Metal lock body toughness strengthening heat treatment process

Abstract

The invention relates to the technical field of metal material heat treatment, in particular to a metal lock body toughness strengthening heat treatment process, a metal lock body is low-carbon steel or medium-carbon steel, the carbon content is 0.12%-0.45%, and the metal lock body toughness strengthening heat treatment process comprises the steps that surface cleaning and stress pretreatment are sequentially conducted on the metal lock body; the treated metal lock body is placed in a heat treatment furnace, and segmented heating is conducted to the austenitizing temperature according to a preset heating curve; first-stage heat preservation is conducted in the austenitizing temperature interval, and then cooling is conducted to the bainite transformation temperature interval for second-stage heat preservation; after double-temperature-area heat preservation is completed, stepped cooling treatment is conducted on the metal lock body; and the cooled metal lock body is sequentially subjected to low-temperature tempering, shot blasting treatment and secondary tempering. Through surface cleaning, stress treatment, segmented heating, double-temperature-zone heat preservation, stepped cooling, low-temperature tempering, graded shot blasting and secondary tempering, lock body stress is fully released, structure defects are reduced, internal stress is slowly released, and toughness, strength and performance stability are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal material heat treatment, and particularly relates to a metal lock body toughness strengthening heat treatment process. BACKGROUND

[0002] As a core component in the security field, the mechanical properties of the metal lock body directly determine the use reliability. At present, low carbon steel or medium carbon steel is generally used as the base material in the industry. The core application requirement of this kind of material is to balance the strength and toughness, that is, to meet the impact resistance in the daily opening and closing process and to avoid deformation or fracture after long-term use. With the improvement of security requirements, the metal lock body heat treatment technology gradually develops from the early single heating, holding and cooling mode to the fine direction. For example, by introducing the segmented heating to optimize the temperature field distribution, using the double temperature zone holding to promote the organization transformation, matching the low temperature tempering to improve the residual stress, and at the same time, in order to reduce the oxidation defects, the auxiliary technologies such as protective gas atmosphere control and furnace temperature monitoring are gradually integrated into the process system. The overall development trend presents from extensive control to precise regulation, aiming to improve the toughness of the lock body through process optimization.

[0003] Although the existing metal lock body toughness strengthening heat treatment technology has formed a basic framework, there are still many limitations in practical application. In the pretreatment stage, some processes do not give full consideration to the thoroughness of surface cleaning and the sufficiency of stress relief, which may lead to residual impurities on the surface of the lock body or incomplete release of internal stress, thus causing defects in the formation of the organization. In the heating process, most schemes use fixed rate heating, without considering the influence of lock body thickness difference on heat conduction, which may cause large temperature difference between the inside and the surface of the thick-walled lock body, incomplete austenitization or poor uniformity. In the double temperature zone holding stage, there is a lack of active measures to promote the organization transformation, which makes it difficult to ensure the uniform nucleation and growth of the toughness organization such as bainite. In the cooling link, the cooling rate is often not dynamically adjusted according to the structure characteristics of the lock body, which may cause internal stress concentration and increase the risk of cracking due to the mismatch between the cooling speed and the material phase change requirement. In the post-processing process, the single parameter is often used in the shot peening treatment, without adapting to the strengthening requirements of different curvature parts of the lock body, which may lead to uneven surface hardness distribution. In addition, the tempering treatment has limited effect on the elimination of residual stress, which finally makes it difficult to achieve the ideal level of the overall toughness of the lock body, and there are still performance short boards when bearing impact or long-term wear. SUMMARY

[0004] In view of the shortcomings of the prior art, the present application provides a metal lock body toughness strengthening heat treatment process. In order to achieve the above purpose, the present application adopts the following technical scheme:

[0005] A metal lock body toughness strengthening heat treatment process, the metal lock body is made of low carbon steel or medium carbon steel, and the carbon content is 0.12% to 0.45%. The process comprises the following steps:

[0006] S1. Pretreatment: The metal lock body is subjected to surface cleaning and stress pretreatment in sequence;

[0007] S2. Segmented heating: Place the pretreated metal lock body in a heat treatment furnace and heat it to the austenitizing temperature in segments according to the preset heating curve.

[0008] S3, Dual-temperature zone insulation: The first stage of insulation is carried out within the austenitizing temperature range, followed by cooling to the bainite transformation temperature range for the second stage of insulation;

[0009] S4. Stepped cooling: After completing the dual-temperature zone insulation, the metal lock body is subjected to stepped cooling treatment.

[0010] S5. Post-composite treatment: The cooled metal lock body is subjected to low-temperature tempering, shot peening, and secondary tempering in sequence.

[0011] Further, in step S1: surface cleaning is performed by sandblasting, using brown corundum sand with a particle size of 80-120 mesh, a sandblasting pressure of 0.4 MPa-0.6 MPa, and a spray angle of 45°-60°; stress pretreatment is performed by low-temperature stress relief treatment, with a temperature of 620°C-680°C and a holding time of 2-4 hours, and argon or nitrogen gas is introduced into the furnace at a flow rate of 1.5 m³ / h. 3 / h~3.0m 3 / h, the furnace pressure is maintained at 105kPa~110kPa.

[0012] Further, in step S2: the segmented heating includes a low-temperature segment, a medium-temperature segment, and a high-temperature segment, with the heating rate of each segment decreasing stepwise as the temperature increases; wherein, the low-temperature segment is room temperature to 350℃, with a heating rate of 10℃ / min to 20℃ / min; the medium-temperature segment is 350℃ to 600℃, with a heating rate of 5℃ / min to 10℃ / min; the high-temperature segment is 600℃ to 850℃ to 950℃, with the heating rate adjusted according to the maximum thickness of the lock body: 3℃ / min to 5℃ / min when the thickness is ≤10mm, and 2℃ / min to 3℃ / min when the thickness is >10mm; before heating in the high-temperature segment, a vacuum is drawn to a vacuum degree of ≤10Pa, and then argon or nitrogen is introduced to atmospheric pressure.

[0013] Furthermore, in step S3, the first stage of heat preservation temperature is 820℃~950℃, and the heat preservation time is 1h~3h; the second stage of heat preservation temperature is 370℃~520℃, and the heat preservation time is adjusted according to the carbon content and total alloy element content of the material. For every 0.1% increase in carbon content and every 0.5% increase in total alloy element content, the heat preservation time is extended by 0.5h~1.0h; during the heat preservation process, pulsed argon gas is introduced, and the flow rate fluctuates periodically by ±20% to promote uniform nucleation of bainite.

[0014] Further, in step S4, the step cooling is first cooled to the pearlite transformation termination temperature at a first cooling rate, the pearlite transformation termination temperature is 650-680 DEG C, and then cooled to room temperature at a second cooling rate; the first cooling rate is adjusted according to the maximum thickness of the lock body: when the thickness is less than or equal to 10 mm, the first cooling rate is 10-15 DEG C / s, and when the thickness is greater than 10 mm, the first cooling rate is 5-8 DEG C / s; the second cooling rate is 0.5-3 DEG C / s; the cooling medium is a polyvinyl alcohol aqueous solution or a polyether aqueous solution with a mass fraction of 5-10%, and the circulating flow rate is 8-15 m 3 / h. 3 / h.

[0015] Further, in step S5, the low-temperature tempering temperature is 200-250 DEG C, the holding time is 2-4 h, the purity of the nitrogen gas is greater than or equal to 99.99%, the oxygen content in the furnace is controlled to be 0.1-0.5%, the shot blasting treatment adopts a hierarchical projectile: for the complex parts with a curvature radius less than or equal to 10 mm, stainless steel projectiles or cast iron projectiles with a diameter of 0.3-0.6 mm are used, for the plane or curved surface with a curvature radius greater than 10 mm, stainless steel projectiles or cast iron projectiles with a diameter of 0.6-1.0 mm are used, the shot blasting pressure is 0.2-0.5 MPa, and the coverage is greater than or equal to 100%; the second tempering temperature is 200-250 DEG C, and the holding time is 0.5-1 h.

[0016] Further, in step S2, the metal lock body is placed in layers with a spacing, the layer spacing is 1.2-2.0 times the maximum thickness of the lock body, and the spacing direction of the lock bodies in the same layer is consistent with the airflow direction in the furnace.

[0017] Further, in step S2, a double thermocouple temperature monitoring is used, which is respectively arranged at the center and the edge of the furnace cavity, and when the temperature deviation exceeds ±3 DEG C, the heating power of the corresponding temperature zone is adjusted, and the adjustment range is 5-15%.

[0018] Further, in step S4, the water-soluble quenching medium is used after being filtered with a precision of 20 mu m, and the medium temperature is controlled to be 25-40 DEG C.

[0019] Further, in step S3, the second stage holding time is calculated according to the formula t=k*d: t is the holding time, d is the maximum thickness of the lock body, the initial k value of carbon steel is 1.2-2.0 h / mm; for alloy steel, the initial k value is increased by 10-20% based on the carbon steel, and the k value is increased by 5% for each increase of 1% of the total content of Cr+Ni+Mo, and the k value is increased by 5-10% for each increase of 0.1% of the carbon content based on the initial value.

[0020] The present application has the following advantages:

[0021] 1、The present application realizes the full release of the metal lock body's early stress, the uniform temperature distribution in the heating process and the complete austenitizing degree, effectively reduces the organizational defects in the lock body, and lays a stable microstructure foundation for improving the lock body toughness.

[0022] 2、The present application realizes the slow release of the internal stress of the lock body in the cooling process, avoids the problems of cracking or uneven organization of the lock body caused by the sudden change of the cooling rate, significantly improves the stability of the mechanical properties of the lock body, and ensures that the lock bodies with different structural characteristics can form uniform organization with strength and toughness.

[0023] 3、The present application realizes the deep elimination of the residual stress of the lock body, improves the surface hardness and overall toughness of the lock body, makes the lock body not easy to deform or break when dealing with the impact and wear in daily use, and meets the mechanical property requirements of the long-term use of the metal lock body. BRIEF DESCRIPTION OF DRAWINGS

[0024] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The drawings illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application.

[0025] In the drawings:

[0026] Figure 1 The flow chart of the metal lock body toughness strengthening heat treatment process in Example 1. DETAILED DESCRIPTION

[0027] The present application will be described in detail below through specific examples, so that the present application can be better understood. However, the following examples do not limit the protection scope of the present application.

[0028] Example 1

[0029] Low carbon steel metal lock body toughness reinforcement heat treatment, this embodiment is aimed at the carbon content of 0.2% low carbon steel metal lock body, the maximum thickness of the lock body is 8mm, the complex part with a curvature radius ≤10mm is the lock tongue card slot, and the part with a curvature radius >10mm is the lock body panel.

[0030] The operation is as follows:

[0031] S1, pretreatment: surface cleaning adopts sand blasting treatment, selects brown corundum sand with a particle size of 100 mesh, sand blasting pressure is 0.5 MPa, spraying angle is 50°, and after treatment, the lock body surface is free of oxide scale, oil stains and processing debris residues; then low-temperature stress relief treatment is carried out, the lock body is placed in a heat treatment furnace, heated to 650 DEG C, and kept for 3h, argon is introduced into the furnace, the gas flow is 2.0m 3 / h, the furnace pressure is maintained at 108kPa, the residual stress accumulated in the lock body during processing is fully released, and deformation or cracking does not occur in the subsequent heating stage.

[0032] S2, segmented heating: the pretreated lock body is placed in layers with an interval of 1.5 times the maximum thickness of the lock body, i.e. 12mm, and the direction of the lock body interval is consistent with the airflow direction in the furnace; double thermocouples are used to monitor the temperature by being placed in the center and the edge area of the furnace cavity respectively, and the temperature is segmented according to the preset curve: the low-temperature section is room temperature-350 DEG C, the heating rate is 15 DEG C / min; the medium-temperature section is 350 DEG C-600 DEG C, the heating rate is 8 DEG C / min; the high-temperature section is 600 DEG C-900 DEG C, because the maximum thickness of the lock body is 8mm, which belongs to the range ≤10mm, the heating rate is set to 4 DEG C / min; before the high-temperature section is heated, vacuum is extracted to a vacuum degree of 8Pa, and then nitrogen is introduced to normal pressure, the temperature deviation between the center and the edge of the furnace cavity throughout the process does not exceed ±2 DEG C, and the heating power does not need to be adjusted, and the temperature inside and outside the lock body is kept uniform, which lays a good foundation for austenite transformation.

[0033] S3, double-temperature-zone holding: the first stage is held at the austenite transformation temperature of 900 DEG C for 2h to ensure that the lock body structure is completely transformed into uniform austenite; then the temperature is lowered to the bainite transformation temperature range of 450 DEG C for the second stage holding, and the holding time is calculated according to the formula t=k×d: the initial k value of the lock body is taken as 1.5h / mm, the maximum thickness d of the lock body is 8mm, so the holding time t=1.5×8=12h; pulse argon is introduced during the holding process, the flow fluctuates periodically by ±20%, which promotes the circulation of the airflow in the furnace, makes the bainite uniformly nucleate in each part of the lock body, and avoids the problem of local structure segregation.

[0034] S4, stepwise cooling: after the double-temperature zone holding is completed, the lock body is first cooled to the pearlite transformation termination temperature of 660°C at a first cooling rate of 12°C / s, which is set according to the case of the maximum thickness of the lock body being 8mm≤10mm; then the lock body is cooled to room temperature at a second cooling rate of 2°C / s; the cooling medium is selected to be an aqueous solution of polyvinyl alcohol with a mass fraction of 8%, which is filtered through a filter with a precision of 20μm before use to remove impurity particles, and the medium temperature is controlled at 30°C, and the circulating flow rate is 12m 3 / h, and the lock body does not appear to be cracked or deformed during the whole cooling process, and there are no oxidation spots on the surface.

[0035] S5, composite post-treatment: the lock body after cooling is first low-temperature tempered, the temperature is set to 220°C, and the holding time is 3h, the nitrogen gas with a purity of 99.995% is introduced into the furnace, and the oxygen content in the furnace is controlled to be 0.3%, so as to further eliminate the residual stress generated in the cooling stage; then the shot blasting treatment is carried out: for the complex parts with a curvature radius≤10mm such as the lock tongue slot, stainless steel shots with a diameter of 0.5mm are used; for the parts with a curvature radius>10mm such as the lock body panel, stainless steel shots with a diameter of 0.8mm are used, the shot blasting pressure is 0.4MPa, and the coverage rate reaches 100%, so as to form a uniform residual compressive stress layer on the surface of the lock body; finally, the lock body is subjected to secondary tempering, the temperature is 220°C, and the holding time is 0.8h, so as to stabilize the microstructure of the lock body.

[0036] It is detected that the impact toughness of the low-carbon steel lock body is improved by 35% compared with the conventional heat treatment process, and the surface hardness reaches HV380, which can meet the impact resistance and wear resistance requirements in daily use.

[0037] Example 2

[0038] Toughness strengthening heat treatment of medium-carbon steel metal lock body

[0039] This embodiment is directed to a medium-carbon steel metal lock body with a carbon content of 0.4%, the maximum thickness of the lock body is 12mm, the complex parts with a curvature radius≤10mm are the lock core holes, and the parts with a curvature radius>10mm are the lock body side plates.

[0040] The operation is as follows:

[0041] S1, pretreatment: the surface cleaning adopts sand blasting treatment, brown corundum sand with a particle size of 120# is selected, the sand blasting pressure is 0.6MPa, and the spraying angle is 60°, and after the treatment, the cleanliness of the surface of the lock body reaches Sa2.5 level; then low-temperature stress relief treatment is carried out, the lock body is placed in a heat treatment furnace, heated to 680°C, and held for 4h, nitrogen gas is introduced into the furnace, the gas flow rate is 3.0m 3 / h, the pressure in the furnace is maintained at 110kPa, the residual stress accumulated in the processing of the lock body is fully released, the release rate of the residual stress in the lock body is more than 90%, and deformation or cracking does not occur in the subsequent heating stage.

[0042] S2, segmented heating: the pretreated lock body is placed in layers with an interval of 1.8 times the maximum thickness of the lock body, i.e. 21.6 mm, and the direction of the interval between the lock bodies in the same layer is consistent with the direction of the airflow in the furnace; a double thermocouple is used to monitor the temperature by being placed in the center and the edge area of the furnace cavity, respectively, and the temperature is raised in segments according to the preset curve: the low-temperature segment is room temperature-350℃, the temperature rising rate is 20℃ / min; the medium-temperature segment is 350℃-600℃, the temperature rising rate is 10℃ / min; the high-temperature segment is 600℃-950℃, because the maximum thickness of the lock body is 12 mm, which belongs to the range of >10 mm, the temperature rising rate is set to 3℃ / min; before the high-temperature segment is heated, the vacuum degree is first extracted to 5 Pa, and then argon is introduced to the normal pressure, when the temperature deviation of the edge of the furnace cavity reaches ±3℃ throughout the process, the heating power of the edge temperature zone is timely adjusted by 10%, and the temperature difference between the inside and outside of the lock body is controlled to be ≤5℃, which lays a good foundation for the austenite transformation.

[0043] S3, double-temperature-zone holding: the first stage is holding at the austenite temperature interval of 950℃ for 3h to ensure that the lock body organization is completely transformed into uniform austenite and the austenitization is complete; then the second stage is holding at the bainite transformation temperature interval of 500℃, the holding time is calculated according to the formula t=k×d: the lock body is carbon steel, the initial k value is taken as 2.0h / mm, the carbon content is 0.4% higher than the reference value by 0.2%, and the k value increases by 8% for every 0.1% increase in carbon content, so k=2.0×(1+8%×2)=2.32h / mm, the maximum thickness d of the lock body is 12 mm, so the holding time t=2.32×12≈27.8h; during the holding process, pulse argon is introduced, the flow fluctuates periodically by ±20%, which promotes the circulation of the airflow in the furnace, makes the bainite uniformly nucleate in each part of the lock body, and finally the uniformity of the bainite organization of the lock body reaches 98%, avoiding the problem of local organization segregation.

[0044] S4, stepwise cooling: after the double-temperature-zone holding is completed, first, the cooling rate is 6℃ / s to cool to the pearlite transformation termination temperature of 680℃, the cooling rate is set according to the condition that the maximum thickness of the lock body is 12 mm >10 mm; then, the cooling rate is 3℃ / s to cool to room temperature; the cooling medium is selected to be a polyether aqueous solution with a mass fraction of 10%, which is filtered through a 20μm precision filter before use to remove impurity particles, the medium temperature is controlled at 40℃, the circulation flow rate is 15m 3 / h, and the lock body does not crack during the whole cooling process, and the surface also does not have defects.

[0045] S5, composite post-processing: the lock body after cooling is first low-temperature tempered, the temperature is set to 250 DEG C, and the temperature is kept for 4h, the purity 99.99% nitrogen is introduced into the furnace, the oxygen content in the furnace is controlled to be 0.5%, and the residual stress generated in the cooling stage is further eliminated; then shot blasting treatment is carried out: for the complex parts such as lock core hole with curvature radius ≤10mm, cast iron shot with diameter 0.6mm is used; for the parts such as lock body side plate with curvature radius >10mm, cast iron shot with diameter 1.0mm is used, the shot blasting pressure is 0.5MPa, the coverage reaches 110%, and the lock body surface forms a uniform residual compressive stress layer; finally, secondary tempering is carried out, the temperature is 250 DEG C, and the temperature is kept for 1h, and the lock body organization form is stabilized. Through detection, the impact toughness of the medium carbon steel lock body is improved by 40% compared with the conventional heat treatment process, the surface hardness reaches HV420, and the dual requirements of high strength and high toughness in daily use can be met.

[0046] The specific embodiments of the present application are described in detail above, but it is only as an example, the present application is not equivalent to the specific embodiments described above. For those skilled in the art, any equivalent modification and replacement of the present application are also within the scope of the present application. Therefore, any equivalent transformation and modification made without departing from the spirit and scope of the present application should be covered within the scope of the present application.

Claims

1. A process for the toughness enhancement heat treatment of metal lock bodies, characterized in that, The metal lock body is made of low carbon steel or medium carbon steel with a carbon content of 0.12% to 0.45%, and includes the following steps: S1, pretreatment: sequentially performing surface cleaning and stress pretreatment on the metal lock body; S2, segmented temperature rising: placing the pretreated metal lock body in a heat treatment furnace and rising the temperature to an austenitizing temperature according to a preset temperature rising curve; S3, double-temperature-zone holding: holding at a first stage in the austenitizing temperature range, and then holding at a second stage in a bainite transformation temperature range after cooling; S4, stepwise cooling: performing stepwise cooling treatment on the metal lock body after the double-temperature-zone holding; S5, composite post-treatment: sequentially performing low-temperature tempering, shot blasting and secondary tempering on the cooled metal lock body.

2. The process for the heat treatment of a metal lock body according to claim 1, characterized in that: In step S1, the surface cleaning is performed by sand blasting, the sand blasting medium is brown corundum sand with a particle size of 80-120 mesh, the sand blasting pressure is 0.4-0.6 MPa, and the spraying angle is 45-60°; the stress pretreatment is low-temperature stress relief treatment, the temperature is 620-680℃, the holding time is 2-4 h, argon or nitrogen is introduced into the furnace, the gas flow is 1.5-3.0 m 3 / h, and the furnace pressure is maintained at 105-110 kPa. 3 ​ 3. The process for the heat treatment of a metal lock body according to claim 2, wherein In step S2, the segmented temperature rising includes a low-temperature section, a medium-temperature section and a high-temperature section, and the temperature rising rate of each section decreases in a stepwise manner as the temperature rises; the low-temperature section is from room temperature to 350℃, and the temperature rising rate is 10℃ / min to 20℃ / min; the medium-temperature section is from 350℃ to 600℃, and the temperature rising rate is 5℃ / min to 10℃ / min; the high-temperature section is from 600℃ to 850℃ to 950℃, and the temperature rising rate is adjusted according to the maximum thickness of the lock body: 3℃ / min to 5℃ / min when the thickness is less than or equal to 10mm, and 2℃ / min to 3℃ / min when the thickness is greater than 10mm; the high-temperature section is vacuumized to a vacuum degree less than or equal to 10Pa before temperature rising, and then argon or nitrogen is introduced to normal pressure.

4. The process for strengthening the toughness of a metal lock body by heat treatment according to claim 3, wherein In step S3, the first stage holding temperature is 820℃ to 950℃, and the holding time is 1h to 3h; the second stage holding temperature is 370℃ to 520℃, and the holding time is adjusted according to the carbon content and the total content of alloying elements: the holding time is extended by 0.5h to 1.0h when the carbon content increases by 0.1% and the total content of alloying elements increases by 0.5%; pulse argon is introduced during the holding process, and the flow fluctuates periodically by ±20% to promote uniform nucleation of bainite.

5. The process for the heat treatment of a metal lock body according to claim 4, characterized in that, In step S4, the stepwise cooling is first cooled to the pearlite transformation termination temperature at a first cooling rate, the pearlite transformation termination temperature is 650-680℃, and then cooled to room temperature at a second cooling rate; the first cooling rate is adjusted according to the maximum thickness of the lock body: 10-15℃ / s when the thickness is ≤10mm, and 5-8℃ / s when the thickness is >10mm; the second cooling rate is 0.5-3℃ / s; the cooling medium is a 5-10% polyvinyl alcohol aqueous solution or a polyether aqueous solution, and the circulating flow rate is 8-15m 3 / h. 3 .

6. The process for the heat treatment of a metal lock body according to claim 5, wherein In step S5, the low-temperature tempering temperature is 200℃ to 250℃, the holding time is 2h to 4h, the purity of the introduced nitrogen is greater than or equal to 99.99%, and the oxygen content in the furnace is controlled to be 0.1% to 0.5%; the shot blasting uses graded pellets: 0.3mm to 0.6mm diameter stainless steel pellets or cast iron pellets are used for complex parts with a curvature radius less than or equal to 10mm, and 0.6mm to 1.0mm diameter stainless steel pellets or cast iron pellets are used for flat surfaces or curved surfaces with a curvature radius greater than 10mm, the shot blasting pressure is 0.2MPa to 0.5MPa, and the coverage rate is greater than or equal to 100%; the secondary tempering temperature is 200℃ to 250℃, and the holding time is 0.5h to 1h.

7. The process for the heat treatment of a metal lock body according to claim 6, wherein In step S2, the metal lock bodies are placed in layers with a layer spacing of 1.2 to 2.0 times the maximum thickness of the lock body, and the spacing direction of the lock bodies in the same layer is consistent with the airflow direction in the furnace.

8. The process for the heat treatment of a metal lock body according to claim 7, wherein In step S2, double thermocouples are used for temperature monitoring, which are respectively placed in the center and the edge area of the furnace cavity, and the heating power of the corresponding temperature zone is adjusted by 5% to 15% when the temperature deviation exceeds ±3℃.

9. The process for the heat treatment of a metal lock body according to claim 8, wherein In step S4, the water-soluble quenching medium is used after being filtered to a precision of 20μm, and the medium temperature is controlled to be 25℃ to 40℃.

10. The process for the heat treatment of a metal lock body according to claim 9, wherein In step S3, the second stage holding time is calculated according to the formula t=kxd, where t is the holding time, d is the maximum thickness of the lock body, the initial k value for carbon steel is 1.2h / mm~2.0h / mm; for alloy steel, the initial k value is increased by 10%~20% on the basis of the carbon steel, and is adjusted according to the total content of Cr+Ni+Mo, and the k value is increased by 5% for each increase of 1% of the total content of alloy elements; and the k value is increased by 5%~10% on the basis of the initial value for each increase of 0.1% of the carbon content.

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