CN114457282A - Hot-rolled steel plate for 415 MPa-grade yield strength longitudinal welded pipe - Google Patents
Hot-rolled steel plate for 415 MPa-grade yield strength longitudinal welded pipe 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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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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
- 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
- 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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- 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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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Abstract
The invention discloses a hot rolled steel plate for longitudinal welded pipes with 415 MPa-level yield strength, which mainly solves the technical problems that the existing hot rolled steel plate for 415 MPa-level pipeline with yield strength has serious center segregation, poor impact toughness and high inclusion content and cannot meet the requirements of manufacturing petroleum and natural gas longitudinal welded pipes. The technical scheme is that the hot rolled steel plate for the longitudinal welded pipe with the yield strength of 415MPa comprises the following chemical components in percentage by weight: c: 0.04-0.06%, Si: 0.09-0.16%, Mn: 0.90-1.00 percent, P is less than or equal to 0.015%, S is less than or equal to 0.004%, N is less than or equal to 0.0060%, Al: 0.010-0.045%, Ti: 0.01 to 0.02%, Nb: 0.045-0.055%, 5-10% of Mn/Si, and the balance of iron and inevitable impurities. Elongation after fracture of hot rolled steel plate A50mm35 to 55 percent.
Description
Technical Field
The invention relates to steel for oil and gas pipelines, in particular to a hot-rolled steel plate for 415 MPa-grade yield strength longitudinal welded pipes, and particularly relates to a hot-rolled steel plate for 415 MPa-grade yield strength longitudinal welded pipes and a manufacturing method thereof, which are used for manufacturing pipelines for conveying oil and gas and belong to the technical field of steel for oil and gas pipelines.
Background
The pipeline transportation is the most economical and safe transportation mode for long-distance petroleum and natural gas transportation, and has the characteristics of high efficiency, economy, safety, no pollution and the like. In order to improve the conveying efficiency, reduce the energy consumption and reduce the investment, the development of long-distance pipelines towards high-pressure and large-caliber conveying is a trend. The development of a newly-built hot continuous rolling unit to a wider specification and higher strength direction is promoted, so that the long-distance and high-pressure requirements of a conveying main line are met. On the other hand, the steel quantity for the small-diameter welding pipe required by pipeline branch engineering and urban pipe networks is also greatly and synchronously improved. In order to produce steel for small-diameter welded pipes required for pipeline branch works and urban pipe networks in wide hot continuous rolling mills, it is necessary to longitudinally cut a wide hot rolled steel strip.
Longitudinal welded pipes are a delicate product among welded pipe products. In contrast to conventional welded pipes which are not cut in the longitudinal direction, longitudinally-cut welded steel is manufactured by High Frequency Welding (HFW) after longitudinally cutting a hot-rolled coil in the longitudinal direction when used by a user. When the slab is solidified, the slab width 1/2 is most likely to generate the defects of component segregation, looseness, cracks, overproof inclusions and the like, in the high-frequency welding process, the defect part is extruded and is easily expanded into the base metal defect of the welding part, the defect is represented as improper flaw detection caused by the cracks or the inclusions, the defects can be discovered only after the flaw detection, and the economic loss caused by the defects is often larger. The advantages are wide steel coil, low production cost of hot coil in steel mill, stable performance control, and large coil delivery.
The existing product has relatively high inclusion content due to reasons of unclear component design and continuous casting slab control specification and the like, the center segregation grade can not meet the requirements of longitudinal welded pipes, and flaw detection failure caused by cracks or inclusions after welding can be easily caused.
Chinese patent application publication No. CN101928877A discloses a steel for oil casing pipes, which can be used for manufacturing J55-grade high-frequency oil casing pipes, and a high-frequency welded oil casing pipe, and a manufacturing method thereof, and a longitudinal section thereof is suitable for manufacturing J55-grade high-frequency welded oil casing pipes having an outer diameter of 244.48mm or less. The chemical components are as follows: 0.13 to 0.18%, Si: 0.15 to 0.25%, Mn: 0.60-1.00%, S is less than or equal to 0.005%, P is less than or equal to 0.015%, Nb: 0.008-0.020%, Ca: 0.0010-0.0045%, Al: 0.010-0.040%, the rest is iron and inevitable impurities. The material can meet the requirements of longitudinal section, but has higher carbon content and low impact toughness, and cannot meet the requirements of manufacturing welded pipes for conveying petroleum and natural gas.
The Chinese patent application with application publication number CN107587072A discloses X60 pipeline steel and a preparation method thereof, which comprises the following steps: smelting and continuously casting to obtain a casting blank; and heating and rolling the casting blank. The weight percentage of the chemical components is as follows: c: 0.05 to 0.07%, Si: 0.15-0.25%, Mn: 1.30-1.50%, P: less than or equal to 0.012%, S: less than or equal to 0.005 percent, Nb: 0.060 to 0.070%, Ti: 0.008-0.018%, Al: 0.020-0.040%, Cr: 0.15-0.25%, N: less than or equal to 50ppm, Pcm: 0.12-0.18%, and the balance of Fe and inevitable impurities. The material is 415MPa grade of yield strength, and 0.060-0.070% of Nb element, 1.30-1.50% of Mn element and 0.15-0.25% of Cr element are required to be added to improve the strength of steel and increase the hardenability. However, the manganese element is too high, which is unfavorable for controlling slab segregation. Meanwhile, if chromium and manganese which are too high are added into steel at the same time, Cr-Mn composite oxides with low melting points are formed, surface cracks are formed in the hot working process, the welding performance is seriously deteriorated, and flaw detection failure of the steel pipe is easily caused. The design does not meet the requirements specific to a longitudinal section line.
Chinese patent application publication No. CN101928882A discloses an X60 pipeline steel and a preparation method thereof, wherein the X60 pipeline steel has the following chemical components: 0.060-0.080% of C, 0.15-0.30% of Si, 1.35-1.55% of Mn, less than or equal to 0.006% of S, less than or equal to 0.020% of P, 0.035-0.055% of Nb, 0.035-0.055% of V, 0.010-0.025% of Ti, less than or equal to 0.008% of N, 0.010-0.040% of Als, and the balance of Fe and inevitable impurities. After heating and descaling, rough rolling and finish rolling are continuously completed on the same double-stand compact steckel mill, and the strengthening effect of microalloying elements such as Nb and V added into steel is fully exerted through delayed rolling control in the rolling process, so that a fine and uniform structure is obtained, mixed crystals are effectively prevented, and the strength and toughness of the X60 pipeline steel are greatly improved. However, the invention adopts the steckel mill to produce the pipeline steel, and simultaneously 0.035-0.055 percent of the V element and 1.35-1.55 percent of the Mn element are added. The manganese element is too high, which is unfavorable for controlling slab segregation. The addition of the noble alloy V element is disadvantageous to control cost. The design does not meet the requirements specific to a longitudinal section line.
Therefore, the chemical components and the product performance of the existing hot rolled steel plate for the pipeline with the yield strength of 415MPa cannot meet the requirements of oil and gas welded pipe manufacturing enterprises on longitudinal cutting and processing of the steel plate.
Disclosure of Invention
The invention aims to provide a hot rolled steel plate for longitudinal welded pipes with 415 MPa-level yield strength and a manufacturing method thereof, and mainly solves the technical problems that the existing hot rolled steel plate for 415 MPa-level pipeline with yield strength has serious center segregation, poor impact toughness and high inclusion content and cannot meet the requirements of manufacturing petroleum and natural gas longitudinal welded pipes.
According to the invention, the Nb and Ti are adopted for alloying, key solid solution strengthening elements such as carbon and manganese which guarantee the final performance of the longitudinal-cutting product are strictly controlled, the Mn/Si ratio is strictly controlled to be 5-10, and the proper steel-making, continuous casting and hot rolling process design is combined, so that the product is guaranteed to have good mechanical properties and process properties such as cold bending and welding, and the processing requirements such as longitudinal-cutting, welding and forming are met.
The invention adopts the technical scheme that a hot rolled steel plate for longitudinal welded pipes with 415 MPa-grade yield strength comprises the following chemical components in percentage by weight: c: 0.04-0.06%, Si: 0.09-0.16%, Mn: 0.90-1.00%, P is less than or equal to 0.015%, S is less than or equal to 0.004%, N is less than or equal to 0.0060%, Al: 0.010-0.045%, Ti: 0.01 to 0.02%, Nb: 0.045-0.055%, 5-10% of Mn/Si, and the balance of iron and inevitable impurities.
The metallographic structure of the hot-rolled steel plate is ferrite and pearlite, the grain size of the ferrite in the metallographic structure is 9-13 grades, and the yield strength R of the hot-rolled steel plate with the thickness of 6.0-12.0 mmt0.5415 to 565MPa, tensile strength Rm520 to 660MPa, elongation after break A50mm35-55%, the-15 ℃ full-size Charpy impact power Akv is 200-450J, and d is qualified as 2a in a 180-degree bending test; detecting according to the mannesmann standard of the plate blank, and the hot rolled steel plate has eccentric centerThe analysis grade is below grade 2.
The hot rolled steel plate is suitable for manufacturing longitudinal welded pipes for petroleum and natural gas transportation.
The reason why the chemical composition of the 415MPa grade hot rolled steel sheet according to the present invention is limited to the above range is as follows:
carbon: carbon is the most basic strengthening element, carbon is dissolved in steel to form an interstitial solid solution and plays a role in solid solution strengthening, and carbon forms carbide precipitation with strong carbide elements and plays a role in precipitation strengthening. The component system makes full use of the strengthening effect of C. However, it is an easily segregating element, and the high content of the easily segregating element increases the center segregation of the continuous casting slab, is not beneficial to the welding of longitudinal steel, and simultaneously reduces the toughness and deteriorates the performance of the material. Meanwhile, carbon is too high to enter the peritectic region of the low-carbon steel. Too low carbon reduces the strength of the steel grade. Therefore, the strengthening effect of C and Mn is comprehensively considered, and the set C content is 0.04-0.06%.
Manganese: manganese is also the main element of the composition system, can play a role in solid solution strengthening, and is the most main and economic strengthening element for compensating strength loss caused by carbon reduction in steel. However, Mn is an easily segregated element, and the high content of Mn increases the center segregation of the continuous casting slab, which is not favorable for welding longitudinal steel. Mn is a strictly controlled element in the component system, and the content of Mn is further limited to be 0.90-1.00%.
Carbon and manganese are key elements for ensuring the final performance of longitudinal-section products, and the range is strictly controlled in order to ensure the stable performance of the hot-rolled steel plates.
Silicon: silicon suitably increases the strength of steel by solid solution strengthening in steel, too high a content of Si lowers the Mn/Si ratio, adversely affects the surface quality of a slab and the weldability of a welded pipe, and the impact toughness after welding increases with the increase in the Mn/Si ratio. However, too low Si will affect the casting quality of Ca-treated steel. The invention limits the Si content to 0.09-0.16%. According to the test and comprehensive consideration, the Mn/Si is in an optimal value of 5-10.
Sulfur and phosphorus: too high sulfur and phosphorus adversely affect the toughness and plasticity of the material, while too low sulfur and Lin increase the cost of desulfurization and dephosphorization in steel making. The invention limits S to be less than or equal to 0.004 percent and P to be less than or equal to 0.015 percent.
Nitrogen: the plasticity and toughness of the material are seriously deteriorated if the nitrogen content is too high, and N is limited to be less than or equal to 0.0060 percent.
Aluminum: the aluminum plays a role in deoxidation in the present invention, and is a strong oxidizing forming element, and forms Al with oxygen in steel2O3Is removed during steel making. Too high an aluminum content can lead to excessive Al formation2O3And the pouring nozzle is easy to block during continuous casting. The invention limits the Al content to be 0.010-0.045%.
Titanium: is a strong solid N element, the stoichiometric ratio of Ti/N is about 3.42, about 0.02 percent of Ti can be used for fixing N in steel, the N content is less than 0.0060 percent, and a fine TiN precipitated phase which is stable at high temperature can be formed when a plate blank is continuously cast. The trace amount of titanium plays a strengthening role, and the influence of the trace amount of titanium is that fine TiN particles can effectively prevent austenite grains from growing when the plate blank is reheated, so that the fine TiN particles have a positive effect on improving the toughness of a final product. A very small amount of Ti gives a remarkable strengthening effect. In addition, the TiN particles can also avoid the growth of crystal grains in a welding heat affected zone during welding, and improve the impact toughness of the welding heat affected zone. The invention limits the content of Ti to 0.010-0.020%.
Niobium: is the main microalloying element of the low-alloy high-strength steel and mainly plays a role in fine grain strengthening. NbC strain is induced and precipitated in the hot rolling process to hinder recovery and recrystallization of the deformed austenite, and the deformed austenite structure rolled in a non-recrystallization region is converted into a fine phase change product during phase change through controlled rolling and controlled cooling, so that the steel has high strength and high toughness. In order to achieve the strength required by the steel grade, the strength is improved by increasing the niobium content to compensate for the strength loss caused by reducing the manganese and silicon contents. According to the test result, the Nb content is limited to be 0.045-0.055%.
The method for manufacturing the hot-rolled steel plate for the longitudinal welded pipe with the yield strength of 415MPa comprises the following steps:
continuously casting molten steel to obtain a continuous casting slab, wherein the molten steel comprises the following chemical components in percentage by weight: c: 0.04-0.06%, Si: 0.09-0.16%, Mn: 0.90-1.00%, P is less than or equal to 0.015%, S is less than or equal to 0.004%, N is less than or equal to 0.0060%, Al: 0.010-0.045%, Ti: 0.01 to 0.02%, Nb: 0.045-0.055%, 5-10% of Mn/Si, and the balance of iron and inevitable impurities; controlling the grade of inclusions in the continuous casting slab, and testing according to the Standard test method for determining the content of inclusions in steel by ASTM E45-13 of American society for testing and materials, by adopting a method A, wherein the A is below 0.5 grade, the C is 0, and the B and D are below 1.5 grade; detecting according to a mannesmann standard of the plate blank, and controlling the central segregation grade of the continuous casting plate blank to be below grade 2;
heating the continuously cast plate blank at 1160-1200 ℃ for 150-240 min, and then carrying out hot rolling, wherein the hot rolling is a two-stage rolling process, the rough rolling is 6-pass continuous rolling, the rolling is carried out at the temperature above the austenite recrystallization temperature, and the finish temperature of the rough rolling is 940-1000 ℃; the thickness of the intermediate blank is 38-49 mm, the finish rolling is 7-pass continuous rolling, the inlet temperature of the finish rolling is 920-980 ℃, and the finish rolling finishing temperature is 800-840 ℃; after finish rolling, the thickness of the steel plate is controlled to be 6.0-12.0 mm, front-end cooling is adopted for laminar cooling, the laminar cooling speed is 15-35 ℃/s, and when the coiling temperature is 500-580 ℃, the hot rolled steel coil is coiled.
According to the detection of the mannesmann standard of the slab, the center segregation grade of the hot-rolled steel plate is below 2 grades.
The hot rolling process and the control of the surface scale of the hot rolled steel plate are the technical key for realizing the invention. By calculation, the component system A of the invention3At 821 ℃ A1Was 702 ℃. The hot rolling process adopted by the invention is based on the composition system and the calculated phase change point.
The reason of the production process system adopted by the invention is as follows:
1. setting of center segregation of continuous casting slab and setting of level of inclusions in continuous casting slab
The control of the center segregation of the continuous casting slab and the control of molten steel inclusions are the technical key for realizing the method, and in order to ensure that when a longitudinal welded pipe is produced, a user longitudinally cuts a hot-rolled coil along the longitudinal direction and then manufactures the pipe; the method is characterized in that the method sets and controls the grade of inclusions in the continuous casting slab, and the grade of the inclusions in the continuous casting slab is tested by adopting a method A according to the standard test method for measuring the content of the inclusions in steel by American society for testing and materials (ASTM E45-13), wherein the A is below 0.5 grade, the C is below 0 grade, and the B and D are below 1.5 grades; and controlling the center segregation grade of the continuous casting slab to be below the Mannesmann standard grade 2.
2. Setting of heating temperature and heating time of continuous casting slab
The heating temperature and time of the continuous casting slab are set to ensure that niobium carbide and niobium carbonitride in the continuous casting slab are fully dissolved and the original crystal grains are not grown too large. Therefore, the heating temperature is very important for the technical scheme of the invention, the temperature is too low or the heating time is too short, and niobium carbide and niobium carbonitride in the continuous casting plate blank can not be fully dissolved; and the temperature is too high, the heating time is too long, the original structure of the plate blank is thick, and the final performance and the surface quality of the steel plate are not facilitated. The heating temperature of the continuous casting plate blank is set to be 1160-1200 ℃, and the heating time is set to be 150-240 min.
3. Setting of roughing finishing temperature
The rough rolling process is controlled to be rolled above the austenite recrystallization temperature, so that uniform and fine austenite grains are ensured to be obtained. Therefore, the rough rolling finishing temperature is set to be 940-1000 ℃.
4. Setting of intermediate billet thickness and finish rolling inlet temperature
In order to obtain good impact toughness, particularly for hot continuous rolled steel sheets with a thickness of 8mm or more, it is necessary to control the effective reduction ratio at the finish rolling stage. The effective reduction rate is the reduction rate of deformation occurring in the temperature range of the austenite non-recrystallization region in the finish rolling stage, and is related to the thickness and temperature of the intermediate billet at the finish rolling inlet. The improvement of the finish rolling compression ratio is beneficial to improving the impact toughness of the steel plate, and the finish rolling compression ratio is controlled to be more than 4, so that the thickness of the intermediate blank is set to be 38-49 mm according to the thickness of the finished product, and the finish rolling inlet temperature is 920-980 ℃.
5. Setting of finish Rolling finishing temperature
The setting of the finishing rolling temperature is to obtain flat austenite grains with deformation zones inside through rolling in an austenite non-recrystallization region, and the flat austenite grains are converted into fine ferrite grains in the subsequent laminar cooling process to play a role of fine grain strengthening. Therefore, the finish rolling finishing temperature is set to be 800-840 ℃.
6. Setting of laminar cooling rate
The set laminar cooling speed after finish rolling is very critical, and the rapid cooling speed is adopted to inhibit the growth of ferrite grains and the precipitation of TiC at a high-temperature stage. The rapid cooling makes it possible to precipitate fine and dispersed particles of TiC and the like in the ferrite at a lower temperature. The cooling speed is too slow, and the advance precipitation of TiC in high-temperature deformation austenite cannot be inhibited; the steel plate is cooled too fast, the toughness of the steel plate is unfavorable, and the plate shape is greatly influenced. The laminar cooling adopts front-section cooling, and the cooling speed is 15-35 ℃/s.
7. Setting of coiling temperature
The coiling temperature mainly affects the structure and performance of the strip steel. The high coiling temperature is beneficial to the precipitation of secondary phases of particles of Ti, Nb alloy carbon and nitrogen, but a banded structure is easily formed, the growth of a matrix ferrite structure is caused, and precipitates of Nb and Ti microalloy carbon and nitride are coarsened, so that the toughness of the steel plate is reduced; if the coiling temperature is too low, secondary phase precipitation of particles of Ti, Nb alloy carbon and nitrogen is suppressed, and the precipitation strengthening effect of improving the strength of the steel sheet is not good. Comprehensively considering, the hot rolling coiling temperature is set to be 500-580 ℃.
The metallographic structure of the hot-rolled steel plate produced by the method is ferrite and pearlite, the grain size of the ferrite in the metallographic structure is 9-13 grades, and the yield strength R of the hot-rolled steel platet0.5415 to 565MPa, tensile strength Rm520 to 660MPa, elongation after break A50mm35-55%, the-15 ℃ full-size Charpy impact power Akv is 200-450J, and d is qualified as 2a in a 180-degree bending test; according to the detection of the mannesmann standard of the slab, the center segregation grade of the hot-rolled steel plate is below 2 grades.
The hot rolled steel plate is suitable for manufacturing longitudinal welded pipes for petroleum and natural gas transportation.
Compared with the prior art, the invention has the following positive effects: 1. according to the invention, Nb and Ti are alloyed, key solid solution strengthening elements of carbon and manganese are strictly controlled to ensure the final performance of a longitudinal-section product, Mn/Si is controlled to be 5-10, and the composition design is ensured to meet the requirement of stable performance of a longitudinal-section hot-rolled steel plate. 2. The invention requires that the center segregation of the continuous casting slab is controlled to be below the Mannesian standard 2 grade, and the inclusion control is performed according to the Standard test method for measuring the content of the inclusions in steel of ASTM E45-13 of the American society for testing materials, wherein the A class is below 0.5 grade, the C class is 0, and the B class and the D class are below 1.5 grade, so that the method can meet the requirement of producing the longitudinal welded pipe after longitudinally cutting the hot rolled coil by a user along the longitudinal direction. 3. Through the design of longitudinal section material components and the design of a manufacturing process, the wide hot continuous rolling unit can be satisfied to produce a wide-specification hot rolled steel strip, and the steel strip is longitudinally cut, so that the steel requirements for small-pipe-diameter welded pipes required by production pipeline branch line engineering and urban pipe networks are satisfied. The wide hot continuous rolling unit can improve the productivity and fully exert the capacity of the wide hot continuous rolling unit on the premise of ensuring the quality of finished products. 4. The component system of the invention combines with proper steelmaking, continuous casting and hot rolling process design to obtain the hot rolled steel plate for the longitudinal welded pipe with the yield strength of 415MPa, compared with other steel plates with the same strength grade, the hot rolled steel plate has stable structure and performance, can better meet the process requirements of longitudinal welding, forming and the like, and reduces the manufacturing cost of small-caliber welded pipes required by pipeline branch line engineering and urban pipe networks. 5. The hot rolled steel plate meets the requirements of welded pipe manufacturing enterprises on mechanical property and technological property of the longitudinal steel plate, and fills the industrial blank.
Drawings
FIG. 1 is a metallographic structure photograph of a hot-rolled steel sheet according to example 1 of the invention.
Detailed Description
The present invention will be further described with reference to examples 1 to 5, which are shown in tables 1 to 3.
Table 1 shows the chemical composition (in weight percent) of the steels of the examples of the invention, with the balance being iron and unavoidable impurities.
Table 1 chemical composition of the steels of the examples of the invention, in units: and (4) weight percentage.
The continuous casting method comprises the steps of smelting in a converter, carrying out desulfurization treatment in an LF ladle refining furnace refining procedure, carrying out vacuum circulating degassing treatment in an RH furnace, finely adjusting components to obtain molten steel meeting the component requirements, and continuously casting to obtain a continuous casting slab. The thickness of the continuous casting plate blank is 210-230 mm, the width is 900-1600 mm, and the length is 8000-11700 mm. The center segregation grades of the continuous casting slabs are all the Mannesmann standard 2 grades.
And (3) conveying the fixed-length plate blanks produced in the steelmaking process to a heating furnace for heating, discharging and descaling, and conveying to a hot continuous rolling unit for rolling. And controlling rolling by a rough rolling and finish rolling continuous rolling unit, coiling after laminar cooling, and carrying out front-section cooling on the laminar cooling to produce a qualified hot-rolled steel coil. The thickness of the hot rolled steel plate is 6.0-12.0 mm. The hot rolling process control parameters are shown in Table 2.
TABLE 2 Hot Rolling Process control parameters of the inventive examples
Referring to fig. 1, the hot-rolled steel plate obtained by the method has a metallographic structure of ferrite and pearlite, the grain size of the ferrite in the metallographic structure is 9-13 grades, and the yield strength R of the hot-rolled steel platet0.5415 to 565MPa, tensile strength Rm520 to 660MPa, elongation after break A50mm35-55%, the-15 ℃ full-size Charpy impact power Akv is 200-450J, and d is qualified as 2a in a 180-degree bending test.
The hot rolled steel plate obtained by the invention is sampled, a transverse sample is obtained by tensile and bending tests, a longitudinal sample is obtained by impact tests, and the tensile test is carried out according to the part 1 of the GB/T228.1-2010 metal material tensile test: room temperature test method ″, tensile test was conducted; performing a bending test according to GB/T232-2010 metal material bending test method; the impact test is carried out according to GB/T229-2007 method for testing charpy pendulum impact of metal materials, and the mechanical properties are shown in Table 3. And according to the Mannesmann standard detection of the slab, the center segregation grade of the hot-rolled steel plate is below grade 2.
The hot rolled steel plate obtained by the invention has good strength and toughness, weldability and bending formability.
TABLE 3 mechanical Properties of Hot rolled Steel sheets according to examples of the present invention
As seen from Table 3, the hot rolled steel sheet obtained by the present invention has good toughness, weldability and bending formability.
In addition to the above embodiments, the present invention may have other embodiments. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.
Claims (5)
1. A hot rolled steel plate for longitudinal welded pipes with 415 MPa-grade yield strength comprises the following chemical components in percentage by weight: c: 0.04-0.06%, Si: 0.09-0.16%, Mn: 0.90-1.00%, P is less than or equal to 0.015%, S is less than or equal to 0.004%, N is less than or equal to 0.0060%, Al: 0.010-0.045%, Ti: 0.01 to 0.02%, Nb: 0.045-0.055%, 5-10% of Mn/Si, and the balance of iron and inevitable impurities; the metallographic structure of the hot-rolled steel plate is ferrite and pearlite, and the grain size of the ferrite in the metallographic structure is 9-13 grades.
2. A hot-rolled steel sheet for a longitudinal welded pipe having a yield strength of 415MPa according to claim 1, wherein the hot-rolled steel sheet has a yield strength R of 6.0 to 12.0mmt0.5415 to 565MPa, tensile strength Rm520 to 660MPa, elongation after break A50mm35-55%, the-15 ℃ full-size Charpy impact power Akv is 200-450J, and d is qualified as 2a in a 180-degree bending test; according to the detection of the mannesmann standard of the slab, the center segregation grade of the hot-rolled steel plate is below 2 grades.
3. A manufacturing method of a hot rolled steel plate for longitudinal welded pipes with 415 MPa-grade yield strength is characterized by comprising the following steps of:
continuously casting molten steel to obtain a continuous casting slab, wherein the molten steel comprises the following chemical components in percentage by weight: c: 0.04-0.06%, Si: 0.09-0.16%, Mn: 0.90-1.00%, P is less than or equal to 0.015%, S is less than or equal to 0.004%, N is less than or equal to 0.0060%, Al: 0.010-0.045%, Ti: 0.01 to 0.02%, Nb: 0.045-0.055%, 5-10% of Mn/Si, and the balance of iron and inevitable impurities; controlling the grade of inclusions in the continuous casting slab, and testing according to the Standard test method for determining the content of inclusions in steel by ASTM E45-13 of American society for testing and materials, by adopting a method A, wherein the A is below 0.5 grade, the C is 0, and the B and D are below 1.5 grade; detecting according to a mannesmann standard of the plate blank, and controlling the central segregation grade of the continuous casting plate blank to be below grade 2;
heating the continuously cast plate blank at 1160-1200 ℃ for 150-240 min, and then carrying out hot rolling, wherein the hot rolling is a two-stage rolling process, the rough rolling is 6-pass continuous rolling, the rolling is carried out at the temperature above the austenite recrystallization temperature, and the finish temperature of the rough rolling is 940-1000 ℃; the thickness of the intermediate blank is 38-49 mm, the finish rolling is 7-pass continuous rolling, the inlet temperature of the finish rolling is 920-980 ℃, and the finish rolling finishing temperature is 800-840 ℃; and after finish rolling, performing front-stage cooling by adopting laminar cooling, wherein the laminar cooling speed is 15-35 ℃/s, and the hot-rolled steel coil is obtained by coiling when the coiling temperature is 500-580 ℃.
4. A method for producing a hot-rolled steel sheet for a longitudinal welded pipe having a yield strength of 415MPa according to claim 3, wherein the thickness of the steel sheet after the hot rolling and the finish rolling is controlled to be 6.0 to 12.0 mm.
5. A method for producing a hot-rolled steel sheet for a longitudinal welded pipe having a yield strength of 415MPa level according to claim 3, wherein the hot-rolled steel sheet has a metallographic structure of ferrite + pearlite, the ferrite has a grain size of 9 to 13 levels in the metallographic structure, and the yield strength R of the hot-rolled steel sheet ist0.5415 to 565MPa, tensile strength Rm520 to 660MPa, elongation after break A50mm35-55%, the-15 ℃ full-size Charpy impact power Akv is 200-450J, and d is qualified as 2a in a 180-degree bending test; according to the slab manAnd the center segregation grade of the hot rolled steel plate is below grade 2 by the Neissmann standard detection.
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| CN117187686A (en) * | 2023-08-01 | 2023-12-08 | 包头钢铁（集团）有限责任公司 | Spiral submerged arc welded pipe hot rolled steel strip for hydrogen-doped conveying pipeline and production method thereof |
| WO2024041820A1 (en) | 2022-08-25 | 2024-02-29 | Tata Steel Ijmuiden B.V. | Hot-rolled high-strength steel sheet with excellent low-temperature impact toughness and method for manufacture the same |
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