CA3058488C - A x80 pipeline steel plate with high carbon equivalent and high toughness at low temperatures used for bent pipes as well as a manufacturing method thereof - Google Patents
A x80 pipeline steel plate with high carbon equivalent and high toughness at low temperatures used for bent pipes as well as a manufacturing method thereof Download PDFInfo
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- CA3058488C CA3058488C CA3058488A CA3058488A CA3058488C CA 3058488 C CA3058488 C CA 3058488C CA 3058488 A CA3058488 A CA 3058488A CA 3058488 A CA3058488 A CA 3058488A CA 3058488 C CA3058488 C CA 3058488C
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
Abstract
A high carbon equivalent and high low-temperature toughness pipeline steel plate for an X80 elbow pipe and a manufacturing method therefor. The method has the characteristics of simple process and high yield. The thickness of the steel plate is 18.4-42 mm. The manufacturing process is as follows: preparing materials according to proportions; smelting same by a converter or an electric furnace; refining same outside the converter or furnace; performing continuous casting; reheating a plate blank; performing rolling, and ACC gradient cooling; and straightening. The steel plate has excellent low-temperature toughness; the manufacturing method therefor is simple and easy, and brings high yield.
Description
DESCRIPTION
A X80 pipeline steel plate with high carbon equivalent and high toughness at low temperatures used for bent pipes as well as a manufacturing method thereof Technical Field The present application relates to a technical field of manufacturing X80 pipeline steel plate for bent pipes, especially relates to a X80 pipeline steel plate for bent pipes with high carbon equivalent and high toughness at low temperatures and a manufacturing method thereof.
Background Art With the dominance of petrochemical energy in the world's energy demand and the rapid growth of petrochemical energy demand under the roaring world economy nowadays, the long-distance pipelines are largely improved for higher transmission efficiency and less investment, and the development trend of long-distance oil and gas pipelines steel is to be in high strength or super high grade. At present, the highest grade of pipeline steel used in the world is X80. In addition to the straight pipe, a pipeline project also includes the bent pipes for the direction change of the pipeline, the bent pipes in stations, and so on. Bent pipes are usually produced by two kinds of processes, namely, cold bending and hot bending, and the cold bending process has been gradually replaced by hot bending process as cold bending process is under the influence of manufacturing process and service environment. The hot bending of bent pipes usually are to heat the main pipe to Ac3 or above by induction heating equipment, and then the heating zone rotates around the fixed center to bend the bent pipe with the required radius of curvature by a fixed turning panel and under the action of back thrust; after bending, the bent pipe outer ring is cooled by an annular cooling ring, and the heated part of the bent pipe undergoes an accelerated cooling similar to ACC because of the limited cooling capacity of the annular cooling ring.
The steel plate after cooling treatment is treated by tempering in a continuous furnace in consideration of the property uniformity. From the view of the whole process, the whole hot bending and cooling bending process are similar to the TMCP process, which is the combination of high-temperature deformation (bending) and ACC
cooling process. Because the Whole hot bending process is deformed to a small extent ¨ 1 ¨
at a high temperature and the subsequent cooling capacity is weak, the hot bending steel plate for bent pipes can only be designed with high carbon-equivalent composition. The high-carbon-equivalent design will bring two main problems to the whole production: 1) the impact toughness is reduced; 2) there would be a defective shape of the steel plate due to the large structural stress in the cooling process, which brings difficulties to the subsequent straightening and affects the production efficiency at the same time.
At home and abroad, there are patent reports on X80 steel grade bent pipes and the steel plate for bent pipes, such as the patent application of CN201410239039.9, which refers to a hot-rolling plate steel for X80 steel grade bent pipe wherein: 1) only the impact toughness of steel plate at -20 C is referred in the patent application, but in fact, more steel plates for bent pipes need the impact toughness at -30 C or even lower temperature at present; 2) slowly stack cooling is required after rolling of steel plate in the application patent, which is unfavorable to mass production efficiency of steel plate and the follow-up production process at the same time.
Another patent application of No. CN201110245761.X has the following characteristics: 1) the patent mainly emphasizes the hot bending process but does not mention what kind of steel plate production process is used for raw material steel plate; 2) the low-temperature toughness impact value at -45 C obtained by the patent is not higher than 200J, and the numerical fluctuation is large.
Considering the whole process of austenite deformation in the hot bending process and that subsequent cooling is relatively simple and insufficient, the design of steel plate for bent pipes usually always adopts a high carbon equivalent composition compared with that of steel plate for straight pipe. The design of high-carbon-equivalent components will lead to a lower impact toughness under low temperatures.
Disclosure of Invention According to the characteristics of the hot bending process for bent pipes, the chemical composition in the application is still designed with high carbon equivalent, but through the innovation of the cooling process in the production process, a pipeline steel plate with high carbon equivalent and high toughness at low temperatures used for bent pipes is obtained with a concise process and a high yield.
The technical scheme adopted by the invention to solve the above technical problems is to manufacture X80 pipeline steel plate for bent pipes with HIC
resistance,
A X80 pipeline steel plate with high carbon equivalent and high toughness at low temperatures used for bent pipes as well as a manufacturing method thereof Technical Field The present application relates to a technical field of manufacturing X80 pipeline steel plate for bent pipes, especially relates to a X80 pipeline steel plate for bent pipes with high carbon equivalent and high toughness at low temperatures and a manufacturing method thereof.
Background Art With the dominance of petrochemical energy in the world's energy demand and the rapid growth of petrochemical energy demand under the roaring world economy nowadays, the long-distance pipelines are largely improved for higher transmission efficiency and less investment, and the development trend of long-distance oil and gas pipelines steel is to be in high strength or super high grade. At present, the highest grade of pipeline steel used in the world is X80. In addition to the straight pipe, a pipeline project also includes the bent pipes for the direction change of the pipeline, the bent pipes in stations, and so on. Bent pipes are usually produced by two kinds of processes, namely, cold bending and hot bending, and the cold bending process has been gradually replaced by hot bending process as cold bending process is under the influence of manufacturing process and service environment. The hot bending of bent pipes usually are to heat the main pipe to Ac3 or above by induction heating equipment, and then the heating zone rotates around the fixed center to bend the bent pipe with the required radius of curvature by a fixed turning panel and under the action of back thrust; after bending, the bent pipe outer ring is cooled by an annular cooling ring, and the heated part of the bent pipe undergoes an accelerated cooling similar to ACC because of the limited cooling capacity of the annular cooling ring.
The steel plate after cooling treatment is treated by tempering in a continuous furnace in consideration of the property uniformity. From the view of the whole process, the whole hot bending and cooling bending process are similar to the TMCP process, which is the combination of high-temperature deformation (bending) and ACC
cooling process. Because the Whole hot bending process is deformed to a small extent ¨ 1 ¨
at a high temperature and the subsequent cooling capacity is weak, the hot bending steel plate for bent pipes can only be designed with high carbon-equivalent composition. The high-carbon-equivalent design will bring two main problems to the whole production: 1) the impact toughness is reduced; 2) there would be a defective shape of the steel plate due to the large structural stress in the cooling process, which brings difficulties to the subsequent straightening and affects the production efficiency at the same time.
At home and abroad, there are patent reports on X80 steel grade bent pipes and the steel plate for bent pipes, such as the patent application of CN201410239039.9, which refers to a hot-rolling plate steel for X80 steel grade bent pipe wherein: 1) only the impact toughness of steel plate at -20 C is referred in the patent application, but in fact, more steel plates for bent pipes need the impact toughness at -30 C or even lower temperature at present; 2) slowly stack cooling is required after rolling of steel plate in the application patent, which is unfavorable to mass production efficiency of steel plate and the follow-up production process at the same time.
Another patent application of No. CN201110245761.X has the following characteristics: 1) the patent mainly emphasizes the hot bending process but does not mention what kind of steel plate production process is used for raw material steel plate; 2) the low-temperature toughness impact value at -45 C obtained by the patent is not higher than 200J, and the numerical fluctuation is large.
Considering the whole process of austenite deformation in the hot bending process and that subsequent cooling is relatively simple and insufficient, the design of steel plate for bent pipes usually always adopts a high carbon equivalent composition compared with that of steel plate for straight pipe. The design of high-carbon-equivalent components will lead to a lower impact toughness under low temperatures.
Disclosure of Invention According to the characteristics of the hot bending process for bent pipes, the chemical composition in the application is still designed with high carbon equivalent, but through the innovation of the cooling process in the production process, a pipeline steel plate with high carbon equivalent and high toughness at low temperatures used for bent pipes is obtained with a concise process and a high yield.
The technical scheme adopted by the invention to solve the above technical problems is to manufacture X80 pipeline steel plate for bent pipes with HIC
resistance,
- 2 -wherein the chemical constituents by mass percentage are as follows: C:
Mn: 1.55-1.90%, Si: <0.45%, S: <0.001%, P: <0.010%, Nb: 0.045-0.08%, Ti: <0.015%, V: <0.008%, Alt: <0.06%, N: <0.0040%, 0: <0.004%, Mo:
<0.40%, Cu: <0.30%, Ni: 0.20--1.5%, Cr: <0.35%, Mo+Cu+Ni+Cr <1.5%, Ceq: 0.35-0.53%, Pcm: 0.17-0.27%, , the balance is Fe and unavoidable impurity elements.
Furthermore, the thickness of the steel plate is 18.4-42mm, the yield strength>600Mpa, the tensile strength >710Mpa, the yield ratio <0.93, the elongation is >35%, the impact energy at -30 C >350J, the impact energy at -50 C>250J, and the impact energy at -60 C >230J.
The composition of the steel in the invention is based on the design principle of high carbon equivalence, and comprises appropriate amount of C, Mn, trace elements of Nb, V, Ti and other micro-alloying elements, as well as a small amount of Mo, Cu, Ni, and other elements, combined with a specific TMCP rolling process, thereby the ultimate mechanical properties are ensured, especially the low-temperature impact toughness under the condition of high carbon equivalence. The principle of adding the elements mentioned above is as follows:
C: C is the most economical and basic strengthening element in steel, and can obviously improve the strength of steel by solid solution strengthening and precipitation strengthening, but have adverse effects on the toughness, ductility, and weldability of steel. Therefore, the development trend of pipeline steel is to reduce C
content, but in order to match the hot bending process, strength and toughness, the C
content is controlled to be 0.05-0.10%.
Mn: Mn is the most important element to compensate for the loss of strength caused by the decrease of C content in pipeline steel, enhances the strength of steel by solid solution strengthening; Mn is an element to enlarge the y phase and reduce the y a transformation temperature of steel, which helps to obtain fine transformation products, improve the toughness of steel, reduce the ductile-brittle transition temperature; Mn is also an element to improve the hardenability of steel.
Considering the harm of Mn segregation to HIC resistance in the process of inspection and with due consideration for both the hot bending process and the strength requirement, the Mn content in the present invention is designed to be 1.55-1.9%, and soft reduction is adopted in continuous casting to alleviate the central segregation caused by high Mn content.
Mn: 1.55-1.90%, Si: <0.45%, S: <0.001%, P: <0.010%, Nb: 0.045-0.08%, Ti: <0.015%, V: <0.008%, Alt: <0.06%, N: <0.0040%, 0: <0.004%, Mo:
<0.40%, Cu: <0.30%, Ni: 0.20--1.5%, Cr: <0.35%, Mo+Cu+Ni+Cr <1.5%, Ceq: 0.35-0.53%, Pcm: 0.17-0.27%, , the balance is Fe and unavoidable impurity elements.
Furthermore, the thickness of the steel plate is 18.4-42mm, the yield strength>600Mpa, the tensile strength >710Mpa, the yield ratio <0.93, the elongation is >35%, the impact energy at -30 C >350J, the impact energy at -50 C>250J, and the impact energy at -60 C >230J.
The composition of the steel in the invention is based on the design principle of high carbon equivalence, and comprises appropriate amount of C, Mn, trace elements of Nb, V, Ti and other micro-alloying elements, as well as a small amount of Mo, Cu, Ni, and other elements, combined with a specific TMCP rolling process, thereby the ultimate mechanical properties are ensured, especially the low-temperature impact toughness under the condition of high carbon equivalence. The principle of adding the elements mentioned above is as follows:
C: C is the most economical and basic strengthening element in steel, and can obviously improve the strength of steel by solid solution strengthening and precipitation strengthening, but have adverse effects on the toughness, ductility, and weldability of steel. Therefore, the development trend of pipeline steel is to reduce C
content, but in order to match the hot bending process, strength and toughness, the C
content is controlled to be 0.05-0.10%.
Mn: Mn is the most important element to compensate for the loss of strength caused by the decrease of C content in pipeline steel, enhances the strength of steel by solid solution strengthening; Mn is an element to enlarge the y phase and reduce the y a transformation temperature of steel, which helps to obtain fine transformation products, improve the toughness of steel, reduce the ductile-brittle transition temperature; Mn is also an element to improve the hardenability of steel.
Considering the harm of Mn segregation to HIC resistance in the process of inspection and with due consideration for both the hot bending process and the strength requirement, the Mn content in the present invention is designed to be 1.55-1.9%, and soft reduction is adopted in continuous casting to alleviate the central segregation caused by high Mn content.
- 3 -Nb: Nb is one of the most important micro-alloying elements in modern microalloyed steels, especially pipeline steels, and has an obvious effect on grain refinement. The recovery and recrystallization of deformed austenite can be hindered by Nb solid solution dragging and Nb (C, N) strain-induced precipitation during hot rolling; the deformed austenite which is not rolled in the recrystallization zone can be transformed into fine phase transformation products during phase transformation by TMCP to give the steel high strength and toughness, and the range of Nb content is determined mainly based on the relationship between C and Nb content in the invention.
V: V has higher precipitation strengthening and weaker grain refinement, and plays a major role in precipitation strengthening when combined with the microalloying elements of Nb, V, and Ti.
Ti: Ti is a strong N-fixing element, and the stoichiometric ratio of Ti/N is 3.42, that is, N below 60 ppm in steel can be fixed by using about 0.02% Ti, and TiN
precipitates can be formed during slab continuous casting, and the fine precipitate is an indispensable element in pipeline steel, which can effectively prevent the growth of austenite grains in slab during heating, help to improve the solid solubility of Nb in austenite, and can improve the impact toughness of the welding heat affected zone, but too much Ti will form large TiN particles, which will affect the falling impact performance, so Ti content will be controlled to be <0.015% in this patent.
Mo: Mo can delay the formation of the preliminary ferrite phase in the y transformation, is the major element to promote the formation of acicular ferrite, and plays an important role in controlling phase transformation and improving the hardenability of steel. Obvious acicular ferrite or bainite can be obtained by adding a certain amount of Mo at a certain cooling rate and final cooling temperature and considering TMCP process and hot bending process, Mo content can be controlled at no less than 0.15%.
S, P: S and P are unavoidable impurity elements in pipeline steel, and the lower the content of S and P, the higher impact toughness pipeline steels have by changing the sulfide morphology through ultra-low sulfur and Ca treatment.
Cu, Ni: As the strength of steel can be improved by solution strengthening, the adding of Ni not only improve the toughness of steel but also prevent the hot brittleness easily caused by Cu in steel, and Ni content is controlled at no less than 0.2%.
V: V has higher precipitation strengthening and weaker grain refinement, and plays a major role in precipitation strengthening when combined with the microalloying elements of Nb, V, and Ti.
Ti: Ti is a strong N-fixing element, and the stoichiometric ratio of Ti/N is 3.42, that is, N below 60 ppm in steel can be fixed by using about 0.02% Ti, and TiN
precipitates can be formed during slab continuous casting, and the fine precipitate is an indispensable element in pipeline steel, which can effectively prevent the growth of austenite grains in slab during heating, help to improve the solid solubility of Nb in austenite, and can improve the impact toughness of the welding heat affected zone, but too much Ti will form large TiN particles, which will affect the falling impact performance, so Ti content will be controlled to be <0.015% in this patent.
Mo: Mo can delay the formation of the preliminary ferrite phase in the y transformation, is the major element to promote the formation of acicular ferrite, and plays an important role in controlling phase transformation and improving the hardenability of steel. Obvious acicular ferrite or bainite can be obtained by adding a certain amount of Mo at a certain cooling rate and final cooling temperature and considering TMCP process and hot bending process, Mo content can be controlled at no less than 0.15%.
S, P: S and P are unavoidable impurity elements in pipeline steel, and the lower the content of S and P, the higher impact toughness pipeline steels have by changing the sulfide morphology through ultra-low sulfur and Ca treatment.
Cu, Ni: As the strength of steel can be improved by solution strengthening, the adding of Ni not only improve the toughness of steel but also prevent the hot brittleness easily caused by Cu in steel, and Ni content is controlled at no less than 0.2%.
- 4 -Cr: The addition of Cr can improve the hardenability of steel and is relatively economical.
The invention also aims to provide the preparation method of a high-carbon-equivalent, low-temperature, and high-toughness X80 pipeline steel plate for bent pipes, which is as follows in sequence: ratio preparation ¨>
converter or electric furnace smelting ¨> out-of-furnace refining ¨> continuous casting ¨>
slab reheating ¨> specific TMCP process + stack cooling after cooling¨*straightening.
The specific process steps are as follows:
The raw materials are processed in sequence by KR molten steel pretreatment, converter smelting, LF refining, RH vacuum refining, continuous casting, wherein Ca-treatment process is used for refining, with a Ca/S molar ratio of not less than 1, and the type B inclusions are controlled to be Grade 1.5 or less. When continuous casting, soft reduction is used to prevent core segregation caused by a high Mn content, to manufacture a continuous casting slab which satisfies composition requirement and has a thickness of not less than 350 mm and a compression ratio of not less than 10.
The continuous casting slab is reheated with multiple heating stages, and the temperature of the second heating stage is controlled at 1250-1300 C; after the furnace is discharged, a specific TMCP process including two-stage rolling and intermediate slab cooling is performed: the first stage is the rolling in the recrystallization zone, wherein the final rolling temperature is not higher than 1200 C, and when rolling in the recrystallization zone, the single-pass rolling reduction ratio of continuous two or three passes is controlled to be not less than 20%; the intermediate slab cooling is to moderately cool the intermediate slab to the temperature of a start rolling temperature in the non-recrystallization zone at the second stage, by a Mild cooling system, wherein the cooling method is to cool the tank body by swinging back and forth, and the cooling rate is 6-12 C/s, to ensure that the austenite grains no longer grow after rolling and shaping in the recrystallization zone, and the temperature difference between the surface of the intermediate slab and the core is small; the second stage is the rolling in the non-recrystallization zone, wherein the start rolling temperature is not higher than 880 C, and the final rolling temperature is controlled at 790-850 C until the reaching of the final thickness.
After rolling, the steel plate is cooled by water, wherein the start cooling temperature is controlled to be not higher than 810 C, the final cooling temperature is
The invention also aims to provide the preparation method of a high-carbon-equivalent, low-temperature, and high-toughness X80 pipeline steel plate for bent pipes, which is as follows in sequence: ratio preparation ¨>
converter or electric furnace smelting ¨> out-of-furnace refining ¨> continuous casting ¨>
slab reheating ¨> specific TMCP process + stack cooling after cooling¨*straightening.
The specific process steps are as follows:
The raw materials are processed in sequence by KR molten steel pretreatment, converter smelting, LF refining, RH vacuum refining, continuous casting, wherein Ca-treatment process is used for refining, with a Ca/S molar ratio of not less than 1, and the type B inclusions are controlled to be Grade 1.5 or less. When continuous casting, soft reduction is used to prevent core segregation caused by a high Mn content, to manufacture a continuous casting slab which satisfies composition requirement and has a thickness of not less than 350 mm and a compression ratio of not less than 10.
The continuous casting slab is reheated with multiple heating stages, and the temperature of the second heating stage is controlled at 1250-1300 C; after the furnace is discharged, a specific TMCP process including two-stage rolling and intermediate slab cooling is performed: the first stage is the rolling in the recrystallization zone, wherein the final rolling temperature is not higher than 1200 C, and when rolling in the recrystallization zone, the single-pass rolling reduction ratio of continuous two or three passes is controlled to be not less than 20%; the intermediate slab cooling is to moderately cool the intermediate slab to the temperature of a start rolling temperature in the non-recrystallization zone at the second stage, by a Mild cooling system, wherein the cooling method is to cool the tank body by swinging back and forth, and the cooling rate is 6-12 C/s, to ensure that the austenite grains no longer grow after rolling and shaping in the recrystallization zone, and the temperature difference between the surface of the intermediate slab and the core is small; the second stage is the rolling in the non-recrystallization zone, wherein the start rolling temperature is not higher than 880 C, and the final rolling temperature is controlled at 790-850 C until the reaching of the final thickness.
After rolling, the steel plate is cooled by water, wherein the start cooling temperature is controlled to be not higher than 810 C, the final cooling temperature is
- 5 ¨
Date Recue/Date Received 2021-05-31 controlled to be not higher than 500 C, and the cooling rate is 10 to 35 C/s; after cooling, the steel plate is straightened, and then the final product is obtained by directly cooling to room temperature. In this cooling process, considering that the finished steel sheet has a high carbon equivalent, a stepwise gradient cooling process is adopted, that is, the cooling water amount of each cooling unit of the ACC
is set to be different: the amount of cooling water in the first 1-6 segments is the largest with a corresponding cooling rate of 25-35 C/s and the amount of cooling water in the ACC
cooling unit in the last 7-12 segments decreases in sequence with a corresponding cooling rate change of 10-20 C/s.
After the final rolling temperature ends, the first 1-6 ACC cooling segments of the steel plate are cooled to the temperature close to Ac3 line in CCT curve by means of the stepwise gradient cooling process. On one hand, it can get a larger degree of supercooling through a fast cooling speed, and obtain more phase-transformation nuclei and finally obtain finer phase-transformation crystal grains. On the other side, the cooling method mention above can shorten the time needed to arrive at the same average cooling speed and the final cooling temperature. Once the temperature is near the Ar3 line, lower cooling speed is adopted to reduce the phase-transformation stress and to reduce the sensitivity of temperature stress in the phase transformation under the condition of a high carbon equivalence. Thereby, the structure in the steel plate is relatively small and the ultimate residual stress is relatively small, and ultimately the steel plate still has high toughness at low temperatures.
The Mild Cooling cooling system adopted in the invention is arranged between the roughing mill and the finishing mill of the rolling mill production line, and the system is a box structure with a total length of 18 m, and spray nozzles are densely distributed on the top of the box to moderately cool the roughed intermediate slab;
Corresponding to different thickness of the intermediate slab, the cooling speed of the intermediate slab is obtained to be 4-18 C/s; the thickness of intermediate slab is usually about 40-180 mm according to product and production requirements, and the intermediate slab whose thickness of is less than 40 mm is not opened for moderate cooling unless necessary, because it is thinner; for thick intermediate slabs, considering the design limit, the maximum cooling speed is 4 C/s, while for thin slabs, the maximum cooling speed can reach 18 C/s.
Furthermore, the operation process of the Mild cooling system is as follows:
the intermediate slab is obtained by the rolling in the recrystallization zone, and the
Date Recue/Date Received 2021-05-31 controlled to be not higher than 500 C, and the cooling rate is 10 to 35 C/s; after cooling, the steel plate is straightened, and then the final product is obtained by directly cooling to room temperature. In this cooling process, considering that the finished steel sheet has a high carbon equivalent, a stepwise gradient cooling process is adopted, that is, the cooling water amount of each cooling unit of the ACC
is set to be different: the amount of cooling water in the first 1-6 segments is the largest with a corresponding cooling rate of 25-35 C/s and the amount of cooling water in the ACC
cooling unit in the last 7-12 segments decreases in sequence with a corresponding cooling rate change of 10-20 C/s.
After the final rolling temperature ends, the first 1-6 ACC cooling segments of the steel plate are cooled to the temperature close to Ac3 line in CCT curve by means of the stepwise gradient cooling process. On one hand, it can get a larger degree of supercooling through a fast cooling speed, and obtain more phase-transformation nuclei and finally obtain finer phase-transformation crystal grains. On the other side, the cooling method mention above can shorten the time needed to arrive at the same average cooling speed and the final cooling temperature. Once the temperature is near the Ar3 line, lower cooling speed is adopted to reduce the phase-transformation stress and to reduce the sensitivity of temperature stress in the phase transformation under the condition of a high carbon equivalence. Thereby, the structure in the steel plate is relatively small and the ultimate residual stress is relatively small, and ultimately the steel plate still has high toughness at low temperatures.
The Mild Cooling cooling system adopted in the invention is arranged between the roughing mill and the finishing mill of the rolling mill production line, and the system is a box structure with a total length of 18 m, and spray nozzles are densely distributed on the top of the box to moderately cool the roughed intermediate slab;
Corresponding to different thickness of the intermediate slab, the cooling speed of the intermediate slab is obtained to be 4-18 C/s; the thickness of intermediate slab is usually about 40-180 mm according to product and production requirements, and the intermediate slab whose thickness of is less than 40 mm is not opened for moderate cooling unless necessary, because it is thinner; for thick intermediate slabs, considering the design limit, the maximum cooling speed is 4 C/s, while for thin slabs, the maximum cooling speed can reach 18 C/s.
Furthermore, the operation process of the Mild cooling system is as follows:
the intermediate slab is obtained by the rolling in the recrystallization zone, and the
- 6 -intermediate slab swings back and forth after entering the Mild cooling system in which the corresponding roller path operates the swing mode, meanwhile the nozzle sprays the water to the intermediate slab, in order to cool the intermediate slab to the start rolling temperature of the second stage at a specific cooling rate, and when the intermediate slab has been cooled to the start rolling temperature of the second stage, the intermediate slab is delivered out of the Mild cooling system and is sent to the rolling process at the second stage.
The invention has the following characteristics:
1) The technical problems of defective or unstable low-temperature impact performance under high carbon equivalent are solved by adopting appropriate composition and specific production technology, which makes the steel plate for bent pipes have excellent low-temperature impact toughness.
2) In the invention, a stepwise gradient cooling process is adopted for steel plate cooling, which can be realized on the spot without additional equipment investment with characteristics of high production efficiency and simple process.
Brief Description of Figures in the Drawings Figure 1 is a comparison of ACC stepwise gradient cooling and a conventional cooling in an embodiment of the invention;
Figure 2 is a structural diagram of a steel plate according to an embodiment of the invention.
Mode(s) for Carrying Out the Invention The present invention is further described in detail with reference to embodiments.
The preparation process of a X80 pipeline steel plate with high carbon equivalent and high toughness at low temperatures, which is used for bent pipes, is as follows in sequence: ratio preparation ¨> converter or electric furnace smelting ¨> out-of-furnace refining ¨> continuous casting ¨> slab reheating ¨) rolling ¨> ACC gradient cooling ¨> straightening.
The specific process steps are as follows: the raw materials are processed in sequence by KR molten steel pretreatment, converter smelting, LF refining, RH
vacuum refining, continuous casting, wherein in refining a Ca/S molar ratio is controlled to be not less than 1, and the type B inclusions are controlled to be Grade 1.5 or less. When continuous casting, soft reduction is used to prevent core ¨ 7 ¨
segregation caused by high Mn content. The continuous casting slab manufactured satisfies composition requirements, has a thickness of 350 mm; when the slab is heated, the temperature of the second-step heating section is controlled at not more than 1300 C, and the residence time in this heating section is not less than 4 hours;
then the process of rolling, ACC stepwise gradient cooling and straightening are sequentially conducted.
The specific TMCP process includes two-stage rolling and intermediate slab cooling: the first stage is the rolling in the recrystallization zone, wherein the final rolling temperature is not higher than 1200 C, and when rolling in the recrystallization zone, the single-pass rolling reduction ratio of continuous two or three passes is controlled to be not less than 20%;
The intermediate slab cooling is quickly cooling the intermediate slab to the temperature of a start rolling temperature in the non-recrystallization zone at the second stage, by a Mild cooling system, wherein the cooling method is to cool the tank body by swinging back and forth, and the cooling rate is 6-12 C/s, to ensure that the austenite grains no longer grow after rolling and shaping in the recrystallization zone, and the temperature difference between the surface of the intermediate slab and the core is small;
The second stage is the rolling in the non-recrystallization zone, wherein the start rolling temperature is not higher than 900 C, and the final rolling temperature is controlled to be no higher than 850 C; after rolling, the steel plate is cooled by water, wherein the start cooling temperature is controlled to be not higher than 800 C, the final cooling temperature is controlled to be not higher than 500 C, and the cooling rate is 10 to 35 C/s; considering that the finished steel sheet has a high carbon equivalent, a stepwise gradient cooling process is adopted in this cooling process, that is, the cooling water amount of each cooling unit of the ACC is set to be different: the amount of cooling water in the first 1-6 segments is the largest with a corresponding cooling rate of 25-35 C/s and the amount of cooling water in the ACC cooling unit in the last 7-12 segments decreases in sequence with a corresponding cooling rate change of 10-20 C/s; after cooling, the steel plate is straightened, and then the final product is obtained by directly cooling to room temperature.
The specific chemical composition of the steel plate involved in each embodiment is shown in Table 1, the specific TMCP process parameters are shown in Table 2, and the main mechanical properties are shown in Table 3.
- 8 ¨
Date Recue/Date Received 2021-05-31 Table 1 Embodiment C Mn Si S P Nb Ti V Alt Mo+Cu+Ni+Cr 1 <0.1 1.55-1.9 <0.35 0.0005 0.01 <0.08 <0.015 <0.007 <0.06 1.5 2 0.10 1.65 0.25 0.0005 0.008 0.070 0.018 0.008 0.028 <1.5 3 0.05 1.9 0.20 0.0005 0.009 0.065 0.018 0.007 0.030 <1.5 Table 2 Embodiment Temperature Rolling in the Cumulative Start Final Cooling Final of the recrystallizati deformation temperature temperatu speed of cooling second-step on zone, the rate of the of the re of the water temperature heating final rolling rolling in the rolling in rolling in cooling C temperature recrystallizat the the Cis C ion zone non-recrysta non-recrys % llization tallization zone zone C
1 <1300 <1100 <55 <900 <850 10-35 <500 2 <1300 <1100 <55 <900 <850 10-35 <500 3 <1300 <1100 <55 <900 <850 10-35 <500 Table 3 Energy absorption under transverse Embodi Yield Strength Tensile Strength Elongation after Yield ratio Re/Rm impact ( V ) J
ment Rt0.5 Rm fracture %
Temperature 1 2 3 1 623 720 41.5 0.87 -30 351 367 355 2 631 719 42.3 0.88 -30 357 350 360 3 598 733 39.2 0.82 -30 389 378 395 Energy absorption under transverse Embodi Yield Strength Tensile Strength Elongation after Yield ratio Re/Rm impact (V) J
ment Rt0.5 Rm fracture % Temperature 1 2 3 1 623 720 41.5 0.87 -45 267 272 251 2 631 719 42.3 0.88 -45 255 255 264 3 598 733 39.2 0.82 -45 361 375 379 Energy absorption under transverse Embodi Yield Strength Tensile Strength Elongation after Yield ratio Re/Rm impact ( V ) J
ment Rt0.5 Rm fracture %
Temperature 1 2 3 1 623 720 41.5 0.87 -50 253 257 251 2 631 719 42.3 0.88 -50 262 255 258 3 598 733 39.2 0.82 -50 353 349 357 Energy absorption under transverse Embodi Yield Strength Tensile Strength Elongation after Yield ratio Re/Rm impact ( V ) J
ment Rt0.5 Rm fracture %
Temperature 1 2 3 1 623 720 41.5 0.87 -60 233 246 239 2 631 719 42.3 0.88 -60 245 253 244 3 598 733 39.2 0.82 -60 339 327 331 ¨ 10 ¨
The invention has the following characteristics:
1) The technical problems of defective or unstable low-temperature impact performance under high carbon equivalent are solved by adopting appropriate composition and specific production technology, which makes the steel plate for bent pipes have excellent low-temperature impact toughness.
2) In the invention, a stepwise gradient cooling process is adopted for steel plate cooling, which can be realized on the spot without additional equipment investment with characteristics of high production efficiency and simple process.
Brief Description of Figures in the Drawings Figure 1 is a comparison of ACC stepwise gradient cooling and a conventional cooling in an embodiment of the invention;
Figure 2 is a structural diagram of a steel plate according to an embodiment of the invention.
Mode(s) for Carrying Out the Invention The present invention is further described in detail with reference to embodiments.
The preparation process of a X80 pipeline steel plate with high carbon equivalent and high toughness at low temperatures, which is used for bent pipes, is as follows in sequence: ratio preparation ¨> converter or electric furnace smelting ¨> out-of-furnace refining ¨> continuous casting ¨> slab reheating ¨) rolling ¨> ACC gradient cooling ¨> straightening.
The specific process steps are as follows: the raw materials are processed in sequence by KR molten steel pretreatment, converter smelting, LF refining, RH
vacuum refining, continuous casting, wherein in refining a Ca/S molar ratio is controlled to be not less than 1, and the type B inclusions are controlled to be Grade 1.5 or less. When continuous casting, soft reduction is used to prevent core ¨ 7 ¨
segregation caused by high Mn content. The continuous casting slab manufactured satisfies composition requirements, has a thickness of 350 mm; when the slab is heated, the temperature of the second-step heating section is controlled at not more than 1300 C, and the residence time in this heating section is not less than 4 hours;
then the process of rolling, ACC stepwise gradient cooling and straightening are sequentially conducted.
The specific TMCP process includes two-stage rolling and intermediate slab cooling: the first stage is the rolling in the recrystallization zone, wherein the final rolling temperature is not higher than 1200 C, and when rolling in the recrystallization zone, the single-pass rolling reduction ratio of continuous two or three passes is controlled to be not less than 20%;
The intermediate slab cooling is quickly cooling the intermediate slab to the temperature of a start rolling temperature in the non-recrystallization zone at the second stage, by a Mild cooling system, wherein the cooling method is to cool the tank body by swinging back and forth, and the cooling rate is 6-12 C/s, to ensure that the austenite grains no longer grow after rolling and shaping in the recrystallization zone, and the temperature difference between the surface of the intermediate slab and the core is small;
The second stage is the rolling in the non-recrystallization zone, wherein the start rolling temperature is not higher than 900 C, and the final rolling temperature is controlled to be no higher than 850 C; after rolling, the steel plate is cooled by water, wherein the start cooling temperature is controlled to be not higher than 800 C, the final cooling temperature is controlled to be not higher than 500 C, and the cooling rate is 10 to 35 C/s; considering that the finished steel sheet has a high carbon equivalent, a stepwise gradient cooling process is adopted in this cooling process, that is, the cooling water amount of each cooling unit of the ACC is set to be different: the amount of cooling water in the first 1-6 segments is the largest with a corresponding cooling rate of 25-35 C/s and the amount of cooling water in the ACC cooling unit in the last 7-12 segments decreases in sequence with a corresponding cooling rate change of 10-20 C/s; after cooling, the steel plate is straightened, and then the final product is obtained by directly cooling to room temperature.
The specific chemical composition of the steel plate involved in each embodiment is shown in Table 1, the specific TMCP process parameters are shown in Table 2, and the main mechanical properties are shown in Table 3.
- 8 ¨
Date Recue/Date Received 2021-05-31 Table 1 Embodiment C Mn Si S P Nb Ti V Alt Mo+Cu+Ni+Cr 1 <0.1 1.55-1.9 <0.35 0.0005 0.01 <0.08 <0.015 <0.007 <0.06 1.5 2 0.10 1.65 0.25 0.0005 0.008 0.070 0.018 0.008 0.028 <1.5 3 0.05 1.9 0.20 0.0005 0.009 0.065 0.018 0.007 0.030 <1.5 Table 2 Embodiment Temperature Rolling in the Cumulative Start Final Cooling Final of the recrystallizati deformation temperature temperatu speed of cooling second-step on zone, the rate of the of the re of the water temperature heating final rolling rolling in the rolling in rolling in cooling C temperature recrystallizat the the Cis C ion zone non-recrysta non-recrys % llization tallization zone zone C
1 <1300 <1100 <55 <900 <850 10-35 <500 2 <1300 <1100 <55 <900 <850 10-35 <500 3 <1300 <1100 <55 <900 <850 10-35 <500 Table 3 Energy absorption under transverse Embodi Yield Strength Tensile Strength Elongation after Yield ratio Re/Rm impact ( V ) J
ment Rt0.5 Rm fracture %
Temperature 1 2 3 1 623 720 41.5 0.87 -30 351 367 355 2 631 719 42.3 0.88 -30 357 350 360 3 598 733 39.2 0.82 -30 389 378 395 Energy absorption under transverse Embodi Yield Strength Tensile Strength Elongation after Yield ratio Re/Rm impact (V) J
ment Rt0.5 Rm fracture % Temperature 1 2 3 1 623 720 41.5 0.87 -45 267 272 251 2 631 719 42.3 0.88 -45 255 255 264 3 598 733 39.2 0.82 -45 361 375 379 Energy absorption under transverse Embodi Yield Strength Tensile Strength Elongation after Yield ratio Re/Rm impact ( V ) J
ment Rt0.5 Rm fracture %
Temperature 1 2 3 1 623 720 41.5 0.87 -50 253 257 251 2 631 719 42.3 0.88 -50 262 255 258 3 598 733 39.2 0.82 -50 353 349 357 Energy absorption under transverse Embodi Yield Strength Tensile Strength Elongation after Yield ratio Re/Rm impact ( V ) J
ment Rt0.5 Rm fracture %
Temperature 1 2 3 1 623 720 41.5 0.87 -60 233 246 239 2 631 719 42.3 0.88 -60 245 253 244 3 598 733 39.2 0.82 -60 339 327 331 ¨ 10 ¨
Claims (4)
1. A X80 pipeline steel plate, comprising chemical components by mass percentage as follows:
C: <0.10%, Mn: 1.55-1.90%, Si: <0.45%, S: <0.001%, P: <0.010%, Nb: 0.045-0.08%, Ti:
<0.015%, V: <0.008%, Alt: <0.06%, N:<0.0040%, 0: <0.004%, Mo: <0.40%, Cu:
<0.30%, Ni: 0.20-1.5%, Cr: <0.35%, Mo+Cu+Ni+Cr <1.5%, Ceq: 0.35-0.53%, Pcm: 0.17-0.27%, the balance being Fe and unavoidable impurity elements.
C: <0.10%, Mn: 1.55-1.90%, Si: <0.45%, S: <0.001%, P: <0.010%, Nb: 0.045-0.08%, Ti:
<0.015%, V: <0.008%, Alt: <0.06%, N:<0.0040%, 0: <0.004%, Mo: <0.40%, Cu:
<0.30%, Ni: 0.20-1.5%, Cr: <0.35%, Mo+Cu+Ni+Cr <1.5%, Ceq: 0.35-0.53%, Pcm: 0.17-0.27%, the balance being Fe and unavoidable impurity elements.
2. The X80 pipeline steel plate according to Claim 1, wherein a thickness of the steel plate is 18.4-42mm, a yield strength of the steel plate is >600Mpa, a tensile strength of the steel plate is >710Mpa, a yield ratio of the steel plate is <0.93, an elongation of the steel plate is >35%, an impact energy at -30 C of the steel plate is >350J, the impact energy at -50 C
of the steel plate is >250J, and the impact energy at-60 C of the steel plate is >230J.
of the steel plate is >250J, and the impact energy at-60 C of the steel plate is >230J.
3. A method of manufacturing a X80 pipeline steel plate , comprising following steps:
processing raw materials in sequence by KR molten steel pretreatment, converter smelting, LF refining, RH vacuum refining and continuous casting, wherein using Ca-treatment for the refining step with a Ca/S molar ratio of not less than 1 and a grade of type B
inclusions being controlled no higher than 1.5, and during the continuous casting step, adopting soft reduction to prevent core segregation caused by a high Mn content to manufacture a continuous casting slab, satisfying composition requirement and having a thickness of not less than 350 mm and a compression ratio of not less than 10;
reheating the continuous casting slab with multiple heating stages, temperature of a second heating stage being controlled at 1250-1300 C;
after a furnace is discharged, performing a specific TMCP process including two-stage rolling and intermediate slab cooling:
the first stage being the rolling in a recrystallization zone, wherein a final rolling temperature is not higher than 1200 C, and during the step of rolling in the recrystallization zone, a single-pass rolling reduction ratio of continuous two or three passes is controlled to be not less than 20%;
the step of intermediate slab cooling being to moderately cool an intermediate slab to the temperature of a start rolling temperature in a non-recrystallization zone at the second stage by a mild cooling system, wherein the cooling method is to cool a tank body by swinging back and forth with a cooling rate of 6-12 C/s to ensure that austenite grains no longer grow after being rolled and shaped in the recrystallization zone, and the temperature difference between the surface and the core of the intermediate slab is small;
Date Recue/Date Received 2021-05-31 the second stage being the rolling in the non-recrystallization zone until a final thickness is reached, wherein the start rolling temperature is not higher than 880 C, and a final rolling temperature is controlled at 790-850 C;
after rolling, cooling the steel plate by water, wherein a start cooling temperature is controlled to be not higher than 810 C, a final cooling temperature is controlled to be not higher than 500 C, and a cooling rate is 10 to 35 C/s; and after cooling, straightening the steel plate, and directly cooling to room temperature to obtain a final product, wherein during the cooling process, being considered that a finished steel sheet has a high carbon equivalent, a stepwise gradient cooling process is adopted, that is, cooling water amount of each ACC cooling unit is set to be different: the cooling water amount in first 1-6 segments is the largest with a corresponding cooling rate of 25-35 C/s and the cooling water amount in 7-12 segments decreases in sequence with a corresponding cooling rate change of 10-20 C/s.
processing raw materials in sequence by KR molten steel pretreatment, converter smelting, LF refining, RH vacuum refining and continuous casting, wherein using Ca-treatment for the refining step with a Ca/S molar ratio of not less than 1 and a grade of type B
inclusions being controlled no higher than 1.5, and during the continuous casting step, adopting soft reduction to prevent core segregation caused by a high Mn content to manufacture a continuous casting slab, satisfying composition requirement and having a thickness of not less than 350 mm and a compression ratio of not less than 10;
reheating the continuous casting slab with multiple heating stages, temperature of a second heating stage being controlled at 1250-1300 C;
after a furnace is discharged, performing a specific TMCP process including two-stage rolling and intermediate slab cooling:
the first stage being the rolling in a recrystallization zone, wherein a final rolling temperature is not higher than 1200 C, and during the step of rolling in the recrystallization zone, a single-pass rolling reduction ratio of continuous two or three passes is controlled to be not less than 20%;
the step of intermediate slab cooling being to moderately cool an intermediate slab to the temperature of a start rolling temperature in a non-recrystallization zone at the second stage by a mild cooling system, wherein the cooling method is to cool a tank body by swinging back and forth with a cooling rate of 6-12 C/s to ensure that austenite grains no longer grow after being rolled and shaped in the recrystallization zone, and the temperature difference between the surface and the core of the intermediate slab is small;
Date Recue/Date Received 2021-05-31 the second stage being the rolling in the non-recrystallization zone until a final thickness is reached, wherein the start rolling temperature is not higher than 880 C, and a final rolling temperature is controlled at 790-850 C;
after rolling, cooling the steel plate by water, wherein a start cooling temperature is controlled to be not higher than 810 C, a final cooling temperature is controlled to be not higher than 500 C, and a cooling rate is 10 to 35 C/s; and after cooling, straightening the steel plate, and directly cooling to room temperature to obtain a final product, wherein during the cooling process, being considered that a finished steel sheet has a high carbon equivalent, a stepwise gradient cooling process is adopted, that is, cooling water amount of each ACC cooling unit is set to be different: the cooling water amount in first 1-6 segments is the largest with a corresponding cooling rate of 25-35 C/s and the cooling water amount in 7-12 segments decreases in sequence with a corresponding cooling rate change of 10-20 C/s.
4. The method of manufacturing X80 pipeline steel plate according to Claim 3,wherein the intermediate slab is obtained by the rolling in the recrystallization zone, and the intermediate slab swings back and forth after entering the mild cooling system in which the corresponding roller path operates the swing mode, meanwhile a nozzle sprays the water to the intermediate slab, in order to cool the intermediate slab to the start rolling temperature of the second stage at a specific cooling rate; and when the intermediate slab has been cooled to the start rolling temperature of the second stage, the intermediate slab is delivered out of the Mild cooling system and is sent to the rolling process at the second stage.
Date Recue/Date Received 2021-05-31
Date Recue/Date Received 2021-05-31
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| CN201710213372.6A CN107099745B (en) | 2017-04-01 | 2017-04-01 | High-carbon-equivalent low-temperature high-toughness pipeline steel plate for X80 elbow and manufacturing method thereof |
| CN201710213372.6 | 2017-04-01 | ||
| PCT/CN2017/105529 WO2018176790A1 (en) | 2017-04-01 | 2017-10-10 | High carbon equivalent and high low-temperature toughness pipeline steel plate for x80 elbow pipe and manufacturing method therefor |
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| CN104250713B (en) * | 2014-09-19 | 2017-01-11 | 江阴兴澄特种钢铁有限公司 | X80-grade large-deformation-resistant pipeline steel plate and manufacturing method thereof |
| CN104404387B (en) * | 2014-10-29 | 2017-04-26 | 江苏沙钢集团有限公司 | Steel plate for ultralow-temperature and high-pressure service delivery tubes, and its making method |
| CN104404378A (en) * | 2014-12-19 | 2015-03-11 | 山东钢铁股份有限公司 | Wide and thick steel plate for hot-bent elbow pipes at X65-X80 levels and manufacturing method of wide and thick steel plate |
| CN105950973B (en) * | 2016-05-13 | 2018-08-31 | 江阴兴澄特种钢铁有限公司 | The excellent think gauge X80 pipeline steels of ultralow temperature block hammer performance and its manufacturing method |
| CN105950972A (en) * | 2016-05-13 | 2016-09-21 | 江阴兴澄特种钢铁有限公司 | Thick-specification X80 pipeline steel plate with process time being shortened and manufacturing method thereof |
| CN106367685B (en) * | 2016-08-30 | 2018-08-07 | 江阴兴澄特种钢铁有限公司 | The effective X80 of deep-sea drilling water proof and following Grade Pipeline Steel and preparation method thereof |
| CN107099745B (en) * | 2017-04-01 | 2019-12-27 | 江阴兴澄特种钢铁有限公司 | High-carbon-equivalent low-temperature high-toughness pipeline steel plate for X80 elbow and manufacturing method thereof |
-
2017
- 2017-04-01 CN CN201710213372.6A patent/CN107099745B/en active Active
- 2017-10-10 CA CA3058488A patent/CA3058488C/en active Active
- 2017-10-10 DE DE112017007384.7T patent/DE112017007384T5/en active Pending
- 2017-10-10 WO PCT/CN2017/105529 patent/WO2018176790A1/en active Application Filing
- 2017-10-10 RU RU2019130660A patent/RU2724257C1/en active
Also Published As
| Publication number | Publication date |
|---|---|
| WO2018176790A1 (en) | 2018-10-04 |
| CA3058488A1 (en) | 2018-10-04 |
| CN107099745A (en) | 2017-08-29 |
| CN107099745B (en) | 2019-12-27 |
| DE112017007384T5 (en) | 2019-12-12 |
| RU2724257C1 (en) | 2020-06-22 |
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