A heat treatment composite process for significantly increasing the total QPQ carburized layer of alloy steel

Abstract

The present invention relates to the field of metal surface heat treatment technology and discloses a composite heat treatment process for significantly increasing the total QPQ (Quick Pulse Quasi-Quenched) layer of alloy steel. The process comprises preheating, nitriding, oxidation, cleaning, vacuum quenching, salt bath tempering, oxidation, cleaning, and, after oxidation, water-cooling the workpiece surface with salt solution and drying. The present invention addresses the prior art issue of a shallow total quartz layer in alloy steel during QPQ treatment, significantly increasing the total quartz layer depth, wear resistance, and corrosion resistance of the QPQ treatment.

Description

Technical Field

[0001] The invention relates to the technical field of metal surface heat treatment, and in particular to a heat treatment composite process for significantly increasing the QPQ total permeation layer of alloy steel. Background Art

[0002] QPQ treatment is a salt bath composite treatment technology. In the molten salt bath, the active nitrogen atoms generated by the decomposition of cyanate are used to penetrate the workpiece, forming a high nitrogen concentration compound layer on the workpiece surface, thereby improving the surface hardness, wear resistance and corrosion resistance of the material. Because the production process does not contain heavy metals, it is an environmentally friendly industrial technology.

[0003] During the processing of alloy steel using the widely used QPQ treatment, once a compound layer with high nitrogen concentration is formed on the surface, nitrogen atoms cannot penetrate further. Ultimately, the total depth of the QPQ penetration layer can only reach about 0.1mm, which is too shallow and cannot grow further. Summary of the Invention

[0004] The present invention aims to provide a heat treatment composite process for significantly increasing the total permeation layer of alloy steel QPQ, so as to solve the problem of shallow total permeation layer of alloy steel in the QPQ treatment process in the prior art.

[0005] To achieve the above object, the present invention adopts the following technical solution: a heat treatment composite process for significantly increasing the total QPQ permeation layer of alloy steel, comprising:

[0006] The first step is preheating. Place the workpiece to be processed into a preheating furnace to dry the moisture on the surface of the workpiece and form an oxide film on the surface.

[0007] The second step is nitriding, where the preheated workpiece is placed in a nitriding furnace and a nitrided layer is formed on the surface of the workpiece in a nitriding salt bath;

[0008] The third step is oxidation. The nitrided workpiece is placed in an oxidation furnace. The nitrided salt brought out is decomposed in the oxidizing salt bath, and an oxide film is formed on the surface.

[0009] The fourth step is cleaning, cleaning the oxidized workpiece with water cooling and drying;

[0010] The fifth step is vacuum quenching. Place the workpiece in a vacuum quenching furnace and heat it to keep it warm. The temperature is controlled at 700-900℃.

[0011] The sixth step is salt bath tempering, which involves placing the quenched workpiece into a nitriding furnace to re-form a nitrided layer on the surface in a nitriding salt bath;

[0012] The seventh step is oxidation. After tempering, the workpiece is placed in an oxidation furnace. The nitride salt brought out is decomposed in the oxidizing salt bath, and an oxide film is formed on the surface again.

[0013] Step 8: Cleaning. After oxidation is completed, clean the surface of the workpiece with salt water and dry it.

[0014] Preferably, as an improvement, in the second step, cyanate decomposes the active nitrogen atom, and the reaction process that occurs is as follows:

[0015] 4CNO→CO3 2- +2CN - +2[N]+CO

[0016] The reaction process between nitrogen atoms and workpiece is as follows:

[0017] 2~3Fe+[N]→Fe 2～3 N.

[0018] Active nitrogen atoms penetrate into the surface of the workpiece to form a main component of Fe 2～3 N nitride layer.

[0019] Preferably, as an improvement, in the fifth step, the reaction occurring during the insulation process is:

[0020] Fe 2～3 N→2~3Fe+[N]

[0021] 2[N]+16Fe→Fe 16 N2

[0022] The nitride layer on the surface of the workpiece decomposes and diffuses further into the interior to form new nitrides.

[0023] Preferably, as an improvement, in the third and seventh steps, the reaction occurring during the oxidation process is,

[0024] CN - +NO3 - →CO3 2- +N2

[0025] 2Fe+O2→2FeO

[0026] 4Fe+3O2→2Fe2O3

[0027] FeO+Fe2O3→Fe3O4

[0028] The oxide film formed is a black ferroferric oxide layer.

[0029] Preferably, as an improvement, in the fourth and eighth steps, cleaning means placing the workpiece after oxidation in an ultrasonic cleaning machine with a temperature of 60-80°C and a frequency of 50-80KHz, ultrasonic cleaning for 30-60 minutes, and then placing the workpiece in a room temperature cleaning water tank for rinsing for 5-15 minutes.

[0030] Preferably, as an improvement, the preheating process in the first step is kept at 380-400°C ± 3°C for 30-60 minutes.

[0031] Preferably, as an improvement, the nitriding salt bath process in the second step is kept at 570-620°C ± 3°C for 120 minutes.

[0032] Preferably, as an improvement, the oxidation salt bath process in the third and seventh steps is kept at 380-400° C.±5° C. for 15 minutes.

[0033] Preferably, as an improvement, in the sixth step, the salt bath tempering is carried out at 450-500°C ± 3°C for 120-180 minutes.

[0034] Preferably, as an improvement, in the fifth step, the quenching temperature is 830±10°C when the workpiece is 40Cr, and the quenching temperature is 850±10°C when the workpiece is 42CrMo.

[0035] Compared to existing QPQ technology, this invention offers the following advantages: This combined heat treatment process can increase the total QPQ carburized layer of alloy steel from 0.1mm to 0.5mm, significantly improving the workpiece's surface hardness, wear resistance, and corrosion resistance. Simultaneously, the workpiece undergoes quenching and tempering, resulting in a stable microstructure and minimal deformation. This process also produces no heavy metals, toxic waste gases, or industrial wastewater, thus meeting environmental standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the metallographic diagram of the 40Cr workpiece after being processed by the existing QPQ process.

[0037] Figure 2 This is a metallographic diagram of a 40Cr workpiece after being processed by the process of Example 1 of the present invention.

[0038] Figure 3 This is the metallographic diagram of the 42CrMo workpiece after being processed by the existing QPQ process.

[0039] Figure 4 This is a metallographic diagram of a 42CrMo workpiece after being processed by the process of Example 2 of the present invention. DETAILED DESCRIPTION

[0040] The following is further described in detail through specific implementation methods:

[0041] Example 1, a heat treatment composite process for significantly increasing the total QPQ permeation layer of alloy steel, applied to the treatment of 40Cr workpieces, comprising the following steps:

[0042] Step 1: Preheating: Place the 40Cr workpiece to be processed in a preheating furnace and keep it at 380℃±3℃ for 45 minutes. The purpose is to dry out the moisture on the workpiece surface, form an oxide film on the surface, and quickly heat the workpiece to the next step.

[0043] Step 2: Nitriding. Place the preheated 40Cr workpiece into the nitriding furnace and keep it at 570℃±3℃ for 120 minutes. During the nitriding process, cyanate decomposes to produce active nitrogen atoms that penetrate into the surface of the workpiece, forming a compound layer with a high nitrogen content. At the same time, this compound layer prevents further penetration of nitrogen atoms, and the total penetration layer depth cannot be further increased. Since the salt bath is in a molten state, there will be a certain amount of loss during the production process. It is necessary to regularly add base salt to maintain the liquid level. When the cyanate concentration decreases, it is necessary to add adjustment salt to keep the cyanate concentration within the appropriate concentration range. The process of cyanate decomposition of active nitrogen atoms is as follows:

[0044] 4CNO - →CO3 2- +2CN - +2[N]+CO

[0045] Active nitrogen atoms penetrate into the surface of the workpiece to form a compound layer, the main components of which are Fe2~3N.

[0046] 2~3Fe+[N]→Fe 2～3 N

[0047] Step 3: Oxidation: Place the nitrided 40Cr workpiece into an oxidation furnace and keep it at 380℃±5℃ for 15 minutes. During the oxidation process, the nitride salts carried out are decomposed to meet environmental protection standards. At the same time, a black oxide film is formed on the surface to increase the corrosion resistance of the workpiece. During the production process, there will be a certain loss of oxide salts, and oxide salts need to be added regularly to maintain the liquid level. The reactions that occur during the oxidation process are:

[0048] CN - +NO3 - →CO3 2- +N2

[0049] 2Fe+O2→2FeO

[0050] 4Fe+3O2→2Fe2O3

[0051] FeO+Fe2O3→Fe3O4

[0052] Step 4: Cleaning: Clean the oxidized 40Cr workpiece with water and dry it; place the workpiece in cold water to clean the salt remaining on the surface.

[0053] Step 5: Vacuum quenching: Place the 40Cr workpiece in a vacuum quenching furnace and heat it to 830±10℃ for 60 minutes. At the quenching temperature, the compound layer on the workpiece surface decomposes, and nitrogen atoms further diffuse into the matrix to form new nitrides, thereby further increasing the total penetration depth. The reactions that occur during the holding process are:

[0054] Fe 2～3 N→2~3Fe+[N]

[0055] 2[N]+16Fe→Fe 16 N2

[0056] Step 6: Salt bath tempering: Place the quenched workpiece in a nitriding furnace and hold it at 500°C ± 3°C for 2 hours. After quenching, the high nitrogen content compound layer on the workpiece surface is decomposed to a certain extent. Salt bath tempering is used to re-form a certain depth of compound layer on the surface, while also improving the workpiece's structural stability.

[0057] Step 7: Oxidation. After tempering, the workpiece is placed in an oxidation furnace and kept at 380℃±5℃ for 15 minutes. During the oxidation process, the nitride salts carried out are decomposed to meet environmental protection standards. At the same time, a black oxide film is formed on the surface to increase the corrosion resistance of the workpiece. During the production process, there will be a certain loss of oxide salts, and oxide salts need to be added regularly to maintain the liquid level. The reactions that occur during the oxidation process are:

[0058] CN - +NO3 - →CO3 2- +N2

[0059] 2Fe+O2→2FeO

[0060] 4Fe+3O2→2Fe2O3

[0061] FeO+Fe2O3→Fe3O4

[0062] Step 8: Cleaning: After oxidation is complete, clean the workpiece surface with salt solution and water cooling, then air dry. Place the workpiece in an ultrasonic cleaning machine at a temperature of 80°C and a frequency of 70KHz for 30 minutes, then rinse the workpiece in a room temperature cleaning tank for 5-10 minutes.

[0063] The 40Cr workpiece processed by the existing QPQ process is obtained under an optical microscope as follows Figure 1 The metallographic image (400 times) of the etchant after selenic acid etching is shown in FIG. The left shadow part is the total infiltration layer. The 40Cr workpiece treated by the process described in Example 1 is obtained under an optical microscope as shown in FIG. Figure 2The metallographic image (400 times) of the workpiece etched with selenic acid shows that the shaded area on the left is the total infiltration layer. Comparison of the two shows that the total infiltration layer depth of the 40Cr workpiece surface treated with the QPQ process of Example 1 is significantly increased.

[0064] Example 2

[0065] In this embodiment, a heat treatment composite process for significantly increasing the total QPQ permeation layer of alloy steel is applied to a 42CrMo workpiece, including the following steps:

[0066] Step 1: Preheating: Place the 42CrMo workpiece to be processed into a preheating furnace and keep it at 400℃±3℃ for 60 minutes; the purpose is to dry out the moisture on the surface of the workpiece, form an oxide film on the surface, and allow the workpiece to quickly reach temperature in the next step.

[0067] Step 2: Nitriding. Place the preheated 42CrMo workpiece into the nitriding furnace and keep it at 620℃±3℃ for 180 minutes. During the nitriding process, cyanate decomposes to produce active nitrogen atoms that penetrate into the surface of the workpiece, forming a compound layer with a high nitrogen content. At the same time, this compound layer prevents further penetration of nitrogen atoms, and the total penetration layer depth cannot be further increased. The salt bath is in a molten state and there will be a certain amount of loss during the production process. Base salt needs to be added regularly to maintain the liquid level. When the cyanate concentration decreases, adjustment salt needs to be added to keep the cyanate concentration within the appropriate concentration range. Cyanate decomposes active nitrogen atoms:

[0068] 4CNO - →CO3 2- +2CN - +2[N]+CO

[0069] Active nitrogen atoms penetrate into the surface of the workpiece to form a compound layer, the main components of which are Fe2~3N.

[0070] 2~3Fe+[N]→Fe 2～3 N

[0071] Step 3: Oxidation: Place the nitrided 42CrMo workpiece into an oxidation furnace and keep it at 400℃±5℃ for 15 minutes. During the oxidation process, the nitride salts carried out are decomposed to meet environmental protection standards. At the same time, a black oxide film is formed on the surface to increase the corrosion resistance of the workpiece. During the production process, there will be a certain loss of oxide salts, and oxide salts need to be added regularly to maintain the liquid level. The reactions that occur during the oxidation process are:

[0072] CN - +NO3 - →CO3 2- +N2

[0073] 2Fe+O2→2FeO

[0074] 4Fe+3O2→2Fe2O3

[0075] FeO+Fe2O3→Fe3O4

[0076] Step 4: Cleaning: clean the oxidized workpiece with water and dry it; place the workpiece in cold water to clean the salt remaining on the surface.

[0077] Step 5: Vacuum quenching: Place the 42CrMo workpiece in a vacuum quenching furnace and heat it to 850±10℃ for 60 minutes. At the quenching temperature, the compound layer on the workpiece surface decomposes, and nitrogen atoms further diffuse into the matrix to form new nitrides, thereby further increasing the total penetration depth. The reactions that occur during the holding process are:

[0078] Fe 2～3 N→2~3Fe+[N]

[0079] 2[N]+16Fe→Fe 16 N2

[0080] Step six, salt bath tempering, put the quenched workpiece into the nitriding furnace and keep it at 460℃±3℃ for 2 hours; after quenching, the surface compound layer with high nitrogen content of the workpiece is decomposed to a certain extent, and salt bath tempering is used to re-form a certain depth of compound layer on the surface, while improving the stability of the workpiece structure.

[0081] Step 7: Oxidation. After tempering, the workpiece is placed in an oxidation furnace and kept at 400℃±5℃ for 30 minutes. During the oxidation process, the nitride salts brought out are decomposed to meet environmental protection standards. At the same time, a black oxide film is formed on the surface to increase the corrosion resistance of the workpiece. During the production process, there will be a certain loss of oxide salts, and oxide salts need to be added regularly to maintain the liquid level. The reactions that occur during the oxidation process are:

[0082] CN - +NO3 - →CO3 2- +N2

[0083] 2Fe+O2→2FeO

[0084] 4Fe+3O2→2Fe2O3

[0085] FeO+Fe2O3→Fe3O4

[0086] After cleaning and oxidation, clean the workpiece surface with salt solution and water cooling, and dry it. Place the workpiece in an ultrasonic cleaning machine at a temperature of 680℃ and a frequency of 80KHz. After ultrasonic cleaning for 60 minutes, place the workpiece in a room temperature cleaning tank and rinse for 10-15 minutes.

[0087] The 42CrMo workpiece processed by the existing QPQ process is obtained under an optical microscope as follows Figure 3 The metallographic image (400 times) of the etchant after selenic acid etching is shown in FIG. The left shadow portion is the total infiltration layer. The 42CrMo workpiece treated by the process described in Example 2 is obtained under an optical microscope as shown in FIG. Figure 4 The metallographic image (400 times) after etching with selenic acid is shown. The left shadow part is the total infiltration layer. Comparison of the two shows that the total infiltration layer depth of the 42CrMo workpiece surface treated by the QPQ process of Example 1 is significantly improved.

[0088] The above is only an embodiment of the present invention. This specific embodiment is only an explanation of the present invention and is not a limitation of the present invention. Common knowledge such as the well-known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, those skilled in the art can make modifications to this embodiment without creative contribution as needed after reading this specification, and these should also be regarded as the scope of protection of the present invention, as long as they are within the scope of the claims of the present invention, they are protected by the patent law. These will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A heat treatment composite process for significantly increasing the total QPQ permeation layer of alloy steel, characterized by: include, The first step is preheating. Place the workpiece to be processed into a preheating furnace to dry the moisture on the surface of the workpiece and form an oxide film on the surface. The second step is nitriding. The preheated workpiece is placed in a nitriding furnace and a nitrided layer is formed on the surface of the workpiece in a nitriding salt bath. The nitriding salt bath is kept at 570~620℃±3℃ for 120 minutes. The third step is oxidation. The nitrided workpiece is placed in an oxidation furnace. The nitrided salt brought out is decomposed in the oxidizing salt bath, and an oxide film is formed on the surface. The fourth step is cleaning, cleaning the oxidized workpiece with water cooling and drying; The fifth step is vacuum quenching. The workpiece is placed in a vacuum quenching furnace and heated and kept warm. The temperature is controlled at 700-900℃. The reactions that occur during the insulation process are: Fe 2～3 N→2~3Fe+[N]; 2[N]+16Fe→Fe 16 N 2； The nitride layer on the surface of the workpiece decomposes and further diffuses into the interior to form new nitrides; The sixth step is salt bath tempering. The quenched workpiece is placed in a nitriding furnace to re-form a nitrided layer on the surface in a nitriding salt bath. Salt bath tempering is carried out at 450~500℃±3℃ for 120~180min. The seventh step is oxidation. After tempering, the workpiece is placed in an oxidation furnace. The nitride salt brought out is decomposed in the oxidizing salt bath, and an oxide film is formed on the surface again. Step 8: Cleaning. After oxidation is completed, clean the surface of the workpiece with salt water and dry it.

2. The heat treatment composite process for significantly increasing the QPQ total permeation layer of alloy steel according to claim 1, characterized in that: In the second step, cyanate decomposes the active nitrogen atom, and the reaction process is as follows: 4CNO →CO3 2- +2CN - +2[N]+CO The reaction process between nitrogen atoms and workpiece is as follows: 2~3Fe+[N]→Fe 2～3 N Active nitrogen atoms penetrate into the surface of the workpiece to form a main component of Fe 2～3 N nitride layer.

3. The heat treatment composite process for significantly increasing the QPQ total permeation layer of alloy steel according to claim 1, characterized in that: In the third and seventh steps, the reaction occurring during the oxidation process is: <h2 style=";text-align:left;direction:ltr">CN<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> +NO3<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> →CO3<h2 style=";text-align:left;direction:ltr"> 2- <h2 style=";text-align:left;direction:ltr"> +N2 2Fe+O2→2FeO 4Fe+3O2→2Fe2O3 FeO+Fe2O3→Fe3O4 The oxide film formed is a black ferroferric oxide layer.

4. The heat treatment composite process for significantly increasing the QPQ total permeation layer of alloy steel according to claim 1, characterized in that: In the fourth and eighth steps, cleaning means placing the workpiece after oxidation in an ultrasonic cleaning machine at a temperature of 60-80°C and a frequency of 50-80KHz, ultrasonically cleaning for 30-60 minutes, and then placing the workpiece in a room temperature cleaning water tank for rinsing for 5-15 minutes.

5. The heat treatment composite process for significantly increasing the QPQ total permeation layer of alloy steel according to claim 1, characterized in that: In the first step, the preheating process is kept at 380-400°C ± 3°C for 30-60 minutes.

6. The heat treatment composite process for significantly increasing the QPQ total permeation layer of alloy steel according to claim 1, characterized in that: In the third and seventh steps, the oxidation salt bath process is kept at 380-400° C.±5° C. for 15 minutes.

7. The heat treatment composite process for significantly increasing the QPQ total permeation layer of alloy steel according to claim 1, characterized in that: In the fifth step, when the workpiece is 40Cr, the quenching temperature is 830±10°C, and when the workpiece is 42CrMo, the quenching temperature is 850±10°C.

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