Heat treatment method of 35CrMoA round steel for sucker rod

Abstract

The application discloses a kind of heat treatment methods of 35CrMoA round steel for sucker rod, belong to the manufacturing technical field of round steel for sucker rod.The method includes the following steps: (1) quenching: after rough machining, 35CrMoA round steel blank for sucker rod is placed in heating furnace, heated to 830 DEG C~870 DEG C, keeps for 50min, then water quenching is carried out;(2) tempering: after quenching, sample is placed in heating furnace, heated to 530 DEG C~570 DEG C, keeps for 120min, then sample is taken out, and cooled in water.The round steel after heat treatment is obtained by accurately controlling quenching temperature, tempering temperature and holding time, and has excellent comprehensive mechanical properties: yield strength is greater than or equal to 885MPa at room temperature, tensile strength is greater than or equal to 1030MPa, elongation is greater than or equal to 12%, reduction of area is greater than or equal to 45%, impact energy KU2 is greater than or equal to 63J, and all kinds of non-metallic inclusions are less than or equal to 1.5 level.

Description

Technical Field

[0001] This invention belongs to the technical field of round steel manufacturing for sucker rods, and specifically relates to a heat treatment method for 35CrMoA round steel for sucker rods. Background Technology

[0002] Sucker rods are critical components in oil extraction, connecting surface pumping units and downhole pumps. They operate under harsh environments with alternating loads and corrosive media such as brine and hydrogen sulfide, thus requiring extremely high standards for the mechanical properties, corrosion resistance, and fatigue life of the materials used. 35CrMoA steel, a medium-carbon alloy structural steel, possesses excellent hardenability and toughness, and is widely used in the manufacture of sucker rods.

[0003] However, 35CrMoA round steel that has not undergone heat treatment or has been improperly heat-treated often suffers from insufficient strength, poor toughness, and uneven microstructure, making it difficult to meet the requirements of the oil extraction industry for material consistency and long-term stability. A proper heat treatment method can optimize the microstructure of the steel, improve its comprehensive mechanical properties, and thus extend the service life of sucker rods.

[0004] In the prior art, there have been some reports on heat treatment methods for 35CrMoA steel. For example, CN103184319A discloses a heat treatment method to improve the low-temperature impact energy of 35CrMoA steel, which adopts a complex process of quenching (850~870℃, oil cooling) + tempering (610~630℃) + sub-temperature quenching (780~800℃) + re-tempering. Although this improves the low-temperature toughness, the process is cumbersome, energy-intensive, and the high tempering temperature leads to a decrease in strength. In addition, the cooling medium in this patent document is oil, which has a slower cooling rate compared to water quenching, making it unfavorable for obtaining high strength.

[0005] Furthermore, different quenching and tempering heat treatment parameters have been disclosed for similar grades of 30CrMoA, such as CN120330423A and CN119980013A. However, the alloy composition of 30CrMoA differs from that of 35CrMoA, and the optimal heat treatment regime cannot be directly applied to 35CrMoA. Therefore, developing a simple heat treatment method for 35CrMoA sucker rod round bars that can stably obtain a high strength and good toughness balance has significant industrial value. Summary of the Invention

[0006] The purpose of this invention is to provide a heat treatment method for 35CrMoA round steel for sucker rods. By optimizing the quenching temperature, tempering temperature and holding time, the material can obtain excellent comprehensive mechanical properties, while simplifying the process, reducing energy consumption and improving production efficiency.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a heat treatment method for 35CrMoA round steel for sucker rods, comprising the following steps:

[0009] (1) Quenching: The rough-machined 35CrMoA sucker rod is placed in a heating furnace using a round steel blank sample, heated to 830℃~870℃, held for 50 minutes, and then water quenched.

[0010] (2) Tempering: Place the quenched sample into a heating furnace and heat it to 530℃~570℃. Hold it for 120 minutes, then take the sample out and cool it in water.

[0011] As a preferred option, in step (1), the temperature is raised to 835°C, held for 50 minutes, and then water quenched.

[0012] Preferably, in step (1), the temperature is raised to 850°C, held for 50 minutes, and then water quenched.

[0013] Preferably, in step (1), the temperature is raised to 865°C, held for 50 minutes, and then water quenched.

[0014] Preferably, in step (2), the temperature is heated to 535°C, kept warm for 120 minutes, and then cooled with water.

[0015] Preferably, in step (2), the temperature is heated to 550°C, kept warm for 120 minutes, and then cooled with water.

[0016] Preferably, in step (2), the temperature is heated to 565°C, kept warm for 120 minutes, and then cooled with water.

[0017] This invention, through research on the phase transformation points of 35CrMoA steel, found that controlling the austenitizing temperature between 830℃ and 870℃ yields a uniform austenitic structure, and holding at this temperature for 50 minutes ensures complete austenitization. Using water as the quenching medium results in rapid cooling and the acquisition of a high-strength martensite structure. Controlling the tempering temperature between 530℃ and 570℃ and holding for 120 minutes decomposes the martensite into tempered sorbite, precipitating fine carbides, thus significantly improving toughness and plasticity while maintaining high strength.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. Heat-treated 35CrMoA round steel has excellent comprehensive mechanical properties: yield strength at room temperature ≥885MPa, tensile strength ≥1030MPa, elongation ≥12%, reduction of area ≥45%, impact absorption energy KU2 ≥63J (preferred requirements: yield strength ≥1037MPa, tensile strength ≥1112MPa, elongation ≥17.5%, reduction of area ≥55%, impact absorption energy KU2 at room temperature ≥73J), and non-metallic inclusions ≤1.5 grade, fully meeting the strict standards of the oil extraction industry for round steel used in sucker rods.

[0020] 2. The method is simple and the parameters are accurate. It only requires one quenching and one tempering, without the need for complicated sub-temperature quenching and other steps, which greatly shortens the production cycle and reduces energy consumption.

[0021] 3. By rationally selecting quenching and tempering temperatures, and using water as the cooling medium, the optimal balance between high strength and good toughness was achieved, while ensuring the uniformity and stability of the material structure.

[0022] 4. The method of this invention is suitable for large-scale industrial production and has significant value for promotion and application. Detailed Implementation

[0023] The present invention will be described in detail below through specific embodiments. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.

[0024] The chemical composition of the 35CrMoA sucker rod round steel used in this embodiment of the invention conforms to GB / T 3077 standard, and the composition meets the following requirements: C 0.32~0.40%, Si 0.17~0.37%, Mn 0.40~0.70%, Cr 0.80~1.10%, Mo 0.15~0.25%, P≤0.025%, S≤0.025%, with the balance being Fe and unavoidable impurities. Specifically, the chemical composition of the 35CrMoA sucker rod round steel used in this embodiment is: C 0.35%, Si 0.22%, Mn 0.50%, Cr 0.87%, Mo 0.20%, P 0.019%, S 0.015%, with the balance being Fe and unavoidable impurities.

[0025] Example 1

[0026] (1) Quenching: The rough-machined 35CrMoA sucker rod is placed in a heating furnace using a round steel blank, heated to 835℃, held for 50 minutes, and then water quenched.

[0027] (2) Tempering: Place the quenched sample into a heating furnace, heat it to 535°C, hold it for 120 minutes, and then take the sample out and cool it in water.

[0028] Example 2

[0029] (1) Quenching: The rough-machined 35CrMoA sucker rod is placed in a heating furnace using a round steel blank, heated to 850℃, held for 50 minutes, and then water quenched.

[0030] (2) Tempering: Place the quenched sample into a heating furnace, heat it to 550°C, hold it for 120 minutes, and then take the sample out and cool it in water.

[0031] Example 3

[0032] (1) Quenching: The rough-machined 35CrMoA sucker rod is placed in a heating furnace using a round steel blank, heated to 865℃, held for 50 minutes, and then water quenched.

[0033] (2) Tempering: Place the quenched sample into a heating furnace, heat it to 565°C, hold it for 120 minutes, and then take the sample out and cool it in water.

[0034] Comparative Example 1

[0035] The same 35CrMoA steel was treated according to the method in Example 1 of CN103184319A: heated to 860℃ and held for 2 hours, then oil quenched; then heated to 620℃ and held for 2 hours, then air cooled (tempering); then heated to 780℃ and held for 2 hours, then oil quenched (sub-temperature quenching); finally heated to 620℃ and held for 2 hours, then air cooled.

[0036] Performance testing

[0037] The mechanical properties, impact toughness, and non-metallic inclusions of the samples obtained in the above embodiments and comparative examples were tested, and the results are shown in Tables 1 to 3.

[0038] Table 1 Mechanical properties at room temperature after heat treatment

[0039]

[0040] Table 2 Impact toughness after heat treatment (room temperature KU2, J)

[0041]

[0042] As shown in Table 2 above, the average impact energy of Comparative Example 1 is 61.2 J, which is lower than the 63 J required by this invention, and its process is complicated.

[0043] Table 3 Non-metallic inclusions (grades) after heat treatment

[0044]

[0045] As can be seen from Tables 1 to 3, the mechanical properties of the embodiments of the present invention significantly exceed the required indicators, especially the yield strength exceeding 1000 MPa, the tensile strength exceeding 1100 MPa, the elongation and reduction of area being excellent, and the average impact toughness all exceeding 79 J, far exceeding the requirement of 63 J. In contrast, although Comparative Example 1 uses a complex process, its average impact toughness is only 61.2 J, and its strength indicators are slightly lower than those of the present invention. Furthermore, the non-metallic inclusions in all embodiments of the present invention are controlled below grade 1.0, resulting in high microstructural purity.

[0046] This invention investigates the effects of quenching temperature, tempering temperature, and holding time on the microstructure and properties of 35CrMoA steel, determining the optimal range of heat treatment parameters. Quenching (water cooling) at 830℃~870℃ achieves sufficient austenitization and forms high-hardness martensite. Subsequent tempering (water cooling) at 530℃~570℃ decomposes the martensite into tempered sorbite, precipitating fine carbides, thus obtaining a combination of high strength and good toughness. Compared with existing technologies, this invention eliminates the need for complex sub-temperature quenching steps, significantly simplifying the process, shortening the production cycle, reducing energy consumption, and simultaneously achieving superior comprehensive mechanical properties.

[0047] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A heat treatment method for 35CrMoA round steel used for sucker rods, characterized in that, Includes the following steps: (1) Quenching: The rough-machined 35CrMoA sucker rod is placed in a heating furnace using a round steel blank sample, heated to 830℃~870℃, held for 50 minutes, and then water quenched. (2) Tempering: Place the quenched sample into a heating furnace and heat it to 530℃~570℃. Hold it for 120 minutes, then take the sample out and cool it in water.

2. The heat treatment method according to claim 1, characterized in that, In step (1), the temperature is raised to 835℃, held for 50 minutes, and then quenched in water.

3. The heat treatment method according to claim 1, characterized in that, In step (1), the temperature is raised to 850℃, held for 50 minutes, and then quenched in water.

4. The heat treatment method according to claim 1, characterized in that, In step (1), the temperature is raised to 865℃, held for 50 minutes, and then quenched in water.

5. The heat treatment method according to claim 1, characterized in that, In step (2), heat to 535°C, keep warm for 120 minutes, and then cool with water.

6. The heat treatment method according to claim 1, characterized in that, In step (2), heat to 550°C, keep warm for 120 minutes, and then cool with water.

7. The heat treatment method according to claim 1, characterized in that, In step (2), heat to 565°C, keep warm for 120 minutes, and then cool with water.

8. The heat treatment method according to claim 1, characterized in that, The chemical composition of the 35CrMoA round steel, by mass percentage, is: C 0.32~0.40%, Si 0.17~0.37%, Mn 0.40~0.70%, Cr 0.80~1.10%, Mo 0.15~0.25%, P≤0.025%, S≤0.025%, with the balance being Fe and unavoidable impurities.

9. The heat treatment method according to claim 1, characterized in that, The mechanical properties of the heat-treated round steel at room temperature meet the following requirements: yield strength ≥ 885 MPa, tensile strength ≥ 1030 MPa, elongation ≥ 12%, reduction of area ≥ 45%, and impact absorption energy KU2 ≥ 63 J; preferably, the following requirements are met: yield strength ≥ 1037 MPa, tensile strength ≥ 1112 MPa, elongation ≥ 17.5%, reduction of area ≥ 55%, and impact absorption energy KU2 ≥ 73 J at room temperature.

10. The heat treatment method according to claim 1, characterized in that, The non-metallic inclusion grades of heat-treated round steel bars shall meet the following requirements: A fine ≤ 1.0 grade, A coarse ≤ 1.0 grade, B fine ≤ 1.0 grade, B coarse ≤ 1.0 grade, C fine ≤ 0 grade, C coarse ≤ 0 grade, D fine ≤ 0.5 grade, D coarse ≤ 0.5 grade.

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