Low-alloy high-strength 890MPa-grade seamless steel tube and manufacturing method thereof

Abstract

The invention discloses a low-alloy high-strength 890MPa-grade seamless steel tube and a manufacturing method thereof, and belongs to the technical field of metallurgical processes. The steel pipe comprises the following components: C, Si, Mn, Cr, Mo, Ni, V, Nb, Ti, Al, P, S, N and the balance of Fe and impurity elements. The method comprises the following steps: smelting after component design; tapping in a converter and deoxidizing and alloying in a steel ladle; refining and tapping; continuously casting after soft blowing; performing segmentation; slowly cooling; and after finishing, blank segmented feeding is carried out, and then perforation rolling and heat treatment are carried out. On the premise of reducing the usage amount of precious alloy, the comprehensive performance of the product is improved by adopting a new alloy design principle, matching with a smelting process, a hot rolling process and a hardening and tempering process and formulating different production processes for seamless steel pipes with different wall thicknesses. A multi-component alloy and microalloy strengthening mechanism and an alloy element narrow component control mechanism are realized on the aspect of chemical components; the structure and performance stability of the seamless steel pipe is achieved, and the purposes of low cost, high strength and easy welding are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical process, and specifically relates to a low-alloy high-strength 890MPa grade seamless steel pipe and a manufacturing method thereof. Background Art

[0002] Crawler cranes are developing rapidly, especially large-tonnage crawler cranes, which put forward higher requirements on the performance of materials. The crane boom is a key component of crawler cranes for carrying, transferring and lifting heavy objects. It must not only have high strength, high plasticity and good toughness, but also good welding performance, and has many specifications and high quality requirements. This type of high-strength seamless steel pipe belongs to low-carbon low-alloy tempered steel. It is obtained by adding alloy and micro-alloying elements and then undergoing quenching and tempering treatment to obtain tempered troostite structure. At the same time, it effectively plays the role of micro-alloying elements in refining grains and precipitation strengthening during tempering, thereby improving the strength and toughness of the material and making the steel have higher comprehensive mechanical properties.

[0003] The 890MPa arm tube in the arm tube standard GB / T 30584-2014 stipulates that the alloy and micro-alloy elements Mo, W, Nb, V, Ti, Al are added to achieve the purpose of precipitation strengthening and fine grain strengthening, and the elements Mn, Cr, and Ni are added to meet the requirements of quenching and tempering process and low temperature performance. The standard also points out that the low-temperature average impact energy is based on -20℃ conditions, and cannot meet the actual low-temperature toughness index requirements of -40℃ and below; currently, customers require the low-temperature average impact energy to be based on -40℃ conditions, and at the same time meet the welding requirements between different strengths, which has a high amount of precious alloys, resulting in increased costs. Summary of the invention

[0004] The object of the present invention is to solve the problems of the prior art and to provide a low-alloy high-strength 890MPa grade seamless steel pipe and a manufacturing method thereof.

[0005] A low alloy high strength 890MPa grade seamless steel pipe, which is composed of C: 0.16%-0.20%, Si: 0.20%-0.35%, Mn: 1.20%-1.70%, Cr: 0.60%-0.80%, Mo: 0.30%-0.50%, Ni: 0.60%-1.0%, V: 0.030%-0.070%, Nb: 0.015%-0.025%, Ti: 0.010%-0.025%, Al≤0.030%, P≤0.012%, S≤0.008%, N≤0.007% and the balance of Fe and impurity elements in terms of weight percentage.

[0006] The above-mentioned method for manufacturing a low-alloy high-strength 890MPa grade seamless steel pipe is carried out according to the following steps:

[0007] 1. According to the weight percentage composition of low alloy high strength 890MPa grade seamless steel pipe, C: 0.16% ~ 0.20%, Si: 0.20% ~ 0.35%, Mn: 1.20% ~ 1.70%, Cr: 0.60% ~ 0.80%, Mo: 0.30% ~ 0.50%, Ni: 0.60% ~ 1.0%, V: 0.030% ~ 0.070%, Nb: 0.015% ~ 0.025%, Ti: 0.010% ~ 0.025%, Al ≤ 0.030%, P ≤ 0.012%, S ≤ 0.008%, N ≤ 0.007% and the balance of Fe and impurity elements are designed;

[0008] 2. Load the molten iron and scrap steel into the converter for smelting. The converter endpoint control meets the following requirements: C≤0.08%; P≤0.006%, and the tapping temperature is ≥1610℃;

[0009] 3. Steel tapping from converter and deoxidation and alloying in ladle: During the steel tapping process, argon is blown from the bottom, with an argon flow rate of 0.5NL / min / t steel. Alloy and refined slag are added when each furnace is tapped. When the alloy is added, lime is added with the steel flow to complete the steel tapping. The steel is then transported to the LF refining station, and ferromolybdenum, ferroniobium and nickel plates are added for alloying. When the temperature reaches 1580-1600℃, silicon-barium alloy is added for deep deoxidation. After 2 minutes, the LF refining station is powered off for steel tapping, and ferrotitanium is added for micro-titanium treatment.

[0010] 4. After the above-mentioned micro-titanium treatment, the steel is refined and then a ladle covering agent is added, and the ladle covering agent is evenly covered on the entire slag surface. The argon gas is adjusted for soft blowing. The argon gas flow rate during soft blowing is 0.2-0.5NL / min / t steel, and the soft blowing time is ≥15min;

[0011] 5. After the soft blowing is completed, the molten steel is transferred to the continuous casting station. The continuous casting process adopts full-process protective pouring to continuously cast the molten steel into continuous casting billets, which are then segmented and transferred to the slow cooling pit for slow cooling. The continuous casting billets that have been slowly cooled out of the pit are subjected to surface inspection and finishing. The finished continuous casting billets are transferred to the rolling workshop for billet segment loading, and then piercing, rolling and heat treatment are performed to obtain low-alloy high-strength 890MPa grade seamless steel pipes, thereby completing the manufacturing method.

[0012] Furthermore, the alloy described in step three: the alloy type and dosage are 3kg / t steel of ferrosilicon alloy, 1.2-1.8kg / t steel of aluminum ingot, 16kg / t steel of medium carbon ferromanganese, 10kg / t steel of low carbon ferrochrome and 0.8kg / t steel of ferrovanadium.

[0013] Furthermore, the mass percentage of the refined slag in step three is: CaO: 55% to 58%, 8%≤SiO2≤10%, MgO: 5% to 8%, Al2O3: 22% to 25%, FeO≤0.7% and the remainder of impurities.

[0014] Furthermore, in step 3, the amount of refined slag added is 220kg / t steel; the amount of lime added is 330kg / t steel; the amount of silicon-barium alloy added is 1kg / t steel; and the amount of ferrotitanium added is 0.5kg / t steel.

[0015] Furthermore, the ladle covering agent in step 4 is carbonized rice husk.

[0016] Furthermore, in the slow cooling pit in step 5, the temperature of the continuous casting billet entering the slow cooling pit is ≥ 400°C, and the continuous casting billet exits the pit when the temperature of the slow cooling pit drops below 200°C;

[0017] Furthermore, the surface inspection and finishing described in step five: the continuous casting billet is surface inspected and finished in accordance with GB / T17426-2019 "Dimensions, wheel shape, weight and allowable deviations of continuous casting billets".

[0018] Furthermore, the piercing and rolling in step five: the heating temperature is 1170-1200°C, the soaking temperature is 1220-1250°C, the start rolling temperature is 1210-1240°C, the graded micro-controlled cold pressure after rolling is 1.0-1.2MPa, and the final rolling temperature is 865-880°C.

[0019] Furthermore, the heat treatment in step five: the quenching furnace heating temperature is 780-880°C, the quenching furnace soaking temperature is 800-880°C, the critical quenching process cooling rate is ≥30°C / s, and the critical quenching process is external shower and internal spray + rapid semi-quenching; the tempering furnace heating temperature is 580-620°C, and the tempering furnace soaking temperature is 580-600°C; if the wall thickness is ≥20mm, a secondary tempering process is required, and the tempering soaking temperature is 580-610°C.

[0020] Advantages of the present invention:

[0021] The present invention provides a method for manufacturing a low-alloy high-strength 890MPa grade seamless steel pipe for a crawler crane boom. Under the premise of reducing the use of precious alloys, the present invention adopts new alloy design principles, coordinated smelting processes, hot rolling processes, quenching and tempering processes, and formulates different production processes (supplemented with secondary tempering) for seamless steel pipes with different wall thicknesses to improve the comprehensive performance of the product.

[0022] In terms of chemical composition, the multi-alloy + micro-alloy strengthening mechanism and the narrow composition control mechanism of alloy elements are realized; the key temperature control during the rolling process realizes the stability of the seamless steel pipe structure, and the key temperature and cooling rate control during the quenching and tempering process realizes the stability of the performance of the seamless steel pipe, thus achieving the goal of low cost, high strength and easy welding.

[0023] Key performance indicators: 890MPa grade, yield strength ≥890MPa, tensile strength 960~1110MPa, elongation ≥15%, -20℃ longitudinal average impact energy ≥65J, -40℃ longitudinal average impact energy ≥55J, quenched and tempered structure, grain size 9.0, no cracks in 180° bending test.

[0024] 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.

[0025] The low-alloy high-strength 890MPa grade seamless steel pipe manufactured by the invention is suitable for the boom of a crawler crane. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 100X metallographic structure diagram of the low alloy high strength 890MPa grade seamless steel pipe obtained in Example 2;

[0027] Figure 2 It is a physical picture of JXY / HJL-125-2024 "Technical Agreement for High-Strength Seamless Steel Pipe for Crawler Crane Boom" in Example 3;

[0028] Figure 3 500X metallographic structure diagram of the low alloy high strength 890MPa grade seamless steel pipe obtained in Example 3;

[0029] Figure 4 This is the test report of the low alloy high strength 890MPa grade seamless steel pipe obtained in Example 4. DETAILED DESCRIPTION

[0030] 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.

[0031] Specific implementation method one: This implementation method is a low-alloy high-strength 890MPa grade seamless steel pipe, which is composed of C: 0.16%~0.20%, Si: 0.20%~0.35%, Mn: 1.20%~1.70%, Cr: 0.60%~0.80%, Mo: 0.30%~0.50%, Ni: 0.60%~1.0%, V: 0.030%~0.070%, Nb: 0.015%~0.025%, Ti: 0.010%~0.025%, Al≤0.030%, P≤0.012%, S≤0.008%, N≤0.007% and the remainder of Fe and impurity elements in weight percentage.

[0032] Specific embodiment 2: This embodiment is different from the specific embodiment 1 in that it is composed of C: 0.16%, Si: 0.21%, Mn: 1.34%, Cr: 0.62%, Mo: 0.35%, Ni: 0.63%, V: 0.065%, Nb: 0.020%, Ti: 0.013%, Al≤0.021%, P≤0.006%, S≤0.004%, N≤0.0059% and the balance of Fe and impurity elements. Other steps and parameters are the same as those of the specific embodiment 1.

[0033] Specific embodiment three: This embodiment is different from the specific embodiment one in that it is composed of C: 0.18%, Si: 0.34%, Mn: 1.41%, Cr: 0.65%, Mo: 0.45%, Ni: 0.91%, V: 0.042%, Nb: 0.020%, Ti: 0.015%, Al≤0.021%, P≤0.006%, S≤0.005%, N≤0.0054% and the balance of Fe and impurity elements. Other steps and parameters are the same as those of the specific embodiment one.

[0034] Specific embodiment 4: This embodiment is different from the specific embodiment 1 in that it is composed of C: 0.18%, Si: 0.25%, Mn: 1.53%, Cr: 0.69%, Mo: 0.41%, Ni: 0.96%, V: 0.056%, Nb: 0.018%, Ti: 0.014%, Al≤0.020%, P≤0.006%, S≤0.004%, N≤0.0056% and the balance of Fe and impurity elements. Other steps and parameters are the same as those of the specific embodiment 1.

[0035] Specific embodiment 5: This embodiment is a method for manufacturing a low-alloy high-strength 890MPa grade seamless steel pipe, which is carried out according to the following steps:

[0036] 1. According to the weight percentage composition of low alloy high strength 890MPa grade seamless steel pipe, C: 0.16% ~ 0.20%, Si: 0.20% ~ 0.35%, Mn: 1.20% ~ 1.70%, Cr: 0.60% ~ 0.80%, Mo: 0.30% ~ 0.50%, Ni: 0.60% ~ 1.0%, V: 0.030% ~ 0.070%, Nb: 0.015% ~ 0.025%, Ti: 0.010% ~ 0.025%, Al ≤ 0.030%, P ≤ 0.012%, S ≤ 0.008%, N ≤ 0.007% and the balance of Fe and impurity elements are designed;

[0037] 2. Load the molten iron and scrap steel into the converter for smelting. The converter endpoint control meets the following requirements: C≤0.08%; P≤0.006%, and the tapping temperature is ≥1610℃;

[0038] 3. Steel tapping from converter and deoxidation and alloying in ladle: During the steel tapping process, argon is blown from the bottom, with an argon flow rate of 0.5NL / min / t steel. Alloy and refined slag are added when each furnace is tapped. When the alloy is added, lime is added with the steel flow to complete the steel tapping. The steel is then transported to the LF refining station, and ferromolybdenum, ferroniobium and nickel plates are added for alloying. When the temperature reaches 1580-1600℃, silicon-barium alloy is added for deep deoxidation. After 2 minutes, the LF refining station is powered off for steel tapping, and ferrotitanium is added for micro-titanium treatment.

[0039] 4. After the above-mentioned micro-titanium treatment, the steel is refined and then a ladle covering agent is added, and the ladle covering agent is evenly covered on the entire slag surface. The argon gas is adjusted for soft blowing. The argon gas flow rate during soft blowing is 0.2-0.5NL / min / t steel, and the soft blowing time is ≥15min;

[0040] 5. After the soft blowing is completed, the molten steel is transferred to the continuous casting station. The continuous casting process adopts full-process protective pouring to continuously cast the molten steel into continuous casting billets, which are then segmented and transferred to the slow cooling pit for slow cooling. The continuous casting billets that have been slowly cooled out of the pit are subjected to surface inspection and finishing. The finished continuous casting billets are transferred to the rolling workshop for billet segment loading, and then piercing, rolling and heat treatment are performed to obtain low-alloy high-strength 890MPa grade seamless steel pipes, thereby completing the manufacturing method.

[0041] The amounts of molten iron and scrap steel used in step 2 of this embodiment can be obtained by those skilled in the art through routine calculations based on the component design in step 1.

[0042] The purpose of adopting full-process protective pouring in the continuous casting process in step 5 of this embodiment is to avoid secondary oxidation of molten steel by air absorption.

[0043] After the heat treatment in step 5 of this embodiment is completed, straightening, non-destructive testing, sampling inspection and surface inspection are carried out in sequence, and the qualified ones are sprayed with labels and put into storage.

[0044] Specific embodiment 6: This embodiment is different from specific embodiment 5 in that the alloys described in step 3 are: 3kg / t steel of ferrosilicon alloy, 1.2-1.8kg / t steel of aluminum ingot, 16kg / t steel of medium carbon ferromanganese, 10kg / t steel of low carbon ferrochrome and 0.8kg / t steel of ferrovanadium. Other steps and parameters are the same as those in specific embodiment 5.

[0045] Specific embodiment 7: This embodiment is different from specific embodiment 5 in that the mass percentage of the refined slag in step 3 is: CaO: 55% to 58%, 8%≤SiO2≤10%, MgO: 5% to 8%, Al2O3: 22% to 25%, FeO≤0.7% and the remainder of impurities. The other steps and parameters are the same as those in specific embodiment 5.

[0046] Specific embodiment eight: This embodiment differs from specific embodiment five in that the amount of refined slag added in step three is 220kg / t steel; the amount of lime added is 330kg / t steel; the amount of silicon-barium alloy added is 1kg / t steel; the amount of ferrotitanium added is 0.5kg / t steel. The other steps and parameters are the same as those in specific embodiment five.

[0047] Specific embodiment 9: This embodiment is different from specific embodiment 5 in that the ladle covering agent in step 4 is carbonized rice husk. The other steps and parameters are the same as those in specific embodiment 5.

[0048] Specific embodiment 10: This embodiment is different from specific embodiment 5 in that the temperature of the slow cooling pit in step 5 is ≥400°C when the continuous casting billet enters the slow cooling pit, and the continuous casting billet exits the pit when the temperature of the slow cooling pit drops below 200°C. Other steps and parameters are the same as those in specific embodiment 5.

[0049] Specific embodiment 11: This embodiment differs from specific embodiment 5 in that the surface inspection and finishing described in step 5: the continuous casting billet is subjected to surface inspection and finishing according to GB / T17426-2019 "Continuous Casting Billet Size, Wheel Shape, Weight and Permissible Deviation". The other steps and parameters are the same as those in specific embodiment 5.

[0050] Specific embodiment 12: This embodiment is different from specific embodiment 5 in that the piercing and rolling in step 5: the heating temperature is 1170-1200°C, the soaking temperature is 1220-1250°C, the start rolling temperature is 1210-1240°C, the graded micro-controlled cold pressure after rolling is 1.0-1.2MPa, and the final rolling temperature is 865-880°C. The other steps and parameters are the same as those in specific embodiment 5.

[0051] Specific embodiment 13: This embodiment is different from specific embodiment 5 in that the heat treatment in step 5: the heating temperature of the quenching furnace is 780-880°C, the quenching furnace soaking temperature is 800-880°C, the critical quenching process cooling rate is ≥30°C / s, and the critical quenching process is external shower and internal spray + rapid semi-quenching; the heating temperature of the tempering furnace is 580-620°C, and the tempering furnace soaking temperature is 580-600°C; if the wall thickness is ≥20mm, a secondary tempering process is required, and the tempering soaking temperature is 580-610°C. Other steps and parameters are the same as those in specific embodiment 5.

[0052] The beneficial effects of the present invention are verified by the following examples:

[0053] Embodiment 1:

[0054] A method for manufacturing a low-alloy high-strength 890MPa grade seamless steel pipe is carried out according to the following steps:

[0055] 1. The composition design is carried out according to the weight percentage composition of low alloy high strength 890MPa grade seamless steel pipe: C: 0.16%, Si: 0.21%, Mn: 1.34%, Cr: 0.62%, Mo: 0.35%, Ni: 0.63%, V: 0.065%, Nb: 0.020%, Ti: 0.013%, Al≤0.021%, P≤0.006%, S≤0.004%, N≤0.0059% and the balance of Fe and impurity elements;

[0056] 2. Loading molten iron and scrap steel into a converter for smelting, the converter endpoint control meets the following conditions: C≤0.08%; P≤0.006%, steel tapping temperature≥1610°C; the molten iron dosage is 961kg / t, and the scrap steel dosage is 100kg / t;

[0057] 3. Steel tapping from converter and deoxidation and alloying in ladle: During the steel tapping process, argon is blown from the bottom, with an argon flow rate of 0.5NL / min / t steel. Alloy and refined slag are added when each furnace is tapped. When the alloy is added, lime is added with the steel flow to complete the steel tapping. The steel is then transported to the LF refining station, and ferromolybdenum, ferroniobium and nickel plates are added for alloying. When the temperature reaches 1580-1600℃, silicon-barium alloy is added for deep deoxidation. After 2 minutes, the LF refining station is powered off for steel tapping, and ferrotitanium is added for micro-titanium treatment.

[0058] 4. After the above-mentioned micro-titanium treatment, the steel is refined and then a ladle covering agent is added, and the ladle covering agent is evenly covered on the entire slag surface. The argon gas is adjusted for soft blowing. The argon gas flow rate during soft blowing is 0.2-0.5NL / min / t steel, and the soft blowing time is ≥15min;

[0059] 5. After the soft blowing is completed, the molten steel is transferred to the continuous casting station. The continuous casting process adopts full-process protective pouring to continuously cast the molten steel into continuous casting billets, which are then segmented and transferred to the slow cooling pit for slow cooling. The continuous casting billets that have been slowly cooled out of the pit are subjected to surface inspection and finishing. The finished continuous casting billets are transferred to the rolling workshop for billet segment loading, and then piercing, rolling and heat treatment are performed to obtain low-alloy high-strength 890MPa grade seamless steel pipes, thereby completing the manufacturing method.

[0060] The purpose of adopting full-process protective pouring in the continuous casting process in step 5 of this embodiment is to avoid secondary oxidation of the molten steel by air absorption.

[0061] After the heat treatment in step 5 of this embodiment is completed, straightening, non-destructive testing, sampling inspection and surface inspection are carried out in sequence, and the qualified ones are sprayed with labels and put into storage.

[0062] The alloys described in step three of this embodiment: the alloy types and amounts are 3kg / t steel of ferrosilicon alloy, 1.5kg / t steel of aluminum ingot, 16kg / t steel of medium carbon ferromanganese, 10kg / t steel of low carbon ferrochrome and 0.8kg / t steel of ferrovanadium.

[0063] The mass percentages of the refined slag in step three of this embodiment are: CaO: 56%, SiO2: 9%, MgO: 6%, Al2O3: 23%, FeO≤0.7% and the remainder of impurities.

[0064] In step 3 of this embodiment, the amount of refined slag added is 220kg / t steel; the amount of lime added is 330kg / t steel; the amount of silicon-barium alloy added is 1kg / t steel; and the amount of ferrotitanium added is 0.5kg / t steel.

[0065] The ladle covering agent in step 4 of this embodiment is carbonized rice husk.

[0066] The slow cooling pit described in step five of this embodiment: the temperature of the continuous casting billet entering the slow cooling pit is ≥400°C, and the continuous casting billet exits the pit when the temperature of the slow cooling pit drops below 200°C.

[0067] Surface inspection and finishing described in step five of this embodiment: The continuous casting billet is surface inspected and finished in accordance with GB / T17426-2019 "Dimensions, wheel shape, weight and allowable deviations of continuous casting billets".

[0068] The piercing and rolling described in step five of this embodiment: the heating temperature is 1170-1200°C, the soaking temperature is 1220-1250°C, the start rolling temperature is 1210-1240°C, the graded micro-controlled cold pressure after rolling is 1.0-1.2MPa, and the final rolling temperature is 865-880°C.

[0069] The heat treatment described in step five of this embodiment: the heating temperature of the quenching furnace is 780-880°C, the soaking temperature of the quenching furnace is 800-880°C, the critical quenching process cooling rate is ≥30°C / s, and the critical quenching process is external showering and internal spraying + rapid semi-quenching; the heating temperature of the tempering furnace is 580-620°C, and the soaking temperature of the tempering furnace is 580-600°C.

[0070] The steel sample analysis results in this embodiment meet the composition design requirements.

[0071] The low-alloy high-strength 890MPa grade seamless steel pipe manufactured in this embodiment has a production specification of φ159*8mm; after testing, the performance indicators are: yield strength 985~992MPa, tensile strength 1035~1041MPa, elongation after fracture 18%, -20℃ longitudinal average impact energy 90~100J, -40℃ longitudinal average impact energy 66~71J, grain size 9, and tempered troostite structure.

[0072] Embodiment 2:

[0073] The difference between this embodiment and embodiment 1 is that in step 1, the composition is designed according to the weight percentage composition of the low-alloy high-strength 890MPa grade seamless steel pipe, which is C: 0.18%, Si: 0.34%, Mn: 1.41%, Cr: 0.65%, Mo: 0.45%, Ni: 0.91%, V: 0.042%, Nb: 0.020%, Ti: 0.015%, Al≤0.021%, P≤0.006%, S≤0.005%, N≤0.0054% and the remainder of Fe and impurity elements; the rest is the same as embodiment 1.

[0074] The steel sample analysis results in this embodiment meet the composition design requirements.

[0075] The low alloy high strength 890MPa grade seamless steel pipe manufactured in this embodiment has a production specification of φ168*16mm. After testing, the performance indicators are: yield strength 976~991MPa, tensile strength 1043~1053MPa, elongation after fracture 17.5%, -20℃ longitudinal average impact energy 87~92J, -40℃ longitudinal average impact energy 67~78J, metallographic structure as shown Figure 1 As shown, the grain size is level 9 and the structure is tempered troostite.

[0076] Embodiment 3:

[0077] The present embodiment is different from the embodiment 1 in that: in step 1, the composition is designed according to the weight percentage composition of the low alloy high strength 890 MPa grade seamless steel pipe: C: 0.18%, Si: 0.25%, Mn: 1.53%, Cr: 0.69%, Mo: 0.41%, Ni: 0.96%, V: 0.056%, Nb: 0.018%, Ti: 0.014%, Al≤0.020%, P≤0.006%, S≤0.004%, N≤0.0056% and the balance of Fe and impurity elements;

[0078] Heat treatment in step 5: quenching furnace heating temperature is 780-880°C, quenching furnace soaking temperature is 800-880°C, critical quenching process cooling rate is ≥30°C / s, and the critical quenching process is external spraying and internal spraying + rapid semi-quenching; tempering furnace heating temperature is 580-620°C, tempering furnace soaking temperature is 580-600°C; because the wall thickness is ≥20mm, a secondary tempering process is required, and the tempering soaking temperature is 580-610°C. Others are the same as Example 1.

[0079] The steel sample analysis results in this embodiment meet the composition design requirements.

[0080] The low-alloy high-strength 890MPa grade seamless steel pipe manufactured in this embodiment has a production specification of φ219.1*22mm; after testing, the performance indicators are: yield strength 976~991MPa, tensile strength 1044~1059MPa, elongation after fracture 18%, -20℃ longitudinal average impact energy 83~91J, -40℃ longitudinal average impact energy 64~77J, grain size 9, and tempered troostite structure.

[0081] The low alloy high strength 890 MPa grade seamless steel pipe manufactured in this embodiment is inspected and tested according to GB 30584-2014 "Seamless Steel Pipe for Crane Boom" and JXY / HJL-125-2024 "Technical Protocol for High Strength Seamless Steel Pipe for Crawler Crane Boom". Figure 2 shown.

[0082] The physical quality of the low-alloy high-strength 890MPa grade φ219.1*22mm seamless steel pipe manufactured in this embodiment was inspected by the steel laboratory of Zhejiang Jiulite Materials Technology Co., Ltd. commissioned by the end customer Sany Group Zhejiang Sany Equipment Co., Ltd. Figure 3 As shown, the seamless steel pipe has the advantages of high strength and high toughness and is suitable for crawler crane booms.

[0083] Embodiment 4:

[0084] The present embodiment is different from the embodiment 1 in that: in step 1, the composition is designed according to the weight percentage composition of the low alloy high strength 890 MPa grade seamless steel pipe: C: 0.18%, Si: 0.25%, Mn: 1.53%, Cr: 0.69%, Mo: 0.41%, Ni: 0.96%, V: 0.056%, Nb: 0.018%, Ti: 0.014%, Al≤0.020%, P≤0.006%, S≤0.004%, N≤0.0056% and the balance of Fe and impurity elements;

[0085] Heat treatment in step 5: quenching furnace heating temperature is 780-880°C, quenching furnace soaking temperature is 800-880°C, critical quenching process cooling rate is ≥30°C / s, and the critical quenching process is external spraying and internal spraying + rapid semi-quenching; tempering furnace heating temperature is 580-620°C, tempering furnace soaking temperature is 580-600°C; because the wall thickness is ≥20mm, a secondary tempering process is required, and the tempering soaking temperature is 580-610°C. Others are the same as Example 1.

[0086] The steel sample analysis results in this embodiment meet the composition design requirements.

[0087] The low alloy high strength 890MPa grade seamless steel pipe prepared in this embodiment is produced according to the requirements of the end customer Sany Group Zhejiang Sany Equipment Co., Ltd., and commissioned by Zhejiang Jiulit Materials Technology Co., Ltd. Steel Laboratory for inspection. The sample size is 219*20mm; the test results meet the customer's requirements. The specific data content is as follows Figure 4 As shown in the test report.

[0088] The above content is a further detailed description of the present invention in combination with specific implementation methods, and it cannot be determined that the present invention is limited to the above specific implementation. Without departing from the overall concept of the present invention and the protection of the claims, several simple deductions or substitutions can be made, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A low alloy high strength 890MPa grade seamless steel pipe, characterized in that It is composed of C: 0.16%-0.20%, Si: 0.20%-0.35%, Mn: 1.20%-1.70%, Cr: 0.60%-0.80%, Mo: 0.30%-0.50%, Ni: 0.60%-1.0%, V: 0.030%-0.070%, Nb: 0.015%-0.025%, Ti: 0.010%-0.025%, Al≤0.030%, P≤0.012%, S≤0.008%, N≤0.007% and the remainder of Fe and impurity elements.

2. A low alloy high strength 890MPa grade seamless steel pipe according to claim 1, characterized in that Its composition by weight percentage is C: 0.16%, Si: 0.21%, Mn: 1.34%, Cr: 0.62%, Mo: 0.35%, Ni: 0.63%, V: 0.065%, Nb: 0.020%, Ti: 0.013%, Al≤0.021%, P≤0.006%, S≤0.004%, N≤0.0059% and the remainder of Fe and impurity elements.

3. The low alloy high strength 890MPa grade seamless steel pipe according to claim 1, characterized in that Its composition by weight percentage is C: 0.18%, Si: 0.34%, Mn: 1.41%, Cr: 0.65%, Mo: 0.45%, Ni: 0.91%, V: 0.042%, Nb: 0.020%, Ti: 0.015%, Al≤0.021%, P≤0.006%, S≤0.005%, N≤0.0054% and the remainder of Fe and impurity elements.

4. The low alloy high strength 890 MPa grade seamless steel pipe according to claim 1, characterized in that Its composition by weight percentage is C: 0.18%, Si: 0.25%, Mn: 1.53%, Cr: 0.69%, Mo: 0.41%, Ni: 0.96%, V: 0.056%, Nb: 0.018%, Ti: 0.014%, Al≤0.020%, P≤0.006%, S≤0.004%, N≤0.0056% and the remainder of Fe and impurity elements.

5. A method for manufacturing a low alloy high strength 890 MPa grade seamless steel pipe as claimed in claim 1, characterized in that It is implemented as follows:

1. According to the weight percentage composition of low alloy high strength 890MPa grade seamless steel pipe, C: 0.16% ~ 0.20%, Si: 0.20% ~ 0.35%, Mn: 1.20% ~ 1.70%, Cr: 0.60% ~ 0.80%, Mo: 0.30% ~ 0.50%, Ni: 0.60% ~ 1.0%, V: 0.030% ~ 0.070%, Nb: 0.015% ~ 0.025%, Ti: 0.010% ~ 0.025%, Al ≤ 0.030%, P ≤ 0.012%, S ≤ 0.008%, N ≤ 0.007% and the balance of Fe and impurity elements are designed; 2. Load the molten iron and scrap steel into the converter for smelting. The converter endpoint control meets the following requirements: C≤0.08%; P≤0.006%, and the tapping temperature is ≥1610℃; 3. Steel tapping from converter and deoxidation and alloying in ladle: During the steel tapping process, argon is blown from the bottom, with an argon flow rate of 0.5NL / min / t steel. Alloy and refined slag are added when each furnace is tapped. When the alloy is added, lime is added with the steel flow to complete the steel tapping. The steel is then transported to the LF refining station, and ferromolybdenum, ferroniobium and nickel plates are added for alloying. When the temperature reaches 1580-1600℃, silicon-barium alloy is added for deep deoxidation. After 2 minutes, the LF refining station is powered off for steel tapping, and ferrotitanium is added for micro-titanium treatment.

4. After the above-mentioned micro-titanium treatment, the steel is refined and then a ladle covering agent is added, and the ladle covering agent is evenly covered on the entire slag surface. The argon gas is adjusted for soft blowing. The argon gas flow rate during soft blowing is 0.2-0.5NL / min / t steel, and the soft blowing time is ≥15min; 5. After the soft blowing is completed, the molten steel is transferred to the continuous casting station. The continuous casting process adopts full-process protective pouring to continuously cast the molten steel into continuous casting billets, which are then segmented and transferred to the slow cooling pit for slow cooling. The continuous casting billets that have been slowly cooled out of the pit are subjected to surface inspection and finishing. The finished continuous casting billets are transferred to the rolling workshop for billet segment loading, and then piercing, rolling and heat treatment are performed to obtain low-alloy high-strength 890MPa grade seamless steel pipes, thereby completing the manufacturing method.

6. The method for manufacturing a low alloy high strength 890 MPa grade seamless steel pipe according to claim 5, characterized in that The alloy described in step three: the alloy type and dosage are 3kg / t steel of ferrosilicon alloy, 1.2-1.8kg / t steel of aluminum ingot, 16kg / t steel of medium carbon ferromanganese, 10kg / t steel of low carbon ferrochrome and 0.8kg / t steel of ferrovanadium; the mass percentage of the refined slag described in step three is: CaO: 55%-58%, 8%≤SiO2≤10%, MgO: 5%-8%, Al2O3: 22%-25%, FeO≤0.7% and the remainder of impurities.

7. The method for manufacturing a low alloy high strength 890 MPa grade seamless steel pipe according to claim 5, characterized in that In step 3, the amount of refined slag added is 220kg / t steel; the amount of lime added is 330kg / t steel; the amount of silicon-barium alloy added is 1kg / t steel; and the amount of ferrotitanium added is 0.5kg / t steel.

8. The method for manufacturing a low alloy high strength 890 MPa grade seamless steel pipe according to claim 5, characterized in that The ladle covering agent described in step four is carbonized rice husk; the slow cooling pit described in step five: the temperature of the continuous casting billet entering the slow cooling pit is ≥400°C, and the continuous casting billet exits the pit when the temperature of the continuous casting billet in the slow cooling pit drops below 200°C; the surface inspection and finishing described in step five: the continuous casting billet is surface inspected and finished in accordance with GB / T17426-2019 "Dimensions, wheel shapes, weights and allowable deviations of continuous casting billets".

9. The method for manufacturing a low alloy high strength 890 MPa grade seamless steel pipe according to claim 5, characterized in that The piercing and rolling described in step five: the heating temperature is 1170-1200°C, the soaking temperature is 1220-1250°C, the start rolling temperature is 1210-1240°C, the graded micro-controlled cold pressure after rolling is 1.0-1.2MPa, and the final rolling temperature is 865-880°C.

10. The method for manufacturing a low alloy high strength 890 MPa grade seamless steel pipe according to claim 5, characterized in that Heat treatment in step five: quenching furnace heating temperature is 780-880°C, quenching furnace soaking temperature is 800-880°C, critical quenching process cooling rate is ≥30°C / s, and the critical quenching process is external spraying and internal spraying + rapid semi-quenching; tempering furnace heating temperature is 580-620°C, tempering furnace soaking temperature is 580-600°C; if the wall thickness is ≥20mm, a secondary tempering process is required, and the tempering soaking temperature is 580-610°C.

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