Manufacturing method of seamless steel pipe for rare earth microalloying low-residual-stress Q620D high-strength structure

Abstract

The invention discloses a manufacturing method of a seamless steel tube for a rare earth microalloying low-residual-stress Q620D high-strength structure. The seamless steel tube comprises the following chemical elements by mass: C < = 0.18%; 0.20 to 0.35 percent of Si; mn is 1.20% to 1.50%; less than or equal to 0.020% of P; s is less than or equal to 0.010%; less than or equal to 0.05% of Ti; nb is less than or equal to 0.05%; v < = 0.15%; re < = 0.002%; and the balance of Fe and inevitable impurities. The manufacturing method comprises the following steps: a steelmaking process: molten iron pretreatment, converter smelting, LF (ladle furnace) refining, VD (vacuum degassing) and round billet continuous casting; the pipe rolling process comprises the steps of round billet preparation, saw cutting, annular furnace heating, perforation, PQF continuous rolling, tension reducing and cooling; and the heat treatment process adopts quenching and tempering treatment, namely quenching and tempering. The invention aims to produce the seamless tube for the high-strength steel structure, which meets the requirements, and the residual stress is less than 88MPa.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical materials, and in particular relates to a method for manufacturing a rare earth micro-alloyed low residual stress Q620D high-strength structural seamless steel pipe. Background Art

[0002] Steel structure is the structural manifestation of advanced steel materials to achieve the target structure. It is a comprehensive embodiment of structural design, material application, and structural function realization. At present, steel structure is mainly used in the construction of industrial plants and large public infrastructure buildings, such as airport terminals, stadiums, exhibition venues, new high-speed rail stations, various types of steel bridges, and industrial and civil buildings.

[0003] The history of foreign steel structure development has been a hundred years, while my country's steel structure industry started late. With the increase in steel production capacity, the national steel structure output has increased more than 10 times since the 1990s. Due to the rapid development of the steel industry and the increasing emphasis on building energy conservation, the policy orientation of my country's construction technology has gradually changed from restricting the use of steel structures many years ago to developing and vigorously promoting the application of steel structures. Many national industrial policies support the development of the steel structure industry. Steel structure buildings are in a rapid rise and have made many achievements, but compared with Western countries, there is still a big gap in the overall level. In the next few years, the proportion of steel structure houses alone is expected to increase from less than 10% to 40%. Seamless steel pipes for steel structures mainly adopt the standard GB / T8162-2018 seamless steel pipes for structures, which are made by seamless pipe making process and are often used in the connection and support parts of steel structures. Domestic steel structure projects use a large number of Q345 MPa grade high-strength steel pipes. In recent years, seamless steel pipes for structures have shown a trend of high strengthening. In some key steel structure projects, higher strength grade steel pipes are usually used, such as Q390, Q420, etc. Baosteel has developed 770MPa and higher-level 890MPa seamless steel pipes for structure. At present, domestic companies such as Tianjin Seamless, Baosteel, and Hengyang Steel Pipe can produce high-strength products. This patent discloses a manufacturing method for high-strength structural steel Q620D.

[0004] According to statistics from the China Steel Structure Association, steel pipe consumption is between 6% and 9% of steel structure output. Based on the output of 20 million tons of steel structures, about 1.5 million tons of steel pipes are used for structural engineering, which is far less than hot-rolled H-shaped steel and far less than the consumption in Japan, Europe, the United States and other countries. This shows that there is still a large room for development of steel pipes in my country. According to an annual update of 15%, 1.5 million tons of steel pipes need to be added each year, and the total annual consumption is about 3 million tons. The present invention relates to a production method for high-strength structural seamless steel pipes of grade Q620D that meet the standard GB / T 8162-2018.

[0005] The sources of residual stress cover all industrial fields and nature, and they are generated, accompanied and affected by the entire manufacturing process and service life cycle of materials and equipment. At this stage, China has put forward new requirements for high-quality development. In the fields of materials and equipment, residual stress is one of the important factors of failure and is closely related to it. According to data, the cost increase caused by residual stress distortion in Europe accounts for more than 4% of the total manufacturing cost; in the bearing industry alone, the additional cost caused by residual stress distortion is estimated to exceed US$1 billion per year. According to a survey by the Federation of German Industries (VDMA), the additional manufacturing cost for eliminating residual stress distortion in the power transmission manufacturing field in Germany is as high as 850 million euros per year. Therefore, the American Society for Metals regards "striving to achieve zero deformation and maximum uniformity of heat-treated parts" as its main research and development goal. The present invention relates to a production method for a low residual stress seamless steel pipe.

[0006] Therefore, the development of seamless steel pipes with low residual stress, high strength and high toughness for structures has become a hot topic for steel pipe manufacturers. The present invention relates to a seamless steel pipe for steel structure and its production method, which not only improves the grade of seamless pipe products and optimizes the product structure, but also brings greater economic and social benefits to enterprises. Summary of the invention

[0007] The purpose of the present invention is to provide a method for manufacturing a rare earth microalloyed low residual stress Q620D high-strength seamless steel pipe for structure, wherein strengthening elements such as vanadium, niobium and titanium are added to low carbon steel, and the high-strength seamless steel pipe for structure is produced through steelmaking, pipe rolling, heat treatment and other processes to meet the following requirements: tensile strength (Rm) target value 710-880MPa, measured value 845MPa, 869MPa; yield strength (R p0.2 ) The target value is greater than 620MPa, the measured values ​​are 822MPa and 807MPa, and the elongation (A) target value is greater than 15%; the V-shaped full-size longitudinal impact energy under -20℃ experimental environment is higher than 47J, and the measured value is 162J.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] The invention discloses a method for manufacturing a rare earth microalloyed low residual stress Q620D high-strength structural seamless steel pipe, wherein the chemical elements and their mass percentages of the seamless steel pipe are as follows: C≤0.18%; Si 0.20-0.35%; Mn 1.20-1.50%; P≤0.020%; S≤0.010%; Ti≤0.05%; Nb≤0.05%; V≤0.15%; Re≤0.002%; the rest are Fe and unavoidable impurities, with a total mass fraction of 100%;

[0010] The manufacturing method thereof comprises:

[0011] Steelmaking production process: molten iron pretreatment → converter smelting → LF refining → VD degassing → round billet continuous casting; incoming molten iron must be pretreated to ensure the quality of molten iron supplied to the converter; in order to suppress the gas content in the material, silicon manganese, ferromanganese and ferrovanadium must be deoxidized and alloyed before adding; converter endpoint control targets: C ≥ 0.06%, P ≤ 0.010%, steel tapping temperature 1610 ~ 1630 ℃; single slag process is used for smelting, and the final slag basicity is ≥ 3.0; slag must be blocked during steel tapping, and slag must be removed if slag blocking fails; in the LF refining process, slag desulfurization, composition adjustment and temperature increase operations are carried out according to the composition and temperature of the converter molten steel, and deoxidation operations are strengthened to make good white steel. Slag, white slag holding time ≥ 20min, and adjust the slag condition according to the situation to ensure white slag tapping; vanadium iron is added in the middle and late stages of refining, and the composition is fine-tuned in the late stage of refining, and rare earth alloys are added in proportion; VD deep vacuum target value ≤ 0.06KPa, deep vacuum time ≥ 13 minutes, after VD is completed, feed an appropriate amount of high calcium wire, and soft blow Ar for no less than 13 minutes after wire feeding to ensure a lower gas content in the material; electromagnetic stirring process is used in the continuous casting process, molten steel superheat ΔT ≤ 30℃, and the appropriate constant pulling speed is selected according to different round billet sections. The round billet should be placed in a slow cooling pit for slow cooling, the pit entry temperature is greater than 600℃, and the slow cooling time is not less than 48 hours;

[0012] Pipe rolling process: round billet → sawing → ring furnace heating → piercing → PQF continuous rolling → tension reducing → cooling; the temperature of the ring furnace insulation section is 1270±10℃, the temperature of the round billet after piercing is 1210±10℃; the continuous rolling inlet temperature is 1100±10℃; the temperature after tension reducing is 910±10℃;

[0013] Heat treatment process: adopt quenching and tempering treatment, that is, quenching + tempering; quenching at 930℃±10℃, keeping warm for 100 minutes, external showering + internal spraying during quenching, time ≥40 seconds; tempering at 590℃±10℃, keeping warm for 150 minutes.

[0014] Furthermore, the chemical elements and their mass percentages of the seamless steel pipe are as follows: C 0.15%; Si 0.28%; Mn 1.37%; P 0.015%; S 0.009%; Ti 0.028%; Nb 0.025%; V 0.14%; Re 0.0005%; the rest are Fe and unavoidable impurities, with a total mass fraction of 100%.

[0015] Furthermore, the chemical elements and their mass percentages of the seamless steel pipe are as follows: C 0.16%; Si 0.29%; Mn 1.46%; P 0.012%; S 0.007%; Ti 0.032%; Nb 0.023%; V 0.14%; Re 0.0005%; the rest are Fe and unavoidable impurities, with a total mass fraction of 100%.

[0016] Furthermore, the chemical elements and their mass percentages of the seamless steel pipe are as follows: C 0.17%; Si 0.29%; Mn 1.40%; P 0.014%; S 0.008%; Ti 0.037%; Nb 0.025%; V 0.13%; Re 0.0004%; the rest are Fe and unavoidable impurities, with a total mass fraction of 100%.

[0017] Furthermore, the chemical elements and their mass percentages of the seamless steel pipe are as follows: C 0.16%; Si 0.30%; Mn 1.49%; P 0.010%; S 0.006%; Ti 0.035%; Nb 0.022%; V 0.13%; Re 0.0005%; the rest are Fe and unavoidable impurities, with a total mass fraction of 100%.

[0018] Furthermore, the chemical elements and their mass percentages of the seamless steel pipe are as follows: C 0.16%; Si 0.30%; Mn 1.32%; P 0.013%; S 0.005%; Ti 0.031%; Nb 0.022%; V 0.13%; Re 0.0004%; the rest are Fe and unavoidable impurities, with a total mass fraction of 100%.

[0019] Furthermore, the residual stress of the seamless steel pipe is less than 88 MPa.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are:

[0021] The present invention enables the steel pipe to have higher strength, lower residual stress, excellent low-temperature impact toughness and high dimensional accuracy through reasonable component design and reasonable process optimization.

[0022] The prepared seamless steel pipe can be widely used in the construction of industrial plants and large-scale public infrastructure buildings, such as airport terminals, stadiums, exhibition venues, new high-speed rail stations, various types of steel bridges, industrial and civil buildings, etc. It has the characteristics of easy production, low cost and excellent performance. DETAILED DESCRIPTION

[0023] The present invention provides a method for manufacturing a rare earth microalloyed low residual stress Q620D high-strength structural seamless steel pipe. The steel pipe obtained by the present invention has a production specification of Φ219×12mm as an example, and its chemical composition is shown in Table 1:

[0024] Table 1 Statistical results of chemical composition of steel pipe of the present invention wt%

[0025] Examples C Si Mn P S Nb V Ti Re 1 0.15 0.28 1.37 0.015 0.009 0.025 0.14 0.028 0.0005 2 0.16 0.29 1.46 0.012 0.007 0.023 0.14 0.032 0.0005 3 0.17 0.29 1.40 0.014 0.008 0.025 0.13 0.037 0.0004 4 0.16 0.30 1.49 0.010 0.006 0.022 0.13 0.035 0.0005 5 0.16 0.30 1.32 0.013 0.005 0.022 0.13 0.031 0.0004

[0026] The chemical composition of the steel pipe fully meets the requirements of the present invention for steel grades. The P and S contents are relatively low, meeting the composition design requirements. Moreover, it can be seen from Table 1 that the deviation of the composition content of each furnace is very small. The stable composition content is conducive to temperature control during heat treatment, thus providing a prerequisite for the pipe to have good organization and performance.

[0027] Steelmaking process: In order to overcome the problem of micro cracks on the surface of round billets, especially for steels containing V alloy elements that are sensitive to cracks, a series of measures have been taken to produce steel pipes with specifications of Φ219×12mm, such as appropriate V content and proportion; stable casting speed during continuous casting to ensure that the temperature of the continuous casting billet in the straightening section is not less than 900℃; a weak and uniform secondary cooling system; selection of appropriate protective slag to improve the centering and arc accuracy of the casting machine; after the billet is off the line, the round billet enters the slow cooling pit for slow cooling, and the pit temperature is greater than 600℃ to eliminate the structural stress and thermal stress. Through the above measures, high-quality round billets are obtained.

[0028] The tube rolling process is: round billet → sawing → ring furnace heating → piercing → PQF continuous rolling → tension reduction (sizing) → cooling. The round billet is heated in a ring furnace with a furnace temperature of 1270°C. The heating temperature deviation of the tube billet is ±10°C. The time in the furnace should not be too long. The piercing adopts a low-speed bite and high-speed rolling process. The temperature after piercing is 1210°C, the temperature entering the continuous rolling mill is 1100°C, the temperature after sizing is 910°C, cooling, and sawing.

[0029] Heat treatment: quenching and tempering treatment is adopted. Combined with the actual situation of on-site equipment and the trial steel pipe specification of Φ219×12mm, the heat treatment process is designed as quenching + tempering. The heating section of the quenching furnace is 920℃, the insulation section is 930℃±10℃, and the insulation time is about 100 minutes. During quenching, external showering + internal spraying are used for a time of ≥40 seconds; the heating section of the tempering furnace is 590℃, the insulation section is 590℃±10℃, and the insulation time is 150 minutes.

[0030] The geometrical dimension control of the steel pipe of the present invention:

[0031] During perforation, the stability of pushing steel into the hole, perforation, holding the tube with rollers and throwing the steel is strictly controlled; in the austenite recrystallization zone, rough rolling is carried out. In order to fully refine the original austenite grains, the reduction is as large as possible. Under the condition that the equipment parameters allow, the total deformation in the rough rolling stage is increased; when deforming in the finishing stage in the non-recrystallization zone, the reduction in the first few passes of finishing rolling is appropriately increased to ensure the uniformity of the structure in the wall thickness direction of the steel pipe, and the tube shape is controlled in the last 3 or 4 passes; in order to ensure the outer surface quality of the steel pipe and prevent surface defects such as pitting, the high-pressure water dephosphorization pressure after continuous rolling, sizing and normalizing is required to be ≥6MPa. The measured out-of-roundness and wall thickness unevenness of the steel pipe do not exceed 80% of the outer diameter and wall thickness tolerances. The outer diameter (D) tolerance of the steel pipe is ±1%D, and the wall thickness (S) unevenness is ≤±10%S. The steel pipe of the present invention has good surface quality and high dimensional accuracy.

[0032] The mechanical properties of the steel pipe of the present invention are shown in Table 2. As can be seen from Table 2, the method of the present invention can well meet the requirements of high-strength steel pipes. The steel pipe with a specification of Φ219×12mm has high strength and excellent low-temperature impact toughness. The longitudinal impact at -20°C reaches 179J, which can well meet the requirements of Q620D steel grade in the national standard GB / T 8160-2018.

[0033] Table 2 Mechanical properties of the steel pipe of the present invention

[0034]

[0035] The residual stress of steel pipe examples 1 to 5 of the present invention is measured by the residual stress ring cutting opening displacement measurement method in the national standard GB / T 43898-2024, which is less than 88MPa, far lower than the recommended minimum limit of residual stress of 100MPa in the standard. It can be seen that the Q620D high-strength steel structure seamless pipe produced by the present invention is a low residual stress seamless steel pipe. Residual stress is an important technical factor that cannot be ignored in affecting the high-quality development of China's high-strength structural pipes. It is mainly reflected in the two aspects of safety and precision. Residual stress affects the dimensional stability of material components, and thus has an important impact on the service life of engineering components and the safety of the structure. At the same time, the influence of residual stress on premature failure forms such as dimensional stability and wear is generated and accompanied by the manufacturing of high-strength structural pipes, the processing of precision components, and the entire process and service life cycle. The influence of residual stress on material precision constitutes a technical obstacle to China's high-quality development at this stage. The Q620D high-strength steel structure seamless pipe produced by the present invention is a low residual stress seamless steel pipe, which can effectively promote the quality upgrade of industrial structural building materials.

[0036] The Q620D high-strength seamless steel pipe for steel structure with a specification of Φ219×12mm produced by the present invention has a reasonable selection of alloy elements and an appropriate ratio of element content, so that the steel has a lower carbon equivalent, is easy to produce, and has low cost. The reasonable smelting and continuous casting process, rolling process and heat treatment process make the steel pipe have lower residual stress, higher strength, excellent low-temperature impact toughness, and high dimensional accuracy. The product of the present invention can be widely used in the construction of industrial plants and large public infrastructure buildings, such as airport terminals, stadiums, exhibition venues, new high-speed rail stations, various types of steel bridges, and industrial and civil buildings, and has the characteristics of easy production, low cost, high strength and high toughness, low residual stress and other excellent performances.

[0037] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for manufacturing a rare earth microalloyed low residual stress Q620D high strength structural seamless steel pipe, characterized in that: The chemical elements and their mass percentages of the seamless steel pipe are as follows: C≤0.18%; Si0.20-0.35%; Mn 1.20-1.50%; P≤0.020%; S≤0.010%; Ti≤0.05%; Nb≤0.05%; V≤0.15%; Re≤0.002%; the rest is Fe and unavoidable impurities, with a total mass fraction of 100%; The manufacturing method thereof comprises: Steelmaking production process: molten iron pretreatment → converter smelting → LF refining → VD degassing → round billet continuous casting; incoming molten iron must be pretreated to ensure the quality of molten iron supplied to the converter; in order to suppress the gas content in the material, silicon manganese, ferromanganese and ferrovanadium must be deoxidized and alloyed before adding; converter endpoint control targets: C ≥ 0.06%, P ≤ 0.010%, steel tapping temperature 1610 ~ 1630 ℃; single slag process is used for smelting, and the final slag basicity is ≥ 3.0; slag must be blocked during steel tapping, and slag must be removed if slag blocking fails; in the LF refining process, slag desulfurization, composition adjustment and temperature increase operations are carried out according to the composition and temperature of the converter molten steel, and deoxidation operations are strengthened to make good white steel. Slag, white slag holding time ≥ 20min, and adjust the slag condition according to the situation to ensure white slag tapping; vanadium iron is added in the middle and late stages of refining, and the composition is fine-tuned in the late stage of refining, and rare earth alloys are added in proportion; VD deep vacuum target value ≤ 0.06KPa, deep vacuum time ≥ 13 minutes, after VD is completed, feed an appropriate amount of high calcium wire, and soft blow Ar for no less than 13 minutes after wire feeding to ensure a lower gas content in the material; electromagnetic stirring process is used in the continuous casting process, molten steel superheat ΔT ≤ 30℃, and the appropriate constant pulling speed is selected according to different round billet sections. The round billet should be placed in a slow cooling pit for slow cooling, the pit entry temperature is greater than 600℃, and the slow cooling time is not less than 48 hours; Pipe rolling process: round billet → sawing → ring furnace heating → piercing → PQF continuous rolling → tension reducing → cooling; the temperature of the ring furnace insulation section is 1270±10℃, the temperature of the round billet after piercing is 1210±10℃; the continuous rolling inlet temperature is 1100±10℃; the temperature after tension reducing is 910±10℃; Heat treatment process: adopt quenching and tempering treatment, that is, quenching + tempering; quenching at 930℃±10℃, keeping warm for 100 minutes, external showering + internal spraying during quenching, time ≥40 seconds; tempering at 590℃±10℃, keeping warm for 150 minutes.

2. The method for manufacturing the rare earth microalloyed low residual stress Q620D high strength structural seamless steel pipe according to claim 1, characterized in that: The chemical elements and their mass percentages of the seamless steel pipe are as follows: C 0.15%; Si 0.28%; Mn 1.37%; P 0.015%; S 0.009%; Ti 0.028%; Nb 0.025%; V 0.14%; Re 0.0005%; the rest are Fe and unavoidable impurities, with a total mass fraction of 100%.

3. The method for manufacturing the rare earth microalloyed low residual stress Q620D high strength structural seamless steel pipe according to claim 1, characterized in that: The chemical elements and their mass percentages of the seamless steel pipe are as follows: C 0.16%; Si 0.29%; Mn 1.46%; P 0.012%; S 0.007%; Ti 0.032%; Nb 0.023%; V 0.14%; Re 0.0005%; the rest are Fe and unavoidable impurities, with a total mass fraction of 100%.

4. The method for manufacturing the rare earth microalloyed low residual stress Q620D high strength structural seamless steel pipe according to claim 1, characterized in that: The chemical elements and their mass percentages of the seamless steel pipe are as follows: C 0.17%; Si 0.29%; Mn 1.40%; P 0.014%; S 0.008%; Ti 0.037%; Nb 0.025%; V 0.13%; Re 0.0004%; the rest are Fe and unavoidable impurities, with a total mass fraction of 100%.

5. The method for manufacturing the rare earth microalloyed low residual stress Q620D high strength structural seamless steel pipe according to claim 1, characterized in that: The chemical elements and their mass percentages of the seamless steel pipe are as follows: C 0.16%; Si 0.30%; Mn 1.49%; P 0.010%; S 0.006%; Ti 0.035%; Nb 0.022%; V 0.13%; Re 0.0005%; the rest are Fe and unavoidable impurities, with a total mass fraction of 100%.

6. The method for manufacturing the rare earth microalloyed low residual stress Q620D high strength structural seamless steel pipe according to claim 1, characterized in that: The chemical elements and their mass percentages of the seamless steel pipe are as follows: C 0.16%; Si 0.30%; Mn 1.32%; P 0.013%; S 0.005%; Ti 0.031%; Nb 0.022%; V 0.13%; Re 0.0004%; the rest are Fe and unavoidable impurities, with a total mass fraction of 100%.

7. The method for manufacturing the rare earth microalloyed low residual stress Q620D high strength structural seamless steel pipe according to claim 1, characterized in that: The residual stress of the seamless steel pipe is less than 88MPa.

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