CN114892102B - Economical steel plate for large-thickness pipe fitting and manufacturing method thereof - Google Patents
Economical steel plate for large-thickness pipe fitting and manufacturing method thereof Download PDFInfo
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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
- C22C38/36—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.7% by weight of carbon
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
- C21C5/28—Manufacture of steel in the converter
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- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/06—Deoxidising, e.g. killing
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- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/072—Treatment with gases
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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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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium 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
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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Abstract
The invention provides an economical steel plate for large-thickness pipe fittings and a production method thereof, wherein the steel plate comprises the following chemical components in percentage by mass: c:0.06-0.09%, si:0.15-0.30%, mn:1.55-1.65%, P is less than or equal to 0.012%, S is less than or equal to 0.002%, al:0.025-0.045%, nb:0.035-0.045%, ti:0.010-0.025%, cr:0.25-0.35%, N is less than or equal to 0.0030%, O is less than or equal to 0.0020%, H is less than or equal to 0.00015%, and the balance is Fe and unavoidable impurities. The thickness of the steel plate produced by the method is 30-50mm, and the steel plate and the sample quenching and tempering performance have higher strength and good low-temperature toughness, can be widely applied to the aspects of steel for pipe fittings in oil and gas transportation industries, and have good popularization significance.
Description
Technical Field
The invention belongs to the technical field of continuous casting production of medium plates, and particularly relates to an economical steel plate for large-thickness pipe fittings with the thickness of 30-50mm and a manufacturing method thereof.
Background
The pipe fitting plays roles of changing direction, strengthening reinforcement and the like in a pipeline, is an important structural member, mainly comprises a tee joint, a sealing head, an elbow pipe and the like, is a new variety with high technical content and high added value, has high strength, also has good extensibility, cold bending performance, welding performance and low-temperature shock resistance, and is mainly applied to the industries of natural gas and petroleum transportation. In practical application, after the high-strength pipe steel is subjected to workpiece tempering, the pipe steel can be applied to more complex service environments, and a large amount of alloy is added in component design to ensure excellent performance of the pipe steel, so that the cost of the pipe steel is increased.
The patent of thick plate for pipeline steel with excellent plasticity and toughness and the production method thereof (CN 111996449B) has higher strength and toughness, but expensive alloying elements such as Mo, ni and the like are added in component design, so that the design cost is higher, the component design adopts ultra-low carbon design, and the smelting difficulty is great in industrial production.
The patent refers to a low-cost wear-resistant pipe steel X65 steel plate and a production method thereof (CN 103725974B), wherein Cr and V are adopted to replace Mo and Ni to reduce cost, and a controlled rolling and controlled cooling post-tempering heat treatment process is adopted, but the strength and toughness of the steel plate are not mentioned, and the 1/2 position of the steel plate cannot be guaranteed to have good low-temperature toughness.
Disclosure of Invention
The invention aims to provide an economical steel plate for large-thickness pipe fittings and a manufacturing method thereof, which are matched with reasonable components, smelting control and controlled rolling and cooling and heat treatment processes to produce a steel plate with thickness of 30-50mm, wherein the quenching and tempering strength of the steel plate and a sample exceeds the L450 steel grade requirement, and the quenching and tempering thickness 1/2 position low-temperature impact performance of the steel plate and the sample can be ensured.
In order to solve the technical problems, the invention adopts the following technical scheme: the steel plate for the economic large-thickness pipe fitting comprises the following chemical components in percentage by mass: c:0.06-0.09%, si:0.15-0.30%, mn:1.55-1.65%, P is less than or equal to 0.012%, S is less than or equal to 0.002%, al:0.025-0.045%, nb:0.035-0.045%, ti:0.010-0.025%, cr:0.20-0.30%, N is less than or equal to 0.0030%, O is less than or equal to 0.0020%, H is less than or equal to 0.00015%, and the balance is Fe and unavoidable impurities, wherein CEpcm is less than or equal to 0.18%.
The invention also discloses an economic steel plate for the large-thickness pipe fitting and a manufacturing method thereof, which are characterized in that: the production steps and parameters of the manufacturing method are as follows:
1. smelting: molten iron pretreatment, converter smelting, LF furnace treatment, RH vacuum treatment and continuous casting;
in the converter smelting, tapping P is less than or equal to 0.010%, S is less than or equal to 0.003%, spot blowing is not allowed, slag discharging in the tapping process is avoided, and an argon station is deoxidized by adding an aluminum wire; slag formation is carried out by adopting a large amount of slag in LF refining, and the white slag holding time is more than or equal to 17min; RH vacuum pressure maintaining (less than or equal to 100 Pa) time is more than or equal to 12min, calcium treatment is carried out before tapping, static argon blowing time after wire feeding is more than or equal to 12min, and gas content is strictly controlled, wherein the mass percentage content is as follows: n is less than or equal to 0.0030 percent, O is less than or equal to 0.0020 percent, and H is less than or equal to 0.00015 percent; the superheat degree in the continuous casting process is controlled to be less than or equal to 20 ℃, two-cooling electromagnetic stirring and light depressing at the solidification tail end are adopted, the constant pulling speed is kept in the casting process of the casting blank, the pulling speed range is 0.6m/min-0.8m/min, and the center segregation C class is less than or equal to 1.0;
2. heating: a walking beam type heating furnace is adopted, so that the temperature of heating is not too high to prevent austenite grains from growing, the temperature of a soaking section is controlled to 1170-1230 ℃, the total heating time of a casting blank in the heating furnace is 260-300min, and the temperature uniformity of the casting blank is ensured;
3. rolling and cooling: adopting a two-stage controlled rolling process of a recrystalization zone and a non-recrystalization zone, wherein the initial rolling temperature of rough rolling is 1020-1100 ℃, the accumulated rolling reduction is 60-70%, the single rolling reduction of the last three passes is more than or equal to 16%, the initial rolling temperature of finish rolling is 860-900 ℃, the finishing rolling temperature is 780-820 ℃, the accumulated rolling reduction is 50-65%, the steel plate is rapidly thrown after the last passes are finished, the steel plate is rapidly fed into a controlled cooling zone, the growth of crystal grains is avoided, the steel plate is cooled by adopting an ACC (alternating current) controlled cooling mode, and the redness temperature of the steel plate is 550-600 ℃.
Wherein the yield strength of the steel plate is more than or equal to 469MPa, the tensile strength is more than or equal to 613MPa, the yield ratio is less than or equal to 0.77, the transverse impact energy at the thickness of 1/2 position at-30 ℃ is more than or equal to 150J, the longitudinal impact energy at the thickness of 1/2 position at-30 ℃ is more than or equal to 200J, and the DWTT at the temperature of minus 20 ℃ is more than or equal to 85%.
Further: the yield strength of the sample after quenching is more than or equal to 504MPa, the tensile strength is more than or equal to 594MPa, the yield ratio is less than or equal to 0.86, the transverse impact power at the thickness of 1/2 position-30 ℃ is more than or equal to 220J, the longitudinal impact power at the thickness of 1/2 position-30 ℃ is more than or equal to 250J, and the DWTT at the temperature of-20 ℃ is more than or equal to 90% after the sample is quenched at the temperature of 910-930 ℃ at the furnace time of 2.0t (t is the thickness of the steel plate), and the tempering temperature of 590-610 ℃ at the furnace time of 3.0t (t is the thickness of the steel plate).
Further: the flaw detection result of the steel plate meets the NB/T47013-2015 standard I-level requirement.
Further: the thickness of the steel plate is 30-50mm, and the thickness of the continuous casting billet/the thickness of the finished steel plate is less than or equal to 8.
Through the process flow, the yield strength of the produced steel plate for the economic large-thickness pipe fitting is more than or equal to 469MPa, the tensile strength is more than or equal to 613MPa, the yield ratio is less than or equal to 0.77, the transverse impact energy at the thickness of 1/2 position-30 ℃ is more than or equal to 150J, the longitudinal impact energy at the thickness of 1/2 position-30 ℃ is more than or equal to 200J, and the DWTT at the temperature of minus 20 ℃ is more than or equal to 85%. The method comprises the steps of carrying out a first treatment on the surface of the The yield strength of the sample after quenching is more than or equal to 504MPa, the tensile strength is more than or equal to 594MPa, the yield ratio is less than or equal to 0.86, the transverse impact power at the thickness of 1/2 position-30 ℃ is more than or equal to 220J, the longitudinal impact power at the thickness of 1/2 position-30 ℃ is more than or equal to 250J, and the DWTT at the temperature of-20 ℃ is more than or equal to 90% after the sample is quenched at the temperature of 910-930 ℃ at the furnace time of 2.0t (t is the thickness of the steel plate), and the tempering temperature of 590-610 ℃ at the furnace time of 3.0t (t is the thickness of the steel plate).
The invention has the advantages that:
1. through reasonable component system design and an optimal rolling and cooling control process, all mechanical property indexes of the produced economic steel plate for large-thickness pipe fittings and the quenched and tempered samples meet the L450 steel grade requirement in the API 5L standard, the actual production steel plate can reach yield strength of more than or equal to 469MPa, tensile strength of more than or equal to 613MPa, yield ratio of less than or equal to 0.77, yield strength of more than or equal to 504MPa, tensile strength of more than or equal to 594MPa and yield ratio of less than or equal to 0.86 after quenching and tempering the samples.
2. The steel plate for the economic large-thickness pipe fitting, which is produced by the invention, has good strength and excellent low-temperature impact performance at the 1/2 position of the thickness, wherein the transverse impact energy of the steel plate at the 1/2 position of the steel plate at the temperature of minus 30 ℃ is more than or equal to 150J, the longitudinal impact energy of the steel plate at the 1/2 position of the steel plate at the temperature of minus 30 ℃ is more than or equal to 200J, the DWTT at the temperature of minus 20 ℃ is more than or equal to 85%, the transverse impact energy of the sample at the 1/2 position of the steel plate at the temperature of minus 30 ℃ is more than or equal to 220J, and the longitudinal impact energy of the sample at the temperature of minus 30 ℃ is more than or equal to 250J, and the DWTT at the temperature of minus 20 ℃ is more than or equal to 90%.
3. The cost of the steel plate component design for the economic large-thickness pipe fitting produced by the invention is greatly reduced by replacing expensive alloy elements such as Mo, ni and the like with low-price alloy elements such as Nb and Cr.
4. The thickness of the steel plate for the economic large-thickness pipe fitting produced by the invention is 30-50mm, the thickness of the continuous casting billet/the thickness of the finished steel plate is less than or equal to 8, the implementation effect can be realized under the condition of smaller total compression, and the thickness requirement on the continuous casting billet is reduced.
5. The flaw detection result of the steel plate for the economic large-thickness pipe fitting produced by the invention meets the NB/T47013-2015 standard I-level requirement.
Drawings
FIG. 1 example 1 an economical steel sheet 1/4 typical microstructure for large thickness pipe.
FIG. 2 example 1 an economical steel sheet 1/2 typical microstructure for large thickness pipe.
Detailed Description
The present invention will be further described with reference to examples.
Example 1
The economical steel plate for the large-thickness pipe fitting has the thickness of 30mm, and comprises the following chemical components in percentage by mass: c:0.06%, si:0.25%, mn:1.65%, P:0.010%, S:0.002%, al:0.045%, nb:0.040%, ti:0.015%, cr:0.2%, N:0.0030%, O:0.0020%, H0.0001%, the balance Fe and unavoidable impurities, CEpcm=0.16%.
The production steps and the technological parameters of the steel plate are as follows:
1. smelting: LF refining white slag is kept for 17min, RH vacuum pressure maintaining time is 12min, and static argon blowing time is 18min;
2. continuous casting: the superheat degree is 12 ℃, the thickness of a casting blank is 250mm, the pulling speed is 0.7m/min, and the center segregation C is 1.0;
3. heating: the temperature of the heating soaking section is 1170 ℃, and the total heating time of the casting blank in the heating furnace is 270min;
4. rolling and cooling: the two-stage controlled rolling process of a recrystalization zone and a non-recrystalization zone is adopted, the initial rolling temperature of rough rolling is 1020 ℃, the accumulated rolling reduction is 68%, the rolling reduction of the last three passes is 16%, 18% and 19%, the initial rolling temperature of finish rolling is 890 ℃, the final rolling temperature is 820 ℃, the accumulated rolling reduction is 63%, the steel plate is rapidly thrown after the last pass is finished, the steel plate is rapidly fed into a controlled cooling zone, the growth of crystal grains is avoided, the steel plate is cooled by adopting an ACC controlled cooling mode, and the redness returning temperature of the steel plate is 600 ℃.
The mechanical properties of the steel plate obtained in the embodiment: the yield strength of the steel plate is 474MPa, the tensile strength is 639MPa, the yield ratio is 0.74, the transverse impact power at the thickness of 1/2 position is 150J at the temperature of minus 30 ℃, the longitudinal impact power at the thickness of 1/2 position is 210J at the temperature of minus 30 ℃, and the DWTT at the temperature of minus 20 ℃ is 86%; the sample is quenched at 910-930 ℃ for 60min (30 x 2) at the furnace time, at 590-610 ℃ at 90min (30 x 3) at the furnace time, and after quenching and tempering, the sample has yield strength of 547MPa, tensile strength of 635MPa, yield ratio of 0.86, transverse impact energy of 220J at the thickness of 1/2 position-30 ℃, longitudinal impact energy of 250J at the thickness of 1/2 position-30 ℃ and DWTT 93 at-20 ℃; the standard is qualified according to the inspection grade I of NB/T47013-2015 standard.
The microstructure of the steel plate produced by adopting the component design and the process parameters is observed, as shown in fig. 1 and 2, the steel plate is a typical acicular ferrite structure, the acicular ferrite structure is compact and mutually interweaved, the dislocation density is high, the 1/2 position structure of the steel plate is uniform and fine, fine carbide, precipitate, M/A islands and the like are contained in crystal grains, and the microstructure not only can ensure the strength of the steel plate, but also can ensure the 1/2 position of the steel plate to have good toughness.
Example 2
The economical steel plate for the large-thickness pipe fitting has the thickness of 30mm, and comprises the following chemical components in percentage by mass: c:0.07%, si:0.26%, mn:1.60%, P:0.012%, S:0.001%, al:0.030%, nb:0.035%, ti:0.010%, cr:0.3%, N:0.0020%, O:0.0020%, H0.0001%, the balance Fe and unavoidable impurities, CEpcm=0.17%.
The production steps and the technological parameters of the steel plate are as follows:
1. smelting: LF refining white slag is kept for 18min, RH vacuum pressure maintaining time is 13min, and static argon blowing time is 16min;
2. continuous casting: the superheat degree is 16 ℃, the thickness of a casting blank is 250mm, the pulling speed is 0.7m/min, and the center segregation is free from class C;
3. heating: the temperature of the heating soaking section is 1170 ℃, and the total heating time of the casting blank in the heating furnace is 260min;
4. rolling and cooling: the two-stage controlled rolling process of the recrystal region and the non-recrystal region is adopted, the initial rolling temperature of rough rolling is 1050 ℃, the accumulated rolling reduction is 70%, the final rolling reduction is 18%, 18% and 19%, the initial rolling temperature of finish rolling is 880 ℃, the final rolling temperature is 800 ℃, the accumulated rolling reduction is 65%, the steel plate is rapidly thrown after the final pass is finished, the steel plate is rapidly conveyed into a controlled cooling region, the growth of crystal grains is avoided, the steel plate is cooled in an ACC controlled cooling mode, and the redness returning temperature of the steel plate is 590 ℃.
The mechanical properties of the steel plate obtained in the embodiment: the yield strength of the steel plate is 495MPa, the tensile strength is 690MPa, the yield ratio is 0.72, the transverse impact energy at the thickness of 1/2 position is 160J at the temperature of minus 30 ℃, the longitudinal impact energy at the thickness of 1/2 position is 200J at the temperature of minus 30 ℃, and the DWTT at the temperature of minus 20 ℃ is 88%; the test sample is quenched at 910-930 ℃ for 60min (30 x 2) and tempered at 590-610 ℃ for 90min (30 x 3), and after quenching and tempering, the test sample has a yield strength of 565MPa, a tensile strength of 657MPa, a yield ratio of 0.86, a transverse impact energy of 240J at a thickness of 1/2 position-30 ℃, a longitudinal impact energy of 255J at a thickness of 1/2 position-30 ℃, and a DWTT of 92% at-20 ℃; the standard is qualified according to the inspection grade I of NB/T47013-2015 standard.
Example 3
The economical steel plate for the large-thickness pipe fitting has the thickness of 40mm, and comprises the following chemical components in percentage by mass: c:0.09%, si:0.15%, mn:1.55%, P:0.011%, S:0.002%, al:0.030%, nb:0.040%, ti:0.020%, cr:0.2%, N:0.0020%, O:0.0010%, H0.0001%, balance Fe and unavoidable impurities, cepcm=0.18%.
The production steps and the technological parameters of the steel plate are as follows:
1. smelting: LF refining white slag is kept for 20min, RH vacuum pressure maintaining time is 15min, and static argon blowing time is 12min;
2. continuous casting: the superheat degree is 14 ℃, the thickness of a casting blank is 250mm, the pulling speed is 0.7m/min, and the center segregation is free from class C;
3. heating: the temperature of the heating soaking section is 1200 ℃, and the total heating time of the casting blank in the heating furnace is 280min;
4. rolling and cooling: the two-stage controlled rolling process of the recrystal region and the non-recrystal region is adopted, the rough rolling start rolling temperature is 1070 ℃, the accumulated rolling reduction is 65%, the last three passes rolling reduction is 16%, 18% and 20%, the finish rolling start rolling temperature is 900 ℃, the finish rolling temperature is 810 ℃, the accumulated rolling reduction is 58%, the steel plate is rapidly thrown after the last pass is finished, the steel plate rapidly enters the controlled cooling region, the growth of crystal grains is avoided, the steel plate is cooled in an ACC controlled cooling mode, and the steel plate redness returning temperature is 570 ℃.
The mechanical properties of the steel plate obtained in the embodiment: the yield strength of the steel plate is 469MPa, the tensile strength is 613MPa, the yield ratio is 0.76, the transverse impact energy is 170J at the thickness of 1/2 position at the temperature of minus 30 ℃, the longitudinal impact energy is 240J at the thickness of 1/2 position at the temperature of minus 30 ℃, and the DWTT is 88 percent at the temperature of minus 20 ℃; the sample is quenched at 910-930 ℃ for 80min (40 x 2) and tempered at 590-610 ℃ for 120min (40 x 3), and after quenching and tempering, the sample has a yield strength of 504MPa, a tensile strength of 594MPa, a yield ratio of 0.85, a transverse impact energy of 245J at a thickness 1/2 position of-30 ℃, a longitudinal impact energy of 270J at a thickness 1/2 position of-30 ℃ and a DWTT 91 at-20 ℃; the standard is qualified according to the inspection grade I of NB/T47013-2015 standard.
Example 4
The economical steel plate for the large-thickness pipe fitting has the thickness of 40mm, and comprises the following chemical components in percentage by mass: c:0.07%, si:0.25%, mn:1.60%, P:0.011%, S:0.001%, al:0.030%, nb:0.045%, ti:0.016%, cr:0.25%, N:0.0030%, O:0.0010%, H0.0001%, balance Fe and unavoidable impurities, cepcm=0.17%.
The production steps and the technological parameters of the steel plate are as follows:
1. smelting: LF refining white slag is kept for 17min, RH vacuum pressure maintaining time is 12min, and static argon blowing time is 15min;
2. continuous casting: the superheat degree is 18 ℃, the thickness of a casting blank is 250mm, the pulling speed is 0.7m/min, and the center segregation C class is 0.5;
3. heating: the temperature of the heating soaking section is 1190 ℃, and the total heating time of the casting blank in the heating furnace is 270min;
4. rolling and cooling: the two-stage controlled rolling process of a recrystalization zone and a non-recrystalization zone is adopted, the initial rolling temperature of rough rolling is 1040 ℃, the accumulated rolling reduction is 64%, the rolling reduction of the last three passes is 18%, 18% and 20%, the initial rolling temperature of finish rolling is 860 ℃, the final rolling temperature is 790 ℃, the accumulated rolling reduction is 55%, the steel plate is rapidly thrown after the last pass is finished, the steel plate is rapidly fed into a controlled cooling zone, the growth of crystal grains is avoided, the steel plate is cooled by adopting an ACC controlled cooling mode, and the redness returning temperature of the steel plate is 580 ℃.
The mechanical properties of the steel plate obtained in the embodiment: the yield strength of the steel plate is 480MPa, the tensile strength is 630MPa, the yield ratio is 0.76, the transverse impact power is 175J at the thickness of 1/2 position at the temperature of minus 30 ℃, the longitudinal impact power is 235J at the thickness of 1/2 position at the temperature of minus 30 ℃, and the DWTT is 87 percent at the temperature of minus 20 ℃; the test sample is quenched at 910-930 ℃ for 80min (40 x 2) and tempered at 590-610 ℃ for 120min (40 x 3), and after quenching and tempering, the test sample has a yield strength of 510MPa, a tensile strength of 600MPa, a yield ratio of 0.85, a transverse impact energy of 240J at a thickness 1/2 position of-30 ℃, a longitudinal impact energy of 260J at a thickness 1/2 position of-30 ℃ and a DWTT 94% at-20 ℃; the standard is qualified according to the inspection grade I of NB/T47013-2015 standard.
Example 5
The economical steel plate for the large-thickness pipe fitting has the thickness of 50mm, and comprises the following chemical components in percentage by mass: c:0.06%, si:0.30%, mn:1.58%, P:0.009%, S:0.001%, al:0.025%, nb:0.040%, ti:0.025%, cr:0.21%, N:0.0030%, O:0.0020%, H0.0001%, the balance Fe and unavoidable impurities, CEpcm=0.16%.
The production steps and the technological parameters of the steel plate are as follows:
1. smelting: LF refining white slag retention time is 19min, RH vacuum pressure maintaining time is 13min, and static argon blowing time is 14min;
2. continuous casting: the superheat degree is 20 ℃, the thickness of a casting blank is 250mm, the pulling speed is 0.7m/min, and the center segregation C type is 0.5;
3. heating: the temperature of the heating soaking section is 1220 ℃, and the total heating time of the casting blank in the heating furnace is 300min;
4. rolling and cooling: the two-stage controlled rolling process of a recrystalization zone and a non-recrystalization zone is adopted, the initial rolling temperature of rough rolling is 1100 ℃, the accumulated rolling reduction is 60%, the rolling reduction of the last three passes is 18%, 20% and 21%, the initial rolling temperature of finish rolling is 870 ℃, the final rolling temperature is 780 ℃, the accumulated rolling reduction is 50%, the steel plate is rapidly thrown after the last pass is finished, the steel plate is rapidly fed into a controlled cooling zone, the growth of crystal grains is avoided, the steel plate is cooled by adopting an ACC controlled cooling mode, and the redness returning temperature of the steel plate is 560 ℃.
The mechanical properties of the steel plate obtained in the embodiment: the yield strength of the steel plate is 485MPa, the tensile strength is 650MPa, the yield ratio is 0.75, the transverse impact power is 165J at the thickness of 1/2 position at the temperature of minus 30 ℃, the longitudinal impact power is 215J at the thickness of 1/2 position at the temperature of minus 30 ℃, and the DWTT is 89 percent at the temperature of minus 20 ℃; the test sample is quenched at 910-930 ℃ for 100min (50 x 2) of furnace time, tempered at 590-610 ℃ for 150min (50 x 3), and after quenching and tempering, the test sample has a yield strength of 540MPa, a tensile strength of 630MPa, a yield ratio of 0.86, a transverse impact energy of 220J at a thickness 1/2 position of-30 ℃, a longitudinal impact energy of 255J at a thickness 1/2 position of-30 ℃, and a DWTT 94% at-20 ℃; the standard is qualified according to the inspection grade I of NB/T47013-2015 standard.
Example 6
The economical steel plate for the large-thickness pipe fitting has the thickness of 50mm, and comprises the following chemical components in percentage by mass: c:0.07%, si:0.26%, mn:1.59%, P:0.010%, S:0.002%, al:0.030%, nb:0.035%, ti:0.015%, cr:0.22%, N:0.0020%, O:0.0010%, H0.00015%, the balance Fe and unavoidable impurities, CEpcm=0.17%.
The production steps and the technological parameters of the steel plate are as follows:
1. smelting: LF refining white slag is kept for 18min, RH vacuum pressure maintaining time is 17min, and static argon blowing time is 13min;
2. continuous casting: the superheat degree is 10 ℃, the thickness of a casting blank is 250mm, the pulling speed is 0.7m/min, and the center segregation is free from class C;
3. heating: the temperature of the heating soaking section is 1220 ℃, and the total heating time of the casting blank in the heating furnace is 290 min;
4. rolling and cooling: the two-stage controlled rolling process of a recrystalization zone and a non-recrystalization zone is adopted, the initial rolling temperature of rough rolling is 1080 ℃, the accumulated rolling reduction is 62%, the final rolling reduction is 18%, 19% and 21% respectively, the initial rolling temperature of finish rolling is 860 ℃, the final rolling temperature is 790 ℃, the accumulated rolling reduction is 53%, the steel plate is rapidly cooled by rapid steel throwing after the final pass is finished, the growth of crystal grains is avoided, the steel plate is cooled by adopting an ACC controlled cooling mode, and the redness returning temperature of the steel plate is 550 ℃.
The mechanical properties of the steel plate obtained in the embodiment: the yield strength of the steel plate is 481MPa, the tensile strength is 625MPa, the yield ratio is 0.77, the transverse impact energy is 155J at the thickness of 1/2 position at the temperature of minus 30 ℃, the longitudinal impact energy is 220J at the thickness of 1/2 position at the temperature of minus 30 ℃, and the DWTT is 86 percent at the temperature of minus 20 ℃; the test sample is quenched at 910-930 ℃ for 100min (50 x 2) of furnace time, tempered at 590-610 ℃ for 150min (50 x 3), and after quenching and tempering, the test sample has a yield strength of 520MPa, a tensile strength of 615MPa, a yield ratio of 0.84, a transverse impact energy of 230J at a thickness 1/2 position of-30 ℃, a longitudinal impact energy of 267J at a thickness 1/2 position of-30 ℃ and a DWTT of 92% at-20 ℃; the standard is qualified according to the inspection grade I of NB/T47013-2015 standard.
Claims (9)
1. An economical steel plate for large-thickness pipe fittings is characterized in that: comprises the following components in percentage by mass: c:0.06-0.09%, si:0.15-0.30%, mn:1.55-1.65%, P is less than or equal to 0.012%, S is less than or equal to 0.002%, al:0.025-0.045%, nb:0.035-0.045%, ti:0.010-0.025%, cr:0.20-0.30%, N is less than or equal to 0.0030%, O is less than or equal to 0.0020%, H is less than or equal to 0.00015%, and the balance of Fe and unavoidable impurities, wherein CEpcm=C+Si/30+ (Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B is less than or equal to 0.18%;
the manufacturing method of the steel plate for the economic large-thickness pipe fitting comprises the following steps: the method comprises the following steps:
(1) Smelting: molten iron pretreatment, converter smelting, LF furnace treatment, RH vacuum treatment and continuous casting;
in the converter smelting, tapping P is less than or equal to 0.010%, S is less than or equal to 0.003%, and an argon station is deoxidized by adding an aluminum wire; in LF refining, the white slag holding time is more than or equal to 17min; RH vacuum pressure maintaining, pressure less than or equal to 100Pa, time more than or equal to 12min, calcium treatment before tapping, static argon blowing time more than or equal to 12min after wire feeding, and gas content control, wherein the mass percentage content is as follows: n is less than or equal to 0.0030 percent, O is less than or equal to 0.0020 percent, and H is less than or equal to 0.00015 percent; the superheat degree in the continuous casting process is controlled to be less than or equal to 20 ℃, a two-cold electromagnetic stirring and solidification end light pressing mode is adopted, the constant pulling speed is kept in the casting process, the pulling speed range is 0.6m/min-0.8m/min, and the center segregation C class is less than or equal to 1.0;
(2) And a heating step: adopting a walking beam type heating furnace, controlling the temperature of a soaking section at 1170-1230 ℃ and the total heating time of casting blanks in the heating furnace at 260-300min;
(3) Rolling and cooling: adopting a two-stage controlled rolling process of a recrystalization zone and a non-recrystalization zone, wherein the initial rolling temperature of rough rolling is 1020-1100 ℃, the accumulated rolling reduction is 60-70%, the single rolling reduction of the last three passes is more than or equal to 16%, the initial rolling temperature of finish rolling is 860-900 ℃, the finishing rolling temperature is 780-820 ℃, the accumulated rolling reduction is 50-65%, the steel plate is rapidly thrown after the last passes are finished, the steel plate is rapidly fed into a controlled cooling zone, the growth of crystal grains is avoided, the steel plate is cooled by adopting an ACC (alternating current) controlled cooling mode, and the redness temperature of the steel plate is 550-600 ℃.
2. An economical steel sheet for large-thickness pipe fittings as claimed in claim 1, wherein: comprises the following components in percentage by mass: c:0.07-0.09%, si:0.15-0.25%, mn:1.55-1.60%, P is less than or equal to 0.012%, S is less than or equal to 0.002%, al:0.025-0.030%, nb:0.040-0.045%, ti:0.016-0.025%, cr:0.25-0.30%, N is less than or equal to 0.0030%, O is less than or equal to 0.0020%, H is less than or equal to 0.00015%, and the balance of Fe and unavoidable impurities, wherein CEpcm=C+Si/30+ (Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B is less than or equal to 0.18%.
3. An economical steel sheet for large-thickness pipe fittings as claimed in claim 1, wherein: comprises the following components in percentage by mass: c:0.07%, si:0.25%, mn:1.60%, P:0.011%, S:0.001%, al:0.030%, nb:0.045%, ti:0.016%, cr:0.25%, N:0.0030%, O:0.0010%, H0.0001%, balance Fe and unavoidable impurities, cepcm=0.17%.
4. The method for manufacturing an economical steel sheet for large-thickness pipe fittings as claimed in claim 1, wherein: the method comprises the following steps:
(1) Smelting: molten iron pretreatment, converter smelting, LF furnace treatment, RH vacuum treatment and continuous casting;
in the converter smelting, tapping P is less than or equal to 0.010%, S is less than or equal to 0.003%, and an argon station is deoxidized by adding an aluminum wire; in LF refining, the white slag holding time is more than or equal to 17min; RH vacuum pressure maintaining, pressure less than or equal to 100Pa, time more than or equal to 12min, calcium treatment before tapping, static argon blowing time more than or equal to 12min after wire feeding, and gas content control, wherein the mass percentage content is as follows: n is less than or equal to 0.0030 percent, O is less than or equal to 0.0020 percent, and H is less than or equal to 0.00015 percent; the superheat degree in the continuous casting process is controlled to be less than or equal to 20 ℃, a two-cold electromagnetic stirring and solidification end light pressing mode is adopted, the constant pulling speed is kept in the casting process, the pulling speed range is 0.6m/min-0.8m/min, and the center segregation C class is less than or equal to 1.0;
(2) And a heating step: adopting a walking beam type heating furnace, controlling the temperature of a soaking section at 1170-1230 ℃ and the total heating time of casting blanks in the heating furnace at 260-300min;
(3) Rolling and cooling: adopting a two-stage controlled rolling process of a recrystalization zone and a non-recrystalization zone, wherein the initial rolling temperature of rough rolling is 1020-1100 ℃, the accumulated rolling reduction is 60-70%, the single rolling reduction of the last three passes is more than or equal to 16%, the initial rolling temperature of finish rolling is 860-900 ℃, the finishing rolling temperature is 780-820 ℃, the accumulated rolling reduction is 50-65%, the steel plate is rapidly thrown after the last passes are finished, the steel plate is rapidly fed into a controlled cooling zone, the growth of crystal grains is avoided, the steel plate is cooled by adopting an ACC (alternating current) controlled cooling mode, and the redness temperature of the steel plate is 550-600 ℃.
5. The method for manufacturing an economical steel sheet for large-thickness pipe fittings as recited in claim 4, wherein: the yield strength of the steel plate is more than or equal to 469MPa, the tensile strength is more than or equal to 613MPa, the yield ratio is less than or equal to 0.77, the transverse impact energy at the thickness of 1/2 position at-30 ℃ is more than or equal to 150J, the longitudinal impact energy at the thickness of 1/2 position at-30 ℃ is more than or equal to 200J, and the DWTT at the temperature of minus 20 ℃ is more than or equal to 85%.
6. The method for manufacturing an economical steel sheet for large-thickness pipe fittings as recited in claim 4, wherein: the yield strength of the sample after quenching is more than or equal to 504MPa, the tensile strength is more than or equal to 594MPa, the yield ratio is less than or equal to 0.86, the transverse impact power at the thickness of 1/2 position-30 ℃ is more than or equal to 220J, the longitudinal impact power at the thickness of 1/2 position-30 ℃ is more than or equal to 250J, and the DWTT at the temperature of-20 ℃ is more than or equal to 90% after the sample is quenched at the temperature of 910-930 ℃ at the furnace time of 2.0t (t is the thickness of the steel plate), and the tempering temperature of 590-610 ℃ at the furnace time of 3.0t (t is the thickness of the steel plate).
7. The method for manufacturing an economical steel sheet for large-thickness pipe fittings as recited in claim 6, wherein: quenching the sample to water quenching.
8. The method for manufacturing an economical steel sheet for large-thickness pipe fittings as recited in claim 4, wherein: the flaw detection result of the steel plate meets the NB/T47013-2015 standard I-level requirement.
9. The method for manufacturing an economical steel sheet for large-thickness pipe fittings as recited in claim 4, wherein: the thickness of the steel plate is 30-50mm, and the thickness of the continuous casting billet/the thickness of the finished steel plate is less than or equal to 8.
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