Low-segregation high-purity low-carbon microalloyed steel round billet with 500mm section and continuous casting method thereof

Abstract

The invention relates to the technical field of casting of round billets for deep sea pipelines, and discloses a low-segregation high-purity low-carbon microalloyed steel 500 mm section round billet and a continuous casting method thereof.The continuous casting method comprises the following steps that smelting raw materials pass through a short-process EAF electric furnace and an LF ladle furnace, alloy materials are added for ingredient adjustment, VD furnace high-vacuum treatment is conducted, liquid molten steel enters a crystallizer, and the molten steel enters the crystallizer; low segregation and high purity of 500mm continuous casting round billets are realized by adjusting a liquid level line, a proper pulling speed, water volume of a crystallizer, vibration frequency, electromagnetic stirring of the crystallizer, water flow of a secondary cooling area, and matching of an electromagnetic stirring tail end combined with an optimal superheat degree range of low-carbon, low-manganese and low-residual alloy steel and an optimal correction value temperature control whole-flow process. And the prepared round billet can meet the requirement for manufacturing a high-dimensional-precision seamless pipeline pipe with the outer diameter of 508 mm for oil gas development and oil gas delivery under deep sea 800 m or above underwater.

Description

Technical Field

[0001] The invention relates to the technical field of casting round billets for deep-sea pipelines, and in particular to a 500mm cross-section round billet of low-segregation, high-purity, low-carbon microalloy steel and a continuous casting method thereof. Background Art

[0002] The water depth of offshore oil and gas exploration and development areas is ≤300 meters, which is called shallow water area; the water depth is 300 meters to 1500 meters, which is called deep water area; the water depth is greater than 1500 meters, which is called ultra-deep water area. In order to meet the requirements of deep and ultra-deep water exploitation, underwater oil and gas development requires pipelines with high dimensional accuracy from the perspective of safe and reliable operation. Usually, the design will consider the problem of misalignment after welding and butt joint, and will require the inner diameter dimensional accuracy of the pipe end to reach ±0.5mm or ±0.25mm or more stringent. This technical requirement can be achieved by direct rolling for small-sized products, but it can be achieved directly for 508mm outer diameter by unconventional hot rolling, and special end sizing or machining is required to achieve the accuracy. The outer diameter of 508mm is the standard outer diameter of conventional onshore pipelines, and the outer diameter or inner diameter of the pipe end is generally required to be ±1.6mm. Generally, onshore pipelines can be used in lengths of 10-13 meters without length restrictions.

[0003] However, due to the limitation of pipe-laying vessels, the length of marine line pipes needs to meet 11.7-12.7 meters, and the usual average length needs to be ≥12.1 meters. Individual short lengths caused by sampling tests can be accepted, which generally does not exceed 5% of the total. Underwater oil and gas development in deepwater and ultra-deepwater areas requires line pipes with an outer diameter of 508mm and a wall thickness of ≥25.4mm, which need to ensure high dimensional accuracy and meet the construction length requirements of marine pipelines at the same time.

[0004] To realize the production of 508mm outer diameter steel pipes, high-quality 500mm outer diameter round billets are required. The types of round billets can be produced through die casting, continuous casting, billet rolling, etc. Among them, continuous casting of round billets is the most efficient and economical production method.

[0005] The high dimensional accuracy of steel pipes requires that the continuous casting round billet has good dimensional accuracy and internal and external surface quality. The internal quality of the continuous casting round billet is usually reflected by the continuous casting macrostructure. The macrostructure can be directly seen after the round billet specimen is acid-immersed. The shrinkage or looseness in the center of the continuous casting round billet is formed by the characteristics of continuous casting and is inevitable. The ideal continuous casting macrostructure should have a lower level of looseness, segregation, shrinkage and higher cleanliness.

[0006] The existing continuous casting process for preparing round billets with large outer diameter has problems such as high porosity in the center of the round billet, low purity, and high segregation. Therefore, it is necessary to improve the existing process to prepare round billets with low segregation and high purity to meet the needs of deep-sea pipelines. Summary of the invention

[0007] In order to overcome the shortcomings of the prior art, the present invention provides a 500mm cross-section round billet of low-segregation, high-purity, low-carbon micro-alloy steel and a continuous casting method thereof, so as to prepare a 500mm cross-section round billet of low-segregation, high-purity, low-carbon micro-alloy steel, which can meet the high-quality round billet requirements of 508mm outer diameter and high dimensional accuracy seamless pipelines for underwater oil and gas development.

[0008] The present invention is implemented by the following technical solutions:

[0009] On the one hand, the present invention provides a 500mm cross-section round billet of low-segregation high-purity low-carbon microalloy steel, the chemical composition of which is as follows by mass percentage: C: 0.045-0.11wt%, Si: 0.25-0.60wt%, Mn: 1.30-1.70wt%, P: ≤0.012wt%, S: ≤0.003wt%, Al: 0.020-0.060wt%, Cr: 0.05-0.15wt%, Mo: 0.11-0.20wt%, Nb: 0.015-0.03wt%, Cu: 0.01-0.06wt%, Ni: 0.05%-0.20wt%, V: 0.025-0.05wt%, Ti:

[0010] 0.01-0.04wt%, B≤0.0005wt%, [H]≤2ppm, CEpcm:0.16-0.22wt%,

[0011] CE IIW :0.34-0.39wt%, CEpcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B, CE IIW =C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15, the remainder being Fe and inevitable impurities.

[0012] Furthermore, in the acid immersion low-magnification analysis of the 500 mm cross-section round billet of the low-segregation high-purity low-carbon microalloyed steel, subcutaneous cracks, shrinkage cavities, central looseness, and core cracks are all ≤ level 1, and there are no visible white spots, delamination, inclusions, and peeling.

[0013] Furthermore, the outer diameter tolerance of the 500mm cross-section round billet of low-segregation high-purity low-carbon microalloy steel is ±3.5mm, the ovality is ≤12.5mm, the curvature per meter should be ≤4mm, and the total curvature should be ≤0.4%L.

[0014] Furthermore, the 500 mm cross-section round billet of the low-segregation high-purity low-carbon microalloyed steel is subjected to non-metallic inclusion analysis after rolling, and the grades of coarse or fine inclusions of types A, B, C, and D are all ≤1.5, and the total of A+B+C+D is ≤4.0.

[0015] Another aspect of the present invention provides a method for continuous casting of a 500 mm cross-section round billet of low-segregation high-purity low-carbon microalloy steel, which specifically comprises the following steps:

[0016] (1) The smelting raw materials are smelted in a short-flow EAF electric furnace (90-110t / furnace) at a tapping temperature of 1620-1690°C, refined in a LF ladle furnace at a refining temperature of 1575-1665°C, alloy materials are added to adjust the composition, and then treated in a VD furnace at a high vacuum temperature of 1550-1670°C for more than 10 minutes, weakly stirred with argon for more than 30 minutes, and wire fed (Ca wire>50m / furnace, Al wire and Ti wire in appropriate amounts) to obtain liquid steel;

[0017] (2) The molten steel is continuously casted under temperature control in a LF ladle furnace, with an overheat temperature of 15-35° C., and enters a 4-6-stream crystallizer through a tundish. The liquid level line is adjusted to a casting speed of 0.20-0.65 m / min, a crystallizer water flow rate of 3500-4500 L / min, a vibration frequency of 60-100 times / min, and an amplitude of 3-4 mm; the crystallizer electromagnetic stirring frequency is 1-3 Hz, the secondary cooling zone water flow rate is 200-300 L / min, the terminal electromagnetic stirring frequency is 5-8 Hz, and the hot straightening temperature is 850-1000° C., thereby preparing a 500 mm cross-section round billet of low-segregation, high-purity, low-carbon microalloy steel;

[0018] The process of the present invention adopts the eccentric furnace bottom tapping EAF mode, uses the double-station LF ladle furnace to perform refining and adjust the appropriate molten steel composition, and then performs VD high vacuum treatment, ensures high vacuum and treatment time, argon weak stirring, and the molten steel after vacuum treatment is cast. High vacuum combined with argon weak stirring can make the composition in the molten steel more uniform, and the P, S content and other impurities are lower. The overheating temperature during casting is controlled at 15-35°C, and the crystallizer electromagnetic stirring and the end electromagnetic stirring are applied at the same time. The crystallizer electromagnetic stirring current is 130-180A, the electromagnetic stirring frequency is 1-3Hz, the end electromagnetic stirring current is 300-400A, and the end electromagnetic stirring is 5-8HZ. The end stirring current intensity is higher than the crystallizer electromagnetic stirring to achieve the lowest segregation, and finally obtain a Φ500mm cross-section round billet.

[0019] Furthermore, the superheat temperature is 15-25°C.

[0020] Furthermore, the electromagnetic stirring current of the crystallizer is 130-180A, and the end electromagnetic stirring current is 300-400A.

[0021] Furthermore, the smelting raw materials are molten iron, pig iron and high-quality scrap steel, the mass percentage of the molten iron is greater than 30%, and the alloy materials include ferrosilicon, ferromanganese, ferrovanadium, ferronickel, ferromolybdenum and ferroniobium.

[0022] Furthermore, the 500mm cross-section round billet of low-segregation high-purity low-carbon microalloyed steel is subjected to pile cooling or pit slow cooling, the pile cooling time is ≥20 hours, the pit slow cooling time is ≥48 hours, and the annular cooling cover can be opened only after the billet temperature is ≤250°C.

[0023] The advantages and positive effects of the present invention are:

[0024] The present invention simultaneously controls the content of each element and CEpcm, combines the strong and weak dual-process stirring (argon weak stirring, crystallizer electromagnetic stirring, and terminal electromagnetic stirring) in the process, controls the effective time of argon weak stirring, and the optimal superheat range of the whole process process matching to achieve low-segregation and high-purity production of 500mm continuous casting round billets, and achieves 500mm cross-section billet dimensional accuracy and excellent quality, which can meet the high-quality round billet requirements of 508mm outer diameter high dimensional accuracy seamless pipelines for underwater oil and gas development. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a macroscopic photograph of a 500 mm cross-section round billet of low-segregation, high-purity, low-carbon microalloyed steel prepared in Example 1.

[0026] Figure 2 This is a microstructure photograph of a 500 mm cross-section round billet of low-segregation, high-purity, low-carbon microalloyed steel prepared in Example 1.

[0027] Figure 3 This is the average particle size distribution diagram of 0.750 μm Al-based inclusions analyzed in situ in the 500 mm cross-section round billet prepared in Example 1.

[0028] Figure 4 This is the average particle size distribution diagram of 0.748 μm of Al-based inclusions analyzed in situ in the 500 mm cross-section round billet prepared in Example 1.

[0029] Figure 5 This is the average particle size distribution diagram of 1.023 μm of Al-based inclusions analyzed in situ in the 500 mm cross-section round billet prepared in Example 1.

[0030] Figure 6 This is the average particle size distribution diagram of 0.734 μm of Al-based inclusions analyzed in situ in the 500 mm cross-section round billet prepared in Example 1.

[0031] Figure 7 Surface photograph of a 500 mm cross-section round billet prepared in the comparative example. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described below in conjunction with embodiments so that those skilled in the art can better understand the present invention, but the present invention is not limited thereto.

[0033] Example 1

[0034] A 500mm cross-section round billet of low-segregation high-purity low-carbon microalloy steel, the composition weight percentage is: C: 0.084wt%, Si: 0.24wt%, Mn: 1.30wt%, P: 0.012wt%, S: 0.003wt%, Al: 0.023wt%, Cr: 0.12wt%, Mo: 0.11wt%, Nb: 0.024wt%, Cu: 0.06wt%, Ni: 0.12wt%, V: 0.04wt%, Ti: 0.010wt%, B: 0.0003wt%, CEpcm: 0.18wt%, CE IIW :0.37wt%, the balance is Fe and inevitable impurities.

[0035] The continuous casting method of a 500 mm cross-section round billet of low-segregation high-purity low-carbon microalloy steel comprises the following steps:

[0036] According to the above chemical composition, smelting raw materials and alloy materials were configured; 74 tons of scrap steel were added to a 100t electric furnace in two batches, and molten iron (molten iron ratio 44%) was added. After the EAF smelting process with electric heating, the smelting cycle was 47 minutes. Before tapping, the C content was 0.06%, P 0.006%, tapping temperature 1655℃, 104 tons of molten steel meeting the requirements are obtained, tapped from the eccentric furnace bottom and refined in the LF ladle furnace, the process is in place, temperature measurement and sampling, the temperature is 1613℃, high manganese iron, ferrosilicon, low manganese iron, ferromolybdenum, ferrovanadium, ferronickel, and ferroniobium raw materials are added, power is supplied to increase the temperature, the composition is adjusted, temperature measurement and sampling are taken, and after the composition meets the requirements, VD temperature measurement is 1669℃, high vacuum treatment, VD minimum vacuum degree 10Pa, time is 15min, air breaking wire feeding treatment, soft blowing argon weak stirring treatment for 40min, feeding calcium wire 190m, titanium wire 130kg, a little Al wire into the LF ladle furnace temperature control for continuous casting, control The superheat temperature is 25℃, and it enters the 4-stream crystallizer through the tundish. By adjusting the liquid level line, the pulling speed of the straightening machine is 0.5m / min, the water flow of the crystallizer is: 3944L / min in zone 1, 3831L / min in zone 2, 3905L / min in zone 3, and 3934L / min in zone 4, the vibration frequency is 80 times / min, and the amplitude is 3-4mm; the electromagnetic stirring of the crystallizer is 1Hz, the electromagnetic stirring current of the crystallizer is 130A, the water flow of the second cooling zone is 350L / min, the electromagnetic stirring at the end is 7Hz, the electromagnetic stirring current at the end is 350A, and the straightening temperature is 950℃. Finally, a 500mm cross-section round billet is obtained. The round billet is cooled by stack cooling for 24 hours. After cooling, the size is measured: the maximum outer diameter is 501mm, the minimum outer diameter is 499mm, the ovality is 2mm, the curvature per meter is 1.5mm, and the total curvature is 5mm.

[0037] The composition analysis and continuous casting acid leaching low-power analysis of the 500 mm cross-section round billet prepared in Example 1 are performed, and the analysis results are shown in Table 1. The analysis of non-metallic inclusions in the rolled steel pipe is shown in Table 2, and the dimensional accuracy of the round billet is shown in Table 3.

[0038] Example 2

[0039] A 500mm cross-section round billet of low-segregation high-purity low-carbon microalloy steel, the composition weight percentage is: C: 0.076wt%, Si 0.29wt%, Mn 1.32wt%, P: 0.009wt%, S: 0.002wt%, Al: 0.025wt%, Cr: 0.12wt%, Mo: 0.127wt%, Nb: 0.03wt%, Cu 0.04wt%, Ni: 0.17wt%, V: 0.05wt%, Ti: 0.018wt%, B: 0.0004wt%, Cepcm: 0.18wt%, CE IIW :0.37wt%, the balance being Fe and unavoidable impurities.

[0040] The continuous casting method of a 500 mm cross-section round billet of low-segregation high-purity low-carbon microalloy steel comprises the following steps:

[0041] The smelting raw materials and alloy materials are configured according to the above chemical composition; 76 tons of scrap steel are added to 100t in two batches, and molten iron (molten iron ratio is 40%) is added. After the short-process EAF electric furnace, the smelting cycle is 50min, the C content is 0.07%, P is 0.007%, the tapping temperature is 1650℃, and 105 tons of molten steel are obtained. The eccentric bottom tapping is refined in the LF ladle furnace, and the process is in place for temperature measurement and sampling, the temperature is 1561℃, high manganese iron, ferrosilicon, low manganese iron, ferromolybdenum, ferrovanadium, nickel iron and other raw materials are added, power is supplied to increase the temperature, the composition is adjusted, the temperature is measured and sampled, and VD is performed after meeting the set composition requirements, the temperature is measured at 1669℃, high vacuum treatment, VD minimum vacuum degree is 10Pa, the time is 15min, air breaking wire feeding treatment, soft blowing argon weak stirring treatment for 40min, feeding calcium wire 60m, entering the LF ladle furnace for temperature control and continuous casting , control the overheating temperature to 15℃, enter the 4-6 stream crystallizer through the tundish, adjust the liquid level line, casting speed 0.29m / min, crystallizer water flow: 4000L / min, vibration frequency 90 times / min, amplitude 3-4mm; crystallizer electromagnetic stirring 2Hz, crystallizer electromagnetic stirring current 180A, secondary cooling zone water flow 200L / min, end electromagnetic stirring 8Hz, end electromagnetic stirring current 300A, straightening temperature 930℃, straightening machine pulling speed 0.4m / min, finally get 500mm cross-section round billet. The round billet is cooled by pit slow cooling, the cooling time is 48 hours, the lifting temperature is 80℃, and the size is measured after cooling: the maximum outer diameter is 502mm, the minimum outer diameter is 498mm, the ovality is 4mm, the curvature per meter should be 1.5mm, and the total curvature is 4mm.

[0042] The 500 mm cross-section round billet prepared in Example 2 was subjected to low-power analysis by continuous casting acid leaching, and the analysis results are shown in Table 1. The analysis of non-metallic inclusions in the rolled steel pipe is shown in Table 2, and the round billet dimensional accuracy is shown in Table 3. The macroscopic photograph of the 500 mm cross-section round billet of low-segregation, high-purity, low-carbon microalloy steel prepared in Example 1 is shown in Table 2. Figure 1 As shown in the microstructure photos Figure 2 As shown, the average particle size distribution of Al inclusions of 0.750μm, 0.748μm, 1.023μm, and 0.734μm in situ analysis is shown in Figure 4-6 shown.

[0043] Example 3

[0044] A 500mm cross-section round billet of low-segregation high-purity low-carbon microalloy steel, the composition weight percentage is: C: 0.094wt%, Si 0.25wt%, Mn 1.34wt%, P: 0.012wt%, S: 0.002wt%, Al: 0.026wt%, Cr: 0.12wt%, Mo: 0.13wt%, Nb: 0.020wt%, Cu 0.06wt%, Ni: 0.16wt%, V: 0.03wt%, Ti: 0.017wt%, B: 0.0004wt%, CEpcm: 0.19wt%, CE IIW :0.39wt% The balance is Fe and inevitable impurities.

[0045] The continuous casting method of a 500 mm cross-section round billet of low-segregation high-purity low-carbon microalloy steel comprises the following steps:

[0046] According to the above chemical composition, smelting raw materials and alloy materials were configured; 80 tons of scrap steel were added in two batches in a 100t electric furnace, and molten iron (molten iron ratio 35%) was added. After the EAF smelting process with electric heating, the smelting cycle was 50min. Before tapping, the C content was 0.06%, P 0.006%, tapping temperature 1655℃, 104 tons of molten steel meeting the conditions are obtained, the eccentric bottom tapping is refined by LF ladle furnace, the process is in place and the temperature is measured and sampled, the temperature is 1597℃, high manganese iron, ferrosilicon, low manganese iron, ferromolybdenum, ferrovanadium, ferronickel, ferroniobium raw materials are added, power is supplied to increase the temperature, adjust the composition, measure the temperature and take samples, after the composition meets the requirements, VD temperature measurement is 1651℃, high vacuum treatment, VD minimum vacuum degree 10Pa, time is 15min, air breaking wire feeding treatment, soft blowing argon weak stirring treatment for 40min, feeding calcium wire 190m, titanium wire 130kg, a little Al wire into LF ladle furnace temperature control for continuous casting, control The overheating temperature is 20℃, and it enters the 4-stream crystallizer through the tundish. By adjusting the liquid level line, the pulling speed of the straightening machine is 0.5m / min, the water flow of the crystallizer is: 3944L / min in zone 1, 3831L / min in zone 2, 3905L / min in zone 3, and 3934L / min in zone 4, the vibration frequency is 80 times / min, and the amplitude is 3-4mm; the electromagnetic stirring of the crystallizer is 3Hz, the electromagnetic stirring current of the crystallizer is 150A, the water flow of the second cooling zone is 300L / min, the electromagnetic stirring at the end is 5Hz, the electromagnetic stirring current at the end is 400A, and the straightening temperature is 950℃. Finally, a 500mm cross-section round billet is obtained. The round billet is cooled by pit slow cooling, the cooling time is 48 hours, the lifting temperature is 80℃, and the size is measured after cooling: the maximum outer diameter is 501mm, the minimum outer diameter is 498mm, the ovality is 3mm, the curvature per meter should be 2mm, and the total curvature is 6mm.

[0047] The results of low-power analysis of continuous casting acid leaching of the 500 mm cross-section round billet prepared in Example 3 are shown in Table 1. The analysis of non-metallic inclusions in the rolled steel pipe is shown in Table 2, and the dimensional accuracy of the round billet is shown in Table 3.

[0048] Comparative Example

[0049] The chemical composition of the comparative example is the same as that of Example 3. The production is carried out during the process exploration. The smelting raw materials and alloy materials are configured according to the chemical composition of the above Example 3; 80 tons of scrap steel are added to a 100t electric furnace in two batches, and molten iron (molten iron ratio is 35%) is added. After the EAF smelting process is powered on and heated, the smelting cycle is 50min, and the C content is 0.06% and P0.006% are sampled and analyzed before tapping. The tapping temperature is 1654°C, and 104 tons of molten steel that meets the conditions are obtained. The eccentric bottom tapping is refined by the LF ladle furnace, and the process is in place and the temperature is measured and sampled. The temperature is 1598°C. High manganese iron, ferrosilicon, low manganese iron, ferromolybdenum, ferrovanadium, ferronickel, and ferroniobium raw materials are added, and the power is sent to heat up, the composition is adjusted, and the temperature is measured and sampled. After the composition meets the requirements, VD temperature measurement is 1652°C, high vacuum treatment, VD minimum vacuum degree 10Pa, time is 10min, breaking wire feeding treatment, soft blowing argon weak stirring treatment for 20min, feeding 120m of calcium wire, 130kg of titanium wire, and a little Al wire into the LF ladle furnace for temperature control for continuous casting, controlling the overheating temperature to 60℃, passing through the tundish and entering the 4-stream crystallizer, by adjusting the liquid level line, the pulling speed of the straightening machine is 0.5m / min, the water flow rate of the crystallizer: 3942L / min in zone 1, 3834L / min in zone 2, 3906L / min in zone 3, and 3931L / min in zone 4, the vibration frequency is 80 times / min, and the amplitude is 3-4mm; the electromagnetic stirring of the crystallizer is 3Hz, the electromagnetic stirring current of the crystallizer is 150A, the water flow rate of the second cooling zone is 190L / min, the electromagnetic stirring at the end is 5Hz, the electromagnetic stirring current at the end is 400A, the straightening temperature is 800℃, and finally a 500mm cross-section round billet is obtained. The round billet is cooled by stack cooling, and the dimensions are measured after cooling: the maximum outer diameter is 503mm, the minimum outer diameter is 497mm, the ovality is 4mm, the curvature per meter should be 5mm, and the total curvature is 10mm. Comparative Example Because the straightening temperature is too low, there are micro cracks on the surface of the billet, see Figure 4 .

[0050] The results of low-power analysis of continuous casting acid leaching of 500 mm cross-section round billets prepared in the comparative example are shown in Table 1. The analysis of non-metallic inclusions in the rolled steel pipe is shown in Table 2, and the size accuracy of the round billet is shown in Table 3. The comparative example has obvious differences from the product in this article in key indicators such as high vacuum control, weak stirring time and superheat. The surface photos are shown in Table 1. Figure 7 As shown, cracks can be seen on the surface.

[0051] Table 1 Statistical table of macrostructure analysis results of round billets with a cross section of 500 mm

[0052]

[0053] Table 2 Analysis of non-metallic inclusions after rolling of round billet with 500mm section

[0054]

[0055] Table 3 Dimensional accuracy of round billets

[0056] Parameter name Outside diameter tolerance mm Ovality mm Curvature per meter (mm) Total curvature mm Example 1 2 2 1.5 5 Example 2 4 4 1.5 4 Example 3 3 3 2 6 Comparative Example 6 4 5 10

[0057] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept, which all belong to the protection scope of the present invention.

Claims

1. A 500mm cross-section round billet of low-segregation, high-purity, low-carbon microalloyed steel, characterized in that: The chemical composition is calculated by mass percentage: C: 0.045-0.11wt%, Si: 0.25-0.60wt%, Mn: 1.30-1.70wt%, P: ≤0.012wt%, S: ≤0.003wt%, Al: 0.020-0.060wt%, Cr: 0.05-0.15wt%, Mo: 0.11-0.20wt%, Nb: 0.015-0.03wt%, Cu: 0.01-0.06wt%, Ni: 0.05%-0.20wt%, V: 0.025-0.05wt%, Ti: 0.01-0.04wt%, B≤0.0005wt%, [H]≤2ppm, Cepcm: 0.16-0.22wt%, C IIW :0.34-0.39wt%, CEpcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B, CE IIW =C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15, the remainder being Fe and inevitable impurities.

2. The low-segregation, high-purity, low-carbon microalloyed steel 500 mm cross-section round billet according to claim 1, characterized in that: In the low-magnification analysis of acid immersion, subcutaneous cracks, shrinkage cavities, central looseness, and core cracks were all ≤ level 1, and there were no visible white spots, delamination, inclusions, or peeling.

3. The low-segregation, high-purity, low-carbon microalloyed steel 500 mm cross-section round billet according to claim 1, characterized in that: The outer diameter tolerance of the 500mm cross-section round billet of low-segregation high-purity low-carbon micro-alloy steel is ±3.0mm, the ovality is ≤12.5mm, the curvature per meter is ≤4mm, and the total curvature is ≤0.4%L.

4. The continuous casting method according to claim 1, characterized in that: In the 500 mm cross-section round billet of the low-segregation high-purity low-carbon microalloy steel, the grades of coarse or fine inclusions of types A, B, C, and D are all ≤1.5, and the total of A+B+C+D is ≤4.

0.

5. The continuous casting method of 500 mm cross-section round billet of low-segregation high-purity low-carbon microalloyed steel according to any one of claims 1 to 4, characterized in that: The steps include: (1) The smelting raw materials are smelted in a short-process EAF electric furnace with a tapping temperature of 1620-1690°C, refined in a double-station LF ladle furnace with a refining temperature of 1575-1665°C, and alloy materials are added to adjust the composition. Then, the raw materials are treated in a VD furnace at a high vacuum temperature of 1550-1670°C for more than 10 minutes, weakly stirred with argon for more than 30 minutes, and aluminum wire, calcium wire, and titanium wire are fed to obtain liquid steel. (2) The molten steel is continuously cast in a LF ladle furnace under controlled temperature, with an overheat temperature of 15-35°C, and enters a 4-6-stream crystallizer through a tundish. The liquid level line is adjusted to a casting speed of 0.20-0.65 m / min, a water flow rate of 3500-4500 L / min in the crystallizer, a vibration frequency of 60-100 times / min, and an amplitude of 3-4 mm; the electromagnetic stirring frequency of the crystallizer is 1-3 Hz, the water flow rate in the secondary cooling zone is 200-300 L / min, the terminal electromagnetic stirring frequency is 5-8 Hz, and the hot straightening temperature is 850-1000°C, thereby preparing a 500 mm cross-section round billet of low-segregation, high-purity, low-carbon microalloy steel.

6. The continuous casting method according to claim 5, characterized in that: The superheat temperature is 15-25°C.

7. The continuous casting method according to claim 5, characterized in that: The current of the electromagnetic stirring of the crystallizer is 130-180A, and the current of the electromagnetic stirring of the end is 300-400A.

8. The continuous casting method according to claim 5, characterized in that: The smelting raw materials include molten iron, pig iron and scrap steel, and the alloy materials include ferrosilicon, ferromanganese, ferrovanadium, ferronickel, ferromolybdenum and ferroniobium.

9. The continuous casting method according to claim 5, characterized in that: The 500mm cross-section round billet of low-segregation high-purity low-carbon microalloy steel is pile-cooled or pit-slow-cooled, the pile-cooling time is ≥20 hours, the pit-slow-cooling time is ≥48 hours, and the annular cooling cover can be opened only after the billet temperature is ≤250°C.

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