Exclusive 960 MPa low-alloy seamless pipe for arm support and manufacturing method of 960 MPa low-alloy seamless pipe

Abstract

The invention discloses a 960 MPa low-alloy seamless pipe special for an arm support and a manufacturing method of the 960 MPa low-alloy seamless pipe, belongs to the technical field of metallurgical processes, and particularly relates to the 960 MPa low-alloy seamless pipe special for the arm support and the manufacturing method of the 960 MPa low-alloy seamless pipe. On the premise that the usage amount of precious alloy is reduced, a new alloy design principle is adopted, a smelting process, a hot rolling process and a hardening and tempering process are matched, different production processes are formulated according to different seamless steel pipes with different wall thicknesses, the comprehensive performance of the product is improved, and the characteristics of low cost and easy welding are achieved. A multi-component alloy and microalloy strengthening mechanism and an alloy element narrow component control mechanism are realized on the aspect of chemical components; in the rolling process, the key temperature is controlled to realize the stability of the seamless steel pipe structure, and in the hardening and tempering process, the key temperature and the cooling speed are controlled to realize the performance stability of the seamless steel pipe.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical process, and specifically relates to a 960 MPa low-alloy seamless pipe exclusively for booms and a manufacturing method thereof. Background Art

[0002] Major construction projects such as nuclear power and petrochemicals are being implemented in countries and regions along the route. These projects are large-scale and require high technology, and the demand for super-large tonnage lattice boom cranes is becoming increasingly urgent. As high-end key core equipment for nuclear power and petrochemical construction, super-large tonnage lattice boom cranes play an irreplaceable role in the construction process of the project, and their performance directly affects the progress and quality of the project.

[0003] In recent years, the state has given strong support to the high-end engineering machinery and equipment industry, which has promoted the rapid development and upgrading of the industry. Under the guidance of policies, the industry has continued to move towards high-end, intelligent and green development, and low-cost lightweight green products have shown an explosive growth trend. This development trend not only meets the requirements of sustainable development, but also wins advantages for enterprises in market competition. In this context, high-end boom pipe products, as key components of high-end lifting equipment, have great significance for the development of the entire industry in terms of performance and quality. Therefore, they have been included in the national key research and development new materials catalog and become the focus of research and development and upgrading. In the design and manufacturing of high-end lifting equipment, structural lightweighting is an important development direction. For boom-specific pipes, it is necessary to develop high-strength steel with high strength and high toughness on the premise of meeting structural performance and safety. By adopting this high-strength steel, the design section can be reduced, the deadweight can be reduced, and the same bearing strength can be achieved at the same time. This can not only reduce the consumption of steel and reduce costs, but also reduce the additional load of components and improve the working efficiency and performance of cranes. However, it is not easy to achieve this goal, and a lot of research and exploration is needed in material research and development, process control and other aspects.

[0004] The boom of a crawler crane is a spatial truss structure welded by four main chords and webs. Its maximum lifting capacity can reach 2,600 tons, the lifting height can reach 226 meters, and the maximum working radius can reach 164 meters. When the crane is working, the truss arm is subjected to complex forces. The boom rods are compressed as a whole, while the main web chords are subjected to a combined load of tension and compression. Therefore, the welding performance and quality of the node welds play a vital role in the safety of the crane. In particular, with the continuous improvement of steel strength, such as ultra-high strength steel above 1000MPa, its weldability tends to decrease, which brings great challenges to the design and development of high-quality boom tubes. How to improve the welding performance between different steel grades and different wall thicknesses has become an urgent problem to be solved. Summary of the invention

[0005] Under the premise of reducing the usage of precious alloys, the present invention formulates different production processes for seamless steel pipes with different wall thicknesses to improve the comprehensive performance of the products, and provides a 960 MPa low-alloy seamless pipe exclusively for booms and a manufacturing method thereof.

[0006] The utility model discloses a 960 MPa low-alloy seamless pipe specially used for booms, wherein the mass percentages are as follows: C is 0.16-0.20%, Si is 0.20-0.35%, Mn is 1.40-1.70%, Cr is 0.80-1.00%, Mo is 0.50-0.70%, Ni is 0.80-1.20%, V is 0.030-0.070%, Nb is 0.015-0.025%, Ti is 0.010-0.025%, Al≤0.030%, P≤0.012%, S≤0.008%, N≤0.007%, and the balance is Fe and unavoidable impurities.

[0007] Furthermore, the arm-exclusive 960 MPa low-alloy seamless pipe is composed of the following mass percentages: C: 0.16%, Si: 0.22%, Mn: 1.44%, Cr: 0.81%, Mo: 0.52%, Ni: 0.83%, V: 0.034%, Nb: 0.018%, Ti: 0.011%, Al: 0.019%, P: 0.008%, S: 0.005%, N: 0.0065%, Fe and unavoidable impurities: 95.918%.

[0008] Furthermore, the arm-exclusive 960 MPa low-alloy seamless pipe is composed of the following mass percentages: C: 0.18%, Si: 0.31%, Mn: 1.52%, Cr: 0.83%, Mo: 0.52%, Ni: 0.90%, V: 0.047%, Nb: 0.019%, Ti: 0.013%, Al: 0.021%, P: 0.001%, S: 0.006%, N: 0.0057%, Fe and unavoidable impurities: 95.727%.

[0009] Furthermore, the arm-exclusive 960 MPa low-alloy seamless pipe is composed of the following mass percentages: C 0.20%, Si 0.25%, Mn 1.61%, Cr 0.86%, Mo 0.54%, Ni 0.92%, V 0.055%, Nb 0.018%, Ti 0.011%, Al 0.020%, P 0.008%, S 0.003%, N 0.0059%, Fe and unavoidable impurities 95.499%.

[0010] A method for manufacturing a 960 MPa low alloy seamless pipe exclusively for a boom is completed by the following steps:

[0011] 1. Smelting: According to the mass percentage: C is 0.16-0.20%, Si is 0.20-0.35%, Mn is 1.40-1.70%, Cr is 0.80-1.00%, Mo is 0.50-0.70%, Ni is 0.80-1.20%, V is 0.030-0.070%, Nb is 0.015-0.025%, Ti is 0.010-0.025%, Al≤0.030%, P≤0.012%, S≤0.008%, N≤0.007%, the balance is Fe and unavoidable impurities, and the converter is used for smelting; when the converter is tapped, the ladle is deoxidized and alloyed, and the order of alloy addition is ferrosilicon alloy. , aluminum ingots, medium carbon ferromanganese, low carbon ferrochrome, ferrovanadium and refined slag. After the alloy is added, lime is added with the steel flow. During the steel tapping process, the bottom blowing argon flow rate is 0.5NL / (t·min) to ensure that the alloy and refined slag are well melted after the steel tapping is completed; Mo, Nb and Ni are alloyed in the refining station, and titanium is alloyed during the refining and steel tapping; deep deoxidation is carried out when all elements except titanium are qualified and the temperature meets the continuous casting requirements. After deep deoxidation, the refining power is turned off and steel is tapped. Titanium iron is added and a micro-titanium treatment process is carried out. Samples are taken to test whether the composition is qualified; after refining and steel tapping, a ladle covering agent is added to make the ladle covering agent evenly cover the entire slag surface, and the argon gas is adjusted to perform soft blowing to even out the composition. After the soft blowing is completed, the clean and qualified molten steel is transferred to the continuous casting;

[0012] 2. Continuous casting and slow cooling: Continuously cast clean and qualified molten steel into continuous casting billets, divide the continuous casting billets into sections, and place them into slow cooling pits at a temperature of ≥400°C. When the temperature of the continuous casting billets in the slow cooling pit drops below 200°C, they are taken out of the pits. The continuous casting process adopts full-process protection pouring.

[0013] 3. Subsequent processing: Surface inspection and finishing of the continuous casting billets out of the pit, transfer qualified continuous casting billets to the steel rolling workshop, saw the billets, heat and perforate them after sawing, and then roll them; then reduce the diameter or sizing by micro-tension, air-cool the cooling bed, monitor the temperature online during air-cooling of the cooling bed, and then saw, sample and inspect, and perform non-destructive testing;

[0014] 4. Heat treatment: Use critical quenching process for quenching, and then tempering;

[0015] 5. Subsequent inspection and warehousing: After heat treatment, straightening, non-destructive testing, sampling inspection, surface inspection, and labeling are carried out in sequence before warehousing.

[0016] Beneficial effects of the present invention:

[0017] Under the premise of reducing the usage of precious alloys, the present invention adopts new alloy design principles, cooperates with smelting technology, hot rolling technology, quenching and tempering technology, and formulates different production processes for seamless steel pipes with different wall thicknesses to improve the comprehensive performance of the product and achieve low-cost and easy welding characteristics. In terms of chemical composition, the multi-element alloy + micro-alloy strengthening mechanism and the alloy element narrow composition control mechanism are realized; the key temperature control during the rolling process realizes the stability of the seamless steel pipe organization; the key temperature and cooling rate control during the quenching and tempering process realizes the stability of the performance of the seamless steel pipe.

[0018] Key performance indicators: yield strength ≥960MPa, tensile strength 1020~1180MPa, elongation after fracture ≥14%, -20℃ impact energy ≥65J, -40℃ impact energy ≥55J, quenched and tempered structure, grain size 9.0, no cracks in 180° bending test.

[0019] Special boom pipes are required to have high strength, plasticity, toughness, and good welding performance. According to the calculation of the carbon equivalent and welding crack sensitivity coefficient of the International Welding Association, reducing the carbon content in the alloy can effectively optimize the welding performance, improve the impact toughness and low temperature resistance, and generally should not exceed 0.30%. In order to achieve the goal of lightweight design, the strength of the material is improved by using Cr and Mo elements to achieve solid solution strengthening. The added V or Nb or Ti or a combination of the three forms stable carbides in the steel, which plays a role in dispersion strengthening, controls the N content + structural transformation temperature in the steel to reduce the precipitation of nitrides, and can refine the grains of the parent material and the weld, improving and stabilizing the welding performance. For equipment serving in cold areas, consider adding Ni to improve low temperature toughness. Reduce the content of harmful elements and gases such as S and P through the pure steel smelting process to improve the comprehensive performance of the material. Eliminate the precious metal W element to reduce the alloy cost. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is not limited to the specific implementation modes listed below, but also includes any combination of the specific implementation modes.

[0021] Specific implementation method one: In this implementation method, a 960 MPa low-alloy seamless pipe exclusively for an arm is prepared by mass percentage as follows: C is 0.16-0.20%, Si is 0.20-0.35%, Mn is 1.40-1.70%, Cr is 0.80-1.00%, Mo is 0.50-0.70%, Ni is 0.80-1.20%, V is 0.030-0.070%, Nb is 0.015-0.025%, Ti is 0.010-0.025%, Al≤0.030%, P≤0.012%, S≤0.008%, N≤0.007%, and the balance is Fe and unavoidable impurities.

[0022] Specific implementation method 2: This implementation method is different from the specific implementation method 1 in that: the arm frame is exclusively made of 960 MPa low alloy seamless pipe with a yield strength of ≥960 MPa, a tensile strength of 1020-1180 MPa, an elongation of ≥14%, a longitudinal impact energy of ≥65 J at -20 ° C, a longitudinal impact energy of ≥55 J at -40 ° C, a quenched and tempered structure, a grain size of ≥9.0, and no cracks in a 180 ° bending test. Others are the same as the specific implementation method 1.

[0023] Specific implementation method three: This implementation method is different from the specific implementation method one in that: the arm-exclusive 960 MPa low-alloy seamless pipe is made of the following mass percentages: C is 0.20%, Si is 0.25%, Mn is 1.61%, Cr is 0.86%, Mo is 0.54%, Ni is 0.92%, V is 0.055%, Nb is 0.018%, Ti is 0.011%, Al is 0.020%, P is 0.008%, S is 0.003%, N is 0.0059%, and the balance is Fe and unavoidable impurities. The rest is the same as the specific implementation method one.

[0024] Specific embodiment 4: This embodiment is different from the specific embodiment 1 in that: the arm-exclusive 960 MPa low-alloy seamless pipe is made of the following mass percentages: C is 0.18%, Si is 0.31%, Mn is 1.52%, Cr is 0.83%, Mo is 0.52%, Ni is 0.90%, V is 0.047%, Nb is 0.019%, Ti is 0.013%, Al is 0.021%, P is 0.001%, S is 0.006%, N is 0.0057%, and the balance is Fe and unavoidable impurities. The rest is the same as the specific embodiment 1.

[0025] Specific implementation method 5: In this implementation method, a method for manufacturing a 960 MPa low-alloy seamless pipe exclusively for a boom is completed by the following steps:

[0026] 1. Smelting: According to the mass percentage: C is 0.16-0.20%, Si is 0.20-0.35%, Mn is 1.40-1.70%, Cr is 0.80-1.00%, Mo is 0.50-0.70%, Ni is 0.80-1.20%, V is 0.030-0.070%, Nb is 0.015-0.025%, Ti is 0.010-0.025%, Al≤0.030%, P≤0.012%, S≤0.008%, N≤0.007%, the balance is Fe and unavoidable impurities, and the converter is used for smelting; when the converter is tapped, the ladle is deoxidized and alloyed, and the order of alloy addition is ferrosilicon alloy. , aluminum ingots, medium carbon ferromanganese, low carbon ferrochrome, ferrovanadium and refined slag. After the alloy is added, lime is added with the steel flow. During the steel tapping process, the bottom blowing argon flow rate is 0.5NL / (t·min) to ensure that the alloy and refined slag are well melted after the steel tapping is completed; Mo, Nb and Ni are alloyed in the refining station, and titanium is alloyed during the refining and steel tapping; deep deoxidation is carried out when all elements except titanium are qualified and the temperature meets the continuous casting requirements. After deep deoxidation, the refining power is turned off and steel is tapped. Titanium iron is added and a micro-titanium treatment process is carried out. Samples are taken to test whether the composition is qualified; after refining and steel tapping, a ladle covering agent is added to make the ladle covering agent evenly cover the entire slag surface, and the argon gas is adjusted to perform soft blowing to even out the composition. After the soft blowing is completed, the clean and qualified molten steel is transferred to the continuous casting;

[0027] 2. Continuous casting and slow cooling: Continuously cast clean and qualified molten steel into continuous casting billets, divide the continuous casting billets into sections, and place them into slow cooling pits at a temperature of ≥400°C. When the temperature of the continuous casting billets in the slow cooling pit drops below 200°C, they are taken out of the pits. The continuous casting process adopts full-process protection pouring.

[0028] 3. Subsequent processing: Surface inspection and finishing of the continuous casting billets out of the pit, transfer qualified continuous casting billets to the steel rolling workshop, saw the billets, heat and perforate them after sawing, and then roll them; then reduce the diameter or sizing by micro-tension, air-cool the cooling bed, monitor the temperature online during air-cooling of the cooling bed, and then saw, sample and inspect, and perform non-destructive testing;

[0029] 4. Heat treatment: Use critical quenching process for quenching, and then tempering;

[0030] 5. Subsequent inspection and warehousing: After heat treatment, straightening, non-destructive testing, sampling inspection, surface inspection, and labeling are carried out in sequence before warehousing.

[0031] This implementation method is based on the strict requirements of high-end lifting equipment, that is, the low-temperature impact energy needs to be based on -40℃ conditions, and at the same time, it must meet the welding requirements between different strengths. By realizing the multi-alloy + micro-alloy strengthening mechanism, combined with the controlled rolling air cooling process and the critical quenching and tempering process, different production processes are formulated for seamless steel pipes of different wall thicknesses while reducing the use of precious alloys, thereby achieving the goals of low cost, high strength, and easy welding, effectively improving the comprehensive performance of the product, and providing a reliable technical solution for the production of pipes for high-end lifting equipment.

[0032] In step 1 of this embodiment, the ladle covering agent is carbonized rice husk.

[0033] In the present embodiment, the argon soft blowing process is preferably performed in such a way that the argon outlet bubbles but does not expose the molten steel surface, and the slag surface creeps.

[0034] In step 1 of this embodiment, alloys are added according to 3kg / t steel of ferrosilicon alloy, 1.5-2kg / t steel of aluminum ingots, 20kg / t steel of medium carbon ferromanganese, 12kg / t steel of low carbon ferrochrome, and 0.8kg / t steel of ferrovanadium. When each furnace is tapped, 200kg of refined slag is added with the alloy. After the alloy is added, 300kg of lime is added with the steel flow. During the tapping process, the bottom blowing argon gas flow rate is 0.5NL / (t·min).

[0035] The content of each alloy element in this embodiment has been carefully adjusted. The content of Mo is controlled at 0.50% to 0.70%. Compared with some traditional high-strength steels or similar products with higher Mo content, this embodiment reduces the amount of Mo while ensuring performance. Mo is a precious metal, and reducing its amount directly helps reduce costs.

[0036] This embodiment uses a reasonable combination of various alloy elements such as C, Si, Mn, Cr, Ni, V, Nb, and Ti to exert the synergistic strengthening effect of multi-element alloys. These elements cooperate with each other to achieve performance requirements such as high strength and high toughness at a lower content of a single element, thereby avoiding excessive reliance on a certain precious alloy element to improve performance and effectively reducing the overall use of precious alloys. For example, Mn and Cr work together to improve the hardenability of steel, and Ni and Mo work together to improve the low-temperature toughness of steel, which reduces the demand for high-content, high-cost alloy elements while meeting performance requirements.

[0037] In this embodiment, during the smelting process, for seamless steel pipes of different wall thicknesses, the amount and timing of each element added can be fine-tuned during the alloying process according to the specific wall thickness requirements. Thicker-walled steel pipes may need to slightly increase the content of strengthening elements to ensure uniformity of performance across the entire wall thickness; while thin-walled steel pipes can more accurately control the addition of alloying elements to avoid excess performance and increased costs caused by over-alloying. This method of flexibly adjusting alloying according to wall thickness lays the foundation for the subsequent formulation of different production processes for different wall thicknesses.

[0038] In this embodiment, the segmentation of the continuous casting billet and the temperature control of entering the slow cooling pit can be differentiated for continuous casting billets with different wall thicknesses. Thicker continuous casting billets may require stricter temperature control and longer slow cooling time to reduce internal stress and structural heterogeneity; while thin-walled continuous casting billets can achieve the same performance requirements in a relatively short time. In subsequent processes such as tube billet sawing, heating, perforation, micro-tension reducing or sizing, process parameters such as heating temperature, rolling speed, reducing amount, etc. can also be adjusted according to the characteristics of steel pipes with different wall thicknesses, thereby realizing personalized production processes for seamless steel pipes with different wall thicknesses and improving product quality and performance stability.

[0039] During the smelting process, precise control of the bottom blowing argon flow rate, alloy addition sequence and time, deep deoxidation treatment and soft blowing can help remove impurities and gases in the molten steel, refine the grains, and improve the purity and uniformity of the steel. These microstructural improvements directly improve the comprehensive performance indicators of the steel pipe, such as strength, toughness and fatigue resistance.

[0040] This embodiment adopts a critical quenching process for quenching treatment and then tempering to obtain an ideal organizational form, such as tempered troostite, which has a good match between strength and toughness. The critical quenching process can make the steel pipe maintain high toughness while obtaining high strength, effectively solving the problem of difficulty in balancing strength and toughness in traditional quenching processes. Through this heat treatment process, the comprehensive performance of the product is further improved, so that it can meet the use requirements of high-end boom pipes under complex stress conditions.

[0041] This implementation method sets up multiple inspection links during the manufacturing process, including surface inspection, non-destructive testing, sampling inspection, etc., which can timely discover and eliminate defects in the product and ensure the stability and reliability of product quality. This comprehensive quality control system ensures that each seamless steel pipe produced has good comprehensive performance, thereby improving the safety and service life of the product in practical applications.

[0042] Specific implementation example 6: This implementation example is different from specific implementation example 5 in that: in step 1, the converter end point is controlled to be: C≤0.07%, P≤0.006%, and the steel tapping temperature is ≥1610° C. The rest is the same as specific implementation example 5.

[0043] Specific embodiment 7: This embodiment is different from specific embodiment 5 in that: the refined slag in step 1 is composed of CaO 52-58%, 8%≤SiO2≤10%, MgO 5-8%, Al2O3 20-25%, FeO≤0.7% by mass percentage; the rest are impurities. The rest is the same as specific embodiment 5.

[0044] Specific embodiment eight: This embodiment differs from specific embodiment five in that the heating temperature in step three is 1170-1240°C, the soaking temperature is 1230-1260°C, the start rolling temperature is 1230-1250°C, the graded micro-controlled cold pressure after rolling is 0.8-1.2MPa, and the final rolling temperature is 850-880°C. Others are the same as specific embodiment five.

[0045] Specific embodiment 9: This embodiment differs from specific embodiment 5 in that the critical quenching in step 4 is external shower and internal spray + rapid semi-immersion, the heating temperature of the quenching furnace is 740-880°C, the quenching furnace soaking temperature is 760-880°C, and the critical quenching process cooling rate is ≥20°C / s. Others are the same as specific embodiment 5.

[0046] Specific embodiment 10: This embodiment differs from specific embodiment 5 in that: the heating temperature of tempering in step 4 is 520-620°C, the soaking temperature is 540-600°C, and a secondary tempering process is added according to the wall thickness, and the soaking temperature is 580-620°C. Others are the same as specific embodiment 5.

[0047] The following examples are used to verify the beneficial effects of the present invention:

[0048] Embodiment 1: A method for manufacturing a 960 MPa low-alloy seamless pipe exclusively for a boom is completed by the following steps:

[0049] 1. Smelting: According to the mass percentage: C is 0.16%, Si is 0.22%, Mn is 1.44%, Cr is 0.81%, Mo is 0.52%, Ni is 0.83%, V is 0.034%, Nb is 0.018%, Ti is 0.011%, Al is 0.019%, P is 0.008%, S is 0.005%, N is 0.0065%, Fe and unavoidable impurities are 95.918% for material preparation, and converter smelting is adopted; when the converter is tapped, the ladle is deoxidized and alloyed, and 3kg / t of ferrosilicon alloy, 1.5-2kg / t of aluminum ingots, 20kg / t of medium carbon ferromanganese, 12kg / t of low carbon ferrochrome, and 0.8kg / t of ferrovanadium are added to the alloy. When each furnace is tapped, 200kg of refined slag is added with the alloy. After the alloy is added, the steel is 300kg of lime is added to the steel flow, and the bottom blowing argon flow rate is 0.5NL / (t·min) during the steel tapping process to ensure that the alloy and refined slag are well melted after the steel tapping is completed; Mo, Nb, and Ni are alloyed in the refining station, and titanium is alloyed during the refining and steel tapping; deep deoxidation is carried out when all elements except titanium are qualified and the temperature meets the continuous casting requirements, and deep deoxidation is completed, the refining power is turned off and steel tapping is completed, and titanium iron is added. The amount of titanium iron added is 0.5kg / t steel, and a micro-titanium treatment process is carried out, and sampling is taken to test the composition. After refining and steel tapping, a ladle covering agent is added to make the ladle covering agent evenly cover the entire slag surface, and the argon gas is adjusted to perform soft blowing to evenly distribute the composition. After the soft blowing is completed, the clean and qualified molten steel is transferred to the continuous casting; the argon gas flow rate is controlled to be 0.2~0.5NL / (t·min) during soft blowing, and the soft blowing time is ≥15min;

[0050] 2. Continuous casting and slow cooling: Continuously cast clean and qualified molten steel into continuous casting billets, divide the continuous casting billets into sections, and place them into slow cooling pits at a temperature of ≥400°C. When the temperature of the continuous casting billets in the slow cooling pit drops below 200°C, they are taken out of the pits. The continuous casting process adopts full-process protection pouring.

[0051] 3. Subsequent processing: Surface inspection and finishing of the continuous casting billets out of the pit, transfer qualified continuous casting billets to the steel rolling workshop, saw the billets, heat and perforate them after sawing, and then roll them; then reduce the diameter or sizing by micro-tension, air-cool the cooling bed, monitor the temperature online during air-cooling of the cooling bed, and then saw, sample and inspect, and perform non-destructive testing;

[0052] 4. Heat treatment: Use critical quenching process for quenching, and then tempering;

[0053] 5. Subsequent inspection and warehousing: After heat treatment, straightening, non-destructive testing, sampling inspection, surface inspection, and labeling are carried out in sequence before warehousing.

[0054] In step 1, the converter endpoint is controlled as follows: C ≤ 0.07%, P ≤ 0.006%, and the tapping temperature ≥ 1610°C;

[0055] The refined slag in step 1 is composed of 52-58% CaO, 8%≤SiO2≤10%, 5-8% MgO, 20-25% Al2O3, and FeO≤0.7% by mass percentage; the rest are impurities;

[0056] In step 3, the heating temperature is 1170-1240°C, the soaking temperature is 1230-1260°C, the start rolling temperature is 1230-1250°C, the graded micro-controlled cold pressure after rolling is 0.8-1.2MPa, and the final rolling temperature is 850-880°C;

[0057] The critical quenching in step 4 is external shower and internal spray + rapid semi-immersion, the heating temperature of the quenching furnace is 740-880°C, the quenching furnace soaking temperature is 760-880°C, and the critical quenching process cooling rate is ≥20°C / s;

[0058] The heating temperature of the tempering in step 4 is 520-620°C, and the soaking temperature is 540-600°C; a secondary tempering process is added according to the wall thickness, and the soaking temperature is 580-620°C.

[0059] Performance indicators: yield strength 1023 ~ 1029MPa, tensile strength 1089 ~ 1094MPa, elongation after fracture 16.5%, -20℃ longitudinal impact energy 97 ~ 101J, -40℃ longitudinal impact energy 71 ~ 76J, grain size 9, organization tempered troostite. (Production specification φ159*13mm)

[0060] Embodiment 2: This embodiment is different from Embodiment 1 in that: in step 1, by mass percentage, C is 0.18%, Si is 0.31%, Mn is 1.52%, Cr is 0.83%, Mo is 0.52%, Ni is 0.90%, V is 0.047%, Nb is 0.019%, Ti is 0.013%, Al is 0.021%, P is 0.001%, S is 0.006%, N is 0.0057%, Fe and unavoidable impurities are 95.727%. Others are the same as Embodiment 1.

[0061] Performance indicators: yield strength 1044~1051MPa, tensile strength 1098~1103MPa, elongation after fracture 17.0%, -20℃ longitudinal impact energy 89~94J, -40℃ longitudinal impact energy 69~75J, grain size 9, organization tempered troostite. (Production specification φ219*20mm)

[0062] Embodiment 3: This embodiment is different from the embodiment 1 in that, by mass percentage, C is 0.20%, Si is 0.25%, Mn is 1.61%, Cr is 0.86%, Mo is 0.54%, Ni is 0.92%, V is 0.055%, Nb is 0.018%, Ti is 0.011%, Al is 0.020%, P is 0.008%, S is 0.003%, N is 0.0059%, Fe and unavoidable impurities are 95.499%. The rest is the same as the embodiment 1.

[0063] Performance indicators: yield strength 1033~1041MPa, tensile strength 1067~1074MPa, elongation after fracture 17.0%, -20℃ longitudinal impact energy 82~87J, -40℃ longitudinal impact energy 63~70J, grain size 9, organization tempered troostite. (Production specification φ273*25mm).

Claims

1. A 960 MPa low alloy seamless pipe exclusively for boom, characterized by The mass percentage of 960 MPa low-alloy seamless pipe exclusively for boom is as follows: C is 0.16-0.20%, Si is 0.20-0.35%, Mn is 1.40-1.70%, Cr is 0.80-1.00%, Mo is 0.50-0.70%, Ni is 0.80-1.20%, V is 0.030-0.070%, Nb is 0.015-0.025%, Ti is 0.010-0.025%, Al≤0.030%, P≤0.012%, S≤0.008%, N≤0.007%, and the balance is Fe and unavoidable impurities.

2. The 960 MPa low alloy seamless pipe exclusively for boom according to claim 1 is characterized in that The arm's exclusive 960 MPa low-alloy seamless pipe has a yield strength of ≥960 MPa, a tensile strength of 1020-1180 MPa, an elongation of ≥14%, a -20°C longitudinal impact energy of ≥65 J, a -40°C longitudinal impact energy of ≥55 J, a quenched and tempered structure, a grain size of ≥9.0, and no cracks in a 180° bending test.

3. The 960 MPa low alloy seamless pipe exclusively for boom according to claim 1 is characterized in that The mass percentage of the boom-exclusive 960 MPa low-alloy seamless pipe is as follows: C is 0.20%, Si is 0.25%, Mn is 1.61%, Cr is 0.86%, Mo is 0.54%, Ni is 0.92%, V is 0.055%, Nb is 0.018%, Ti is 0.011%, Al is 0.020%, P is 0.008%, S is 0.003%, N is 0.0059%, and the balance is Fe and unavoidable impurities.

4. The 960 MPa low alloy seamless pipe exclusively for boom according to claim 1 is characterized in that The mass percentage of the boom-exclusive 960 MPa low-alloy seamless pipe is as follows: C is 0.18%, Si is 0.31%, Mn is 1.52%, Cr is 0.83%, Mo is 0.52%, Ni is 0.90%, V is 0.047%, Nb is 0.019%, Ti is 0.013%, Al is 0.021%, P is 0.001%, S is 0.006%, N is 0.0057%, and the balance is Fe and unavoidable impurities.

5. The method for manufacturing a 960 MPa low alloy seamless pipe exclusively for booms as claimed in claim 1, characterized in that The manufacturing method of the 960 MPa low alloy seamless pipe exclusively for the boom is completed in the following steps:

1. Smelting: According to the mass percentage: C is 0.16-0.20%, Si is 0.20-0.35%, Mn is 1.40-1.70%, Cr is 0.80-1.00%, Mo is 0.50-0.70%, Ni is 0.80-1.20%, V is 0.030-0.070%, Nb is 0.015-0.025%, Ti is 0.010-0.025%, Al≤0.030%, P≤0.012%, S≤0.008%, N≤0.007%, the balance is Fe and unavoidable impurities, and the converter is used for smelting; when the converter is tapped, the ladle is deoxidized and alloyed, and the order of alloy addition is ferrosilicon alloy. , aluminum ingots, medium carbon ferromanganese, low carbon ferrochrome, ferrovanadium and refined slag. After the alloy is added, lime is added with the steel flow. During the steel tapping process, the bottom blowing argon flow rate is 0.5NL / (t·min) to ensure that the alloy and refined slag are well melted after the steel tapping is completed; Mo, Nb and Ni are alloyed in the refining station, and titanium is alloyed during the refining and steel tapping; deep deoxidation is carried out when all elements except titanium are qualified and the temperature meets the continuous casting requirements. After deep deoxidation, the refining power is turned off and steel is tapped. Titanium iron is added and a micro-titanium treatment process is carried out. Samples are taken to test whether the composition is qualified; after refining and steel tapping, a ladle covering agent is added to make the ladle covering agent evenly cover the entire slag surface, and the argon gas is adjusted to perform soft blowing to even out the composition. After the soft blowing is completed, the clean and qualified molten steel is transferred to the continuous casting; 2. Continuous casting and slow cooling: Continuously cast clean and qualified molten steel into continuous casting billets, divide the continuous casting billets into sections, and place them into slow cooling pits at a temperature of ≥400°C. When the temperature of the continuous casting billets in the slow cooling pit drops below 200°C, they are taken out of the pits; The continuous casting process adopts full protection pouring; 3. Subsequent processing: Surface inspection and finishing of the continuous casting billets out of the pit, transfer qualified continuous casting billets to the steel rolling workshop, saw the billets, heat and perforate them after sawing, and then roll them; then reduce the diameter or sizing by micro-tension, air-cool the cooling bed, monitor the temperature online during air-cooling of the cooling bed, and then saw, sample and inspect, and perform non-destructive testing; 4. Heat treatment: Use critical quenching process for quenching, and then tempering; 5. Subsequent inspection and warehousing: After heat treatment, straightening, non-destructive testing, sampling inspection, surface inspection, and labeling are carried out in sequence before warehousing.

6. The method for manufacturing a 960 MPa low alloy seamless pipe exclusively for boom according to claim 5, characterized in that In step 1, the converter endpoint is controlled as follows: C≤0.07%, P≤0.006%, and steel tapping temperature≥1610°C.

7. The method for manufacturing a 960 MPa low alloy seamless pipe exclusively for boom according to claim 5, characterized in that The refined slag in step 1 is composed of 52-58% CaO, 8%≤SiO2≤10%, 5-8% MgO, 20-25% Al2O3, and FeO≤0.7% by mass percentage; the rest are impurities.

8. The method for manufacturing a 960 MPa low alloy seamless pipe exclusively for boom according to claim 5, characterized in that In step three, the heating temperature is 1170-1240°C, the soaking temperature is 1230-1260°C, the start rolling temperature is 1230-1250°C, the graded micro-controlled cold pressure after rolling is 0.8-1.2MPa, and the final rolling temperature is 850-880°C.

9. The method for manufacturing a 960 MPa low alloy seamless pipe exclusively for boom according to claim 5, characterized in that The critical quenching described in step 4 is external shower and internal spray + rapid semi-immersion, the heating temperature of the quenching furnace is 740-880°C, the quenching furnace uniform temperature is 760-880°C, and the critical quenching process cooling rate is ≥20°C / s.

10. The method for manufacturing a 960 MPa low alloy seamless pipe exclusively for boom according to claim 5, characterized in that The heating temperature of the tempering in step 4 is 520-620°C, and the absorptive temperature is 540-600°C; a secondary tempering process is added according to the wall thickness, and the absorptive temperature is 580-620°C.