CN113930684B - Economical aging-resistant high-strain precipitation-strengthened pipeline steel and production method thereof - Google Patents

Abstract

The invention provides economic aging-resistant high-strain precipitation-strengthened pipeline steel and a production method thereof, wherein the steel comprises the following components in percentage by weight: c: 0.045% -0.070%, Si: 0.26-0.45%, Mn: 1.65-1.85%, P is less than or equal to 0.012%, S is less than or equal to 0.002%, Nb: 0.035 to 0.075%, Ti: 0.012% -0.025%, V: 0.01% -0.04%, Ni: 0.12-0.22%, Cu: 0.15-0.29%, Ni/Cu not less than 0.7%, Cr: < 0.30%, Al: 0.010% -0.025% of steel, 0.0010% -0.0045% of N, and CE _Pcm Is controlled to be 0.165 to 0.190 percent, wherein, CE _Pcm C + Si/30+ (Mn + Cu + Cr)/20+ Ni/60+ Mo/15+ V/10+5B, with the balance being iron and unavoidable impurities. After the steel plate is subjected to heat preservation for 1 hour at 250 ℃, the longitudinal yield strength can reach 450-550 MPa, the longitudinal tensile strength reaches 650-730 MPa, and the longitudinal uniform elongation rate U _EL More than or equal to 9 percent, the longitudinal yield ratio is not more than 0.75, and the longitudinal strain hardening index n is more than or equal to 0.10.

Description

Economical aging-resistant high-strain precipitation-strengthened pipeline steel and production method thereof

technical field

The invention belongs to the field of metal materials, and in particular relates to an economical, aging-resistant, high-strain, precipitation-strengthened pipeline steel and a production method thereof.

Background technique

With the increasing demand for oil and gas resources and the reduction of land oil and gas resources, natural oil exploitation is developing into a complex and harsh environment. For example, cold areas, geologically complex and active areas, and oceans, among which the large temperature difference between day and night in cold areas, the high frequency of crustal movement in geologically active areas, frequent ocean currents in the marine environment, high water pressure, and uneven seafloor unevenness affect oil and gas serving in complex and harsh environments. The use of steel pipes for transportation puts forward higher technical requirements.

Pipeline steel plates used to make steel pipes serving in complex environments need to meet high strain properties such as high strength and toughness in both transverse and longitudinal directions, as well as high uniform elongation, low yield ratio, high strain hardening rate, and low aging sensitivity; moreover, In order to improve the delivery pressure and safety or meet the needs of deep water service, the steel plate is required to have a larger thickness; however, the increase in thickness will lead to an increase in the temperature gradient of the thickness section during the production of the steel plate, a decrease in the uniformity of microstructure and properties in the thickness direction, and strength-toughness. There are many problems such as the intensification of contradictions and the significant increase in the difficulty of crack arrest toughness control. The complex and diverse technical index requirements have significantly increased the difficulty of designing and manufacturing high-plasticity pipeline steel sheets. At the same time, reducing costs and improving economy is also one of the important development directions of the design and research of such products.

At present, there are some studies on high-strain pipeline steel sheets at home and abroad, and some patents and literatures have been found through search, but the contents recorded there are obviously different from those described in the technical solution of the present invention in terms of composition, production method, performance, product category, etc.

The patent document "NbC Nanoparticle Strengthened Steel Plate for X80 Plastic Pipe and Its Manufacturing Method" (Publication No.: CN109023069A) discloses a steel plate for X80 plastic pipe and its production method. The content of precious alloy Nb (0.07%~0.15%) in the composition is high , the economy is insufficient; in terms of production methods, high temperature solid solution + medium temperature isothermal process needs to be used to achieve the NbC strengthening effect after the steel plate is completed with controlled rolling and cooling. The process is complicated, the energy consumption and cost are high, and the manufacturing cycle is long.

The deep-sea pipeline steel plate disclosed in the patent document "X80M deep-sea strain-resistant pipeline steel plate and rolling process" (publication number: CN109234623B) adopts high Ni (0.65%~0.85%) and high Mo (0.31%~0.36%) in the composition. The design scheme, alloy content and cost are too high.

The seawater corrosion-resistant steel sheet disclosed in the patent document "Seawater-resistant corrosion-resistant steel sheet with high crack arrest and anti-strain aging embrittlement properties and its manufacturing method" (Publication No.: CN109423572B) adopts high Ni (0.60%~1.00%) in its composition. , High Cu (0.90%~1.20%) design, at the same time, after the controlled rolling and cooling of the steel plate, the over-aging tempering treatment is used to promote the precipitation of ε-Cu; the alloy addition amount is high and the process is many.

The patent document "Pipeline Steel with Excellent Low-Temperature Toughness and Low Yield Ratio" (publication number: KR2119975B1) discloses a pipeline steel plate and a production method, in which a large amount of Nb (0.08%~0.12%), Mo ( 0.20%~0.40%) and other elements, the cost is high.

Document: "Research and Development of X70 Grade Large Thickness Subsea Pipeline Steel Plate" ("Medium Plate" Volume 22, Issue 2, Zhang Zhijun, Zhang Haijun) discloses X70 steel plate for submarine pipeline with a thickness of 30.8mm, and Nb and Ti are not disclosed in the composition , Mo, Ni element content; high deformation temperature (≥800℃) and final cooling temperature (≥540℃) in non-recrystallization zone, relatively high yield strength of steel plate, insufficient plasticity.

To sum up, the research on the economical age-resistant and high-strain pipeline steel strengthened by fine precipitation is still insufficient in the prior art.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the above problems and deficiencies and provide a thick-walled, high-strength, high-toughness, high-uniform elongation, low-yield-to-tensile ratio, high strain hardening rate, low aging sensitivity and other technical indicators matching and taking into account the economy. Economical aging-resistant high-strain precipitation-strengthened pipeline steel and production method thereof.

The economical, aging-resistant, high-strain, precipitation-strengthened pipeline steel of the invention is suitable for making straight seam submerged arc welded pipes for oil and gas production and transportation in cold, complex geological regions and underwater environments. The thickness of the economical aging-resistant and high-strain pipeline steel strengthened by the fine precipitation of the present invention is ≥20mm; in the composition design, C, Mn, Si, Ni, Cu are used as the basic strengthening elements, and Nb, Ti, V are used to form fine carbonitride precipitation, and play an important role. Strengthen and refine grains and reduce aging sensitivity; at the same time, reduce the impact on toughness; use Mo-free design to improve aging resistance, and improve economy.

The object of the present invention is achieved in this way:

An economical aging-resistant high-strain precipitation-strengthening pipeline steel, the composition of the steel is as follows in weight percentage: C: 0.045%-0.070%, Si: 0.26%-0.45%, Mn: 1.65%-1.85%, P≤0.012 %, S≤0.002%, Nb: 0.035%~0.075%, Ti: 0.012%~0.025%, V: 0.01%~0.04%, Ni: 0.12%~0.22%, Cu: 0.15%~0.29%, Ni/Cu ≥0.7, Cr: <0.30%, Al: 0.010%~0.025%, N: 0.0010%~0.0045%, the pipeline steel CE _Pcm is controlled at 0.165%~0.190%, where CE _Pcm =C+Si/30+ (Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B, the balance is iron and inevitable impurities.

Further, the microstructure of the pipeline steel is bainite + polygonal ferrite + a small amount of M/A, wherein the volume percentage of polygonal ferrite is 15% to 50%, and bainite includes granular bainite and lath shellfish. Intenite; the average grain diameter is less than 10 μm; the steel plate contains 0.03%~0.07% carbonitride precipitation, of which the fine precipitation carbonitride precipitation below 10nm accounts for ≥30% of the total carbonitride precipitation.

The volume percentage of the lath bainite is 30%-70%.

Further, the thickness of the economical aging-resistant high-strain pipeline steel strengthened by fine precipitation is ≥20mm, the transverse yield strength can reach 460-550MPa, the transverse tensile strength can reach 660-740MPa, the transverse yield-to-strength ratio does not exceed 0.75, and the transverse yield strength at -60°C can reach 0.75. The mean value of impact energy is ≥300J, the transverse DWTT shear area at -15℃ is ≥85%; the longitudinal yield strength can reach 430~530MPa, the longitudinal tensile strength can reach 640~730MPa, the longitudinal uniform elongation U _EL ≥10%, the longitudinal yield-strength ratio Not more than 0.73, the longitudinal strain hardening index n≥0.11; after 250 ℃ heat preservation and aging for 1h, the longitudinal yield strength can reach 450~550MPa, the longitudinal tensile strength can reach 650~730MPa, the longitudinal uniform elongation U _EL ≥ 9%, the longitudinal yield strength The strength ratio does not exceed 0.75, and the longitudinal strain hardening index n ≥ 0.10.

The reasons for the composition design of the present invention are as follows:

C mainly plays its role in two forms of alloy carbide precipitation and interstitial solid solution; the present invention mainly utilizes the characteristics of C in the steel plate at temperature deformation and forming a precipitation phase below 10 nm with Nb when it is warm to promote the formation of fine precipitation, thereby increasing the At the same time, C in the form of solid solution can increase the strength and hardness of the hard phase in the multiphase structure, increase the difference in mechanical properties of the soft and hard phases, and help reduce the yield ratio and stress ratio. However, the increase of carbon is detrimental to plasticity and toughness. For thick-walled high-strength pipeline steel plates, the contradiction between strength and toughness is more prominent. Therefore, the upper limit of C needs to be strictly controlled. The present invention believes that C is controlled at 0.045%~ 0.070% is more suitable.

Si can improve the strength, but if its content is too high, the M/A in the microstructure will increase, and the toughness and plasticity will decrease. The suitable range is 0.26%~0.45%.

Mn can effectively improve the strength, and can also improve the stability and hardenability of austenite, so that the microstructure is more refined and homogenized; however, too high manganese content can easily induce segregation and promote the formation of inclusions. It is more appropriate to control the content at 1.65%~1.85%.

P and S are harmful impurity elements in the present invention; P will reduce the toughness, and the present invention controls P to be less than or equal to 0.012%; the increase in the content of S will promote the formation and growth of inclusions, destroy the continuity of the matrix, and lead to performance degradation. Therefore, S≤0.002%.

Nb The present invention mainly utilizes the effect of Nb that can form fine Nb (CN) precipitation below 10nm under proper process, exerts the effect of fine grains and improves the strength, and at the same time, due to the small size of the precipitation phase, it will not lead to a decrease in toughness; The precipitation of Nb(CN) can reduce the mass fraction of solid solution C and N, thereby inhibiting the formation of M(CN) during aging and reducing the aging sensitivity. In addition, Nb can also inhibit the growth of austenite grains, refine the microstructure, and reduce the limit of rolling deformation; however, if the content of niobium is too high, the toughness after welding will decrease, and the cost will be increased. The present invention considers that the content of Nb should be controlled 0.035%~0.075% is more suitable.

Ti can exert the effect of solid N and solid C, form a Ti(CN) precipitation phase with a higher solid solution temperature, inhibit the grain growth of austenite under high temperature conditions, reduce the content of solid solution C and N, and reduce the aging sensitivity; At the same time, Ti can also refine the welding structure and improve the toughness of the heat-affected zone after welding. The present invention considers that it is more appropriate to control the Ti content to 0.012% to 0.025%.

V has the effect of solid solution and precipitation, and has a strong tendency to combine with C and N. It can combine with C and N to form fine precipitation during rolling and cooling, and also has the effect of reducing aging sensitivity; In contrast, the precipitation temperature of V is relatively low, which is beneficial to the refinement of the precipitation phase; however, an excessively high content of V will affect the steel plate and the toughness after welding. Therefore, the content of V in the present invention is 0.01% to 0.04%.

Ni, Cu: Ni can improve the strength, reduce the critical cooling rate, delay the transformation of pearlite, which is beneficial to the control of the microstructure and grain refinement, and improves the low temperature toughness; but the price of Ni is high, and it is not advisable to add too much; The content is controlled at 0.12%~0.22%. Cu can improve the strength and make up for the strength loss of the design without Mo; it can also increase the stability of austenite and improve the cooling effect of the thick-walled steel plate, but too high content of Cu is unfavorable to the toughness, and it is easy to cause the embrittlement of the steel plate. The Cu content of the present invention is controlled At 0.15%~0.29%, and at the same time, Ni/Cu≥0.7, the influence of Cu on toughness can be suppressed.

Cr has a strengthening effect, can also harden hardenability, reduce the austenite transformation temperature, and is beneficial to improve the uniformity of the microstructure in the thickness direction. Moreover, Cr is cheap and can replace precious alloying elements to reduce costs; but too high Cr content will Increase the sensitivity of welding cracks, so the Cr content is controlled below 0.30%.

Al is a deoxidizing element and has a certain effect of solid N, but if the content is too high, it will promote the increase of Al-containing inclusions, and it is not good for the weldability.

N can form fine precipitates with Nb, Ti, V, play the role of strengthening and grain refinement, and improve the strength and toughness, but the content is too high to deteriorate the toughness, and its content should be controlled at 0.0010%~0.0045%.

The CE _Pcm of the present invention is controlled at 0.165% to 0.190%, which can not only meet the strength and toughness requirements of the steel plate, but also reduce the tendency of welding cracking, so that the steel plate has good weldability.

The second technical solution of the present invention is to provide an economical production method of aging-resistant and high-strain precipitation-strengthened pipeline steel, including smelting, continuous casting, heating rolling, and cooling;

(1) Smelting and continuous casting: when the converter is tapping, the tapping temperature is less than or equal to 1640℃, C is less than or equal to 0.045%, and the slag is blocked for tapping. During the tapping process, lime and fluorite are added in the proportion of 4/1~5/1 to make top slag; The RH vacuum treatment time in the refining process is ≥10min; the casting superheat degree of the continuous casting billet is 10~30℃, and the continuous casting billet pulling speed is 0.8~1.2m/min. Low carbon, low temperature, and slag-retaining tapping in the converter can effectively control the carbon content of the final product, ensure the dephosphorization effect, and reduce phosphorus and sulfur return; top slag making and vacuum refining can effectively remove non-metallic harmful elements; casting superheat and continuous The control of the billet pulling speed can effectively reduce the quality defects of the billet.

(2) Heating: The continuous casting slab is heated in multiple stages of preheating section, heating section I, heating section II and soaking section. The temperature of soaking section is 1170~1200℃, and the time of soaking section is 0.4min/mm~0.8min/ mm. The multi-stage heating of the continuous casting slab is beneficial to improve the heating efficiency and uniformity; the heating temperature is mainly designed according to the content of niobium, carbon and other elements, which not only meets the needs of alloy solid solution, but also prevents the excessive growth of austenite grains; the time of soaking stage is controlled It can ensure the overall temperature uniformity of the continuous casting slab.

(3) Rolling: Rough rolling includes two stages. The final rolling temperature of the first stage is ≥1100 °C, and then it is cooled to 1051~1100 °C at a cooling rate of ≥2 °C/s for the second stage rough rolling. The rolling temperature is 970~1030℃, the deformation rate of each pass in the second stage of rough rolling is ≥16%, and spray cooling is performed during rolling, and the rolling speed is 1.0m/s~2.0m/s. The high temperature and low temperature two-stage rolling + rapid cooling process for rough rolling is beneficial to promote the refinement of austenite and increase the temperature gradient of the slab section, and the lower rolling speed can promote the penetration of rolling deformation to the center of the slab thickness , refine the structure near the thickness center, and improve the uniformity of the thickness section structure and performance.

The thickness of the intermediate billet to be warmed is 3.3t~4.8t, where t is the thickness of the finished steel sheet, the finishing rolling temperature is 800~860℃, and the finishing rolling temperature is 720~770℃. Appropriate intermediate green thickness can satisfy the accumulation of austenite deformation and deformation energy in the unrecrystallized area; the low temperature finishing rolling process combined with austenite transformation control can promote the induced precipitation of fine precipitates and increase the nucleation position , and can also form a small amount of deformed ferrite, which is beneficial to the improvement of plasticity and toughness.

(4) Cooling: After rolling, the steel plate is air-cooled for 20s~60s and then accelerated by water cooling. The initial water cooling temperature is 690~740℃, the final cooling temperature is 160~290℃, the water cooling time is 15s~35s, and the water cooling rate is 10℃/s~25 °C/s; subsequently, straightening and air cooling were performed. The combination of short-term air cooling after steel plate rolling and low-temperature final rolling, and then through the control of the initial water cooling temperature, is conducive to the precipitation of fine particles and the further formation of soft-phase polygonal ferrite; the final cooling temperature can promote hard-phase bainite and a small amount of M/ The formation of A, and ensuring sufficient hardness difference between the soft phase and the hard phase, thereby increasing the tensile strength and stress ratio.

The final microstructure of the steel plate is bainite + polygonal ferrite + a small amount of M/A, and the volume percentage of polygonal ferrite is 15%~50%; bainite includes granular bainite and lath bainite, among which, The volume percentage of lath bainite is 30% to 70%. The average grain diameter is less than 10 μm; the matrix contains 0.03%~0.07% of carbonitride precipitation by mass fraction, among which, the fine precipitation carbonitride precipitation below 10nm accounts for ≥30% of the total carbonitride precipitation. The steel plate has comprehensive technical characteristics such as thick wall, high strength, high toughness, high uniform deformation rate, low yield ratio, high strain hardening rate, low aging sensitivity, etc. Requirements for straight seam submerged arc welded pipes for oil and gas production and transportation.

The invention is matched with suitable smelting, heating, rolling, cooling and other production processes to obtain comprehensive properties such as thick wall, high strength, high toughness, high uniform deformation rate, low yield ratio, high strain hardening rate, low aging sensitivity and the like. ideal microstructure.

The beneficial effects of the present invention are:

(1) The composition of the present invention is based on C, Mn, Si, Ni, and Cu as strengthening elements, and makes full use of Nb, Ti, and V to form fine carbonitride precipitation, which exerts the effect of strengthening and fine-graining, reduces aging sensitivity, and at the same time, reduces Influence on toughness; adopt Mo-free design to improve aging resistance, and improve economy; coupled with unique production process, it solves the problem of matching technical indicators such as large wall thickness, toughness, high strain and other technical indicators of pipeline steel plates for complex service environments And has good economy.

(2) The ideal microstructure of bainite + polygonal ferrite + a small amount of M/A is obtained by the composition design and production method of the present invention, the effective control of the grain size is realized, and at the same time, a large amount of dispersed and distributed fine precipitation is obtained , played an important role in improving the performance of the steel plate.

(3) The thickness of the economical aging-resistant and high-strain pipeline steel strengthened by the fine precipitation of the present invention is ≥20mm, the transverse yield strength can reach 460~550MPa, the transverse tensile strength can reach 660~740MPa, and the transverse yield strength ratio does not exceed 0.75, - The mean value of transverse impact energy at 60°C is ≥300J, the transverse DWTT shear area at -15°C is ≥85%; the longitudinal yield strength can reach 430~530MPa, the longitudinal tensile strength can reach 640~730MPa, the longitudinal uniform elongation U _EL ≥10%, the longitudinal The yield-strength ratio does not exceed 0.73, the longitudinal strain hardening exponent n≥0.11; after 250℃ heat preservation and aging for 1h, the longitudinal yield strength can reach 450~550MPa, the longitudinal tensile strength can reach 650~730MPa, and the longitudinal uniform elongation U _EL ≥9% , the longitudinal yield ratio does not exceed 0.75, and the longitudinal strain hardening index n ≥ 0.10.

Description of drawings

FIG. 1 is a microstructure diagram of Example 1 of the present invention.

FIG. 2 is a fine precipitation diagram of Example 1 of the present invention.

Detailed ways

The present invention will be further illustrated by the following examples.

In the embodiment of the present invention, smelting, continuous casting, rolling and cooling are performed according to the component distribution ratio of the technical solution.

Smelting: When the converter is tapping, the tapping temperature is ≤1640℃, C≤0.045%, and the slag is blocked for tapping. During the tapping process, lime and fluorite are added in the proportion of 4/1~5/1 to make top slag; RH vacuum treatment time in the refining process ≥10min;

Continuous casting: During the continuous casting process, the casting superheat degree of the continuous casting billet is 10~30℃, and the casting speed of the continuous casting billet is 0.8~1.2m/min;

Heating: The continuous casting slab is heated in multiple stages of preheating section, heating section I, heating section II, and soaking section. The temperature of soaking section is 1170~1200℃, and the time of soaking section is 0.4~0.8min/mm;

Rolling: Rough rolling consists of two stages. The final rolling temperature of the first stage is ≥1100 °C, and then cooled to 1051~1100 °C at a cooling rate of ≥2 °C/s for the second stage of rough rolling. The final rolling temperature of the second stage is 970~1030℃, the deformation rate of each pass in the second stage of rough rolling is ≥16%, and spray cooling is performed during rolling, and the rolling speed is 1.0~2.0m/s;

The thickness of the intermediate billet to be warmed is 3.3t~4.8t, where t is the thickness of the finished steel plate, the finishing rolling temperature is 800~860℃, and the finishing rolling temperature is 720~770℃;

Cooling: After rolling, the steel plate is air-cooled for 20s~60s and then accelerated by water cooling. The initial cooling temperature of water cooling is 690~740℃, the final cooling temperature is 160~290℃, the cooling time of water cooling is 15s~35s, and the cooling rate of water cooling is 10℃/s~25℃/s ; then, straightening and air cooling.

The composition of the steel in the embodiment of the present invention is shown in Table 1. The main process parameters of smelting and continuous casting of the steel in the embodiment of the present invention are shown in Table 2. The main technical parameters of the rolling of the steel in the embodiment of the present invention are shown in Table 3. The main cooling process parameters of the steel in the embodiment of the present invention are shown in Table 4. The longitudinal properties of the steel of the embodiment of the present invention are shown in Table 5. The longitudinal properties of the steel of the embodiment of the present invention after aging are shown in Table 6. Table 7 shows the toughness and microstructure of the steel of the embodiment of the present invention.

Table 1 Composition (wt%) of the steel of the embodiment of the present invention

Table 2 The main process parameters of smelting and continuous casting of the steel of the embodiment of the present invention

Example Smelting tapping temperature/℃ Smelting tap C content/% Top slag lime/fluorite RH vacuum treatment time/min Pouring superheat/℃ Continuous casting billet drawing speed/m/min Soaking temperature/℃ Soaking time/min/mm 1 1618 0.037 4.3 25 12 0.8 1183 0.5 2 1633 0.032 4.8 19 28 0.8 1177 0.4 3 1631 0.027 4.1 twenty two 19 0.8 1191 0.6 4 1616 0.039 4.3 17 16 1.1 1189 0.7 5 1620 0.026 4.6 twenty one 13 1.1 1195 0.6 6 1632 0.035 4.3 16 15 1.1 1181 0.5 7 1618 0.032 4.6 twenty three twenty four 1.1 1196 0.7 8 1625 0.039 4.6 13 19 1.1 1195 0.7

Table 3 Main rolling process parameters of the steel in the embodiment of the present invention

Table 4 The main cooling process parameters of the steel in the embodiment of the present invention

Table 5 Properties of the steel of the embodiment of the present invention

Note: The tensile specimen is a full-thickness rectangular specimen, and the width of the parallel test section is 38.1 mm.

Table 6 Longitudinal properties of the steel according to the embodiment of the present invention after aging

Note: The aging process is 250℃ for 1h.

Table 7 Toughness and microstructure of the steel of the embodiment of the present invention

Note: The size of the impact sample is 10*55*55mm; the DWTT sample is a full-thickness sample.

The thickness of the economical aging-resistant high-strain pipeline steel produced by the application of the invention is greater than or equal to 20 mm, the transverse yield strength can reach 460-550 MPa, the transverse tensile strength can reach 660-740 MPa, and the transverse yield-to-strength ratio does not exceed 0.75, -60 ℃ The average transverse impact energy is ≥300J, the transverse DWTT shear area at -15℃ is ≥85%; the longitudinal yield strength can reach 430~530MPa, the longitudinal tensile strength can reach 640~730MPa, the longitudinal uniform elongation U _EL ≥10%, the longitudinal yield strength The ratio does not exceed 0.73, the longitudinal strain hardening index n≥0.11; after 250 ℃ heat preservation and aging for 1h, the longitudinal yield strength can reach 450~550MPa, the longitudinal tensile strength can reach 650~730MPa, the longitudinal uniform elongation U _EL ≥ 9%, the longitudinal The yield-strength ratio should not exceed 0.75, and the longitudinal strain hardening exponent n ≥ 0.10.

In order to express the present invention, the present invention has been properly and fully described above through the examples. The above embodiments are only used to illustrate the present invention, but not to limit the present invention. Under the circumstance of the spirit and scope of the invention, various changes and modifications can also be made, and any modifications, equivalent replacements, improvements, etc. made should be included within the protection scope of the present invention, and the patent protection scope of the present invention should be The claims are limited.

Claims (6)

1. an economical aging-resistant high-strain precipitation-strengthening pipeline steel, characterized in that the composition of the steel is as follows by weight percentage: C: 0.045% ~ 0.070%, Si: 0.26% ~ 0.45%, Mn: 1.65% ~ 1.85%, P≤0.012%, S≤0.002%, Nb: 0.035%~0.075%, Ti: 0.012%~0.025%, V: 0.01%~0.04%, Ni: 0.12%~0.22%, Cu: 0.15%~ 0.29%, Ni/Cu≥0.7, Cr: <0.30%, Al: 0.010%~0.025%, N: 0.0010%~0.0045%, pipeline steel CE _Pcm is controlled at 0.165%~0.190%, among which, CE _Pcm =C+ Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B, the balance is iron and unavoidable impurities; the economical aging-resistant high-strain precipitation Production methods for strengthening pipeline steel, including smelting, continuous casting, heating, rolling, and cooling; (1) Heating: The continuous casting slab is heated in multiple stages of preheating section, heating section I, heating section II and soaking section. The temperature of soaking section is 1170~1200℃, and the time of soaking section is 0.4~0.8min/mm; (2) Rolling: Rough rolling consists of two stages. The final rolling temperature of the first stage is ≥1100 °C, and then it is cooled to 1051~1100 °C at a cooling rate of ≥2 °C/s for the second stage rough rolling. The rolling temperature is 970~1030℃, the deformation rate of each pass in the second stage of rough rolling is ≥16%, and spray cooling is performed during rolling, and the rolling speed is 1.0~2.0m/s; The thickness of the intermediate billet to be warmed is 3.3t~4.8t, where t is the thickness of the finished steel plate, the finishing rolling temperature is 800~860℃, and the finishing rolling temperature is 720~770℃; (3) Cooling: After rolling, the steel plate is air-cooled for 20s~60s and then accelerated by water cooling. The starting water cooling temperature is 690~740℃, the final cooling temperature is 160~290℃, the water cooling cooling time is 15s~35s, and the water cooling rate is 10℃/s~25 °C/s; subsequently, straightening and air cooling were performed. 2. An economical aging-resistant high-strain precipitation-strengthening pipeline steel according to claim 1, wherein the microstructure of the pipeline steel is bainite+polygonal ferrite+a small amount of M/A, wherein polygonal The volume percentage of ferrite is 15%~50%, bainite includes granular bainite and lath bainite; the average grain diameter is below 10μm; the steel plate contains 0.03%~0.07% mass fraction of carbonitride precipitation, Among them, the fine precipitation carbonitride precipitation below 10 nm accounts for ≥30% of the total carbonitride precipitation. 3 . The economical aging-resistant high-strain precipitation-strengthened pipeline steel according to claim 2 , wherein the lath bainite volume percentage is 30% to 70%. 4 . 4. An economical aging-resistant high-strain precipitation-strengthened pipeline steel according to claim 1, wherein the pipeline steel has a thickness of ≥ 20 mm, a transverse yield strength of 460 to 550 MPa, a transverse tensile strength of 660 to 740 MPa, and a transverse tensile strength of 660 to 740 MPa. The yield-strength ratio does not exceed 0.75; the longitudinal yield strength is 430~530MPa, the longitudinal tensile strength is 640~730MPa, the longitudinal uniform elongation U _EL ≥10%, the longitudinal yield-strength ratio does not exceed 0.73, and the longitudinal strain hardening index n≥0.11; -60 The mean value of transverse impact energy at ℃ is ≥300J, and the shear area of transverse DWTT at -15℃ is ≥85%; after 250℃ heat preservation and aging for 1h, the longitudinal yield strength is 450~550MPa, the longitudinal tensile strength is 650~730MPa, and the longitudinal uniform elongation U _EL ≥ 9%, the longitudinal yield ratio does not exceed 0.75, and the longitudinal strain hardening index n≥0.10. 5. An economical aging-resistant high-strain precipitation-strengthening pipeline steel according to claim 1, characterized in that, the smelting: tapping temperature≤1640°C, C≤0.045%, slag-retaining tapping during converter tapping , in the tapping process, lime and fluorite are added in the proportion of 4/1~5/1 to make top slag; the RH vacuum treatment time in the refining process is ≥10min. 6. An economical aging-resistant high-strain precipitation-strengthening pipeline steel according to claim 1, characterized in that in the continuous casting process, the continuous casting billet has a pouring superheat of 10 to 30°C, and a continuous casting billet pulling speed of 0.8 to 0.8°C. 1.2m/min.

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