890MPa-grade oil cylinder pipe and manufacturing method thereof

Abstract

The invention provides a 890MPa-grade oil cylinder pipe, which contains Fe and inevitable impurities, and further contains the following chemical elements in percentage by mass: 0.14-0.20% of C, 0.12-0.12% of Cr, 0.12-0.12% of Mo, 0.12-0.12% of Mo and the balance of Fe. 0.15 to 0.55 percent of Si; mn: 0.5 to 1.5%; 0.5 to 1.5 percent of Cr; 0.25 to 0.65 percent of Mo; 0.3 to 0.8 percent of W; 0.05 to 0.1 percent of V; 0.02 to 0.06 percent of Nb; 0.01 to 0.05 percent of Al; and 0.0005% to 0.005% of Ca. Correspondingly, the invention further discloses a manufacturing method of the 890 MPa level oil cylinder pipe. According to the oil cylinder pipe, reasonable chemical element composition design is matched with a specific process, so that the oil cylinder pipe can reach higher strength, and the oil cylinder pipe has lower residual stress and yield ratio and also has good welding performance.

Description

Technical Field

[0001] The invention relates to a steel material and a manufacturing method thereof, in particular to an oil cylinder tube and a manufacturing method thereof. Background Art

[0002] At present, the requirements for lightweight construction machinery are getting higher and higher, which puts higher and higher strength requirements on cylinder tubes. However, as the strength increases, the carbon equivalent of the tube increases and the performance of the welding machine decreases. At the same time, due to the increase in strength, the residual stress in the cylinder tube increases, resulting in dimensional changes in the tube after machining and oil leakage in the cylinder.

[0003] The publication number is CN116162849A, the publication date is May 26, 2023, and the name is "A cylinder tube and its manufacturing method". The weight percentage of its components is: C 0.16~0.3%, Si 0.15~0.5%, Mn 1.2~1.8%, P≤0.01%, S≤0.001%, Nb 0.02~0.04, Mo 0.1~0.2%, and when the wall thickness of the cylinder tube is ≥20mm, Ti and B are added, Ti 0.015~0.03%, B 0.0015~0.0035%, and the rest are Fe and other unavoidable impurities. This invention patent adopts different graded cooling processes after the steel pipe is stretched and quenched. By increasing the stiffness and straightness level of the steel pipe, the distribution of phase change and thermal stress throughout the wall thickness of the cylinder pipe is controlled, and the distribution of ferrite in the microstructure of the cylinder pipe is controlled, thereby obtaining a cylinder pipe with higher strength and lower residual stress. The yield strength of the cylinder pipe is ≥600MPa, the tensile strength is ≥730MPa, and the residual stress is ≤50MPa.

[0004] However, the above patent documents still cannot meet the requirements of higher strength. Summary of the invention

[0005] One of the purposes of the present invention is to provide an 890MPa grade oil cylinder tube, which, through reasonable chemical element composition design and process design, achieves higher strength, has lower residual stress and yield strength ratio, and also has good welding performance.

[0006] In order to achieve the above object, the present invention provides a 890MPa grade oil cylinder tube, which contains Fe and inevitable impurities, and further contains the following chemical elements in the following mass percentages:

[0007] C: 0.14-0.20%; Si: 0.15-0.55%; Mn: 0.5-1.5%; Cr: 0.5-1.5%; Mo: 0.25-0.65%; W : 0.3-0.8%; V: 0.05-0.1%; Nb: 0.02-0.06%; Al: 0.01-0.05%; Ca: 0.0005-0.005%.

[0008] Correspondingly, the present invention also provides an 890MPa grade oil cylinder tube, the mass percentage of each element of which is:

[0009] C: 0.14-0.20%; Si: 0.15-0.55%; Mn: 0.5-1.5%; Cr: 0.5-1.5%; Mo: 0.25-0.65%; W: 0.3-0.8%; V: 0.05-0.1%; Nb: 0.02-0.06%; Al: 0.01-0.05%; Ca: 0.0005-0.005%; the balance is Fe and other inevitable impurities.

[0010] In the 890MPa grade oil cylinder tube of the present invention, the design principles of the chemical elements are as follows:

[0011] C: In the 890MPa grade oil cylinder pipe of the present invention, C is a basic element to ensure strength and hardenability. At the same time, the C content will affect the carbon equivalent and welding performance. If the C content in the steel is less than 0.14%, the hardenability of the steel is poor and the strength cannot meet the requirements. If the C content in the steel exceeds 0.2%, the C content is too high, which will lead to poor welding performance of the steel and deteriorate its plastic toughness. Therefore, the mass percentage of the C element is controlled between 0.14-0.2% in the present invention.

[0012] Si: In the 890MPa grade oil cylinder tube described in the present invention, Si is an important deoxidizer in steel. The Si element can be dissolved in ferrite to increase the yield strength of the steel. However, it should be noted that the content of Si in the steel should not be too high. When the Si content in the steel is higher than 0.55%, the processing performance and toughness of the steel will deteriorate; and if the Si content in the steel is too low, lower than 0.15%, the steel will become easily oxidized. Therefore, the mass percentage of the Si element is controlled between 0.15-0.55% in the present invention.

[0013] Mn: In the 890MPa grade oil cylinder tube of the present invention, the Mn element is a deoxidizing and desulfurizing agent, which has a great influence on the hardenability and toughness level of the steel. When the Mn content in the steel is above 0.5%, a better effect can be produced, but too much Mn will make the hardenability of the steel too high, reduce the toughness of the heat affected zone of the steel welding, and cause center segregation during continuous casting, deteriorating the impact toughness of the parent material. Therefore, the mass percentage of the Mn element is controlled between 0.5-1.5% in the present invention.

[0014] Cr: In the 890MPa grade oil cylinder tube of the present invention, the Cr element can increase the strength and hardenability of the steel, and the Cr element and the Mo element have a better effect. However, it should be noted that if the Cr content in the steel is too high, the carbon equivalent will be significantly increased, resulting in increased sensitivity to welding cracking and reduced toughness of the welding heat affected zone. Therefore, the mass percentage of the Cr element is controlled between 0.5-1.5% in the present invention.

[0015] Mo: In the 890MPa grade oil cylinder tube described in the present invention, Mo is one of the main added elements, which can improve the hardenability of steel. The composite effect of Mo and Cr can better improve the hardenability. In addition, the Mo element also has good precipitation strengthening and solid solution strengthening effects. Mo has a good interaction with micro-alloying elements, which can effectively refine the precipitated phase, increase the stability and volume fraction of the precipitated phase, and improve the toughness of the welding heat affected zone. However, it should be noted that the Mo element is expensive. Adding too high a content of Mo to the steel will not only lead to an excessively high carbon equivalent, but also increase the cost of the alloy. Therefore, the present invention controls the mass percentage of the Mo element between 0.25-0.65%.

[0016] W: W element is used as the main added element in this steel grade. It can improve the strength well in the form of solid solution strengthening without increasing the carbon equivalent and having no obvious effect on the welding performance. At the same time, it has a good effect on maintaining the strength after welding. In the present invention, the W content is required to be in the range of 0.3-0.8%.

[0017] V: In the 890MPa grade oil cylinder tube of the present invention, the V element can refine the grains in the steel, and the carbides formed by it can greatly improve the strength of the steel. However, when the amount of V added to the steel reaches a certain level, its strengthening effect is not obvious, and V is a relatively expensive alloy element and should not be added in excess. Therefore, in the present invention, the mass percentage of the V element is controlled between 0.05-0.1%.

[0018] Nb: The main function of the Nb element is to refine the phase transformation and grains through the precipitation of carbides. In the present invention, a small amount of Nb element is added, which has a good effect on improving the post-weld softening while refining the structure and improving the strength-toughness matching.

[0019] Al: In the 890MPa grade oil cylinder tube of the present invention, Al is a good deoxidizing element, but adding too much Al into the steel will easily cause aluminum oxide inclusions. It is necessary to increase the proportion of acid-soluble aluminum to the total aluminum as much as possible, and then feed Al wire in appropriate amounts after vacuum degassing. Therefore, the mass percentage of Al element is controlled between 0.01-0.05% in the present invention.

[0020] Ca: In the 890MPa grade oil cylinder tube of the present invention, Ca can purify the molten steel, promote the spheroidization of MnS, and improve the impact toughness of the material. However, it should be noted that the Ca content in the steel should not be too high. When the Ca content in the steel is too high, coarse non-metallic inclusions are easily formed, which affects the performance of the steel. Therefore, the mass percentage of the Ca element is controlled between 0.0005-0.005% in the present invention.

[0021] In addition, it should be noted that in the 890 MPa grade oil cylinder tube of the present invention, there are some unavoidable impurity elements, which are mainly S and P. If technical conditions permit, in order to obtain an oil cylinder tube with better performance and better quality, the content of impurity elements should be reduced as much as possible.

[0022] Furthermore, in the 890MPa grade oil cylinder tube of the present invention, the mass percentage of each chemical element further satisfies at least one of the following items:

[0023] Si: 0.15-0.35%;

[0024] Mn: 1.1-1.5%;

[0025] Cr: 0.5-1%.

[0026] Furthermore, in the 890MPa grade oil cylinder tube of the present invention, its carbon equivalent is ≤0.7.

[0027] Furthermore, in the 890MPa grade oil cylinder tube of the present invention, the carbon equivalent is 0.45-0.65.

[0028] In the present invention, carbon equivalent=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu)15, wherein each chemical element is substituted into the numerical value before the percentage sign corresponding to the mass percentage content of each chemical element.

[0029] Furthermore, in the 890MPa grade oil cylinder tube of the present invention, the outer wall and center structure are tempered troostite structure + less than 10% bainite, and the inner wall structure is tempered troostite structure + bainite and ferrite with a total volume content of less than 20%.

[0030] The present invention obtains a tempered bainite structure + a small amount of bainite in the outer wall and the center through the ratio of components and processes, and a tempered bainite structure + a small amount of bainite + a small amount of ferrite in the inner wall. This is because when only the outer wall is cooled, the temperature of the inner wall drops below Ar3, and part of the ferrite is precipitated. At this time, after the inner wall is sprayed with water, the remaining austenite is transformed into martensite and bainite, and the tempered bainite + a small amount of bainite + ferrite structure is transformed during the tempering process.

[0031] Furthermore, in the 890MPa-grade oil cylinder tube described in the present invention, its performance meets the following requirements: yield strength ≥ 890MPa, tensile strength of 960-1100MPa, yield strength ratio ≤ 0.93, and -40°C impact toughness KV8 ≥ 45J.

[0032] Furthermore, in the 890MPa-grade oil cylinder tube of the present invention, the residual stress is -100MPa-48MPa.

[0033] Correspondingly, another object of the present invention is to provide a method for manufacturing an 890MPa grade oil cylinder tube.

[0034] In order to achieve the above object, the present invention proposes a method for manufacturing an 890MPa grade oil cylinder tube, which comprises the following steps:

[0035] Smelting and continuous casting to obtain tube billets;

[0036] Heating, perforating, rolling and sizing;

[0037] Online controlled cooling: the starting temperature is ≥800℃, the outer wall water spraying method is used for cooling, the average cooling rate is controlled to be 20-40℃ / s, and the final cooling temperature is 600℃-680℃; then air cooling to room temperature;

[0038] Quenching: Control the heating temperature to 820-880℃, and keep it warm for 20-40min. After quenching, use water cooling to cool the steel pipe. During cooling, the steel pipe rotates, and the outer wall of the steel pipe is sprayed with water. After cooling for 35-40s, start spraying water on the inner wall of the steel pipe;

[0039] Tempering.

[0040] The present invention adopts the design of low-carbon steel containing W, Cr, Mo, and micro-alloy steel, and controls the carbon equivalent of the steel to ≤0.7, so that it has good welding performance. At the same time, the above-mentioned online controlled cooling process is matched, and the rapid cooling technology using the residual heat after pipe rolling is used to refine the rolled structure, thereby further refining the structure after quenching and tempering heat treatment, ensuring a good combination of strength and toughness. In addition, when performing the quenching and tempering heat treatment process, the process of cooling the outer wall first and delaying the inner wall to spray water for cooling is adopted. The seamless pipe produced by this process has the characteristics of easy welding, low yield ratio, and low residual stress.

[0041] Among them, in order to further refine the rolling structure, thereby utilizing the genetic characteristics of the structure and refining the final quenching and tempering heat treatment structure, the rapid cooling technology after sizing is adopted to effectively utilize the residual heat of the rolling tube. The thermal deformation in the sizing process causes more dislocations in the tube body. After rapid cooling to a certain temperature, these dislocations are effectively retained, and these dislocations can become nucleation points for phase transformation and precipitation phases. In addition, rapid cooling increases the supercooling degree of phase transformation, thereby increasing the driving force of phase transformation. Both aspects lead to obvious refinement of the rolled structure. Based on this, the online controlled cooling adopted by the present invention: the start cooling temperature is ≥800℃, and the outer wall water spraying method is adopted for cooling, the average cooling rate is controlled to be 20-40℃ / s, and the final cooling temperature is 600℃-680℃; then air cooling is performed to room temperature, and then subsequent quenching and tempering heat treatment is performed. In the present invention, in the online controlled cooling step, water is sprayed on the outer wall to cool it, so that a hardened layer is formed on the outer wall, which increases the deformation resistance of the outer wall, ensures that the pipe body is less likely to bend and deform during the subsequent cooling process, ensures the straightness of the pipe body, and reduces the residual stress level of the entire pipe. Since the surface is a hardened layer, compressive stress is generated, which increases the tolerance of the pipe body to surface defects.

[0042] The present invention adopts water cooling after quenching. During cooling, the steel pipe rotates, and the outer wall of the steel pipe is sprayed with water for cooling. After cooling for 35-40 seconds, the inner wall is sprayed with water to ensure that the positions with poor cooling effect during outer wall cooling are fully cooled by the inner wall. Since the external spraying water cools the entire length of the steel pipe at the same time, the steel pipe rotates during cooling to achieve better cooling uniformity, which increases the rigidity of the steel pipe. Its better cooling uniformity ensures a better straightness level of the steel pipe, avoiding the subsequent large residual stress caused by bending and straightening deformation of the pipe. Compared with the simultaneous cooling method of external spraying of the outer wall + axial flow of the inner wall, a better straightness level can be obtained.

[0043] In addition, the residual stress of the steel pipe is closely related to the phase change and thermal stress during the cooling process. Through this cooling method, a gradient distribution of phase change and thermal stress is obtained in the wall thickness direction. After water cooling, the outer wall produces compressive stress due to thermal expansion and contraction, and the phase change stress is tensile stress. The sum of the two is in the range of 0-200MPa. The thermal stress at the center of the wall thickness is tensile stress, and the phase change stress is compressive stress. The sum of the two is a negative value. The thermal stress and phase change stress of the inner wall are both positive. There is a certain risk of cracking on the inner wall, so tempering treatment is required as soon as possible after cooling.

[0044] Furthermore, in the quenching step of the manufacturing method of the present invention, the flow density of the water spray cooling on the outer wall of the steel pipe is 3000-3500m 3 / (h*mm 2 ), where "h" stands for hours.

[0045] Furthermore, in the tempering step of the manufacturing method described in the present invention, the tempering temperature is controlled to be 500-600° C., and the holding time is 20-30 min.

[0046] In the present invention, the residual stress in the wall thickness direction of the tube body is reduced after tempering, but the gradient distribution trend does not change. The residual stress level of the entire tube body after tempering is: -100MPa to 48MPa.

[0047] The 890MPa grade oil cylinder tube and the manufacturing method thereof of the present invention have the following advantages and beneficial effects:

[0048] The present invention adopts the design of low-carbon, micro-alloyed steel containing W, Cr, and Mo, and controls the carbon equivalent of the steel to ≤0.7, so that it has good welding performance. At the same time, it is matched with the online controlled cooling process, and the rapid cooling technology using the residual heat after rolling is used to refine the rolled structure, thereby further refining the structure after quenching and tempering heat treatment, ensuring a good combination of strength and toughness. In addition, when performing the quenching and tempering heat treatment process, the process of cooling the outer wall first and delaying the inner wall to spray water for cooling is adopted. The seamless pipe produced by this process has the characteristics of easy welding, low yield ratio, and low residual stress.

[0049] In some embodiments, the 890MPa grade oil cylinder tube of the present invention has the following properties: yield strength ≥890MPa, tensile strength of 960-1100MPa, yield strength ratio ≤0.93, -40°C impact toughness KV8 ≥45J, and residual stress of -100MPa to 48MPa. DETAILED DESCRIPTION

[0050] The 890MPa grade oil cylinder tube and the manufacturing method thereof described in the present invention will be further explained and illustrated below in conjunction with specific embodiments. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

[0051] Examples 1-8 and Comparative Examples 1-8

[0052] The 890MPa grade oil cylinder tube of Examples 1-8 is prepared by the following steps:

[0053] (1) Smelting and continuous casting are carried out according to conventional processes to obtain a tube blank;

[0054] (2) heating, punching, rolling and sizing the tube blank according to conventional processes to obtain a tube body;

[0055] (3) Utilize the residual heat of tube rolling and control cooling online after sizing: the starting cooling temperature is ≥800℃, and the outer wall water spraying method is used for cooling, the average cooling rate is controlled to be 20-40℃ / s, and the final cooling temperature is 600℃-680℃; then air cool to room temperature;

[0056] (4) Quenching: Control the heating temperature to 820-880°C, and keep the temperature for 20-40 minutes after reaching the temperature. After quenching, use water cooling to cool the steel pipe. During cooling, the steel pipe is rotated, and the outer wall of the steel pipe is sprayed with water for cooling. After cooling for 35-40 seconds, start spraying water on the inner wall of the steel pipe until the pipe body is cooled to below 100°C. In some embodiments, the flow density of the water spraying on the outer wall of the steel pipe is 3000-3500m 3 / (h*mm 2 ). The pressure of the water spray can be 0.5MPa.

[0057] (5) Tempering: Control the tempering temperature to 500-600℃ and the holding time to 20-30min.

[0058] It should be noted that the chemical element composition and related process design of the 890MPa grade oil cylinder pipe of Examples 1-8 described in the present invention meet the design specification requirements of the present invention. While the steps and processes of Comparative Examples 1-8 are roughly the same as those of the present invention, their chemical element content or specific process parameters are not in accordance with the present invention.

[0059] Table 1 lists the mass percentages of the chemical elements of the 890 MPa grade oil cylinder tubes of Examples 1-8 and the comparative oil casing tubes of Comparative Examples 1-8.

[0060] Table 1. (wt%, the balance is Fe and other unavoidable impurities)

[0061] C Si Mn Cr Mo W V Nb Al Ca Carbon Equivalent Example 1 0.14 0.16 1.5 0.5 0.3 0.3 0.06 0.025 0.01 0.0005 0.56 Example 2 0.15 0.25 1 0.6 0.25 0.35 0.07 0.035 0.025 0.002 0.50 Example 3 0.19 0.35 0.6 1.5 0.28 0.4 0.05 0.02 0.035 0.0015 0.66 Example 4 0.2 0.55 0.5 1.1 0.3 0.8 0.1 0.06 0.03 0.003 0.58 Example 5 0.17 0.45 0.7 1.1 0.6 0.55 0.1 0.045 0.025 0.005 0.65 Example 6 0.16 0.3 0.8 1.2 0.65 0.6 0.09 0.045 0.045 0.003 0.68 Example 7 0.15 0.28 0.9 1.3 0.4 0.7 0.08 0.048 0.025 0.0009 0.66 Example 8 0.16 0.32 1 1.4 0.5 0.55 0.07 0.035 0.05 0.001 0.72 Comparative Example 1 0.23 0.25 0.6 0.8 0.5 0.5 0.075 0.025 0.03 0.002 0.61 Comparative Example 2 0.12 0.24 0.9 0.9 0.55 0.6 0.085 0.03 0.02 0.001 0.58 Comparative Example 3 0.21 0.31 1.5 1.5 0.65 0.75 0.1 0.04 0.035 0.0015 0.91 Comparative Example 4 0.16 0.27 0.9 0.9 0.4 0.6 0.095 0.06 0.025 0.0025 0.59 Comparative Example 5 0.17 0.3 0.6 0.6 0.5 0.45 0.095 0.04 0.025 0.002 0.51 Comparative Example 6 0.18 0.35 0.7 0.8 0.35 0.52 0.09 0.05 0.025 0.002 0.54 Comparative Example 7 0.19 0.32 1 0.8 0.5 0.43 0.08 0.025 0.03 0.0015 0.63 Comparative Example 8 0.16 0.23 1.1 0.8 0.55 0.7 0.07 0.02 0.04 0.002 0.63

[0062] Note: Carbon equivalent = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) 15. Since this case does not contain Cu and Ni elements, the values ​​of these two elements are substituted into 0 for calculation.

[0063] Table 2 lists the specific process parameters of the 890 MPa grade oil cylinder tubes of Examples 1-8 and the comparative oil casings of Comparative Examples 1-8 in the online controlled cooling and tempering steps.

[0064] Table 2.

[0065]

[0066] Note: The three columns of data for online controlled cooling in comparative example 4 are “ / ”, indicating that online controlled cooling is not adopted in this comparative example; the internal spray opening delay time in comparative example 8 is “ / ”, indicating that internal spray water is not turned on in this comparative example.

[0067] The 890 MPa grade oil cylinder pipes of Examples 1-8 and the comparative pipes of Comparative Examples 1-8 were sampled and tested, and the test results are listed in Table 3. The relevant test process is as follows:

[0068] (1) Microstructure observation: Take the cross section of the tube for structure observation, grind and polish the sample, and use 4% nitric acid + alcohol to etch the metallographic structure. The structure is observed under a metallographic microscope.

[0069] (2) Tensile test: The room temperature tensile property test is carried out according to GB / T 228.1-2000 standard.

[0070] (3) Impact test: -40℃ impact energy test is carried out according to GB / T 229-2007 “Metallic Materials Charpy Pendulum Impact Test Method”.

[0071] (4) Welding performance testing: Welding evaluation shall be carried out in accordance with NB / T-47014-2011 Welding procedure assessment for pressure-bearing equipment.

[0072] (5) Residual stress detection: Measure according to ISO / TR 10400 standard.

[0073] Table 3 lists the test results of the 890 MPa grade cylinder tubes of Examples 1-8 and Comparative Examples 1-8.

[0074] Table 3.

[0075]

[0076] It can be seen from Table 3 that the yield strength of the 890MPa grade cylinder tubes of Examples 1-8 of the present invention is ≥900MPa, the tensile strength is ≥1025MPa, the impact energy at -40°C is ≥70J, the yield strength ratio is ≤0.91, the residual stress is -30MPa-40MPa, and it also has good weldability.

[0077] However, since the chemical element composition of Comparative Examples 1-3 does not meet the design requirements of the present invention, Comparative Example 4 does not perform online controlled cooling, and the quenching of Comparative Examples 5-8 does not meet the requirements of the present invention, it is impossible for them to achieve high strength, low yield ratio, good low-temperature toughness and excellent welding performance.

[0078] It should be noted that the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0079] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

Claims

1. A 890MPa grade oil cylinder tube containing Fe and inevitable impurities, characterized in that: It also contains the following chemical elements in the following mass percentages: C: 0.14-0.20%; Si: 0.15-0.55%; Mn: 0.5-1.5%; Cr: 0.5-1.5%; Mo: 0.25-0.65％；W：0.3-0.8％； V：0.05-0.1％； Nb: 0.02-0.06%; Al: 0.01-0.05%; Ca: 0.0005-0.005%.

2. The 890MPa grade oil cylinder tube according to claim 1, characterized in that: The mass percentage of each element is: C: 0.14-0.20%; Si: 0.15-0.55%; Mn: 0.5-1.5%; Cr: 0.5-1.5%; Mo: 0.25-0.65%; W: 0.3-0.8%; V：0.05-0.1％； Nb: 0.02-0.06%; Al: 0.01-0.05%; Ca: 0.0005-0.005%; the balance is Fe and other inevitable impurities.

3. The 890MPa grade oil cylinder tube according to claim 1 or 2, characterized in that: The mass percentage of each chemical element further satisfies at least one of the following items: Si: 0.15-0.35%; Mn: 1.1-1.5%; Cr：0.5-1％。 4. The 890MPa grade oil cylinder tube according to claim 1 or 2, characterized in that: Its carbon equivalent is ≤0.

7.

5. The 890MPa grade oil cylinder tube according to claim 4, characterized in that: Its carbon equivalent is 0.45-0.

65.

6. The 890MPa grade oil cylinder tube according to claim 1 or 2, characterized in that: The outer wall and center structure are tempered troostite structure + bainite with a volume content of less than 10%; the inner wall structure is tempered troostite structure + a small amount of bainite + a small amount of ferrite, wherein the total volume content of bainite and ferrite in the inner wall structure is less than 20%.

7. The 890MPa grade oil cylinder tube according to claim 1 or 2, characterized in that: Its performance meets the following requirements: yield strength ≥890MPa, tensile strength 960-1100MPa, yield strength ratio ≤0.93, -40℃ impact toughness KV8 ≥45J.

8. The 890MPa grade oil cylinder tube according to claim 1 or 2, characterized in that: Its residual stress is -100MPa-48MPa.

9. The method for manufacturing a 890 MPa grade oil cylinder tube according to any one of claims 1 to 8, characterized in that: It includes the steps of: Smelting and continuous casting to obtain tube billets; Heating, perforating, rolling and sizing; Online controlled cooling: the starting temperature is ≥800℃, the outer wall water spraying method is used for cooling, the average cooling rate is controlled to be 20-40℃ / s, and the final cooling temperature is 600℃-680℃; then air cooling to room temperature; Quenching: Control the heating temperature to 820-880℃, and keep it warm for 20-40min. After quenching, use water cooling to cool the steel pipe. During cooling, the steel pipe rotates, and the outer wall of the steel pipe is sprayed with water. After cooling for 35-40s, start spraying water on the inner wall of the steel pipe; (5) Tempering.

10. The manufacturing method according to claim 9, characterized in that: In the quenching step, the outer wall of the steel pipe is cooled by spraying water with a flow density of 3000-3500m 3 / (h*mm 2 ).

11. The manufacturing method according to claim 9, characterized in that: In the tempering step, the tempering temperature is controlled to be 500-600°C and the holding time is 20-30 minutes.

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