Resistance reducing salt for reducing QPQ nitriding salt bath cyanogen and preparation process and application method thereof

Abstract

The invention relates to the technical field of QPQ, and discloses a resistance-reducing salt for reducing QPQ nitriding salt bath cyanogens and a preparation process and application method thereof, and the resistance-reducing salt comprises a mixture formed by combining target raw materials; the target raw materials comprise potassium chloride, potassium carbonate, sodium chloride, sodium nitrate, potassium nitrate, sodium nitrite and battery-grade lithium carbonate. When the resistance-reducing salt is added into the nitriding salt solution, cyanide in the nitriding salt solution can be effectively reduced, other components are not influenced, the balance of the proportion of ions in the whole nitriding salt solution can be ensured, and component segregation is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of QPQ, and specifically relates to a resistance-reducing salt for reducing cyanide radical in QPQ nitriding salt bath, its preparation process and application method. Background Art

[0002] The QPQ technology is a composite process composed of liquid nitriding and liquid oxygenation processes. The metal surface after QPQ treatment has extremely high wear resistance and corrosion resistance at the same time. At present, this technology is widely used in industries such as automobiles, construction machinery, petroleum industry, aerospace, and military industry.

[0003] The core process of the QPQ technology is liquid nitriding. For example, in the QPQ nitriding salt bath - nitriding treatment is carried out in the salt bath. The metal workpiece is placed in a salt bath medium (i.e., nitriding salt solution) containing elements such as nitrogen and carbon. Under certain temperature and time conditions, elements such as nitrogen and carbon penetrate into the metal surface to form a nitrided layer with high hardness, high wear resistance, and high corrosion resistance. Through subsequent processes such as polishing and secondary quenching, the surface quality and performance of the workpiece are further improved.

[0004] Among them, the basic reaction formula of the nitriding salt solution is as follows:

[0005]

[0006] It can be seen from this that liquid nitriding relies on the decomposition of cyanate radical (CNO - ) to generate active nitrogen atoms ([N]) to achieve the strengthening of the infiltration layer. However, cyanide radical (CN - ) is inevitably generated during this process. As the use time of the salt bath extends, the concentration of CN - gradually accumulates. When it exceeds the critical threshold, it will cause a significant decrease in the activity of the salt bath, manifested as insufficient infiltration layer thickness, increased surface looseness, and even the occurrence of corrosion defects on the workpiece surface, causing irreparable damage to the workpiece to be processed. In addition, the existence of high-concentration CN - poses a threat to the safety of the production environment, and its toxicity may cause environmental protection compliance risks. Therefore, developing a resistance-reducing salt that can efficiently degrade CN - and its supporting process is not only the key technical requirement for improving the quality of QPQ treatment, but also an inevitable choice for the industry to achieve green upgrading.

[0007] According to the reaction mechanism, to reduce the content of CN - , an oxidizing resistance-reducing agent is transported into the nitriding salt bath, and its mechanism is as follows: CN - + resistance-reducing agent → CO2↑+ N2↑+….

[0008] Based on this, at present, in the QPQ process, CN -The control mainly relies on two categories of traditional methods: one is to remove the residual CN on the workpiece surface through the strong oxidizing property of an oxidation salt bath (such as a nitrate system); - the other is to introduce air into the nitriding salt bath to oxidize and decompose CN by using oxygen; - . However, for the former, an additional oxidation salt bath needs to be configured, which not only increases the equipment and energy consumption costs, but also introduces new pollutants due to the high-temperature volatility of nitrates; although the latter has the advantage of in-situ treatment, the oxygen introduction efficiency is low (the CN - degradation rate ≤ 0.05% / h), the reaction kinetics is slow (based on the monitoring data of the previous QPQ production furnace indicators, under normal production conditions, compressed air is continuously introduced for six months, and the cyanide ion concentration hardly changes, with low efficiency and long-term need), and the introduction of excessive oxygen may exacerbate the salt bath composition fluctuation, resulting in deterioration of nitriding uniformity. Moreover, during the process of introducing air, the salt solution tumbles, easily causing salt solution splashing and scalding production personnel, posing a safety hazard and being unfavorable for safe production. More critically, both traditional methods require additional treatment links outside the nitriding process, and cannot achieve real-time dynamic regulation of CN - , making it difficult to adapt to the requirements of continuous production. Summary of the Invention

[0009] The present invention aims to provide a resistance-reducing salt for reducing cyanide in the QPQ nitriding salt bath, its preparation process and application method, which can effectively reduce the cyanide in the nitriding salt solution without affecting other components, can ensure the balance of the ion ratios in the overall nitriding salt solution, and avoid component segregation.

[0010] To achieve the above object, the present invention provides the following basic solutions.

[0011] Solution 1

[0012] The resistance-reducing salt for reducing cyanide in the QPQ nitriding salt bath comprises a mixture composed of target raw materials; the target raw materials include: potassium chloride, potassium carbonate, sodium chloride, sodium nitrate, potassium nitrate, sodium nitrite, battery-grade lithium carbonate.

[0013] Further, the weight percentages of the respective components of the target raw materials in the mixture are: potassium chloride 5% - 25%, potassium carbonate 5% - 35%, sodium chloride 2% - 22%, sodium nitrate 1% - 10%, potassium nitrate 0.5% - 5%, sodium nitrite 5% - 20%, battery-grade lithium carbonate 1% - 10%.

[0014] Further, the melting point of the mixture is not higher than 580°C.

[0015] Solution 2

[0016] The preparation process of the resistance-reducing salt for reducing cyanide in the QPQ nitriding salt bath, which is used to prepare the resistance-reducing salt for reducing cyanide in the QPQ nitriding salt bath as described in Solution 1; includes the following steps:

[0017] Step 1, mixing; successively add each component of the target raw materials into a stirring tank, then start a stirrer to make each component evenly mixed and obtain a basic mixture.

[0018] Step 2, smelting; put the basic mixture into a crucible, heat it to 500 - 550 °C to make it melt; keep it warm for 1 - 2 h to ensure that there is no unmelted substance at the bottom of the crucible and obtain a molten salt solution.

[0019] Step 3, cooling; introduce compressed air into the molten salt solution and stir, take out the salt solution and let it cool naturally to obtain a mixture, which is the resistance - reducing salt for reducing the cyanide radical in the QPQ nitriding salt bath.

[0020] Step 4, crushing; crush the resistance - reducing salt obtained in Step 3 into blocks and bag it for standby.

[0021] Further, in Step 1, the stirring time is 5 - 120 minutes.

[0022] Further, the crucible is a crucible made of pure titanium and is heated by a pit - type furnace; the compressed air is dried compressed air.

[0023] Further, in Step 4, the size of the crushed blocks is less than 5 cm * 5 cm * 5 cm.

[0024] Solution Three

[0025] Application method of the resistance - reducing salt for reducing the cyanide radical in the QPQ nitriding salt bath, including the following steps:

[0026] Step One, chemical analysis; detect the content of cyanide radical in the QPQ nitriding salt bath according to the chemical titration method.

[0027] Step Two, calculation; calculate the mass of the resistance - reducing salt to be added based on the mass of the nitriding salt solution in the QPQ nitriding salt bath.

[0028] Step Three, addition; batch - add the resistance - reducing salt prepared by the preparation process of the resistance - reducing salt for reducing the cyanide radical in the QPQ nitriding salt bath as described in Solution Two into the nitriding salt solution to make it fully react with the nitriding salt solution.

[0029] Further, in Step Two, when calculating the mass of the resistance - reducing salt to be added, it is calculated based on the following formula:

[0030] x = ΔC·M / 100·k;

[0031] Wherein, x is the mass of the resistance-reducing salt to be added, with the unit of kg; M is the initial mass of the nitriding salt solution, with the unit of kg; ΔC is the target percentage reduction of cyanide radical, with the unit of %; k is the percentage reduction of cyanide radical when adding 1% of the resistance-reducing salt to the salt bath mass, and its value range is 0.1% - 0.3%.

[0032] Further, in step three, when adding the resistance-reducing salt to the nitriding salt solution, the furnace temperature is set to 450 - 550 °C; and in the batch addition, after each addition, wait until the liquid surface is calm before adding again. After all the required resistance-reducing salt is added, set the furnace temperature to 580 - 620 °C, and set the heat preservation time to 30 min - 180 min; then restore it to the operating temperature.

[0033] The working principle and advantages of the present invention are as follows:

[0034] The resistance-reducing salt for reducing cyanide radical in the QPQ nitriding salt bath of the present invention, its preparation process and application method can effectively reduce the cyanide radical in the nitriding salt solution without affecting other components, can ensure the balance of the ion ratio in the overall nitriding salt solution, and avoid component segregation. The key points are as follows:

[0035] For Solution 1: The resistance-reducing salt provided by this solution can form a multi-component synergistic oxidation system to achieve a relatively high cyanide reduction efficiency. Among them, a gradient oxidation system can be constructed by setting sodium nitrate, potassium nitrate, and sodium nitrite. Nitrate (MeNO3) serves as the main oxidant and releases strongly oxidizing active oxygen atoms [O] at high temperatures (500 - 550 °C) to directly oxidize CN - to and N2; Nitrite (MeNO2): As an intermediate oxidation state, it can both react with CN - and can be re-oxidized by oxygen or nitrate to to form an oxidation cycle, reducing the consumption of the oxidant. Then, in combination with battery-grade lithium carbonate (Li2CO3), its lithium ions (Li + ) can reduce the viscosity of the molten salt, enhance the ion mobility of the oxidant, and at the same time form a eutectic phase (the melting point is reduced to below 400 °C) with to improve the fluidity of the salt bath and avoid local enrichment of CN - . Under the synergy of multiple components, this resistance-reducing salt can achieve hierarchical degradation of CN - and realize rapid degradation of cyanide radical and efficient removal of cyanide radical.

[0036] And during this process, due to the presence of potassium chloride, potassium carbonate, and sodium chloride in the formulation, their proportions (totaling 50%-70%) highly match the melting point and ionic environment of conventional QPQ nitriding base salts (such as potassium cyanate KCNO). Among them, the potassium chloride / sodium chloride ratio (5%-25% vs. 2%-22%) controls the viscosity of the molten salt, avoiding a decrease in fluidity caused by the addition of oxidants (excessively high viscosity will hinder the diffusion of [N]); potassium carbonate (5%-35%) can neutralize acidic intermediates (such as HNO2) generated by the oxidation reaction, maintaining the salt bath pH≥9.5 and preventing the nitriding active atom [N] from being protonated and inactivated. With such settings, while degrading CN - at the same time, the base salt components composed of potassium chloride, potassium carbonate, and sodium chloride can reduce the imbalance of the salt bath components through ionic compensation (such as K + supplementation), ensuring the balance of the ion ratios in the overall nitriding salt solution, avoiding component segregation, and avoiding the problem of loose nitrided layers caused by traditional resistance-reducing salts.

[0037] Regarding Solution 2: By applying this preparation method, reliable resistance-reducing salt products can be prepared. Among them, through sufficient stirring in Step 1, the components can be fully premixed, reducing local component segregation during subsequent smelting. Through the high-temperature smelting in Step 2, the components can be promoted to form a eutectic mixture, and using a pure titanium crucible to replace traditional graphite or steel containers can avoid the reaction of molten salts (especially nitrates and nitrites) with the crucible material at high temperatures to generate carbides or metal impurities (such as Fe 3+ ), ensuring the purity of the eutectic mixture. By introducing dry compressed air in Step 3, the formation of salt crystals can be accelerated; at the same time, the dry air can prevent the hydrolysis of the salt solution caused by the intrusion of water vapor, and trace amounts of oxygen can pre-oxidize CN - (assisting in cyanide reduction). Then, through Step 4, the resistance-reducing salt is crushed into regular blocks, facilitating product application.

[0038] Regarding Solution 3: By adding the resistance-reducing salt to the nitriding salt solution in this solution, the resistance-reducing salt and cyanide ions can directly react directionally without affecting other components, ensuring the balance of the ion ratios of K + , Na + etc. in the overall nitriding salt solution, avoiding component segregation from affecting the performance of the special salt and the quality of the treated products, being able to rapidly degrade cyanide ions, efficiently remove cyanide ions, and achieve the purpose of restoring the activity of the salt solution. Moreover, by applying this solution, the accurate quantitative regulation of cyanide ions can be realized, meeting the requirements of continuous production. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the preparation process flow of the resistance-reducing salt for reducing cyanide ions in the QPQ nitriding salt bath, its preparation process, and the application method according to the embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0040] The following is a further detailed description through specific embodiments:

[0041] Example 1

[0042] The resistance-reducing salt for reducing cyanide in the QPQ nitriding salt bath includes a mixture composed of target raw materials; the target raw materials include: potassium chloride, potassium carbonate, sodium chloride, sodium nitrate, potassium nitrate, sodium nitrite, and battery-grade lithium carbonate.

[0043] The weight percentages of the components of the target raw materials in the mixture are: potassium chloride 5%-25%, potassium carbonate 5%-35%, sodium chloride 2%-22%, sodium nitrate 1%-10%, potassium nitrate 0.5%-5%, sodium nitrite 5%-20%, and battery-grade lithium carbonate 1%-10%.

[0044] In this embodiment, based on the actual situation of formula test development, to ensure that the ratio of K + , Na + is balanced with the nitriding salt and has a high ability to degrade cyanide, while the reaction intensity is moderate, the weight percentages of the components of the target raw materials are preferably: potassium chloride 20%, potassium carbonate 25%, sodium chloride 20%, sodium nitrate 8%, potassium nitrate 10%, sodium nitrite 12%, and battery-grade lithium carbonate 5%

[0045] The melting point of the mixture is not higher than 580°C. This melting point setting is adapted to the working temperature of the nitriding salt bath, which can ensure that the resistance-reducing salt is completely melted within the temperature range of the nitriding salt bath, achieve molten state homogenization, effectively improve the cyanide reduction efficiency, and avoid the risk of component segregation.

[0046] As shown in the appendix Figure 1 , this embodiment also provides a preparation process for the resistance-reducing salt for reducing cyanide in the QPQ nitriding salt bath, which is used to prepare the resistance-reducing salt for reducing cyanide in the QPQ nitriding salt bath as described above; it includes the following steps:

[0047] Step 1, mixing materials; according to the weight percentages of the components of the target raw materials, add the components of the target raw materials into the stirring tank in sequence, and then start the stirrer to make the components mix evenly and obtain a basic mixture.

[0048] Among them, the stirring time is 5-120 minutes.

[0049] In this embodiment, various component raw materials with the weights weighed according to the weight percentages of the components of the target raw materials are added into the stirring tank in sequence, and the total mass is 50 kg. Then start the stirrer, and the stirring time is set to 60 minutes, which can fully mix the raw materials.

[0050] Step 2, smelting; Put the basic mixture into a crucible, heat it to 500 - 550 °C to melt it; Keep it warm for 1 - 2 h to ensure that there is no unmelted substance at the bottom of the crucible and obtain molten salt solution.

[0051] Among them, the crucible is a φ500*700 crucible made of pure titanium and is heated by a pit furnace.

[0052] In this embodiment, the basic mixture is heated to 530 °C and kept warm for 1 h.

[0053] Step 3, cooling; Pass compressed air into the molten salt solution and stir for 3 min, take out the salt solution and place it in a stainless - steel basin to cool naturally, and obtain a mixture, which is the resistance - reducing salt for reducing the cyanide radical in the QPQ nitriding salt bath.

[0054] The compressed air used is dried compressed air.

[0055] Step 4, crushing; Use a jaw crusher to crush the resistance - reducing salt obtained in Step 3 into blocks and bag it for standby.

[0056] The size of the crushed blocks is less than 5 cm * 5 cm * 5 cm.

[0057] This embodiment also provides an application method of the resistance - reducing salt for reducing the cyanide radical in the QPQ nitriding salt bath, including the following steps:

[0058] Step 1, chemical analysis; Detect the content (mass percentage) of cyanide radical in the QPQ nitriding salt bath according to the chemical titration method.

[0059] In this embodiment, the existing chemical titration method is used for detection, and no detailed description is given here. The content of cyanide radical in the detected QPQ nitriding salt bath is 3.2%.

[0060] Step 2, calculation; Calculate the mass of the resistance - reducing salt to be added based on the mass of the nitriding salt solution in the QPQ nitriding salt bath.

[0061] Specifically, when calculating the mass of the resistance - reducing salt to be added, it is calculated based on the following formula:

[0062] x = ΔC·M / 100·k;

[0063] In the formula, x is the mass of the resistance - reducing salt to be added, in kg; M is the initial mass of the nitriding salt solution, in kg; ΔC is the target percentage reduction of cyanide radical, in %; k is the percentage reduction of cyanide radical when adding 1% of the resistance - reducing salt to the mass of the salt bath, and its value range is 0.1% - 0.3%. That is, for every 1% of the mass of the resistance - reducing salt added to the nitriding salt bath (nitriding salt solution) in the furnace, the cyanide radical can be reduced by 0.1% - 0.3%.

[0064] For example, if it is necessary to reduce the cyanide ion concentration by ΔC = 1%, and the initial mass M of the nitriding salt solution is 150 kg, taking k = 0.1, then x = 1×150 / 100×0.1 = 15 kg; that is, 15 kg of resistance-reducing salt needs to be added.

[0065] Step 3, addition; the resistance-reducing salt prepared by the preparation process of the resistance-reducing salt for reducing the cyanide in the QPQ nitriding salt bath as described above is added to the nitriding salt solution in batches to make it fully react with the nitriding salt solution.

[0066] In this step, when adding the resistance-reducing salt to the nitriding salt solution, the furnace temperature is set to 450 - 550 °C (in this embodiment, preferably 540 °C); and in the batch addition, after each addition, wait until the liquid surface is calm before adding again. After all the required resistance-reducing salt has been added, set the furnace temperature to 580 - 620 °C (in this embodiment, preferably 600 °C), and the heat preservation time is set to 30 min - 180 min (in this embodiment, preferably 30 min); then restore it to the use temperature (in this embodiment, set to 560 °C).

[0067] The nitriding salt solution after adding the resistance-reducing salt is tested, and its cyanide ion content is 2%, reaching the target percentage of cyanide reduction and slightly increasing.

[0068] The resistance-reducing salt for reducing the cyanide in the QPQ nitriding salt bath, its preparation process and application method provided in this embodiment can effectively reduce the cyanide in the nitriding salt solution without affecting other components, can ensure the balance of the ion ratios in the overall nitriding salt solution, and avoid component segregation.

[0069] The following combines 1 comparative example to further illustrate the application effect of this embodiment.

[0070] Comparative Example 1 - Applying this resistance-reducing salt in a small-scale test equipment to verify the use performance and effect of this resistance-reducing salt formula:

[0071] Referring to Example 1, the difference from Example 1 is that the crucible model of the loaded nitriding salt solution is type crucible, the loaded nitriding salt solution is 45 kg, its cyanide ion content is 2.4%, and the mass of the added resistance-reducing salt is 2.25 kg; other technical features are the same as those in Example 1.

[0072] The nitriding salt solution after adding the resistance-reducing salt in Comparative Example 1 is tested, and its cyanide ion content is 1.8%.

[0073] From the data of this comparative example, it can be known that when applied in a small-scale test equipment, adding 5% of the resistance-reducing salt can effectively reduce the cyanide by 0.6%, achieving the expected effect of the formula.

[0074] Example Two

[0075] A resistance-reducing salt for reducing cyanide in QPQ nitriding salt bath, comprising a mixture composed of target raw materials; the target raw materials include: potassium chloride, potassium carbonate, sodium chloride, sodium nitrate, potassium nitrate, sodium nitrite, and battery-grade lithium carbonate.

[0076] The weight percentages of the components of the target raw materials in the mixture are: potassium chloride 22%, potassium carbonate 23%, sodium chloride 16%, sodium nitrate 12%, potassium nitrate 8%, sodium nitrite 14%, and battery-grade lithium carbonate 5%.

[0077] In this embodiment, the contents of the components in the target raw materials are slightly adjusted to simulate the situation in actual production where some components evaporate to a certain extent when heated. This situation will cause changes in the nitriding salt bath, but does not significantly affect the use performance of the nitriding salt bath. By adjusting the formula components in this embodiment, the effects of this situation on the performance of the nitriding salt bath and the performance of degrading cyanide can be verified, and the effectiveness of this resistance-reducing salt in this situation can be verified.

[0078] This embodiment also provides a preparation process for a resistance-reducing salt for reducing cyanide in QPQ nitriding salt bath, which is used to prepare the resistance-reducing salt for reducing cyanide in QPQ nitriding salt bath as described above; it includes the following steps:

[0079] Step 1, mixing; according to the weight percentages of the components of the target raw materials, add the components of the target raw materials into the stirring tank successively, and then start the mixer to make the components mix evenly and obtain a basic mixture.

[0080] In this embodiment, various component raw materials with the weights weighed according to the weight percentages of the components of the target raw materials are added into the stirring tank successively, and their total mass is 200 kg. Then start the mixer, and the stirring time is set to 90 minutes, so that the raw materials can be fully mixed.

[0081] Step 2, melting; put the basic mixture into a crucible, heat it to 540 °C to make it melt; keep it warm for 2 h to ensure that there is no unmelted material at the bottom of the crucible, and obtain a molten salt solution.

[0082] Step 3, cooling; introduce dried compressed air into the molten salt solution and stir for 5 min, take out the salt solution and place it in a stainless steel basin to cool naturally, and obtain a mixture, which is the resistance-reducing salt for reducing cyanide in QPQ nitriding salt bath.

[0083] Step 4, crushing; use a jaw crusher to crush the resistance-reducing salt obtained in Step 3 into blocks and bag it for standby. The size of the crushed blocks is less than 5 cm * 5 cm * 5 cm.

[0084] This embodiment also provides an application method for a resistance-reducing salt for reducing cyanide in QPQ nitriding salt bath, which includes the following steps:

[0085] Step 1, chemical analysis; detect the content (mass percentage) of cyanide in the QPQ nitriding salt bath according to the chemical titration method.

[0086] In this embodiment, the existing chemical titration method is used for detection, which will not be elaborated here. The content of cyanide in the QPQ nitriding salt bath detected is 4.6%.

[0087] Step 2, calculation; calculate the mass of the resistance-reducing salt to be added based on the mass of the nitriding salt solution in the QPQ nitriding salt bath.

[0088] Based on the standard that for every 1% (by mass) of the resistance-reducing salt added to the nitriding salt bath (nitriding salt solution) in the furnace, the cyanide can be reduced by 0.1% - 0.3%, calculate the mass of the resistance-reducing salt to be added; the nitriding furnace containing the nitriding salt solution is filled with 600 kg of nitriding salt solution, and 90 kg of resistance-reducing salt is added to the nitriding salt solution.

[0089] Step 3, addition; add the resistance-reducing salt prepared by the preparation process of the resistance-reducing salt for reducing cyanide in the QPQ nitriding salt bath as described above to the nitriding salt solution in batches, so that it reacts fully with the nitriding salt solution.

[0090] In this step, when adding the resistance-reducing salt to the nitriding salt solution, the furnace temperature is set at 530 °C; and during the batch addition, after each addition, wait until the liquid surface is calm before adding again. After all the required resistance-reducing salt is added, set the furnace temperature to 610 °C, and the heat preservation time is set to 60 min; then restore it to the use temperature of 580 °C.

[0091] Conduct chemical analysis on the nitriding salt solution after adding the resistance-reducing salt, and its cyanide content is 1.6%.

[0092] A kind of resistance-reducing salt for reducing cyanide in the QPQ nitriding salt bath, its preparation process and application method provided by this embodiment can, in the case of a certain degree of evaporation of some components due to heat, also achieve rapid degradation of cyanide and efficient removal of cyanide, so as to achieve the purpose of restoring the activity of the salt solution.

[0093] The following further illustrates the application effect of this embodiment in combination with 2 comparative examples.

[0094] Comparative Example 2 - Apply this resistance-reducing salt in a large-scale test equipment to verify the use performance and effect of this resistance-reducing salt formula:

[0095] Referring to Example 2, the difference from Example 2 is that the crucible model of the nitriding salt solution filled is type crucible, the nitriding salt solution filled is 800 kg, its cyanide content is 5.4%, the mass of the resistance-reducing salt added is 160 kg, and other technical features are the same as those in Example 2.

[0096] The cyanide content of the nitriding salt solution after adding the resistance-reducing salt in Comparative Example 2 was tested, and it was found to be 1.4%.

[0097] From the data of this comparative example, it can be known that when applied in large-scale test equipment, adding 20% of the resistance-reducing salt can effectively reduce the cyanide content by 4%, meeting the expected effect of the formula.

[0098] Comparative Example 3

[0099] Referring to Example 2, the difference from Example 2 is that sodium nitrate in the target raw materials was replaced with sodium sulfate in equal proportion, while the proportions of other components remained unchanged. The resistance-reducing salt was manufactured using the same process flow, and its effect was detected.

[0100] The crucible for containing the nitriding salt solution was of the φ800*1500 type, and the nitriding salt solution contained was 1000 kg, with a cyanide content of 4.5%. The mass of the added resistance-reducing salt was 100 kg, and other technical features were the same as those in Example 2.

[0101] The cyanide content of the nitriding salt solution after adding the resistance-reducing salt in Comparative Example 3 was tested, and it was found to be 4.3%. Moreover, abnormal situations such as red component segregation in the salt solution and sulfur corrosion of the product occurred.

[0102] In this comparative example, the core oxidant in the resistance-reducing salt was replaced with sodium sulfate, which has oxidation properties at high temperatures, but the cyanide reduction ability decreased significantly. According to the actual data of the comparative example, adding 10% of the resistance-reducing salt only effectively reduced the cyanide content by 0.2%. At the same time, quality problems such as red component segregation in the salt solution and sulfur corrosion of the product occurred, and the effect was not as expected.

[0103] It can be seen that the component formula proposed in the present invention has obvious advantages. Specifically, through the technical counter-evidence by introducing sodium sulfate, it can be seen that the single and inefficient oxidation path of sodium sulfate cannot replace the multi-stage synergistic mechanism of nitrate / nitrite constructed in the present invention, verifying the necessity of the composite oxidant design. Secondly, the melting point of sodium sulfate is relatively high and it is difficult to completely melt, which will then form local enrichment areas in the salt bath, causing component segregation and destroying the homogeneity of the salt bath. However, the component formula designed in the present invention has the characteristic of eutectic melting and will not show component segregation. Furthermore, the introduction of sulfur elements leads to corrosion and toxicity problems, which reversely proves the rationality of the sulfur-free design of the component formula proposed in the present invention.

[0104] The above are only embodiments of the present invention. Common general knowledge such as specific structures and characteristics known in the art is not described in detail herein. Those of ordinary skill in the art know all the common general knowledge in the technical field to which the invention pertains before the filing date or the priority date, are able to know all the prior art in this field, and have the ability to apply conventional experimental means before this date. Those of ordinary skill in the art can, under the inspiration given in this application, complete and implement this solution in combination with their own capabilities. Some typical well-known structures or well-known methods should not become an obstacle for those of ordinary skill in the art to implement this application. It should be noted that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can still be made, and these should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent.

Claims

1. A resistance-reducing salt for reducing cyanide radical in QPQ nitriding salt bath, characterized in that, It includes a mixture composed of target raw materials; the target raw materials include: potassium chloride, potassium carbonate, sodium chloride, sodium nitrate, potassium nitrate, sodium nitrite, and battery-grade lithium carbonate.

2. The resistance-reducing salt for reducing cyanide radical in QPQ nitriding salt bath according to claim 1, wherein The weight percentages of the components of the target raw materials in the mixture are: potassium chloride 5%-25%, potassium carbonate 5%-35%, sodium chloride 2%-22%, sodium nitrate 1%-10%, potassium nitrate 0.5%-5%, sodium nitrite 5%-20%, and battery-grade lithium carbonate 1%-10%.

3. The resistance-reducing salt for reducing cyanide radical in the QPQ nitriding salt bath according to claim 1, characterized in that, The melting point of the mixture is not higher than 580°C.

4. Preparation process of resistance-reducing salt for reducing cyanide radical in QPQ nitriding salt bath, characterized in that, For preparing the resistance-reducing salt for reducing cyanide in the QPQ nitriding salt bath as described in any one of claims 1 to 3; it includes the following steps: Step 1, mixing materials; successively add the components of the target raw materials into a stirring tank, and then start the stirrer to make the components mix evenly and obtain a basic mixture. Step 2, melting; put the basic mixture into a crucible, heat it to 500-550°C to make it melt; keep it warm for 1-2 hours to ensure that there is no unmelted substance at the bottom of the crucible and obtain a molten salt solution. Step 3, cooling; introduce compressed air into the molten salt solution and stir, take out the salt solution and let it cool naturally to obtain a mixture, which is the resistance-reducing salt for reducing cyanide in the QPQ nitriding salt bath. Step 4, crushing; crush the resistance-reducing salt obtained in Step 3 into blocks and bag it for standby.

5. The preparation process of the resistance-reducing salt for reducing cyanide radical in the QPQ nitriding salt bath according to claim 4, characterized in that, In Step 1, the stirring time is 5 to 120 minutes.

6. The preparation process of the resistance-reducing salt for reducing cyanide radical in QPQ nitriding salt bath according to claim 4, characterized in that, The crucible is a crucible made of pure titanium and is heated by a pit furnace; the compressed air is dried compressed air.

7. The preparation process of the resistance-reducing salt for reducing the cyanide radical in the QPQ nitriding salt bath according to claim 4, characterized in that, In Step 4, the size of the crushed block is less than 5cm*5cm*5cm.

8. Application method of resistance-reducing salt for reducing cyanide radical in QPQ nitriding salt bath, characterized in that, It includes the following steps: Step 1, testing; Detect the content of cyanide in the QPQ nitriding salt bath according to the chemical titration method. Step 2, calculating; calculate the mass of the resistance-reducing salt to be added based on the mass of the nitriding salt solution in the QPQ nitriding salt bath. Step 3, adding; add the resistance-reducing salt prepared by the preparation process of the resistance-reducing salt for reducing cyanide in the QPQ nitriding salt bath as described in any one of claims 4 to 7 in batches to the nitriding salt solution to make it react fully with the nitriding salt solution.

9. The application method of the resistance-reducing salt for reducing cyanide radical in the QPQ nitriding salt bath according to claim 8, characterized in that, In Step 2, when calculating the mass of the resistance-reducing salt to be added, it is calculated based on the following formula: x = ΔC·M / 100·k; In the formula, x is the mass of the resistance-reducing salt to be added, in kg; M is the initial mass of the nitriding salt solution, in kg; ΔC is the target percentage reduction of cyanide, in %; k is the percentage reduction of cyanide when adding 1% of the resistance-reducing salt to the salt bath mass, and its value range is 0.1% to 0.3%.

10. The application method of the resistance-reducing salt for reducing the cyanide radical in the QPQ nitriding salt bath according to claim 8, characterized in that, In Step 3, when adding the resistance-reducing salt to the nitriding salt solution, the furnace temperature is set to 450-550°C; and in the batch addition, after each addition, wait until the liquid surface is calm and then add again. After all the required resistance-reducing salt is added, set the furnace temperature to 580-620°C, and the holding time is set to 30min-180min; then restore to the use temperature.

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