Wide and thick high-strength pipeline steel plate designed on basis of strain, and production method therefor

Abstract

A wide and thick high-strength pipeline steel plate designed on the basis of strain, and a production method therefor. The steel plate comprises the following chemical components in percentages by weight: C: 0.030%-0.065%, Si: 0.20%-0.45%, Mn: 1.70%-1.85%, Nb<0.030%, V: 0.060%-0.15%, (Nb+V): 0.075%-0.170%, Ti: 0.005%-0.025%, Ti / N≤2.0, Ni<0.15%, Mo<0.15%, Cr: 0.20%-0.50%, Cu<0.15%, (Ni+Mo+Cr+Cu): 0.40%-0.80%, Zr≤0.025%, Al: 0.005%-0.025%, N: 0.005%-0.015%, Ca: 0.0015%-0.0040%, Ca / S≥1.6, P≤0.010%, S≤0.002%, H≤0.00015%, and O≤0.0018%, with the balance being iron and inevitable impurities. The CEIIW of the wide and thick high-strength pipeline steel plate is controlled at 0.42%-0.49%, and the CEPcm thereof is controlled at 0.17%-0.21%. By means of specific heating, rolling and cooling production processes, a wide and thick high-strength pipeline steel plate having high strength, high toughness, strain resistance and good weldability is obtained.

Description

A high-strength pipeline thick steel plate based on strain design and its production method Technical Field

[0001] This invention belongs to the field of low alloy steel technology, and particularly relates to a high-strength pipeline thick steel plate with a thickness ≥30mm, high strength, high toughness, good strain resistance and weldability based on strain design, and its production method. Background Technology

[0002] With the depletion of conventional oil and gas resources, oil and gas extraction is increasingly extending to regions with complex geological and environmental conditions, such as polar regions, oceans, high-altitude frigid zones, and geologically active areas. The demand for high-strength pipeline steel plates for service in these complex regions is becoming increasingly urgent, posing a significant bottleneck in the construction of long-distance pipelines. To meet the requirements of service in complex regions, strain-designed high-strength pipeline steel plates must possess excellent strain characteristics, including high uniform elongation, high stress ratio, and low yield strength ratio. Simultaneously, to ensure safe pipeline operation and efficient transport capacity, the steel plates must possess comprehensive technical characteristics such as good transverse and longitudinal strength, high toughness, and thick walls and wide dimensions. Furthermore, these products are prone to embrittlement and softening in the weld heat-affected zone after welding, leading to reduced strength and hardness, directly impacting service safety; therefore, good weldability is essential. These complex and diverse technical requirements significantly increase the design and manufacturing difficulty of strain-designed thick-walled, high-strength pipeline steel plates.

[0003] The invention patent CN109234623B, entitled "An X80M Deep-Sea Strain-Resistant Pipeline Steel Plate and its Rolling Process," provides an X80-grade deep-sea pipeline steel plate with a high Ni (0.65%–0.85%) and high Mo (0.31%–0.36%) composition, resulting in excessively high alloy content and cost. The invention patent JP2021155823A, entitled "Manufacturing Method of Low Yield Ratio High-Strength Steel Plate," provides a steel plate with a tensile strength of 550-650 MPa, insufficient to meet the requirements of X80-grade strain-designed pipeline steel. In summary, existing technologies for strain-designed thick-walled, high-strength pipeline steel plates, especially those combining high strength, high toughness, strain resistance, and good weldability, as well as their production technologies, are still insufficient.

[0004] Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the present invention aims to provide a high-strength, thick pipeline steel plate with a thickness ≥30mm, high strength, high toughness, good strain resistance and weldability, based on strain design, and its production method. The high-strength, thick pipeline steel plate of the present invention is based on C, Mn, V, Cr, and Si. The addition of Mn, Cr, and Si ensures basic tensile strength. Low Nb and Mo design promotes polygonal ferrite phase transformation while reducing alloy costs. Furthermore, low Nb reduces the inhibition of V precipitates, fully utilizing the role of V. Through the composite addition of V, C, and N and the control of Al and Ti content, appropriate amounts of carbonitride precipitation are obtained. On the one hand, this promotes phase deformation nuclei and grain refinement, particularly beneficial for improving the microstructure and performance uniformity of thick-walled pipeline steel plates; on the other hand, it exerts precipitation strengthening effects, effectively suppressing weld embrittlement and softening. The addition of elements such as Zr and Ca controls inclusions, playing a beneficial role in phase transformation and welding processes. Toughness is improved by reducing the content of P, S, H, and O and controlling the quality of continuously cast billets; combined with smelting, heating, rolling, and cooling processes that match the alloy composition, steel plates can obtain comprehensive technical characteristics such as high strength, high toughness, strain resistance, good weldability, and large wall thickness, as well as an ideal microstructure.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a high-strength, thick steel plate for pipelines based on strain design. Its chemical composition and weight percentages are: C: 0.030%–0.065%, Si: 0.20%–0.45%, Mn: 1.70%–1.85%, Nb < 0.030%, V: 0.060%–0.15%, (Nb+V): 0.075%–0.170%, Ti: 0.005%–0.025%, Ti / N ≤ 2.0, Ni < 0.15%, Mo < 0.15%. Cr: 0.20%–0.50%, Cu < 0.15%, (Ni+Mo+Cr+Cu): 0.40%–0.80%, Zr ≤ 0.025%, Al: 0.005%–0.025%, N: 0.005%–0.015%, Ca: 0.0015%–0.0040%, Ca / S ≥ 1.6, P ≤ 0.010%, S ≤ 0.002%, H ≤ 0.00015%, O ≤ 0.0018%, with the balance being iron and unavoidable impurities.

[0008] Based on the above technical solution, further, the high-strength pipeline thick steel plate CE based on strain design... IIW Controlled within 0.42% to 0.49%, CE Pcm Controlled within 0.17% to 0.21%, of which CE IIW=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15; CE Pcm =C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B.

[0009] Based on the above technical solution, further, Ti / N: 0.6~1.9, (Ni+Mo+Cr+Cu): 0.40%~0.70%, Ca / S: 1.7~3.5.

[0010] The rationale for the design of the components in this invention is as follows:

[0011] Carbon (C) is a fundamental element for improving strength, exerting its effects through both alloy carbide precipitation and interstitial solid solution. In addition to utilizing C's solid solution strengthening, this invention leverages C's ability to form fine precipitates with V and other elements during intermediate-temperature deformation, slow cooling, and welding of steel plates. This promotes phase deformation nuclei, refines the microstructure, increases strength, and reduces weld joint softening. Simultaneously, C significantly improves hardenability and tensile strength, contributing to a lower yield strength ratio and enhanced strain performance. However, increased carbon content is detrimental to plasticity and toughness. In this invention, a C content of 0.030%–0.065% is considered optimal.

[0012] Si enhances hardenability and strength, which is beneficial for increasing the strain hardening rate. At the same time, in order to create favorable conditions for VN precipitation, the Al content is strictly controlled in this invention, and Si is used to partially replace Al to play the role of deoxidizer. However, if the Si content is too high, the M / A ratio in the microstructure will increase, and the toughness and plasticity will decrease. The suitable range for Si in this invention is 0.20% to 0.45%.

[0013] Mn is a major strengthening element that can improve hardenability and is beneficial for homogenizing the microstructure of thick-walled steel plates. Moreover, Mn is inexpensive and can improve the economic efficiency of products. However, excessive manganese content can easily induce segregation and lower the phase transformation temperature, which is not conducive to the formation of soft ferrite and thus affects strain resistance. In this invention, the Mn content is controlled at 1.70% to 1.85%.

[0014] Nb can form fine Nb(CN) precipitates under appropriate processes, which has a grain-refining effect and can improve strength and toughness. However, if the Nb content is too high, on the one hand, the heating temperature of the continuous casting billet needs to be increased to ensure the solidification effect, and on the other hand, it will increase the recrystallization temperature of austenite, requiring the use of higher temperature rolling. At the same time, it will also inhibit the formation of V-containing precipitates. This invention controls the Nb content to below 0.030%.

[0015] V has solid solution and precipitation effects, and has a strong tendency to combine with C and N. It can combine with C and N to form fine precipitates during rolling, cooling and welding, refine the grains, promote ferrite nucleation during austenite phase transformation, which is beneficial to obtaining polygonal ferrite and can also improve the uniformity of microstructure of steel plate thickness section. At the same time, V can improve the toughness and hardness of welded joints and prevent or reduce weld softening. However, too high V content is detrimental to toughness and weldability. Therefore, in this invention, V is controlled at 0.060% to 0.15%.

[0016] Controlling Nb+V between 0.075% and 0.170% helps ensure fine and dispersed precipitates and prevents excessive growth of precipitates; at the same time, it is beneficial for controlling the microstructure and alloy cost.

[0017] Ti readily forms Ti(CN) precipitates with high solution temperatures, inhibiting austenite grain growth under high-temperature conditions. Simultaneously, Ti can refine the weld microstructure and improve the toughness of the heat-affected zone after welding. Furthermore, it has an oxygen-fixing effect. However, excessively high Ti and Ti / N ratios can increase precipitate size and inhibit the formation of Nb and V-containing precipitates. In this invention, the Ti content is controlled at 0.005%–0.025%, and the Ti / N ratio is ≤2.0.

[0018] Ni can improve strength, delay pearlite transformation, facilitate microstructure control and grain refinement, improve low-temperature toughness, and reduce Cu embrittlement; however, Ni is expensive and should not be added in excess; therefore, the Ni content in this invention is controlled below 0.15%.

[0019] Mo can improve hardenability, promote the transformation of microstructure at medium and low temperatures, and has a certain grain-refining effect. It can also improve post-weld strength and hardness. However, excessive molybdenum content will inhibit ferrite transformation, which is not conducive to the control of multiphase microstructure and strain performance. At the same time, Mo is expensive, and excessive addition will significantly increase the cost. Therefore, this invention controls the Mo content to below 0.15%.

[0020] Cr can increase hardenability and tensile strength, which is beneficial for improving the uniformity of the microstructure in the thickness direction. Moreover, it has a weaker inhibition of the transformation of austenite to polygonal ferrite, which is conducive to increasing the "hardness difference" between the soft and hard phases in the microstructure, making it easier to control strain and yield strength ratio. In addition, Cr, as an inexpensive element, can replace expensive alloying elements such as Mo, Ni, and Cu, effectively reducing costs. However, excessive Cr content will increase the sensitivity to welding cracks. Therefore, the Cr content in this invention is controlled at 0.20% to 0.50%.

[0021] Cu improves hardenability, increases the hardness and tensile strength of the hard phase structure, and improves the cooling effect of thick-walled steel plates. However, excessive Cu content is detrimental to toughness. In this invention, the Cu content is controlled at <0.15%.

[0022] Controlling the (Ni+Mo+Cr+Cu) content to 0.40%-0.80% can ensure hardenability and strengthening effect. At the same time, it is beneficial to phase transformation and microstructure control, and improve strain performance.

[0023] Zr is a strong deoxidizing element. This invention utilizes Zr oxides formed by the combination of Zr and oxygen. These oxides have a small density difference with molten steel, facilitating dispersed distribution. Simultaneously, the Zr oxides in molten steel carry an electric charge and possess a certain degree of conductivity, making them less prone to aggregation and growth. This promotes the fine and dispersed distribution of Zr oxides within the steel, fostering phase deformation nuclei, refining grains, and improving performance. Furthermore, Zr can refine the microstructure of the weld heat-affected zone, improving toughness. Moreover, the interaction between Zr and oxygen can reduce the interaction between V and oxygen, promoting V precipitation. However, excessively high Zr content leads to decreased toughness; therefore, in this invention, Zr ≤ 0.025%.

[0024] Al has a strong affinity for O and N and is a deoxygenating element. However, excessive Al content will promote the increase of Al-containing inclusions and the decrease of free N, affecting the formation of VN and other precipitates. In this invention, the Al content is preferably controlled between 0.005% and 0.025%.

[0025] N: In this invention, N forms fine precipitates with V, Nb, and Ti, which strengthens and refines the grains, improving toughness and weld joint performance. However, excessive N content can deteriorate toughness and may lead to defects in steel plate quality. It is advisable to control the N content between 0.005% and 0.015%.

[0026] Ca and Ca / S can promote the modification and spheroidization of inclusions and reduce the adverse effects of inclusions on plasticity and toughness. In this invention, Ca is 0.0015% to 0.0040% and Ca / S is ≥1.6.

[0027] In this invention, P and S are considered harmful impurity elements. P can reduce toughness, and this invention controls P to ≤0.010%. Increased S content promotes the formation and growth of inclusions and disrupts the continuity of the matrix; therefore, S ≤0.002%.

[0028] Increased H and O content leads to decreased toughness, increased inclusions, and reduced performance. Therefore, this invention controls H ≤ 0.00015% and O ≤ 0.0018%.

[0029] This invention CE IIW Controlled within 0.42% to 0.49%, CE Pcm By controlling the concentration between 0.17% and 0.21%, the strength and toughness requirements of the steel plate can be met, while also reducing the tendency for welding cracks, thus giving the steel plate good weldability.

[0030] Based on the above technical solution, further, the high-strength pipeline thick steel plate based on strain design has a thickness ≥30mm, a microstructure of polygonal ferrite + lath bainite and a small amount of granular bainite, a polygonal ferrite volume percentage of 20-80%, a grain size of 4-10μm, and fine precipitates with a particle size <20nm dispersed in the matrix. The transverse yield strength reaches 490-570MPa, the transverse tensile strength reaches 680-770MPa, the transverse yield ratio is <0.78, the average transverse impact energy at -60℃ is ≥220J, the average transverse impact energy in the weld heat-affected zone at -20℃ is ≥180J, and the transverse DWTT shear area at -25℃ is ≥85%; the longitudinal yield strength reaches 450-550MPa, the longitudinal tensile strength reaches 660-760MPa, and the longitudinal uniform elongation U... EL ≥12%, longitudinal yield strength ratio <0.77, longitudinal stress ratio Rt 1.5 / Rt 0.5 ≥1.12, Rt 2.0 / Rt 1.0 ≥1.06.

[0031] The present invention also provides a method for producing the above-mentioned high-strength pipeline thick steel plate based on strain design, comprising the following steps:

[0032] (1) Heating: The continuous casting billet adopts a multi-stage heating process of preheating, heating and homogenization, with a furnace exit temperature of 1100~1160℃ and a total heating time of 1.0~2.0min / mm;

[0033] (2) Rolling: including roughing and finishing. Roughing includes three stages: roughing stage one, intermediate cooling, and roughing stage two. The starting temperature of roughing is 1070-1130℃, the finishing temperature of roughing is 980-1030℃, and the total reduction rate of roughing is ≥60%. Among them, the last 2-3 passes of roughing stage one, intermediate cooling and roughing stage two all adopt rapid spray water cooling with an average cooling rate ≥1℃ / s. The starting temperature of roughing stage two is below 1050℃, the total deformation rate is ≥30%, the deformation rate of each pass is ≥15% and increases with each pass, and the roughing rolling speed is 1.0-2.0m / s.

[0034] After rough rolling, the intermediate billet is rapidly cooled to 850-900℃ with an average cooling rate of ≥2℃ / s. Then, it is allowed to heat up to the finishing rolling start temperature. The deformation rate in the finishing rolling stage is 60-75%, the finishing rolling start temperature is 790-840℃, and the finishing rolling finish temperature is Ar3±20℃, where Ar3=910-273*C-74*Mn-57*Ni-16*Cr-58*Mo-18*Cu.

[0035] (3) Cooling: The air cooling time t of the rolled steel plate, pre-straightening after air cooling, and then two-stage water cooling. The average cooling rate of the first stage is 10-20℃ / s, the average cooling rate of the second stage is 3-10℃ / s, and the water cooling end temperature is <250℃.

[0036] Based on the above technical solution, further, the total deformation rate of the two roughing stages in step (2) is 30-50%.

[0037] Based on the above technical solution, further, the finishing rolling temperature in step (2) is 730~760℃.

[0038] Based on the above technical solution, further, in step (3), the air cooling time t=(FRT-Ar3) / a+k*h, t is the air cooling time, s; FRT is the final rolling temperature, ℃; a is a coefficient related to the cooling rate, with a value range of 0.4~1.0℃ / s; k is a coefficient, with a value range of 0.9~2.0s / mm; h is the steel plate thickness in mm; and the water cooling end temperature is 100~200℃.

[0039] Based on the above technical solution, further, the preparation of the continuous casting billet in step (1) includes converter smelting, ladle refining and continuous casting; the converter tapping temperature of the converter smelting is ≤1640℃, the tapping C is ≤0.045%, the slag is blocked during tapping, and the slag layer thickness is ≤40mm; after refining and deoxidation, Ti is added first, and then Zr and V are added; after ladle refining, the molten steel is calmed for ≥10min before being put on the machine; during the continuous casting process, the superheat of the continuous casting billet is 10~40℃, the residence time of the molten steel in the tundish during casting is ≥350s, the dynamic light reduction of the billet is ≥4mm, and the continuous casting adopts constant casting speed, with the casting speed control range of 0.6~1.2m / min.

[0040] Based on the above technical solution, furthermore, lime and fluorite are added in a ratio of 4 / 1 to 5 / 1 to form top slag during the converter smelting process, and the weight percentage of FeO+MnO in the slag is controlled to be ≤1%.

[0041] Based on the above technical solution, further, the center segregation of the continuously cast billet is ≤C0.5 grade, the center porosity is ≤0.5 grade, and the inclusions of A / B / C / D types are controlled within grade 1.

[0042] The reason for adopting the above-described production method in this invention is as follows:

[0043] Low-carbon, low-temperature converter tapping with slag blocking can effectively control the carbon content of the final product, ensure dephosphorization, and reduce phosphorus and sulfur reversion. White slag formation and control of FeO+MnO in the slag can ensure the slag's reducing capacity, fully desulfurize, reduce inclusions, and improve cleanliness.

[0044] The order of adding Ti, Zr, and V after refining and deoxidation can more effectively improve the yield and efficiency of the corresponding elements; the control of pre-cast steel killing, casting superheat, and tundish dwell time can homogenize the steel temperature and effectively promote the flotation and removal of inclusions; the control of dynamic light reduction and continuous casting billet pulling speed can effectively improve the billet quality and reduce defects such as cracks and segregation. The control of center segregation, center porosity, and inclusions is an effective guarantee for the quality of continuous casting billets and the performance of steel plates.

[0045] The control of multi-stage heating and total heating time of continuously cast billets is beneficial to improving heating efficiency and uniformity. Since the Nb content in this invention is low, the element solid solution requirement can be met by heating at low temperature. At the same time, the austenite grain size can be effectively reduced. Moreover, it is more conducive to reducing the rough rolling temperature and the rolling time in the rough rolling stage, so as to achieve efficient low-temperature rolling.

[0046] This invention focuses on a low-temperature rolling process combined with a high temperature gradient deformation of the thickness section during roughing. Because the V-containing and low-Nb design of this invention lowers the austenite recrystallization temperature, the low-temperature rolling in the roughing stage promotes austenite grain recrystallization and effectively inhibits grain growth. Multi-stage rapid cooling significantly increases the temperature gradient of the thickness section, and the low-temperature, low-speed rolling in the second stage of roughing promotes the penetration of rolling deformation towards the center of the billet thickness. Simultaneously, the combined effect of V and the low temperature significantly refines the microstructure near the thickness center, improving the microstructure and performance uniformity of thick-gauge steel plates. The progressively increasing deformation rate in the second stage of roughing further promotes sufficient austenite recrystallization.

[0047] The deformation rate in the finishing rolling stage can balance the distribution of deformation rates in roughing and finishing rolling while ensuring the deformation and flattening degree of austenite in the non-recrystallization zone of finishing rolling. Rapid cooling of the intermediate billet after roughing rolling can quickly reduce the temperature and effectively inhibit austenite growth. The finishing rolling stage uses low temperature and critical phase transformation temperature rolling, which on the one hand is conducive to the formation of substructures and the accumulation of deformation energy in the microstructure; on the other hand, it can promote the formation of ferrite induced by a small amount of deformation, improve plasticity, toughness and strain properties; it can also provide good thermodynamic and kinetic conditions for the precipitation of V(CN) and Nb(CN), thus playing a role in grain refinement, pinning, and promoting phase deformation nucleation. Air cooling after rolling is conducive to controlling the phase transformation of polygonal ferrite and the further precipitation of precipitates. Pre-straightening of the steel plate is conducive to improving the uniformity of water cooling and ensuring the shape of the steel plate. Using a low final cooling temperature can form a high-hardness structure dominated by bainite. The segmented water cooling process with fast cooling at the beginning and slow cooling at the end can increase the cooling rate of the high-temperature section and inhibit the high-temperature phase transformation. At the same time, the smaller cooling water volume in the low-temperature section can reduce internal stress and improve the shape of the plate after cooling.

[0048] The advantages of this invention over the prior art are as follows:

[0049] (1) The steel plate composition of the present invention is based on C, Mn, V, Cr and Si. By adding V, C and N in combination and controlling the content of Al and Ti, an appropriate amount of carbonitride precipitation is obtained. On the one hand, it promotes the nucleation of phase deformation and grain refinement, which is especially beneficial to improving the microstructure and performance uniformity of the thick section of the thick-walled pipeline steel plate. On the other hand, it plays a role in precipitation strengthening. In addition, it effectively suppresses welding embrittlement. By reducing the addition of Nb and Mo, it promotes the transformation of polygonal ferrite phase and reduces the cost of alloy. Moreover, reducing Nb can reduce the suppression of V precipitation and give full play to the role of V. By adding Zr, Ca and other elements, it controls inclusions and plays a beneficial role in phase transformation and welding. By reducing the content of P, S, H and O and controlling the quality of continuous casting billets, it improves toughness. With the smelting, heating, rolling and cooling production processes that match the alloy composition, the steel plate obtains comprehensive technical characteristics such as high strength, high toughness, strain resistance, good weldability and large wall thickness, as well as an ideal microstructure.

[0050] (2) Based on the composition design of this invention, the following production methods were adopted: low temperature heating, high temperature gradient deformation of thick section in rough rolling + low temperature rolling, rapid cooling of intermediate billet after rough rolling, low temperature critical deformation in fine rolling, air cooling after rolling and multi-stage water cooling based on rolling temperature and steel plate thickness control. Polygonal ferrite + lath bainite, and may also include a small amount of granular bainite microstructure and finely dispersed precipitates. The proportion of each phase, the size and distribution of precipitates are ideally controlled, which plays an important role in obtaining good comprehensive performance of steel plate.

[0051] (3) The high-strength pipeline thick steel plate based on strain design described in this invention has a thickness ≥30mm, a transverse yield strength of 490~570MPa, a transverse tensile strength of 680~770MPa, a transverse yield ratio <0.78, an average transverse impact energy ≥220J at -60℃, an average transverse impact energy ≥180J at -20℃ in the weld heat-affected zone, and a transverse DWTT shear area ≥85% at -25℃; a longitudinal yield strength of 450~550MPa, a longitudinal tensile strength of 660~760MPa, and a longitudinal uniform elongation U EL The longitudinal yield strength ratio is ≥12%, the longitudinal stress ratio is <0.77, the longitudinal stress ratio Rt1.5 / Rt0.5≥1.12, Rt2.0 / Rt1.0≥1.06, and the manufactured steel pipe meets the requirements of X80 grade based on strain design. Attached Figure Description

[0052] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0053] Figure 1 shows the typical microstructure of the steel plate of Embodiment 3 of the present invention.

[0054] Figure 2 shows a typical precipitated phase of the steel plate in Embodiment 2 of the present invention. Detailed Implementation

[0055] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0056] Examples 1-8

[0057] This embodiment provides a high-strength pipeline thick steel plate based on strain design and its production method. The chemical composition and weight percentage of the high-strength pipeline thick steel plate are shown in Table 1.

[0058] Table 1. Chemical composition and weight percentage (wt%) of high-strength pipeline thick steel plates in Examples 1-8

[0059] Includes the following steps:

[0060] Converter smelting: Add lime and fluorite in a ratio of 4 / 1 to 5 / 1 to form top slag, control the weight percentage of FeO+MnO in the slag to be ≤1%, the converter tapping temperature to be ≤1640℃, the tapping C to be ≤0.045%, tapping with slag blocking, and the slag layer thickness to be ≤40mm. See Table 2 for specific parameters.

[0061] Ladle refining: After refining and deoxidation, Ti is added first, followed by Zr and V; the molten steel is settling for ≥10 minutes before being fed onto the ladle.

[0062] Continuous casting: The superheating temperature of the continuously cast billet is 10-40℃. The residence time of molten steel in the tundish during casting is ≥350s. The dynamic light reduction of the billet is ≥4mm. The continuous casting adopts constant casting speed, with the casting speed control range of 0.6-1.2m / min. The center segregation of the continuously cast billet is ≤C0.5 grade, the center porosity is ≤0.5 grade, and the inclusions of A / B / C / D types are controlled within grade 1. Specific parameters are shown in Table 3.

[0063] Heating: The continuous casting billet adopts a multi-stage heating process of preheating, heating and homogenization, with a total heating time of 1.0 to 2.0 min / mm and a furnace exit temperature of 1100 to 1160℃. Specific parameters are shown in Table 4.

[0064] Rolling: Includes roughing and finishing. Roughing includes three stages: roughing stage one, intermediate cooling, and roughing stage two. The initial rolling temperature of roughing is 1070-1130℃, and the final rolling temperature is 980-1030℃. The total reduction rate of roughing is ≥60%. The initial rolling temperature of roughing stage two is below 1050℃, and the total deformation rate is ≥30%. The deformation rate per pass is ≥15% and increases with each pass. The rolling speed of roughing is 1.0-2.0 m / s. Among them, the last 2-4 passes of roughing stage one, intermediate cooling, and roughing stage two all adopt rapid spray water cooling with an average cooling rate of ≥1℃ / s. Specific parameters are shown in Table 4.

[0065] After rough rolling, the intermediate billet is rapidly cooled to 850-900℃ with an average cooling rate of ≥2℃ / s. Then, it is heated to the finishing rolling start temperature. The deformation rate in the finishing rolling stage is 60-75%, the finishing rolling start temperature is 790-840℃, and the finishing rolling finish temperature is Ar3±20℃, preferably 730-760℃. Specific parameters are shown in Table 5.

[0066] Cooling: The air cooling time t of the rolled steel plate, pre-straightening after air cooling, and then two-stage water cooling. The average cooling rate of the first stage is 10-20℃ / s, and the average cooling rate of the second stage is 3-10℃ / s. The water cooling end temperature is <250℃, preferably 100-200℃. Specific parameters are shown in Table 5.

[0067] The microstructure of the high-strength pipeline thick steel plates produced in the above embodiments is shown in Table 6, and the mechanical properties are shown in Table 7.

[0068] Table 2 Smelting processes of Examples 1-8

[0069] Table 3 Refining and continuous casting processes of Examples 1-8

[0070] Table 4 Heating and roughing processes of Examples 1-8

[0071] Table 5. Finishing and cooling processes for Examples 1-8

[0072] Table 6 shows the microstructure of the steel plates in Examples 1-8.

[0073] Figure 2 shows a typical precipitate phase of the steel plate in Example 2 of the present invention. As can be seen, fine precipitates with a particle size of <20nm are dispersed in the matrix, which play a beneficial role in promoting nucleation, fine grains, improving the uniformity of the structure, and strengthening in the present invention.

[0074] Table 7 Mechanical properties of steel plates from Examples 1-8 Note: The tensile specimen is a full-thickness rectangular specimen with a parallel test section width of 38.1 mm; the impact specimen size is 10*55*55 mm.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high strength pipeline wide and thick steel plate based on strain design, characterized by, The chemical composition and their weight percentages are as follows: C: 0.030%–0.065%, Si: 0.20%–0.45%, Mn: 1.70%–1.85%, Nb < 0.030%, V: 0.060%–0.15%, (Nb+V): 0.075%–0.170%, Ti: 0.005%–0.025%, Ti / N ≤ 2.0, Ni < 0.15%, Mo < 0.15%, Cr: 0.20%–0.50%, Cu < 0. 0.15%, (Ni+Mo+Cr+Cu): 0.40%~0.80%, Zr≤0.025%, Al: 0.005%~0.025%, N: 0.005%~0.015%, Ca: 0.0015%~0.0040%, Ca / S≥1.6, P≤0.010%, S≤0.002%, H≤0.00015%, O≤0.0018%, with the balance being iron and unavoidable impurities; the high-strength pipeline thick steel plate CE IIW Controlled within 0.42% to 0.49%, CE Pcm Controlled within 0.17% to 0.21%, of which CE IIW =C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15; CE Pcm =C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B.

2. The high strength pipeline heavy gauge plate based on strain design according to claim 1, characterized in that, Ti / N: 0.6~1.9, (Ni+Mo+Cr+Cu): 0.40%~0.70%, Ca / S: 1.7~3.

5.

3. The high strength pipeline heavy gauge plate based on strain design according to claim 1 or 2, characterized in that, The high-strength pipeline thick steel plate has a thickness ≥30mm, and its microstructure consists of polygonal ferrite + lath bainite and a small amount of granular bainite. The volume percentage of polygonal ferrite is 20-80%, the grain size is 4-10μm, and fine precipitates with a particle size <20nm are dispersed in the matrix. The transverse yield strength reaches 490-570MPa, the transverse tensile strength reaches 680-770MPa, the transverse yield ratio is <0.78, the average transverse impact energy at -60℃ is ≥220J, the average transverse impact energy at -20℃ in the weld heat-affected zone is ≥180J, and the transverse DWTT shear area at -25℃ is ≥85%. The longitudinal yield strength reaches 450-550MPa, the longitudinal tensile strength reaches 660-760MPa, and the longitudinal uniform elongation U EL ≥12%, longitudinal yield strength ratio <0.77, longitudinal stress ratio Rt 1.5 / Rt 0.5 ≥1.12, Rt 2.0 / Rt 1.0 ≥1.

06.

4. The production method of high strength pipeline heavy gauge steel plate based on strain design according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Heating: The continuous casting billet adopts a multi-stage heating process of preheating, heating and homogenization, with a furnace exit temperature of 1100~1160℃ and a total heating time of 1.0~2.0min / mm; (2) Rolling: including roughing and finishing. Roughing includes three stages: roughing stage one, intermediate cooling, and roughing stage two. The starting temperature of roughing is 1070-1130℃, the finishing temperature of roughing is 980-1030℃, and the total reduction rate of roughing is ≥60%. Among them, the last 2-3 passes of roughing stage one, intermediate cooling and roughing stage two all adopt rapid spray water cooling with an average cooling rate ≥1℃ / s. The starting temperature of roughing stage two is below 1050℃, the total deformation rate is ≥30%, the deformation rate of each pass is ≥15% and increases with each pass, and the roughing rolling speed is 1.0-2.0m / s. After rough rolling, the intermediate billet is rapidly cooled to 850-900℃ with an average cooling rate of ≥2℃ / s, and then heated to the finishing rolling start temperature. The deformation rate in the finishing rolling stage is 60-75%, the finishing rolling start temperature is 790-840℃, and the finishing rolling finish temperature is Ar3±20℃, where Ar3=910-273*C-74*Mn-57*Ni-16*Cr-58*Mo-18*Cu; (3) Cooling: The air cooling time t of the rolled steel plate, pre-straightening after air cooling, and then two-stage water cooling. The average cooling rate of the first stage is 10-20℃ / s, the average cooling rate of the second stage is 3-10℃ / s, and the water cooling end temperature is <250℃.

5. The method of producing a high strength pipeline heavy gauge steel plate based on strain design according to claim 4, characterized in that, In step (2), the total deformation rate of the roughing rolling stage is 30-50%, and the finishing rolling temperature is 730-760℃.

6. The method of producing a high strength pipeline heavy gauge steel plate based on strain design according to claim 4, characterized in that, In step (3), the air cooling time t = (FRT-Ar3) / a + k*h, where t is the air cooling time (s), FRT is the final rolling temperature (°C), a is a coefficient related to the cooling rate (range 0.4-1.0°C / s), k is a coefficient (range 0.9-2.0s / mm), and h is the steel plate thickness (mm). The water cooling end temperature is 100-200°C.

7. The method of producing a high strength pipeline heavy gauge steel plate based on strain design according to claim 4, characterized in that, The preparation of the continuously cast billet in step (1) includes converter smelting, ladle refining and continuous casting; the converter tapping temperature of the converter smelting is ≤1640℃, the tapping C is ≤0.045%, slag is blocked during tapping, and the slag layer thickness is ≤40mm; after refining and deoxidation, Ti is added first, followed by Zr and V; after ladle refining, the molten steel is calmed for ≥10min before being loaded onto the ladle; during continuous casting, the superheat of the continuously cast billet is 10~40℃, the residence time of the molten steel in the tundish is ≥350s, the dynamic light reduction of the billet is ≥4mm, and the continuous casting adopts a constant casting speed with a casting speed control range of 0.6~1.2m / min.

8. The method of producing a high strength pipeline heavy gauge steel plate based on strain design according to claim 7, characterized in that, During the converter smelting process, lime and fluorite are added in a ratio of 4 / 1 to 5 / 1 to form top slag, and the weight percentage of FeO+MnO in the slag is controlled to be ≤1%.

9. The method of producing a high strength pipeline heavy gauge steel plate based on strain design according to claim 7, characterized in that, The center segregation of the continuously cast billet is ≤C0.5 grade, the center porosity is ≤0.5 grade, and the inclusions of type A / B / C / D are controlled within grade 1.

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