Low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe and preparation method thereof

Abstract

The invention discloses a low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe, which is prepared from the following chemical components in percentage by mass: 0.27 to 0.30 percent of C, 0.15 to 0.35 percent of Si, 1.45 to 1.75 percent of Mn, 0.005 to 0.020 percent of Ti, 0.005 to 0.040 percent of Al, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, 0.001 to 0.005 percent of RE and the balance of Fe and trace impurities, and the total mass fraction is 100 percent. The invention further discloses a preparation method. After the heat treatment hardening and tempering process is carried out, the performance of the material can meet the performance requirement of the P110 steel grade of the API 5CT standard, the transverse full-size 0 DEG C impact energy of the material meets the requirement of being larger than or equal to 60 J, and the material has stable mechanical performance, good toughness and good economical efficiency at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of material metallurgy, and in particular relates to a low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe and a preparation method thereof. Background Art

[0002] As oil prices continue to rise, more and more oil companies are investing more money to develop more oil fields. As a country with a large demand for oil, my country is still committed to increasing oil production as the main direction of its national energy strategy. In recent years, the depth of oil production in my country has continued to increase. When the well depth reaches 5,000 to 6,000 meters, high-grade P110 oil pipe products are usually used. Due to its good comprehensive performance, the annual demand continues to increase.

[0003] Domestic and foreign enterprises also have different material selection, which can be roughly divided into carbon manganese series, chromium-molybdenum series, manganese-molybdenum series and chromium-manganese series. Most steel mills mainly use chromium-manganese series. As the competition in the steel pipe industry becomes increasingly fierce, the call for reducing the production cost of enterprises by reducing the alloy composition of steel grades while ensuring that the performance meets the requirements is growing. This patent optimizes the chemical composition ratio, adds rare earth to improve the toughness of the material, and continuously optimizes the heat treatment process. At the same time, it has good strength and plastic toughness at a low cost, and the material performance is stable.

[0004] After searching, it was found that three literature patents are most relevant to the utility model technology, and the specific contents are described as follows:

[0005] After searching, similar background technologies include: "An economical P110 steel grade oil casing and its manufacturing method" (patent application number: 201811319735.5). The difference from the present invention is that in terms of composition design, the present invention adopts the rare earth C-Mn steel rare earth microalloying design concept, while the retrieved similar patents adopt the C-Mn-Cr design concept. The design steel types are different, and this patent is more economical and has lower cost; in addition, the heat treatment system is also different.

[0006] After searching, similar background technologies include: "A method for preparing Cr micro-alloyed P110 grade petroleum casing steel" (patent application number: 202011499118.5). The difference from the present invention is that: in terms of composition design, the present invention adopts the rare earth micro-alloying design concept of rare earth C-Mn steel, while the retrieved similar patents adopt the C-Mn-Cr design concept. The design steel types are different, and this patent is more economical and has lower cost; in addition, the production processes are different. The retrieved patent is only applicable to medium and thick plates, while the applied patent is applicable to seamless steel pipes.

[0007] After searching, similar background technologies include: "A 110ksi grade ERW oil casing steel strip and its production method (patent application number: 201210419329.2), which is different from the present invention in that: in terms of composition design, the present invention adopts the C-Mn and rare earth micro-alloying design concept, while the searched similar patent adopts the C-Mn-Cr-Mo design concept, with different chemical compositions; in addition, the production processes are different, the searched patent is used for ERW process to manufacture casing, while the applied patent is applicable to seamless steel pipes. Summary of the invention

[0008] The purpose of the present invention is to provide a low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe and a preparation method thereof. The material properties after heat treatment and tempering process can meet the API 5CT standard P110 steel grade performance requirements, and its transverse full-size 0°C impact energy meets the requirement of ≥60J. It has stable mechanical properties, good toughness and good economy.

[0009] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0010] The invention discloses a low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe. The chemical composition mass percentage of the rare earth-containing P110 steel grade high-strength and high-toughness oil pipe is: C 0.27-0.30%, Si 0.15-0.35%, Mn 1.45-1.75%, Ti 0.005-0.020%, Al 0.005-0.040%, P≤0.015%, S≤0.005% and RE 0.001-0.005%, and the rest is Fe and trace impurities, and the mass fraction is 100% in total.

[0011] Furthermore, the chemical composition mass percentage of the rare earth-containing P110 steel grade high-strength and high-toughness oil pipe is: C0.27%, Si 0.23%, Mn 1.57%, Ti 0.008%, Al 0.024%, P 0.008%, S 0.003% and RE0.002%, and the rest is Fe and trace impurities, with a total mass fraction of 100%.

[0012] Furthermore, the chemical composition mass percentage of the rare earth-containing P110 steel grade high-strength and high-toughness oil pipe is: C0.29%, Si 0.25%, Mn 1.69%, Ti 0.010%, Al 0.029%, P 0.007%, S 0.004% and RE0.004%, and the rest is Fe and trace impurities, with a total mass fraction of 100%.

[0013] Furthermore, the chemical composition mass percentage of the rare earth-containing P110 steel grade high-strength and high-toughness oil pipe is: C0.28%, Si 0.23%, Mn 1.50%, Ti 0.015%, Al 0.018%, P 0.008%, S 0.003% and RE0.003%, and the rest is Fe and trace impurities, with a total mass fraction of 100%.

[0014] Furthermore, the chemical composition mass percentage of the rare earth-containing P110 steel grade high-strength and high-toughness oil pipe is: C0.29%, Si 0.29%, Mn 1.72%, Ti 0.009%, Al 0.031%, P 0.010%, S 0.005% and RE0.002%, and the rest is Fe and trace impurities, with a total mass fraction of 100%.

[0015] A method for preparing a low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe, comprising:

[0016] Steel smelting process: molten iron pretreatment → converter smelting → LF refining → VD degassing → round billet continuous casting;

[0017] The incoming molten iron is first pre-treated and desulfurized by KR stirring method. The sulfur content in the molten iron is removed by more than 90%, and the sulfur content of the molten iron for converter steelmaking is as low as 0.020%; while blowing oxygen at the top of the converter, nitrogen and argon are blown into the bottom of the furnace for double blowing and stirring to achieve smelting goals such as dephosphorization, desulfurization, appropriate steel-making carbon, steel-making temperature, and low oxygen content. The single slag process is used for smelting, and the final slag basicity is controlled at 3.0. The endpoint control targets are: P≤0.015%, S≤0.004%; during the LF refining process, an appropriate amount of calcium wire is fed, and the soft blowing time after wire feeding is 10 to 15 minutes; LF refining completes metallurgical functions such as deoxidation, desulfurization, composition control, temperature control, and inclusion control. After LF and before VD, 50kg of rare earth cerium iron alloy is fed per 100t of molten steel. , soft blowing time 8 ~ 10min, VD vacuum degree ≤ 0.10KPa, deep vacuum time 12min ~ 15min, through soft blowing and calming to further reduce the inclusions and oxygen content in the steel, after treatment [S] can be controlled to 0.004%, hydrogen content as low as 2ppm, [O] content as low as 30ppm, [N] content as low as 60ppm, inclusion ∑I = A + B + C + D less than 5.0 level, single item less than 1.5 level; the continuous casting process adopts protective pouring, electromagnetic stirring and end electromagnetic stirring process, the superheat of molten steel is controlled within 5 ~ 30 ℃, the constant pulling speed control process is adopted, the starting pulling speed is 0.5m / s, the horizontal fixed pulling speed is controlled at 1.4 ~ 1.7m / min, which can improve the quality of continuous casting billets, and the tube billets are stacked for slow cooling;

[0018] The steel rolling process includes: round billet → sawing → heating → piercing → tube rolling → tension reduction → cooling on cooling bed; the tube billet heating temperature is 1220℃~1260℃; the round billet piercing temperature is 1200℃~1250℃; the steel tube rolling temperature is 1050℃~1150℃; the final rolling temperature is ≥760℃; there is a descaling device before the continuous rolling entrance, and the surface oxide scale of the incoming rough tube needs to be cleaned;

[0019] The heat treatment process of rolled steel includes: quenching + tempering;

[0020] The quenching temperature is 860℃-880℃. The seamless steel pipe is raised to the quenching temperature at a speed of 35℃ / min and kept at this temperature for 30min~45min. After the holding time is reached, the oil pipe is quickly taken out of the furnace and then water-cooled. The internal spray flow rate of cooling water is controlled to be 580±50m3 / h, the external spray flow rate is 1600±50m3 / h, and the external spray time is 10~12s. The temperature of the pipe body after cooling should be lower than 100℃ to ensure that the oil pipe can obtain more than 50% martensite structure and is not prone to quenching cracks.

[0021] (2) Open all the burners of the tempering heating furnace and use pulse control to make the flame burn completely. When the temperature in the furnace rises to 400°C, put the quenched seamless steel pipe into the tempering heating furnace to ensure the uniformity of the tempering temperature of the pipe body. Then, raise the temperature of the seamless steel pipe to 500°C and 560°C at a rate of 15°C / min. Start timing after the seamless steel pipe reaches the temperature, and the insulation time is 60 to 90 minutes;

[0022] The steel pipe with a temperature lowered to between 450℃ and 530℃ is sent to a roller straightening machine for warm straightening, and then sent to a step-type cooling bed for natural cooling, and then sent to a gang saw for cut-to-size.

[0023] Furthermore, the wall thickness is ≥6 mm, and the dephosphorization water pressure ranges from 8 to 16 MPa.

[0024] Compared with the prior art, the beneficial technical effects of the present invention are:

[0025] 1. The present invention discloses a low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe material. Through the coordinated cooperation of C-Mn and rare earth micro-alloying and process, the Mn alloy content is reduced and the precious alloy elements such as Cr and Mo are replaced, thereby reducing the cost of P110 steel grade seamless oil pipe alloy. The material has good strength and plastic toughness, and the material performance is stable.

[0026] 2. The low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe material of the present invention, by adding rare earth ferrocerium alloy, plays a role in purifying grain boundaries and reduces the influence of carbides on impact toughness; micro-Ti treatment plays a role in refining grains and precipitation strengthening, reduces the anisotropy of the material, and improves the toughness of the material while ensuring strength. DETAILED DESCRIPTION

[0027] The following are specific embodiments of the present invention.

[0028] A method for preparing a low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe, comprising:

[0029] The steel smelting process is: hot metal pretreatment → converter smelting → LF refining → VD degassing → round billet continuous casting. The chemical composition of each example is tested, and the chemical composition is shown in Table 1:

[0030] Table 1 Chemical composition percentages of each embodiment (weight percentage %)

[0031]

[0032] The steel rolling process includes round billet → sawing → heating → perforation → tube rolling → diameter reduction → cooling on a cooling bed. The tube billet heating temperature is 1220℃~126℃. At this temperature, all alloy elements can be dissolved and diffused evenly without overburning the billet. Controlling the maximum tube billet heating temperature to 1260℃ can reduce the grain coarsening of the ingot. The round billet perforation temperature is 1200℃~1250℃, and the tube rolling temperature is 1050℃~1150℃. Within this temperature range, the steel has good shaping, good perforation bite, and is easy to deform, which can ensure the quality of the inner and outer surfaces of the steel pipe. The final rolling temperature is guaranteed to be ≥760℃. A high final rolling temperature is equivalent to normalizing the steel pipe, which can evenly refine the structure. The specific rolling process of each embodiment is shown in Table 2:

[0033] Table 2 Rolling process of each embodiment

[0034]

[0035] The chemical mechanical properties test results of each embodiment are shown in Table 3:

[0036] Table 3 Mechanical properties test results of each embodiment

[0037]

[0038] The test results of non-metallic inclusions and grain size of each embodiment are shown in Table 4:

[0039]

[0040] It can be seen from the above test results that the low-cost economical rare earth-containing P110 steel grade oil pipe material of the present invention has good mechanical properties after heat treatment and tempering, and the material has good toughness while having high strength. The material strength can meet the P110 steel grade requirements in the API 5CT standard. At the same time, the material alloy element ratio is reasonable, and after adding rare earth alloy elements, the purity of the steel is guaranteed, and the inclusions are small and the number is small.

[0041] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe, characterized in that: The chemical composition mass percentage of the rare earth-containing P110 steel grade high-strength and high-toughness oil pipe is: C 0.27-0.30%, Si 0.15-0.35%, Mn 1.45-1.75%, Ti 0.005-0.020%, Al 0.005-0.040%, P≤0.015%, S≤0.005% and RE 0.001-0.005%, and the rest is Fe and trace impurities, and the total mass fraction is 100%.

2. The low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe according to claim 1 is characterized in that: The chemical composition mass percentage of the rare earth-containing P110 steel grade high-strength and high-toughness oil pipe is: C 0.27%, Si 0.23%, Mn 1.57%, Ti0.008%, Al 0.024%, P 0.008%, S 0.003% and RE 0.002%, and the rest is Fe and trace impurities, with a total mass fraction of 100%.

3. The low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe according to claim 1 is characterized in that: The chemical composition mass percentage of the rare earth-containing P110 steel grade high-strength and high-toughness oil pipe is: C 0.29%, Si 0.25%, Mn 1.69%, Ti0.010%, Al 0.029%, P 0.007%, S 0.004% and RE 0.004%, and the rest is Fe and trace impurities, with a total mass fraction of 100%.

4. The low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe according to claim 1 is characterized in that: The chemical composition mass percentage of the rare earth-containing P110 steel grade high-strength and high-toughness oil pipe is: C 0.28%, Si 0.23%, Mn 1.50%, Ti0.015%, Al 0.018%, P 0.008%, S 0.003% and RE 0.003%, and the rest is Fe and trace impurities, with a total mass fraction of 100%.

5. The low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe according to claim 1 is characterized in that: The chemical composition mass percentage of the rare earth-containing P110 steel grade high-strength and high-toughness oil pipe is: C 0.29%, Si 0.29%, Mn 1.72%, Ti0.009%, Al 0.031%, P 0.010%, S 0.005% and RE 0.002%, and the rest is Fe and trace impurities, with a total mass fraction of 100%.

6. The method for preparing a low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe according to any one of claims 1 to 5, characterized in that: include: Steel smelting process: molten iron pretreatment → converter smelting → LF refining → VD degassing → round billet continuous casting; The incoming molten iron is first pre-treated and desulfurized by KR stirring method. The sulfur content in the molten iron is removed by more than 90%, and the sulfur content of the molten iron for converter steelmaking is as low as 0.020%; while blowing oxygen at the top of the converter, nitrogen and argon are blown into the bottom of the furnace for double blowing and stirring to achieve smelting goals such as dephosphorization, desulfurization, appropriate steel-making carbon, steel-making temperature, and low oxygen content. The single slag process is used for smelting, and the final slag basicity is controlled at 3.

0. The endpoint control targets are: P≤0.015%, S≤0.004%; during the LF refining process, an appropriate amount of calcium wire is fed, and the soft blowing time after wire feeding is 10 to 15 minutes; LF refining completes metallurgical functions such as deoxidation, desulfurization, composition control, temperature control, and inclusion control. After LF and before VD, 50kg of rare earth cerium iron alloy is fed per 100t of molten steel. , soft blowing time 8 ~ 10min, VD vacuum degree ≤ 0.10KPa, deep vacuum time 12min ~ 15min, through soft blowing and calming to further reduce the inclusions and oxygen content in the steel, after treatment [S] can be controlled to 0.004%, hydrogen content as low as 2ppm, [O] content as low as 30ppm, [N] content as low as 60ppm, inclusion ∑I = A + B + C + D less than 5.0 level, single item less than 1.5 level; the continuous casting process adopts protective pouring, electromagnetic stirring and end electromagnetic stirring process, the superheat of molten steel is controlled within 5 ~ 30 ℃, the constant pulling speed control process is adopted, the starting pulling speed is 0.5m / s, the horizontal fixed pulling speed is controlled at 1.4 ~ 1.7m / min, which can improve the quality of continuous casting billets, and the tube billets are stacked for slow cooling; The steel rolling process includes: round billet → sawing → heating → piercing → tube rolling → tension reduction → cooling on cooling bed; the tube billet heating temperature is 1220℃~1260℃; the round billet piercing temperature is 1200℃~1250℃; the steel tube rolling temperature is 1050℃~1150℃; the final rolling temperature is ≥760℃; there is a descaling device before the continuous rolling entrance, and the surface oxide scale of the incoming rough tube needs to be cleaned; The heat treatment process of rolled steel includes: quenching + tempering; The quenching temperature is 860℃-880℃. The seamless steel pipe is raised to the quenching temperature at a speed of 35℃ / min and kept at this temperature for 30min~45min. After the holding time is reached, the oil pipe is quickly taken out of the furnace and then water-cooled. The internal spray flow rate of cooling water is controlled to be 580±50m3 / h, the external spray flow rate is 1600±50m3 / h, and the external spray time is 10~12s. The temperature of the pipe body after cooling should be lower than 100℃ to ensure that the oil pipe can obtain more than 50% martensite structure and is not prone to quenching cracks. (2) Open all the burners of the tempering heating furnace and use pulse control to make the flame burn completely. When the temperature in the furnace rises to 400°C, put the quenched seamless steel pipe into the tempering heating furnace to ensure the uniformity of the tempering temperature of the pipe body. Then, raise the temperature of the seamless steel pipe to 500°C and 560°C at a rate of 15°C / min. Start timing after the seamless steel pipe reaches the temperature, and the insulation time is 60 to 90 minutes; The steel pipe with a temperature lowered to between 450℃ and 530℃ is sent to a roller straightening machine for warm straightening, and then sent to a step-type cooling bed for natural cooling, and then sent to a gang saw for cut-to-size.

7. The method for preparing a low-cost rare earth-containing P110 steel grade high-strength and high-toughness oil pipe according to claim 6, characterized in that: The wall thickness is ≥6mm, and the dephosphorization water pressure range is 8~16MPa.

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