A 1200mpa grade steel plate for marine environment mineral conveying pipeline and a production method thereof

Abstract

The application belongs to the field of metal materials, and provides a 1200MPa-grade steel plate for a marine environment ore conveying pipeline and a production method thereof.The composition of the steel plate is as follows in terms of percentage by weight: C: 0.18%-0.22%, Si: 0.51%-0.80%, Mn: 1.21%-1.50%, P: ≤0.015%, S: ≤0.001%, Cr: 0.91%-1.20%, Mo: 0.36%-0.50%, Al: 0.010%-0.050%, Nb: 0.06%-0.10%, Ti: 0.005%-0.025%, Ni: 1.01%-1.30%, Cu: 1.11%-1.40%, Ce: 0.01%-0.06%, and the balance of Fe and inevitable impurities.The production method comprises smelting, continuous casting, heating, rolling, accelerated cooling and tempering.The steel plate produced by the application has excellent comprehensive mechanical properties, and each performance meets the technical requirements of the 1200MPa-grade anti-erosion ore conveying pipeline in a marine environment.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and in particular relates to a steel plate for ore transport pipelines in marine environments with a pressure rating of 1200MPa and its production method. Background Technology

[0002] Long-distance pipelines are the main technological means to transport deep-sea mineral resources from the seabed to the surface and are indispensable equipment for deep-sea mining projects. However, the mixture of minerals and seawater results in a complex composition of the transport medium. In addition, the pipelines need to penetrate deep into the seabed and endure the extremely harsh deep-sea environment, which makes it imperative to improve the comprehensive performance of pipeline materials in terms of high pressure resistance, wear resistance, and corrosion resistance.

[0003] Pipeline lift mining systems are widely recognized globally as the most promising commercial deep-sea mining and ore transportation technology due to their advantages such as continuous operation, high mining efficiency, and relatively low energy consumption. The ore riser transports a mixture of seabed ore and seawater from the mining equipment to the surface at a specific speed and concentration, making it an indispensable piece of equipment for deep-sea mining projects. The working environment of deep-sea mining requires ore transport pipelines to be wear-resistant, seawater corrosion-resistant, and clog-resistant. To improve transportation efficiency while ensuring good pressure resistance in the deep-sea environment, wear-resistant and corrosion-resistant straight seam welded pipes made of steel plates are the preferred material due to their excellent pipe shape, moderate diameter, and uniform wall thickness.

[0004] Patent application number 202410369306.8 discloses a low-cost HB400-grade wear-resistant steel plate that does not require quenching and tempering, and its production method. Its chemical composition is: C: 0.10%–0.30%, Si: 0.30%–0.50%, Mn: 1.70%–1.90%, P≤0.020%, S≤0.010%, Als: 0.30%–0.60%, Cr: 0.20%–0.40%, Ti: 0.25%–0.45%, with the remainder being Fe and unavoidable impurities. Excellent wear resistance is achieved by forming a TiC particle-reinforcing phase. However, the wear-resistant design scheme differs from that of this invention. Furthermore, it lacks a specific design for seawater corrosion resistance and is not suitable for marine service environments.

[0005] Patent application number 202110178493.8 discloses a high-strength, wear-resistant steel and its preparation method. Its chemical composition is: C 0.12%–0.16%, Si 0.45%–0.55%, Mn 4.50%–5.50%, P ≤ 0.008%, S ≤ 0.0008%, Alt 0.01%–0.05%, with the balance being iron and unavoidable impurities. By adding more than 4.5% Mn, more than 90% lath martensite is obtained, resulting in extremely high wear resistance. However, such a high martensite content makes the steel brittle, which is detrimental to its formability and weldability, making it unsuitable for the forming and welding of deep-sea ore pipelines.

[0006] Patent application number 202211106045.8 discloses an HB500 grade high cold-bending wear-resistant steel and its production method. Its chemical composition is: C 0.15%–0.30%, Si 0–0.08%, Mn 1.0%–4.0%, P ≤0.015%, S ≤0.005%, Al 0.03%–0.06%, Ti 0.005%–0.030%, Cr 0.4%–1.0%, Mo 0–0.3%, with the balance being Fe and impurities. A martensitic structure is obtained by achieving an ultra-high cooling rate of over 100℃ / s, giving the steel plate good wear resistance. However, this design lacks resistance to seawater corrosion and is unsuitable for the highly abrasive environment of transporting seawater-containing minerals, failing to meet the stringent service conditions of deep-sea mineral transport.

[0007] In summary, the main problems currently existing in the production of steel for ore conveying risers are as follows:

[0008] (1) There is no matching design of the material’s wear resistance and fatigue resistance for the characteristics of mineral transportation and marine service conditions. It is not suitable for the strong abrasive environment of mineral transportation and cannot meet the harsh service conditions of deep-sea mineral transportation.

[0009] (2) The alloy content is high, with the total amount of alloying elements such as Cr and Ni exceeding 16%, which is detrimental to the formability and weldability of the steel plate and significantly increases the cost of the alloy. Summary of the Invention

[0010] The purpose of this invention is to overcome the above-mentioned problems and deficiencies and provide a 1200MPa grade marine environment ore transport pipeline steel plate and its production method that are suitable for the highly abrasive environment of mineral transport and meet the harsh service conditions of deep-sea mineral transport.

[0011] The objective of this invention is achieved as follows:

[0012] A 1200MPa grade marine ore transport pipeline steel plate, the steel plate having the following composition by weight percentage: C: 0.18%~0.22%, Si: 0.51%~0.80%, Mn: 1.21%~1.50%, P≤0.015%, S≤0.001%, Cr: 0.91%~1.20%, Mo: 0.36%~0.50%, Al: 0.010%~0.050%, Nb: 0.06%~0.10%, Ti: 0.005%~0.025%, Ni: 1.01%~1.30%, Cu: 1.11%~1.40%, Ce: 0.01%~0.06%, with the balance being Fe and unavoidable impurities.

[0013] Furthermore, the Cr+Mo content in the steel plate is ≥1.35%.

[0014] Furthermore, the Nb / Ce ratio in the steel plate is ≥1.5.

[0015] Furthermore, the microstructure of the steel plate is a mixture of tempered celestial body and nanoscale precipitates; wherein, by area percentage, the proportion of nanoscale precipitates is 6% to 7%, of which more than 90% of the precipitates are ≤30nm in size and are diffusely distributed.

[0016] Furthermore, the steel plate has a yield strength of 1250~1350MPa, a tensile strength of 1300~1500MPa, and an elongation of ≥10%; the steel plate has an impact energy of ≥110J at -20℃, a hardness of ≥420HBW, and an abrasion rate of less than 40% of that of Q460C steel in a simulated marine environment.

[0017] The rationale for the design of the components in this invention is as follows:

[0018] Carbon (C): A fundamental strengthening element in steel, C is the main element ensuring strength and hardness in the technical solution of this invention. Adding an appropriate amount of C can significantly improve the strength and hardness of the steel plate. C can also combine with V and Nb to form fine granular precipitates, further enhancing the strength and toughness of the steel. However, excessive C is detrimental to the welding, toughness, and plasticity of the steel plate. Therefore, considering factors such as cost and performance, the range of C in this invention is controlled to be 0.18%~0.22%.

[0019] Si (Si): Si can improve the hardenability of materials and play a solid solution strengthening role, increasing the strength and hardness of steel plates, thereby improving the wear resistance of steel. Adding an appropriate amount of Si to steel can also inhibit the precipitation of cementite, hinder the growth of carbides, and promote the finer and more dispersed distribution of carbides in the matrix, resulting in finer abrasive particles generated during wear, thus reducing the degree of wear and further improving wear resistance. However, high Si content can cause steel to become brittle and reduce toughness. Considering the balance between strength, wear resistance, and toughness, the Si content in this invention is controlled at 0.51%–1.20%.

[0020] Mn (manganese) is a common strengthening element in steel. It can dissolve in large quantities in the Fe matrix, increasing strength through solid solution strengthening. Manganese can lower the critical cooling rate of steel, promote martensite formation, significantly improve hardenability, and significantly lower the brittle transition temperature of steel, improve impact toughness, and refine the microstructure of steel, making it an important strengthening and toughening element. However, excessive Mn content can easily lead to segregation in steel, which adversely affects its corrosion resistance. Considering all factors, this invention controls the Mn content to be in the range of 1.21% to 1.50%.

[0021] Cr and Mo: These components improve the hardenability of steel, enabling accelerated cooling at high temperatures to promote microstructural transformation at medium and low temperatures, thus increasing the strength and hardness of the steel plate and significantly improving its wear resistance. In corrosive environments, Cr can form a dense passivation film on the steel surface, protecting the substrate. Mo improves the steel's resistance to chloride ion corrosion and reduces the tendency for pitting corrosion caused by chloride ions in seawater environments. The combined addition of Cr and Mo can further enhance corrosion resistance in marine environments. In this invention, the Cr content is controlled within the range of 0.91% to 1.20%, and the Mo content is controlled within the range of 0.36% to 0.50%, preferably Cr + Mo ≥ 1.35%.

[0022] Nitrogen (Nb) is a grain-refining element. When heated, undissolved Nb carbon and nitride particles are distributed along the austenite grain boundaries, hindering austenite grain growth during heating. It effectively delays the recrystallization of deformed austenite, prevents austenite grain growth, refines ferrite grains, improves the impact toughness of steel, and lowers its brittle transition temperature. Nb can also increase the solid solution content of rare earth elements such as Ce in steel, thereby improving the corrosion resistance of the steel. In this invention, the Nb content is controlled at 0.06%~0.10%, preferably Nb / Ce ≥ 1.5.

[0023] Ti is a strong nitrogen-containing element. Adding trace amounts of Ti to Al-containing steel can significantly reduce the corrosion rate, and Ti preferentially combines with nitrogen in the steel, reducing the amount of AlN and improving weldability. However, when the Ti content exceeds a certain value, the TiN particles coarsen, causing a deterioration in low-temperature toughness. Therefore, this invention selects a Ti content of 0.010% to 0.025%.

[0024] Al: Commonly used as a deoxidizer in steel, insufficient deoxidation leads to the formation of oxides from easily oxidized elements such as Ti; excessive aluminum content increases alumina inclusions, reducing the cleanliness of the steel. Therefore, this invention controls the Al content to be in the range of 0.010% to 0.050%.

[0025] Ni can improve the strength of steel, lower the critical cooling temperature, facilitate microstructure control and grain refinement, and improve low-temperature toughness. In this invention, the Ni content is controlled at 1.01%~1.30%.

[0026] Cu: Adding Cu to steel can improve its corrosion resistance and strength, as well as its formability and weldability. When used in conjunction with Ni, it can also prevent hot brittleness. An appropriate amount of Cu can also form fine, dispersed Cu-containing precipitates in the steel, which not only significantly improves strength and hardness but also does not negatively affect toughness. In this invention, the Cu content is controlled at 1.11%~1.40%.

[0027] Ce: Ce has a strong affinity for O and S, and can preferentially react with O and S in steel to form stable oxides and sulfides. This promotes the full flotation of these compounds in molten steel, which is more conducive to the removal of inclusions. Therefore, adding a small amount of Ce during steelmaking can improve the quality of steel by changing the morphology and distribution of inclusions. Furthermore, during the solidification process of steel, Ce can act as a nucleation core, increasing the number of crystal nuclei, thereby refining the grains and significantly improving the strength, toughness, and corrosion resistance of the steel. This invention controls the Ce content to be 0.01%~0.06%.

[0028] P and S: As impurity elements, phosphorus and sulfur significantly deteriorate the toughness, plasticity and weldability of steel, so their content in steel should be reduced as much as possible. In this invention, the content of P and S is required to be controlled at P≤0.015% and S≤0.001%, respectively.

[0029] The second technical solution of the present invention is to provide a method for producing steel plates for marine ore transport pipelines with a pressure rating of 1200MPa, including smelting, continuous casting, heating, rolling, accelerated cooling and tempering;

[0030] Heating: The slab adopts a multi-stage stepped temperature heating method, in which the high temperature heating section is 1200~1250℃, the soaking section is 1180~1220℃, and the time of the high temperature heating section + soaking section is not less than 120min;

[0031] The heating process is designed primarily to ensure the solid solution formation of elements such as Mn, Cr, Mo, Ni, Cu, and Nb, enabling them to play a role in subsequent rolling and accelerated cooling. At the same time, it effectively controls austenite grain growth. The heating time ensures heating effect and temperature uniformity.

[0032] Rolling: Steel plate rolling is carried out in two stages: roughing and finishing. The finishing temperature of the roughing stage is ≥1050℃, and the single-pass reduction rate of the last two passes of roughing is ≥14%, so as to fully break down and refine the original austenite grains. The intermediate billet thickness of the finishing stage is 3.0~3.5t, where t is the thickness of the finished steel plate (12~20mm). The initial rolling temperature is 880~930℃, the single-pass reduction rate of the first three passes of finishing is ≥13%, and the final rolling temperature is 820~860℃.

[0033] The design of the roughing rolling process primarily considers the full deformation of the steel at high temperatures, especially with the last two passes employing large single-pass reductions. The aim is to achieve excellent thickness-direction microstructure uniformity, while simultaneously promoting the formation of nanoscale precipitates, pinning grain boundaries and dislocations, refining the grains, and improving the steel's strength and toughness. The finishing rolling process is designed to increase the dislocation density and nucleation sites in the steel, further refining the grains, and completing the rolling deformation within a relatively lower temperature range to achieve a good balance of strength and toughness.

[0034] After the steel plate is rolled, it is accelerated cooled. The cooling rate of the accelerated cooling is 20~30℃ / s, and the final cooling temperature is <300℃.

[0035] Tempering: The cooled steel plate is tempered at a temperature of 430~480℃ for 4~5 min / mm. After being taken out of the furnace, the steel plate is air-cooled to room temperature.

[0036] The final microstructure control target was a mixed microstructure of tempered sorbite and nanoscale precipitates. The proportion of nanoscale precipitates was 6%–7%, with over 90% of the precipitates having a size ≤30 nm and exhibiting a diffuse distribution. Tempered sorbite possesses high comprehensive mechanical properties of strength, hardness, and toughness. The diffusely distributed nanoscale Cu-containing precipitates, acting as hard phase particles, not only significantly improve the hardness and wear resistance of the steel, but also maintain their diffuse precipitation state during welding, ensuring the strength of the weld heat-affected zone, significantly improving heat-affected zone softening, and enhancing the overall performance uniformity of the steel pipe.

[0037] The beneficial effects of this invention are as follows:

[0038] 1) This invention, based on C and Mn, adds appropriate amounts of alloying elements such as Cr, Mo, Ni, Cu, and Nb. Through the interaction between these elements and with suitable heating, rolling, cooling, and tempering heat treatment processes, a multiphase microstructure of tempered sorbite and nanoscale precipitates is ultimately obtained. Compared with existing technologies, this invention employs targeted composition and microstructure design to improve the strength-toughness balance and enhance the wear and corrosion resistance of steel plates, resulting in steel plates with excellent strength, toughness, and wear and corrosion resistance.

[0039] 2) The steel plate possesses excellent comprehensive mechanical properties, with a yield strength of 1250~1350MPa, tensile strength of 1300~1500MPa, and elongation ≥10%. The steel plate has an impact energy ≥110J at -20℃, a hardness ≥420HBW, and its abrasion rate in simulated marine environments is only less than 40% of that of Q460C steel. All properties meet the technical requirements for 1200MPa-grade abrasion-resistant ore transport pipelines in marine environments. Attached Figure Description

[0040] Figure 1This is a metallographic image of the microstructure of Embodiment 1 of the present invention.

[0041] Figure 2 This is a characteristic diagram of the nanoscale precipitated phase in Example 1 of the present invention. Detailed Implementation

[0042] The present invention will be further illustrated below through examples.

[0043] According to the component ratio of the technical solution, the embodiments of the present invention carry out smelting, continuous casting, heating, rolling, accelerated cooling and tempering.

[0044] Heating: The slab adopts a multi-stage stepped temperature heating method, in which the high temperature heating section is 1200~1250℃, the soaking section is 1180~1220℃, and the time of the high temperature heating section + soaking section is not less than 120min;

[0045] Rolling: Steel plate rolling is carried out in two stages: roughing and finishing. The finishing temperature of the roughing stage is ≥1050℃, and the single-pass reduction rate of the last two passes of roughing is ≥14%. The intermediate billet thickness of the finishing stage is 3.0~3.5t, where t is the thickness of the finished steel plate. The initial rolling temperature is 880~930℃, the single-pass reduction rate of the first three passes of finishing is ≥13%, and the final rolling temperature is 820~860℃.

[0046] After the steel plate is rolled, it is accelerated cooled. The cooling rate of the accelerated cooling is 20~30℃ / s, and the final cooling temperature is <300℃.

[0047] Tempering: The cooled steel plate is tempered at a temperature of 430-480℃ for 4-5 min / mm. After being taken out of the furnace, the steel plate is air-cooled to room temperature.

[0048] The composition of the steels in the embodiments and comparative examples of this invention is shown in Table 1. The main process parameters for heating the steels in the embodiments and comparative examples of this invention are shown in Table 2. The main process parameters for rolling, cooling, and tempering of the steels in the embodiments and comparative examples of this invention are shown in Table 3. The properties of the steels in the embodiments and comparative examples of this invention are shown in Table 4. The wear resistance and microstructure of the steels in the embodiments and comparative examples of this invention are shown in Table 5.

[0049] Table 1. Composition of steels in the embodiments and comparative examples of the present invention.

[0050]

[0051] Table 2 Main process parameters for heating steel in the embodiments and comparative examples of the present invention.

[0052]

[0053] Table 3. Main process parameters for steel rolling, cooling, and tempering in the embodiments and comparative examples of this invention.

[0054]

[0055] Table 4. Properties of steels in embodiments and comparative examples of the present invention.

[0056]

[0057] Table 5. Wear resistance and microstructure of the steels used in the embodiments and comparative examples of the present invention.

[0058]

[0059] As shown above, the steel plate possesses excellent comprehensive mechanical properties, with a yield strength of 1250~1350MPa, tensile strength of 1300~1500MPa, and elongation ≥10%. The steel plate has an impact energy ≥110J at ~20℃, a hardness ≥420HBW, and its abrasion rate in a simulated marine environment is only less than 40% of that of Q460C steel. All properties meet the technical requirements for 1200MPa-grade abrasion-resistant ore transport pipelines in marine environments.

[0060] To illustrate the present invention, the present invention has been appropriately and sufficiently described above through embodiments. The above embodiments are only for illustrating the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., should be included within the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A steel plate for ore transport pipelines in marine environments with a pressure rating of 1200MPa, characterized in that, The composition of the steel plate, by weight percentage, is as follows: C: 0.18%~0.22%, Si: 0.51%~0.80%, Mn: 1.21%~1.50%, P≤0.015%, S≤0.001%, Cr: 0.91%~1.20%, Mo: 0.36%~0.50%, Al: 0.010%~0.050%, Nb: 0.06%~0.10%, Ti: 0.005%~0.025%, Ni: 1.01%~1.30%, Cu: 1.11%~1.40%, Ce: 0.01%~0.02%. The content of the impurities is 0.06% to 0.06%, with the balance being Fe and unavoidable impurities; the microstructure of the steel plate is a mixed structure of tempered celestial body and nano-sized precipitates; wherein, by area percentage, the proportion of nano-sized precipitates is 6% to 7%, of which more than 90% of the precipitates have a size ≤30nm; the yield strength of the steel plate is 1250 to 1350MPa, the tensile strength is 1300 to 1500MPa, and the elongation is ≥10%; the impact energy of the steel plate at -20℃ is ≥110J, the hardness is ≥420HBW, and the abrasion rate in a simulated marine environment is less than 40% of that of Q460C steel.

2. The steel plate for ore transport pipelines in marine environments with a pressure rating of 1200MPa as described in claim 1, characterized in that, The steel plate contains Cr+Mo≥1.35%.

3. The steel plate for ore transport pipelines in marine environments with a pressure rating of 1200MPa as described in claim 1, characterized in that, The Nb / Ce ratio in the steel plate is ≥1.

5.

4. A method for producing a 1200MPa grade marine ore transport pipeline steel plate according to any one of claims 1-3, comprising smelting, continuous casting, heating, rolling, accelerated cooling and tempering; characterized in that: Heating: The slab adopts a multi-stage stepped temperature heating method, in which the high temperature heating section is 1200~1250℃, the soaking section is 1180~1220℃, and the time of the high temperature heating section + soaking section is not less than 120min; Rolling: Steel plate rolling is carried out in two stages: roughing and finishing. The finishing temperature of the roughing stage is ≥1050℃, and the single-pass reduction rate of the last two passes of roughing is ≥14%. The intermediate billet thickness of the finishing stage is 3.0~3.5t, where t is the thickness of the finished steel plate. The initial rolling temperature is 880~930℃, the single-pass reduction rate of the first three passes of finishing is ≥13%, and the final rolling temperature is 820~860℃. After the steel plate is rolled, it is accelerated cooled. The cooling rate of the accelerated cooling is 20~30℃ / s, and the final cooling temperature is <300℃. Tempering: The cooled steel plate is tempered at a temperature of 430~480℃ for 4~5 min / mm. After being taken out of the furnace, the steel plate is air-cooled to room temperature.

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