen partial pressure deep nitriding, the layered nitriding process from the outside to the inside and from shallow to deep is completed. The first stage forms a loose and porous vanadium nitride layer and ammonia diffusion channels on the outer layer, and the second stage forms a dense vanadium nitride layer on the inner layer. The two stages work together to avoid the phenomenon of excessive densification of the surface layer and insufficient nitriding of the inner layer caused by traditional one-time high-concentration ammonia nitriding. A vanadium-nitrogen alloy billet with an outer nitrogen content of 17-19%, an inner nitrogen content of 15-17%, and an overall nitrogen content deviation within ±3% is obtained.

[0063] Step 6: Cooling, Testing and Packaging (1) Detailed cooling plan for the program: After deep nitriding, a three-stage cooling process is employed to prevent thermal stress and nitrogen escape. The first stage is high-temperature protective cooling: 1300℃→900℃, cooling rate 8-15℃ / min (preferably 12℃ / min), with continued purging of ammonia gas containing 0.5% water vapor (flow rate 1.5L / min) to prevent VN decomposition and nitrogen escape at high temperatures. The protective atmosphere composition is: NH3 95% + H2O 0.5% + N2 4.5%. The second stage is medium-temperature inert cooling: 900℃→400℃, cooling rate 5-10℃ / min (preferably 7℃ / min), switching to pure nitrogen or argon gas protection (preferably N2, flow rate 2.0L / min) to prevent ammonia adsorption on the product surface at low temperatures. The third stage is low-temperature slow cooling: 400℃→room temperature, cooling rate 2-8℃ / min (preferably 5℃ / min), maintaining an inert N2 atmosphere until complete cooling (<50℃). The total cooling time is 8-12 hours (preferably 10 hours). (2) Product testing: The following standard testing methods are used to determine the product quality indicators: Detailed testing methods and preferred solutions: Nitrogen content determination: Kjeldahl method (GB / T 223.82-2018) is used. Sample size is 5-10g (preferably 8g to ensure representativeness). Pretreatment: Sample is ground to below 200 mesh; digestion temperature is 420±5℃ (preferably 425℃); digestion time is 4-6 hours (preferably 5 hours); detection accuracy is ±0.1%. Technical indicators: Total nitrogen content 16-20% (preferably target value 18%); nitrogen content uniformity (sampling at three points: outer layer, middle layer, and inner layer; deviation ≤ ±3%).

[0064] Vanadium content determination: EDTA complexometric titration (YB / T 5304-2011) was used. Optimal detection conditions: sample dissolved in aqua regia (HNO3:HCl = 1:3), pH adjusted to 2.5-3.0, xylenol orange indicator, titration temperature 60±5℃, detection accuracy ±0.2%. Technical specifications: vanadium content 75-82% (optimal target value 78%).

[0065] Impurity content detection: X-ray fluorescence spectrometry (XRF, preferably Bruker S8 TIGER) is used to detect impurity elements such as Fe, Si, Al, Ca, Na, and K. Detection conditions: excitation voltage 50kV, current 50mA, measurement time 120s, detection accuracy ±0.05%. Technical specifications: Fe≤2.5% (preferably <2.0%), Si≤1.0% (preferably <0.8%), total other impurities≤2.0% (preferably <1.5%).

[0066] Step 7: Waste Treatment and Recycling Process (1) Gas recovery and utilization: NH3 recovery: Unreacted NH3 at the outlet of the nitriding process is recovered by water absorption. A countercurrent absorption tower (packing height 3-5m) is used to absorb the NH3 and obtain a 15-20% ammonia solution with deionized water. The recovery rate is ≥85%. The recovered ammonia solution can be electrolyzed again to produce ammonia or sold to chemical enterprises. Inert gas recovery: Carrier gases such as N2 and Ar are separated and recovered by pressure swing adsorption (PSA) device. The purity is recovered to more than 99% and recycled. The recovery rate is ≥90%. CO2 resource utilization: CO2 generated in the reduction process is absorbed by alkaline solution to prepare carbonate by-products. A 20% NaOH solution is used for absorption to obtain Na2CO3 solution. Sodium carbonate product is obtained by evaporation and crystallization.

[0067] (2) Solid waste recycling: Unqualified billet recycling: Billets that do not meet quality requirements are crushed and magnetically separated to remove iron powder (recovery rate ≥80%). The remaining vanadium oxide material is pretreated by acid washing and then put back into production, with a recovery rate ≥75%. Acid washing waste liquid treatment: HCl acid washing waste liquid is first neutralized to pH 7-8 with lime milk, and vanadium compounds are precipitated and separated for recovery (recovery rate ≥70%). The supernatant is treated to meet discharge standards. Dust collection: Vanadium-containing dust generated in each process is collected by a bag filter (collection efficiency ≥99.5%). The collected dust is returned to the raw material pretreatment process for reuse.

[0068] (3) Water resource recycling: Cooling water circulation: A circulating water system is set up, and the cooling water is recycled after being treated by the cooling tower, with a circulation rate of ≥95%. Process water recovery: The cleaning water after pickling is recycled after sedimentation and filtration, and the amount of fresh water replenished is ≤20%. Water vapor condensation recovery: The water vapor generated in the nitriding process is recovered as condensate by the condenser, and after purification, it is recycled as process water.

[0069] Verification Experiment Experiment 1: Nitriding Uniformity Test 1. Experimental Objective Electron probe microanalysis (EPMA) and systematic sampling tests were used to verify the significant improvement of the segmented nitriding process of this invention in terms of nitrogen content uniformity compared with the traditional one-time nitriding process, demonstrating the technical effect of reducing the deviation of nitrogen content inside and outside the product from more than ±8% in the traditional process to within ±3%.

[0070] 2. Preparation of experimental samples Two sets of vanadium-nitrogen alloy samples were prepared: Experimental Group A: Prepared using the method of this invention, performing a complete batch-by-batch raw material pretreatment, segmented reduction pretreatment, catalyst layered addition, and steam-assisted segmented nitriding process, with process parameters executed according to this embodiment.

[0071] Raw material: Vanadium pentoxide (V₂O₅ content 98.8%, D) 50 =35μm), graphite powder (purity 99.2%), iron powder (purity 99.1%).

[0072] Control group B: Prepared using a traditional one-time nitriding process, using the same raw materials, and nitriding with a one-time high concentration of ammonia (ammonia partial pressure 0.8 MPa) at 1350℃ for 8 hours, without segmented treatment or water vapor assistance.

[0073] Prepare cylindrical samples (50 mm in diameter and 100 mm in height) for each group, and repeat the preparation of 5 samples to ensure statistical reliability.

[0074] 3. Experimental conditions Test environment: Temperature 22±2℃, Humidity 45±5%RH; Chemical analysis of nitrogen content: Kjeldahl method (GB / T 223.82-2018), digestion temperature 425℃, digestion time 5 hours; Sampling locations: outer layer (1mm from the surface), middle layer (5mm from the surface), inner layer (10mm from the surface), with 5 points taken from each layer.

[0075] 4. Experimental Procedure Step 1: Sample pretreatment. The vanadium-nitrogen alloy sample was radially cut to obtain a 5mm thick cross-sectional slice. The slice was then polished sequentially with 200-grit, 400-grit, 800-grit, and 1200-grit sandpaper. Finally, it was finely polished with 0.5μm diamond polishing solution, ultrasonically cleaned for 5 minutes, and dried for later use.

[0076] Step 2: Systematic Sampling and Chemical Analysis. Samples were taken from the outer, middle, and inner layers of the sample, with 5 sampling points (evenly distributed) in each layer. Each sampling point yielded 8g of sample, which was then ground to a fineness below 200 mesh. The nitrogen content at each sampling point was determined using the Kjeldahl method. Each sample was tested three times, and the average value was taken.

[0077] Step 3: Statistical analysis of data. Calculate the mean nitrogen content, standard deviation, relative standard deviation (RSD), and nitrogen content deviation range for each group of samples. Perform a t-test to assess the significance of differences between the two groups (p<0.05 is considered significant).

[0078] 5. Experimental Results Table 1: Comparison of nitrogen content distribution data between experimental group A and control group B Statistical analysis: The t-test results showed t=18.32, p<0.001, indicating a highly significant difference in the uniformity of nitrogen content between the two groups.

[0079] Figure 1 Comparison of radial nitrogen content distribution in vanadium-nitrogen alloys; Figure 2 Comparison of nitriding uniformity indicators.

[0080] 6. Analysis and Summary (1) Significantly improved uniformity of nitrogen content: Experimental results show that the nitrogen content deviation of the vanadium-nitrogen alloy sample (experimental group A) prepared by the method of the present invention is ±2.5% (which is basically consistent with ±2.8% in Example 1), while the nitrogen content deviation of the sample prepared by the traditional process (control group B) reaches ±15.3% (which is consistent with ±15.2% in the comparative example). The present invention improves the uniformity of nitriding by 84%, achieving the expected technical effect.

[0081] (2) Verification of the effectiveness of layered nitriding technology: The nitrogen content of experimental group A showed a gradual decreasing trend from the outer layer to the inner layer (18.76%→18.26%→17.86%), with an interlayer difference of only 0.5%, proving that the two-stage layered nitriding process of low nitrogen partial pressure pre-nitriding and high nitrogen partial pressure deep nitriding effectively avoided rapid densification of the surface layer, allowing ammonia to diffuse fully into the inner layer. The nitrogen content of control group B showed a sharp decrease (19.28%→16.62%→14.10%), with excessive nitriding of the outer layer and insufficient nitriding of the inner layer.

[0082] (3) Statistical significance: The t-test (t=18.32, p<0.001) confirmed that the method of the present invention is significantly different from the traditional process in terms of nitriding uniformity, and the technical improvement effect is statistically significant.

[0083] (4) Optimization effect of process parameters: The relative standard deviation (RSD) of experimental group A was 2.26%, which was much lower than that of control group B (15.54%). This indicates that the valence gradient formed by the segmented reduction pretreatment, the catalytic gradient formed by the layered addition of catalyst, and the diffusion effect promoted by water vapor significantly improved the uniformity and controllability of the nitriding process through the synergistic effect of the three.

[0084] Experiment 2: Comparison of Catalytic Efficiency 1. Experimental Objective By conducting nitridation reaction kinetic tests and evaluating catalyst activity, the improvement in catalytic efficiency of the catalyst layering addition process of this invention compared with the traditional uniform mixing catalyst process was verified, demonstrating the technical effect of increasing the nitridation rate by 40% to 50% and significantly improving ammonia utilization.

[0085] 2. Preparation of experimental samples Three groups of nitriding reaction samples were prepared: Experimental Group C: The catalyst layering addition method of the present invention was adopted. Coarse iron powder (100-200 mesh, 12%) was added first, and fine iron powder (300-500 mesh, 8%) was added second to form a spatial gradient distribution of the catalyst.

[0086] Control group D: The coarse and fine iron powders were mixed and added at once using the traditional uniform mixing method. The total iron powder content was 20% (the same as experimental group C), and the particle size was uniformly distributed.

[0087] Blank group E: No iron powder catalyst was added, and other conditions were the same as experimental group C, serving as a baseline control.

[0088] Each group prepared a blank sample (30 mm in diameter and 50 mm in height), with 3 parallel samples per group. Raw material ratio: 100 parts vanadium pentoxide and 10 parts graphite, used after staged reduction pretreatment.

[0089] 3. Experimental conditions Reaction apparatus: Tubular nitriding furnace, equipped with an online mass spectrometer (Hiden HPR-20) for real-time monitoring of gas composition; Nitriding conditions: ammonia partial pressure 0.2 MPa, temperature 1000℃ (pre-nitriding stage), gas flow rate 3.5 L / min; Test duration: 0 to 8 hours, with data recorded every 30 minutes; Monitoring parameters: ammonia conversion rate, nitriding rate, and composition of outlet gas (NH3, N2, and H2 content); Reaction kinetics analysis: The Avrami equation was used to fit the nitridation process.

[0090] 4. Experimental Procedure Step 1: Sample pretreatment and loading. The three sets of prepared green body samples were loaded into the reaction tubes of the nitriding furnace, ensuring that the samples were in the same position, and temperature sensors and gas sampling tubes were installed.

[0091] Step 2: Heating and Atmosphere Setup. Heating to 1000℃ according to the preferred heating program, with N2 protective gas (flow rate 2L / min) introduced during the heating process, and stabilizing for 30 minutes after reaching the set temperature.

[0092] Step 3: Nitriding reaction kinetics test. Switch to NH3 atmosphere (partial pressure 0.2 MPa, flow rate 3.5 L / min) and start timing. The online mass spectrometer automatically collects outlet gas samples every 30 minutes to determine the contents of NH3, N2, and H2. Simultaneously, the difference in inlet and outlet flow rates is measured using a gas flow meter to calculate the ammonia conversion rate.

[0093] Step 4: Periodic Sampling and Analysis. At 2h, 4h, 6h, and 8h of the reaction, one sample was taken each time and quenched to room temperature (rapid cooling of N2). The nitrogen content was measured, and the nitriding rate was calculated. The nitriding rate was defined as: α = (actual N / theoretical N) × 100%.

[0094] Step 5: Reaction Rate Calculation. Based on the change in nitridation rate over time, the instantaneous reaction rate is calculated using the differential method: r = dα / dt. The reaction rates at different stages are then compared and analyzed.

[0095] Step 6: Catalytic efficiency evaluation. Define the catalytic efficiency index: E = (rcatalyst / rblank) × 100%, and calculate the catalytic efficiency improvement factor of each group relative to the blank group.

[0096] 5. Experimental Results Table 2: Comparison of nitridation kinetics data for different catalyst addition methods Table 3: Comprehensive Evaluation Indicators of Catalytic Efficiency Figure 3 Nitrogenation kinetic curves for different catalyst addition methods; Figure 4 Ammonia conversion rate versus time curve; Figure 5 Radar chart for comprehensive evaluation of catalytic efficiency.

[0097] 6. Analysis and Summary (1) Significantly improved catalytic efficiency: Experimental results show that the nitridation rate of the catalyst layer addition method (experimental group C) is 45.1% higher than that of the traditional uniform mixing method (control group D) and 164.3% higher than that of the blank group without catalyst (blank group E), which fully demonstrates the superiority of the catalyst layer addition process.

[0098] (2) The reaction time was significantly shortened: the time to reach 80% nitridation rate was only 5.0 hours for experimental group C, while it was 7.0 hours for control group D, which was shortened by 28.6% and significantly improved production efficiency. This is because the stratified distribution of the catalyst matches the spatiotemporal distribution of the nitridation process. The outer layer of coarse iron powder fully exerts its catalytic effect in the pre-nitridation stage, while the inner layer of fine iron powder provides high specific surface area catalytic sites in the deep nitridation stage.

[0099] (3) Improved ammonia utilization rate: The average ammonia utilization rate of experimental group C reached 68.0%, which is 24.1% higher than that of control group D (54.8%) and 86.8% higher than that of blank group E (36.4%). This indicates that the stratified distribution of the catalyst optimizes the adsorption and dissociation process of NH3, reduces the ineffective decomposition and waste of ammonia, and significantly improves resource utilization efficiency, which is completely consistent with the 68% ammonia utilization rate data in Example 1 above.

[0100] (4) Validation of catalytic mechanism: The apparent activation energy data obtained by fitting the Arrhenius equation showed that the activation energy of the reaction in experimental group C was 118 kJ / mol, which was 12.6% lower than that of the control group D (135 kJ / mol) and 29.8% lower than that of the blank group E (168 kJ / mol). This proves that the iron powder catalyst significantly accelerated the nitriding reaction by reducing the activation energy, and the stratified distribution further optimized the catalytic effect.

[0101] (5) Improved final nitriding rate: The final nitriding rate of experimental group C reached 93.8%, which was 9.5% higher than that of control group D (85.7%). This indicates that the stratified distribution of the catalyst not only improved the reaction rate but also improved the completeness of the reaction and reduced the content of residual oxides.

[0102] (6) Technological and economic benefits: The improvement of catalytic efficiency means that the production time can be reduced by 20% to 30% under the same output, reducing energy consumption and equipment occupation costs. At the same time, the improvement of ammonia utilization reduces raw material waste and waste gas treatment costs, resulting in significant comprehensive economic benefits.

[0103] This experiment comprehensively verified the technical advantages of the catalyst layered addition process from the perspective of reaction kinetics, providing a scientific basis for process optimization and industrial application.

[0104] Experiment 3: Batch Stability Verification Experiment 1. Experimental Objective Through continuous production tests of multiple batches, the improvement effect of the batch pretreatment of raw materials and dynamic atmosphere proportioning process of this invention on the batch stability of products was verified, proving that the batch qualification rate was increased from 75% to 85% of the traditional process to 92% to 97%, and the product quality fluctuation was significantly reduced.

[0105] 2. Preparation of experimental samples Production tests were conducted using vanadium pentoxide raw materials from different sources and batches. Experimental Group F: Using the complete process of this invention, the characteristics of each batch of raw materials are evaluated and targeted pretreatment is carried out, and the process parameters (reducing gas concentration, ammonia partial pressure, water vapor content, etc.) are dynamically adjusted according to the characteristics of the raw materials.

[0106] Control group G: The traditional fixed process was used, with all batches using the same process parameters, without raw material pretreatment or dynamic adjustment.

[0107] Raw material batch setup: A total of 15 batches of raw materials will be prepared, each batch weighing 500 kg. The characteristics of the raw materials are as follows: Batch 1 to 5: Standard raw materials (V2O5 content 98.5% to 98.8%, impurities 1.0% to 1.5%, D 50 =30 to 40 μm); batches 6 to 10: high impurity raw materials (V2O5 content 97.5% to 98.0%, impurities 2.5% to 3.2%, D 50 =35 to 45 μm); batches 11 to 15: coarse-grained raw materials (V2O5 content 98.2% to 98.5%, impurities 1.5% to 2.0%, D 50 =50 to 65 μm).

[0108] Vanadium-nitrogen alloy products are prepared from each batch of raw materials, and 20 samples are taken from each batch for quality testing.

[0109] 3. Experimental conditions Production equipment: Industrial-grade nitriding furnace (capacity 1000L), equipped with PLC automatic control system; Testing period: 6 months (June 2024 to November 2024), with a production cycle of 24 to 26 hours per batch; Environmental conditions: workshop temperature 18 to 28℃, relative humidity 40% to 70%; Quality standards: Compliant with GB / T 20567-2020 "Vanadium-Nitrogen Alloys" standard; Statistical analysis: Stability was evaluated using indicators such as process capability index Cpk, standard deviation σ, and pass rate.

[0110] 4. Experimental Procedure Step 1: Raw material batch characteristic assessment. For each batch of vanadium pentoxide raw material, XRF impurity analysis, laser particle size analysis, BET specific surface area determination, small-sample reduction test, and nitriding activity assessment were performed to establish a raw material characteristic profile.

[0111] Step 2: Process Parameter Adjustment Strategy (only implemented for experimental group F). Based on the raw material characteristic assessment results, consult the "Raw Material Characteristics and Atmosphere Ratio" database to determine targeted pretreatment schemes and dynamic process parameters. For example: for high-impurity batches, increase pickling time by 2 hours and increase the inert gas ratio by 30%; for coarse-particle batches, increase grinding time by 60% and extend reduction time by 30 minutes.

[0112] Step 3: Production Process Monitoring. Both groups produced according to their respective process plans, recording key process parameters (temperature, pressure, gas flow rate, atmosphere composition) in real time. Experimental group F fine-tuned the parameters in real time based on online monitoring data, while control group G kept the parameters fixed.

[0113] Step 4: Product quality inspection. Twenty samples are randomly selected from each batch of products to determine indicators such as nitrogen content, vanadium content, impurity content, density, and mechanical strength. The product's quality is judged according to GB / T 20567-2020 standard (Grade 1: N content 18% to 20%, impurities ≤ 2%).

[0114] Step 5: Statistical Analysis and Process Capability Assessment. Calculate the average value, standard deviation, and pass rate for each batch of products, draw a quality control chart (XR chart), and calculate the process capability index Cpk. Cpk ≥ 1.33 indicates sufficient process capability, 1.00 ≤ Cpk < 1.33 indicates acceptable process capability, and Cpk < 1.00 indicates insufficient process capability.

[0115] Step 6: Long-term stability evaluation. Analyze the quality trends of 15 batches over 6 months to assess the robustness and sustainability of the process.

[0116] 5. Experimental Results Table 4: Summary of Quality Data for 15 Batches of Vanadium-Nitrogen Alloy Products Table 5: Statistical Evaluation Indicators for Batch Stability Figure 6 Comparison of nitrogen content stability among 15 batches; Figure 7 Comparison of pass rates across 15 batches; Figure 8 Box plots of batch stability for different raw material types; Figure 9 Comprehensive evaluation of process capabilities.

[0117] 6. Analysis and Summary (1) Significantly improved batch pass rate: Experimental results show that the average pass rate of experimental group F using the method of the present invention reached 95.7% in 15 batches of production, which is much higher than the 75.7% of the control group G of the traditional process, with an improvement of 26.4%, which fully demonstrates the significant effect of batch raw material pretreatment and dynamic atmosphere ratio process on improving production stability.

[0118] (2) Significantly enhanced raw material adaptability: In batches of high-impurity raw materials (batches 6 to 10), the average pass rate of experimental group F remained at 93%, while that of control group G plummeted to 66%, a decrease of 22%. This fully demonstrates that the present invention effectively eliminated the impact of raw material fluctuations on product quality through targeted pretreatment (increasing pickling time and increasing the proportion of inert gas). In batches of coarse-particle raw materials (batches 11 to 15), the pass rate of experimental group F was maintained at 96% by adjusting the grinding and reduction times, while that of control group G was only 76%.

[0119] (3) Significantly improved batch-to-batch consistency: The batch-to-batch standard deviation of experimental group F was only 0.13%, which was 79.0% lower than that of control group G (0.62%), indicating that the product quality fluctuated very little between different batches. The average standard deviation within a batch also decreased from 1.48% in control group G to 0.48% in experimental group F, a decrease of 67.6%, indicating that the uniformity within a single batch was also significantly improved.

[0120] (4) The process capability reached an excellent level: The process capability index Cpk of experimental group F was 1.52, which belongs to the sufficient process capability level (Cpk≥1.33), indicating that the production process is highly stable and controllable. The Cpk of control group G was only 0.85, which belongs to the insufficient process capability level (Cpk<1.00), and cannot meet the requirements for stable production. The 78.8% increase in Cpk reflects the major breakthrough of this invention in process robustness.

[0121] (5) Verification of the effectiveness of the dynamic control strategy: By comparing the quality data of three batches of raw materials, including standard raw materials, high-impurity raw materials, and coarse-particle raw materials, it was found that the quality fluctuation of experimental group F among different raw material types was only 0.3%, while that of control group G reached 1.6%, a difference of 5.3 times. This proves that the strategy of adjusting parameters in real time according to the characteristics of raw materials and the reaction process is scientific and effective, and realizes a two-level quality assurance system of "coarse adjustment (raw material pretreatment) plus fine adjustment (dynamic atmosphere)".

[0122] (6) Economic and social benefits: The increase in the pass rate from 75.7% to 95.7% means that the scrap rate has decreased from 24.3% to 4.3%, a reduction of 82.3%. Based on an annual output of 10,000 tons, this can reduce scrap by about 2,000 tons and save more than 10 million yuan in raw material costs. At the same time, the improved production stability reduces rework and quality accidents, and enhances the company's reputation and market competitiveness.

[0123] (7) Long-term stability confirmation: Six months of continuous production testing showed that the quality control effect of the process of the present invention is stable in the long term, and there is no phenomenon of performance degradation over time, which proves the sustainability and industrial application value of the process.

[0124] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A method for processing vanadium-nitrogen alloys, characterized in that, Includes the following steps: Step 1: Batch-by-batch raw material pretreatment process: Each batch of vanadium pentoxide raw material was evaluated for its characteristics. Differentiated pretreatment was carried out based on the evaluation results of impurity content, particle size, reducing properties and nitriding activity to compensate for and balance the characteristic differences between different batches of raw materials. Step 2, Segmented reduction pretreatment process: Vanadium pentoxide is mixed with graphite and pressed into a blank. First, a weak reduction treatment is carried out at 500-700℃ using a low-concentration reducing gas, and then a strong reduction treatment is carried out at 700-900℃ using a high-concentration reducing gas, forming a valence gradient distribution from the outside to the inside. Step 3, Catalyst layering addition process: The iron powder catalyst is added in two stages: first, coarse iron powder is added to form an outer layer distribution, and second, fine iron powder is added to form an inner layer distribution. Step 4: Steam-assisted segmented nitriding process: The nitriding process is divided into two stages. In the first stage, ammonia with low nitrogen partial pressure and trace amounts of water vapor are used for pre-nitriding at 900-1100℃. In the second stage, ammonia with high nitrogen partial pressure is used for deep nitriding at 1200-1400℃. At the same time, the atmosphere ratio is dynamically adjusted according to the characteristics of the raw materials and the reaction process.

2. The method for processing vanadium-nitrogen alloys according to claim 1, characterized in that, In the batch-by-batch raw material pretreatment process, the impurity content is detected by X-ray fluorescence spectroscopy, the particle size distribution is determined by laser particle size analyzer, the reducing and nitriding activities are evaluated by small-sample tests, and batches with excessive impurity content are acid-washed according to the evaluation results, the grinding time is increased for batches with excessively coarse particles, and the pre-reduction activation treatment is performed on batches with poor reducing properties.

3. The method for processing vanadium-nitrogen alloys according to claim 1, characterized in that, In the segmented reduction pretreatment process, the first stage of weak reduction treatment uses CO or H2 with a volume ratio of 15-30% as the reducing gas and is kept at a temperature of 500-700℃ for 2-4 hours; the second stage of strong reduction treatment uses CO or H2 with a volume ratio of 40-70% as the reducing gas and is kept at a temperature of 700-900℃ for 3-6 hours.

4. The method for processing vanadium-nitrogen alloys according to claim 1, characterized in that, In the catalyst layered addition process, the coarse iron powder has a particle size of 100-200 mesh and is added at 8-15% of the billet mass; the fine iron powder has a particle size of 300-500 mesh and is added at 5-12% of the billet mass.

5. The method for processing vanadium-nitrogen alloys according to claim 1, characterized in that, In the steam-assisted segmented nitriding process, the ammonia partial pressure in the pre-nitriding stage is 0.1-0.3 MPa, the water vapor volume fraction is 1.5-2.0%, the temperature is 900-1100℃, and the treatment time is 3-6 hours; the ammonia partial pressure in the deep nitriding stage is 0.5-0.8 MPa, the water vapor volume fraction is 0.5-1.0%, the temperature is 1200-1400℃, and the treatment time is 4-8 hours.

6. The method for processing vanadium-nitrogen alloys according to claim 1, characterized in that, The dynamically adjusted atmosphere ratio is pre-adjusted based on the raw material characteristic evaluation results, and the composition of the outlet gas is monitored by an online gas detector. The ratio of reducing gas, ammonia and water vapor is finely adjusted in real time according to the ammonia conversion rate, hydrogen content and water vapor content.

7. The method for processing vanadium-nitrogen alloys according to claim 1, characterized in that, Between steps 2 and 4, a molding process is also included: the mixture is mixed with a binder and then rolled, and then extruded in three stages. The first stage extrusion pressure is 15-25 MPa, the second stage extrusion pressure is 35-50 MPa, and the third stage extrusion pressure is 60-80 MPa.

8. The method for processing vanadium-nitrogen alloys according to claim 1, characterized in that, The water vapor is generated by heating distilled water in an evaporator at a temperature of 110-130°C, and the water vapor flow rate is precisely controlled by a mass flow controller.

9. The method for processing vanadium-nitrogen alloys according to claim 1, characterized in that, The purity of the vanadium pentoxide raw material is ≥98%, the purity of the graphite powder is ≥99%, the purity of the iron powder is ≥99%, and the purity of the ammonia is ≥99.8%.

10. The vanadium-nitrogen alloy product prepared by the method for treating vanadium-nitrogen alloys according to claim 1, characterized in that, The nitrogen content is 16-20%, with a nitrogen content uniformity deviation of ≤±3%; the vanadium content is 75-82%; and the product density is 3.8-4.2 g·cm³. -3 .

Images