A HL-grade hydrogen-resistant sucker rod steel and its preparation method

Abstract

This invention discloses an HL-grade hydrogen-resistant sucker rod steel and its preparation method, belonging to the field of special steel technology. The chemical composition and mass percentages are as follows: C: 0.30–0.32%, Si: 0.23–0.27%, Mn: 0.90–1.10%, Mo: 0.24–0.26%, Cr: 1.0–1.1%, Ni: 1.1–1.3%, V: 0.07–0.09%, P≤0.01%, S≤0.01%, with the balance being iron and unavoidable impurities. The preparation method includes smelting, forging, rolling, and heat treatment processes. The HL-grade hydrogen-resistant sucker rod steel obtained by this invention meets the following performance requirements: yield strength ≥900 MPa, tensile strength ≥1100 MPa, elongation ≥15%, reduction of area ≥60%, and impact energy KV2 ≥80 J, meeting the national standard for HL-grade sucker rod steel and exhibiting excellent resistance to hydrogen embrittlement.

Description

Technical Field

[0001] This invention belongs to the field of special steel technology and relates to an H-grade hydrogen-resistant sucker rod steel with excellent comprehensive mechanical properties and hydrogen resistance, and its preparation method. Background Technology

[0002] Mechanical oil recovery is currently the main method of crude oil extraction in my country. Rod pump oil recovery is the most widely used method within mechanical oil recovery. As the main load-bearing component of rod pump oil recovery equipment, the sucker rod undergoes reciprocating motion under tensile and compressive loads, making it highly susceptible to deformation, wear, and fatigue, ultimately leading to fracture. As oil exploration and extraction gradually expand into deeper, low-permeability, deep-sea, and polar regions, the operating environment becomes increasingly harsh, placing higher demands on sucker rods. High strength, corrosion resistance, and low cost are the main development trends.

[0003] To meet the requirements of upstream and downstream customers in the market, designing a high-performance, corrosion-resistant, and low-cost sucker rod steel has broad application prospects. Summary of the Invention

[0004] This invention provides an HL-grade hydrogen-resistant sucker rod steel and its preparation method. Through reasonable composition equipment and appropriate heat treatment process, a high-performance, low-cost HL-grade hydrogen-resistant sucker rod steel with certain hydrogen resistance properties is obtained.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: an HL-grade hydrogen-resistant sucker rod steel, wherein the chemical composition and mass percentage of the hydrogen-resistant sucker rod steel are as follows: C: 0.30-0.32%, Si: 0.23-0.27%, Mn: 0.90-1.10%, Mo: 0.24-0.26%, Cr: 1.0-1.1%, Ni: 1.1-1.3%, V: 0.07-0.09%, P≤0.01%, S≤0.01%, with the balance being iron and unavoidable impurities.

[0006] The steel for hydrogen-resistant sucker rods described in this invention has a yield strength ≥900MPa, tensile strength ≥1100MPa, elongation ≥15%, reduction of area ≥60%, and impact energy KV2 ≥80J.

[0007] The metallographic structure of the hydrogen-resistant sucker rod steel described in this invention is tempered bainite.

[0008] The hydrogen-resistant sucker rod steel described in this invention exhibits a hydrogen embrittlement sensitivity index I under fully hydrogen-charged conditions. HE ≤75%, compared with 30Ni2CrMnMoVA steel (I HE Compared to ≥90%, resistance to hydrogen embrittlement sensitivity is improved by at least 15%.

[0009] Another objective of this invention is to provide a method for preparing the above-mentioned HL-grade hydrogen-resistant sucker rod steel, the method comprising smelting, forging, rolling, and heat treatment processes, the specific steps of which are as follows:

[0010] (1) Smelting: Vacuum induction furnace smelting, and hot casting of molten steel to obtain ingots;

[0011] (2) Forging: The ingot is forged into a rectangular blank at a forging temperature of 1150-1200℃ in order to obtain a blank with a dense structure and uniform composition, which provides the necessary conditions for obtaining a uniform product structure in the future.

[0012] (3) Rolling: Heat the billet to 1080~1110℃, hold for 2.0~2.5h, and roll it into a smooth round bar of specified specifications in multiple passes. The temperature during hot rolling is maintained in the range of 950~1050℃. After rolling, air cooling is used.

[0013] (4) Heat treatment: Quenching and tempering heat treatment process is adopted.

[0014] The heat treatment process of the present invention involves heating the rolled billet in a furnace to above the austenitizing temperature and holding it for a certain time, quenching it at a temperature of 850-900°C for 45-60 minutes, and then water quenching it to room temperature.

[0015] The heat treatment process described in this invention involves a tempering temperature of 550–640°C for 60–90 minutes, followed by air cooling to room temperature.

[0016] The diameter of the round bar described in this invention is Ф19-25mm.

[0017] The sucker rod steel described in this invention adopts a low-Ni design. Compared with 30Ni2CrMnMoVA steel, reducing Ni effectively lowers production costs while ensuring a certain level of hydrogen resistance. Appropriately increasing the Cr content helps improve hydrogen embrittlement resistance and ensure strength. The increase in Mn content compensates for strength loss. Finally, experimental verification shows that the quenching and tempering heat treatment process more easily yields HL-grade sucker rod steel that meets both mechanical and hydrogen embrittlement resistance requirements.

[0018] After the above heat treatment process, the microstructure obtained by the present invention is tempered bainite, with fine, irregular strip-shaped and granular carbides uniformly and diffusely distributed on the ferrite matrix, resulting in stronger and tougher properties. At the same time, the precipitates generated during the tempering process are uniformly distributed at the grain boundaries and within the grains, which, together with the carbides, increase the number of irreversible hydrogen traps in the steel, thereby achieving a good balance of strength and toughness and a low hydrogen embrittlement sensitivity index.

[0019] The beneficial effects of adopting the above technical solution are as follows:

[0020] 1. The composition of this invention adopts a low-Ni, high-Cr, and high-Mn design scheme, reducing alloy costs and having profound significance for improving and optimizing the comprehensive performance of HL-grade hydrogen-resistant sucker rod steel, as well as reducing costs and increasing efficiency. 2. The HL-grade hydrogen-resistant sucker rod steel of this invention uses a quenching and tempering heat treatment process, achieving a tempered bainitic structure within a wide temperature range of 550–640℃. Compared to the tempered sorbite structure of 30Ni2CrMnMoVA steel, it achieves excellent strength and toughness matching while exhibiting lower hydrogen embrittlement sensitivity. 3. During the heat treatment process of this invention, a tempered bainitic structure can be obtained within a wide temperature range of 550–640℃. Compared to the heat treatment regime of 30Ni2CrMnMoVA steel, this is more convenient for production line application. 4. The microstructure obtained by this invention can contain more carbides and precipitates, increasing the number of irreversible hydrogen traps in the microstructure, resulting in lower hydrogen embrittlement sensitivity. While ensuring mechanical properties, it can significantly improve the hydrogen resistance of the material during service. Attached Figure Description

[0021] Figure 1 Metallographic structure of Example 3 (1000X);

[0022] Figure 2 SEM carbide morphology of Example 3 (5KX);

[0023] Figure 3 Comparative SEM morphology (10KX).

[0024] Figure 4 TEM morphology of the precipitate in Example 3 (26KX). Detailed Implementation

[0025] The present invention will be further described in detail below with reference to specific embodiments.

[0026] Examples 1-6

[0027] A method for preparing HL-grade hydrogen-resistant sucker rod steel includes smelting, forging, rolling, and heat treatment processes, with the specific steps as follows:

[0028] (1) Smelting: The steel for sucker rods No. 1-6 and the comparative proportion were smelted in a 50kg vacuum induction furnace. After hot casting of the molten steel, a rectangular ingot with a cross-section of 160mm×160mm was obtained.

[0029] (2) Forging: The ingot is forged into a rectangular blank with a cross-section of 50mm×50mm, and the forging temperature is 1150~1200℃;

[0030] (3) Rolling: Heat the billet to 1080~1110℃, hold for 2.0~2.5h, and roll it into a smooth round bar of Ф19-25mm in multiple passes. The single pass reduction rate is ≥20%. The temperature during hot rolling is maintained in the range of 950~1050℃. After rolling, air cooling is used.

[0031] (4) Heat treatment: The smooth round bar after hot rolling is subjected to a suitable quenching and tempering heat treatment process. The quenching temperature is 850-900℃, the holding time is 45-60min, and the water quenching is carried out to room temperature. The tempering temperature is 550-640℃, the time is 60-90min, and the air cooling is carried out to room temperature.

[0032] The chemical composition control of each embodiment is shown in Table 1, the control parameters are shown in Table 2, and the mechanical property test results are shown in Table 3.

[0033] Table 1 Chemical composition and percentage content (wt%) of steel used for sucker rods in Examples 1-6

[0034]

[0035] Table 2. Process control parameters for the preparation of sucker rod steel in Examples 1-6

[0036]

[0037] Table 3. Test results of mechanical properties of steel used for sucker rods in Examples 1-6

[0038]

[0039] The performance of the comparative example (30Ni2CrMnMoVA steel) was compared with that of the products obtained in Examples 1-6. The chemical composition of the comparative example 30Ni2CrMnMoVA steel is as follows: C: 0.30%, Si: 0.25%, Mn: 0.85%, Mo: 0.25%, Cr: 0.85%, Ni: 1.61%, V: 0.08%, P: 0.0080%, S: 0.0060%.

[0040] The products prepared in Examples 1-6 and the comparative examples were subjected to mechanical property tests, including a pre-charged slow-rate tensile test (SSRT). The SSRT was performed at 5 mA / cm². 2 Pre-charged with hydrogen for 24 hours under constant current, with a stretching rate of 1×10⁻⁶. -6 / s, hydrogen embrittlement susceptibility is calculated using elongation after fracture and tensile strength, i.e., I HE =1-[σ H (1+δ) H The mechanical property test results of each embodiment and comparative example are shown in Table 3.

[0041] Compared with the comparative examples, the products of Examples 1-6 of this invention have better strength and toughness; under the slow-rate hydrogen charging tensile test conditions, the hydrogen embrittlement sensitivity index I of the products of Examples 1-6 of this invention is... H With a hydrogen embrittlement sensitivity of ≤75%, the hydrogen embrittlement resistance is significantly reduced, indicating a marked improvement in its resistance to hydrogen embrittlement.

[0042] The microstructure characteristics of the heat-treated materials from Examples 1-6 and the comparative examples were observed. It was found that the microstructure of Examples 1-6 was tempered bainite, such as... Figure 1 As shown (other examples are similarly omitted), the comparative example is tempered sorbite. Since tempered bainite has fewer dislocations than tempered sorbite, the number of reversible hydrogen traps in the steel is less, resulting in lower hydrogen embrittlement sensitivity. Scanning electron microscopy (SEM) revealed that the microstructure of Examples 1-6 showed a uniformly dispersed distribution of fine, irregular, lamellar, and granular carbides in the ferrite matrix. With increasing tempering temperature, spheroidization and coarsening occurred. Transmission electron microscopy (TEM) revealed a certain amount of precipitates uniformly distributed at grain boundaries and within the grains. These carbides and precipitates can pin hydrogen, forming irreversible hydrogen traps, inhibiting hydrogen diffusion, reducing the content of free hydrogen in the material, lowering the material's hydrogen embrittlement sensitivity, and thus enhancing the material's resistance to hydrogen.

[0043] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A type of HL-grade hydrogen-resistant sucker rod steel, characterized in that: The chemical composition and mass percentage of the steel used for the hydrogen-resistant sucker rod are as follows: C: 0.30-0.32%, Si: 0.23-0.27%, Mn: 0.90-1.10%, Mo: 0.24-0.26%, Cr: 1.0-1.1%, Ni: 1.1-1.3%, V: 0.07-0.09%, P≤0.01%, S≤0.01%, with the balance being iron and unavoidable impurities; The metallographic structure of the steel used for the hydrogen-resistant sucker rod is tempered bainite. The hydrogen-resistant sucker rod steel exhibits a hydrogen embrittlement sensitivity index I under fully hydrogen-charged conditions. HE ≤75%; The preparation method of the hydrogen-resistant sucker rod steel includes smelting, forging, rolling, and heat treatment processes, with the specific steps as follows: (1) Smelting: Vacuum induction furnace smelting, and hot casting of molten steel to obtain ingots; (2) Forging: The ingot is forged into a rectangular billet at a forging temperature of 1150-1200℃; (3) Rolling: Heat the billet to 1080~1110℃, hold for 2.0~2.5h, and roll it into a smooth round bar of specified specifications in multiple passes. The temperature during hot rolling is maintained in the range of 950~1050℃. After rolling, air cooling is used. (4) Heat treatment: Quenching and tempering heat treatment process is adopted; The heat treatment process involves quenching at 850–900°C for 45–60 minutes, followed by water quenching to room temperature. The heat treatment process involves tempering at a temperature of 550–640°C for 60–90 minutes, followed by air cooling to room temperature.

2. The HL-grade hydrogen-resistant sucker rod steel according to claim 1, characterized in that: The steel used for the hydrogen-resistant sucker rod has a yield strength ≥900MPa, tensile strength ≥1100MPa, elongation ≥15%, reduction of area ≥60%, and impact energy KV2 ≥80J.

3. The method for preparing HL-grade hydrogen-resistant sucker rod steel according to claim 1 or 2, characterized in that: The preparation method includes smelting, forging, rolling, and heat treatment processes, with the specific steps as follows: (1) Smelting: Vacuum induction furnace smelting, and hot casting of molten steel to obtain ingots; (2) Forging: The ingot is forged into a rectangular billet at a forging temperature of 1150-1200℃; (3) Rolling: Heat the billet to 1080~1110℃, hold for 2.0~2.5h, and roll it into a smooth round bar of specified specifications in multiple passes. The temperature during hot rolling is maintained in the range of 950~1050℃. After rolling, air cooling is used. (4) Heat treatment: Quenching and tempering heat treatment process is adopted; The heat treatment process involves quenching at 850–900°C for 45–60 minutes, followed by water quenching to room temperature. The heat treatment process involves tempering at a temperature of 550–640°C for 60–90 minutes, followed by air cooling to room temperature.

4. The method for preparing HL-grade hydrogen-resistant sucker rod steel according to claim 3, characterized in that: The diameter of the round bar is Ф19-25mm.

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