Production method of 900 MPa-grade high-strength sucker rod round steel based on rare earth microalloying

Abstract

The invention discloses a production method of 900 MPa-grade high-strength sucker rod round steel based on rare earth microalloying, and belongs to the technical field of steel and iron material production. A proper amount of rare earth elements are added into the steel, and the purification, modification and alloying effects of the rare earth elements are utilized, so that the inclusion form and distribution of the steel are improved, grains are refined, and the strength, toughness and corrosion resistance of the steel are improved; meanwhile, by reasonably controlling production process parameters of smelting, continuous casting, rolling, heat treatment and the like, the structure uniformity and the mechanical property stability of the steel are ensured. Compared with a traditional production method, the 900 MPa-grade high-strength sucker rod round steel produced through the method has higher strength and better toughness and corrosion resistance, and the requirement of the oil exploitation industry for high-end sucker rod materials can be met.

Description

Technical Field

[0001] The invention belongs to the technical field of steel material production, and in particular relates to a production method of 900MPa-grade high-strength pumping rod round steel based on rare earth microalloying. Background Art

[0002] In the oil and gas industry, sucker rods are crucial downhole tools, their performance directly impacting the efficiency and safety of oil production. As oil production progresses deeper, higher requirements are placed on the strength, toughness, and corrosion resistance of sucker rods. As a key material for their manufacture, 900MPa high-strength sucker rod round steel must possess excellent comprehensive mechanical properties.

[0003] Currently, traditional high-strength pumper rod round steel production methods primarily rely on alloying elements such as carbon, manganese, silicon, and chromium to enhance the steel's strength. However, relying solely on the addition of these alloying elements makes it difficult to effectively improve the steel's toughness and corrosion resistance while simultaneously increasing its strength. This addition can also lead to an increase in internal inclusions, compromising the steel's quality stability. Furthermore, in traditional production processes, inaccurate control of heat treatment parameters can also result in poor structural uniformity and significant fluctuations in mechanical properties.

[0004] Rare earth elements possess unique physical and chemical properties. Adding appropriate amounts of these elements to steel can improve the morphology and distribution of inclusions, refine grain size, and enhance the steel's toughness, corrosion resistance, and oxidation resistance. Therefore, developing a method for producing 900 MPa high-strength pumper rod round steel based on rare earth microalloying is of great practical significance. Summary of the Invention

[0005] The purpose of the present invention is to provide a production method of 900MPa grade high-strength pumping rod round steel based on rare earth microalloying, which improves the strength, toughness and corrosion resistance of the steel and improves the quality stability of the steel by rationally controlling the alloy composition and production process parameters.

[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 producing 900MPa grade high-strength pumping rod round steel based on rare earth microalloying, comprising:

[0008] Smelting: The prepared raw materials are added to an electric arc furnace or converter for smelting, and the smelting temperature is controlled at 1550-1650℃. During the smelting process, sufficient deoxidation and desulfurization are carried out to ensure the purity of the molten steel. In the later stage of smelting, rare earth alloys are added. The amount of rare earth alloy added is calculated based on the target content of rare earth elements in the molten steel. It is added in batches to ensure that the rare earth elements are evenly distributed in the molten steel.

[0009] Continuous casting: The smelted molten steel is poured into the continuous casting machine for continuous casting, and the continuous casting temperature is controlled at 1500-1550℃ and the continuous casting speed is 0.8-1.2m / min. During the continuous casting process, the crystallizer electromagnetic stirring technology is used to improve the solidification structure of the molten steel and reduce segregation and the accumulation of inclusions. At the same time, the cooling intensity is controlled by using air-water atomization cooling method, and the secondary cooling area is divided into four sections for fine control: the first section is located 0-1m from the crystallizer outlet. The temperature of the ingot is high. To prevent the surface from cracking due to sudden cooling, the water flow rate is set at 8-12m 3 / h, air pressure 0.3-0.5MPa; the second section is 1-2m, the solidified shell thickens, and the water flow rate increases to 12-16m 3 / h, air pressure 0.4-0.6MPa; third section 2-3m, water flow 14-18m 3 / h, air pressure 0.5-0.7MPa; the fourth section 3m to the front of the tensioning and leveling machine, when solidification is almost completed, the water flow rate is adjusted back to 10-14m 3 / h, air pressure 0.4-0.6MPa; make the cooling rate of the billet uniform and avoid crack defects;

[0010] Heating: The continuous casting billet is sent to the heating furnace for heating at a temperature of 1150-1250°C and a holding time of 2-3 hours to ensure uniform heating of the billet and eliminate internal stress;

[0011] Rolling: The heated ingot is rolled in three stages: rough rolling, intermediate rolling, and finishing rolling. The rough rolling stage is performed at a temperature of 1100-1200°C with 4-6 passes to form the ingot into a billet of a certain shape. The intermediate rolling stage is performed at a temperature of 950-1050°C with 6-8 passes to further refine the grains and improve the structural properties of the steel. The finishing rolling stage is performed at a temperature of 850-950°C with 4-6 passes to control the dimensional accuracy and surface quality of the steel. During the rolling process, high-pressure water descaling technology is used to remove the iron oxide scale on the steel surface to ensure a smooth surface.

[0012] Heat treatment: The rolled steel is heat treated. The heat treatment process includes quenching and tempering.

[0013] The quenching temperature is 850-900℃, the holding time is 30-60 minutes, and then water or oil is used for cooling to make the steel obtain martensite structure, thereby improving the strength and hardness of the steel;

[0014] The tempering temperature is 500-600℃, and the holding time is 60-120 minutes. After tempering, it is cooled by air or furnace to eliminate quenching stress and improve the toughness and plasticity of the steel.

[0015] Its chemical composition in mass percentage is: C: 0.25%-0.35%, Si: 0.20%-0.40%, Mn: 1.20%-1.60%, P≤0.025%, S≤0.020%, Cr: 0.30%-0.60%, Ni: 0.20%-0.40%, Mo: 0.15%-0.30%, RE: 0.01%-0.05%, and the balance is Fe and unavoidable impurities.

[0016] Furthermore, it also includes surface treatment: surface treatment of the heat-treated steel to remove surface oxide scale and impurities, thereby improving the surface quality and corrosion resistance of the steel; surface treatment methods can include pickling, sandblasting, etc.

[0017] Furthermore, it also includes testing and inspection: various performance tests and quality inspections are carried out on the produced steel, including chemical composition analysis, mechanical property testing, metallographic structure inspection, surface quality inspection, etc., to ensure that the quality of the steel meets the requirements.

[0018] Furthermore, its chemical composition in mass percentage is: C: 0.30%, Si: 0.30%, Mn: 1.40%, P: 0.020%, S: 0.015%, Cr: 0.45%, Ni: 0.30%, Mo: 0.22%, RE: 0.03%, and the balance is Fe and inevitable impurities.

[0019] Furthermore, rolling: rough rolling temperature is 1150℃, rolling passes are 5; intermediate rolling temperature is 1000℃, rolling passes are 7; finishing rolling temperature is 900℃, rolling passes are 5, and high-pressure water descaling technology is used.

[0020] Further, heat treatment: quenching temperature is 870℃, holding time is 45 minutes, cooling with water; tempering temperature is 550℃, holding time is 90 minutes, cooling with air.

[0021] Furthermore, the mechanical properties are: yield strength 920MPa, tensile strength 1050MPa, elongation after fracture 15%, impact absorption energy 80J, and good corrosion resistance.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] The present invention adds an appropriate amount of rare earth elements to steel, utilizing their purification, modification, and alloying properties to improve the steel's inclusion morphology and distribution, refine grain size, and enhance the steel's strength, toughness, and corrosion resistance. Furthermore, by rationally controlling production process parameters such as smelting, continuous casting, rolling, and heat treatment, the steel's structural uniformity and mechanical property stability are ensured. Compared to traditional production methods, the 900MPa-grade high-strength sucker rod round steel produced by the present invention exhibits higher strength, improved toughness, and corrosion resistance, meeting the oil extraction industry's demand for high-end sucker rod materials. DETAILED DESCRIPTION

[0024] Example 1

[0025] Raw material preparation: Select raw materials such as iron ore and scrap steel, and control the chemical composition of the raw materials so that the C content is 0.30%, the Si content is 0.30%, the Mn content is 1.40%, the P content is 0.020%, the S content is 0.015%, the Cr content is 0.45%, the Ni content is 0.30%, the Mo content is 0.22%, the RE content is 0.03%, and the balance is Fe and impurities.

[0026] Smelting: The raw materials are added to an electric arc furnace for smelting at a temperature of 1600°C. After deoxidation and desulfurization, rare earth alloys are added in the later stage of smelting. The amount of rare earth alloy added is 0.03% of the mass of the molten steel. It is added in batches and fully stirred to ensure uniform distribution of the rare earth elements.

[0027] Continuous casting: The molten steel temperature is controlled at 1520℃, the continuous casting speed is 1.0m / min, the crystallizer electromagnetic stirring technology is adopted, and the cooling intensity is moderate to obtain the casting billet.

[0028] Heating: Place the ingot into a heating furnace at a temperature of 1200°C for 2.5 hours.

[0029] Rolling: Rough rolling temperature is 1150℃, rolling passes are 5; intermediate rolling temperature is 1000℃, rolling passes are 7; finishing rolling temperature is 900℃, rolling passes are 5, and high-pressure water descaling technology is used.

[0030] Heat treatment: quenching temperature is 870℃, holding time is 45 minutes, cooling with water; tempering temperature is 550℃, holding time is 90 minutes, air cooling.

[0031] Surface treatment: Use pickling method to remove surface oxide scale.

[0032] Testing and inspection: The steel was tested and the chemical composition met the requirements. The mechanical properties were: yield strength 920MPa, tensile strength 1050MPa, elongation after fracture 15%, impact absorption energy (V-notch, 20℃) 80J, and good corrosion resistance.

[0033] Comparative Example 1

[0034] Compared with Example 1, Comparative Example 1 does not add rare earth elements, and other production process parameters are the same. The mechanical properties of the steel obtained by testing are: yield strength 850 MPa, tensile strength 980 MPa, elongation after fracture 13%, impact absorption energy (V-notch, 20°C) 60 J, and poor corrosion resistance.

[0035] Comparative Example 2

[0036] Compared to Example 1, Comparative Example 2 increased the rare earth element addition to 0.08%, while maintaining the same other production process parameters. Testing revealed the following mechanical properties for the steel: yield strength 900 MPa, tensile strength 1020 MPa, elongation after fracture 14%, and impact energy absorption (V-notch, 20°C) 70 J. Due to the excessive addition of rare earth elements, a small amount of rare earth inclusions were generated within the steel, resulting in a decrease in corrosion resistance.

[0037] Comparative Example 3

[0038] Compared to Example 1, in Comparative Example 3, the tempering temperature was lowered to 450°C during the heat treatment process, while maintaining the same other production process parameters. Testing revealed the following mechanical properties for the steel: yield strength of 950 MPa, tensile strength of 1100 MPa, elongation after fracture of 12%, and impact energy absorption (V-notch, 20°C) of 50 J. Due to the excessively low tempering temperature, the steel's toughness decreased significantly.

[0039] Table 1 Mechanical properties of each embodiment

[0040] project Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Yield strength (MPa) 920 850 900 950 Tensile strength (MPa) 1050 980 1020 1100 Elongation after break (%) 15 13 14 12 Impact absorption energy (J) 80 60 70 50 Corrosion resistance good Poor medium medium

[0041] A performance comparison shows that the steel produced in Example 1 exhibits excellent strength, toughness, and corrosion resistance, demonstrating that the production method of the present invention can effectively improve the overall performance of steel. Comparative Example 1, in which no rare earth elements are added, results in decreased strength, toughness, and corrosion resistance. Comparative Example 2 incorporates excessive amounts of rare earth elements, impacting steel quality. Comparative Example 3 utilizes an excessively low tempering temperature, reducing steel toughness. Therefore, by rationally controlling the amount of rare earth elements added and production process parameters, the present invention is able to produce 900 MPa-grade high-strength pumper rod round steel with excellent performance.

[0042] 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 producing 900MPa grade high-strength sucker rod round steel based on rare earth microalloying, characterized in that: include: Smelting: The prepared raw materials are added to an electric arc furnace or converter for smelting, and the smelting temperature is controlled at 1550-1650℃. During the smelting process, sufficient deoxidation and desulfurization are carried out to ensure the purity of the molten steel. In the later stage of smelting, rare earth alloys are added. The amount of rare earth alloy added is calculated based on the target content of rare earth elements in the molten steel. It is added in batches to ensure that the rare earth elements are evenly distributed in the molten steel. Continuous casting: The smelted molten steel is poured into the continuous casting machine for continuous casting, and the continuous casting temperature is controlled at 1500-1550℃ and the continuous casting speed is 0.8-1.2m / min. During the continuous casting process, the crystallizer electromagnetic stirring technology is used to improve the solidification structure of the molten steel and reduce segregation and the accumulation of inclusions. At the same time, the cooling intensity is controlled by using air-water atomization cooling method, and the secondary cooling area is divided into four sections for fine control: the first section is located 0-1m from the crystallizer outlet. The temperature of the ingot is high. To prevent the surface from cracking due to sudden cooling, the water flow rate is set at 8-12m 3 / h, air pressure 0.3-0.5MPa; the second section is 1-2m, the solidified shell thickens, and the water flow rate increases to 12-16m 3 / h, air pressure 0.4-0.6MPa; third section 2-3m, water flow 14-18m 3 / h, air pressure 0.5-0.7MPa; the fourth section 3m to the front of the tensioning and leveling machine, when solidification is almost completed, the water flow rate is adjusted back to 10-14m 3 / h, air pressure 0.4-0.6MPa, to make the cooling rate of the billet uniform and avoid crack defects; Heating: The continuous casting billet is sent to the heating furnace for heating at a temperature of 1150-1250°C and a holding time of 2-3 hours to ensure uniform heating of the billet and eliminate internal stress; Rolling: The heated ingot is rolled in three stages: rough rolling, intermediate rolling, and finishing rolling. The rough rolling stage is performed at a temperature of 1100-1200°C with 4-6 passes to form the ingot into a billet of a certain shape. The intermediate rolling stage is performed at a temperature of 950-1050°C with 6-8 passes to further refine the grains and improve the structural properties of the steel. The finishing rolling stage is performed at a temperature of 850-950°C with 4-6 passes to control the dimensional accuracy and surface quality of the steel. During the rolling process, high-pressure water descaling technology is used to remove the iron oxide scale on the steel surface to ensure a smooth surface. Heat treatment: The rolled steel is heat treated. The heat treatment process includes quenching and tempering. The quenching temperature is 850-900℃, the holding time is 30-60 minutes, and then water or oil is used for cooling to make the steel obtain martensite structure, thereby improving the strength and hardness of the steel; The tempering temperature is 500-600℃, and the holding time is 60-120 minutes. After tempering, it is cooled by air or furnace to eliminate quenching stress and improve the toughness and plasticity of the steel. Its chemical composition in mass percentage is: C: 0.25%-0.35%, Si: 0.20%-0.40%, Mn: 1.20%-1.60%, P≤0.025%, S≤0.020%, Cr: 0.30%-0.60%, Ni: 0.20%-0.40%, Mo: 0.15%-0.30%, RE: 0.01%-0.05%, and the balance is Fe and unavoidable impurities.

2. The method for producing 900MPa grade high-strength sucker rod round steel based on rare earth microalloying according to claim 1, characterized in that: It also includes surface treatment: surface treatment of heat-treated steel to remove surface oxide scale and impurities, and improve the surface quality and corrosion resistance of the steel; surface treatment methods can include pickling and sand blasting.

3. The method for producing 900MPa grade high-strength sucker rod round steel based on rare earth microalloying according to claim 1, characterized in that: It also includes testing and inspection: various performance tests and quality inspections are carried out on the produced steel, including chemical composition analysis, mechanical property testing, metallographic structure inspection, surface quality inspection, etc., to ensure that the quality of the steel meets the requirements.

4. The method for producing 900 MPa grade high-strength sucker rod round steel based on rare earth microalloying according to claim 1, characterized in that: Its chemical composition in mass percentage is: C: 0.30%, Si: 0.30%, Mn: 1.40%, P: 0.020%, S: 0.015%, Cr: 0.45%, Ni: 0.30%, Mo: 0.22%, RE: 0.03%, and the balance is Fe and inevitable impurities.

5. The method for producing 900MPa grade high-strength sucker rod round steel based on rare earth microalloying according to claim 4, characterized in that: Rolling: Rough rolling temperature is 1150℃, rolling passes are 5; intermediate rolling temperature is 1000℃, rolling passes are 7; finishing rolling temperature is 900℃, rolling passes are 5, and high-pressure water descaling technology is used.

6. The method for producing 900 MPa grade high-strength sucker rod round steel based on rare earth microalloying according to claim 5, characterized in that: Heat treatment: quenching temperature is 870℃, holding time is 45 minutes, cooling with water; tempering temperature is 550℃, holding time is 90 minutes, air cooling.

7. The method for producing 900 MPa grade high-strength sucker rod round steel based on rare earth microalloying according to claim 6, characterized in that: The mechanical properties are: yield strength 920MPa, tensile strength 1050MPa, elongation at break 15%, impact absorption energy 80J, and good corrosion resistance.