Electric pulse heat treatment method for medium carbon steel

Abstract

The invention belongs to the technical field of steel heat treatment processing, and particularly relates to an electric pulse heat treatment method for medium carbon steel. The method comprises the following steps that S1, a steel billet is rolled, the deformation amount of the steel billet is controlled to be 70%-85% in the rolling process, and deformed steel is obtained; and S2, the deformed steel is subjected to electric pulse treatment for 10-60 min under the condition that the peak pulse current density is 45-55 A / mm < 2 >, and then the high-strength and high-plasticity steel is obtained through cooling. A large number of dislocations, vacancies and other defects can be introduced into metal through cold deformation, a large number of cementite nanoparticles are rapidly and evenly separated out in the material in cooperation with high-density pulse current, and the strength of the 45 steel is improved. In addition, the recrystallization temperature of the material can be reduced through the high-density pulse current, the material is promoted to be recovered and recrystallized within a short time, fine recrystallized grains are generated, and the strength and plasticity of the 45 steel are both improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel heat treatment processing, and in particular relates to an electric pulse heat treatment method for medium carbon steel. Background Art

[0002] 45 steel is a high-quality carbon structural steel with good strength, hardness and wear resistance. It is usually used in the manufacture of mechanical parts that need to withstand large loads and require a long service life, such as shafts, gears, pins, connecting rods, nuts and bolts. In addition, 45 steel cold-rolled plates are also suitable for the manufacture of building structures and brackets. In these applications, its strength and hardness can ensure the stability and bearing capacity of the building structure. With the development of my country's national economy and science and technology, the use of 45 steel materials is increasing, and higher requirements are also put forward for the comprehensive performance of 45 steel materials. Therefore, improving the comprehensive performance of 45 steel materials is of great significance to promoting the further development of my country's metal products industry.

[0003] Strength and plasticity are two contradictory performance indicators in metal materials. When the strength is increased, the plasticity usually decreases. The biggest problem in the strengthening process of 45 steel materials is that it is difficult to increase both the strength and plasticity at the same time. At present, the commonly used methods to improve the mechanical properties of 45 steel at home and abroad include refining the pearlite interlamellar spacing and adding alloying elements. These methods have improved the strength of 45 steel materials to a certain extent, but at the same time, the plasticity has decreased to varying degrees. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present invention provides an electric pulse heat treatment method for medium carbon steel, which can improve the strength and plasticity of 45 steel at the same time.

[0005] To achieve the above object, the technical solution provided by the present invention is as follows:

[0006] In a first aspect, the present application provides an electric pulse heat treatment method for medium carbon steel, comprising the following steps:

[0007] S1: The steel billet is subjected to rolling treatment, and the deformation of the steel billet is controlled to be 70-85% during the rolling process to obtain a deformed steel;

[0008] S2: For deformed steel, the peak pulse current density is 45-55A / mm 2 The high-strength and high-plasticity steel is obtained by subjecting the steel to electric pulse treatment for 10-60 minutes and then cooling.

[0009] Optionally, a unidirectional electric pulse is used in the electric pulse treatment process, the pulse current duty cycle is 10%, and the pulse frequency is 100 Hz.

[0010] Optionally, the steel billet is deformed along the length direction during the rolling process.

[0011] Optionally, the rolling process is carried out using a double-roll rolling mill.

[0012] Optionally, the billet rolling is performed at room temperature.

[0013] Optionally, the cooling in S2 is performed by air cooling.

[0014] Optionally, the steel billet is 45 steel.

[0015] Optionally, the deformation amount of the steel billet is 80%.

[0016] Optionally, during the electric pulse treatment, the surface temperature of the steel billet is 210-550°C.

[0017] Optionally, after the electric pulse treatment, cementite nanoparticles with an average particle size of 60-80 nm are precipitated inside the steel billet.

[0018] Compared with the prior art, this application has the following beneficial effects:

[0019] The present invention can introduce a large number of defects such as dislocations and vacancies into the metal through cold deformation, and can promote the precipitation of solute atoms and precipitation phases in the material in combination with high-density pulse current, so that a large number of cementite nanoparticles are quickly and evenly precipitated inside the material, thereby improving the strength of 45 steel. At the same time, the electric pulse treatment method of the present invention can significantly reduce the recrystallization temperature of the material, promote the recovery and recrystallization of the material in a short time, produce fine recrystallized grains, and improve the plasticity and toughness of 45 steel; the rapid heat treatment of the material is achieved through the Joule heat effect and electron wind effect of the high-density pulse current, thereby shortening the heat treatment cycle and reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a SEM image of the deformed steel after rolling treatment in Example 1;

[0021] Figure 2 is a SEM image of the steel after electric pulse treatment in Example 1;

[0022] Figure 3 Schematic diagram of the engineering stress-strain curve of steel under different treatment conditions. DETAILED DESCRIPTION

[0023] In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with the accompanying drawings and specific examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0024] The experimental methods used in the embodiments of the present invention are conventional methods unless otherwise specified.

[0025] The reagents and materials used in this example can all be purchased conventionally. The quantitative experiments involved in the examples were repeated at least three times, and the results were averaged.

[0026] Raw material 45 steel billet: tensile strength is 590.69MPa; elongation is 35.20%.

[0027] Example 1

[0028] An electric pulse heat treatment method for medium carbon steel, the specific steps are as follows:

[0029] 1: The 45 steel billet is cold rolled to obtain a 1mm thick deformed steel. The billet deformation is 80%. The tensile strength of the deformed steel is 1090MPa and the elongation is 9.98%. At this time, the microstructure inside the plate is as follows: Figure 1 As shown in the figure, the cementite layers were squeezed and even adhered together. The cementite was broken and the cracks extended along the rolling direction. At the same time, white flocs were observed on the cementite surface.

[0030] Second: Then the deformed steel is subjected to electric pulse treatment. The electric pulse treatment parameters are: using unidirectional electric pulse; wherein the pulse current duty cycle is 10%, the pulse frequency is 100Hz, and the peak pulse current density is 50A / mm 2 The pulse time is 10 min. The temperature at equilibrium recorded by infrared thermometer during the treatment is about 330℃.

[0031] The high-strength and high-plasticity steel obtained in Example 1 was subjected to SEM and mechanical property tests. The SEM test results are as follows: Figure 3 As shown, a large number of cementite nanoparticles are precipitated in the steel, and the average size of the cementite nanoparticles is 70.34 nm. The tensile strength of the high-strength and high-plasticity steel obtained in this embodiment is 1126 MPa, and the elongation is 11.57%.

[0032] By comparison Figure 1 and Figure 2 It was found that rolling treatment introduced a large number of dislocations into 45 steel, and stress concentration caused the original cementite lamellae to bend, twist, and be squeezed and broken. After electric pulse treatment, a large number of nano-cementite particles precipitated in the pearlite area. The carbon nanoparticles prevented the movement of dislocations through the pinning effect, thereby improving the strength of the material.

[0033] Example 2

[0034] An electric pulse heat treatment method for medium carbon steel, the specific steps are as follows:

[0035] 1. The 45 steel billet is cold rolled to obtain a deformed steel material with a thickness of 1 mm, and the deformation of the billet is 80% (the first step is exactly the same as in Example 1);

[0036] 2. The deformed steel is subjected to electric pulse treatment, and the electric pulse parameters are: using unidirectional electric pulse; wherein the pulse current duty cycle is 10%, the pulse frequency is 100Hz, and the peak pulse current is 45A / mm 2 The pulse time is 30 minutes. The temperature in the equilibrium state recorded by the infrared thermometer during the treatment process is about 260℃. After the electric pulse treatment is completed, high-strength and high-plasticity steel can be obtained by air cooling to room temperature.

[0037] The high-strength and high-plasticity steel obtained in Example 2 was tested for mechanical properties, and its tensile strength was 1146 MPa and its elongation was 13.05%.

[0038] Example 3

[0039] An electric pulse heat treatment method for medium carbon steel, the specific steps are as follows:

[0040] Take a 45 steel billet with a thickness of 1mm and directly perform electric pulse treatment on the billet. The electric pulse treatment parameters are: use unidirectional electric pulse; among which, the pulse current duty cycle is 10%, the pulse frequency is 100Hz, and the peak pulse current density is 50A / mm 2 The pulse time is 10 min. The temperature at equilibrium recorded by infrared thermometer during the treatment is about 330℃.

[0041] The high-strength and high-plasticity steel obtained in Example 3 was subjected to a mechanical property test. The high-strength and high-plasticity steel obtained in this example had a tensile strength of 538.81 MPa and an elongation of 41.77%.

[0042] The mechanical property curve test results of Example 1, Example 2 and the original and rolled 45 steel materials (deformed steel obtained in step 1 of Example 1) are as follows: Figure 3 As shown in the figure, it can be seen that the tensile strength and elongation of the steel after electric pulse treatment are further improved compared with those of deformed steel, and the method is simple to operate, has a short processing time and low energy consumption.

[0043] After large deformation cumulative rolling at room temperature, high-density dislocations are generated at the interface between cementite and ferrite, and the interaction between dislocations and carbon atoms is stronger than that between carbon atoms and iron atoms. Therefore, cementite is dissolved, and carbon atoms diffuse from cementite to ferrite to form supersaturated ferrite. After the pulse current is passed, the Joule effect directly causes the material temperature to rise rapidly, causing the supersaturated ferrite to precipitate cementite nanoparticles. The carbon nanoparticles prevent the movement of dislocations through the pinning effect, thereby improving the strength of the material. In addition, under the action of the electronic wind force of the pulse current, drift electrons and lattice dislocations intersect with each other, promoting the migration of dislocations and intensifying the lattice dislocation effect. This effect is conducive to the recrystallization nucleation of the material, so that the material can be recrystallized at a lower temperature. Recrystallization can eliminate the work hardening phenomenon, reduce the internal stress inside the metal, and restore the plasticity of large deformation cold-rolled 45 steel. At the same time, finer grains may be formed during the recrystallization process, and the fine grain strengthening effect improves the strength and plasticity of the material. Therefore, electric pulse treatment improves the comprehensive mechanical properties of 45 steel.

[0044] The embodiments described in the present invention are preferred solutions, but it should be noted that it is entirely possible for professionals in the art to make some adjustments and optimizations without violating the core principles of the present invention. These adjustments and optimizations are also considered to be within the scope of protection of the present invention.

Claims

1. An electric pulse heat treatment method for medium carbon steel, characterized in that: The steps include: S1: The steel billet is subjected to rolling treatment, and the deformation of the steel billet is controlled to be 70-85% during the rolling process to obtain a deformed steel; S2: For deformed steel, the peak pulse current density is 45-55A / mm 2 , performing electric pulse treatment at a pulse frequency of 80-100 Hz for 10-60 minutes, and then cooling to obtain the high-strength and high-plasticity steel.

2. The electric pulse heat treatment method for medium carbon steel according to claim 1, characterized in that: During the electric pulse treatment, unidirectional electric pulses were used, the pulse current duty cycle was 10%, and the pulse frequency was 100 Hz.

3. The electric pulse heat treatment method for medium carbon steel according to claim 1, characterized in that: During the rolling process, the steel billet is deformed along the length direction.

4. The electric pulse heat treatment method for medium carbon steel according to claim 1, characterized in that: The rolling process is carried out using a double-roll rolling mill.

5. The electric pulse heat treatment method for medium carbon steel according to claim 1, characterized in that: Billet rolling is carried out at room temperature.

6. The electric pulse heat treatment method for medium carbon steel according to claim 1, characterized in that: The cooling described in S2 is performed by air cooling.

7. The electric pulse heat treatment method for medium carbon steel according to claim 1, characterized in that: The steel billet is 45 steel.

8. The electric pulse heat treatment method for medium carbon steel according to claim 1, characterized in that: The deformation amount of the steel billet is 80%.

9. The electric pulse heat treatment method for medium carbon steel according to claim 1, characterized in that: During the electric pulse treatment, the surface temperature of the steel billet is 210-550°C.

10. The electric pulse heat treatment method for medium carbon steel according to claim 1, characterized in that: After electric pulse treatment, cementite nanoparticles with an average particle size of 60-80nm are precipitated inside the steel billet.

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