Industrial manufacturing method of economical thick-specification steel hot-rolled plate coil for carbon dioxide pipeline transportation

Abstract

The invention discloses an industrial manufacturing method of an economical thick-specification steel hot-rolled plate coil for carbon dioxide pipeline transportation. The economical thick-specification steel hot-rolled plate coil comprises the following chemical components in percentage by mass: less than or equal to 0.07% of C, less than or equal to 0.25% of Si, 1.35-1.50% of Mn, less than or equal to 0.013% of P, less than or equal to 0.002% of S, 0.03-0.04% of Nb, less than or equal to 0.02% of Ti, less than or equal to 0.25% of Cr, less than or equal to 0.18% of Ni and the balance of Fe and inevitable impurities. The invention further discloses a specific production process flow. According to the economical industrial manufacturing method for the steel hot-rolled plate coil for carbon dioxide pipeline transportation, low-carbon C-Mn steel is taken as a main component design, trace Nb, Cr and the like are added for alloying, and an ultra-low sulfur and phosphorus smelting control technology and a TMCP controlled rolling and controlled cooling technology are combined, so that the steel hot-rolled plate coil with excellent transverse and longitudinal strength plasticity, low-temperature toughness and welding formability is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of pipeline steel industrial manufacturing, and in particular relates to an industrial manufacturing method of an economical thick-gauge hot-rolled steel coil for carbon dioxide pipeline transportation. Background Art

[0002] Long-distance CO2 pipeline transportation is a key link in the CCUS industry chain connecting CO2 capture, utilization and storage, and also meets the development needs of high-efficiency and low-cost transportation.

[0003] 1. Document 1, "A Carbon Dioxide Transport Pipeline Steel and Its Production Method" (CN 119287276A), discloses an alloy composition of Mn+Nb+Ti+Cr+Ni+Mo, and the finished product is a wide and thick steel plate, using a wide and thick plate rolling process. This patented alloy composition is Mn+Nb+Ti+Cr+Ni, without the addition of the precious metal element Mo, resulting in lower alloy cost. The finished product is a coil, and the process uses TMCP hot continuous rolling and laminar cooling control.

[0004] 2. Reference 2, "An X65-Grade Supercritical Carbon Dioxide Pipeline Steel, Preparation Method, and Application thereof" (CN118497606A), discloses an alloy composition of Mn+Nb+Ti+Cr+Ni+Mo+Cu. This patented alloy composition is exclusively Mn+Nb+Ti+Cr+Ni, without the addition of precious metal elements Mo and Cu. The upper limits of Cr ≤ 0.25% and Ni ≤ 0.18% are significantly lower than those in Reference 2, resulting in a lower overall alloy cost. Furthermore, the patent utilizes an ultra-low phosphorus and sulfur control process to achieve high clean steel levels of P ≤ 0.013% and S ≤ 0.002%, further enhancing low-temperature toughness and corrosion resistance.

[0005] 3. Document 3, "A Production Method for X65MC Supercritical Carbon Dioxide Transport Pipeline Steel" (CN 118186302A), discloses an alloy composition of Mn+Nb+Ti+Cr+Mo, and the finished product is a wide and thick steel plate, using the same rolling process. This patented alloy composition is Mn+Nb+Ti+Cr+Ni, but uses the more cost-effective Ni instead of the precious metal Mo, resulting in a lower total alloy cost. Refining utilizes a LF+RH combination, with 230mm continuous casting billets hot-charged at ≤600°C, a target tapping temperature of 1160°C-1170°C, and a heating time of 170-270 minutes, making it more energy-efficient and efficient than Document 1. Summary of the Invention

[0006] The purpose of the present invention is to provide an economical and thick-gauge hot-rolled steel coil industrial manufacturing method for carbon dioxide pipeline transportation. The composition design is mainly low-carbon C-Mn steel, with trace amounts of Nb, Cr and other alloying elements added. Combined with ultra-low phosphorus and sulfur smelting control technology and TMCP controlled rolling and controlled cooling process, a pipeline steel hot-rolled coil with excellent transverse and longitudinal strength and plasticity, low-temperature toughness and weldability is obtained.

[0007] The hot-rolled coils produced meet the following performance requirements: transverse yield strength of 490MPa-570MPa, tensile strength of 550MPa-620MPa, elongation ≥40%, yield ratio ≤0.88; longitudinal yield strength of 450MPa-500MPa, tensile strength of 550MPa-620MPa, elongation ≥35%, yield ratio ≤0.85. Charpy impact energy (Akv) at -40°C is ≥300J, grain size is >Grade 11, and drop weight shear fracture rate at -25°C is ≥90%. After welding, the steel pipes have passed welding and girth welding compatibility evaluations conducted by a recognized organization and meet the technical specifications for a CO2 pipeline project.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] The present invention discloses an economical, thick-gauge hot-rolled steel coil for carbon dioxide pipeline transportation. The production process comprises the following steps: KR molten iron desulfurization pretreatment - converter top and bottom blowing - LF refining - RH refining - slab continuous casting - reheating - controlled rolling of roughing and finishing mills - cooling - coiling - pallet transport system - sampling and inspection. The controlled rolling steps of the roughing and finishing mills include roughing high-pressure water descaling - fixed-width press - E1R1 roughing mill - E2R2 roughing mill - insulation cover - flying shear - finishing high-pressure water descaling - F1-F7 finishing mills. Cooling adopts encrypted laminar flow cooling. Specifically:

[0010] Ultra-low sulfur and phosphorus smelting and continuous casting control process: The hot metal must undergo KR desulfurization treatment. The sulfur content of the hot metal entering the converter must be ≤0.005%, the P content of the hot metal supplied to the converter must be ≤0.16%, and the desulfurized slag removal area must be greater than 95%. The tapping temperature must be ≥1620°C to ensure that the composition and temperature are coordinated. If a new taphole or an abnormal ladle turnover occurs, the tapping temperature may be increased by 10-15°C above the upper limit. Ferroaluminum, ferrosilicon, and ferromanganese are added during the converter tapping process for deoxidation and alloying. The LF furnace undergoes slag desulfurization, and ferroaluminum, ferrosilicon, ferromanganese, and ferroniobium alloys are added to adjust the composition to the target range. The vacuum level in the RH process must be ≤2.6 mbar, maintained for ≥15 minutes, and the circulating pure degassing time must be ≥10 minutes. Temperature measurement and sampling must be performed during the RH vacuum treatment. Calcium treatment is performed after the RH vacuum treatment, and the soft blowing time after wire feeding must be greater than 10 minutes to prevent exposed molten steel. Soft reduction technology for continuous casting ingots is used to control center segregation.

[0011] High-efficiency slab heating and rolling process: Continuous casting slabs with a thickness of 230mm are loaded into the furnace at a temperature of <600°C, heated to 1160°C-1180°C in a walking beam furnace, and then subjected to two-stage controlled rolling through ≤8 passes of rough rolling and 7 passes of finishing rolling. The intermediate slab is ≤60mm, and the finishing temperature of finishing rolling is ≤850°C. Subsequently, the slab is cooled quickly and evenly using an intensified laminar cooling method, and coiled at a temperature of ≤550°C.

[0012] The chemical composition of the hot-rolled coil, calculated by mass percentage, is C≤0.07%, Si≤0.25%, Mn1.35%-1.50%, P≤0.013%, S≤0.005%, Nb 0.03%-0.04%, Ti≤0.02%, Cr≤0.25%, Ni≤0.18%, and the balance is Fe and unavoidable impurities.

[0013] Furthermore, the chemical composition of the hot-rolled coil is C 0.06%, Si 0.20%, Mn 1.44%, P 0.011%, S 0.001%, Nb+V+Ti 0.064%, Cr+Ni 0.29%, and the balance is Fe and unavoidable impurities.

[0014] Furthermore, the chemical composition of the hot-rolled coil is C 0.05%, Si 0.19%, Mn 1.41%, P 0.007%, S 0.001%, Nb+V+Ti 0.061%, Cr+Ni 0.29%, and the balance is Fe and unavoidable impurities.

[0015] Furthermore, the chemical composition of the hot-rolled coil is C 0.06%, Si 0.18%, Mn 1.47%, P 0.010%, S 0.001%, Nb+V+Ti 0.059%, Cr+Ni 0.30%, and the balance is Fe and unavoidable impurities.

[0016] Furthermore, the performance of the hot-rolled coil meets the following technical requirements: transverse yield strength 490MPa-570MPa, tensile strength 550MPa-620MPa, elongation ≥40%, and yield strength ratio ≤0.88.

[0017] Furthermore, the performance of the hot-rolled coil meets the following technical requirements: longitudinal yield strength 450MPa-500MPa, tensile strength 550MPa-620MPa, elongation ≥35%, and yield strength ratio ≤0.85.

[0018] Furthermore, the performance of the hot-rolled coil meets the following technical requirements: -40℃ Charpy impact energy A kv ≥300J, grain size>11 grade, -25℃ drop hammer tear shear fracture rate ≥90%.

[0019] The main elements were chosen for the following reasons:

[0020] C: Increasing the carbon content in steel increases yield strength and tensile strength, but reduces ductility and toughness. For pipeline steel, excessively high carbon content can dramatically reduce toughness and impair weldability. Therefore, adopting a low-carbon design approach is a prerequisite for high-toughness pipeline product design. Therefore, the present invention controls the carbon content to ≤ 0.07%.

[0021] Mn: Manganese can form an unlimited solid solution substitution with iron, making it a highly effective solid solution strengthening element. It is primarily used in pipeline steel to compensate for the strength loss caused by reduced carbon content, making it the most important and economical strengthening element. Mn also expands the γ phase region, lowering the γ-α transition temperature of steel. This helps produce finer transformation products, improves steel toughness, and lowers the ductile-brittle transition temperature. Therefore, the manganese content in this invention is 1.35%-1.50%.

[0022] P: P in steel can inhibit cementite precipitation and significantly strengthen ferrite through solid solution. However, excessive P content can affect the steel's performance, such as causing cold brittleness at low temperatures. The coiled steel of the present invention, in particular, requires low-temperature toughness. Therefore, the P content must be strictly controlled. In the present invention, the P content is controlled to ≤0.013%.

[0023] Nb: Niobium improves the strength and toughness of steel, making it the most typical and widely used microalloying element. Niobium carbonitrides can precipitate from austenite during heating and rolling, at phase boundaries during phase transformation, or from supersaturated ferrite during final cooling to refine grains. Niobium most significantly increases the recrystallization temperature of austenite and lowers the brittle transition temperature. However, Nb is a precious element, so the niobium content in this invention is controlled to 0.03% to 0.04%.

[0024] Cr, Ni: Chromium and nickel improve the hardenability of steel, imparting improved plasticity and toughness after quenching. Chromium significantly enhances steel's corrosion and oxidation resistance, while nickel offers high corrosion resistance to acids and alkalis, as well as rust prevention and heat resistance at high temperatures. However, chromium and nickel alloys are also expensive, so their contents are generally controlled to ≤0.25% for Cr and ≤0.18% for Ni.

[0025] Compared with the prior art, the present invention has the following beneficial technical effects:

[0026] The design is simple and economical, mainly using low-carbon medium-manganese steel. The absence of V, Mo, and Cu precious metal elements ensures strength performance and matches the energy-saving and efficient heating system, which helps enterprises reduce costs and increase efficiency. The ultra-low phosphorus and sulfur control process achieves a high clean steel control level of P≤0.013% and S≤0.002%, which is more conducive to ensuring the low-temperature toughness and corrosion resistance of the product, and has good economic benefits and significant progress.

[0027] The hot-rolled coils produced meet the following performance requirements: transverse yield strength of 490MPa-570MPa, tensile strength of 550MPa-620MPa, elongation ≥40%, yield ratio ≤0.88; longitudinal yield strength of 450MPa-500MPa, tensile strength of 550MPa-620MPa, elongation ≥35%, yield ratio ≤0.85. Charpy impact energy (Akv) at -40°C is ≥300J, grain size is >Grade 11, and drop weight shear fracture rate at -25°C is ≥90%. After welding, the steel pipes have passed welding and girth welding compatibility evaluations conducted by a recognized organization and meet the technical specifications for a CO2 pipeline project. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below with reference to the accompanying drawings.

[0029] Figure 1 The metallographic structure of the embodiment is polygonal ferrite + a small amount of bainite, and the grain size is above 11 levels.

[0030] Figure 2 This is the result of the adaptability evaluation of the steel pipe girth welding process. DETAILED DESCRIPTION

[0031] Example

[0032] The present invention will be further described below by way of examples.

[0033] The chemical compositions of Examples 1 and 2 are shown in Table 1 below, the specific process systems used in each Example are shown in Table 2 below, and the mechanical properties of the hot-rolled coils obtained in each Example are shown in Table 3 below.

[0034] Table 1: Chemical composition of example steel (wt, %)

[0035] Example C Si Mn P S Nb+V+Ti Cr+Ni 1 0.06 0.20 1.44 0.011 0.001 0.064 0.29 2 0.05 0.19 1.41 0.007 0.001 0.061 0.27 3 0.06 0.18 1.47 0.010 0.001 0.059 0.30

[0036] Table 2: Process system of the embodiment

[0037]

[0038] Table 3: Mechanical properties of steel in the examples

[0039]

[0040]

[0041] As can be seen from the examples, the chemical composition and mechanical properties of the steel in the examples of the present invention meet the requirements of the API 5LL450M grade standard with a moderate margin. The steel has a transverse yield strength of 490MPa-570MPa, a tensile strength of 550MPa-620MPa, an elongation of ≥40%, and a yield strength ratio of ≤0.88. The longitudinal yield strength is 450MPa-500MPa, a tensile strength of 550MPa-620MPa, an elongation of ≥35%, and a yield strength ratio of ≤0.85. The Charpy impact energy (Akv) at -40°C is ≥300J, the grain size is >11, and the drop weight tear shear fraction at -25°C is ≥90%. After welding, the steel pipe has passed welding and girth welding suitability evaluations by a recognized organization and meets the technical specifications of a CO2 pipeline project.

[0042] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. An economical method for industrially manufacturing thick-gauge hot-rolled steel coils for carbon dioxide pipeline transportation, characterized by: include: Ultra-low sulfur and phosphorus smelting and continuous casting control process: The hot metal must undergo KR desulfurization treatment. The sulfur content of the hot metal entering the converter must be ≤0.005%, the P content of the hot metal supplied to the converter must be ≤0.16%, and the desulfurized slag removal area must be greater than 95%. The tapping temperature must be ≥1620°C to ensure that the composition and temperature are coordinated. If a new taphole or an abnormal ladle turnover occurs, the tapping temperature may be increased by 10-15°C above the upper limit. Ferroaluminum, ferrosilicon, and ferromanganese are added during the converter tapping process for deoxidation and alloying. The LF furnace undergoes slag desulfurization, and ferroaluminum, ferrosilicon, ferromanganese, and ferroniobium alloys are added to adjust the composition to the target range. The vacuum level in the RH process must be ≤2.6 mbar, maintained for ≥15 minutes, and the circulating pure degassing time must be ≥10 minutes. Temperature measurement and sampling must be performed during the RH vacuum treatment. Calcium treatment is performed after the RH vacuum treatment, and the soft blowing time after wire feeding must be greater than 10 minutes to prevent exposed molten steel. Soft reduction technology for continuous casting ingots is used to control center segregation. High-efficiency slab heating and rolling process: Continuous casting slabs with a thickness of 230mm are loaded into the furnace at a temperature of <600°C, heated to 1160°C-1180°C in a walking beam furnace, and then subjected to two-stage controlled rolling through ≤8 passes of rough rolling and 7 passes of finishing rolling. The intermediate slab is ≤60mm, and the finishing temperature of finishing rolling is ≤850°C. Subsequently, the slab is cooled quickly and evenly using an intensified laminar cooling method, and coiled at a temperature of ≤550°C. The chemical composition of the hot-rolled coil, calculated by mass percentage, is C≤0.07%, Si≤0.25%, Mn1.35%-1.50%, P≤0.013%, S≤0.005%, Nb 0.03%-0.04%, Ti≤0.02%, Cr≤0.25%, Ni≤0.18%, and the balance is Fe and unavoidable impurities.

2. The method for industrially manufacturing an economical thick-gauge hot-rolled steel coil for carbon dioxide pipeline transportation according to claim 1, characterized in that: The chemical composition of the hot-rolled coil is C 0.06%, Si 0.20%, Mn 1.44%, P 0.011%, S 0.001%, Nb+V+Ti 0.064%, Cr+Ni 0.29%, and the balance is Fe and unavoidable impurities.

3. The method for industrially manufacturing an economical thick-gauge hot-rolled steel coil for carbon dioxide pipeline transportation according to claim 1, characterized in that: The chemical composition of the hot-rolled coil is C 0.05%, Si 0.19%, Mn 1.41%, P 0.007%, S 0.001%, Nb+V+Ti 0.061%, Cr+Ni 0.29%, and the balance is Fe and unavoidable impurities.

4. The method for industrially manufacturing an economical thick-gauge hot-rolled steel coil for carbon dioxide pipeline transportation according to claim 1, characterized in that: The chemical composition of the hot-rolled coil is C 0.06%, Si 0.18%, Mn 1.47%, P 0.010%, S 0.001%, Nb+V+Ti 0.059%, Cr+Ni 0.30%, and the balance is Fe and unavoidable impurities.

5. The method for industrially manufacturing an economical thick-gauge hot-rolled steel coil for carbon dioxide pipeline transportation according to claim 1, characterized in that: The performance of the hot-rolled coil meets the following technical requirements: transverse yield strength 490MPa-570MPa, tensile strength 550MPa-620MPa, elongation ≥40%, and yield strength ratio ≤0.

88.

6. The method for industrially manufacturing an economical thick-gauge hot-rolled steel coil for carbon dioxide pipeline transportation according to claim 1, characterized in that: The performance of the hot-rolled coil meets the following technical requirements: longitudinal yield strength 450MPa-500MPa, tensile strength 550MPa-620MPa, elongation ≥35%, and yield strength ratio ≤0.

85.

7. The method for industrially manufacturing an economical thick-gauge hot-rolled steel coil for carbon dioxide pipeline transportation according to claim 1, characterized in that: The performance of the hot rolled coil meets the following technical requirements: -40℃ Charpy impact energy A kv ≥300J, grain size>11 grade, -25℃ drop hammer tear shear fracture rate ≥90%.

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