555 MPa-grade pipeline steel suitable for hot delivery and hot charging and manufacturing method of 555 MPa-grade pipeline steel

Abstract

The 555 MPa-grade pipeline steel comprises the following components in percentage by mass: 0.040 to 0.070 percent of C, 0.10 to 0.30 percent of Si, 1.65 to 1.85 percent of Mn, 0.15 to 0.30 percent of Cr, 0.06 to 0.20 percent of Mo, 0.050 to 0.070 percent of Nb, 0.008 to 0.020 percent of Ti, 0.01 to 0.04 percent of Al, 0.001 to 0.004 percent of Ca, 0.0010 to 0.0045 percent of N, less than or equal to 0.015 percent of P, less than or equal to 0.002 percent of S and the balance of Fe and other inevitable impurities, and the conditions that 1.5 Mo + Cr + 6Nb is more than or equal to 0.65 percent and less than or equal to 0.90 percent, and Ti / N is more than or equal to 3.5 are simultaneously met. According to the method, through plate blank hot charging, precipitation of microalloy elements in the plate blank cooling process is reduced, and the grain refining effect of Nb is more efficiently played, so that the usage amount of other alloys is reduced, the alloy cost is effectively controlled, and through manufacturing process control, the potential quality problem caused by high-temperature hot charging is solved.

Description

Technical Field

[0001] The present invention relates to the field of pipeline steel, and in particular to a 555MPa grade pipeline steel suitable for hot delivery and hot loading and a manufacturing method thereof. Background Art

[0002] As the main clean fossil energy, natural gas accounts for an increasing proportion in the energy consumption structure year by year. Pipeline transportation, as the most economical and efficient way to transport natural gas over long distances, has long-term construction needs, which brings about a continuous demand for pipeline steel products. The manufacturing technology of pipeline steel also needs to continue to improve.

[0003] The steel industry is rapidly promoting extreme energy efficiency and reducing energy consumption and carbon emissions in the manufacturing process of steel products. Among them, hot delivery and hot charging technology can effectively utilize the sensible heat of continuous casting billets and reduce the energy consumption of slabs in heating furnaces. Therefore, increasing the hot charging temperature and proportion is one of the technical paths for energy conservation and efficiency improvement that has attracted much attention in the steel industry.

[0004] However, when the hot charging temperature of microalloyed steel reaches the two-phase region (Ar1~Ar3), some quality problems are prone to occur. It is mainly manifested in two aspects. First, in this temperature range, the surface of the ingot is prone to form a network of pro-eutectoid ferrite along the austenite grain boundary, and carbonitride second phase particles are precipitated to weaken the austenite grain boundary. When the slab is heated again in the furnace, the tensile stress is formed due to the α→γ phase transformation and contraction, which may cause surface cracks. On the other hand, when the two-phase region is charged into the furnace, the original cast austenite grains are coarse, and the grains of some ferrite that has undergone phase transformation and austenitized again are relatively small, resulting in the austenite grains being in a mixed crystal state. If it cannot be improved by the rolling process, the finished steel plate will show lower toughness. As a typical microalloyed high-strength steel, high-grade pipeline steel has higher quality requirements on the strength and toughness of the steel plate, and it is more necessary to adopt effective technical solutions to solve the quality risks of hot delivery and hot charging processes.

[0005] Chinese patent publication number CN109202029B discloses a "production method for preventing straightening and hot delivery cracks of micro-alloyed steel continuous casting billets". The method reduces the surface temperature of the continuous casting billets to 450°C or above by rapidly cooling the continuous casting billets before straightening the slabs; controlling the surface temperature of the billets to ≤600°C during the straightening stage; and controlling the temperature of the continuous casting billets to return to normal after straightening and before cutting. The surface temperature of the continuous casting billets after temperature return is less than the Ar3 temperature of the steel grade. This method can improve the surface quality of the continuous casting billets, but the heat loss of the slabs is large, and the effect of saving energy consumption is relatively limited.

[0006] Chinese patent publication number CN109128074B discloses "a method for producing microalloyed steel capable of hot transport and hot charging", which improves the stability of supercooled austenite by adding 0.001% to 0.004wt% of the element B, inhibits the nucleation of proeutectoid ferrite on grain boundaries, and inhibits the precipitation of carbonitrides on the interface between austenite and ferrite, thereby avoiding the formation of grain boundary-imitation ferrite and the resulting star cracking during the austenitization heating process after hot transport and hot charging of the microalloyed steel. However, the element B will reduce the low-temperature toughness of pipeline steel, and the deliberate addition of the element B is not allowed in the pipeline steel specification.

[0007] Chinese patent publication number CN115341129A discloses "a method for hot delivery and hot loading production of microalloyed low-alloy structural steel", which realizes hot loading and rolling by matching the content of Ti and Nb elements and stipulating the soaking time of the heating furnace. However, the public text does not mention a technical solution to the potential quality problems of high-temperature hot loading. Summary of the invention

[0008] The purpose of the present invention is to provide a 555MPa grade pipeline steel suitable for hot delivery and hot charging and a manufacturing method thereof. By hot charging of slabs, the precipitation of micro-alloy elements during the cooling process of the slabs is reduced, and the grain refinement effect of Nb is more efficiently exerted, thereby saving the use of other alloys, effectively controlling the alloy cost, and solving the potential quality problems caused by high-temperature hot charging through manufacturing process control.

[0009] To achieve the above object, the technical solution of the present invention is:

[0010] A 555MPa grade pipeline steel suitable for hot delivery and hot loading, the composition mass percentage of which is: C: 0.040-0.070%, Si: 0.10-0.30%, Mn: 1.65-1.85%, Cr: 0.15-0.30%, Mo: 0.06-0.20%, Nb: 0.050-0.070%, Ti: 0.008-0.020%, Al: 0.01-0.04%, Ca: 0.001-0.004%, N: 0.0010-0.0045%, P≤0.015%, S≤0.002%, the balance includes Fe and other unavoidable impurities, and the following conditions must be met at the same time: 0.65%≤1.5Mo+Cr+6Nb≤0.90%, Ti / N≥3.5.

[0011] Furthermore, the balance is Fe and other inevitable impurities.

[0012] Preferably, Mo: 0.06-0.15%.

[0013] The microstructure of the pipeline steel described in the present invention is a complex phase structure of acicular ferrite + a small amount of fine polygonal ferrite and Mao components; wherein the volume percentage of acicular ferrite is ≥75%, the average grain size is ≤8μm, and it also contains nano-scale Nb (C, N) precipitation phase, wherein the precipitated Nb content accounts for ≥40% of the total added Nb content.

[0014] Yield strength Rt of pipeline steel of the present invention 0.5 555~675MPa, tensile strength Rm is 630~750MPa, yield strength ratio Rt 0.5 / Rm≤0.93; Charpy impact energy AKV at -30℃≥250J; DWTT fracture shear area rate SA% at -20℃≥85%.

[0015] In the composition design of the 555MPa grade pipeline steel of the present invention:

[0016] C: C is the most basic strengthening element, which has the effects of solid solution strengthening and carbide precipitation strengthening, but too high C content will reduce the low temperature toughness and welding performance of steel. The present invention controls the C content to 0.040-0.070%.

[0017] Si: Si is a deoxidizing element in steel and also has a solid solution strengthening effect, but too high Si content will affect the welding performance of pipeline steel. In the present invention, the mass percentage of Si is controlled to be between 0.10 and 0.30%.

[0018] Mn: Mn is an important solid solution strengthening element and can reduce the phase transition point and refine the phase transition structure, but too high a Mn content will increase the difficulty of controlling center segregation and reduce toughness. The present invention controls the Mn content to 1.65-1.85%.

[0019] Cr: Cr can effectively improve the hardenability of steel, improve the uniformity of the structure and performance of the steel plate in the thickness direction, and improve the strength of the steel. However, it should be noted that if the Cr content in the steel is too high, the steel plate is prone to form a hard phase structure during the rapid cooling process, which is not conducive to low-temperature toughness. The present invention controls the Cr content to 0.15-0.30%.

[0020] Mo: Mo element has the function of expanding the γ phase area, which can reduce the γ→α phase transformation temperature of steel. During the cooling process of the slab, it can inhibit the formation of a reticular proeutectoid ferrite on the surface of the slab. During the cooling process of the steel plate after rolling, it can also play a role in refining the phase transformation structure. In addition, Mo element can also effectively inhibit the softening of the heat affected zone during pipeline welding. However, it should be noted that Mo element is expensive and should not be added in excess. The present invention controls the Mo content to 0.06-0.20%, preferably between 0.06-0.15%.

[0021] Nb: Nb is the most important microalloying element for grain refinement. During the rough rolling process, the solid solution Nb can pin the deformed austenite grain boundaries through the solute drag effect, hindering the growth of recrystallized austenite grains. In addition, Nb also has the effect of increasing the recrystallization temperature, which can increase the strain accumulation in the non-recrystallized zone during the finishing rolling process, and the Nb carbonitride precipitates on the deformation band of the deformed austenite, which can play a role in refining the phase transformation structure during the γ→α phase transformation process, and it also has a precipitation strengthening effect. However, it should be noted that when the Nb content in the steel is too high, it will be limited by the solubility product of C and Nb. The present invention controls the Nb content to 0.050-0.070%.

[0022] Ti: Ti has a strong binding force with N and is a strong carbonitride-forming element. TiN formed by Ti element has high thermal stability and can prevent the growth of austenite grains during slab heating and rough rolling recrystallization. In addition, Ti can effectively fix the N element and inhibit the precipitation of AlN at the austenite / ferrite grain boundary on the slab surface, thereby reducing the surface cracking tendency of the hot-charged slab. However, if the Ti content is too high, larger and more numerous Ti carbonitrides will be formed, which is not conducive to the toughness of the steel. The present invention controls the Ti content to be 0.008-0.020%.

[0023] Al: In the economical low yield ratio high strength steel described in the present invention, Al is a deoxidizing element, but if the Al content is too high, inclusions and AlN precipitates are easily formed. The present invention controls the Al content to 0.01-0.04%.

[0024] Ca: The morphology of sulfides can be controlled by micro-Ca treatment, thereby inhibiting the formation of MnS inclusions. The present invention controls the Ca content to 0.001-0.004%.

[0025] N: N element can form TiN particles with high melting point with Ti, thus inhibiting the coarsening of austenite grains during reheating. However, the N element content must be controlled at a low level to reduce the precipitation of AlN. In the present invention, the N content is controlled to be 0.0010-0.0045%.

[0026] Furthermore, the present invention also controls 0.65%≤1.5Mo+Cr+6Nb≤0.90%, because when the hot charging temperature is in the two-phase region, ferrite precipitates on the surface of the slab. After entering the heating furnace, the ferrite phase transformation shrinkage will produce tensile stress. In order to ensure that the invention steel has good high-temperature thermoplasticity and avoid surface cracks, it is necessary to control the upper limit of 1.5Mo+Cr+6Nb. At the same time, Mo, Cr, and Nb are key strengthening elements in the steel of the present invention. In order to ensure that the steel of the present invention achieves the desired high strength, its lower limit must also be controlled.

[0027] In addition, it is also necessary to control Ti / N≥3.5, so that Ti can fix N, inhibit the precipitation of AlN at the austenite / ferrite grain boundary on the slab surface, and reduce the surface cracking tendency of the hot-charged slab.

[0028] In the above relationship formula, Mo, Cr, Nb, N and Ti all represent the mass percentage of the corresponding elements.

[0029] Furthermore, among other inevitable impurities, S is easy to form MnS inclusions, which are long strips after rolling. P is an element that is easy to segregate. If the content of P and S impurity elements in steel is too high, the performance of the steel will be reduced. The present invention controls P≤0.015% and / or S≤0.002%.

[0030] The present invention also provides a method for manufacturing the 555MPa grade pipeline steel suitable for hot delivery and hot loading, which comprises the following steps:

[0031] 1) Smelting and casting

[0032] Smelting and casting into billets according to the above ingredients;

[0033] 2) Reheating

[0034] The charging temperature is 600-730℃, the reheating temperature is 1100-1170℃, and the total time in the furnace is T≥0.7H, where T is in min and H is the slab thickness in mm; the heating rate of the slab below 800℃ is ≤1.5℃ / min;

[0035] 3) Rolling

[0036] Rough rolling: control the total rough rolling reduction rate to be ≥70%, the rolling temperature of the last two passes of rough rolling to be controlled at 950-990°C, and the single pass reduction rate to be ≥18%;

[0037] Finish rolling: rolling in the non-recrystallization temperature range, the final rolling temperature is 790-840℃;

[0038] 4) Cooling

[0039] Adopting online direct quenching DQ + accelerated cooling ACC two-stage cooling,

[0040] In the online direct quenching DQ cooling section, the cooling rate is controlled at 25-35°C / s and the stop cooling temperature is 550-620°C;

[0041] Accelerated cooling ACC cooling section, control the cooling rate to 15 ~ 25 ℃ / s, stop cooling temperature 450 ~ 530 ℃.

[0042] Preferably, in step 1), continuous casting is used for casting, and in the horizontal section of continuous casting, the surface of the slab is quickly cooled by spraying water to achieve rapid cooling of the surface of the slab, and the instantaneous temperature of the slab surface at the outlet of the horizontal section of continuous casting is controlled to be ≤680°C, and then the slab is naturally heated up.

[0043] In the manufacturing method of the present invention:

[0044] In step 1), continuous casting is preferably used for casting. In the horizontal section of continuous casting, the surface of the slab is quickly cooled by spraying water to achieve rapid cooling of the surface of the slab, thereby inhibiting the formation of a network-like proeutectoid ferrite along the austenite grain boundaries due to slow cooling on the surface of the slab, and reducing the precipitation of carbonitrides along the austenite grain boundaries on the surface of the slab. The instantaneous temperature of the slab surface at the outlet of the horizontal section of continuous casting is controlled to be ≤680°C, and then the slab is naturally heated up.

[0045] In the step 2), after the continuous casting billet is cut, it is sent to the heating furnace as soon as possible for reheating of the billet, and the furnace temperature is between 600 and 730°C. During the heating process, the heating rate of the billet needs to be controlled before the billet reaches the complete austenitizing temperature. The present invention controls the heating rate of the billet below 800°C to ≤1.5°C / min, and then heats the billet to the target reheating temperature, and controls the reheating temperature to be 1100 to 1170°C.

[0046] The present invention adopts a higher hot charging temperature, which can reduce the precipitation of microalloying elements during the cooling process of the slab, so that more microalloying elements are in a solid solution state, which is conducive to more efficient use of the microalloying elements, especially the Nb element. In the subsequent rough rolling process, the Nb in the solid solution state inhibits the growth of austenite recrystallized grains through the solute drag effect, and can give full play to the role of grain refinement.

[0047] In addition, during high-temperature hot charging, the temperature of the core of the slab is higher than that of the surface layer. In the heating furnace, the temperature uniformity of the slab in the thickness direction is better than that of the cold billet charging, and it can ensure that the micro-alloy elements in the core of the slab are effectively dissolved during the heating process, and it is conducive to achieving temperature uniformity and uniformity of organizational properties in the thickness direction. However, there are some problems with high-temperature hot charging. When the charging temperature is in the two-phase region, there is a ferrite + austenite mixed structure on the surface of the slab. During the heating process, the ferrite transforms to austenite, and tensile stress is generated locally, which easily leads to surface defects. Therefore, in order to avoid surface defects, the heating rate of the slab before complete austenitization needs to be controlled. The present invention controls the heating rate of the slab below 800°C to ≤1.5°C / min.

[0048] In addition, 1.5Mo+Cr+6Nb is controlled to be ≤ 0.90% to ensure that the invention steel has good thermoplasticity when the temperature is raised in the two-phase region to avoid surface cracks. At the same time, Ti / N is controlled to be ≥ 3.5, and Ti is used to fix N to inhibit the precipitation of AlN at the austenite / ferrite grain boundary on the slab surface, thereby reducing the surface cracking tendency of the hot-charged slab.

[0049] Furthermore, the present invention controls the reheating temperature to be 1100-1170°C. To prevent the austenite grain size of the slab from being too large, the present invention adopts a lower reheating temperature as much as possible. To ensure sufficient solid solution of Nb, the reheating temperature should not be too low.

[0050] In step 3), due to the presence of a mixed structure of ferrite + austenite locally in the slab during high-temperature hot loading, after the slab is reheated and austenitized, mixed crystals exist in the austenite grains. It is necessary to achieve austenite grain refinement through sufficient recrystallization during the rough rolling process. Therefore, the total rough rolling reduction rate is controlled to be ≥70%, and the lower the recrystallization temperature, the smaller the austenite grain size after recrystallization, but it cannot be lower than the critical recrystallization temperature. In addition, in order to ensure that the rolling deformation penetrates into the core of the slab, a higher single-pass reduction rate needs to be controlled. Therefore, the present invention controls the rolling temperature of the last two passes of rough rolling to be in the range of 950-990°C, and the single-pass reduction rate is ≥18%. Furthermore, the finishing rolling is performed in the non-recrystallization zone, and the austenite accumulates strain energy storage and deformation bands through deformation, thereby increasing the nucleation rate of subsequent phase transformation. However, the deformed austenite will recover at high temperature and release the strain energy storage. Therefore, the lower the rolling temperature, the less the recovery, and the easier it is for deformation-induced ferrite to precipitate, which is beneficial for obtaining polygonal ferrite and acicular ferrite structures with fine grain sizes. At the same time, in order to promote the precipitation of Nb(C, N) induced by rolling deformation, the rolling temperature should not be too low. The present invention controls the finishing rolling temperature range to be 790-840°C.

[0051] In step 4), a two-stage cooling process of DQ (i.e., online direct quenching) + ACC (i.e., accelerated cooling) is adopted. The cooling rate of the DQ cooling stage is controlled to be a relatively fast cooling rate of 25 to 35°C / s to suppress the quasi-polygonal ferrite and pearlite structures. The ACC cooling stage is controlled to be a relatively slow cooling rate of 15 to 25°C / s to avoid continuous rapid cooling to form too many hard phase structures that are unfavorable to low-temperature toughness, and also to avoid continuous rapid cooling to suppress the precipitation of Nb. In addition, in the present invention, the ACC cooling stop temperature is controlled at 450 to 530°C, and a structure mainly composed of fine polygonal ferrite + acicular ferrite can be obtained, and a certain amount of Nb precipitation phase can be obtained.

[0052] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0053] 1. The 555MPa grade pipeline steel suitable for hot delivery and hot charging of the present invention adopts a relatively high hot charging temperature to give full play to the role of the Nb microalloying element. Different from the prior art, the present invention controls the range of the 1.5Mo+Cr+6Nb alloy element combination to obtain the desired strength while avoiding the risk of surface defects caused by high-temperature hot charging. Moreover, it does not contain precious elements such as Cu and Ni, and has good economy.

[0054] Furthermore, the microstructure of the 555MPa grade pipeline steel suitable for hot delivery and hot loading described in the present invention is a complex phase structure mainly composed of acicular ferrite, containing a small amount of fine polygonal ferrite and Mahor components, wherein the volume percentage of acicular ferrite is ≥75%, the average grain size is ≤8μm, and it also contains nanoscale Nb (C, N) precipitation phase, wherein the content of precipitated Nb accounts for ≥40% of the total added Nb content.

[0055] 2. Conventional hot delivery and hot charging processes do not have special process designs for slabs and heating systems. In order to avoid the risk of surface defects and reduced toughness caused by high-temperature hot charging, the hot charging temperature is usually controlled below 600°C.

[0056] The present invention adopts a relatively high hot charging temperature of 600-730°C, which can reduce the precipitation of micro-alloying elements during the cooling process of the slab, so that more micro-alloying elements are in a solid solution state, which is conducive to more efficient use of the micro-alloying elements. Moreover, during high-temperature hot charging, the temperature of the core of the slab is higher than that of the surface layer. In the heating furnace, the temperature uniformity in the thickness direction of the slab is better than that of the cold billet charging, and it can ensure that the micro-alloying elements in the core of the slab are effectively dissolved during the heating process. Conventional cold billet charging requires a longer insulation time for the core to reach the desired temperature. In addition, in industrial production, in order to speed up the production rhythm, when the insulation time is insufficient, the core performance of the steel plate will be poor.

[0057] 3. In order to solve the potential quality problems caused by high-temperature hot charging, especially hot charging in two-phase zone, the present invention quickly cools the surface of the slab to control the upper limit of the heating rate before the slab is fully austenitized, controls the upper limit of 1.5Mo+Cr+6Nb in composition, and uses technical means such as Ti solid N to solve the problem of surface defects. In addition, during the rolling process, with the help of higher solid solution Nb content, combined with the rough rolling temperature and reduction rate process design, the austenite is fully recrystallized and refined, and the problem of local austenite mixed crystals caused by two-phase zone charging is solved.

[0058] The present invention adopts a higher hot charging temperature, which can save energy. Furthermore, the core temperature of the slab is higher than the surface layer. After heating, the temperature uniformity of the slab in the thickness direction is better than that of the cold slab charged into the furnace. Furthermore, the precipitation of microalloying elements during the cooling process of the slab can be reduced, which is conducive to more efficient use of the microalloying elements.

[0059] In addition, the present invention controls the upper limit of the heating rate before the slab is completely austenitized by rapidly cooling the surface of the slab, solves the problem of surface defects by technical means such as Ti solidifying N in composition, and solves the problem of local austenite mixed crystals caused by loading steel in the two-phase zone through rolling process design during the rolling process. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1This is a metallographic structure photograph of the pipeline steel Example 1 of the present invention under a 500-fold microscope. DETAILED DESCRIPTION

[0061] The present invention will be further described below in conjunction with embodiments and drawings.

[0062] The composition of the pipeline steel of the embodiment of the present invention is shown in Table 1, and the remainder is Fe and other inevitable impurities except P and S. Table 2 lists the specific process parameters of the manufacturing method of the embodiment. Table 3 lists the mechanical property test results of the pipeline steel of the embodiment.

[0063] It can be seen from Table 3 that the yield strength Rt of each embodiment of the present invention is 0.5 In the range of 555~675MPa, the tensile strength Rm is in the range of 630~750MPa, and the yield strength ratio Rt 0.5 / Rm≤0.93, Charpy impact energy AKV≥250J at -30℃, DWTT fracture shear area rate SA%≥85% at -20℃, with excellent strength and toughness.

[0064] Figure 1 The metallographic structure photograph of the pipeline steel of Example 1 under a 500-fold microscope is shown. The volume percentage of acicular ferrite is 80% as determined by image analysis software, and the average grain size is 6.1 μm as measured by EBSD; in addition, the Nb content in the precipitated phase is measured by wet extraction of the precipitate and ICP (inductively coupled plasma spectrometer), and the proportion of the precipitated Nb content to the total added Nb content is measured to be 45%.

[0065] It should be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with by those skilled in the art from the contents disclosed in the present invention, and all should belong to the protection scope of the present invention.

[0066]

[0067]

[0068]

Claims

1. A 555MPa grade pipeline steel suitable for hot delivery and hot loading, wherein the composition by mass percentage is: C: 0.040-0.070%, Si: 0.10-0.30%, Mn: 1.65-1.85%, Cr: 0.15-0.30%, Mo: 0.06-0.20%, Nb: 0.050-0.070%, Ti: 0.008-0.020%, Al: 0.01-0.04%, Ca: 0.001-0.004%, N: 0.0010-0.0045%, P≤0.015%, S≤0.002%, the balance includes Fe and other unavoidable impurities, and the following conditions must be met at the same time: 0.65%≤1.5Mo+Cr+6Nb≤0.90%, Ti / N≥3.

5.

2. The 555MPa grade pipeline steel suitable for hot delivery and hot loading as claimed in claim 1, characterized in that: The balance is Fe and other inevitable impurities.

3. The 555MPa grade pipeline steel suitable for hot delivery and hot loading as claimed in claim 1 or 2, characterized in that: Mo: 0.06~0.15%.

4. The 555MPa grade pipeline steel suitable for hot delivery and hot loading as claimed in claim 1, 2 or 3, characterized in that: The microstructure of the pipeline steel is a complex phase structure of acicular ferrite + a small amount of fine polygonal ferrite and Maao components; wherein the volume percentage of acicular ferrite is ≥75%, and the average grain size is ≤8μm.

5. The 555MPa grade pipeline steel suitable for hot delivery and hot loading as claimed in claim 1, 2, 3 or 4, characterized in that: The microstructure of the pipeline steel contains nano-scale Nb (C, N) precipitated phase, wherein the proportion of the precipitated Nb content to the total added Nb content is ≥40%.

6. The 555MPa grade pipeline steel suitable for hot transport and hot loading as claimed in claim 1, 2, 3, 4 or 5, characterized in that: The yield strength Rt of the pipeline steel 0.5 The tensile strength Rm is 555-675MPa, the yield strength ratio Rt is 630-750MPa, and the 0.5 / Rm≤0.93; Charpy impact energy AKV at -30℃≥250J; DWTT fracture shear area rate SA% at -20℃≥85%.

7. The method for manufacturing 555MPa grade pipeline steel suitable for hot delivery and hot loading according to any one of claims 1 to 6, characterized in that: The steps include: 1) Smelting and casting Smelting and casting into billets according to the composition of claim 1, 2 or 3; 2) Reheating The charging temperature is 600-730℃, the reheating temperature is 1100-1170℃, and the total time in the furnace is T≥0.7H, where T is in min and H is the slab thickness in mm; the heating rate of the slab below 800℃ is ≤1.5℃ / min; 3) Rolling Rough rolling: control the total rough rolling reduction rate to be ≥70%, the rolling temperature of the last two passes of rough rolling to be controlled at 950-990°C, and the single pass reduction rate to be ≥18%; Finish rolling: rolling in the non-recrystallization temperature range, the final rolling temperature is 790-840℃; 4) Cooling Adopting online direct quenching DQ + accelerated cooling ACC two-stage cooling, In the online direct quenching DQ cooling section, the cooling rate is controlled at 25-35°C / s and the stop cooling temperature is 550-620°C; Accelerated cooling ACC cooling section, control the cooling rate to 15 ~ 25 ℃ / s, stop cooling temperature to 450 ~ 530 ℃.

8. The method for manufacturing 555MPa grade pipeline steel suitable for hot delivery and hot loading as claimed in claim 7, characterized in that: In step 1), continuous casting is used for casting. In the horizontal section of continuous casting, the surface of the slab is quickly cooled by spraying water to achieve rapid cooling of the surface of the slab. The instantaneous surface temperature of the slab at the outlet of the horizontal section of continuous casting is controlled to be ≤680°C, and then the slab is naturally heated up.

Images