Method for avoiding end cracks in medium-frequency quenching of medium-carbon alloy steel

Abstract

The invention relates to a method for avoiding end cracks in medium-frequency quenching of alloy steel, which comprises the following steps of: firstly, controlling the walking speed of parts to ensure that the distance between every two parts is 40-60mm in the heating process of the parts, and reducing the quenching stress by adopting a measure of increasing pre-cooling of the parts before quenching and cooling; by adjusting the power of the three sets of thyristor intermediate frequency converters and the rotating speed of the three sets of rotary pushing devices in the intermediate frequency parameters, all sets of parameter values reach the optimal matching value, the lowest heating temperature value is adopted on the premise that the technical requirements of parts are met, and the purpose of reducing thermal stress in the quenching cooling process is achieved. The quality problem of cracking of the two end faces is solved, the end face crack sawing procedure after heat treatment is omitted, and the production efficiency is improved by about 30%.

Description

Technical Field

[0001] The invention belongs to the field of heat treatment, and in particular relates to a method for preventing end cracks during medium-frequency quenching of medium-carbon alloy steel. Background Art

[0002] With the rapid development of technology in the machinery industry, the mechanical properties of shaft parts in mechanical parts are constantly improving, and the requirements for hardness, strength and toughness are more stringent. The traditional heat treatment equipment gas furnace quenching can no longer meet the technical requirements of parts. For this reason, medium frequency induction equipment is used, which is mainly used for quenching of shaft parts with a diameter of φ39-60 and a length of 4-6 meters. The advantages of medium frequency quenching are small deformation of parts, high production efficiency, energy saving and environmental protection, and easy automation of the process.

[0003] The medium frequency quenching process used in this original production method has the following shortcomings:

[0004] 1. Alloy steel parts are prone to cracks of 5 to 20 mm in length on both end surfaces.

[0005] 2. The manufacturing process is complicated. Due to the end face crack problem, the length of each piece needs to be extended by 50mm when feeding. After heat treatment, the material is cut to the specified size, so the cutting process needs to be added. Summary of the invention

[0006] The invention provides a method for preventing end cracks during medium-frequency quenching of medium-carbon alloy steel, and the technical problem to be solved is to solve the problem of heat treatment of cracking at both end surfaces of medium-carbon alloy steel during quenching.

[0007] A method for medium frequency quenching of medium carbon alloy steel to avoid end cracks, characterized by: using a thyristor medium frequency inverter to control a heating sensor to achieve heating, equalization and insulation of parts, using a rotary push device to control the travel speed of the parts, and adjusting the power of the thyristor medium frequency inverter and the rotation speed of the rotary push device in the medium frequency parameters to make each group of parameter values ​​reach the best matching value, and then pre-cooling is performed before quenching.

[0008] Furthermore, three groups of thyristor medium frequency inverters are used to control three groups of heating sensors for heating, equalizing and keeping the parts warm, and three groups of rotary push devices are used to control the travel speed of the parts.

[0009] Further, the sensor heating temperature is controlled as follows:

[0010] The first stage controls the temperature at 450±30℃, and the corresponding parameters of the intermediate frequency are: current 580~620A, frequency 780~820HZ;

[0011] The second stage controls the temperature at 700±20℃, and the corresponding parameters of the intermediate frequency are: current 490~530A, frequency 1280~1320HZ;

[0012] The third stage controls the temperature at 830±20℃, and the corresponding parameters of the intermediate frequency are: current 230~270A, frequency 1680~1720HZ.

[0013] Furthermore, the voltage corresponding to the first intermediate frequency is 380V; the roller rotation speed is 20 to 22 rpm.

[0014] Furthermore, the voltage corresponding to the second intermediate frequency is 400V, and the roller rotation speed is 20 to 22 rpm.

[0015] Furthermore, the voltage corresponding to the third intermediate frequency is 600V; the roller rotation speed is 20 to 22 rpm.

[0016] Furthermore, the moving speed of the parts is controlled to ensure that there is a distance of 40 to 60 mm between each part during the heating process to prevent the end faces of the parts from contacting each other and the end temperature from overheating.

[0017] Furthermore, the travel speed of the parts is controlled by adjusting the rotation speed of the rollers.

[0018] Furthermore, the heating temperature of the first 5 to 20 mm end of the part entering the water is 20° C. lower than the temperature of the rest of the part.

[0019] Furthermore, the parts are cooled by an annular cylinder spray cooling device, the cooling medium temperature is 20-40°C, and the distance between the annular cylinder spray cooling device and the heating sensor is adjusted to control the precooling time of the parts before quenching.

[0020] Beneficial effects: The present invention utilizes the existing medium frequency heating furnace production line at the heat treatment site, solves the quality problem of cracking of both end faces, reduces the process of sawing end face cracks after heat treatment, and improves production efficiency by about 30%.

[0021] The present invention can solve the quality problem of cracking at both end faces of medium-frequency quenching of medium-carbon alloy steel with a specification of φ39-60 and a length of 4-6 meters, reduce the process of sawing end face cracks after heat treatment, and has the effect of improving production efficiency by about 30%. Through actual tests, it has been applied. DETAILED DESCRIPTION

[0022] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below.

[0023] The present invention proposes a method for medium-frequency quenching of medium-carbon alloy steel to avoid end cracks, which uses a thyristor medium-frequency inverter to control a heating sensor to achieve heating, equalization and heat preservation of parts, and a rotary push device to control the travel speed of the parts. The above components all belong to existing structures;

[0024] By adjusting the power of three groups of thyristor medium frequency inverters and the rotation speed of three groups of rotary push devices in the medium frequency parameters, the values ​​of each group of parameters can reach the best matching value. The lowest heating temperature value is used while meeting the technical requirements of the parts to achieve the purpose of reducing the thermal stress in the quenching cooling process.

[0025] Three groups of thyristor medium frequency inverters control three groups of sensors, which are mainly used for heating, equalizing and keeping warm the parts. Three groups of rotary push devices control the travel speed of the parts. The best matching value is set by each group of parameter values ​​to achieve the best quenching temperature in each zone.

[0026] The first stage controls the temperature at 450±30℃. The corresponding parameters of the intermediate frequency are: current 580~620A, voltage 380V, frequency 780~820HZ. The roller rotation speed is 20~22 rpm.

[0027] The second stage controls the temperature at 700±20℃. The corresponding parameters of the intermediate frequency are: current 490~530A, voltage 400V, frequency 1280~1320HZ. The roller rotation speed is 20~22 rpm.

[0028] The third stage controls the temperature at 830±20℃. The corresponding parameters of the intermediate frequency are: current 230~270A, voltage 600V, frequency 1680~1720HZ. The roller rotation speed is 20~22rpm.

[0029] Control the moving speed of the parts to ensure that there is a distance of 40 to 60 mm between each part during the heating process to prevent the end faces of the parts from contacting each other and the end temperature from overheating.

[0030] illustrate:

[0031] 1. When heating, keep a gap of 40 to 60 mm between parts to prevent the ends of the parts from overheating.

[0032] 2. The travel speed of parts is controlled by adjusting the inclined rolling rotation speed.

[0033] 3. The parts are placed on the loading rack, and the rotary push device uses a screw-in oblique roller to realize walking. A dedicated person manually controls the distance between the parts within the specified process value next to the loading rack, so that the heating temperature of the 5-20mm end of the part entering the water is 20℃ lower than the temperature of the rest of the part.

[0034] In order to reduce quenching stress and avoid quenching cracking at the ends of parts, this process adopts the measure of adding pre-cooling measures before quenching the parts.

[0035] According to the part specifications and technical requirements, the pre-cooling time of the parts before quenching can be controlled by adjusting the distance between the two sets of ring-shaped cylinder spray cooling devices and the heating inductor. For example, for parts with specifications of φ39×4000, the distance between the two sets of ring-shaped cylinder spray cooling devices and the heating inductor is 250-270mm;

[0036] illustrate:

[0037] The quenching method to avoid cracking is to control the distance between the water spray circle and the sensor to 250-270mm. Precool the end of the part before quenching water spray.

[0038] After quenching, the hardness value is tested along the axial direction within 200mm from the first water-entering end. The hardness value within 5 to 20mm is about 20HB lower than that of the rest, but it does not affect the use of the parts.

[0039] Since then, a method for achieving crack-free end face of medium-carbon alloy steel during medium-frequency quenching has been completed.

[0040] Example

[0041] Material: 42CrMo

[0042] Specification: φ39×4000

[0043] Process flow: loading--feeding--induction heating--spraying--unloading---pit furnace tempering

[0044] Table 1: Thermal and mechanical parameters

[0045]

[0046] Table 2: Medium frequency electrical parameters

[0047]

[0048]

[0049] The present invention is applicable to: φ39~60, length 4~6 meters, material is medium carbon alloy steel, and the quality problem of cracking on both end faces after medium frequency quenching is solved. It reduces the process of sawing end face cracks after heat treatment, and has the effect of improving production efficiency by about 30%. It has been applied through actual tests.

[0050] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preventing end cracks during medium frequency quenching of medium carbon alloy steel, characterized in that: The thyristor medium frequency inverter is used to control the heating sensor to achieve the heating, equalization and insulation of the parts. The rotary push device is used to control the walking speed of the parts. By adjusting the thyristor medium frequency inverter power and the rotation speed of the rotary push device in the medium frequency parameters, the values ​​of each group of parameters can reach the best matching value, and then pre-cooling is carried out before quenching.

2. A method for preventing end cracks during medium frequency quenching of medium carbon alloy steel according to claim 1, characterized in that: Three groups of thyristor medium frequency inverters are used to control three groups of heating sensors for heating, equalizing and keeping warm the parts, and three groups of rotary push devices are used to control the travel speed of the parts.

3. A method for preventing end cracks during medium frequency quenching of medium carbon alloy steel according to claim 1, characterized in that: The sensor heating temperature is controlled as follows: The first stage controls the temperature at 450±30℃, and the corresponding parameters of the intermediate frequency are: current 580~620A, frequency 780~820HZ; The second stage controls the temperature at 700±20℃, and the corresponding parameters of the intermediate frequency are: current 490~530A, frequency 1280~1320HZ; The third stage controls the temperature at 830±20℃, and the corresponding parameters of the intermediate frequency are: current 230~270A, frequency 1680~1720HZ.

4. A method for preventing end cracks during medium frequency quenching of medium carbon alloy steel according to claim 3, characterized in that: The voltage corresponding to the first intermediate frequency is 380V; the roller rotation speed is 20 to 22 rpm.

5. A method for preventing end cracks during medium frequency quenching of medium carbon alloy steel according to claim 3, characterized in that: The voltage corresponding to the second intermediate frequency is 400V, and the roller rotation speed is 20 to 22 rpm.

6. A method for preventing end cracks during medium frequency quenching of medium carbon alloy steel according to claim 3, characterized in that: The voltage corresponding to the third intermediate frequency is 600V; the roller rotation speed is 20 to 22 rpm.

7. A method for preventing end cracks during medium frequency quenching of medium carbon alloy steel according to claim 1, characterized in that: Control the moving speed of the parts to ensure that there is a distance of 40 to 60 mm between each part during the heating process to prevent the end faces of the parts from contacting each other and the end temperature from overheating.

8. The method for preventing end cracks during medium frequency quenching of medium carbon alloy steel according to claim 1, characterized in that: The parts travel speed is controlled by adjusting the roller rotation speed.

9. A method for preventing end cracks during medium frequency quenching of medium carbon alloy steel according to claim 1, characterized in that: The heating temperature of the first 5 to 20 mm of the part entering the water is 20°C lower than the temperature of the rest of the part.

10. The method for preventing end cracks during medium frequency quenching of medium carbon alloy steel according to claim 1, characterized in that: The parts are cooled by the annular cylinder spray cooling device, the cooling medium temperature is 20-40℃, and the distance between the annular cylinder spray cooling device and the heating sensor is adjusted to control the pre-cooling time of the parts before quenching.

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