1000mpa grade steel plate for marine environment mineral conveying pipeline and production method thereof

Abstract

The application belongs to the field of metal materials, and provides a 1000MPa-grade steel plate for ocean 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: 0.31%-0.50%, Mn: 0.90%-1.20%, 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: 0.75%-1.00%, Cu: 0.85%-1.10%, 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 yield strength of the steel plate produced by the application is 1000-1100MPa, the tensile strength is 1150-1250MPa, and the elongation is ≥18%.The steel plate has an impact energy of ≥110J at-20℃ and a hardness of ≥370HBW, and the abrasion rate in a simulated ocean environment is only 50% or less than that of Q460C steel.The performance meets the technical requirements of the 1000MPa-grade abrasion-resistant ore conveying pipeline in the ocean environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal materials, and particularly relates to a 1000MPa-grade steel plate for an ocean environment ore-conveying pipeline and a production method thereof. BACKGROUND

[0002] When deep-sea mining is performed, it is difficult and costly to crush ore on the seabed, and ore is generally crushed after being lifted to the sea surface, so the ore conveyed by the vertical lifting pipeline has a relatively large particle size and various shapes. The coarse particles with different shapes will cause wear to the inner wall of the vertical lifting pipeline, and the mixing of minerals and seawater will also cause corrosion, which puts extremely strict requirements on the comprehensive performance of the pipeline material in terms of high-pressure resistance, wear resistance and corrosion resistance.

[0003] The pipeline lifting mining system has the advantages of continuous operation, high mining efficiency and relatively low energy consumption, and is currently recognized as the most promising commercial deep-sea mining and ore-conveying technology in the world. The ore-conveying vertical pipe conveys the mixture of seabed ore and seawater at a certain speed and concentration from the mining equipment to the sea surface, and is an indispensable equipment for implementing deep-sea mining projects. The working environment of deep-sea mining requires the ore-conveying pipeline to have the characteristics of wear resistance, seawater corrosion resistance and anti-blocking. In order to improve the conveying efficiency and take into account the good pressure collapse resistance of the pipeline in the deep-sea environment, the abrasion-resistant straight seam welded pipe made of steel plate becomes the first choice due to its excellent pipe type, moderate caliber and uniform wall thickness.

[0004] The patent document with the application number 202310984654.1 discloses a low-alloy high-wear-resistant steel and a preparation method thereof, and the chemical composition thereof is: C: 0.10%-0.18%, Mn: 0.2%-1.3%, P≤0.020%, S≤0.010%, Al: 0.03%-0.06%, Nb: 0.01%-0.02%, Ti: 0.005%-0.02%, Si≤0.020% or B≤0.003% or both are added in any proportion, and the rest is Fe and impurities. The production process adopts hot rolling-coiling, continuous uncoiling and quenching+low-temperature tempering. Its purpose is to manufacture mechanical equipment in the fields of metallurgy, mining, railway and coal that require high wear resistance, but it does not have seawater corrosion resistance and is not suitable for service in the marine environment.

[0005] Patent document with application number 201811584851.X discloses "High-toughness anti-fatigue nano precipitate reinforced maraging-austenitic duplex steel and its preparation method", its chemical composition is: C: 0.06%-0.20%; Si: 0.05%-0.20%; Mn: 2.50%-5.00%; P≤0.01%; S≤0.01%; Cu:≤1.00%; Ni:≤2.00%; Mo:0.20%-0.50%; Cr:1.00%-1.50%; V:0.10%-0.80%; the rest is Fe and inevitable impurities. Through quenching and tempering heat treatment, tempered martensite + reverse austenite is obtained, and then excellent anti-fatigue performance and corrosion resistance are obtained. However, the content of alloying elements added in the steel is high, especially the content of Mn reaches more than 2.5%, not only greatly increases the cost of alloy, but also has adverse effect on the weldability of the steel.

[0006] Patent document with application number 202410698271.2 discloses "Ultra-fine bainite wear-resistant steel NM300 and its production method", its chemical composition is: C0.13%-0.15%, Si0.4%-0.6%, Mn1.3%-1.5%, Alt0.3%-0.5%, Nb0.01%-0.03%, Ti0.01%-0.03%, B0.001%-0.004%, the balance is Fe and trace impurity elements. By adding B element and realizing cooling speed≥80℃ / s, ultra-fine bainite + residual austenite structure is obtained, so that the steel plate with thickness of 2-8mm obtains good wear resistance. However, this design does not have seawater corrosion resistance, and the steel plate wall thickness is too small, the compression crushing performance is poor, and it is not suitable for deep sea high pressure environment and strong abrasive environment containing seawater minerals, and cannot meet the harsh service conditions of deep sea mineral transportation.

[0007] Patent document with application number 201810492367.8 discloses "High-strength steel resistant to seawater corrosion and its production method", its chemical composition is: C≤0.09%, Si≤0.40%, Mn0.80%-0.90%, P0.090%-0.10%, S≤0.005%, Cu0.52%-0.58%, Ni0.42%-0.48%, Ti0.030%-0.050%, Al0.02%-0.06%, Re0.01%-0.05%, the balance is Fe and inevitable impurities. By adopting Cu-P-Ni composition system design and proportion matching, process matching, the effect of resisting seawater corrosion is achieved. It is used to manufacture seawater corrosion resistant pile pipe, and does not have wear resistance and anti-fatigue performance.

[0008] In summary, the current production of steel for mineral conveying riser does not match the material wear resistance and fatigue resistance comprehensive performance according to the characteristics of mineral conveying and marine service conditions, is not suitable for the strong abrasive environment of mineral conveying, and cannot meet the harsh service conditions of deep sea mineral conveying. SUMMARY

[0009] The present application aims to overcome the above problems and deficiencies and provide a 1000MPa grade steel plate for ocean environment mineral conveying pipeline with good strength and toughness and wear resistance and a production method thereof.

[0010] The present application is achieved as follows:

[0011] A 1000MPa grade steel plate for mineral conveying pipeline suitable for marine environment, the composition of the steel plate is as follows in terms of percentage by weight: C: 0.18%~0.22%, Si: 0.31%~0.50%, Mn: 0.90%~1.20%, 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: 0.75%~1.00%, Cu: 0.85%~1.10%, Ce: 0.01%~0.06%, the balance being Fe and inevitable impurities.

[0012] Further, Cr+Mo≥1.35% in the steel plate.

[0013] Further, Nb / Ce≥1.5 in the steel plate.

[0014] The yield strength of the steel plate is 1000~1100MPa, the tensile strength is 1150~1250MPa, and the elongation after fracture is ≥18%. The impact energy of the steel plate at-20℃ is ≥110J, the hardness is ≥370HBW, and the abrasion rate in the simulated marine environment is only 50% or less than that of Q460C steel.

[0015] The microstructure of the steel plate is a mixed structure of tempered sorbite + nanoscale precipitates; wherein, in terms of area percentage: nanoscale precipitates 5%~6%, of which more than 90% of the precipitates have a size ≤40nm and are dispersedly distributed.

[0016] The component design reasons of the present application are as follows:

[0017] C: the basic strengthening element in steel, which is the main element to ensure the strength and hardness in the technical scheme of the application. The 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 improving the strength and toughness of the steel, but too much C is not conducive to the welding, toughness and plasticity of the steel plate. Therefore, considering the cost, performance and other factors, the range of C in the application is controlled to be 0.18%~0.22%.

[0018] Si: the appropriate amount of Si added in the steel can form a protective rust layer on the surface of the steel, which has a beneficial effect on the seawater corrosion resistance of the steel plate. Si can improve the strength and hardness of the steel, thereby improving the wear resistance of the steel. The appropriate amount of Si added in the steel will be enriched around the carbide, causing the carbide to become fine and dispersedly distributed in the matrix, inhibiting the precipitation of cementite and hindering the growth of carbide, further improving the wear resistance. However, higher content of Si will cause the ductile-brittle transition temperature of the steel to rise, reduce the low temperature toughness of the steel plate, and deteriorate the toughness and reduce the plasticity of the steel. The content of Si in the application is controlled to be 0.31%~0.50%.

[0019] Mn: a common strengthening element in steel, which can be largely solid-solved in the Fe matrix to improve the strength through solid solution strengthening. Manganese can reduce the critical cooling rate of the steel, promote the formation of martensite, greatly improve the hardenability, and significantly reduce the brittle transition temperature of the steel, improve the impact toughness, and refine the microstructure of the steel, which is an important strengthening and toughening element. However, too high content of Mn can cause segregation in the steel, which is not conducive to the corrosion resistance of the steel. Therefore, the range of Mn in the application is controlled to be 0.90%~1.20%.

[0020] Cr, Mo: can improve the hardenability of the steel, promote the occurrence of low temperature structure transformation of the steel under high temperature state through accelerated cooling, increase the strength and hardness of the steel plate, and significantly improve the wear resistance of the steel. Cr can form a dense passivation film on the surface of the steel in a corrosive environment, which can protect the matrix. Mo can improve the corrosion resistance of the steel to chloride ions and reduce the tendency of pitting corrosion caused by chloride ions in seawater environment. The combined addition of Cr and Mo can further improve the corrosion resistance in marine environment. The range of Cr in the application is controlled to be 0.91%~1.20%, the content of Mo is controlled to be 0.36%~0.50%, and Cr+Mo≥1.35%.

[0021] Nb: is a grain refining element, undissolved Nb carbon, nitride particles distributed on the austenite grain boundary when heating can hinder the growth of austenite grain when heating; can effectively delay the recrystallization of deformed austenite, prevent the growth of austenite grain, refine ferrite grain, can improve the impact toughness of steel and reduce the brittle transition temperature. Nb can also increase the solid solution amount of Ce and other rare earths in the steel, when Nb and Ce are added together, Ce can be fully dissolved in the steel to improve the corrosion resistance of the steel. The Nb content of the present application is controlled at 0.06%~0.10%, and Nb / Ce≥1.5.

[0022] Ti: is a strong solid N element, the corrosion rate can be obviously reduced when a small amount of Ti is added in Al-containing steel, and Ti can combine with N in the steel first, reduce the amount of AlN in the steel, and improve the weldability. However, when the Ti content exceeds a certain value, the TiN particles will be coarsened, causing the low temperature toughness to deteriorate. Therefore, the Ti content of the present application is selected as 0.010%~0.025%.

[0023] Al: is usually used as a deoxidizer in steel, and if the aluminum content is too low, the deoxidation will not be sufficient, and Ti and other easily oxidized elements will form oxides; if the aluminum content is too high, the aluminum oxide inclusions will increase, reducing the cleanliness of the steel. Therefore, the Al content of the present application is controlled in the range of 0.010%~0.050%.

[0024] Ni: can improve the strength of the steel, reduce the critical cooling temperature, be beneficial to microstructure control and grain refinement, and improve the low temperature toughness. The Ni content of the present application is controlled at 0.75%~1.00%.

[0025] Cu: adding Cu in the steel can improve the corrosion resistance and strength of the steel, and improve the formability and weldability. When used with Ni, it can also avoid thermal brittleness. The appropriate amount of Cu can also form fine and dispersed Cu-containing precipitates in the steel, which can not only significantly improve the strength and hardness, but also have no adverse effect on toughness. The Cu content of the present application is controlled at 0.85%~1.10%.

[0026] Ce: Ce has strong affinity with O and S, can chemically react with O and S in the steel to form stable oxides and sulfides, and promote the full floating of these compounds in the steel liquid, which is more conducive to the removal of inclusions, so that a small amount of Ce is added in the steelmaking process can improve the quality of the steel by changing the morphology and distribution of inclusions in the steel. In addition, during the solidification process of the steel, Ce can act as a nucleation core to increase the number of crystal nuclei, thereby refining the grains and significantly improving the strength and toughness and corrosion resistance of the steel. The Ce content of the present application is controlled at 0.01%~0.06%.

[0027] P, S: As impurity elements, phosphorus and sulfur significantly deteriorate the toughness, plasticity and weldability of the steel, so the content in the steel should be reduced as much as possible, and in the present application, the content of P and S is required to be controlled at P≤0.015% and S≤0.001% respectively.

[0028] The second technical scheme of the present application provides a production method of a 1000MPa-grade steel plate for a marine environment ore conveying pipeline, including smelting, continuous casting, heating, rolling, accelerated cooling and tempering,

[0029] Heating: The slab adopts a multi-stage stepped temperature heating mode, wherein the high-temperature heating section temperature is 1200-1250℃, the soaking section temperature is 1180-1220℃, and the high-temperature heating section + soaking section time is not less than 120min.

[0030] The design of the heating process is mainly to ensure the solid solution of elements such as Mn, Cr, Mo, Ni, Cu and Nb, so that they can play a role in subsequent rolling and accelerated cooling, and at the same time, effectively control the growth of austenite grains; the heating time can ensure the heating effect and temperature uniformity.

[0031] Rolling: The steel plate rolling is divided into two stages of rough rolling and finish rolling, wherein the rough rolling stage end temperature is ≥1050℃, the single pass reduction rate of the last two passes of rough rolling is ≥14%, so that the original austenite grains are fully broken and refined. The intermediate billet thickness in the finish rolling stage is 3.0-3.5t, wherein t is the thickness of the finished steel plate (12-20mm), the opening rolling temperature is 880-930℃, the single pass reduction rate of the first three passes before finish rolling is ≥13%, and the finish rolling temperature is 820-860℃.

[0032] The design of the rough rolling process mainly considers that the steel is deformed sufficiently at a high temperature stage, especially the single pass large reduction amount is adopted in the last two passes of rough rolling, the purpose is to obtain excellent thickness direction organization uniformity, and at the same time, promote the formation of nanoscale precipitates, pin the grain boundary and dislocation, refine the grains, and improve the strength and toughness of the steel. The design of the finish rolling process is to increase the dislocation density and nucleation site in the steel, so that the grains are further refined, and the rolling deformation is completed in a relatively low temperature range to obtain a good matching of strength-toughness comprehensive performance.

[0033] Accelerated cooling: After the steel plate is finished rolling, accelerated cooling is carried out, and the cooling rate of the accelerated cooling is 20-30℃ / s, and the final cooling temperature is 300-370℃.

[0034] Tempering: The steel plate after cooling is subjected to tempering treatment, the tempering temperature is 500-550℃, the tempering time is 5-6min / mm, and the steel plate after discharging is air cooled to room temperature.

[0035] The finally obtained microstructure control target is a mixed microstructure of tempered sorbite + nanoscale precipitated phase. The nanoscale precipitated phase accounts for 5% to 6% in terms of area percentage, and more than 90% of the precipitated phase has a size of ≤40 nm and is in a dispersed distribution. The tempered sorbite has high comprehensive mechanical properties of strength, hardness and toughness, and the dispersed nanoscale Cu-containing precipitated phase as a hard phase particle not only significantly improves the hardness and wear resistance of the steel, but also can keep a dispersed precipitated state in the welding process, ensures the strength of the heat affected zone, and significantly improves the softening of the heat affected zone and the performance uniformity of the whole steel pipe.

[0036] The present application has the following advantages:

[0037] (1) The present application adds appropriate amounts of Cr, Mo, Ni, Cu and Nb alloy elements on the basis of C and Mn elements, and through the interaction between the elements and the appropriate heating, rolling, cooling and tempering heat treatment process, finally obtains a complex microstructure of tempered sorbite + nanoscale precipitated phase. Compared with the prior art, the present application is targeted for component design and microstructure design to improve the strength and toughness matching of the steel plate and improve the corrosion resistance of the steel plate, and the produced steel plate has good strength and toughness and corrosion resistance.

[0038] (2) The steel plate has excellent comprehensive mechanical properties, with a yield strength of 1000-1100 MPa, a tensile strength of 1150-1250 MPa, and an elongation of ≥18%. The steel plate has an impact energy of ≥110 J at -20 ℃, a hardness of ≥370 HBW, and an abrasion rate in a simulated marine environment of only 50% or less of that of Q460C steel. The performance meets the technical requirements of 1000 MPa grade corrosion-resistant mine conveying pipes in marine environment. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is a microstructure metallographic graph of the embodiment 1 of the present application.

[0040] Figure 2 It is a nanoscale precipitated phase characteristic graph of the embodiment 1 of the present application. DETAILED DESCRIPTION

[0041] The present application will be further described below through examples.

[0042] The embodiment of the present application is smelted, continuously cast, heated, rolled, accelerated cooled and tempered according to the component ratio of the technical scheme.

[0043] Heating: The slab is heated in a multi-stage stepped temperature heating mode, wherein the high-temperature heating section temperature is 1200-1250 ℃, the soaking section temperature is 1180-1220 ℃, and the high-temperature heating section + soaking section time is not less than 120 min;

[0044] Rolling: including rough rolling and finish rolling; wherein the rough rolling stage end temperature is ≥1050℃, the single pass reduction rate of the last two passes of rough rolling is ≥14%; the intermediate billet thickness in the finish rolling stage is 3.0~3.5t, wherein t is the thickness of the finished steel plate, the roughing temperature is 880~930℃, the single pass reduction rate of the first three passes before finish rolling is ≥13%, and the finish rolling temperature is 820~860℃;

[0045] Accelerated cooling: the steel plate is subjected to accelerated cooling after finishing rolling, the cooling rate of the accelerated cooling is 20~30℃ / s, and the final cooling temperature is 300~370℃;

[0046] Tempering: the cooled steel plate is subjected to tempering treatment, the tempering temperature is 500~550℃, the tempering time is 5~6min / mm, and the steel plate after discharging is air-cooled to room temperature.

[0047] The components of the steel in the embodiments and the comparative examples of the present application are shown in Table 1. The main process parameters of the steel in the embodiments and the comparative examples of the present application are shown in Table 2. The rolling, cooling and tempering process parameters of the steel in the embodiments and the comparative examples of the present application are shown in Table 3. The properties of the steel in the embodiments and the comparative examples of the present application are shown in Table 4. The microstructure of the steel in the embodiments and the comparative examples of the present application is shown in Table 5.

[0048] Table 1 Components of the steel in the embodiments and the comparative examples of the present application

[0049]

[0050] Table 2 Main process parameters of the steel in the embodiments and the comparative examples of the present application

[0051]

[0052] Table 3 Rolling, cooling and tempering process parameters of the steel in the embodiments and the comparative examples of the present application

[0053]

[0054] Table 4 Properties of the steel in the embodiments and the comparative examples of the present application

[0055]

[0056] Table 5 Microstructure of the steel in the embodiments and the comparative examples of the present application

[0057]

[0058] The steel plate produced by the application has excellent comprehensive mechanical properties, the yield strength is 1000-1100 MPa, the tensile strength is 1150-1250 MPa, the elongation is greater than or equal to 18%, the steel plate impact energy at-20 DEG C is greater than or equal to 110J, the hardness is greater than or equal to 370HBW, and the abrasion rate in the simulated marine environment is only 50% or less of that of Q460C steel. The performance meets the technical requirements of 1000MPa grade abrasion-resistant mine pipeline in marine environment.

[0059] In order to describe the application, the application is appropriately and sufficiently described by the above examples, the above embodiments are only used to illustrate the application, and are not limited to the application. Any modification, equivalent replacement, improvement and the like made by those skilled in the art without departing from the spirit and scope of the application shall be included in the protection scope of the application, and the patent protection scope of the application shall be defined by the claims.

Claims

1. A steel plate for a 1000 MPa grade ore transportation pipe suitable for marine environments, characterized in that, The steel plate has the following components in percentage by weight: C: 0.18%-0.22%, Si: 0.31%-0.50%, Mn: 0.90%-1.20%, 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: 0.75%-1.00%, Cu: 0.85%-1.10%, Ce: 0.01%-0.06%, and the balance of Fe and inevitable impurities; The production method of the 1000MPa grade ore conveying pipeline steel plate suitable for marine environment comprises smelting, continuous casting, heating, rolling, accelerated cooling and tempering; Heating: the slab adopts a multi-stage ladder temperature heating mode, wherein the high-temperature heating section temperature is 1200-1250℃, the soaking section temperature is 1180-1220℃, and the high-temperature heating section + soaking section time is not less than 120min; Rolling: including rough rolling and finish rolling; wherein the rough rolling stage end temperature is ≥1050℃, the single pass reduction rate of the last two passes of rough rolling is ≥14%; the intermediate billet thickness in the finish rolling stage is 3.0-3.5t, wherein t is the thickness of the finished steel plate, the roughing temperature is 880-930℃, the single pass reduction rate of the first three passes before finish rolling is ≥13%, and the finish rolling temperature is 820-860℃; Accelerated cooling: the steel plate is subjected to accelerated cooling after finishing rolling, and the accelerated cooling rate is 20-30℃ / s, and the final cooling temperature is 300-370℃; Tempering: the cooled steel plate is subjected to tempering treatment, the tempering temperature is 500-550℃, the tempering time is 5-6min / mm, and the steel plate after discharging is air cooled to room temperature.

2. The steel plate for a 1000 MPa grade ore transportation pipe used in marine environments according to claim 1, characterized by, The Cr+Mo in the steel plate is ≥1.35%.

3. The steel plate for a 1000 MPa grade ore transportation pipe used in marine environments according to claim 1, characterized by, The Nb / Ce in the steel plate is ≥1.

5.

4. The steel plate for a 1000 MPa grade ore transportation pipe used in marine environments according to claim 1, characterized by, The microstructure of the steel plate is a mixed structure of tempered sorbite + nanoscale precipitates; wherein, in terms of volume percentage: the nanoscale precipitates are 5%-6%, and more than 90% of the precipitates have a size ≤40nm.

5. The steel plate for a 1000 MPa grade ore transportation pipe used in marine environments according to claim 1, characterized by, The thickness of the steel plate is 12-20mm; the yield strength of the steel plate is 1000-1100MPa, the tensile strength is 1150-1250MPa, the elongation after fracture is ≥18%, the impact energy of the steel plate at-20℃ is ≥110J, and the hardness is ≥370HBW.

6. The production method of the 1000MPa grade ore conveying pipeline steel suitable for marine environment according to any one of claims 1-5, comprising smelting, continuous casting, heating, rolling, accelerated cooling and tempering; characterized in that: Heating: the slab adopts a multi-stage ladder temperature heating mode, wherein the high-temperature heating section temperature is 1200-1250℃, the soaking section temperature is 1180-1220℃, and the high-temperature heating section + soaking section time is not less than 120min; Rolling: including rough rolling and finish rolling; wherein the rough rolling stage ends at a temperature of ≥1050℃, the single pass reduction rate of the last two passes of rough rolling is ≥14%; the intermediate slab thickness in the finish rolling stage is 3.0~3.5t, wherein t is the thickness of the finished steel plate, the starting rolling temperature is 880~930℃, the single pass reduction rate of the first three passes before finish rolling is ≥13%, and the finish rolling temperature is 820~860℃; Accelerated cooling: the steel plate is subjected to accelerated cooling after rolling, the cooling rate of the accelerated cooling is 20~30℃ / s, and the final cooling temperature is 300~370℃; Tempering: the cooled steel plate is subjected to tempering treatment, the tempering temperature is 500~550℃, the tempering time is 5~6min / mm, and the steel plate is air-cooled to room temperature after being discharged.

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