Economical ultralow-temperature high-strength dynamic tearing resistance pipeline steel and production method thereof

Abstract

The invention belongs to the technical field of metal material preparation, and particularly relates to economical ultralow-temperature high-strength dynamic tearing resistance pipeline steel and a production method thereof. According to the method, the high-performance ultralow-temperature high-strength pipeline steel with the dynamic tearing resistance is manufactured through the production process of molten iron pretreatment, converter smelting, external refining, continuous casting, heating, hot continuous rolling, controlled cooling and coiling, and the component design adopts the composite component design of low C, medium Mn, micro Nb and micro high Ti and Cr; a rolling unit simultaneously adopts a novel rolling process for increasing the thickness of an intermediate billet and moving the large pressure backwards, the thickness of the intermediate billet is controlled to be 62-68 mm, the laminar cooling rate is accurately controlled to be 18-25 DEG C / s, the structure is achieved through a granular bainite and M / A component composite structure, all performance indexes of the pipeline steel are qualified, and meanwhile the production cost is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal material preparation, and particularly relates to an economic ultra-low-temperature high-strength dynamic tear resistance pipeline steel and a production method thereof. BACKGROUND

[0002] The ultra-low-temperature high-strength dynamic tear resistance pipeline steel is mainly used in the domestic and foreign pipeline network pipeline construction industry for oil and gas transportation, and with the development needs of the energy strategies of various countries in the world, the environment of pipeline laying areas is harsh. The ultra-low-temperature toughness pipeline steel can maintain good toughness and strength in such an ultra-low-temperature environment, effectively prevents brittle fracture caused by low temperature, and ensures the safe and stable operation of long-distance oil and gas transportation pipelines. The dynamic tear resistance DWTT is a key evaluation index. The ultra-low-temperature dynamic tear resistance pipeline steel is a special working environment ultra-low-temperature high-toughness pipeline steel, has the characteristics of maintaining good toughness and strength in an ultra-low-temperature environment, and therefore has important applications in many fields.

[0003] The traditional process design method of such a pipeline steel is to design a low-carbon composition with a large amount of addition of niobium, molybdenum and nickel precious alloy elements. The alloy cost is greatly increased. The process is controlled in the entry finish rolling temperature, the steel is treated in the intermediate section between rough rolling and finish rolling, and the austenite phase transformation temperature is controlled. The traditional rolling process reduces the rolling efficiency, causes high process cost, and has large energy consumption, which does not meet the requirements of green, low-carbon and low-energy industry development, and the product market competitiveness is not strong.

[0004] The application adopts a production process of "hot metal pretreatment (DS) → converter smelting (LD) → secondary refining (LF+RH) → continuous casting (CC) → heating → hot continuous rolling → controlled cooling → coiling", and outputs an economic new type of ultra-low-temperature high-strength dynamic tear resistance pipeline steel to meet the requirements of mechanical properties, ultra-low-temperature toughness properties, welding properties and user use. SUMMARY

[0005] The application aims to provide an economic ultra-low-temperature high-strength dynamic tear resistance pipeline steel and a production method thereof. The method adopts a production process of "hot metal pretreatment (DS) → converter smelting (LD) → secondary refining (LF+RH) → continuous casting (CC) → heating → hot continuous rolling → controlled cooling → coiling" to produce and manufacture a high-performance ultra-low-temperature high-strength dynamic tear resistance pipeline steel. The yield strength is greater than or equal to 520 Mpa, the tensile strength is greater than or equal to 620 Mpa, the elongation A is greater than or equal to 42, the impact energy value at-80 DEG C is greater than or equal to 260 J, and the shear area single value of DWTT at-80 DEG C is greater than or equal to 82% and the average value is greater than or equal to 85%. 50 In order to achieve the above purpose, the application adopts the following technical scheme:

[0006] An economical ultra-low temperature high-strength dynamic tearing resistance pipeline steel, the chemical components in the steel are as follows in percentage by weight: C: 0.040%-0.080%, Si: 0.15%-0.35%, Mn: 1.55%-1.80%, P: ≤0.010%, S: ≤0.010%, Ti: 0.030%-0.045%, Ca: ≤0.0015%, Al: ≤0.040%, Nb: 0.035%-0.055%, Cr: 0.15%-0.35%, N: ≤0.0040%, O: ≤0.0020%, and the balance is Fe and inevitable impurities.

[0007] The component design reasons of the application are as follows:

[0008] C: The C content has a great influence on the strength, toughness and plasticity of the steel and its structure, and should not be too high. If the C content is too high, the plasticity will rapidly decrease, and the C content in the application is controlled to be ≤0.080%.

[0009] Si: Adding a certain amount of Si can make the weld metal calm, accelerate the deoxidation process of the molten pool metal, ensure the compactness of the weld, and also improve the strength of the weld. However, excessive Si content is easy to form silicate inclusions and also easy to cause silicon cracking. The Si content in the application is controlled to be ≤0.35%.

[0010] Mn: Mn can refine the grains, improve the low-temperature impact toughness, and has a deoxidation and desulfurization effect, and the addition of Mn ensures the strength lost due to the decrease of carbon. The Mn content is controlled to be 1.55%-1.80%.

[0011] P and S: P and S are harmful elements, and their contents are controlled to improve the purity, and thus are required to reach a low level. The P content is ≤0.010%, and the S content is ≤0.010%.

[0012] Ti: Ti can combine with N and C to form TiN and TiC particles as crystal nuclei to prevent the growth of austenite grains and refine the austenite grains in the rolling process. Ti alloy makes the grains refined and reduces the cost, and also utilizes the fine-grain strengthening and precipitation strengthening to greatly improve the strength. Large TiC and TiN particles will reduce the toughness. The rolling process must be increased in the amount of reduction in the finishing mill train, and the TiC and TiN particles make the grain size finer and more uniform. The Ti content in the design process of the application is 0.030-0.045%.

[0013] Nb: Refine the grain, niobium can form very stable compounds with carbon, nitrogen and other elements in steel, such as niobium carbide (NbC), niobium nitride (NbN). In the process of solidification and heating of steel, these compounds will be dispersed in the form of fine particles, prevent the growth of austenite grains. When the steel cools, undissolved NbC, NbN particles will become new nucleation core, make ferrite grain further refinement. Significant grain refinement, the total area of grain boundary increases, the resistance to dislocation movement increases, thereby improving the strength and toughness of steel. Refinement of grain can effectively improve the anisotropy of steel, so that the steel has more uniform performance in different directions. Precipitation strengthening, in the process of heating and rolling, a part of niobium will dissolve in austenite, in the subsequent cooling process, supersaturated niobium will be precipitated from the solid solution in the form of fine carbide or nitride. These precipitates will interact with dislocations, hinder the slip of dislocations, thereby producing precipitation strengthening effect. Effectively improve the strength and hardness of steel, while the toughness of steel is less affected. By controlling the content and precipitation behavior of niobium, the strength of the steel can be significantly improved while ensuring the toughness of the steel, meeting the requirements of low temperature dynamic tear resistant pipeline steel for high strength. Fine grain and uniform distribution of precipitates can effectively prevent the initiation and propagation of cracks. In low temperature environment, fine grain and dispersed precipitates can reduce the tendency of brittle fracture, improve the toughness of steel. In addition, niobium can also reduce the ductile-to-brittle transition temperature of steel, so that the steel can maintain good toughness at low temperature. In low temperature environment, the steel can still withstand dynamic tearing load without brittle fracture, ensuring the safe operation of the pipeline under low temperature working conditions. Fine grain and uniform structure can reduce stress concentration and reduce the possibility of fatigue crack initiation. At the same time, the existence of precipitation strengthening and precipitates can improve the strength of the steel, so that the steel can better resist the propagation of fatigue cracks when subjected to alternating load. Improve the fatigue resistance of steel, prolong the service life of pipeline steel, reduce accidents caused by fatigue failure. In the welding process, niobium can inhibit the growth of grains in the heat affected zone, reduce the hardness of the heat affected zone, and improve the toughness of the heat affected zone. This is because niobium can form stable carbides and nitrides at high temperatures, which can hinder grain growth and reduce the segregation of harmful elements in the heat affected zone. Improve the performance of the welding heat affected zone, so that the welded joint has similar comprehensive performance to the base material, ensuring the overall quality and reliability of the pipeline steel after welding. Nb content control in: 0.035%~0.055%.

[0014] Al: Too high aluminum content in molten steel is easy to react with oxygen in the air to form Al2O3, continuous casting is easy to flocculation; Al and O have strong affinity during welding, which reduces the oxygen partial pressure and increases the hydrogen partial pressure in the welding pool, causing the generation of hydrogen pores. Aluminum as a harmful element is strictly controlled Al≤0.040%.

[0015] Cr: Cr element plays an important role in high-strength ultra-low-temperature pipeline steel, including improving strength and hardness, enhancing oxidation resistance and corrosion resistance, and improving welding performance. Through reasonable alloy composition design and process optimization, the performance of high-strength ultra-low-temperature pipeline steel can be effectively improved to meet the application requirements in various complex environments. It should be controlled at 0.15% to 0.35% during the design process.

[0016] Ca: Control inclusion morphology, calcium can combine with sulfur in steel to form low melting point and plastic CaS inclusions, replacing hard and brittle MnO, FeS inclusions. This significantly improves the morphology and distribution of inclusions, changes the inclusions from sharp edges and corners to spherical shape, reduces the adverse effects of inclusions on the strength, toughness and especially fatigue performance of the steel, and improves the safety of the pipeline steel under alternating load. Calcium can also change the morphology of alumina inclusions, making them change from coarse blocky or flaky to fine and dispersed granular, thereby reducing the harm of alumina inclusions to steel performance. Improve the fluidity of molten steel; calcium can reduce the surface tension of molten steel and increase its fluidity, which is beneficial to the pouring and filling of molten steel during continuous casting, reduces the blocking phenomenon during casting, and improves the quality and production efficiency of continuous casting billets. Calcium can inhibit the growth of austenite grains in steel and refine the grain structure. Fine-grain strengthening can simultaneously improve the strength and toughness of the steel, so that the pipeline steel has better low-temperature toughness and anti-brittle fracture ability while ensuring strength. Desulfurization, calcium has strong affinity with sulfur, which can effectively remove sulfur in steel during steelmaking. Low sulfur content helps to improve the toughness, weldability and corrosion resistance of the steel, meeting the requirements of pipeline steel in different service environments.

[0017] The yield strength of the pipeline steel is ≥520Mpa, the tensile strength is ≥620Mpa; the elongation A 50 ≥42, -80℃ impact energy value ≥260J, -80℃ DWTT shear area single value ≥82%, average value ≥85%; and with sufficient excess amount, better strength requirements and ultra-low-temperature toughness, the steel plate hardness HV10 ≤260, hardness uniformity.

[0018] The grain size of the pipeline steel is 11-14 grade, and the microstructure is granular bainite + elliptical island M / A composite structure.

[0019] An economical ultra-low-temperature high-strength dynamic tear-resistant pipeline steel production method, including hot metal pretreatment (DS) → converter smelting (LD) → refining (LF+RH) → continuous casting (CC) → heating → hot continuous rolling → controlled cooling → coiling, the specific method comprising:

[0020] 1) The molten iron pretreatment desulfurization control[S]≤0.0030%; the refining adopts RH vacuum degassing and LF furnace double station; the converter smelting molten iron accounts for 85%~88%, scrap steel accounts for 12%~15%, and the tapping temperature is 1580~1650℃.

[0021] By a specific desulfurization process, the content of sulfur element in the molten iron is reduced. Sulfur element can seriously affect the hot working performance and welding performance of steel, and reducing the content of sulfur can effectively improve the toughness, crack resistance and other performances of steel, so that the pipeline steel can still maintain good performance in ultra-low temperature environment, meet the requirements of high strength and dynamic tear resistance. RH vacuum degassing can effectively remove hydrogen, nitrogen and other gas impurities in the molten steel, and LF furnace can further adjust the chemical composition and temperature of the molten steel, and carry out operations such as deoxidation, desulfurization, fine adjustment of alloy composition, etc. Reducing gas impurities and accurately controlling the chemical composition can help to improve the purity and uniformity of the steel, thereby improving the strength, toughness and fatigue resistance of the steel, and ensuring the reliability of the pipeline steel under complex working conditions, the molten iron pretreatment desulfurization control[S]≤0.0030%.

[0022] 2) The liquidus temperature of the tundish is controlled at 1550~1580℃, and liquid core light pressing down is adopted, the center C segregation of the casting blank is controlled to be less than 1.0 level, and the whole process adopts protective pouring, and the tundish superheat is controlled to be ΔT≤25℃;

[0023] Controlling the liquidus temperature of the tundish in the appropriate range is beneficial to the stable solidification process of the molten steel. Liquid core light pressing down can reduce the porosity and segregation in the center area of the casting blank. Protective pouring can prevent the secondary oxidation of the molten steel and avoid the generation of inclusions. Controlling the tundish superheat can reduce the stress concentration in the casting blank. Reducing the center segregation of the casting blank improves the quality of the casting blank, and further improves the internal organizational uniformity of the steel, enhances the strength and toughness of the steel, and ensures the performance stability of the pipeline steel under ultra-low temperature.

[0024] 3) The continuous casting is thick to 190mm~230mm of casting blank, and the casting blank reheating adopts offline cleaning of corner cracks and then cold charging into the furnace;

[0025] The appropriate casting blank thickness range is determined to meet the requirements of the subsequent rolling process. Offline cleaning of corner cracks can avoid the expansion of cracks in the subsequent processing process, which affects the quality of the steel. Cold charging into the furnace can reduce the thermal stress on the surface of the casting blank, and prevent the generation of new cracks. Ensuring the quality of the casting blank provides good billet for subsequent rolling, ensures the smooth progress of the rolling process, improves the yield and performance quality of the steel.

[0026] 4) The casting blank is heated in the heating furnace for 3.5~4.5 hours, the casting blank discharge temperature is controlled at 1180~1250℃, and the alloy elements in the casting blank are fully dissolved;

[0027] Heating in a certain time and temperature range, promotes the alloying elements in the casting blank to uniformly dissolve in the matrix to form a solid solution, so that the steel material obtains good comprehensive performance, improves the strength, toughness and processing performance, and meets the performance requirements of the pipeline steel in the aspect of ultra-low temperature high strength dynamic tear resistance.

[0028] 5) The hot continuous rolling: rough rolling and finish rolling are carried out in a hot continuous rolling unit, the intermediate blank thickness before entering the finish rolling is 62-68mm; the finish rolling opening rolling temperature is 930-980 DEG C, the finish rolling temperature is controlled at 790-850 DEG C, and the finished product thickness after finish rolling is 20-25mm;

[0029] The reasonable process parameter setting of the rough rolling and the finish rolling can make the casting blank gradually deform to the target thickness, and the controlled rolling temperature can affect the recrystallization process and the grain size of the steel material. Through the controlled rolling process, the grain is refined, the strength and toughness of the steel material are improved, the required finished product thickness and performance index are obtained, and the use performance of the pipeline steel is met.

[0030] 6) The steel plate after the finish rolling is subjected to continuous laminar cooling, the cooling speed is controlled at 18-25 DEG C / s, and the coiling temperature of the cooled steel plate is at 480-550 DEG C.

[0031] The continuous laminar cooling can realize uniform and rapid cooling, and the cooling speed and the coiling temperature can change the organization form of the steel material. The organization beneficial to improving the strength and toughness of the steel material is formed, the granular bainite is presented in the organization, and the ultra-low temperature high strength dynamic tear resistance of the pipeline steel is further improved.

[0032] The above technical parameters cooperate with each other and jointly act on the production process of the pipeline steel. From the hot metal pretreatment, the impurities such as sulfur content are strictly controlled to provide a pure molten steel basis for subsequent processes. The molten steel quality is further improved in the refining link, the gas and impurities are reduced, and the composition is accurately adjusted. In the continuous casting process, the liquidus temperature is controlled, and measures such as liquid core light pressing down are adopted to improve the internal quality of the casting blank. In the casting blank heating and rolling link, the steel material obtains good organization performance through reasonable temperature control and process parameters. Finally, through the cooling and coiling process, the required final organization structure is formed, so that the technical effect of the ultra-low temperature high strength dynamic tear resistance of the pipeline steel is realized. The whole production process is closely linked, the control of each parameter has an important influence on the final steel performance, and the economic type ultra-low temperature high strength dynamic tear resistance pipeline steel meeting the use requirements is jointly ensured.

[0033] Compared with the prior art, the beneficial effects of the present application are:

[0034] An economical ultra-low temperature high strength dynamic tear resistance pipeline steel and its production method, the method adopts a production process of "hot metal pretreatment (DS) -> converter smelting (LD) -> secondary refining (LF+RH) -> continuous casting (CC) -> heating -> hot continuous rolling -> controlled cooling -> coiling" to produce high-performance ultra-low temperature high strength dynamic tear resistance pipeline steel, the yield strength is greater than or equal to 520Mpa, the tensile strength is greater than or equal to 620Mpa, the elongation A 50 ≥42, the impact energy at -80 DEG C is greater than or equal to 260J, the DWTT shear area at -80 DEG C is greater than or equal to 82% and the average value is greater than or equal to 85%. The end user can use the steel in a severe low temperature environment. The component design adopts a new economical component design of "low C+medium Mn+micro Nb, micro high Ti and Cr", the rolling unit adopts a new rolling process of increasing the thickness of the intermediate blank and moving the large pressure force backward, the laminar cooling rate is accurately controlled at 18-25 DEG C / s to realize the composite structure of granular bainite+M / A group elements, the performance indexes of the ultra-low temperature dynamic tear resistance pipeline steel are qualified, and the production cost of the high strength ultra-low temperature pipeline steel is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is the process flow chart of the 2300mm hot rolling production line of the present application.

[0036] Figure 1 M: 1, hot metal desulfurization; 2, converter; 3, LF furnace refining; 4, RH furnace refining; 5, continuous casting; 6, casting blank; 7, heating furnace; 8, hot rolling mill; 9, holding cover; 10, finishing mill; 11, laminar cooling; 12, coiler.

[0037] Figure 2 is the microstructure diagram of the thickness direction edge of example 1 of the present application.

[0038] Figure 3 is the microstructure diagram of the 1 / 4 place of the thickness direction of example 1 of the present application.

[0039] Figure 4 is the microstructure diagram of the center of the thickness direction of example 1 of the present application.

[0040] Figure 5 is the Vickers hardness test position diagram of the example of the present application. DETAILED DESCRIPTION

[0041] The specific embodiments of the present application are further described below in combination with examples.

[0042] In order to guarantee the quality of the ultra-low temperature high-strength dynamic tear resistance pipeline steel casting blank, the present application controls the carbon center segregation, the casting blank center porosity or shrinkage hole and other defects through the effective measures such as the molten steel superheat, the blank pulling speed, the continuous casting crystallizer electromagnetic stirring and the terminal electromagnetic stirring. The practical production steps of the ultra-low temperature high-strength dynamic tear resistance pipeline steel manufactured by the technical scheme of the present application are as follows:

[0043] 1, KR hot metal pretreatment: the hot metal pretreatment desulfurization and slagging are carried out on the charging hot metal, after the desulfurization treatment of the charging hot metal, the [S] of the charging converter is ensured to be ≤0.0030%, and the thickness of the top slag after the hot metal slagging is ≤20mm. The scrap steel is the refined scrap steel, and the charging amount of S, P and other impurity elements in the scrap steel is strictly controlled. The active high-quality lime is used for the molten steel smelting.

[0044] 2, converter smelting: the hot metal accounts for about 85% to 88%, the scrap steel accounts for about 12% to 15%, and the scrap steel is prohibited to add desulfurization slag steel. The Cr iron 7.3-7.8 kg / t steel is added into the top and bottom combined blowing converter for smelting, the tapping temperature is 1580-1650℃, the tapping endpoint C is ≤0.045%, P is ≤0.006%, and the slagging is strictly prohibited: the point blowing is avoided. The endpoint carbon content and temperature are ensured to be hit once, and the secondary point blowing is carried out.

[0045] 3, ladle alloying: the low aluminum silicon iron and low carbon manganese iron are used for alloying, and the argon blowing time is ≥8min. The auxiliary materials lime 17.5-18.0kg / t steel, limestone 49-50kg / t steel, dolomite 15-16kg / t steel, sintered ore 23.5-24.5kg / t steel; the target amount of alloy added per ton of steel: low aluminum silicon iron 2.3-2.4kg / t steel, low carbon manganese iron 19.2-20.2kg / t steel.

[0046] 4, static argon blowing: the argon blowing time is ≥5 minutes, the middle blowing is carried out first for 2 minutes, and then the weak blowing is carried out; the temperature after the treatment is 1570℃-1585℃.

[0047] 5. LF furnace refining: maintain a slight positive pressure of 40-70 kPa in the furnace, adopt submerged arc heating, and the arc light does not leak out. Add active lime 6.3-6.5 kg / t of steel, fluorite 0.65-0.70 kg / t of steel, carbide slag 0.70-0.75 kg / t, and silicon iron powder 0.83-0.85 kg / t of steel, use silicon iron powder and carbide to diffuse deoxidize in the slag, and make a reducing slag. Fine-tune the silicon and manganese alloy after deoxidization is completed, add low-aluminum silicon iron 1.15-1.25 kg / t of steel, and low-carbon manganese iron 3.5-3.7 kg / t of steel. Titanium alloying is completed after the white slag is formed for more than 15 minutes and the power supply is completed, add titanium iron cored wire (wire feeding speed 4.5 m / s), after titanium alloying (100 m of titanium wire remains, and 20-30 m of pure calcium wire is added at the same time), the soft blowing time is ≥15 min. The LF furnace off-site temperature is 1590-1610 °C.

[0048] 6. RH furnace refining: vacuum degree: 67 Pa (primary pump starts) → 200 Pa (maintained for 10 minutes) lifting gas flow: argon flow 1.2-1.5 Nm 3 / min, circulation times ≥5 times, add FeNb (0.08%) and FeCr (0.04%) in batches, the composition fluctuation control is ±0.005%, and CaSi wire (1.2 m / t) is fed at the same time, modify the Al2O3 inclusions into 12CaO·7Al2O3 low melting point phase, the soft blowing argon time is ≥15 minutes, promote the further floating of inclusions, and the molten steel superheat before casting is controlled: ΔT≤25 °C.

[0049] 7. Continuous casting: adopt the whole process protection casting process and clean the tundish with argon before casting starts, the blowing time is ≥2 min. The electromagnetic stirring current of the crystallizer is 250 A, the frequency is 3 Hz, continuous, the electromagnetic stirring current of the end is 320 A, the frequency is 8 Hz, and the alternating. The crystallizer protection slag uses a special protection slag containing titanium. The superheat is kept ΔT≤25 °C, the casting speed is 1.0-1.2 m / min, the constant casting speed, and the liquid level fluctuation is reduced.

[0050] 8. Heating process: improve the heating temperature and prolong the soaking time in the soaking section. The soaking time in the soaking section is guaranteed to be more than 50 minutes, the cast blank is heated in the heating furnace for 3.5-4.5 hours, the cast blank out-of-furnace temperature is controlled to be 1180-1250 °C, the alloying elements in the cast blank are fully solid-solubilized, the alloying elements are fully melted in, the high-strength steel has good plasticity and good plate shape during rolling, and the rolling process requirements are met.

[0051] 9. Rolling process: slab thickness 230 mm, rough rolling mode: 0+7; rough rolling last pass temperature control requirements are as follows: the 7th pass steel temperature ≤960℃, after the 7th pass rolling, immediately enter the finishing rolling unit for rolling; R2 the 6th pass deformation amount ≥20%, the 7th pass deformation amount ≥25%; the intermediate billet thickness before entering the finishing rolling is 62-68 mm; the finishing rolling opening rolling temperature is 930-980℃, the finishing rolling outlet temperature is 790-850℃; the precise control coiling temperature is 480-550℃, and the cooling rate is controlled at 18-25℃ / s.

[0052] The chemical composition of the examples is shown in Table 1; the main process parameters of the examples are shown in Table 2; the low-magnification defect inspection results of the cast slabs of the examples are shown in Table 3; the mechanical properties of the examples are shown in Table 4; the bending test (test temperature -80℃) of the examples is shown in Table 5; the Charpy impact test results of the examples are shown in Table 6; the drop weight tear test of the examples is shown in Table 7; the Vickers hardness test position is shown in Table 8; the metallographic structure analysis of the examples is shown in Table 9. Figure 5 The experimental results are shown in Table 8; the metallographic structure analysis of the examples is shown in Table 9.

[0053] Table 1 Chemical composition design of examples (%)

[0054] C Si Mn P S Cr Ti Nb Ca Al O N 1 0.062 0.23 1.53 0.007 0.003 0.32 0.039 0.042 0.0012 0.028 0.0020 0.0022 2 0.070 0.16 1.74 0.008 0.002 0.17 0.032 0.048 0.0009 0.034 0.0015 0.0028 3 0.077 0.33 1.62 0.008 0.002 0.22 0.038 0.053 0.0010 0.032 0.0022 0.0025 4 0.068 0.30 1.65 0.008 0.003 0.26 0.042 0.040 0.0014 0.025 0.0018 0.0029 5 0.043 0.28 1.56 0.009 0.005 0.29 0.034 0.037 0.0013 0.030 0.0020 0.0030

[0055] Table 2 Main process parameters of examples

[0056]

[0057]

[0058] Table 3 Low-magnification defect inspection results of cast slabs of examples

[0059] Serial number center porosity center segregation shrinkage cavity corner crack edge crack intermediate crack center crack subsurface bubble non-metallic inclusion 1 0.5 0.5 1.0 0.5 0.5 0.5 0.5 0.5 0.5 2 0.5 0.5 0.5 0.5 0.5 1.0 0.5 0.5 0.5 3 1.0 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 4 0.5 0.5 1.0 0.5 0.5 1.0 0.5 0.5 0.5 5 0.5 0.5 1.0 0.5 0.5 0.5 0.5 0.5 0.5

[0060] Table 4 Mechanical properties of examples

[0061]

[0062] Table 5 Bending test of examples (test temperature -80℃)

[0063]

[0064] Table 6 Charpy impact test results of examples

[0065]

[0066]

[0067] Table 7 Drop weight tear test of examples

[0068]

[0069] Table 8 Vickers Hardness Test Results

[0070]

[0071] Table 9 Metallographic Analysis of Examples

[0072]

[0073] Note: B particles - granular bainite.

Claims

1. An economical, ultra-low temperature, high-strength pipeline steel with resistance to dynamic tearing, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C: 0.040%–0.080%, Si: 0.15%–0.35%, Mn: 1.55%–1.80%, P≤0.010%, S≤0.010%, Ti: 0.030%–0.045%, Ca≤0.0015%, Al≤0.040%, Nb: 0.035%–0.055%, Cr: 0.15%–0.35%, N≤0.0040%, O≤0.0020%, with the balance being Fe and unavoidable impurities.

2. The economical ultra-low temperature high-strength pipeline steel with dynamic tear resistance according to claim 1, characterized in that, Pipeline steel has a yield strength ≥ 520 MPa and a tensile strength ≥ 620 MPa; elongation A 50 ≥42, impact energy value at -80℃ ≥260J, single value of DWTT shear area at -80℃ ≥82%, average value ≥85%; hardness HV10≤260, uniform hardness.

3. The economical ultra-low temperature high-strength pipeline steel with dynamic tear resistance according to claim 1, characterized in that, The grain size of the pipeline steel is grade 11-14, and the metallographic structure is a composite structure of granular bainite and elliptical island M / A.

4. A method for producing economical ultra-low temperature high-strength pipeline steel with dynamic tear resistance as described in any one of claims 1-3, comprising: hot metal pretreatment → converter smelting → refining → continuous casting → heating → hot continuous rolling → controlled cooling → coiling, characterized in that, Specific methods include: 1) The liquidus temperature of the tundish in the continuous casting process is controlled at 1550-1580℃, and the liquid core is lightly pressed down, and the superheat of the tundish is controlled at ΔT≤25℃; 2) The billet is heated in the heating furnace for 3.5 to 4.5 hours, and the billet exiting the furnace is controlled at 1180 to 1250℃; 3) Hot continuous rolling: roughing and finishing are carried out in the hot continuous rolling mill. The thickness of the intermediate billet before entering the finishing mill is 62-68 mm. The starting temperature of the finishing mill is 930℃-980℃, the finishing temperature is controlled at 790-850℃, and the thickness of the finished product is 20-25 mm. 4) After finishing rolling, the steel plate is cooled by continuous laminar flow, with the cooling rate controlled at 18-25℃ / s, and the coiling temperature of the cooled steel plate is 480-550℃.

5. The method for producing an economical, ultra-low temperature, high-strength pipeline steel with dynamic tear resistance according to claim 4, characterized in that, The converter smelting process involves 85%–88% molten iron and 12%–15% scrap steel, with a tapping temperature of 1580–1650℃.

6. The method for producing an economical, ultra-low temperature, high-strength pipeline steel with dynamic tear resistance according to claim 4, characterized in that, The desulfurization control of the molten iron pretreatment is [S] ≤ 0.0030%; the refining adopts RH vacuum degassing and LF furnace dual-station operation.

7. The method for producing an economical, ultra-low temperature, high-strength pipeline steel with dynamic tear resistance according to claim 4, characterized in that, The thickness of the billet is 190mm to 230mm. After the billet is reheated, the corner cracks are cleaned off the production line and then it is cold-loaded into the furnace.

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