Method for improving mechanical property of round steel for sucker rod

Abstract

The invention discloses a method for improving the mechanical property of round steel for a sucker rod, and belongs to the technical field of steel. The method comprises the following steps: adjusting chemical components, removing vanadium element, properly increasing the contents of titanium, silicon and chromium, and reducing the contents of carbon and manganese; the heat treatment process is optimized, and the comprehensive performance of the steel is improved through hot rolling air cooling, tempering slow cooling at 440 DEG C and natural aging treatment. Through verification, the mechanical property of the steel can be remarkably improved, the steel can completely meet or exceed the SY / T6272-1997 standard requirement, and compared with the prior art, the method has the advantages of being simple in process, low in cost and excellent in performance and is suitable for large-scale industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of steel, and in particular relates to a method for improving the mechanical properties of round steel for pumping rods. Background Art

[0002] With the continuous development of the petroleum industry, sucker rods, as a crucial component of oil production equipment, are subject to increasingly stringent performance requirements for the steel used. Commonly used sucker rod steels on the market include quenched and tempered 20CrMo, 35CrMo, and 40Mn2, as well as non-quenched and tempered bainitic steels such as FG20. While these steels demonstrate excellent tensile strength and impact toughness, their plasticity properties, such as elongation and reduction of area, fall short of the requirements for HL-type sucker rod steel in the latest industry standard, SY / T6272-1997.

[0003] Taking FG20 steel as an example, by optimizing its composition design and heat treatment process, it is possible to obtain granular bainite structure under air cooling conditions and has high comprehensive mechanical properties. However, since it is difficult to completely avoid mixed structures (such as granular bainite and granular structure) during the production process, the plasticity index of FG20 steel has certain limitations in meeting the requirements of the new standard. In addition, traditional quenching and tempering heat treatment processes usually require large equipment, such as medium-frequency quenching furnaces and box-type tempering furnaces, which not only increases investment and operating costs, but also has problems such as high energy consumption, high pollution and unstable quality.

[0004] Therefore, current research on pumper rod steel focuses on improving its overall performance, particularly its plasticity (such as elongation and reduction of area), through simple and economical processes. To address this challenge, a new method combining chemical composition optimization and heat treatment improvements has been developed. This approach not only meets higher performance requirements but also simplifies the process and reduces production costs, thus possessing significant research and application value. Summary of the Invention

[0005] The present invention aims to provide a method for improving the mechanical properties of round steel used in pumper rods. This method can significantly increase the tensile strength, elongation, and reduction of area of ​​the steel, particularly in terms of plasticity, meeting or exceeding the requirements of the latest industry standard SY / T 6272-1997.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for improving the mechanical properties of round steel for pumping rods, comprising: optimizing chemical composition and optimizing heat treatment process; wherein:

[0008] Chemical composition optimization: Based on the existing FG20 steel, vanadium is removed and the titanium content is appropriately increased to refine the grains; the silicon and chromium contents are increased, and the carbon and manganese ratios are reduced. The optimized chemical composition by weight percentage is: C 0.18%-0.22%, Si 1.00%-1.10%, Mn 1.40%-1.50%, P≤0.015%, S≤0.010%, Cr 0.90-1.00%, Mo 0.15-0.25%, Ti 0.04-0.07%, and the rest is Fe and unavoidable impurities, thereby improving the strength, toughness and plasticity of the steel;

[0009] Optimization of heat treatment process: After hot rolling, the steel is air-cooled and then tempered at 440±10℃ for 1 hour using a slow cooling method; combined with natural aging treatment to eliminate internal stress and further improve the plasticity of the steel.

[0010] Further, it was tempered at 440°C for 1 hour.

[0011] Furthermore, the chemical composition of the weight percentage after optimization is: C 0.21%, Si 1.05%, Mn 1.45%, P 0.012%, S 0.007%, Cr 0.97%, Mo 0.21%, Ti 0.055%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

[0012] Furthermore, the steel is smelted in an electric furnace and then rolled into round steel with a diameter of 25 mm.

[0013] Furthermore, the cooling rate of the slow cooling is 1-2°C / s.

[0014] Furthermore, the cooling rate of the slow cooling is 1.5°C / s.

[0015] Furthermore, the method adopts slow cooling and natural aging treatment, which simplifies the traditional complex quenching process and reduces production costs and energy consumption.

[0016] The design ideas of chemical composition are as follows:

[0017] C: Controlled at 0.18% to 0.22%, it provides the basic strength and hardness of the steel. However, too high a carbon content will reduce the plasticity. Therefore, the carbon content is controlled within a moderate range to balance strength and plasticity.

[0018] Si: The content is controlled at 1.00% to 1.10%. As a solid solution strengthening element, it improves the strength of steel and promotes bainite transformation, improving plasticity and toughness.

[0019] Mn: The content is controlled at 1.40% to 1.50% to enhance the hardenability and toughness of the steel. However, excessive manganese will increase brittleness, so the manganese content should be appropriately reduced to optimize the overall performance.

[0020] Cr: designed to be 0.90-1.00%, improving the corrosion resistance and hardenability of steel, while refining the structure and improving strength and toughness;

[0021] Mo: The content is controlled at 0.15-0.25%, which improves high temperature strength and tempering stability and reduces the secondary hardening effect;

[0022] Ti: Add 0.04-0.07% to improve strength and toughness through grain refinement and precipitation strengthening mechanism;

[0023] P and S: strictly control P≤0.015%, S≤0.010%. As impurity elements, their content is controlled to reduce the adverse effect on the toughness of steel;

[0024] Compared with the prior art, the present invention has the following beneficial technical effects:

[0025] Through the above design, the steel can not only meet the high performance requirements of HL type sucker rod steel, but also has the advantages of simple process, low energy consumption and cost-effectiveness, and is suitable for large-scale industrial production.

[0026] This method improves the mechanical properties of round steel for pumper rods by optimizing its chemical composition and heat treatment process, successfully increasing the steel's tensile strength, elongation, and reduction of area. In particular, its plasticity index meets the latest industry standards. This method is simple, cost-effective, and suitable for large-scale industrial production, providing an innovative technical solution for improving the performance of pumper rod steel.

[0027] Advantages of the present invention: (1) The optimized round steel has higher tensile strength, elongation, and cross-sectional reduction, and its comprehensive performance meets or exceeds industry standard requirements. (2) By eliminating complex quenching equipment and optimizing the heat treatment process, production costs are reduced, while energy consumption and environmental pollution are also reduced. (3) This method is suitable for large-scale industrial production, can meet the high-performance requirements of the oil industry for pump rod steel, and has wide promotion and application value. DETAILED DESCRIPTION

[0028] The following is a further detailed description of a method for improving the mechanical properties of round steel for pumping rods according to the present invention.

[0029] A method for improving the mechanical properties of round steel for a sucker rod. The chemical composition of the round steel comprises, by weight percentage, C 0.18% to 0.22%, Si 1.00% to 1.10%, Mn 1.40% to 1.50%, P ≤ 0.015%, S ≤ 0.010%, Cr 0.90% to 1.00%, Mo 0.15% to 0.25%, Ti 0.04% to 0.07%, and the remainder being Fe and unavoidable trace impurities, with the total weight fraction being 100%.

[0030] The key steps of the method for improving the mechanical properties of round steel for pumping rods in this embodiment are: chemical composition optimization and heat treatment process optimization.

[0031] Furthermore, on the basis of the existing FG20 steel, vanadium is removed and the titanium content is appropriately increased to refine the grains; the silicon and chromium contents are increased, and the carbon and manganese ratios are reduced. The chemical composition is C 0.18% to 0.22%, Si 1.00% to 1.10%, Mn 1.40% to 1.50%, P ≤ 0.015%, S ≤ 0.010%, Cr 0.90 to 1.00%, Mo 0.15 to 0.25%, and Ti 0.04 to 0.07%, thereby improving the strength, toughness, and plasticity of the steel.

[0032] Furthermore, the steel is air-cooled after hot rolling and then tempered at 440°C for 1 hour with slow cooling; combined with natural aging treatment to eliminate internal stress and further improve the plasticity of the steel;

[0033] Example 1:

[0034] The chemical composition is C 0.21%, Si 1.05%, Mn 1.45%, P 0.012%, S 0.007%, Cr 0.97%, Mo 0.21%, Ti 0.055%, and the remainder is Fe and unavoidable trace impurities, totaling 100% by mass. The steel was smelted in an electric furnace and rolled into 25mm diameter round steel. The samples were aged under natural conditions for 30 days before tempering. The following heat treatment was performed: tempering temperature: 440°C, time: 1 hour; cooling method: slow cooling (1.5°C / s). The steel achieved a tensile strength of 980 MPa, an elongation of 12.5%, and a reduction of area of ​​45%, meeting the SY / T6272-1997 standard.

[0035] Comparative Example 1:

[0036] In Comparative Example 1, the steel grade was FG20 steel, and its chemical composition was C 0.25%, Si 0.85%, Mn 1.80%, P 0.015%, S 0.009%, Cr 0.80%, Mo 0.20%, V 0.060%, with the remainder being Fe and unavoidable trace impurities, totaling 100% by mass. Using the same smelting and heat treatment processes as in the example, test results showed a tensile strength of 960 MPa, an elongation of 10%, and a reduction of area of ​​40%.

[0037] Comparative Example 2:

[0038] In Comparative Example 2, except that the slow cooling and heat treatment process was not used, the rest was identical to the embodiment. In this comparative example, the tensile strength was 978 MPa, which did not change significantly, but the elongation dropped to 10% and the cross-sectional shrinkage dropped to 35%.

[0039] Comparative Example 3:

[0040] Comparative Example 3, which was identical to the Example except that it was tempered directly after rolling without undergoing natural aging, had a tensile strength of 970 MPa, slightly lower than that of the Example. Its elongation and reduction of area were also lower than those of the Example, at 11% and 40%, respectively.

[0041] The present invention greatly improves the comprehensive mechanical properties of round steel for sucker rods by adjusting the chemical composition and optimizing the heat treatment process, especially in terms of elongation and cross-sectional shrinkage. Compared with traditional methods, it has significant advantages and is novel and practical.

[0042] As can be seen from the above examples and comparative examples:

[0043] (1) The optimized steel is superior to the control in key indicators such as tensile strength, elongation and cross-sectional reduction, especially in terms of plasticity.

[0044] (2) By removing vanadium and increasing the contents of titanium, silicon, and chromium, the optimized steel can better form a single granular bainite structure, thereby improving the overall performance;

[0045] (3) The use of slow cooling and natural aging treatment simplifies the traditional complex quenching process and reduces production costs and energy consumption;

[0046] (4) The heat treatment parameters used in the present invention have good adaptability to industrial production and can effectively avoid quality fluctuations caused by equipment problems in traditional processes;

[0047] (5) This method is not only applicable to the production of round steel for sucker rods, but can also be extended to other fields that require high-strength and high-plasticity steel.

[0048] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for improving the mechanical properties of round steel for sucker rods, characterized in that: include: Chemical composition optimization and heat treatment process optimization; among them: Chemical composition optimization: Based on the existing FG20 steel, vanadium is removed and the titanium content is appropriately increased to refine the grains; the silicon and chromium contents are increased, and the carbon and manganese ratios are reduced. The optimized chemical composition by weight percentage is: C 0.18%-0.22%, Si 1.00%-1.10%, Mn 1.40%-1.50%, P≤0.015%, S≤0.010%, Cr 0.90-1.00%, Mo 0.15-0.25%, Ti 0.04-0.07%, and the rest is Fe and unavoidable impurities, thereby improving the strength, toughness and plasticity of the steel; Optimization of heat treatment process: After hot rolling, the steel is air-cooled and then tempered at 440±10℃ for 1 hour using a slow cooling method; combined with natural aging treatment to eliminate internal stress and further improve the plasticity of the steel.

2. The method for improving the mechanical properties of round steel for sucker rods according to claim 1, characterized in that: Tempering at 440°C for 1 hour.

3. The method for improving the mechanical properties of round steel for sucker rod according to claim 1, characterized in that: The chemical composition of the optimized weight percentage is: C 0.21%, Si 1.05%, Mn 1.45%, P 0.012%, S 0.007%, Cr0.97%, Mo 0.21%, Ti 0.055%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

4. The method for improving the mechanical properties of round steel for sucker rod according to claim 1, characterized in that: It is smelted in an electric furnace and then rolled into round steel with a diameter of 25mm.

5. The method for improving the mechanical properties of round steel for sucker rod according to claim 1, characterized in that: The cooling rate of the slow cooling is 1-2°C / s.

6. The method for improving the mechanical properties of round steel for sucker rods according to claim 5, characterized in that: The cooling rate of the slow cooling is 1.5°C / s.

7. The method for improving the mechanical properties of round steel for sucker rods according to claim 1, characterized in that: This method uses slow cooling and natural aging treatment, which simplifies the traditional complex quenching process and reduces production costs and energy consumption.