CN113930685B - 700 MPa-grade high-plasticity-transformation precipitation strengthening pipeline steel plate and production method thereof - Google Patents

700 MPa-grade high-plasticity-transformation precipitation strengthening pipeline steel plate and production method thereof Download PDF

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CN113930685B
CN113930685B CN202111194034.5A CN202111194034A CN113930685B CN 113930685 B CN113930685 B CN 113930685B CN 202111194034 A CN202111194034 A CN 202111194034A CN 113930685 B CN113930685 B CN 113930685B
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steel plate
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CN113930685A (en
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张帅
任毅
王爽
高红
付成哲
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Angang Steel Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • C21D2211/00—Microstructure comprising significant phases
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
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Abstract

The invention provides a 700MPa grade high plastic precipitation strengthening pipeline steel plate and a production method thereof, wherein the steel plate comprises the following components in percentage by weight: c: 0.030% -0.055%, Si: 0.21-0.40%, Mn: 1.71-1.85%, P is less than or equal to 0.012%, S is less than or equal to 0.002%, Nb: 0.035-0.065%, Ti: 0.012% -0.025%, Mo: 0.08% -0.19%, V: 0.01% -0.04%, Ni: 0.08 to 0.18%, Cu: 0.08-0.19%, Ni/Cu not less than 0.7, Cr: < 0.20%, Al: 0.010-0.025 percent of N, 0.0010-0.0045 percent of N; the thickness of the steel plate produced by the method is more than or equal to 25.4mm, the transverse yield strength can reach 480-560 MPa, the transverse tensile strength reaches 710-770 MPa, the transverse yield ratio is not more than 0.73, the average value of transverse impact power at minus 60 ℃ is more than or equal to 300J, and the transverse DWTT shearing area at minus 15 ℃ is more than or equal to 85 percent; longitudinal flexionThe clothing strength can reach 470-540 MPa, the longitudinal tensile strength reaches 700-760 MPa, and the longitudinal uniform elongation rate U is realized EL ≥10％。

Description

700 MPa-grade high-plasticity-transformation precipitation strengthening pipeline steel plate and production method thereof
Technical Field
The invention belongs to the field of metal materials, and particularly relates to a 700 MPa-level pipeline steel plate with a thick wall with a thickness of more than or equal to 25.4mm, high uniform elongation, high stress ratio and good toughness and a production method thereof.
Background
Along with the increasing demand of oil and gas resources and the reduction of land oil and gas resources, the oil and gas exploitation is continuously developed to a complex and severe environment. For example, cold regions, geologically complex active regions, oceans and the like, wherein the cold regions have large day-night temperature difference, the geologically active regions have high crustal motion frequency, frequent ocean currents, high water pressure, uneven seabed and the like, which put higher technical requirements on the oil-gas production and transmission steel pipes serving in complex severe environments.
The pipeline steel plate for manufacturing the service steel pipe in the complex environment needs to meet the requirements of high strength, high toughness, high uniform elongation, high stress ratio, low aging sensitivity and other high plastic deformation performances in the transverse direction and the longitudinal direction; in addition, in order to improve the output pressure and the safety or meet the requirement of deepwater service, the steel plate is required to have larger thickness; however, the increase of the thickness causes various problems of the increase of the temperature gradient of the thickness section, the reduction of the microstructure and the performance uniformity in the thickness direction, the excitation of the strength-toughness contradiction, the remarkable increase of the difficulty of controlling the crack arrest toughness and the like during the production of the steel plate. The complex and various technical index requirements obviously increase the design and manufacturing difficulty of the high plastic deformation pipeline steel plate.
At present, some researches are carried out on high-plasticity pipeline steel plates at home and abroad, and partial patents and documents are found through retrieval, but the contents recorded in the researches are obviously different from the aspects of components, production methods, properties, product categories and the like in the technical scheme of the invention.
Patent document NbC nano-particle reinforced X80 plastic tube steel plate and manufacturing method thereof (publication number: CN109023069A) provides an X80 grade plastic tube steel plate and production method thereof, the content of noble alloy Nb (0.07-0.15%) in the components is high, and the economy is not enough; in the aspect of the production method, after the steel plate is subjected to controlled rolling and controlled cooling, a high-temperature solid solution and medium-temperature isothermal process is required to achieve the NbC strengthening effect, the process is complex, the energy consumption and the cost are high, and the manufacturing period is long.
Patent document "an X80M deep sea strain-resistant pipeline steel plate and rolling process" (publication number: CN109234623B) provides an X80 grade deep sea pipeline steel plate, which adopts a design scheme of high Ni (0.65% -0.85%) and high Mo (0.31% -0.36%) in the components, and the alloy content and cost are too high.
Patent document "a steel plate for submarine pipeline with low yield ratio X80MO and manufacturing method thereof" (publication No. CN110331343A), provides an X80 grade steel plate for submarine pipeline and production method thereof, which is high in cost because more elements such as Ni and Nb are added into the components; the microstructure is difficult to control by adopting high-temperature rolling (more than or equal to 910 ℃); the cooling speed after rolling is required to be 25-35 ℃/s, and the process is difficult to realize for thick steel plates.
Patent document KR2119975B1 discloses an X80 grade pipeline steel plate with good toughness, which contains more elements such as Nb (0.08-0.12%), Ni (0.20-0.35%), Mo (0.20-0.40%) and the like, and has high cost.
The document "development of X70-grade large-wall-thickness steel plate for subsea pipelines" (medium plate, "volume 22, 2 nd, zhangshijun, zhanghaijun) discloses a steel plate for X70 subsea pipelines with a thickness of 30.8mm, and does not disclose the contents of Nb, Ti, Mo, and Ni elements in the components; the deformation temperature of a non-recrystallization zone is high (more than or equal to 800 ℃), the final cooling temperature is high (more than or equal to 540 ℃), the yield ratio of the steel plate is high, and the plasticity is insufficient.
In summary, the prior art has not been sufficiently studied on the fine precipitation-strengthened high plastic deformation line steel plate.
Disclosure of Invention
The invention aims to overcome the problems and the defects and provide a 700MPa grade high-plasticity modified pipeline steel plate which is applicable to the pipeline steel plate thick wall used in the complex service environment, has high strength, high toughness, high uniform deformation rate, low yield ratio, high stress ratio and low aging sensitivity, has the thickness of more than or equal to 25.4mm and is based on fine precipitation strengthening, and a production method thereof.
The purpose of the invention is realized as follows:
the thickness of the fine precipitation-strengthened 700MPa grade high-plasticity change pipeline steel plate is more than or equal to 25.4 mm; in the component design, C, Mn, Si, Mo, Ni and Cu are used as basic strengthening elements, and fine carbonitride precipitation is formed by Nb, Ti and V, so that the strengthening and fine grain effects are exerted, and the aging sensitivity is reduced; at the same time, the influence on the toughness is reduced.
A700 MPa-grade high-plasticity precipitation strengthening pipeline steel plate comprises the following components in percentage by weight: c: 0.030% -0.055%, Si: 0.21-0.40%, Mn: 1.71-1.85%, P is less than or equal to 0.012%, S is less than or equal to 0.002%, Nb: 0.035-0.065%, Ti: 0.012% -0.025%, Mo: 0.08-0.19%, V: 0.01% -0.04%, Ni: 0.08-0.18%, Cu: 0.08-0.19%, Ni/Cu not less than 0.7, Cr: < 0.20%, Al: 0.010% -0.025%, N0.0010% -0.0045%, and CE Pcm Controlling the content of the iron and the inevitable impurities to be 0.155-0.180 percent, and the balance of the iron and the inevitable impurities; wherein, CE Pcm ＝C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B。
The microstructure of the pipeline steel plate is bainite, polygonal ferrite and a small amount of M/A, the volume percentage of the polygonal ferrite is 30-70%, and the bainite comprises granular bainite and lath bainite; the average grain size of the steel plate is less than 10 mu m in diameter; the steel plate contains 0.04-0.09% by mass of precipitated carbonitrides, wherein the amount of the precipitated carbonitrides with the particle size of less than 10nm in the total precipitated carbonitrides is not less than 40%.
The volume percentage of the lath bainite is 51% -90%.
The transverse yield strength of the steel plate can reach 480-560 MPa, the transverse tensile strength reaches 710-770 MPa, the transverse yield ratio is not more than 0.73, the average value of transverse impact power at-60 ℃ is not less than 300J, and the shearing area of transverse DWTT at-15 ℃ is not less than 85%; the longitudinal yield strength can reach 470-540 MPa, the longitudinal tensile strength can reach 700-760 MPa, and the longitudinal uniform elongation rate U is EL More than or equal to 10 percent, the longitudinal yield ratio is not more than 0.72, the longitudinal stress ratio Rt1.5/Rt0.5 is more than or equal to 1.13, and Rt2.0/Rt1.0 is more than or equal to 1.06.
The invention has the following design reasons:
c mainly plays a role in two existing modes of alloy carbide precipitation and interstitial solid solution; the invention emphasizes the utilization of the characteristic that C forms a precipitated phase below 10nm with Nb during medium-temperature deformation of the steel plate and waiting for temperature, thereby promoting the formation of fine precipitates, increasing nucleation positions and refining microstructures; meanwhile, the C in a solid solution form can increase the strength and hardness of a hard phase in a multi-phase structure, so that the difference of the mechanical properties of the hard phase and the soft phase is increased, and the reduction of the yield ratio and the improvement of the stress ratio are facilitated; however, the increase in carbon is disadvantageous to plasticity and toughness, and the contradiction between toughness and toughness is more prominent for thick-walled high-strength pipeline steel plates, so the upper limit of C needs to be strictly controlled, and the invention considers that C is preferably controlled to be 0.030% -0.055%.
Si can improve the strength, but the content of Si is too high, so that the M/A in a microstructure is increased, the toughness and the plasticity are reduced, and the proper range is 0.21-0.40%.
Mn can effectively improve the strength and the stability and hardenability of austenite, so that the microstructure is more refined and homogenized; however, too high manganese content tends to induce segregation and promote the formation of inclusions, and the present invention is suitable for controlling the Mn content to 1.71-1.85%.
P, S are harmful impurity elements in the present invention; p can cause toughness reduction, and the invention controls P to be less than or equal to 0.012%; the increase of S content can promote the generation and growth of inclusions, destroy the continuity of a matrix and cause the performance reduction, so that S is less than or equal to 0.002 percent.
The invention mainly utilizes the function that Nb can form tiny Nb (CN) precipitation below 10nm under a proper process, plays a role of fine grains and improves the strength, and simultaneously, the toughness can not be reduced because the size of a precipitated phase is small; further, precipitation of fine nb (cn) can reduce the mass fraction of solid solution C, N, thereby suppressing the formation of m (cn) during aging and reducing aging sensitivity. In addition, Nb can also inhibit austenite grains from growing large, refine microstructure and reduce rolling deformation limit; however, too high content of niobium may cause decrease in post-weld toughness and increase in cost, and it is considered that the present invention is suitable to control the content of Nb to 0.035% to 0.065%.
Ti can exert the effects of fixing N and C, form Ti (CN) precipitation phase with higher solid solution temperature, inhibit the growth of austenite grains under the high-temperature condition, reduce the solid solution C, N content and reduce the aging sensitivity; meanwhile, Ti can also refine welding structures and improve the toughness of a heat affected zone after welding, and the invention considers that the Ti content is controlled to be more suitable to be 0.012-0.025 percent.
Mo can improve hardenability, promote medium and low temperature tissue transformation and has a certain fine grain effect; however, too high molybdenum content can inhibit ferrite transformation, which is not beneficial to control of multiphase structure and plastic deformation performance, and too high molybdenum content can cause age hardening and reduce the plastic deformation performance after aging; meanwhile, the price of Mo is high, and the cost is obviously increased by adding a large amount of Mo, so that the content of Mo is controlled to be 0.08-0.19 percent.
V has solid solution and precipitation effects, has a strong bonding tendency with C, N, can be bonded with C, N during rolling and cooling to form fine precipitation, and also has the effect of reducing aging sensitivity; moreover, compared with Nb and Ti, the precipitation temperature of V is relatively low, which is beneficial to refining precipitated phases; however, the steel plate and the post-welding toughness are affected by the excessively high V content, so that the V content is 0.01-0.04 percent.
Ni and Cu: ni can improve the strength, reduce the critical cooling speed, delay the transformation of pearlite, facilitate the control of microstructure and the refinement of crystal grains and improve the low-temperature toughness; but the price of Ni is higher, so that too much Ni is not suitable to be added; therefore, the Ni content of the invention is controlled to be 0.08-0.18%. Cu can improve the strength and make up for the strength loss caused by the reduction of carbon content; the stability of austenite can be improved, the cooling effect of the thick-wall steel plate is improved, but the toughness is unfavorable due to the excessively high Cu content, the steel plate is easy to embrittle, the Cu content is controlled to be 0.08-0.19%, and meanwhile, the Ni/Cu ratio is more than or equal to 0.7, so that the influence of Cu on the toughness can be inhibited.
Cr has strengthening function, hardenability, austenite phase transition temperature reduction, and is beneficial to improving the uniformity of microstructure in the thickness direction, and the Cr is cheap and can replace precious alloy elements to reduce the cost; however, since the Cr content is too high to increase the weld crack sensitivity, the Cr content is controlled to 0.20% or less.
Al is a deoxidizing element and has a certain N fixing function, the increase of Al-containing inclusions is promoted by excessively high content, and the welding performance is not favorable, so that the invention considers that the content of the aluminum is preferably controlled to be 0.010-0.025 percent.
N can form fine precipitates with Nb, Ti and V to play a role of strengthening and fine grains and improve the toughness, but the toughness is deteriorated due to the excessively high content, and the content is preferably controlled to be 0.0010-0.0045%.
CE of the invention Pcm The control is 0.155-0.180%, the steel plate toughness requirement can be met, the welding cracking tendency can be reduced, and the steel plate has good weldability.
The second technical scheme of the invention is to provide a production method of a 700MPa grade high plastic deformation precipitation strengthening pipeline steel plate, which comprises smelting, refining, continuous casting, heating, rolling and cooling;
(1) smelting:
when tapping is carried out by the converter, the tapping temperature is less than or equal to 1640 ℃, the C is less than or equal to 0.035%, slag is removed and tapped, and lime and fluorite are added according to the proportion of 4/1-5/1 in the tapping process to make top slag; the RH vacuum treatment time in the refining process is more than or equal to 10 min; the casting superheat degree of the continuous casting billet is 10-30 ℃, and the casting speed of the continuous casting billet is 0.8-1.2 m/min. The carbon content of the final product can be effectively controlled by low-carbon, low-temperature and slag-stopping tapping of the converter, the dephosphorization effect is ensured, and rephosphorization and resulfurization are reduced; top slag making and vacuum refining can effectively remove non-metallic harmful elements; the control of the casting superheat degree and the continuous casting billet pulling speed can effectively reduce the quality defect of the casting billet.
(2) Heating:
the continuous casting billet is heated by adopting a preheating section, a heating section I, a heating section II and a soaking section in multiple stages, wherein the temperature of the soaking section is 1170-1200 ℃, and the time of the soaking section is 0.4-0.8 min/mm. The multi-stage heating of the continuous casting billet is beneficial to improving the heating efficiency and uniformity; the heating temperature is designed according to the contents of elements such as niobium, carbon and the like, so that the solid solution requirement of the alloy is met, and the austenite grains are prevented from growing excessively; the time control of the soaking section can ensure the integral temperature uniformity of the continuous casting billet.
(3) Rolling:
the rough rolling comprises two stages, wherein the finish rolling temperature of the first stage is more than or equal to 1100 ℃, then the second stage rough rolling is carried out after the first stage rough rolling is carried out at the cooling speed of more than or equal to 2 ℃/s and the second stage rough rolling is carried out, the finish rolling temperature of the second stage is 980-1040 ℃, the deformation rate of each pass of the second stage rough rolling is more than or equal to 16%, and the rough rolling is carried out at the rolling speed of 1.0-2.0 m/s by spray cooling. The rough rolling adopts a high-temperature and low-temperature two-stage rolling and rapid cooling process, which is favorable for promoting austenite refining and increasing the temperature gradient of the section of the casting blank, and can promote the penetration of rolling deformation to the thickness center of the casting blank by matching with a lower rolling speed, refine the structure near the thickness center and improve the thickness section structure and performance uniformity.
The thickness of the intermediate temperature-waiting blank is 3.2 t-4.5 t, wherein t is the thickness of a finished steel plate, the rolling start temperature of finish rolling is 790-830 ℃, and the rolling finish temperature of finish rolling is 710-750 ℃. The thickness of the intermediate blank to be heated can meet the requirement of the accumulation of austenite deformation and deformation energy in a non-recrystallization region; the low-temperature finish rolling process combined with austenite phase transformation control can promote the induced precipitation of fine precipitated phases, increase nucleation positions, form a small amount of deformed ferrite and be beneficial to the improvement of plastic deformation and toughness.
(4) And (3) cooling:
air cooling the rolled steel plate for 40-90 s, and then performing accelerated water cooling, wherein the starting water cooling temperature is 680-720 ℃, the final cooling temperature is 80-200 ℃, the water cooling time is 15-45 s, and the water cooling speed is 12-25 ℃/s; subsequently, straightening and air cooling are performed. Air cooling for a short time after the steel plate is rolled is matched with low-temperature finish rolling, and then the control of the water cooling starting temperature is favorable for the precipitation of fine particles and the further formation of soft-phase polygonal ferrite; the final cooling temperature promotes the formation of hard phase bainite and small amounts of M/A and ensures sufficient hardness differential between the soft and hard phases, thereby increasing tensile strength and stress ratio.
The final microstructure of the steel plate is bainite, polygonal ferrite and a small amount of M/A, and the volume percentage of the polygonal ferrite is 30-70%; the bainite comprises granular bainite and lath bainite, wherein the volume percentage of the lath bainite is 51-90%. The average grain size of the steel plate is less than 10 mu m in diameter; the steel plate contains 0.04-0.09% of precipitated carbonitrides, wherein the number percentage of fine precipitates below 10nm in all precipitated carbonitrides is more than or equal to 40%.
The steel plate has the comprehensive technical characteristics of thick wall, high strength, high toughness, high uniform deformation rate, low yield ratio, high stress ratio, low aging sensitivity and the like, and meets the requirements of manufacturing longitudinal submerged arc welded pipes for oil and gas mining and transmission in cold areas, geological complex active areas, underwater complex environments and the like.
The invention has the beneficial effects that:
(1) the components of the invention take C, Mn, Si, Mo, Ni and Cu as basic strengthening elements, fully utilize Nb, Ti and V to form fine carbonitride precipitation, play the roles of strengthening and fine grain, reduce the aging sensitivity and simultaneously reduce the influence on the toughness; the matching problem of technical indexes such as large wall thickness, high toughness, high plastic deformation and the like of the pipeline steel plate for the complex service environment is solved by matching with a unique production process.
(2) The component design and the production method of the invention are adopted to obtain an ideal microstructure of bainite, polygonal ferrite and a small amount of M/A, thereby realizing the effective control of the grain size, simultaneously obtaining a large amount of dispersed and distributed fine precipitates and playing an important role in improving the performance of the steel plate.
(3) The thickness of the fine precipitation-strengthened 700MPa grade high-plasticity pipeline steel plate is more than or equal to 25.4mm, the transverse yield strength can reach 480-560 MPa, the transverse tensile strength reaches 710-770 MPa, the transverse yield ratio is not more than 0.73, the transverse impact work mean value at minus 60 ℃ is more than or equal to 300J, and the transverse DWTT shearing area at minus 15 ℃ is more than or equal to 85%; the longitudinal yield strength can reach 470-540 MPa, the longitudinal tensile strength can reach 700-760 MPa, and the longitudinal uniform elongation rate U is EL More than or equal to 10 percent, the longitudinal yield ratio is not more than 0.72, the longitudinal stress ratio Rt1.5/Rt0.5 is more than or equal to 1.13, and Rt2.0/Rt1.0 is more than or equal to 1.06.
Drawings
FIG. 1 is a microstructure diagram of example 1 of a pipeline steel according to the present invention.
FIG. 2 is a fine resolution of the steel for a line pipe of example 1 of the present invention.
Detailed Description
The present invention is further illustrated by the following examples.
According to the embodiment of the invention, smelting, continuous casting, heating, rolling and cooling are carried out according to the component proportion of the technical scheme.
Smelting: when tapping is carried out by the converter, the tapping temperature is less than or equal to 1640 ℃, the C is less than or equal to 0.035%, slag is removed and tapped, and lime and fluorite are added according to the proportion of 4/1-5/1 in the tapping process to make top slag; the RH vacuum treatment time in the refining process is more than or equal to 10 min;
continuous casting: the casting superheat degree of the continuous casting billet is 10-30 ℃, and the casting speed of the continuous casting billet is 0.8-1.2 m/min;
heating: the continuous casting billet is heated by adopting a preheating section, a heating section I, a heating section II and a soaking section in multiple stages, wherein the temperature of the soaking section is 1170-1200 ℃, and the time of the soaking section is 0.4-0.8 min/mm;
rolling: the rough rolling comprises two stages, wherein the finish rolling temperature of the first stage is more than or equal to 1100 ℃, then the second stage rough rolling is carried out after the first stage rough rolling is carried out by cooling to 1000-1050 ℃ at a cooling speed of more than or equal to 2 ℃/s, the finish rolling temperature of the second stage is 980-1040 ℃, the deformation rate of each pass of the second stage rough rolling is more than or equal to 16%, and the rough rolling is carried out by spray cooling at the rolling speed of 1.0-2.0 m/s;
the thickness of the intermediate temperature-waiting blank is 3.2 t-4.5 t, wherein t is the thickness of a finished steel plate, the rolling start temperature of finish rolling is 790-830 ℃, and the rolling finishing temperature of finish rolling is 710-750 ℃;
and (3) cooling: air cooling the rolled steel plate for 40-90 s, and then performing accelerated water cooling, wherein the starting water cooling temperature is 680-720 ℃, the final cooling temperature is 80-200 ℃, the water cooling time is 15-45 s, and the water cooling speed is 12-25 ℃/s; subsequently, straightening and air cooling are performed.
The compositions of the steels of the examples of the invention are shown in table 1. The main process parameters of the steel smelting and continuous casting of the embodiment of the invention are shown in Table 2. The main process parameters of rough rolling of the steel of the embodiment of the invention are shown in Table 3. The main process parameters of the steel finish rolling and cooling of the embodiment of the invention are shown in Table 4. The mechanical properties of the steels of the examples of the invention are shown in Table 5. The low temperature toughness of the steels of the examples of the invention are shown in Table 6. The microstructure of the steel of the inventive examples is shown in Table 7.
TABLE 1 composition (wt%) of steels of examples of the present invention
Examples C Si Mn P S Nb Ti Mo
1 0.043 0.27 1.79 0.009 0.0014 0.058 0.015 0.13
2 0.051 0.31 1.81 0.011 0.0018 0.048 0.022 0.09
3 0.036 0.21 1.82 0.008 0.0010 0.051 0.013 0.16
4 0.049 0.36 1.77 0.009 0.0015 0.039 0.018 0.08
5 0.038 0.26 1.84 0.005 0.0011 0.046 0.016 0.10
6 0.035 0.25 1.79 0.010 0.0016 0.048 0.021 0.16
7 0.039 0.33 1.83 0.007 0.0011 0.055 0.020 0.18
8 0.045 0.28 1.76 0.008 0.0015 0.062 0.016 0.09
Examples V Ni Cu Ni/Cu Cr Al N CEP cm
1 0.02 0.11 0.09 1.22 0.08 0.020 0.0038 0.163
2 0.01 0.08 0.11 0.73 0 0.017 0.0027 0.166
3 0.02 0.16 0.15 1.07 0 0.024 0.0022 0.157
4 0.02 0.14 0.08 1.75 0.13 0.020 0.0041 0.170
5 0.03 0.09 0.12 0.75 0 0.016 0.0039 0.156
6 0.03 0.18 0.16 1.13 0.09 0.023 0.0026 0.162
7 0.02 0.09 0.09 1.00 0.12 0.018 0.0030 0.168
8 0.03 0.16 0.07 2.29 0.14 0.024 0.0025 0.165
TABLE 2 Main Process parameters for smelting and continuous casting of steel in the examples of the present invention
Figure BDA0003302343550000091
TABLE 3 roughing Main Process parameters of Steel of the examples of the present invention
Figure BDA0003302343550000092
TABLE 4 Main Process parameters for finish-rolling and Cooling of steels according to examples of the invention
Figure BDA0003302343550000101
Remarking: t is the thickness of the finished steel plate
TABLE 5 mechanical Properties of steels of examples of the invention
Figure BDA0003302343550000102
Note: the tensile sample is a full-thickness rectangular sample, and the plate width of a parallel test section is 38.1 mm.
TABLE 6 Low temperature toughness of steels of examples of the invention
Examples Thickness of plate/mm Transverse KV -60℃ /J Transverse DWTT SA-15℃ /％
1 26.4 366 92
2 26.4 347 90
3 26.4 410 93
4 30.8 351 90
5 30.8 372 87
6 33 320 86
7 33 381 90
8 33 338 87
Note: impact specimen size 10 x 55 mm; the DWTT specimens were full thickness specimens.
TABLE 7 microstructure of inventive example steels
Figure BDA0003302343550000111
According to the invention, the thickness of the high plastic deformation pipeline steel plate is more than or equal to 25.4mm, the transverse yield strength can reach 480-560 MPa, the transverse tensile strength reaches 710-770 MPa, the transverse yield ratio is not more than 0.73, the transverse impact power mean value at minus 60 ℃ is more than or equal to 300J, and the transverse DWTT shearing area at minus 15 ℃ is more than or equal to 85%; the longitudinal yield strength can reach 470-540 MPa, the longitudinal tensile strength can reach 700-760 MPa, and the longitudinal uniform elongation rate U is EL More than or equal to 10 percent, the longitudinal yield ratio is not more than 0.72, the longitudinal stress ratio Rt1.5/Rt0.5 is more than or equal to 1.13, and Rt2.0/Rt1.0 is more than or equal to 1.06.
In order to express the present invention, the above embodiments are properly and fully described by way of examples, and the above embodiments are only used for illustrating the present invention and not for limiting the present invention, and those skilled in the relevant art can make various changes and modifications without departing from the spirit and scope of the present invention, and any modifications, equivalent substitutions, improvements, etc. made by the persons skilled in the relevant art should be included in the protection scope of the present invention, and the protection scope of the present invention should be defined by the claims.

Claims (6)

1. The 700 MPa-grade high-plasticity precipitation strengthening pipeline steel plate is characterized by comprising the following components in percentage by weight: c: 0.030% -0.055%, Si: 0.21% -0.40%, Mn: 1.76-1.85 percent of N, less than or equal to 0.012 percent of P, less than or equal to 0.002 percent of S, and Nb: 0.035% -0.065%, Ti: 0.012% -0.025%, Mo: 0.08% -0.19%, V: 0.01% -0.04%, Ni: 0.08% -0.18%, Cu: 0.08-0.19%, Ni/Cu not less than 0.7%, Cr: < 0.20%, Al: 0.010-0.025%, N0.0010-0.0045%, and CE Pcm Controlling the content of the iron to be 0.155-0.180 percent, and the balance of iron and inevitable impurities; wherein, CE Pcm = C + Si/30+ (Mn + Cu + Cr)/20+ Ni/60+ Mo/15+ V/10+ 5B; the production method of the 700MPa grade high plastic deformation precipitation strengthening pipeline steel plate comprises smelting, refining, continuous casting, heating, rolling and cooling;
(1) heating:
the continuous casting billet is heated by adopting a preheating section, a heating section I, a heating section II and a soaking section in multiple stages, wherein the temperature of the soaking section is 1170-1200 ℃, and the time of the soaking section is 0.4-0.8 min/mm;
(3) rolling:
the rough rolling comprises two stages, wherein the finish rolling temperature of the first stage is more than or equal to 1100 ℃, then the second stage rough rolling is carried out after the first stage rough rolling is carried out by cooling to 1000-1050 ℃ at a cooling speed of more than or equal to 2 ℃/s, the finish rolling temperature of the second stage is 980-1040 ℃, the deformation rate of each pass of the second stage rough rolling is more than or equal to 16%, and spray cooling is carried out during rolling, and the rolling speed is 1.0-2.0 m/s;
the thickness of the intermediate temperature-waiting blank is 3.2 t-4.5 t, wherein t is the thickness of a finished steel plate, the rolling start temperature of finish rolling is 790-830 ℃, and the rolling finish temperature of finish rolling is 710-740 ℃;
(4) and (3) cooling:
air cooling the rolled steel plate for 40-90 s, and then performing accelerated water cooling, wherein the starting water cooling temperature is 680-720 ℃, the final cooling temperature is 80-182 ℃, the water cooling time is 15-45 s, and the water cooling speed is 12-25 ℃/s; subsequently, straightening and air cooling are performed.
2. The 700MPa grade high-plasticity precipitation strengthening pipeline steel plate is characterized by comprising bainite, polygonal ferrite and a small amount of M/A, wherein the microstructure of the steel plate comprises granular bainite and lath bainite, and the volume percentage of the polygonal ferrite is 40-70%; the average grain size of the steel plate is less than 10 mu m in diameter; the steel plate contains 0.04-0.09% by mass of precipitated carbonitrides, wherein the number percentage of fine precipitates below 10nm in all precipitated carbonitrides is more than or equal to 40%.
3. The 700MPa grade high-plasticity precipitation strengthening pipeline steel plate as claimed in claim 2, wherein the volume percentage of lath bainite is 51% -90%.
4. The 700 MPa-grade high-plasticity precipitation strengthening pipeline steel plate as claimed in claim 1, wherein the transverse yield strength of the steel plate is 480-560 MPa, the transverse tensile strength is 710-770 MPa, and the transverse yield ratio is not more than 0.73; longitudinal yield strength of 470-540 MPa, longitudinal tensile strength of 700-760 MPa, and longitudinal uniform elongation rate U EL More than or equal to 10 percent, the longitudinal yield ratio is not more than 0.72, the longitudinal stress ratio Rt1.5/Rt0.5 is more than or equal to 1.13, and Rt2.0/Rt1.0 is more than or equal to 1.06; the average value of the horizontal impact energy at minus 60 ℃ is more than or equal to 300J, and the horizontal DWTT shearing area at minus 15 ℃ is more than or equal to 85 percent.
5. The 700MPa grade high yield precipitation strengthening pipeline steel plate according to claim 1, is characterized by being prepared by smelting: when tapping is carried out by the converter, the tapping temperature is less than or equal to 1640 ℃, the C is less than or equal to 0.035%, slag is removed and tapped, and lime and fluorite are added according to the proportion of 4/1-5/1 in the tapping process to make top slag; the RH vacuum treatment time in the refining process is more than or equal to 10 min.
6. The 700MPa grade high-plasticity precipitation strengthening pipeline steel plate as claimed in claim 1, is characterized in that the superheat degree of continuous casting is 10-30 ℃, and the casting speed of the continuous casting is 0.8-1.2 m/min.
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