Composite inorganic salt water-based quenching medium and heat treatment method of steering knuckle

Abstract

The invention provides a composite inorganic salt water-based quenching medium and a heat treatment method of a steering knuckle, and belongs to the technical field of heat treatment, the composite inorganic salt water-based quenching medium comprises the following components by weight: 1%-3% of sodium chloride, 10%-14% of pyrophosphate, 4%-6% of potassium sulfate, 3%-5% of hexametaphosphate, 3%-9% of an antirust preservative and the balance of water. According to the composite inorganic salt water-based quenching medium disclosed by the invention, in the heat treatment of the automobile steering knuckle, the three-stage cooling process is optimized through the synergistic effect of all inorganic salt components, so that the hardness and metallographic structure uniformity of the quenched steering knuckle are remarkably improved, and the rejection rate of the steering knuckle is remarkably reduced; the use temperature of the composite inorganic salt water-based quenching medium is wider than the applicable temperature range of the traditional PAG medium; and the medium-carbon alloy steel steering knuckle is quenched at the temperature of about 800 DEG C, the quenching temperature is reduced by 40-60 DEG C compared with the prior art, and the energy saving performance is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat treatment, in particular to a composite inorganic salt water-based quenching medium and a heat treatment method of a steering knuckle. BACKGROUND

[0002] The steering knuckle is a key safety part of the automobile chassis for transmitting steering torque and bearing impact load, and its performance directly determines the driving stability and passenger safety. In order to ensure that no fracture or excessive wear occurs under extreme conditions, the whole part must have uniform hardness and fine metallographic structure. The quenching stage is the core link to determine the uniformity of the workpiece organization. Quenching process refers to heating the workpiece to a specified phase transition temperature region, then immediately immersed in a quenching medium for rapid cooling, so that the workpiece obtains the required hardness and strength.

[0003] Traditional quenching media include PAG polymer medium, water medium and oil medium. PAG polymer medium contains organic components, high-temperature decomposition will produce VOC pollution, waste liquid is difficult to degrade, and there is a problem of unstable cooling performance caused by long-term use viscosity change. Water is a strong cooling quenching medium. It is widely available, low in price, stable in composition and not prone to deterioration. The disadvantage is that the cooling speed is too fast, which causes the steering knuckle to deform and crack, and a higher quenching temperature (usually 840-870℃) is required. Oil medium quenching is easy to cause oil smoke pollution, is flammable and has high energy consumption.

[0004] Therefore, it is necessary to continue to develop a green and efficient quenching medium to achieve high-quality quenching of the steering knuckle. SUMMARY

[0005] In view of the technical problems in the background art, the present application provides a composite inorganic salt water-based quenching medium and a heat treatment method of a steering knuckle, aiming to solve the technical problems of environmental pollution, high energy consumption, high scrap rate and poor hardness uniformity of forgings caused by using traditional quenching media in the quenching process of the steering knuckle.

[0006] In the first aspect, the present application provides a composite inorganic salt water-based quenching medium, which comprises the following components by weight percentage: 1% to 3% of sodium chloride, 10% to 14% of pyrophosphate, 4% to 6% of potassium sulfate, 3% to 5% of hexametaphosphate, 3% to 9% of anti-rust and anti-corrosion agent, and the balance of water.

[0007] Preferably, the soluble pyrophosphate includes at least one of potassium pyrophosphate and sodium pyrophosphate; the soluble hexametaphosphate includes at least one of potassium hexametaphosphate and sodium hexametaphosphate.

[0008] Preferably, the anti-rust and anti-corrosion agent includes soluble nitrite and soluble carbonate.

[0009] Preferably, the soluble nitrite salt includes at least one of sodium nitrite and potassium nitrite; and the soluble carbonate salt includes at least one of sodium carbonate, potassium carbonate and ammonium carbonate.

[0010] Preferably, the mass ratio of the soluble nitrite salt to the soluble carbonate salt is (1-5):(2-4).

[0011] In a second aspect, the application provides a preparation method of the composite inorganic salt water-based quenching medium, including the following steps: Dissolve sodium chloride, pyrophosphate, potassium sulfate, hexametaphosphate and anti-rust and anti-corrosion agent in water, and stir uniformly to obtain the composite inorganic salt water-based quenching medium.

[0012] In a third aspect, the application provides an application of the composite inorganic salt water-based quenching medium in heat treatment of an automobile steering knuckle.

[0013] In a fourth aspect, the application provides a heat treatment method of a steering knuckle, including the following steps: After the steering knuckle is heated to 785-815 DEG C, the steering knuckle is kept warm for 2-3 hours, pre-cooled to 775-805 DEG C, and then immersed in the quenching medium for quenching treatment, and the quenching treatment time is 60-70 seconds; wherein the temperature of the quenching medium is 20-45 DEG C.

[0014] Preferably, the stirring frequency of the quenching medium in the quenching treatment is 5-15 Hz; or the quenching medium is not stirred in the quenching treatment.

[0015] Preferably, the steering knuckle includes a medium-carbon alloy structural steel steering knuckle.

[0016] Compared with the prior art, the application has the following beneficial effects: The application provides a composite inorganic salt water-based quenching medium, which is prepared by dissolving several specific inorganic salts in water, does not contain organic components, has no organic volatile substances, and can be directly treated by biochemical treatment, and has good environmental protection. In the heat treatment of the automobile steering knuckle, the composite inorganic salt water-based quenching medium optimizes the three-stage cooling process through the synergistic effect of the inorganic salt components, significantly improves the hardness and the uniformity of the metallographic structure of the quenched steering knuckle, and significantly reduces the waste product rate of the steering knuckle; the use temperature of the composite inorganic salt water-based quenching medium is wider than that of the traditional PAG medium; and the medium-carbon alloy steel steering knuckle is quenched at a temperature of 800 DEG C, which reduces the quenching temperature by 40-60 DEG C compared with the prior art, and improves the energy saving.

[0017] The composite inorganic salt water-based quenching medium and the steering knuckle heat treatment method have been verified through a production line of 500,000 steering knuckles per year of a vehicle enterprise, and the original PAG quenching process reduces CO2 emission by 18,500 tons per year, has significant industrial application value, and has good application prospect in the heat treatment field of other complex shafts and rod parts. Attached Figure Description

[0018] Figure 1 This is a comparison of the cooling curves of the composite inorganic salt water-based quenching medium and the PAG medium of this invention. Detailed Implementation

[0019] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0020] To address the environmental pollution, high energy consumption, and high scrap rate caused by using traditional quenching media in the steering knuckle quenching process, this invention provides a composite inorganic salt water-based quenching medium and a steering knuckle heat treatment method. By compounding specific inorganic salts, a high-quality steering knuckle quenching effect is achieved through a synergistic cooling mechanism, which is also highly environmentally friendly and reduces energy consumption.

[0021] In a first aspect, embodiments of the present invention provide a composite inorganic salt water-based quenching medium, comprising the following components by weight percentage: 1%~3% sodium chloride, 10%~14% pyrophosphate, 4%~6% potassium sulfate, 3%~5% hexametaphosphate, 3%~9% rust and corrosion inhibitor, and the balance water.

[0022] In the technical scheme of the embodiment of the present application, the composite inorganic salt water-based quenching medium selects specific inorganic salts for compounding, and the three stages of cooling are optimized, and the specific action mechanism is as follows: vapor film stage: after hexametaphosphate is dissolved in water, the surface tension of the quenching medium is reduced, thereby improving the wettability of the medium. By improving the wettability, hexametaphosphate helps to reduce the adhesion of bubbles generated when the vapor film breaks on the metal surface, forms a uniform cooling film on the metal surface, reduces the duration of the vapor film stage (film boiling), speeds up the cooling rate in the high-temperature zone, and avoids soft spots, deformation, and even cracking caused by uneven local cooling. Boiling stage: the combination of sodium chloride / potassium sulfate makes the cooling in the boiling stage more uniform, avoiding stress concentration caused by local intense boiling. At the same time, the addition of potassium sulfate inhibits the excessive cooling in the convection stage, reduces the risk of quenching deformation and cracking, and controls the cooling speed in the boiling stage to be 80-120℃ / s. Convection stage: pyrophosphate reduces the cooling speed fluctuation range, improves the cooling uniformity, reduces the cross-section hardness difference, keeps the hardness consistent, and reduces the scale thickness to maintain the surface integrity. Among them, hexametaphosphate in the quenching medium also has multiple effects: (1) It has strong chelating property and forms a soluble complex with multivalent metal ions (such as calcium, magnesium, and other metal ions) in water, preventing the quenching liquid from being turbid or scaling due to hard water ion precipitation, maintaining the uniformity and stability of the solution; (2) It has dispersing property, preventing inorganic salt particles from aggregating and precipitating, prolonging the actual effectiveness and service life of the quenching liquid; (3) It has rust and corrosion inhibition effects, forming a protective film on the metal surface to inhibit the rusting of the workpiece after quenching, while reducing the corrosion of the quenching liquid to the equipment; (4) It maintains the acid-base balance of the solution; (5) It adjusts the cooling speed, and by changing the viscosity and surface tension of the quenching liquid, the cooling curve can be optimized to make the quenching process more uniform.

[0023] Further, in some embodiments, the composite inorganic salt water-based quenching medium comprises the following components by weight percentage: sodium chloride 2%, soluble pyrophosphate 12%, potassium sulfate 5%, soluble hexametaphosphate 4%, rust and corrosion inhibitor 6%, and the balance of water.

[0024] Further, in some embodiments, the soluble pyrophosphate comprises at least one of potassium pyrophosphate and sodium pyrophosphate.

[0025] Further, in some embodiments, the soluble hexametaphosphate comprises at least one of potassium hexametaphosphate and sodium hexametaphosphate.

[0026] Further, in some embodiments, the rust and corrosion inhibitor comprises soluble nitrite and soluble carbonate.

[0027] In the technical scheme of the embodiment of the present application, the nitrite reacts with the metal surface to generate a dense γ-Fe2O3 or composite oxide film (Fe2O3·Fe3O4) in an alkaline environment (pH≥9), which blocks the contact of oxygen and water to inhibit the oxidation of the knuckle surface, the hydrolysis of sodium carbonate provides stable alkaline conditions, maintains pH 9.5-10.5, improves the passivation efficiency of sodium nitrite, and inhibits the generation of hydrolysis by-products (such as HNO2) to avoid acid corrosion.

[0028] Further, in some embodiments, the soluble nitrite salt includes at least one of sodium nitrite and potassium nitrite.

[0029] Further, in some embodiments, the soluble carbonate salt includes at least one of sodium carbonate, potassium carbonate, and ammonium carbonate.

[0030] Further, in some embodiments, the mass ratio of the soluble nitrite salt to the soluble carbonate salt is (1-5):(2-4).

[0031] In a second aspect, the embodiment of the present application provides a preparation method of a composite inorganic salt water-based quenching medium, including the following steps: Dissolve sodium chloride, pyrophosphate, potassium sulfate, hexametaphosphate, and antirust and anticorrosion agents in water, and stir uniformly to obtain a composite inorganic salt water-based quenching medium.

[0032] In a third aspect, the embodiment of the present application provides an application of a composite inorganic salt water-based quenching medium in heat treatment of an automobile knuckle.

[0033] In a fourth aspect, the embodiment of the present application provides a heat treatment method of a knuckle, including the following steps: After heating the knuckle to 785-815℃, heat preservation is performed for 2-3 hours, pre-cooling is performed to 775-805℃, and then quenching treatment is performed by immersing in a quenching medium, and the quenching treatment time is 60-70s; wherein the temperature of the quenching medium is 20-45℃.

[0034] Further, in some embodiments, the stirring frequency of the quenching medium in the quenching treatment is 5-15Hz; or the quenching medium is not stirred in the quenching treatment.

[0035] Further, in some embodiments, the knuckle includes a medium-carbon alloy structural steel knuckle.

[0036] In the present application, the knuckle includes but is not limited to the 40Cr steel automobile knuckle, the 42CrMo steel automobile knuckle, and the SAE5137 steel automobile knuckle listed in the embodiments, and other types of medium-carbon alloy structural steel knuckles can also be applicable.

[0037] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are intended to explain the present application, and should not be construed as limiting the present application. The technical or conditions not specified in the examples are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained by purchase.

[0038] Example 1 The formula of the quenching medium is as follows (in percentage by weight): sodium chloride 2%, potassium pyrophosphate 12%, potassium sulfate 5%, potassium hexametaphosphate 4%, sodium carbonate 3%, anhydrous sodium nitrite 3%, and deionized water 71%.

[0039] The inorganic salts were dissolved in water in proportion, and the composite inorganic salt water-based quenching medium was obtained after uniform stirring.

[0040] The heat treatment process of the 42CrMo steel knuckle includes the following steps: The forged knuckle workpiece after forging was heated at a temperature of 810℃ for 150 minutes by using a continuous mesh belt furnace, and pre-cooled to 800℃ before quenching. Then it was immersed in the above quenching medium for quenching, the temperature of the quenching medium was 35℃, the cooling time of the knuckle workpiece in the quenching medium was 70s, and the quenching medium was not stirred during quenching.

[0041] Comparative Example 1 The present comparative example provides a heat treatment process of a 42CrMo steel knuckle, which includes the following steps: The forged knuckle workpiece after forging was heated at a temperature of 840℃ for 150 minutes by using a continuous mesh belt furnace, and then immersed in PAG medium for quenching, the temperature of the quenching medium was 35℃, the cooling time of the knuckle workpiece in the quenching medium was 90s, and the quenching medium was stirred at a frequency of 15Hz during quenching.

[0042] Comparative Example 2 The present comparative example provides a heat treatment process of a 42CrMo steel knuckle, which includes the following steps: The forged knuckle workpiece after forging was heated at a temperature of 835℃ for 150 minutes by using a continuous mesh belt furnace, and then immersed in pure water medium for quenching, the temperature of the quenching medium was 35℃, the cooling time of the knuckle workpiece in the quenching medium was 90s, and the quenching medium was stirred at a frequency of 10Hz during quenching.

[0043] Example 2 The formula of the quenching medium is as follows (in percentage by weight): sodium chloride 2%, potassium pyrophosphate 12%, potassium sulfate 5%, potassium hexametaphosphate 4%, sodium carbonate 3%, anhydrous sodium nitrite 3%, and deionized water 71%.

[0044] The inorganic salts of each component are taken in proportion, and a composite inorganic salt water-based quenching medium is obtained by stirring uniformly in water.

[0045] 40Cr steel arm knuckle heat treatment process, comprising the following steps: The knuckle forging after forging is heated at 815℃ for 150 minutes by a continuous mesh belt furnace, pre-cooled to 805℃ before quenching, then immersed in the above quenching medium for quenching, the temperature of the quenching medium is 20℃, the cooling time of the knuckle forging in the quenching medium is 60s, and the quenching medium is not stirred during quenching.

[0046] Comparative Example 3 This comparative example provides a 40Cr steel arm knuckle heat treatment process, comprising the following steps: The knuckle forging after forging is heated at 835℃ for 150 minutes by a continuous mesh belt furnace, then immersed in PAG medium for quenching, the temperature of the quenching medium is 20℃, the cooling time of the knuckle forging in the quenching medium is 85s, and the quenching medium is stirred at a frequency of 10Hz during quenching.

[0047] Comparative Example 4 This comparative example provides a 40Cr steel arm knuckle heat treatment process, comprising the following steps: The knuckle forging after forging is heated at 835℃ for 150 minutes by a continuous mesh belt furnace, then immersed in pure water medium for quenching, the temperature of the quenching medium is 20℃, the cooling time of the knuckle forging in the quenching medium is 75s, and the quenching medium is stirred at a frequency of 5Hz during quenching.

[0048] Comparative Example 5 This comparative example provides a 40Cr steel arm knuckle heat treatment process, which is different from Example 2 in that the composite inorganic salt water-based quenching medium does not contain potassium hexametaphosphate, and the specific formula is as follows (by weight percentage): sodium chloride 3%, potassium pyrophosphate 13%, potassium sulfate 6%, sodium carbonate 4%, anhydrous sodium nitrite 4%, and deionized water 70%. The remaining process parameters are the same as those of Example 2.

[0049] Performance test The hardness of the knuckle forgings after heat treatment of each example and comparative example is detected, the test method refers to GB / T230.1, and the scrap rate and ton piece energy consumption of each example and comparative example heat treatment process are counted, and the results are shown in Table 1 below.

[0050] Table 1

[0051] The data in Table 1 show that the knuckle forgings obtained by heat treatment using the composite inorganic salt water-based quenching medium have better hardness uniformity (increased to more than 95%), and the scrap rate and energy consumption per piece are significantly reduced. The data in Comparative Example 5 show that potassium hexametaphosphate can make the hardenability and internal and external hardness uniformity of the forgings more excellent, and the scrap rate is reduced.

[0052] The cooling curve of the composite inorganic salt water-based quenching medium (the formula is consistent with that in Example 1) of the present application and the PAG medium was compared, and the test method was as follows: The test method was carried out according to ISO 9950, the test probe diameter was 12.5 mm, the material was Inconel 600, and the KHR-A portable cooling medium performance detector was used for detection.

[0053] Figure 1 The cooling curve of the composite inorganic salt water-based quenching medium (the formula is consistent with that in Example 1) of the present application and the PAG medium was compared, and the test method was as follows: Figure 1 It is shown that the V300 average cooling rate of the composite inorganic salt water-based quenching medium of the present application is increased by about 10% compared with the PAG medium, and the maximum cooling rate is increased by about 80%. The cooling rate is not much different below the Ms point. This is because at high temperature, salt particles are precipitated on the surface at high temperature and explode, mechanically damaging the steam film, so that the workpiece directly contacts the liquid, greatly improving the cooling rate. And the boiling point of the salt water is higher, which will enter the efficient convection cooling stage in advance. In the low temperature stage, the salt particles crystallize and adhere to the surface of the workpiece to act as a protective layer, reducing the heat transfer efficiency. At this time, controlling the water outlet surface temperature can achieve hardenability and crack prevention effect.

[0054] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, and other ways constructed by combining part of the components in the embodiments are also included in the scope of the present application.

Claims

1. A composite inorganic salt water-based quenching medium, characterized by, The compound inorganic salt water-based quenching medium comprises the following components by weight percentage: sodium chloride 1%~3%, pyrophosphate 10%~14%, potassium sulfate 4%~6%, hexametaphosphate 3%~5%, anti-rust and anti-corrosion agent 3%~9%, and the balance of water.

2. The composite inorganic salt water-based quenching medium according to claim 1, characterized in that, The soluble pyrophosphate comprises at least one of potassium pyrophosphate and sodium pyrophosphate. And / or, the soluble hexametaphosphate comprises at least one of potassium hexametaphosphate and sodium hexametaphosphate.

3. The composite inorganic salt water-based quenching medium according to claim 1, wherein, The anti-rust and anti-corrosion agent comprises soluble nitrite and soluble carbonate.

4. The composite inorganic salt water-based quenching medium according to claim 3, wherein, The soluble nitrite comprises at least one of sodium nitrite and potassium nitrite. And / or, the soluble carbonate comprises at least one of sodium carbonate, potassium carbonate and ammonium carbonate.

5. The composite inorganic salt water-based quenching medium according to claim 3, wherein, The mass ratio of the soluble nitrite to the soluble carbonate is (1~5):(2~4).

6. The method of claim 1 to 5, wherein the composite inorganic salt water-based quenching medium is prepared by the steps of: (a) mixing the inorganic salt, the water, and the additive to prepare a mixture; (b) adding the mixture to a container; (c) adding the additive to the mixture; and (d) stirring the mixture. The method comprises the following steps: Dissolving sodium chloride, pyrophosphate, potassium sulfate, hexametaphosphate and anti-rust and anti-corrosion agent in water, stirring uniformly to obtain the compound inorganic salt water-based quenching medium.

7. The compound inorganic salt water-based quenching medium according to any one of claims 1~5 is applied to heat treatment of an automobile steering knuckle.

8. A heat treatment method of a knuckle, characterized by, The method comprises the following steps: After heating the steering knuckle to 785~815℃, holding for 2~3 hours, pre-cooling to 775~805℃, then immersing in the quenching medium for quenching treatment, and the quenching treatment time is 60~70s; The quenching medium is the compound inorganic salt water-based quenching medium according to any one of claims 1~5; and the temperature of the quenching medium is 20~45℃.

9. The heat treatment method of a knuckle according to claim 8, wherein The stirring frequency of the quenching medium in the quenching treatment is 5~15Hz; or the quenching medium is not stirred in the quenching treatment.

10. The heat treatment method of a knuckle according to claim 8, characterized by, The steering knuckle comprises a medium-carbon alloy structural steel steering knuckle.

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