Oil and gas transmission pipeline steel and preparation method thereof

Abstract

The invention relates to an oil and gas pipeline steel and a preparation method thereof. The oil and gas pipeline steel comprises, by weight percentage, C 0.11-0.13wt%, Si 0.23-0.27wt%, Mn 1.23-1.27wt%, P≤0.012wt%, S≤0.001wt%, Cr 0.1-0.14wt%, Nb 0.025-0.035wt%, V 0.04-0.06wt%, N 0.008-0.01wt%, Ca 0.001-0.0025wt%, and the balance is Fe and inevitable impurities. The oil and gas pipeline steel provided by the invention improves the component segregation inside the steel body, improves and stabilizes the impact toughness and mechanical strength after normal forging and heat treatment, and can meet the standard requirements for resistance to hydrogen-induced cracking and resistance to sulfide stress cracking.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to an oil and gas transmission pipeline steel and a preparation method thereof. Background Art

[0002] During the oil and gas extraction, storage and transportation process, leakage of crude oil and natural gas caused by corrosion will seriously pollute the environment and even lead to catastrophic consequences. Therefore, the oil industry urgently needs to develop oil and natural gas pipeline steel materials that are resistant to sulfide stress cracking and hydrogen-induced cracking.

[0003] Long-distance oil and gas pipeline steel not only requires high strength, toughness, fatigue resistance and fracture resistance, but also requires good resistance to sulfide stress cracking and hydrogen-induced cracking. When the transmission medium contains acidic gas or the pipeline material is used in an acidic environment for a long time, due to the particularity of the use environment, strict requirements are placed on the steel composition design, smelting technology, rolling process and metallurgical equipment level.

[0004] CN 104404383A discloses an ultra-low carbon hydrogen sulfide corrosion resistant X80 pipeline steel and a preparation method, belonging to the technical field of pipeline steel. The chemical composition weight percentage of the pipeline steel is: C 0.02-0.04%, Si 0.20-0.40%, Mn 0.90-1.10%, Cu 0.20-0.26%, Cr 0.40-0.70%, Nb 0.02-0.04%, Ni 0.20-0.40%, Mo 0.20-0.30%, Ti 0.01-0.03%, V 0.04-0.07%, P≤0.03%, S≤0.008%, and the balance is Fe and unavoidable impurities. The steel was prepared by TMCP, the organization was controlled and the grains were refined, multiple passes were rolled in the lower temperature areas of the austenite recrystallization zone and the austenite non-recrystallization zone, and a faster cooling rate of 20-30°C / s was used to obtain a fine-grained organization dominated by bainite + ferrite. However, the sulfur content of the pipeline steel is high, and hydrogen-induced cracking and stress corrosion cracking need to be improved.

[0005] CN 105886909A discloses a hydrogen-induced cracking resistant pressure vessel steel plate and a manufacturing method thereof, wherein the chemical composition by weight percentage is C: 0.16-0.20%, Si: 0.15-0.40%, Mn: 1.05-1.20%, P: ≤0.008%, S: ≤0.002%, Nb: ≤0.01%, V: ≤0.01%, Ti: ≤0.01%, B: ≤0.0005%, the remainder is Fe and unavoidable impurity elements, the carbon equivalent Ceq is ≤0.42%, and the calculation formula is: Ceq=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15. However, the tensile strength and yield strength of the steel plate provided by the invention are still low, and cannot meet the requirements of oil and gas pipeline steel.

[0006] When the sulfur content is low to a certain extent, the number and size of sulfides and oxides in the steel can be greatly reduced, and the probability of hydrogen-induced cracking and stress corrosion cracking is close to zero. Therefore, most steels currently used to resist hydrogen sulfide corrosion require the sulfur content in the steel to be controlled within a relatively low range. In order to meet the sulfur content requirements of steel used in special fields, stable and mass production of low-sulfur steel materials is of great practical significance.

[0007] Therefore, in view of the shortcomings of the prior art, it is necessary to provide a pipeline steel with low sulfur content, good strength and impact toughness, and resistance to sulfide stress cracking and hydrogen-induced cracking. Summary of the invention

[0008] The object of the present invention is to provide an oil and gas pipeline steel and a preparation method thereof. By reducing the C and S contents in the oil and gas pipeline steel, increasing the Mn content, and adding appropriate amounts of Cr, Nb and V elements, the component segregation inside the steel body is improved, the impact toughness and mechanical strength after normal forging and heat treatment are improved and stabilized, and the resistance to hydrogen-induced cracking and sulfide stress cracking can meet the standard requirements.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides an oil and gas pipeline steel, which comprises, by weight percentage, C 0.11-0.13wt%, Si 0.23-0.27wt%, Mn 1.23-1.27wt%, P≤0.012wt%, S≤0.001wt%, Cr 0.1-0.14wt%, Nb 0.025-0.035wt%, V 0.04-0.06wt%, N 0.008-0.01wt%, Ca 0.001-0.0025wt%, and the balance is Fe and unavoidable impurities.

[0011] The mass percentage of C in the oil and gas pipeline steel of the present invention is 0.11-0.13wt%, for example, it can be 0.11wt%, 0.115wt%, 0.12wt%, 0.125wt% or 0.13wt%, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 0.12-0.13%.

[0012] In the present invention, the plasticity and toughness of the steel can be significantly improved by appropriately reducing the C content.

[0013] The mass percentage of Si in the oil and gas pipeline steel of the present invention is 0.23-0.27wt%, for example, it can be 0.23wt%, 0.24wt%, 0.25wt%, 0.26wt% or 0.27wt%, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 0.24-0.26%.

[0014] The mass percentage of Mn in the oil and gas pipeline steel of the present invention is 1.23-1.27wt%, for example, it can be 1.23wt%, 1.24wt%, 1.25wt%, 1.26wt% or 1.27wt%, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 1.24-1.26%.

[0015] Mn is an element that is easy to segregate. It is easy to form manganese sulfide inclusions with sulfur, which becomes the root cause of hydrogen-induced cracking. Therefore, in order to utilize the strengthening effect of Mn, the S content in the steel must be reduced; Mn is a low-cost alloying element. Although it is easy to segregate, the finished steel produced by continuous casting round billet rolling and heat treatment can greatly reduce the segregation and banded structure caused by Mn. Therefore, the Mn content in this application can be appropriately increased.

[0016] The mass percentage of P in the oil and gas pipeline steel of the present invention is ≤0.012wt%, for example, it can be 0.012wt%, 0.011wt%, 0.01wt%, 0.009wt% or 0.008wt%, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably ≤0.01wt%.

[0017] The mass percentage of S in the oil and gas pipeline steel of the present invention is ≤0.001wt%, for example, it can be 0.001wt%, 0.0009wt%, 0.00008wt%, 0.0007wt% or 0.0006wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] When the sulfur content is controlled to be no higher than 0.001wt%, the number and size of sulfides and oxides in the steel can be reduced to a great extent, and the probability of hydrogen-induced cracking and stress corrosion cracking is close to zero. Therefore, the sulfur content is limited to less than 0.001wt% in this application.

[0019] The mass percentage of Cr in the oil and gas pipeline steel of the present invention is 0.1-0.14wt%, for example, it can be 0.1wt%, 0.11wt%, 0.12wt%, 0.13wt% or 0.14wt%, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable, preferably 0.11-0.13%.

[0020] The introduction of Cr element can make it have good corrosion resistance stability and oxidation resistance, and the strength and hardness are further improved. Cr is very beneficial for slowing down the corrosion rate in acidic environment, so the present invention controls the Cr content to 0.1-0.14wt%, which can take into account the material has good strength, hardness, toughness and corrosion resistance.

[0021] The mass percentage of Nb in the oil and gas pipeline steel of the present invention is 0.025-0.035wt%, for example, it can be 0.025wt%, 0.028wt%, 0.03wt%, 0.032wt% or 0.035wt%, but is not limited to the listed values. Other values ​​not listed in the numerical range are also applicable, preferably 0.028-0.032%.

[0022] As a microalloying element, Nb can refine the grains, effectively improve the yield strength and toughness of the steel, and reduce the brittle transition temperature of the steel.

[0023] The mass percentage of V in the oil and gas pipeline steel of the present invention is 0.04-0.06wt%, for example, it can be 0.04wt%, 0.045wt%, 0.05wt%, 0.055wt% or 0.06wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] The introduction of V element will precipitate VC and VN during and after the transformation of austenite to ferrite, which has a significant strengthening effect; V also has good casting properties and is not prone to transverse and high-temperature cracks during the casting process.

[0025] The mass percentage of N in the oil and gas pipeline steel of the present invention is 0.008-0.01wt%, for example, it can be 0.008wt%, 0.0085wt%, 0.009wt%, 0.0095wt% or 0.01wt%, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 0.0085-0.0095%.

[0026] In the present invention, the strength of the steel body can be further improved by appropriately introducing the N element, but its content range needs to be strictly controlled. Too high a content will have an adverse effect on the comprehensive properties of the steel body.

[0027] The mass percentage of Ca in the oil and gas pipeline steel of the present invention is 0.001-0.0025wt%, for example, it can be 0.001wt%, 0.0015wt%, 0.002wt%, 0.0022wt% or 0.0025wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, in the oil and gas pipeline steel, Al / N≥2, Ca / S≥1.

[0029] The Al / N ratio in the oil and gas pipeline steel is ≥ 2, for example, it can be 2, 2.2, 2.5, 2.8 or 3, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] The Ca / S ratio in the oil and gas pipeline steel is ≥1, for example, it can be 1, 1.2, 1.5, 1.8 or 2, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] The reason why the range of Al / N is limited in the present invention is that the binary particles precipitated from low carbon steel are mainly Al / N. By studying the solid solution and precipitation rules of AlN and limiting a reasonable Al / N range, an important basis can be provided for the formulation of the production process of low carbon aluminum killed steel; and controlling the range of Ca / S can change the oxides from the original high hardness and high melting point Al2O3 and SiO2 to CaO-Al2O3-SiO2 composite eutectic low melting point oxides, and a small amount of oxides are also located in the sulfide or composited with it, thereby obtaining better performance than a single sulfur system.

[0032] Preferably, the total mass percentage of Nb+V in the oil and gas pipeline steel is 0.07-0.09wt%, for example, it can be 0.07wt%, 0.075wt%, 0.08wt%, 0.085wt% or 0.09wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] The microalloying composite strengthening of Nb+V contains Nb and V precipitation phases in the steel, and can play a pinning role in the steel matrix, while refining the grains and increasing the dislocation density. Nb+V is limited to the preferred range, which can play a role in both precipitation strengthening and grain refinement strengthening, greatly improving the yield strength of the steel, thereby meeting the strength requirements of oil and gas pipeline steel.

[0034] In a second aspect, the present invention provides a method for preparing the oil and gas pipeline steel as described in the first aspect, the preparation method comprising:

[0035] The formulated molten iron is sequentially subjected to pretreatment, converter smelting, LF refining, VD vacuum, continuous casting, slow cooling and finishing to obtain the oil and gas pipeline steel.

[0036] The preparation method provided by the present invention controls the process parameters in the LF refining, VD vacuum, continuous casting and slow cooling processes, so that the prepared oil and gas pipeline steel has higher strength and toughness, and can meet the requirements of resistance to hydrogen-induced cracking and resistance to sulfide stress cracking.

[0037] Preferably, argon gas is introduced during the LF refining.

[0038] Introducing argon during the deep desulfurization process of refined slag can reduce the oxygen activity in the steel and increase the sulfur activity coefficient.

[0039] Preferably, the slag basicity is controlled within the range of 3-5 during LF refining, for example, 3, 3.5, 4, 4.5 or 5, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] In the LF refining, the slag basicity is appropriately increased within a reasonable range, so as to achieve the purpose of reducing the oxidizability of the slag.

[0041] Preferably, the LF refining off-station temperature is 1617-1637°C, for example, it can be 1617°C, 1620°C, 1625°C, 1630°C or 1637°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] In the LF refining, the temperature leaving the station is appropriately increased and controlled within a reasonable range, which can improve the fluidity of sulfur in the slag and facilitate the smooth progress of the desulfurization reaction.

[0043] Preferably, the VD vacuum evacuation time is 20-25 min, for example, 20 min, 21 min, 22 min, 23 min or 25 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] Preferably, the soft blowing time of the VD vacuum is ≥20 min, for example, it can be 20 min, 21 min, 22 min, 23 min or 25 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] Preferably, the continuous casting pulling speed is 0.21-0.85 m / min, for example, it can be 0.21 m / min, 0.35 m / min, 0.55 m / min, 0.7 m / min or 0.85 m / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] Preferably, the specific water content of the continuous casting is 0.35-0.45 L / kg, for example, it can be 0.35 L / kg, 0.38 L / kg, 0.4 L / kg, 0.42 L / kg or 0.45 L / kg, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] Preferably, the current of the electromagnetic stirring of the crystallizer during the continuous casting is 200-350A, and the frequency of the electromagnetic stirring of the crystallizer is 2-2.5Hz.

[0048] The current of electromagnetic stirring of the crystallizer in the continuous casting is 200-350A, for example, it can be 200A, 220A, 250A, 300A or 350A, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] The frequency of the electromagnetic stirring of the crystallizer is 2-2.5 Hz, for example, 2 Hz, 2.1 Hz, 2.2 Hz, 2.3 Hz or 2.5 Hz, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0050] Preferably, the current of the terminal electromagnetic stirring during the continuous casting is 600-900A, and the frequency of the terminal electromagnetic stirring is 6-10Hz.

[0051] The current of the terminal electromagnetic stirring in the continuous casting is 600-900A, for example, 600A, 650A, 700A, 800A or 900A, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0052] The frequency of the terminal electromagnetic stirring is 6-10 Hz, for example, 6 Hz, 7 Hz, 8 Hz, 9 Hz or 10 Hz, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0053] Preferably, the slow cooling time is ≥120 h, for example, it can be 120 h, 122 h, 125 h, 128 h or 130 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0054] As a preferred technical solution of the preparation method described in the second aspect of the present invention, the preparation method comprises:

[0055] The formulated molten iron is sequentially subjected to pretreatment, converter smelting, LF refining, VD vacuum, continuous casting, slow cooling for ≥120h and finishing to obtain the oil and gas pipeline steel;

[0056] Argon is introduced during the LF refining; during the LF refining, the slag basicity is controlled at 3-5, and the leaving station temperature is 1617-1637°C; the vacuum extraction time of the VD vacuum is 20-25min, and the soft blowing time is ≥20min; the pulling speed of the continuous casting is 0.21-0.85m / min, and the specific water amount is 0.35-0.45L / kg; the current of the electromagnetic stirring of the crystallizer during the continuous casting is 200-350A, and the frequency of the electromagnetic stirring of the crystallizer is 2-2.5Hz; the current of the terminal electromagnetic stirring during the continuous casting is 600-900A, and the frequency of the terminal electromagnetic stirring is 6-10Hz.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] The oil and gas pipeline steel provided by the present invention reduces the C and S contents in the oil and gas pipeline steel, increases the Mn content, and adds appropriate amounts of Cr, Nb and V elements, thereby improving the component segregation inside the steel body, improving and stabilizing the impact toughness and mechanical strength after normal forging and heat treatment, the impact energy can reach 113J, the tensile strength reaches 755MPa, the yield strength reaches 562MPa, and the resistance to hydrogen-induced cracking and sulfide stress cracking can meet the standard requirements, and can be used for industrial-scale production. DETAILED DESCRIPTION

[0059] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0060] Example 1

[0061] The present embodiment provides an oil and gas pipeline steel, which includes, by mass percentage, C 0.12wt%, Si 0.25wt%, Mn 1.25wt%, P 0.008wt%, S 0.0006wt%, Cr 0.12wt%, Nb 0.03wt%, V 0.05wt%, N 0.009wt%, Ca 0.002wt%, and the balance is Fe and unavoidable impurities; the total mass percentage of Nb+V in the oil and gas pipeline steel is 0.08wt%; Al / N in the oil and gas pipeline steel is 2.5, and Ca / S is 3.3.

[0062] The preparation method of the oil and gas pipeline steel comprises:

[0063] The formulated molten iron is sequentially subjected to pretreatment, converter smelting, LF refining, VD vacuum, continuous casting, slow cooling for 125 hours and finishing to obtain the oil and gas pipeline steel;

[0064] Argon is introduced during the LF refining; during the LF refining, the slag basicity is controlled at 4, and the leaving station temperature is 1625°C; the vacuum extraction time of the VD vacuum is 22 min, and the soft blowing time is 22 min; the pulling speed of the continuous casting is 0.55 m / min, and the specific water amount is 0.4 L / kg; the current of the electromagnetic stirring of the crystallizer during the continuous casting is 250 A, and the frequency of the electromagnetic stirring of the crystallizer is 2.2 Hz; the current of the terminal electromagnetic stirring during the continuous casting is 700 A, and the frequency of the terminal electromagnetic stirring is 8 Hz.

[0065] Example 2

[0066] The present embodiment provides an oil and gas pipeline steel, which includes, by mass percentage, C 0.115wt%, Si 0.24wt%, Mn 1.26wt%, P 0.009wt%, S 0.0007wt%, Cr0.13wt%, Nb 0.032wt%, V 0.055wt%, N 0.0095wt%, Ca 0.0022wt%, and the remainder is Fe and unavoidable impurities; the total mass percentage of Nb+V in the oil and gas pipeline steel is 0.087wt%; Al / N and Ca / S in the oil and gas pipeline steel are 2.8 and 3.14.

[0067] The preparation method of the oil and gas pipeline steel comprises:

[0068] The formulated molten iron is sequentially subjected to pretreatment, converter smelting, LF refining, VD vacuum, continuous casting, slow cooling for 128 hours and finishing to obtain the oil and gas pipeline steel;

[0069] Argon is introduced during the LF refining; during the LF refining, the slag basicity is controlled at 3.5, and the leaving station temperature is 1620°C; the vacuum extraction time of the VD vacuum is 23 min, and the soft blowing time is 23 min; the pulling speed of the continuous casting is 0.7 m / min, and the specific water amount is 0.42 L / kg; the current of the electromagnetic stirring of the crystallizer during the continuous casting is 300 A, and the frequency of the electromagnetic stirring of the crystallizer is 2.3 Hz; the current of the terminal electromagnetic stirring during the continuous casting is 800 A, and the frequency of the terminal electromagnetic stirring is 9 Hz.

[0070] Example 3

[0071] The present embodiment provides an oil and gas pipeline steel, which includes, by mass percentage, C 0.125wt%, Si 0.26wt%, Mn 1.24wt%, P 0.01wt%, S 0.0008wt%, Cr 0.11wt%, Nb 0.028wt%, V 0.045wt%, N 0.0085wt%, Ca 0.0015wt%, and the remainder is Fe and unavoidable impurities; the total mass percentage of Nb+V in the oil and gas pipeline steel is 0.073wt%; Al / N and Ca / S in the oil and gas pipeline steel are 2.2 and 1.88.

[0072] The preparation method of the oil and gas pipeline steel comprises:

[0073] The formulated molten iron is sequentially subjected to pretreatment, converter smelting, LF refining, VD vacuum, continuous casting, slow cooling for 122 hours and finishing to obtain the oil and gas pipeline steel;

[0074] Argon is introduced during the LF refining; during the LF refining, the slag basicity is controlled at 4.5, and the leaving station temperature is 1630°C; the vacuum extraction time of the VD vacuum is 21 min, and the soft blowing time is 21 min; the pulling speed of the continuous casting is 0.35 m / min, and the specific water amount is 0.38 L / kg; the current of the electromagnetic stirring of the crystallizer during the continuous casting is 220 A, and the frequency of the electromagnetic stirring of the crystallizer is 2.1 Hz; the current of the end electromagnetic stirring during the continuous casting is 650 A, and the frequency of the end electromagnetic stirring is 7 Hz.

[0075] Example 4

[0076] The present embodiment provides an oil and gas pipeline steel, which includes, by mass percentage, C 0.11wt%, Si 0.23wt%, Mn 1.27wt%, P 0.011wt%, S 0.0009wt%, Cr 0.14wt%, Nb 0.035wt%, V 0.06wt%, N 0.01wt%, Ca 0.0025wt%, and the remainder is Fe and unavoidable impurities; the total mass percentage of Nb+V in the oil and gas pipeline steel is 0.095wt%; Al / N in the oil and gas pipeline steel is 3, and Ca / S is 2.78.

[0077] The preparation method of the oil and gas pipeline steel comprises:

[0078] The formulated molten iron is sequentially subjected to pretreatment, converter smelting, LF refining, VD vacuum, continuous casting, slow cooling for 130 hours and finishing to obtain the oil and gas pipeline steel;

[0079] Argon is introduced during the LF refining; during the LF refining, the slag basicity is controlled at 3 and the leaving station temperature is 1617°C; the vacuum extraction time of the VD vacuum is 25 min, and the soft blowing time is 25 min; the pulling speed of the continuous casting is 0.85 m / min, and the specific water amount is 0.45 L / kg; the current of the electromagnetic stirring of the crystallizer during the continuous casting is 350 A, and the frequency of the electromagnetic stirring of the crystallizer is 2.5 Hz; the current of the terminal electromagnetic stirring during the continuous casting is 900 A, and the frequency of the terminal electromagnetic stirring is 10 Hz.

[0080] Example 5

[0081] The present embodiment provides an oil and gas pipeline steel, which includes, by mass percentage, C 0.13wt%, Si 0.27wt%, Mn 1.23wt%, P 0.012wt%, S 0.001wt%, Cr 0.1wt%, Nb0.025wt%, V 0.04wt%, N 0.008wt%, Ca 0.001wt%, and the balance is Fe and unavoidable impurities; the total mass percentage of Nb+V in the oil and gas pipeline steel is 0.065wt%; Al / N in the oil and gas pipeline steel is 2, and Ca / S is 1.

[0082] The preparation method of the oil and gas pipeline steel comprises:

[0083] The formulated molten iron is sequentially subjected to pretreatment, converter smelting, LF refining, VD vacuum, continuous casting, slow cooling for 120 hours and finishing to obtain the oil and gas pipeline steel;

[0084] Argon is introduced during the LF refining; during the LF refining, the slag basicity is controlled at 5 and the leaving station temperature is 1637°C; the vacuum extraction time of the VD vacuum is 20 min, and the soft blowing time is 20 min; the pulling speed of the continuous casting is 0.21 m / min, and the specific water amount is 0.35 L / kg; the current of the electromagnetic stirring of the crystallizer during the continuous casting is 200 A, and the frequency of the electromagnetic stirring of the crystallizer is 2 Hz; the current of the end electromagnetic stirring during the continuous casting is 600 A, and the frequency of the end electromagnetic stirring is 6 Hz.

[0085] Example 6

[0086] This embodiment provides an oil and gas pipeline steel. The difference between the preparation method of the oil and gas pipeline steel and that of Example 1 is that no argon is introduced during the LF refining, and the rest is the same as that of Example 1.

[0087] Example 7

[0088] This embodiment provides an oil and gas pipeline steel. The difference between the preparation method of the oil and gas pipeline steel and that of Example 1 is that the slag basicity is controlled at 2 during the LF refining, and the rest is the same as that of Example 1.

[0089] Example 8

[0090] This embodiment provides an oil and gas pipeline steel. The difference between the preparation method of the oil and gas pipeline steel and that of Example 1 is that the leaving station temperature in the LF refining is 1610° C., and the rest is the same as that of Example 1.

[0091] Comparative Example 1

[0092] This comparative example provides an oil and gas pipeline steel, which is different from Example 1 in that the mass percentage of C in the oil and gas pipeline steel is adjusted to 0.14wt%, and the rest is the same as Example 1.

[0093] Comparative Example 2

[0094] This comparative example provides an oil and gas pipeline steel, which is different from Example 1 in that the mass percentage of Mn in the oil and gas pipeline steel is adjusted to 1.22wt%, the mass percentage of S is adjusted to 0.002wt%, the mass percentage of Ca is adjusted to 0.001wt%, the adaptability obtains Ca / S to be 0.5, Al / N to be adjusted to 1, and the rest is the same as Example 1.

[0095] Comparative Example 3

[0096] This comparative example provides an oil and gas pipeline steel, which is different from Example 1 in that the mass percentage of Nb in the oil and gas pipeline steel is adjusted to 0.02wt%, the mass percentage of V is adjusted to 0.03wt%, and the mass percentage of Nb+V is adapted to be 0.05wt%, and the rest is the same as Example 1.

[0097] Comparative Example 4

[0098] This comparative example provides an oil and gas pipeline steel, which is different from Example 1 in that the mass percentage of Nb in the oil and gas pipeline steel is adjusted to 0.03wt%, the mass percentage of V is adjusted to 0.07wt%, and the mass percentage of Nb+V is adapted to be 0.1wt%, and the rest is the same as Example 1.

[0099] The oil and gas pipeline steel bodies obtained by conventional forging and heat treatment of the oil and gas pipeline steels provided in Examples 1-8 and Comparative Examples 1-4 were subjected to mechanical property tests according to GB / T 17185-2012 steel flange pipe fittings. The results are shown in Table 1.

[0100] The oil and gas pipeline steel bodies obtained by conventional forging and heat treatment of the oil and gas pipeline steels provided in Examples 1-8 and Comparative Examples 1-4 were subjected to hydrogen induced cracking (HIC) resistance test according to standard NACE TM0284 "Test Method for Evaluation of Hydrogen Induced Cracking Resistance of Steel for Pipelines and Pressure Vessels", and sulfide stress cracking (SSC) resistance test was performed according to standard NACE TM0177 "Test Method for Resistance of Metals to Sulfide Stress Cracking, Stress Cracking and Stress Corrosion Cracking in H2S Environments". The results are shown in Table 2.

[0101] Table 1

[0102]

[0103]

[0104] Table 2

[0105]

[0106] It can be seen from Table 1 and Table 2 that the oil and gas pipeline steel provided by the present invention improves the component segregation inside the steel body, improves and stabilizes the impact toughness and mechanical strength, and the resistance to hydrogen-induced cracking and sulfide stress cracking can meet the standard requirements;

[0107] From the comparison between Example 1 and Examples 6-8, it can be seen that the absence of reducing atmosphere, low slag basicity, and low production temperature will have an adverse effect on the deep desulfurization of refined slag, thereby reducing the mechanical properties and impact toughness of the steel body;

[0108] By comparing Example 1 with Comparative Example 1, it can be seen that when the C content is too high, the impact toughness and mechanical strength of the steel body are negatively affected, and the resistance to hydrogen-induced cracking is reduced; by comparing Example 1 with Comparative Example 2, it can be seen that when the Mn content is too low, the S content is too high, and Ca / S and Al / N both exceed the lower limit, the tensile strength and yield strength of the steel body will be significantly reduced, the impact resistance will be deteriorated, and hydrogen blistering and cracks will exist; by comparing Example 1 with Comparative Examples 3 and 4, it can be seen that when the Nb and V contents exceed the specified range and the total mass percentage of Nb+V also exceeds the specified range, the mechanical properties of the steel body will be significantly reduced.

[0109] In summary, the oil and gas pipeline steel provided by the present invention improves the component segregation inside the steel body by reducing the C and S contents in the oil and gas pipeline steel, increasing the Mn content, and adding appropriate amounts of Cr, Nb and V elements, thereby improving and stabilizing the impact toughness and mechanical strength after normal forging and heat treatment, the impact energy can reach 113J, the tensile strength can reach 755MPa, the yield strength can reach 562MPa, and the resistance to hydrogen-induced cracking and sulfide stress cracking can meet the standard requirements, and can be used for industrial-scale production.

[0110] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. An oil and gas pipeline steel, characterized in that: The oil and gas pipeline steel comprises, in terms of mass percentage, C 0.11-0.13wt%, Si 0.23-0.27wt%, Mn 1.23-1.27wt%, P≤0.012wt%, S≤0.001wt%, Cr 0.1-0.14wt%, Nb 0.025-0.035wt%, V 0.04-0.06wt%, N 0.008-0.01wt%, Ca 0.001-0.0025wt%, and the balance is Fe and unavoidable impurities; Wherein, the total mass percentage of Nb+V in the oil and gas pipeline steel is 0.07-0.09wt%; In the oil and gas pipeline steel, 3≥Al / N≥2.

2. The oil and gas pipeline steel according to claim 1, characterized in that: Calculated in percentage by mass, the oil and gas pipeline steel includes: C 0.12-0.13wt%, Si 0.24-0.26wt%, Mn 1.24-1.26wt%, P≤0.01wt%, S≤0.001wt%, Cr 0.11-0.13wt%, Nb 0.028-0.032wt%, V 0.04-0.06wt%, N 0.0085-0.0095wt%, Ca 0.001-0.0025wt%, and the balance is Fe and unavoidable impurities.

3. The oil and gas pipeline steel according to claim 1, characterized in that: In the oil and gas pipeline steel, Ca / S≥1.

4. A method for preparing oil and gas pipeline steel according to any one of claims 1 to 3, characterized in that: The preparation method comprises: The formulated molten iron is sequentially subjected to pretreatment, converter smelting, LF refining, VD vacuum, continuous casting, slow cooling and finishing to obtain the oil and gas pipeline steel.

5. The preparation method according to claim 4, characterized in that: Argon gas was passed through the LF refining.

6. The preparation method according to claim 4, characterized in that: In the LF refining, the slag basicity is controlled at 3-5.

7. The preparation method according to claim 4, characterized in that: The LF refining has a leaving station temperature of 1617-1637°C.

8. The preparation method according to claim 4, characterized in that: The vacuuming time of the VD vacuum is 20-25 minutes.

9. The preparation method according to claim 4, characterized in that: The soft blowing time of the VD vacuum is ≥20min.

10. The preparation method according to claim 4, characterized in that: The continuous casting speed is 0.21-0.85 m / min.

11. The preparation method according to claim 4, characterized in that: The specific water content of the continuous casting is 0.35-0.45 L / kg.

12. The preparation method according to claim 4, characterized in that: The current of electromagnetic stirring of the crystallizer during the continuous casting is 200-350A, and the frequency of electromagnetic stirring of the crystallizer is 2-2.5Hz.

13. The preparation method according to claim 4, characterized in that: The current of the terminal electromagnetic stirring in the continuous casting is 600-900A, and the frequency of the terminal electromagnetic stirring is 6-10Hz.

14. The preparation method according to claim 4, characterized in that: The slow cooling time is ≥120h.

15. The preparation method according to claim 4, characterized in that: The preparation method comprises: The formulated molten iron is sequentially subjected to pretreatment, converter smelting, LF refining, VD vacuum, continuous casting, slow cooling for ≥120h and finishing to obtain the oil and gas pipeline steel; Argon is introduced during the LF refining; during the LF refining, the slag basicity is controlled at 3-5, and the leaving station temperature is 1617-1637°C; the vacuum extraction time of the VD vacuum is 20-25min, and the soft blowing time is ≥20min; the pulling speed of the continuous casting is 0.21-0.85m / min, and the specific water amount is 0.35-0.45L / kg; the current of the electromagnetic stirring of the crystallizer during the continuous casting is 200-350A, and the frequency of the electromagnetic stirring of the crystallizer is 2-2.5Hz; the current of the terminal electromagnetic stirring during the continuous casting is 600-900A, and the frequency of the terminal electromagnetic stirring is 6-10Hz.

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