A corrosion-resistant steel and its preparation method

Abstract

The present invention relates to a corrosion-resistant steel and a preparation method thereof. The corrosion-resistant steel comprises, by mass percentage: C 0.12 - 0.16%, Si 0.2 - 0.35%, Mn 1.25 - 1.4%, V 0.05 - 0.08%, N 0.005 - 0.007%, P ≤ 0.02%, S ≤ 0.008%, and the balance is Fe and unavoidable impurities. The corrosion-resistant steel provided by the present invention designs the composition of the steel. Specifically, the C and Mn contents are designed to ensure the toughness of the material. A certain amount of V element is added, and V and N are combined under a certain nitrogen content to promote the refinement of the grain structure in the steel during the heat treatment process, improve the tempering stability of the thick-walled pipe, thereby improving the corrosion resistance and extending the service life of the steel pipe in a harsh environment.

Description

Technical Field

[0001] The present invention relates to the field of steel, and particularly to a corrosion-resistant steel and a preparation method thereof. Background Art

[0002] At present, during the process of oil and gas transportation, steel pipes underground are usually damaged and cracked due to corrosion by S, H, etc. under environmental conditions.

[0003] Conventional X60Q grade pipeline steel uses V, Ti or Cr, Mo alloy combination to ensure the corrosion resistance, tensile strength, yield strength and other properties of the material.

[0004] For example, CN105063482A discloses an X60 pipeline steel and a production method thereof. The chemical composition thereof by weight percentage is: C: 0.05 - 0.10%, Si: 0.10 - 0.30%, Mn: 1.20 - 1.40%, P: ≤0.020%, S: ≤0.010%, Nb: 0.020 - 0.034%, V: 0.05 - 0.08%, Ti: 0.008 - 0.019%, and the rest are Fe and inevitable impurities. The solution of the present invention does not need to add expensive elements such as Mo, Ni, etc., has relatively low cost, and has a simple rolling process and strong operability.

[0005] CN107587072A discloses an X60 pipeline steel and a preparation method thereof. The above preparation method includes: smelting and continuous casting to obtain a billet; heating and rolling the billet, wherein: the heating temperature is 1160 - 1180°C, and the total in-furnace time ≥200 min; the rolling is divided into the first stage and the second stage rolling: the first stage is rolled in the austenite recrystallization zone. During the rolling process, the starting rolling temperature is 1150 - 1170°C, the reduction ratio of the first pass > 10%, and the reduction ratio of the last pass ≥20%; the second stage is rolled in the austenite non-recrystallization zone, the starting rolling temperature of finish rolling ≤920°C, the finish rolling temperature is 820 - 850°C, the finish rolling compression ratio ≥3, and the cumulative reduction ratio is 71.4%; cooling. By reasonable chemical composition design and adopting the controlled rolling and controlled cooling process, this method can obtain an X60 pipeline steel with a microstructure of fine and uniform ferrite and pearlite, a grain size of 13 grades, high strength, high toughness, drop weight tear performance, and low cost.

[0006] However, during the heat treatment process of steel pipes, there is a problem that the obtained steel has a large grain structure and poor tempering stability, resulting in poor corrosion resistance. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of the present invention is to provide a corrosion-resistant steel and its preparation method, especially a pipeline steel for onshore acidic service oil and gas and its preparation method, so as to solve the problem of poor corrosion resistance caused by large grain structure and poor tempering stability of the steel during the heat treatment process.

[0008] To achieve this purpose, the present invention adopts the following technical solutions:

[0009] The present invention provides a corrosion-resistant steel, which includes, by mass percentage: C 0.12 - 0.16%, Si 0.2 - 0.35%, Mn 1.25 - 1.4%, V 0.05 - 0.08%, N 0.005 - 0.007%, P ≤ 0.02%, S ≤ 0.008%, and the balance is Fe and inevitable impurities.

[0010] For the corrosion-resistant steel provided by the present invention, through the design of the composition of the steel, specifically, the C and Mn contents are designed to ensure the toughness of the material, a certain amount of V element is added, and V and N are combined under a certain nitrogen content to promote the refinement of the grain structure in the steel during the heat treatment process, improve the tempering stability of the thick-walled pipe, thereby improving the corrosion resistance and extending the service life of the steel pipe in harsh environments.

[0011] In the present invention, the C in the corrosion-resistant steel is 0.12 - 0.16% by mass percentage, for example, it can be 0.12%, 0.122%, 0.124%, 0.126%, 0.128%, 0.13%, 0.132%, 0.134%, 0.136%, 0.138%, 0.14%, 0.142%, 0.144%, 0.146%, 0.148%, 0.15%, 0.152%, 0.154%, 0.156%, 0.158% or 0.16% etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0012] In the present invention, the Si in the corrosion-resistant steel is 0.2 - 0.35% by mass percentage, for example, it can be 0.2%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.3%, 0.31%, 0.32%, 0.33%, 0.34% or 0.35% etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0013] In the present invention, the mass percentage of Mn in the corrosion-resistant steel is 1.25 - 1.4%, for example, it can be 1.25%, 1.26%, 1.27%, 1.28%, 1.29%, 1.3%, 1.31%, 1.32%, 1.33%, 1.34%, 1.35%, 1.36%, 1.37%, 1.38%, 1.39% or 1.4%, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0014] In the present invention, the mass percentage of V in the corrosion-resistant steel is 0.05 - 0.08%, for example, it can be 0.05%, 0.052%, 0.054%, 0.056%, 0.058%, 0.06%, 0.062%, 0.064%, 0.066%, 0.068%, 0.07%, 0.072%, 0.074%, 0.076%, 0.078% or 0.08%, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0015] In the present invention, the mass percentage of N in the corrosion-resistant steel is 0.005 - 0.007%, for example, it can be 0.005%, 0.0051%, 0.0052%, 0.0053%, 0.0054%, 0.0055%, 0.0056%, 0.0057%, 0.0058%, 0.0059%, 0.006%, 0.0061%, 0.0062%, 0.0063%, 0.0064%, 0.0065%, 0.0066%, 0.0067%, 0.0068%, 0.0069% or 0.007%, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0016] In the present invention, the mass percentage of P in the corrosion-resistant steel is ≤ 0.02%, for example, it can be 0.02%, 0.019%, 0.018%, 0.017%, 0.016%, 0.015%, 0.014%, 0.013%, 0.012%, 0.011%, 0.01%, 0.009%, 0.008%, 0.007%, 0.006%, 0.005%, 0.004%, 0.002% or 0.001%, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0017] In the present invention, the sulfur (S) in the corrosion-resistant steel is ≤ 0.008% by mass percentage. For example, it can be 0.008%, 0.0078%, 0.0076%, 0.0074%, 0.0072%, 0.007%, 0.0068%, 0.0066%, 0.0064%, 0.0062%, 0.006%, 0.0055%, 0.005%, 0.0045%, 0.004%, 0.0035%, 0.003%, 0.0025%, 0.002%, 0.0015% or 0.001%, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0018] As a preferred technical solution of the present invention, the corrosion-resistant steel includes, by mass percentage: C 0.13 - 0.14%, Si 0.24 - 0.31%, Mn 1.28 - 1.32%, V 0.06 - 0.07%, N 0.0054 - 0.0057%, P ≤ 0.02%, S ≤ 0.008%, and the balance is Fe and unavoidable impurities.

[0019] In the second aspect, the present invention provides a preparation method of the corrosion-resistant steel as described in the first aspect. The preparation method includes:

[0020] Pre-treating molten iron, converting steel in a converter, refining in LF, vacuum degassing in VD, continuous casting, heating, rolling, quenching and tempering in sequence to obtain the corrosion-resistant steel;

[0021] Adding a V-containing alloy during the LF refining;

[0022] Adding an N-containing alloy during the VD vacuum degassing;

[0023] The tempering temperature is 510 - 530 °C.

[0024] In the present invention, the tempering temperature is 510 - 530 °C. For example, it can be 510 °C, 511 °C, 512 °C, 513 °C, 514 °C, 515 °C, 516 °C, 517 °C, 518 °C, 519 °C, 520 °C, 521 °C, 522 °C, 523 °C, 524 °C, 525 °C, 526 °C, 527 °C, 528 °C, 529 °C or 530 °C, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0025] As a preferred technical solution of the present invention, the pre-treatment is KR desulfurization treatment;

[0026] Preferably, a desulfurizing agent is added during the pre-treatment;

[0027] Preferably, the desulfurizer includes calcium oxide, fluorite powder and aluminum powder, and the addition amounts are 10 - 15 kg / t, 1.5 - 2.5 kg / t and 0.5 - 1 kg / t respectively;

[0028] In the present invention, the addition amount of calcium oxide in the desulfurizer is 10 - 15 kg / t. For example, it can be 10 kg / t, 10.5 kg / t, 11 kg / t, 11.5 kg / t, 12 kg / t, 12.5 kg / t, 13 kg / t, 13.5 kg / t, 14 kg / t, 14.5 kg / t or 15 kg / t, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0029] In the present invention, the addition amount of fluorite powder in the desulfurizer is 1.5 - 2.5 kg / t. For example, it can be 1.5 kg / t, 1.6 kg / t, 1.7 kg / t, 1.8 kg / t, 1.9 kg / t, 2 kg / t, 2.1 kg / t, 2.2 kg / t, 2.3 kg / t, 2.4 kg / t or 2.5 kg / t, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0030] In the present invention, the addition amount of aluminum powder in the desulfurizer is 0.5 - 1 kg / t. For example, it can be 0.5 kg / t, 0.55 kg / t, 0.6 kg / t, 0.65 kg / t, 0.7 kg / t, 0.75 kg / t, 0.8 kg / t, 0.85 kg / t, 0.9 kg / t, 0.95 kg / t or 1 kg / t, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0031] Preferably, the rotation speed of stirring in the pretreatment is 70 - 85 r / min, and the time is 12 - 15 min;

[0032] In the present invention, the rotation speed of stirring in the pretreatment is 70 - 85 r / min. For example, it can be 70 r / min, 71 r / min, 72 r / min, 73 r / min, 74 r / min, 75 r / min, 76 r / min, 77 r / min, 78 r / min, 79 r / min, 80 r / min, 81 r / min, 82 r / min, 83 r / min, 84 r / min or 85 r / min, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0033] In the present invention, the stirring time of the pretreatment is 12 - 15 min. For example, it can be 12 min, 13 min, 14 min or 15 min, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0034] Preferably, the sulfur content in the hot metal after pretreatment is ≤0.001% by mass percentage, for example, it can be 0.001%, 0.0009%, 0.0008%, 0.0007%, 0.0006%, 0.0005%, 0.0004%, 0.0003%, 0.0002% or 0.0001%, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0035] As a preferred technical solution of the present invention, the tapping temperature of the converter steelmaking is 1600 - 1650 °C. For example, it can be 1600 °C, 1610 °C, 1620 °C, 1630 °C, 1640 °C or 1650 °C, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0036] Preferably, the end-point carbon of the converter steelmaking is ≤0.05% by mass percentage. For example, it can be 0.05%, 0.04%, 0.03% or 0.02%, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0037] Preferably, the end-point phosphorus of the converter steelmaking is ≤0.005% by mass percentage. For example, it can be 0.005%, 0.004%, 0.003%, 0.002% or 0.001%, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0038] As a preferred technical solution of the present invention, the deoxidizer used in the LF refining includes aluminum powder and / or silicon carbide.

[0039] Preferably, the holding time of the white slag in the LF refining is 15 - 30 min. For example, it can be 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 30 min, 31 min, 32 min, 33 min, 34 min or 35 min, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0040] Preferably, the S content in the LF refining process is ≤0.002% by mass percentage. For example, it can be 0.002%, 0.0018%, 0.0016%, 0.0014%, 0.0012% or 0.001%, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0041] Preferably, the slag system composition of the LF refining includes, by mass percentage: CaO 45 - 53%, MgO 3 - 6%, SiO2 ≤8%, and the balance is Al2O3.

[0042] Preferably, the V alloy includes ferrovanadium alloy and / or flake vanadium.

[0043] In the present invention, in the ferrovanadium alloy, the mass percentage content of vanadium is 48-55%.

[0044] Preferably, the V-containing alloy is supplemented after the first power-on of refining for ≥15 min, and stirred for 2-3 min. For example, it can be 2 min, 2.5 min, 3 min, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0045] Preferably, the tapping temperature of the LF refining is 1635-1655 °C. For example, it can be 1635 °C, 1640 °C, 1645 °C, 1650 °C, 1655 °C, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0046] Preferably, the time of LF refining is ≥60 min. For example, it can be 60 min, 65 min, 70 min, 75 min, 80 min, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0047] Preferably, the molten steel composition at the end of LF refining includes, by mass percentage: C 0.11-0.13%, Si 0.26-0.30%, Mn 1.25-1.30%, S≤0.002%, P≤0.015%, V 0.05-0.07%, and the balance is Fe and inevitable impurities.

[0048] As a preferred technical solution of the present invention, the N alloy includes a manganese-nitrogen alloy wire.

[0049] Preferably, the time of deep vacuum in VD is ≥15 min. For example, it can be 15 min, 20 min, 25 min, 30 min, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0050] Preferably, the absolute vacuum degree of the VD vacuum is ≤67 MPa. For example, it can be 67 MPa, 65 MPa, 64 MPa, 62 MPa, 60 MPa, 55 MPa, 50 MPa, 45 MPa, 40 MPa, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0051] Preferably, a heat preservation agent is added after breaking the vacuum in the VD vacuum, and soft blowing is ≥20 min. For example, it can be 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0052] In the present invention, the heat insulator may be a commonly used heat insulator in the art such as carbonized rice husk, and 40 - 45 kg is added per heat treatment.

[0053] Preferably, the tapping temperature of the molten iron in the VD vacuum is 1545 - 1565 °C. For example, it may be 1545 °C, 1550 °C, 1555 °C, 1560 °C, 1565 °C, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0054] Preferably, the final molten iron composition in the VD vacuum, by mass percentage, includes: C 0.11 - 0.13%, Si 0.26 - 0.30%, Mn 1.31 - 1.35%, S ≤ 0.002%, P ≤ 0.015%, V 0.05 - 0.07%, N 0.0050 - 0.0070%, H ≤ 0.0002%, and the balance is Fe and unavoidable impurities.

[0055] As a preferred technical solution of the present invention, the superheat temperature of the molten steel in the continuous casting is 15 - 35 °C. For example, it may be 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0056] Preferably, in the continuous casting, the casting machine adopts a constant casting speed, and the casting speed is 1.5 - 1.7 m / min. For example, it may be 1.5 m / min, 1.52 m / min, 1.54 m / min, 1.56 m / min, 1.58 m / min, 1.6 m / min, 1.62 m / min, 1.64 m / min, 1.66 m / min, 1.68 m / min, 1.7 m / min, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0057] Preferably, the tapping temperature of the continuous casting billet is 1250 - 1270 °C. For example, it may be 1250 °C, 1252 °C, 1254 °C, 1256 °C, 1258 °C, 1260 °C, 1262 °C, 1264 °C, 1266 °C, 1268 °C, 1270 °C, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0058] Preferably, the heating time ≥ 300 min. For example, it may be 300 min, 310 min, 320 min, 330 min, 340 min, 350 min, 360 min, 370 min, 380 min, 390 min, 400 min, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0059] Preferably, the final temperature of the heating is the rolling starting temperature.

[0060] Preferably, the starting rolling temperature of the rolling is ≥900°C. For example, it can be 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, 1020°C, 1050°C, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0061] Preferably, the finishing rolling temperature of the rolling is 760 - 850°C. For example, it can be 760°C, 765°C, 770°C, 775°C, 780°C, 785°C, 790°C, 795°C, 800°C, 805°C, 810°C, 815°C, 825°C, 830°C, 835°C, 840°C, 845°C, 850°C, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0062] As a preferred technical solution of the present invention, the quenching temperature is 910 - 930°C. For example, it can be 910°C, 911°C, 912°C, 913°C, 914°C, 915°C, 916°C, 917°C, 918°C, 919°C, 920°C, 921°C, 922°C, 923°C, 924°C, 925°C, 926°C, 927°C, 928°C, 929°C, 930°C, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0063] Preferably, the quenching time is 90 - 120 min. For example, it can be 90 min, 92 min, 94 min, 96 min, 98 min, 100 min, 102 min, 104 min, 106 min, 108 min, 110 min, 112 min, 114 min, 116 min, 118 min, 120 min, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0064] Preferably, the tempering time is 90 - 120 min. For example, it can be 90 min, 92 min, 94 min, 96 min, 98 min, 100 min, 102 min, 104 min, 106 min, 108 min, 110 min, 112 min, 114 min, 116 min, 118 min, 120 min, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0065] In the present invention, through the KR process, the S content of the steel grade is ensured to be ≤0.001%, the difficulty of refining desulfurization is reduced, a specific ternary refining slag is used to reduce the entry of foreign inclusions. And during refining, the composition is accurately controlled to ensure the welding performance of the material and the stability of the performance after subsequent heat treatment. Through VD, the gas content is ensured to be H≤1.2 ppm and N≤50 - 70 ppm.

[0066] As a preferred technical solution of the present invention, the preparation method includes: sequentially performing pretreatment on hot metal, converter steelmaking, LF refining, VD vacuum, continuous casting, heating, rolling, quenching and tempering to obtain the corrosion-resistant steel;

[0067] The pretreatment is KR desulfurization treatment; a desulfurizing agent is added during the pretreatment; the desulfurizing agent includes calcium oxide, fluorite powder and aluminum powder, and the addition amounts are 10 - 15 kg / t, 1.5 - 2.5 kg / t and 0.5 - 1 kg / t respectively; the stirring speed during the pretreatment is 70 - 85 r / min and the time is 12 - 15 min; the sulfur content in the hot metal after the pretreatment is ≤0.001% by mass percentage;

[0068] The tapping temperature of the converter steelmaking is 1600 - 1650°C; the end-point carbon of the converter steelmaking is ≤0.05% by mass percentage; the end-point phosphorus of the converter steelmaking is ≤0.005% by mass percentage;

[0069] The deoxidizer used in the LF refining includes aluminum powder and / or silicon carbide; the holding time of the white slag in the LF refining is 15 - 30 min; the S content during the LF refining process is ≤0.002% by mass percentage; the slag system composition of the LF refining includes, by mass percentage: CaO 45 - 53%, MgO 3 - 6%, SiO2≤8%, and the balance is Al2O3; a V-containing alloy is supplemented during the LF refining; the V-containing alloy includes ferrovanadium alloy and / or flake vanadium; the V-containing alloy is supplemented after the first power-on of the refining for ≥15 min and stirred for 2 - 3 min; the tapping temperature of the LF refining is 1635 - 1655°C; the time of the LF refining is ≥60 min; the end-point molten steel composition of the LF refining includes, by mass percentage: C 0.11 - 0.13%, Si 0.26 - 0.30%, Mn 1.25 - 1.30%, S≤0.002%, P≤0.015%, V 0.05 - 0.07%, and the balance is Fe and inevitable impurities;

[0070] The VD vacuum supplements N-containing alloy; the N alloy includes manganese-nitrogen alloy wire; the time of deep vacuum in the VD vacuum is ≥15 min; the absolute vacuum degree of the VD vacuum is ≤67 MPa; a heat preservation agent is added after breaking the vacuum in the VD vacuum, and soft blowing is ≥20 min; the off-station temperature of the molten iron in the VD vacuum is 1545 - 1565 °C; the composition of the molten iron at the end point of the VD vacuum includes, by mass percentage: C 0.11 - 0.13%, Si 0.26 - 0.30%, Mn 1.31 - 1.35%, S ≤0.002%, P ≤0.015%, V 0.05 - 0.07%, N 0.0050 - 0.0070%, H ≤0.0002%, and the balance is Fe and unavoidable impurities;

[0071] The superheat temperature of the molten steel in the continuous casting is 15 - 35 °C; the continuous casting machine adopts a constant casting speed, and the casting speed is 1.5 - 1.7 m / min; the tapping temperature of the continuous casting billet is 1250 - 1270 °C;

[0072] The heating time is ≥300 min; the end point temperature of heating is the starting rolling temperature of rolling; the starting rolling temperature of rolling is ≥900 °C; the final rolling temperature of rolling is 760 - 850 °C;

[0073] The quenching temperature is 910 - 930 °C; the quenching time is 90 - 120 min;

[0074] The tempering temperature is 510 - 530 °C; the tempering time is 90 - 120 min.

[0075] Compared with the prior art solutions, the present invention has the following beneficial effects:

[0076] The steel provided by the present invention, through the design of the composition of the steel, by reducing the tempering temperature, improves the temperature stability and enhances the hydrogen sulfide corrosion resistance of the steel. The performance of the steel pipe meets the use requirements, and the performance is excellent, with the final performance of yield strength ≥549.8 MPa, tensile strength ≥666.2 MPa, and elongation ≥22.6%. Specific Embodiments

[0077] To better illustrate the present invention and facilitate understanding of the technical solutions of the present invention, the typical but non-limiting embodiments of the present invention are as follows:

[0078] Example 1

[0079] This embodiment provides a corrosion-resistant steel, specifically a pipeline steel for onshore acidic service oil and gas. The corrosion-resistant steel comprises, by mass percentage: C 0.14%, Si 0.25%, Mn 1.3%, V 0.06%, N 0.006%, P 0.02%, S 0.008%, and the balance is Fe and inevitable impurities.

[0080] The preparation process is as follows:

[0081] The molten iron is successively subjected to pretreatment, converter steelmaking, LF refining, VD vacuum treatment, continuous casting, heating, rolling, quenching and tempering to obtain the corrosion-resistant steel;

[0082] The pretreatment is KR desulfurization treatment; a desulfurizing agent is added in the pretreatment; the desulfurizing agent comprises calcium oxide, fluorite powder and aluminum powder, and the addition amounts are 12 kg / t, 2 kg / t and 0.75 kg / t respectively; the stirring speed in the pretreatment is 77 r / min and the time is 13 min; the sulfur content in the molten iron after pretreatment is 0.001% by mass percentage;

[0083] The tapping temperature of the converter steelmaking is 1625 °C; the end point carbon of the converter steelmaking is 0.05% by mass percentage; the end point phosphorus of the converter steelmaking is 0.005% by mass percentage;

[0084] The deoxidizer used in the LF refining is silicon carbide; the holding time of the white slag in the LF refining is 20 min; the S content in the LF refining process is 0.002% by mass percentage; the slag system composition of the LF refining is, by mass percentage: CaO 50%, MgO 5%, SiO2 8%, and the balance is Al2O3; a V-containing alloy is supplemented in the LF refining; the V-containing alloy is flake vanadium; the V-containing alloy is supplemented 15 min after the first power-on in the refining and stirred for 2 min; the tapping temperature of the LF refining is 1640 °C; the time of the LF refining is 60 min; the end point molten steel composition of the LF refining is, by mass percentage: C 0.12%, Si 0.28%, Mn 1.27%, S 0.002%, P 0.015%, V 0.06%, and the balance is Fe and inevitable impurities;

[0085] The VD vacuum supplements N-containing alloy; the N alloy includes manganese-nitrogen alloy wire; the time of deep vacuum in the VD vacuum is 15 min; the absolute vacuum degree of the VD vacuum is 67 MPa; after breaking the vacuum in the VD vacuum, a heat preservation agent (carbonized rice husk, 40 kg) is added and soft blowing is carried out for 20 min; the tapping temperature of the molten iron in the VD vacuum is 1550 °C; the end-point molten iron composition of the VD vacuum includes, by mass percentage: C 0.12%, Si 0.28%, Mn 1.31%, S 0.002%, P 0.015%, V 0.06%, N 0.0057%, H 0.000137%, and the balance is Fe and inevitable impurities;

[0086] The superheat temperature of the molten steel in the continuous casting is 20 °C; the continuous casting machine adopts a constant casting speed, and the casting speed is 1.6 m / min; the tapping temperature of the continuous casting billet is 1260 °C;

[0087] The heating time is 300 min; the end-point temperature of heating is the rolling starting temperature; the rolling starting temperature is 900 °C; the final rolling temperature is 800 °C;

[0088] The quenching temperature is 920 °C; the quenching time is 100 min;

[0089] The tempering temperature is 520 °C; the tempering time is 110 min.

[0090] The mechanical properties of the obtained steel are shown in Table 1 in detail.

[0091] Example 2

[0092] This embodiment provides a corrosion-resistant steel, specifically a pipeline steel for onshore acidic service oil and gas, and the corrosion-resistant steel includes, by mass percentage: C 0.12%, Si 0.35%, Mn 1.4%, V 0.05%, N 0.007%, P 0.01%, S 0.001%, and the balance is Fe and inevitable impurities.

[0093] The preparation process is specifically as follows:

[0094] The molten iron is pretreated, converted into steel in a converter, refined in LF, vacuum-treated in VD, continuously cast, heated, rolled, quenched and tempered in sequence to obtain the corrosion-resistant steel;

[0095] The pretreatment is KR desulfurization treatment; a desulfurizing agent is added in the pretreatment; the desulfurizing agent includes calcium oxide, fluorite powder and aluminum powder, and the addition amounts are 10 kg / t, 2.5 kg / t and 0.5 kg / t respectively; the rotation speed of stirring in the pretreatment is 70 r / min and the time is 15 min; the sulfur content in the hot metal after the pretreatment is 0.0001% by mass percentage;

[0096] The tapping temperature of the converter steelmaking is 1600 °C; the final carbon of the converter steelmaking is 0.01% by mass percentage; the final phosphorus of the converter steelmaking is 0.001% by mass percentage;

[0097] The deoxidizer used in the LF refining is aluminum powder; the holding time of the white slag in the LF refining is 30 min; the S content during the LF refining process is 0.001% by mass percentage; the slag system composition of the LF refining includes by mass percentage: CaO 45%, MgO 6%, SiO2 3%, and the balance is Al2O3; a V-containing alloy is supplemented in the LF refining; the V alloy is ferroniobium alloy (composition: vanadium 48%, and the balance is iron and inevitable impurities); the V-containing alloy is supplemented 30 min after the first power-on in the refining and stirred for 3 min; the tapping temperature of the LF refining is 1655 °C; the time of the LF refining is 70 min; the final molten steel composition of the LF refining includes by mass percentage: C 0.11%, Si 0.27%, Mn 1.29%, S 0.002%, P 0.01%, V 0.055%, and the balance is Fe and inevitable impurities;

[0098] A N-containing alloy is supplemented in the VD vacuum; the N alloy includes a manganese-nitrogen alloy wire; the time of deep vacuum in the VD vacuum is 35 min; the absolute vacuum degree of the VD vacuum is 27 MPa; a heat preservation agent (carbonized rice husk, 40 kg) is added after breaking the vacuum in the VD vacuum and soft blowing is carried out for 30 min; the off-station temperature of the hot metal in the VD vacuum is 1545 °C; the final hot metal composition of the VD vacuum includes by mass percentage: C 0.12%, Si 0.27%, Mn 1.33%, S 0.002%, P 0.01%, V 0.06%, N 0.0056%, H 0.0001%, and the balance is Fe and inevitable impurities;

[0099] The superheat temperature of the molten steel in the continuous casting is 15 °C; a constant casting speed is adopted in the continuous casting machine, and the casting speed is 1.7 m / min; the tapping temperature of the continuous casting billet is 1250 °C;

[0100] The heating time is 400 min; the end temperature of heating is the starting rolling temperature of rolling; the starting rolling temperature of rolling is 1000 °C; the final rolling temperature of rolling is 760 °C;

[0101] The quenching temperature is 910 °C; the quenching time is 120 min;

[0102] The tempering temperature is 530 °C; the tempering time is 90 min.

[0103] The mechanical properties of the obtained steel are shown in Table 1 in detail.

[0104] Example 3

[0105] This embodiment provides a corrosion-resistant steel, specifically a pipeline steel for onshore acidic service oil and gas. The corrosion-resistant steel comprises, by mass percentage: C 0.16%, Si 0.2%, Mn 1.25%, V 0.08%, N 0.005%, P 0.001%, S 0.004%, and the balance is Fe and inevitable impurities.

[0106] The preparation process is as follows:

[0107] The hot metal is pretreated, converted into steel in a converter, refined by LF, vacuum-treated by VD, continuously cast, heated, rolled, quenched and tempered in sequence to obtain the corrosion-resistant steel;

[0108] The pretreatment is KR desulfurization treatment; a desulfurizer is added in the pretreatment; the desulfurizer comprises calcium oxide, fluorite powder and aluminum powder, and the addition amounts are 15 kg / t, 1.5 kg / t and 1 kg / t respectively; the rotation speed of stirring in the pretreatment is 85 r / min and the time is 12 min; the sulfur content in the hot metal after pretreatment is 0.0005% by mass percentage;

[0109] The tapping temperature of the converter steelmaking is 1650 °C; the final carbon content of the converter steelmaking is 0.03% by mass percentage; the final phosphorus content of the converter steelmaking is 0.002% by mass percentage;

[0110] The deoxidizer used in the LF refining is silicon carbide; the holding time of the white slag in the LF refining is 15 min; the S content in the LF refining process is 0.0002% by mass percentage; the slag system composition of the LF refining includes, by mass percentage: 53% CaO, 3% MgO, 5% SiO2, and the balance is Al2O3; a V-containing alloy is supplemented in the LF refining; the V alloy is flake vanadium; the V-containing alloy is supplemented 45 min after the first power-on in the refining and stirred for 2 min; the tapping temperature of the LF refining is 1635 °C; the time of the LF refining is 90 min; the final molten steel composition of the LF refining includes, by mass percentage: 0.11% C, 0.28% Si, 1.26% Mn, 0.002% S, 0.015% P, 0.06% V, and the balance is Fe and inevitable impurities;

[0111] A N-containing alloy is supplemented in the VD vacuum; the N alloy includes a manganese-nitrogen alloy wire; the time of deep vacuum in the VD vacuum is 25 min; the absolute vacuum degree of the VD vacuum is 35 MPa; a heat preservation agent (carbonized rice husk, 40 kg) is added after breaking the vacuum in the VD vacuum and soft blown for 40 min; the off-station temperature of the molten iron in the VD vacuum is 1565 °C; the final molten iron composition of the VD vacuum includes, by mass percentage: 0.13% C, 0.28% Si, 1.32% Mn, 0.002% S, 0.015% P, 0.06% V, 0.0063% N, 0.00012% H, and the balance is Fe and inevitable impurities;

[0112] The superheat temperature of the molten steel in the continuous casting is 35 °C; the continuous casting machine adopts a constant casting speed, and the casting speed is 1.5 m / min; the tapping temperature of the continuous casting billet is 1270 °C;

[0113] The heating time is 500 min; the final heating temperature is the starting rolling temperature of the rolling; the starting rolling temperature of the rolling is 1200 °C; the final rolling temperature of the rolling is 850 °C;

[0114] The quenching temperature is 930 °C; the quenching time is 90 min;

[0115] The tempering temperature is 510 °C; the tempering time is 120 min.

[0116] The mechanical properties of the obtained steel are shown in Table 1 in detail.

[0117] Example 4

[0118] The difference from Example 1 is only that the content of N element in the steel is 0.01%, and the increased amount is to reduce the same amount of Fe. The mechanical properties of the obtained steel are shown in Table 1 in detail.

[0119] Example 5

[0120] The difference from Example 1 is only that the content of N element in the steel is 0.001%, and the insufficient amount is made up with an equal amount of Fe. The mechanical properties of the obtained steel are shown in Table 1 for details.

[0121] Example 6

[0122] The difference from Example 1 is only that the content of V element in the steel is 0.001%, and the insufficient amount is made up with an equal amount of Fe. The mechanical properties of the obtained steel are shown in Table 1 for details.

[0123] Example 7

[0124] The difference from Example 1 is only that the tempering temperature is 600 °C. The mechanical properties of the obtained steel are shown in Table 1 for details.

[0125] Example 8

[0126] The difference from Example 1 is only that the tempering temperature is 400 °C. The mechanical properties of the obtained steel are shown in Table 1 for details.

[0127] In the present invention, the mechanical property test and corrosion resistance test of the steel obtained in the above examples are carried out according to ASTM A370-2021 and NACE TM0284-2016 respectively.

[0128] Table 1

[0129]

[0130] From the results of the above examples, it can be seen that the corrosion-resistant steel provided by the present invention is designed by designing the composition of the steel. Specifically, the contents of C and Mn are designed to ensure the toughness of the material, a certain amount of V element is added, and V and N are combined under a certain nitrogen content to promote the refinement of the grain structure in the steel during the heat treatment process, improve the tempering stability of the thick-walled pipe, thereby improving the corrosion resistance, extending the service life of the steel pipe in a harsh environment, having good hydrogen-induced cracking resistance, and the steel does not crack under the detection conditions.

[0131] It is stated that the present invention uses the above examples to illustrate the detailed structural features of the present invention, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of the components selected by the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0132] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0133] In addition, it should be noted that, in the various specific technical features described in the above specific embodiments, they can be combined in any suitable manner without conflict. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0134] Furthermore, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A corrosion-resistant steel, characterized in that, The corrosion-resistant steel contains, by mass percentage: C 0.13 - 0.14%, Si 0.24 - 0.31%, Mn 1.28 - 1.32%, V 0.06 - 0.07%, N 0.0054 - 0.0057%, P ≤ 0.02%, S ≤ 0.008%, and the balance is Fe and unavoidable impurities.

2. A preparation method of the corrosion-resistant steel as described in claim 1, characterized in that, The preparation method includes: Pre-treating hot metal, converting steel in a converter, refining in LF, vacuum degassing in VD, continuous casting, heating, rolling, quenching, and tempering in sequence to obtain the corrosion-resistant steel; Adding V-containing alloy during LF refining; Adding N-containing alloy during VD vacuum degassing; The tempering temperature is 510 - 530 °C.

3. The preparation method according to claim 2, characterized in that, The pre-treatment is KR desulfurization treatment.

4. The preparation method according to claim 2, characterized in that, A desulfurizing agent is added during the pre-treatment.

5. The preparation method according to claim 4, characterized in that, The desulfurizing agent includes calcium oxide, fluorite powder, and aluminum powder, and the addition amounts are 10 - 15 kg / t, 1.5 - 2.5 kg / t, and 0.5 - 1 kg / t respectively.

6. The preparation method according to claim 2, wherein The stirring speed during the pre-treatment is 70 - 85 r / min, and the time is 12 - 15 min.

7. The preparation method according to claim 2, characterized in that, The sulfur content in the hot metal after the pre-treatment is ≤ 0.001% by mass percentage.

8. The preparation method according to claim 2, characterized in that, The tapping temperature of the converter steelmaking is 1600 - 1650 °C.

9. The preparation method according to claim 2, wherein, The final carbon content of the converter steelmaking is ≤ 0.05% by mass percentage.

10. The preparation method according to claim 2, characterized in that, The final phosphorus content of the converter steelmaking is ≤ 0.005% by mass percentage.

11. The preparation method according to claim 2, characterized in that, The deoxidizer used during LF refining includes aluminum powder and / or silicon carbide.

12. The preparation method according to claim 2, wherein, The holding time of the white slag during LF refining is 15 - 30 min.

13. The preparation method according to claim 2, characterized in that, The S content during LF refining process is ≤ 0.002% by mass percentage.

14. The preparation method according to claim 2, characterized in that, The slag system composition of LF refining includes, by mass percentage: CaO 45 - 53%, MgO 3 - 6%, SiO2 ≤ 8%, and the balance is Al2O3.

15. The preparation method according to claim 2, wherein The V alloy includes ferrovanadium alloy and / or flake vanadium.

16. The preparation method according to claim 2, wherein, The V-containing alloy is added after the first power-on of refining for ≥ 15 min and stirred for 2 - 3 min.

17. The preparation method according to claim 2, wherein The tapping temperature of LF refining is 1635 - 1655 °C.

18. The preparation method according to claim 2, characterized in that, The time of LF refining is ≥ 60 min.

19. The preparation method according to claim 2, characterized in that, The final molten steel composition of LF refining includes, by mass percentage: C 0.11 - 0.13%, Si 0.26 - 0.30%, Mn 1.25 - 1.30%, S ≤ 0.002%, P ≤ 0.015%, V 0.05 - 0.07%, and the balance is Fe and unavoidable impurities.

20. The preparation method according to claim 2, characterized in that, The N alloy includes manganese nitride alloy wire.

21. The preparation method according to claim 2, wherein The deep vacuum time during VD vacuum degassing is ≥ 15 min.

22. The preparation method according to claim 2, characterized in that, The absolute vacuum degree of VD vacuum is ≤ 67 MPa.

23. The preparation method according to claim 2, wherein A heat preservation agent is added after breaking the vacuum during VD vacuum, and soft blowing is ≥ 20 min.

24. The preparation method according to claim 2, wherein, The off-station temperature of the hot metal during VD vacuum is 1545 - 1565 °C.

25. The preparation method according to claim 2, wherein The molten iron composition at the end of the VD vacuum contains, by mass percentage: C 0.11 - 0.13%, Si 0.26 - 0.30%, Mn 1.31 - 1.35%, S ≤ 0.002%, P ≤ 0.015%, V 0.05 - 0.07%, N 0.0050 - 0.0070%, H ≤ 0.0002%, and the balance is Fe and unavoidable impurities.

26. The preparation method according to claim 2, characterized in that, The superheat temperature of the molten steel in the continuous casting is 15 - 35 °C.

27. The preparation method according to claim 2, characterized in that, In the continuous casting, the casting machine adopts a constant casting speed, and the casting speed is 1.5 - 1.7 m / min.

28. The preparation method according to claim 2, characterized in that, In the continuous casting, the tapping temperature of the billet is 1250 - 1270 °C.

29. The preparation method according to claim 2, wherein The heating time ≥ 300 min.

30. The preparation method according to claim 2, wherein, The end temperature of the heating is the rolling starting temperature.

31. The preparation method according to claim 30, characterized in that, The rolling starting temperature ≥ 900 °C.

32. The preparation method according to claim 2, characterized in that, The final rolling temperature of the rolling is 760 - 850 °C.

33. The preparation method according to claim 2, characterized in that, The quenching temperature is 910 - 930 °C.

34. The preparation method according to claim 2, characterized in that, The quenching time is 90 - 120 min.

35. The preparation method according to claim 2, characterized in that, The tempering time is 90 - 120 min.

36. The preparation method according to claim 2, characterized in that, The preparation method includes: Pre-treating the molten iron, converting steel in a converter, refining in LF, performing VD vacuum, continuous casting, heating, rolling, quenching and tempering in sequence to obtain the corrosion-resistant steel; The pre-treatment is KR desulfurization treatment; a desulfurizing agent is added in the pre-treatment; the desulfurizing agent includes calcium oxide, fluorite powder and aluminum powder, and the addition amounts are respectively 10 - 15 kg / t, 1.5 - 2.5 kg / t and 0.5 - 1 kg / t; the stirring speed in the pre-treatment is 70 - 85 r / min, and the time is 12 - 15 min; the sulfur content in the molten iron after the pre-treatment is ≤ 0.001% by mass percentage; The tapping temperature of the converter steelmaking is 1600 - 1650 °C; the end carbon in the converter steelmaking is ≤ 0.05% by mass percentage; the end phosphorus in the converter steelmaking is ≤ 0.005% by mass percentage; The deoxidizer used in the LF refining includes aluminum powder and / or silicon carbide; the holding time of the white slag in the LF refining is 15 - 30 min; the S content in the LF refining process is ≤ 0.002% by mass percentage; the slag system composition of the LF refining includes, by mass percentage: CaO 45 - 53%, MgO 3 - 6%, SiO2 ≤ 8%, and the balance is Al2O3; a V-containing alloy is supplemented in the LF refining; the V-containing alloy includes ferrovanadium alloy and / or flake vanadium; the V-containing alloy is supplemented after the first power-on in the refining for ≥ 15 min and stirred for 2 - 3 min; the tapping temperature of the LF refining is 1635 - 1655 °C; the time of the LF refining ≥ 60 min; the molten steel composition at the end of the LF refining includes, by mass percentage: C 0.11 - 0.13%, Si 0.26 - 0.30%, Mn 1.25 - 1.30%, S ≤ 0.002%, P ≤ 0.015%, V 0.05 - 0.07%, and the balance is Fe and unavoidable impurities; Add N-containing alloy in the VD vacuum; the N-containing alloy includes manganese-nitrogen alloy wire; the deep vacuum time in the VD vacuum is ≥15 min; the absolute vacuum degree of the VD vacuum is ≤67 MPa; add a heat preservation agent after breaking the vacuum in the VD vacuum, and soft blow for ≥20 min; the tapping temperature of the molten iron in the VD vacuum is 1545 - 1565 °C; the end-point molten iron composition of the VD vacuum includes, by mass percentage: C 0.11 - 0.13%, Si 0.26 - 0.30%, Mn 1.31 - 1.35%, S ≤0.002%, P ≤0.015%, V 0.05 - 0.07%, N 0.0050 - 0.0070%, H ≤0.0002%, and the balance is Fe and inevitable impurities; The superheat temperature of the molten steel in the continuous casting is 15 - 35 °C; the continuous casting machine adopts a constant casting speed, and the casting speed is 1.5 - 1.7 m / min; the tapping temperature of the continuous casting billet is 1250 - 1270 °C; The heating time is ≥300 min; the end-point temperature of heating is the rolling starting temperature; the rolling starting temperature is ≥900 °C; the final rolling temperature is 760 - 850 °C; The quenching temperature is 910 - 930 °C; the quenching time is 90 - 120 min; The tempering temperature is 510 - 530 °C; the tempering time is 90 - 120 min.

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