800mpa 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 800MPa-grade marine environment ore conveying pipeline steel plate 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: 0.15%-0.30%, Mn: 0.80%-0.95%, P≤0.015%, S≤0.001%, Cr: 0.60%-0.90%, Mo: 0.20%-0.35%, Al: 0.010%-0.050%, Nb: 0.03%-0.05%, 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 steel plate produced by the application has excellent comprehensive mechanical properties, and each performance meets the technical requirements of the 800MPa-grade marine environment wear-resistant ore conveying pipeline.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal materials, and particularly relates to a 800MPa-grade steel plate for ocean environment mineral conveying pipeline and a production method thereof. BACKGROUND

[0002] With the long-term exploitation of land mineral resources, the supply of land metal mineral resources is showing signs of fatigue, and the development of mineral resources is also expanding from land to ocean in various countries around the world. Deep sea contains a large amount of important mineral resources needed for the development of human society. The pipeline lifting mining system is recognized as the most promising commercial deep-sea mining and mineral conveying technology in the world due to its continuous operation, high mining efficiency and relatively low energy consumption ratio. Long-distance pipeline is the main technical approach to realize the transportation of deep-sea mineral resources from the seabed to the water surface, and is an indispensable equipment for implementing deep-sea mining engineering. However, the mixture of minerals and seawater makes the composition of the conveying medium complex, and the extremely harsh deep-sea environment leads to obvious deficiencies in the transportation efficiency and reliability of the existing mineral resource pipeline system, especially the comprehensive performance of the pipeline material in terms of high-pressure resistance, wear resistance and corrosion resistance needs to be improved.

[0003] A low-alloy high-wear-resistant steel and a preparation method thereof are disclosed in a patent with application number 202310984654.1. The chemical composition is as follows: C: 0.10% to 0.18%, Mn: 0.2% to 1.3%, P≤0.020%, S≤0.010%, Al: 0.03% to 0.06%, Nb: 0.01% to 0.02%, Ti: 0.005% to 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 ocean environment.

[0004] Patent with application number 202111192650.7 discloses a corrosion-resistant and fatigue-resistant pipeline steel for underwater oil and gas production and its production method. Its chemical composition is: C 0.030%-0.055%, Si 0.26%-0.40%, Mn 1.11%-1.18%, P≤0.010%, S≤0.0015%, Nb 0.035%-0.060%, Ti 0.012%-0.025%, V 0.01%-0.04%, Ni 0.10%-0.19%, Cu 0.16%-0.25%, Mo 0.10%-0.19%, Cr<0.25%, Alt 0.010%-0.025%, Ca 0.0015%-0.0050%, the balance being iron and unavoidable impurities. A low-C composition design is adopted, and by controlling the organizational type to be 15%-60% polygonal ferrite + bainite + a small amount of M / A, a high fatigue resistance steel pipe is obtained, which is used for transporting oil and gas medium. However, the strength of the steel plate is low, and it is not suitable for the strong abrasive environment of mineral transportation, and cannot meet the severe service conditions of deep sea mineral transportation.

[0005] Patent with application number 201810492367.8 discloses a high-strength steel resistant to seawater corrosion and its production method. Its chemical composition is: C≤0.09%, Si≤0.40%, Mn 0.80%-0.90%, P 0.090%-0.10%, S≤0.005%, Cu 0.52%-0.58%, Ni 0.42%-0.48%, Ti 0.030%-0.050%, Al 0.02%-0.06%, Re 0.01%-0.05%, the balance being Fe and unavoidable 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 pipes, and does not have wear resistance.

[0006] In summary, the production of steel for mineral transportation riser does not match the material wear-resistant performance according to the characteristics of mineral transportation and marine service conditions, and is not suitable for the strong abrasive environment of mineral transportation, and cannot meet the severe service conditions of deep sea mineral transportation and the forming, manufacturing and welding of deep sea mineral transportation pipe. SUMMARY

[0007] The purpose of the present application is to overcome the above problems and deficiencies and provide an 800MPa grade steel plate for marine environment mineral transportation pipe with good strength and toughness and wear resistance and its production method.

[0008] The purpose of the present application is achieved as follows:

[0009] The steel plate for 800MPa grade marine environment ore conveying pipeline has the following components in percentage by weight: C: 0.18%-0.22%, Si: 0.15%-0.30%, Mn: 0.80%-0.95%, P: 0.015% or less, S: 0.001% or less, Cr: 0.60%-0.90%, Mo: 0.20%-0.35%, Al: 0.010%-0.050%, Nb: 0.03%-0.05%, 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.

[0010] Further, Cr+Mo in the steel plate is greater than or equal to 0.90%.

[0011] Further, Nb / Ce in the steel plate is greater than or equal to 0.82.

[0012] The microstructure of the steel plate is a mixed structure of tempered sorbite and nanoscale precipitates, wherein the proportion of nanoscale precipitates is 4%-5% in percentage by volume, and more than 90% of the precipitates have a size of less than or equal to 50nm and are distributed in a dispersed manner.

[0013] The steel plate has a thickness of 12-20mm, a yield strength of 610-680MPa, a tensile strength of 850-960MPa, an elongation of greater than or equal to 24%, an impact energy at-20 DEG C of greater than or equal to 110J, a hardness of greater than or equal to 300HBW, and an abrasion rate in a simulated marine environment of less than or equal to 60% of that of Q460C steel.

[0014] The component design of the present application is as follows:

[0015] C: a basic strengthening element in steel, which is the main element for ensuring strength and hardness in the technical solution of the present application. Appropriate addition 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. However, 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 present application is controlled to be 0.18%-0.22%.

[0016] Si: can improve the strength and hardness of the steel plate by solid solution strengthening effect, has the effect of improving the hardenability, wear resistance and corrosion resistance of the material. Adding appropriate amount of Si in the steel can promote the formation of protective rust layer on the steel surface, thereby improving the corrosion resistance. Under certain carbon content conditions, it can also inhibit the precipitation of cementite, at the same time, Si will enrich around the carbide, hinder the growth of carbide, make the carbide become fine and dispersedly distributed in the matrix, so that the abrasive particles generated in wear are small, thereby reducing the degree of wear. But higher content of Si makes the steel tend to graphitize, makes the steel brittle, reduces the plasticity and deteriorates the toughness. The content of Si in the application is controlled at 0.15%-0.30%.

[0017] Mn: is a common strengthening element in steel, can be dissolved in Fe matrix in large amount, and can improve the strength by solid solution strengthening. Manganese can reduce the critical cooling rate of steel, promote the formation of martensite, greatly improve the hardenability, and significantly reduce the brittle transition temperature of steel, improve the impact toughness, and refine the microstructure of steel. It is an important strengthening and toughening element. However, too high content of Mn can form segregation in the steel, which has adverse effects on the corrosion resistance of the steel. Considering comprehensively, the content of Mn in the application is controlled in the range of 0.80%-0.95%.

[0018] Cr, Mo: can improve the hardenability of the steel, promote the occurrence of low-temperature structure transformation of the steel under high-temperature state by accelerated cooling, increase the strength and hardness of the steel plate, and significantly improve the wear resistance of the steel. Adding a certain amount of Cr and Mo in the steel can also effectively fill the voids formed by chloride ion point corrosion in the marine environment, form a dense protective film, prevent the development of pitting corrosion, and thus play a role in corrosion resistance in marine environment. The content of Cr in the application is controlled in the range of 0.60%-0.90%, the content of Mo is controlled in the range of 0.20%-0.35%, and Cr+Mo≥0.90%.

[0019] Nb: is a grain refining element, the undissolved Nb carbon and nitride particles distributed on the austenite grain boundary can hinder the growth of austenite grains during heating; can effectively delay the recrystallization of deformed austenite, prevent the growth of austenite grains, refine the ferrite grains, improve the impact toughness of the steel and reduce the brittle transition temperature. Nb can also increase the solid solution amount of Ce and other rare earths in the steel. Since the solid solubility of Ce in austenite is much higher than that in ferrite, and Nb can lower the phase transition temperature of austenite to ferrite, the temperature range of austenite phase is expanded, therefore, when Nb and Ce are added together, Ce can be fully dissolved in the steel to improve the corrosion resistance of the steel. The content of Nb in the application is controlled in the range of 0.03%-0.05%, and Nb / Ce≥0.82.

[0020] Ti: is a strong solid N element, and the corrosion rate can be obviously reduced by adding trace Ti in Al-containing steel, and Ti can be combined with N in steel, reduce the amount of AlN in 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 in the present application is selected as 0.010%-0.025%.

[0021] Al: usually used as a deoxidizer in steel, if the aluminum content is too low, the deoxidation is insufficient, and Ti and other easily oxidized elements will form oxides; if the aluminum content is too high, the aluminum oxide inclusions increase, and the cleanliness of the steel deteriorates. Therefore, the Al content is controlled in the range of 0.010%-0.050% in the present application.

[0022] Ni: can improve the strength of the steel, reduce the critical cooling temperature, be beneficial to the microstructure control and grain refinement, and improve the low temperature toughness. The Ni content in the present application is controlled as 0.75%-1.00%.

[0023] Cu: adding Cu in 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. 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 in the present application is controlled as 0.85%-1.10%

[0024] Ce: adding a small amount of Ce in steel can improve the quality of the steel by changing the shape and distribution of inclusions in the steel, Ce has strong affinity with O and S, and can preferentially react with O and S in the steel to form stable oxides and sulfides, and can also convert strip-shaped MnS inclusions into spherical shape, and promote the floating of these compounds in the molten steel, thereby reducing the generation of large particle inclusions and reducing the fragmentation of irregular inclusions and large particle inclusions to the matrix. The effect of purifying molten iron can be achieved. 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, fatigue resistance and corrosion resistance of the steel. The Ce content in the present application is controlled as 0.01%-0.06%.

[0025] P, S: as impurity elements, phosphorus and sulfur significantly deteriorate the toughness, plasticity and weldability of the steel, so the content of the steel should be reduced as much as possible, and the P and S content in the present application is required to be controlled as P≤0.015%, S≤0.001%.

[0026] The second technical scheme of the present application provides a production method of 800MPa grade marine environment mine pipeline steel plate, including smelting, continuous casting, heating, rolling, accelerated cooling and tempering.

[0027] Heating: The slab is heated by multi-stage ladder temperature heating, 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.

[0028] 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.

[0029] Rolling: The steel plate rolling is divided into two stages of rough rolling and finish rolling, wherein the rough rolling 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℃.

[0030] The design of the rough rolling process mainly considers that the steel is fully deformed at high temperature, especially the single pass large reduction amount is adopted in the last two passes of rough rolling, the purpose is to increase the dislocation density in the crystal nucleus, so that the original large size grains form new small crystal nucleus due to dislocation division, so as to break and further refine the austenite grains, and inhibit the excessive growth of austenite grains during the period from the end of rough rolling to the beginning of finish rolling. The design of the finish rolling process, on the one hand, ensures the austenite to be fully flattened and deformed by the intermediate billet thickness, and on the other hand, promotes the nanoscale precipitated phase of Nb and V to induce precipitation by single pass large reduction rate, pins the grain boundary and dislocation, increases the nucleation site, and further refines the grains. By controlling the opening rolling temperature and the finish rolling temperature, the steel completes the deformation process in a relatively low temperature range, which can not only obtain good matching of strength and toughness, but also avoid the occurrence of ferrite phase transformation to cause mixed crystal and affect the low temperature toughness.

[0031] Accelerated cooling: After the steel plate is rolled, it is subjected to accelerated cooling, and the cooling rate of the accelerated cooling is 20-30℃ / s, and the final cooling temperature is 350-420℃. The above accelerated cooling process can effectively inhibit the formation of blocky structure, and lay a foundation for obtaining short and small needle-shaped target structure after tempering.

[0032] Tempering: The cooled steel plate is subjected to tempering treatment, the tempering temperature is 580-630℃, the tempering time is 6-7min / mm, and the steel plate after discharging is air cooled to room temperature.

[0033] The finally obtained microstructure control target is a mixed microstructure of tempered sorbite + nanoscale precipitates. The proportion of the nanoscale precipitates is 4%-5%, and more than 90% of the precipitates have a size of ≤50 nm and are in a dispersed distribution. The tempered sorbite has high comprehensive mechanical properties of strength, hardness and toughness, and the dispersed nanoscale Cu-containing precipitates as hard phase particles not only significantly improve the hardness and wear resistance of the steel, but also can maintain a dispersed precipitated state in the welding process, ensure the strength of the heat affected zone, significantly improve the softening of the heat affected zone and improve the performance uniformity of the whole steel pipe.

[0034] The present application has the following advantages:

[0035] 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 precipitates. The present application is targeted for improving the strength-toughness matching of the steel plate and improving the wear resistance of the steel plate, and the produced steel plate has good strength-toughness and wear resistance.

[0036] 2) The steel plate has excellent comprehensive mechanical properties, the yield strength is 610-680 MPa, the tensile strength is 850-960 MPa, and the elongation is ≥24%. The steel plate has an impact energy of ≥110 J at -20 ℃, a hardness of ≥300 HBW, and an abrasion rate in a simulated marine environment of only 60% or less of that of Q460C steel. The performance meets the technical requirements of 800 MPa grade wear-resistant marine pipeline in marine environment. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is a microstructure metallographic graph of the embodiment 1 of the present application.

[0038] Figure 2 It is a nanoscale precipitate characteristic graph of the embodiment 1 of the present application. DETAILED DESCRIPTION

[0039] The present application will be further described below through examples.

[0040] According to the component ratio of the technical scheme, the embodiment of the present application is smelted, continuously cast, heated, rolled, accelerated cooled and tempered.

[0041] Heating: The slab is heated in a multi-stage step 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;

[0042] Rolling: the steel plate rolling is divided into two stages of rough rolling and finish rolling, wherein the rough rolling stage ends at a temperature of greater than or equal to 1050 DEG C, and the single pass reduction rate of the last two passes of the rough rolling is greater than or equal to 14%; the intermediate blank thickness in the finish rolling stage is 3.0-3.5t, wherein t is the finished steel plate, the rough rolling temperature is 880-930 DEG C, and the finish rolling temperature is 820-860 DEG C;

[0043] Accelerated cooling: after the steel plate is finished rolling, accelerated cooling is carried out, the cooling rate is 20-30 DEG C / s, and the final cooling temperature is 350-420 DEG C;

[0044] Tempering: the cooled steel plate is subjected to tempering treatment, the tempering temperature is 580-630 DEG C, the tempering time is 6-7 min / mm, and the steel plate after discharging is air-cooled to room temperature.

[0045] Further; the single pass reduction rate of the first three passes before finish rolling is greater than or equal to 13%.

[0046] 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 main process parameters of the steel in the embodiments and the comparative examples of the present application are shown in Table 3. The properties and the microstructure of the steel in the embodiments of the present application are shown in Table 4. The microstructure of the steel in the embodiments of the present application is shown in Table 5.

[0047] Table 1 Components of the steel in the embodiments and the comparative examples of the present application

[0048]

[0049] Table 2 Main process parameters of the steel in the embodiments and the comparative examples of the present application

[0050]

[0051] Table 3 Main process parameters of the steel in the embodiments and the comparative examples of the present application

[0052]

[0053] Table 4 Properties of the steel in the embodiments and the comparative examples of the present application

[0054]

[0055] Table 5 Microstructure of the steel in the embodiments and the comparative examples of the present application

[0056]

[0057] The steel plate produced by the application has excellent comprehensive mechanical properties, the yield strength is 610-680 MPa, the tensile strength is 850-960 MPa, the elongation is greater than or equal to 24%, the steel plate impact energy at-20 DEG C is greater than or equal to 110J, the hardness is greater than or equal to 300HBW, and the abrasion rate in the simulated marine environment is only 60% or less of that of Q460C steel. The performance meets the technical requirements of the 800MPa grade abrasion-resistant mine pipeline in the marine environment.

[0058] 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 should be included in the protection scope of the application, and the patent protection scope of the application should be limited by the claims.

Claims

1. A steel plate for ore transport pipelines in marine environments with a pressure rating of 800MPa, characterized in that, The composition of this steel plate, by weight percentage, is as follows: C: 0.18%~0.22%, Si: 0.15%~0.30%, Mn: 0.80%~0.95%, P≤0.015%, S≤0.001%, Cr: 0.60%~0.90%, Mo: 0.20%~0.35%, Al: 0.010%~0.050%, Nb: 0.03%~0.05%, Ti: 0.005%. ~0.025%, Ni: 0.75%~1.00%, Cu: 0.85%~1.10%, Ce: 0.01%~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 volume percentage, the proportion of nano-sized precipitates is 4%~5%, of which more than 90% of the precipitates are ≤50nm in size and are diffusely distributed.

2. The steel plate for ore transportation pipelines in marine environments with a pressure rating of 800MPa as described in claim 1, characterized in that, The steel plate contains Cr+Mo≥0.90%.

3. The steel plate for ore transport pipelines in marine environments with a pressure rating of 800MPa as described in claim 1, characterized in that, The Nb / Ce ratio in the steel plate is ≥0.

82.

4. The steel plate for ore transport pipelines in marine environments with a pressure rating of 800MPa as described in claim 1, characterized in that, The steel plate has a thickness of 12~20mm; a yield strength of 610~680MPa, a tensile strength of 850~960MPa, and an elongation of ≥24%; an impact energy of ≥110J at -20℃, a hardness of ≥300HBW, and a wear rate in a simulated marine environment that is less than 60% of that of Q460C steel.

5. A method for producing a steel plate for ore transport pipelines in marine environments with a pressure rating of 800MPa as described in any one of claims 1-4, 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 finished steel plate. The initial rolling temperature is 880~930℃, and the final rolling temperature is 820~860℃. Accelerated cooling: After the steel plate is rolled, it is accelerated cooled at a rate of 20~30℃ / s and a final cooling temperature of 350~420℃. Tempering: The cooled steel plate is tempered at a temperature of 580~630℃ for 6.7~7 min / mm. After being taken out of the furnace, the steel plate is air-cooled to room temperature.

6. The method for producing a steel plate for ore transport pipelines in a marine environment with a pressure rating of 800MPa according to claim 5, characterized in that: The single-pass reduction rate of the first three passes of finishing rolling is ≥13%.

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