Low-cost high-toughness super-thick 450MPa-grade marine pipeline steel and production method thereof

Abstract

The invention relates to low-cost high-toughness super-thick specification 450 MPa-grade marine pipeline steel. A hot-rolled coiled plate comprises the following chemical components in percentage by mass: 0.040-0.080% of C, 1.10-1.30% of Mn, 0.07-0.25% of Si, less than or equal to 0.0020% of S, less than or equal to 0.015% of P, 0.010-0.030% of Ti, 0.025-0.050% of Nb, 0.20-0.30% of Cr, less than or equal to 0.0005% of B, less than or equal to 1.5 ppm of H, less than or equal to 50 ppm of N and the balance of Fe and inevitable impurities. The production method comprises the working procedures of converter smelting, LF + RH refining, continuous casting, heating, rolling, ultra-fast cooling + laminar cooling and coiling. Low-carbon, manganese and niobium composite microalloying is utilized, medium-carbon ferromanganese is adopted to replace metal manganese, the low heating temperature is matched with the low-pressure ultra-fast cooling and layer cooling process, and the material cost is reduced on the premise that the performance of the ultra-thick steel strip is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline steel metallurgy, and in particular to a low-cost, high-toughness, ultra-thick 450MPa-grade marine pipeline steel and a production method thereof. Technical Background

[0002] Due to the harsh marine environment, the quality and product performance requirements for oil and gas pipeline steel in marine engineering are higher than those for land pipelines. Therefore, marine pipelines must have high transverse strength, longitudinal strength, good low-temperature crack arrest toughness, and deformation resistance. At the same time, they must also have strong resistance to seawater and corrosion resistance to transported acidic media.

[0003] Existing technologies primarily achieve the high toughness requirements and excellent acid corrosion resistance of pipeline steel by employing low C and Mn content, microalloying with Nb, V, and Ti, and adding alloying elements such as Cr, Cu, Ni, and Mo. Precious alloying elements like Ni, Cu, and Mo are expensive, so choosing relatively inexpensive alloys to reduce costs while simultaneously meeting the high toughness and corrosion resistance requirements of marine pipeline steel is particularly important for hot-rolling production lines.

[0004] Patent application CN109234487A discloses a production method for submarine pipeline steel X65MO. Its chemical composition and main process are as follows: C = 0.03-0.08%, Si = 0.10-0.30%, Mn = 0.80-1.00%, P ≤ 0.015%, S ≤ 0.0015%, Nb = 0.01-0.02%, V = 0.02-0.05%, Ti = 0.008-0.015%, Cr = 0.10-0.30%, Al = 0.008-0.020%, N = 0.008-0.012%, B ≤ 0.0005%, with the remainder being Fe and unavoidable impurities. The production process is pretreatment - converter - RH refining - LF refining - continuous casting - hot rolling - slow cooling pit. This is a process for producing wide and heavy plates.

[0005] Patent publication number CN111118399A discloses "A 15-22mm thick, corrosion-resistant, high-crack arrest submarine pipeline steel X65MO and its production method." Its chemical composition is as follows: C: 0.05%-0.08%; Si: 0.10%-0.20%; Mn: 1.10%-1.30%; P ≤ 0.015%; S ≤ 0.002%; Al ≤ 0.040%; Nb: 0.035%-0.050%; Ti: 0.015%-0.025%; Cr: 0.20%-0.30%; Ce: 0.0010%-0.0020%; Mo: 0.10-0.20%; H ≤ 2.0 ppm; O ≤ 30 ppm; N ≤ 60 ppm, with the remainder being Fe and unavoidable inclusions. The production process is converter-LF refining-continuous casting-hot rolling. This patent adds precious alloying elements Mo and rare earth element Ce, resulting in high alloy costs.

[0006] The invention patent application with publication number CN112575158B discloses "A high-plasticity thick-gauge pipeline steel plate and its manufacturing method", whose chemical composition and mass percentage are: C: 0.03-0.10%, Si: 0.1-0.5%, Mn: 1.51-1.85%, P≤0.015%, S≤0.002%, Cr: 0.05-0.3%, Mo: 0.05-0.20%, Cu: 0.06-0.3%, Ni: 0.17-0.50%, Nb: 0.05-0.10%, Ti: 0.005-0.02%, Ca: 0.001-0.005%, Al: 0.02-0.045%, N≤0.006%, B≤0.0002%, O≤0.005%, and the remainder is Fe and unavoidable inclusions; and 0.06≤J C×Mn ≤0.14, carbon-manganese product parameter J C×Mn =C*Mn*10 4 The production process is billet casting-hot rolling. This patent adds precious alloy elements Cu, Ni, and Mo, which increases the alloy cost.

[0007] Patent application CN116463552A discloses "A Thick-Gauge, Economical, High-Performance Hot-Rolled Steel Coil for Submarine Pipelines and Its Production Method." Its chemical composition and percentage by mass are as follows: C: 0.045%-0.065%, Si: 0.21%-0.30%, Mn: 1.30%-1.42%, P ≤ 0.011%, S ≤ 0.0015%, Ti: 0.010%-0.020%, Nb: 0.035%-0.045%, Cr: 0.25%-0.35%, Al: 0.020%-0.050%, N: 0.0025%-0.0050%, O ≤ 0.0030%, H ≤ 0.0002%, with the remainder being Fe and unavoidable impurities. The production process is converter-LF refining-RH refining-continuous casting-hot rolling. This patent only studies the impact toughness but does not study the fracture toughness CTOD, which has certain limitations. At the same time, the thickness of the hot-rolled steel coil is 15-20 mm. Summary of the Invention

[0008] In response to the deficiencies in the prior art, the present invention provides a low-cost, high-toughness, ultra-thick 450MPa-grade marine pipeline steel and a production method, which significantly reduces production costs while ensuring the performance requirements of 450MPa-grade marine pipeline steel.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is: A low-cost, high-toughness, ultra-thick 450MPa-grade marine pipeline steel. The chemical composition and weight percentage of the hot-rolled steel strip are as follows: C: 0.040-0.080%, Mn: 1.10-1.30%, Si: 0.07-0.25%, S: ≤0.0020%, P: ≤0.015%, Ti: 0.010-0.030%, Nb: 0.025-0.050%, Cr: 0.20-0.30%, B: ≤0.0005%, H: ≤1.5ppm, N: ≤50ppm, and the balance is Fe and unavoidable impurities.

[0010] The low-cost, high-toughness, ultra-thick 450MPa-grade marine pipeline steel disclosed in the present invention has a hot-rolled coil yield strength of 450-500MPa, a tensile strength of 530-600MPa, a yield strength ratio of ≤0.90, a low-temperature Charpy impact energy of ≥300J at -60°C, a drop hammer shear area of ≥85% at -40°C, a fracture toughness CTOD characteristic value of infinity, an HIC resistance index of 0, and a SSC resistance of no cracks or fractures. The thickness is 20-25mm.

[0011] The mass percentage of Nb in the present invention is 0.025% to 0.050%. Nb is a strong carbonitride-forming element. By combining niobium microalloying technology with a controlled rolling and controlled cooling process, the effects of grain refinement and precipitation strengthening are fully exerted, while the formation of acicular ferrite structure is promoted, thereby significantly improving the strength and toughness of the steel.

[0012] The present invention does not add precious alloy elements such as Cu, Ni, and Mo, thereby significantly reducing alloy costs.

[0013] The present invention provides a method for preparing a low-cost, high-toughness, ultra-thick 450MPa-grade marine pipeline steel, comprising the following steps: converter smelting, LF+RH refining, continuous casting, billet heating, rolling, ultra-fast cooling+laminar cooling, and coiling.

[0014] KR desulfurization treatment is used before the converter smelting process to ensure that the sulfur content of molten iron is less than or equal to 0.0030%; In the converter smelting process, argon is blown from the bottom throughout the converter smelting process, the final C content is less than or equal to 0.030%, the final P content is less than or equal to 0.010%, and medium carbon ferromanganese is used for alloying during the steelmaking process.

[0015] In the LF refining process, deep desulfurization is carried out using white slag, and the S content is less than or equal to 0.0030%.

[0016] RH refining process, vacuum degree ≤ 150Pa, RH refining time ≥ 15 minutes.

[0017] The continuous casting process adopts full protection casting, the casting speed is 1.0-1.5m / min, and the superheat is controlled at 15-30℃.

[0018] The heating process of the casting is carried out at a temperature of 1180-1220°C and a residence time of 195-300 minutes.

[0019] In the rolling process, the rough rolling adopts the 1+5 mode, the intermediate billet is 55-60mm, the steel is swung before the finishing rolling, the finishing rolling entrance temperature is controlled at <1050℃, the final rolling temperature is 850-890℃, and the final reduction rate is ≥10%.

[0020] Ultra-fast cooling + laminar cooling process, the laminar cooling adopts low-pressure ultra-fast cooling + laminar cooling mode, the cooling rate is 25-40℃ / s, and it is cooled to 460℃~520℃ for coiling.

[0021] The beneficial effects of the technical solution are: The present invention adopts a low-cost composition design with low C, low Mn, low Nb and Ti composite microalloying without adding Cu, Ni and Mo. Under the premise of ensuring sufficient solid solution of the alloy elements, a low heating temperature is adopted in combination with a reasonable low-pressure ultra-fast cooling + layer cooling process to obtain a uniform and fine grain structure. The hot-rolled coil produced achieves excellent corrosion resistance while meeting the requirements of high strength and high toughness.

[0022] The present invention realizes, in a low-cost component system, that the 450MPa-grade marine pipeline steel hot-rolled coil has a yield strength of 450-500MPa, a tensile strength of 530-600MPa, a yield strength ratio of ≤0.90, a low-temperature Charpy impact energy of ≥300J at -60°C, a drop weight shear area of ≥85% at -40°C, a fracture toughness CTOD characteristic value of infinity, an HIC resistance index of 0, and a SSC resistance of no cracks or fractures. The steel meets the requirements for use under complex marine environmental conditions, has broad prospects for promotion and application, and can generate significant economic and social benefits.

[0023] The present invention utilizes low-C, low-Mn, and low-Nb composite microalloying, adopts medium-carbon ferromanganese to replace metallic manganese, and achieves a low-cost component design without adding Cu, Ni, and Mo. While ensuring sufficient solid solution of the alloying elements, the present invention adopts a low heating temperature and combines a reasonable low-pressure ultra-fast cooling + layer cooling process. This reduces material costs while ensuring the material properties, HIC resistance, and SSC resistance of the 20-25 mm ultra-thick steel strip. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely. Example 1

[0025] Smelting: After molten iron pretreatment (S≤0.0030%), the molten iron enters the converter for smelting. The smelting process adopts bottom blowing of argon throughout the process. The final carbon content is 0.028%, and the final phosphorus content is 0.008%. Medium carbon ferromanganese is added for alloying during the steelmaking process.

[0026] The LF refining furnace uses white slag for refining, and the sulfur content at the outlet is 0.0012%.

[0027] The RH refining furnace maintained a vacuum degree of ≤150Pa for 16 minutes, and the hydrogen content at the outlet was 0.85ppm.

[0028] The continuous casting speed is 1.2m / min, the superheat is controlled at 19-22℃, and the billet thickness is 230mm.

[0029] The thickness of the low-cost, high-toughness, ultra-thick 450 MPa grade marine pipeline steel in this embodiment is 22.0 mm, and its chemical composition and mass percentage are shown in Table 1.

[0030] The heating temperature of the casting is 1185-1202℃, and the residence time is controlled at 195min.

[0031] Rough rolling 1+5 mode, intermediate billet 55mm, pre-finishing swing steel, finishing rolling entrance temperature controlled at 1043℃, final rolling temperature 860℃, last pass reduction rate 12%.

[0032] The layer cooling adopts low-pressure ultra-fast cooling + laminar cooling mode with a cooling rate of 30℃ / s, and is cooled to 460℃ for coiling.

[0033] The properties of the low-cost, high-toughness, ultra-thick 450 MPa grade marine pipeline steel hot-rolled coil in this embodiment are shown in Table 2, the HIC resistance properties are shown in Table 3, and the SSCC resistance properties are shown in Table 4. Example 2

[0034] Smelting: After molten iron pretreatment (S≤0.0030%), the molten iron enters the converter for smelting. The smelting process adopts bottom blowing of argon throughout the process. The final carbon content is 0.030%, and the final phosphorus content is 0.009%. Medium carbon ferromanganese is added for alloying during the steelmaking process.

[0035] The LF refining furnace uses white slag for refining, and the sulfur content at the outlet is 0.0008%.

[0036] The RH refining furnace maintained a vacuum degree of ≤150Pa for 16 minutes, and the hydrogen content at the outlet was 0.68ppm.

[0037] The continuous casting speed is 1.5m / min, the superheat is controlled at 18-20℃, and the thickness of the casting is 230mm.

[0038] The thickness of the low-cost, high-toughness, ultra-thick 450 MPa grade marine pipeline steel in this embodiment is 24.2 mm, and its chemical composition and mass percentage are shown in Table 1.

[0039] The heating temperature of the casting is 1190-1212℃, and the residence time is controlled at 196min.

[0040] Rough rolling 1+5 mode, intermediate billet 58mm, pre-swing steel for finishing rolling, finishing rolling inlet temperature controlled at 1035℃, final rolling temperature 870℃, and final pass reduction rate 10%.

[0041] The layer cooling adopts low-pressure ultra-fast cooling + laminar cooling mode with a cooling rate of 29℃ / s, and is cooled to 510℃ for coiling.

[0042] The properties of the low-cost, high-toughness, ultra-thick 450 MPa grade marine pipeline steel hot-rolled coil in this embodiment are shown in Table 2, the HIC resistance properties are shown in Table 3, and the SSCC resistance properties are shown in Table 4. Example 3

[0043] Smelting: After molten iron pretreatment (S≤0.0030%), the molten iron enters the converter for smelting. The smelting process adopts bottom blowing of argon throughout the process. The final carbon content is 0.030%, and the final phosphorus content is 0.01%. Medium carbon ferromanganese is added for alloying during the steelmaking process.

[0044] The LF refining furnace uses white slag for refining, and the sulfur content at the outlet is 0.003%.

[0045] The RH refining furnace maintained a vacuum degree of ≤150Pa for 15 minutes, and the hydrogen content at the outlet was 0.68ppm.

[0046] The continuous casting speed is 1.0m / min, the superheat is controlled at 15-30℃, and the thickness of the casting is 230mm.

[0047] The thickness of the low-cost, high-toughness, ultra-thick 450 MPa grade marine pipeline steel in this embodiment is 24.2 mm, and its chemical composition and mass percentage are shown in Table 1.

[0048] The heating temperature of the casting is 1180-1220℃, and the residence time is controlled at 300min.

[0049] Rough rolling 1+5 mode, intermediate billet 58mm, pre-swing steel for finishing rolling, finishing rolling inlet temperature controlled at 1035℃, final rolling temperature 870℃, and final pass reduction rate 10%.

[0050] The layer cooling adopts low-pressure ultra-fast cooling + laminar cooling mode with a cooling rate of 29℃ / s, and is cooled to 510℃ for coiling.

[0051] The properties of the low-cost, high-toughness, ultra-thick 450 MPa grade marine pipeline steel hot-rolled coil in this embodiment are shown in Table 2, the HIC resistance properties are shown in Table 3, and the SSCC resistance properties are shown in Table 4. Example 4

[0052] Smelting: After molten iron pretreatment (S≤0.0030%), the molten iron enters the converter for smelting. The smelting process adopts bottom blowing of argon throughout the process. The final carbon content is 0.030%, and the final phosphorus content is 0.01%. Medium carbon ferromanganese is added for alloying during the steelmaking process.

[0053] The LF refining furnace uses white slag for refining, and the sulfur content at the outlet is 0.003%.

[0054] The RH refining furnace maintained a vacuum degree of ≤150Pa for 15 minutes, and the hydrogen content at the outlet was 0.68ppm.

[0055] The continuous casting speed is 1.0m / min, the superheat is controlled at 15-30℃, and the thickness of the casting is 230mm.

[0056] The thickness of the low-cost, high-toughness, ultra-thick 450 MPa grade marine pipeline steel in this embodiment is 24.2 mm, and its chemical composition and mass percentage are shown in Table 1.

[0057] The heating temperature of the casting is 1180-1220℃, and the residence time is controlled at 300min.

[0058] Rough rolling 1+5 mode, intermediate billet 60mm, pre-finishing swing steel, finishing rolling entrance temperature controlled at 1035℃, final rolling temperature 870℃, last pass reduction rate 10%.

[0059] The layer cooling adopts low-pressure ultra-fast cooling + laminar cooling mode with a cooling rate of 40℃ / s, and is cooled to 510℃ for coiling.

[0060] The properties of the low-cost, high-toughness, ultra-thick 450 MPa grade marine pipeline steel hot-rolled coil in this embodiment are shown in Table 2, the HIC resistance properties are shown in Table 3, and the SSCC resistance properties are shown in Table 4.

[0061] Table 1 Chemical composition and composition of low-cost, high-toughness, ultra-thick 450MPa grade marine pipeline steel hot-rolled steel strip of Example 1-2 (%)

[0062] Table 2 Performance of low-cost, high-toughness, ultra-thick 450MPa grade marine pipeline steel hot-rolled coils in Example 1-2

[0063] Table 3 Test data of HIC resistance of hot-rolled coil of low-cost, high-toughness, ultra-thick 450MPa grade marine pipeline steel in Example 1-2

[0064] Table 4: Test data on the SSC resistance of hot-rolled coils of low-cost, high-toughness, ultra-thick 450 MPa marine pipeline steel in Example 1-2

[0065] In summary, the low-cost, high-toughness, ultra-thick 450MPa grade marine pipeline steel obtained by the present invention has the characteristics of cost-effectiveness, low-temperature toughness and crack arrest performance, and corrosion resistance, and can be used for the construction of pipeline projects under complex marine environmental conditions.

[0066] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A low-cost, high-toughness, ultra-thick 450MPa grade marine pipeline steel, characterized by: The chemical composition of the hot-rolled steel strip and its mass percentage are: C: 0.040-0.080%, Mn: 1.10-1.30%, Si: 0.07-0.25%, S: ≤0.0020%, P: ≤0.015%, Ti: 0.010-0.030%, Nb: 0.025-0.050%, Cr: 0.20-0.30%, B: ≤0.0005%, H: ≤1.5ppm, N: ≤50ppm, and the balance is Fe and unavoidable impurities.

2. The low-cost, high-toughness, ultra-thick 450MPa grade marine pipeline steel according to claim 1, characterized in that: The yield strength of the hot-rolled coil is 450-500MPa, the tensile strength is 530-600MPa, the yield ratio is ≤0.90, the low-temperature Charpy impact energy at -60℃ is ≥300J, the drop hammer shear area at -40℃ is ≥85%, the fracture toughness CTOD characteristic value is infinite, the HIC resistance index is 0, the SSC resistance is no crack or fracture, and the thickness is 20-25mm.

3. A method for preparing a low-cost, high-toughness, ultra-thick 450MPa grade marine pipeline steel according to claim 1, characterized in that: The process includes converter smelting, LF+RH refining, continuous casting, billet heating, rolling, ultra-fast cooling + laminar cooling and coiling.

4. The method for preparing a low-cost, high-toughness, ultra-thick 450MPa grade marine pipeline steel according to claim 3, characterized in that: KR desulfurization treatment is used before the converter smelting process to ensure that the sulfur content of molten iron is less than or equal to 0.0030%; In the converter smelting process, argon is blown from the bottom throughout the entire process, and the mass percentage of C at the end point is less than or equal to 0.030%, and the mass percentage of P at the end point is less than or equal to 0.010%.

5. The method for preparing a low-cost, high-toughness, ultra-thick 450MPa grade marine pipeline steel according to claim 3, characterized in that: In the LF refining process, deep desulfurization is carried out using white slag, and the S content by mass is less than or equal to 0.0030%.

6. The method for preparing a low-cost, high-toughness, ultra-thick 450MPa grade marine pipeline steel according to claim 3, characterized in that: RH refining process, vacuum degree ≤150Pa, RH refining time ≥15 minutes.

7. The method for preparing a low-cost, high-toughness, ultra-thick 450MPa grade marine pipeline steel according to claim 3, characterized in that: Continuous casting process, fully protected casting, casting speed 1.0-1.5m / min, superheat 15-30℃.

8. The method for preparing a low-cost, high-toughness, ultra-thick 450MPa grade marine pipeline steel according to claim 3, characterized in that: The heating process of the casting is carried out at a temperature of 1180-1220°C and a residence time of 195-300 minutes.

9. The method for preparing a low-cost, high-toughness, ultra-thick 450MPa grade marine pipeline steel according to claim 3, characterized in that: In the rolling process, the rough rolling adopts the 1+5 mode, the intermediate billet is 55-60mm, the steel is swung before the finishing rolling, the finishing rolling entrance temperature is controlled at <1050℃, the final rolling temperature is 850-890℃, and the final reduction rate is ≥10%.

10. The method for preparing a low-cost, high-toughness, ultra-thick 450MPa grade marine pipeline steel according to claim 3, characterized in that: Low-pressure ultra-fast cooling + laminar cooling process, with a cooling rate of 25-40°C / s, cooling to 460-520°C for coiling.

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