WO2021052431A1 - Acier à forte expansion de trou obtenu par coulée continue en bandes minces et procédé pour le fabriquer - Google Patents

Acier à forte expansion de trou obtenu par coulée continue en bandes minces et procédé pour le fabriquer Download PDF

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WO2021052431A1
WO2021052431A1 PCT/CN2020/115960 CN2020115960W WO2021052431A1 WO 2021052431 A1 WO2021052431 A1 WO 2021052431A1 CN 2020115960 W CN2020115960 W CN 2020115960W WO 2021052431 A1 WO2021052431 A1 WO 2021052431A1
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steel
continuous casting
thin strip
strip
expansion
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PCT/CN2020/115960
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English (en)
Chinese (zh)
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吴建春
周坚刚
方园
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宝山钢铁股份有限公司
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Priority to JP2022517914A priority Critical patent/JP2022549235A/ja
Publication of WO2021052431A1 publication Critical patent/WO2021052431A1/fr

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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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
    • B22D11/0622—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by two casting wheels
    • 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
    • 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
    • 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
    • C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
    • 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
    • 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
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
    • 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
    • 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
    • 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
    • C21D2211/002—Bainite
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the invention relates to a high-reamed steel manufacturing technology, in particular to a thin strip continuous casting high-reamed steel and a manufacturing method thereof.
  • tin (Sn) and copper (Cu) are typical residual elements or harmful elements in steel. It is very difficult and very expensive to fully remove Sn and Cu during the steelmaking process. Once the steel contains Sn , Cu, basically can not be completely eliminated, only by diluting molten steel to reduce the content of Sn, Cu, these all cause the increase in the smelting cost of steel products.
  • Traditional thin strip steel is mostly produced by continuous rolling of cast billets with a thickness of 70-200mm through multiple passes.
  • the traditional hot rolling process is: continuous casting + billet reheating and heat preservation + rough rolling + finishing rolling + cooling + Coiling, that is, firstly obtain a cast slab with a thickness of about 200mm through continuous casting. After reheating and holding the cast slab, rough rolling and finishing rolling are performed to obtain a steel strip with a thickness generally greater than 2mm, and finally the steel strip is processed Laminar cooling and coiling complete the entire hot rolling production process. If you want to produce steel strips with a thickness of less than 1.5mm (inclusive), the difficulty is relatively large, and the hot-rolled steel strips are usually subjected to subsequent cold rolling and annealing to complete. In addition, the long process flow, high energy consumption, many units and equipment, and high capital construction costs result in high production costs.
  • the thin slab continuous casting and rolling process is: continuous casting + slab heat preservation and soaking + hot continuous rolling + cooling + coiling.
  • the main difference between this process and the traditional process is that the thickness of the cast slab in the thin slab process is greatly reduced to 50-90mm. Because the cast slab is thin, the cast slab only needs to undergo 1 to 2 passes of rough rolling (the thickness of the cast slab is 70-90mm When the thickness of the cast slab is 50mm, the thickness of the continuous casting slab in the traditional process must be repeatedly rolled to reduce the thickness to the required specifications before the finish rolling; and the thin slab casting process is not necessary to go through rough rolling (when the thickness of the cast slab is 50mm).
  • the billet directly enters the soaking furnace for soaking and heat preservation, or a small amount of temperature compensation, so the thin slab process greatly shortens the process flow, reduces energy consumption, reduces investment, and reduces production costs.
  • the faster cooling rate of thin slab continuous casting and rolling the strength of the steel will increase and the yield ratio will increase, thereby increasing the rolling load, so that the thickness specification of the hot-rolled product can be economically produced and the thickness specification is not too thin, generally ⁇ 1.5mm, see Chinese patents CN200610123458.1, CN200610035800.2 and CN200710031548.2, and these patents do not involve the elements Sn and Cu.
  • ESP all-headless thin slab continuous casting and rolling process
  • slab flame cutting and heating furnace for heat preservation and soaking and slab transition are eliminated, and the length of the entire production line is greatly shortened to about 190 meters.
  • the slab casted by the continuous casting machine The thickness is 90-110mm, and the width is 1100-1600mm.
  • the continuously cast slab passes through a section of induction heating roller table to keep and heat the slab, and then enters rough rolling, finishing rolling, layer cooling, and coiling in turn.
  • the hot-rolled sheet is obtained through the process.
  • the thinnest hot-rolled sheet of 0.8mm thickness can be obtained by this process, which expands the specification range of the hot-rolled sheet, and its single production line output can reach 2.2 million t/year scale.
  • the process has been rapidly developed and promoted.
  • the shorter process flow than thin slab continuous casting and rolling is the thin strip continuous casting and rolling process.
  • the thin strip continuous casting technology is a cutting-edge technology in the field of metallurgy and materials research. Its appearance has brought a revolution to the steel industry. It changes the production process of steel strip in the traditional metallurgical industry, integrating continuous casting, rolling, and even heat treatment into a whole, so that the produced thin strip will be formed into thin steel strip at one time after one online hot rolling.
  • the production process is simplified and the production cycle is shortened.
  • the length of the process line is only about 50m; the equipment investment is also reduced, and the product cost is significantly reduced. It is a low-carbon and environmentally friendly hot-rolled thin strip production process.
  • the twin-roll thin strip continuous casting process is a main form of the thin strip continuous casting process, and it is also the world's only industrialized thin strip continuous casting process.
  • the typical process flow of twin-roll thin strip continuous casting is shown in Figure 1.
  • the molten steel in the ladle 1 is directly poured into one by two through the ladle nozzle 2, the tundish 3, the immersion nozzle 4 and the distributor 5
  • the molten steel solidifies on the rotating circumferential surfaces of the crystallizing rollers 8a, 8b to form a solidified shell and gradually grow, and then the two
  • the minimum gap (nip point) between the crystallizing rolls 8a and 8b forms a cast strip 11 with a thickness of 1-5mm.
  • the cast strip 11 is guided by the guide plate 9 to the pinch roll 12 and sent to the rolling mill 13 to be rolled into a thin strip of 0.7-2.5mm. Then it is cooled by the cooling device 14, and cut by the flying shear device 16, and finally sent to the coiler 19 to be wound into a roll.
  • High-reamed steel is an important steel grade of advanced high-strength steel (AHSS). It has high strength, elongation, excellent formability and flanging performance, and can meet the requirements of complex shape automotive zero
  • the component requirements such as the swing arm of the rear axle suspension of the car chassis, can also be used for other components that require flange flanging.
  • the flanging capacity is expressed by the hole expansion rate.
  • the hole expansion performance is a formability index of steel, which reflects the resistance of the material in the direction perpendicular to the hole edge due to the excessive local elongation and deformation of the hole edge during the hole expansion process. The ability to locally crack.
  • the hole reaming performance of the steel plate is related to the composition, strength and uniformity of the steel plate. Because it contains more precious alloying elements Cr, Nb, Ti, V and Mo, etc., although the cooling rate is lower Under the conditions, a ferrite/bainite dual phase structure can be obtained, but its cost is relatively high.
  • the most commonly used high-reamed steel strength grades are mainly concentrated in the 440MPa and 590MPa grades, and their microstructures are mainly ferrite and bainite, and sometimes contain a small amount of martensite.
  • the hole reaming performance of the steel plate is related to many factors, these factors mainly include: the level of inclusions, the performance difference of each phase in the structure, the uniformity of the structure, the yield ratio and the type of organization.
  • ferrite and bainite structures have relatively high hole expansion performance, but their strength is relatively low, and it is difficult to reach the level of 780MPa and above. This is also the current high hole expansion steel mainly concentrated in 440MPa and 590MPa. The main reason for each intensity level. High-reamed steel has become one of the important varieties of automotive steel plates.
  • thin strip continuous casting Due to the advantages of the natural process flow of thin strip continuous casting, compared with the traditional hot rolling process, thin strip continuous casting is easy to generate bainite type microstructure during the cooling process after rolling, and it is easy to produce products with excellent expansion. Hole performance. Therefore, the use of thin strip continuous casting to produce high-expansion steel has natural advantages.
  • the use of thin strip continuous casting to produce high-reamed steel is mainly aimed at the hot-rolled thin-gauge automotive steel market with a thickness of less than 1.8mm (inclusive). Due to the thinner thickness, the thin strip continuous casting process has strong manufacturing and cost advantages.
  • the product specifications of the high-reamed steel strip directly supplied in the hot-rolled/pickled state are 1.2mm, 1.25mm, 1.4mm, 1.5mm, 1.6mm, 1.7mm, 1.8mm, etc. Due to the thinner product thickness, traditional Many manufacturers often cannot supply thin-gauge high-expansion steel due to the capacity limitations of traditional hot-rolling lines; or use the hot-rolling process first and then cold-rolled. This production process adds thin-gauge, high-expansion steel. The production cost of Kong Gang.
  • thin strip continuous casting due to its own rapid solidification process characteristics, thin strip continuous casting generally has the problems of uneven structure, low elongation, high yield ratio, and poor formability.
  • the cast strip has austenite crystals. The grains have obvious non-uniformity, which will cause the final product structure obtained after austenite transformation to be non-uniform, resulting in unstable product performance. Therefore, it is difficult and challenging to use thin strip continuous casting production lines to produce some products with high hole expansion performance required by the automotive industry and petrochemical industry. Therefore, when using thin strip continuous casting to produce high hole expansion steel, copy the traditional The composition process of the product cannot be produced, and a breakthrough in the composition and process is required.
  • Chinese patent CN103602890 discloses a high-expanded steel plate with a tensile strength of 540MPa and a manufacturing method thereof. This patent adopts traditional continuous casting + traditional hot rolling process to produce, and adopts one-stage conventional laminar cooling method.
  • Chinese patent CN103602890 discloses a high-expanded steel plate with a tensile strength of 440MPa and a manufacturing method thereof. This patent adopts traditional continuous casting + traditional hot rolling process to produce, and adopts one-stage conventional laminar cooling method.
  • Chinese patents CN105154769 and CN106119702 respectively disclose a 780MPa and 980MPa grade hot-rolled high-strength and high-reamed steel and its manufacturing method, both of which belong to the category of high-strength steel. They are compared by adding Ti, Mo and Ti, Nb, Cr, V, etc. Multiple microalloying elements are used to strengthen the steel grade, and the alloy cost is relatively high; at the same time, its production method adopts traditional continuous casting + traditional hot rolling process to produce.
  • the purpose of the present invention is to provide a thin strip continuous casting high-expansion steel and a manufacturing method thereof, which fully utilizes scrap steel as a raw material to reduce the cost of molten steel, and can further reduce the production process cost and improve product performance through thin strip continuous casting.
  • the invention utilizes the residual Sn, Cu and other elements in the scrap steel to smelt molten steel, and selectively adds B and other microalloy elements to the steel; in the smelting process, the basicity of the slag, the type and melting point of the inclusions in the steel are controlled during the smelting process.
  • the gas atomization cooling method can effectively reduce the thickness of the oxide scale on the surface of the strip. Improve the temperature uniformity of the strip, and greatly improve the surface quality and hole reaming performance of the strip.
  • the final produced steel coil can be used directly as a hot-rolled sheet, or it can be used after pickling and leveling.
  • a thin strip continuous casting high-expansion steel of the present invention has a chemical composition weight percentage: C: 0.01-0.05%, Si: 0.2-0.6%, Mn: 0.8-1.5%, P ⁇ 0.02%, S ⁇ 0.005%, N ⁇ 0.008%, Als ⁇ 0.001%, Ca ⁇ 0.0050%, B: 0.001-0.006%, Mn/S>250, total oxygen [O] T : 0.007 ⁇ 0.020%, the balance is Fe and Other unavoidable impurities, and also contain one or two elements of Cu: 0.1-0.6% and Sn: 0.005-0.04%.
  • the microstructure of the thin strip continuous casting high-expansion steel of the present invention is ferrite + bainite, and the volume ratio of the bainite phase is more than or equal to 15%.
  • the yield strength of the thin strip continuous casting high-expansion steel of the present invention is ⁇ 290MPa, the tensile strength is ⁇ 440MPa, the elongation rate is ⁇ 29%, and the hole expansion rate is ⁇ 110%.
  • the thickness of the thin strip continuous casting high-expansion steel of the present invention is 0.8-2.5mm, preferably 1.0-1.8mm.
  • C is the most economical and basic strengthening element in steel. It improves the strength of steel through solid solution strengthening and precipitation strengthening. C is an essential element for the precipitation of cementite during austenite transformation. Therefore, the level of C content determines the strength level of steel to a large extent, that is, a higher C content corresponds to a higher strength level.
  • the interstitial solid solution and precipitation of C have great harm to the plasticity and toughness of steel, and the excessively high C content is detrimental to the welding performance, so the C content cannot be too high, and the strength of the steel can be compensated by adding alloy elements appropriately .
  • casting in the peritectic reaction zone is prone to slab surface cracks, and breakout accidents may occur in severe cases.
  • the casting strip in the peritectic reaction zone is prone to surface cracks, and in severe cases, the strip will break. Therefore, the continuous casting of Fe-C alloy thin strip also needs to avoid the peritectic reaction zone. Therefore, the C content range used in the present invention is 0.01-0.05%.
  • Si plays a role of solid solution strengthening in steel.
  • adding Si also plays a role of deoxidation, which can improve the purity of steel; at the same time, Si can expand the range of ferrite formation and avoid the appearance of pearlite phase.
  • the Si content is too high, it is easy to form "red iron scale" defects on the surface of the steel sheet after rolling. Therefore, the range of Si content used in the present invention is 0.2-0.6%.
  • Mn is one of the cheapest alloying elements. It can improve the hardenability of steel and has a considerable solid solubility in steel. It can improve the strength of steel through solid solution strengthening, and at the same time, it can basically improve the plasticity and toughness of steel. No damage, it is the most important strengthening element to increase the strength of steel, and it can also play a role in deoxidizing steel. However, excessive Mn content will cause deterioration of weldability and toughness of the welding heat-affected zone. Therefore, the range of Mn content used in the present invention is 0.8-1.5%.
  • P High content of P is easy to segregate in grain boundaries, increase the cold brittleness of steel, deteriorate welding performance, reduce plasticity, and deteriorate cold bending performance.
  • the solidification and cooling rate of the cast strip is extremely fast, which can effectively inhibit the segregation of P, thereby effectively avoiding the disadvantages of P and giving full play to the advantages of P. Therefore, in the present invention, a higher P content than the traditional production process is adopted, the content of P element is appropriately relaxed, and the dephosphorization process is eliminated in the steelmaking process. In actual operation, there is no need to deliberately perform the dephosphorization process, and no additional process is required. Add phosphorus, the range of P content is less than 0.02%.
  • S Under normal circumstances, S is a harmful element in steel, causing steel to produce hot brittleness, reducing the ductility and toughness of steel, and causing cracks during rolling. S is easy to form MnS in steel.
  • the amount and shape of sulfide in steel directly affect the hole expansion rate of steel plate. S must be less than 0.005%.
  • the number and morphology of inclusion elements have a great influence on the hole expansion performance of the steel plate, especially the strip-shaped sulfide inclusions are likely to cause cracks during deformation. Therefore, in the present invention, S is controlled as an impurity element, and its content range is ⁇ 0.005%, and Mn/S>250.
  • N Similar to the C element, the N element can improve the strength of the steel through interstitial solid solution.
  • the present invention uses the effect of N and B in the steel to generate the precipitated phase of BN, which requires a certain amount of N in the steel.
  • the interstitial solid solution of N has great harm to the plasticity and toughness of steel.
  • the existence of free N will increase the yield ratio of steel, so the N content cannot be too high.
  • the range of N content used in the present invention is ⁇ 0.008%. In some embodiments, the N content is 0.004-0.008%.
  • Ca It can change the form of sulfide in steel, transform long MnS inclusions into spherical CaS inclusions, improve the plasticity and toughness of the steel plate, and help increase the hole expansion rate of the steel plate.
  • the invention controls Ca ⁇ 0.0050%. In some embodiments, the Ca content is 0.001-0.005%.
  • Cu It mainly plays a role of solid solution and precipitation strengthening in steel. Because Cu is an element that is easy to segregate, the Cu content is generally strictly controlled in the traditional process. Using the rapid solidification effect of thin strip continuous casting, the present invention increases the upper limit of Cu to 0.60%.
  • Figure 2 shows the effect of copper on the interface heat flow. Copper elements of different compositions are added to steel. It can be seen from the experimental results that as the copper content increases, the peak heat flow of the interface heat transfer of the steel decreases, and the average heat flow also decreases. When the Cu content reaches 0.80%, there is still a high peak heat flow and average heat flow. When the Cu content is greater than 2.5%, the peak heat flow and average heat flow are significantly reduced.
  • the present invention controls the content of Cu to be between 0.1% and 0.6%, and the peak heat flow and average heat flow caused by the Cu element have little effect.
  • the increase of Cu content can, to a certain extent, realize the effective use of copper in scrap steel or inferior mineral resources (high copper ore), promote the recycling of steel, reduce production costs, and achieve the purpose of sustainable development. It is worth noting that, in the present invention, the Cu element in the scrap steel is fully utilized, and no additional metal Cu is required, which will increase the cost of steelmaking.
  • Sn element is also one of the main participating elements in scrap steel. It is recognized as a harmful element in steel. Because Sn is an element that is easy to segregate, a small amount of Sn will be enriched at the grain boundary, resulting in cracks and other defects. In the traditional process, the content of Sn element is strictly controlled. Due to the characteristics of rapid solidification of thin strip continuous casting, the segregation of elements in the dendrites is greatly reduced, which can greatly increase the amount of solid solution of the elements. Therefore, under the conditions of the thin strip continuous casting process, the range of Sn elements can be expanded, so it can greatly Reduce steelmaking costs.
  • Figure 3 is the relationship between the Sn element and the average heat flux. It can be seen from Fig.
  • Figure 4 shows the relationship between Sn content and surface roughness. Because the cracks on the surface of the cast strip are usually produced at the uneven wrinkles on the surface of the cast strip, the surface roughness is used to characterize the occurrence of surface cracks. If the roughness is large, the probability of occurrence of cracks is high. It can be seen from Fig. 4 that the increase in Sn content does not adversely affect the surface quality of the cast strip under the conditions of rapid solidification. From the results of Fig. 3 and Fig. 4, it can be seen that Sn has no adverse effect on the solidification and surface quality of the cast strip.
  • the requirements for Sn content can be further relaxed, and the design Sn content range is 0.005-0.04%. It is worth noting that, in the present invention, the Sn element in the scrap steel is fully utilized, and there is no need to add metal Sn, which will increase the steelmaking cost.
  • B The significant effect of B in steel is: a very small amount of boron can double the hardenability of steel, and B can preferentially precipitate BN particles in high-temperature austenite, thereby inhibiting the precipitation of AlN and weakening the effect of AlN on grain boundaries.
  • the pinning effect of Zn enhances the growth ability of grains, thereby making the austenite grains more uniform; in addition, the combination of B and N can effectively prevent the appearance of the low-melting-point phase B 2 O 3 at the grain boundary.
  • B is a lively and easily segregated element, which is easy to segregate in the grain boundary.
  • the B content is generally controlled very strictly, generally around 0.001-0.003%; while in the thin strip continuous casting process, solidification and cooling The faster rate can effectively inhibit the segregation of B, and solid-dissolve more B content, so the B content can be appropriately relaxed; it can also be controlled to generate BN particles through a reasonable process to play a role in nitrogen fixation.
  • Studies have also shown that B will reduce the tendency of C atoms to segregate and avoid the precipitation of Fe23(C,B)6 at the grain boundary, so more B can be added. Therefore, in the present invention, a higher B content than the traditional process is used, and the range is 0.001-0.006%.
  • the manufacturing method of thin strip continuous casting high-expansion steel according to the present invention includes the following steps:
  • the free oxygen [O] Free range is: 0.0005 to 0.005%, and the composition of molten steel contains Mn/S>250;
  • the continuous casting adopts double-roll thin strip continuous casting to form a 1.5-3mm thick cast strip at the smallest gap between the two crystallizing rolls; the diameter of the crystallizing roll is between 500-1500mm, preferably 800mm; the inside of the crystallizing roll is cooled by water.
  • the casting speed of the machine is 60-150m/min; the continuous casting flow adopts a two-stage molten steel distribution flow system, that is, the tundish + flow distributor;
  • the temperature of the casting belt is between 1420 and 1480 °C, and it enters the lower closed chamber directly.
  • the lower closed chamber is filled with non-oxidizing gas.
  • the oxygen concentration (volume ratio) in the lower closed chamber is controlled at ⁇ 5%, and the lower closed chamber is closed.
  • the temperature of the casting strip at the outlet of the chamber is between 1150-1300°C;
  • the cast strip is sent to the rolling mill via pinch rolls in the lower enclosed chamber, and rolled into strip steel.
  • the rolling temperature is 1100-1250°C.
  • the hot rolling reduction rate is controlled to 10-50%, and the hot rolling reduction rate is preferably 30-50. %; the thickness of the strip after hot rolling is 0.8-2.5mm, preferably 1.0-1.8mm;
  • the strip after hot rolling is cooled after rolling, and the cooling adopts gas atomization cooling method, and the cooling rate is ⁇ 20°C/s;
  • the cooled hot-rolled steel strip is coiled into coils at a coiling temperature of 550-650°C.
  • the smelting raw material can be 100% scrap steel, without pre-screening, the molten steel smelting adopts electric furnace steelmaking; or, the smelting is through the converter steelmaking, and the scrap steel is added to the converter at a ratio of more than 20% of the smelting raw material , Without pre-screening; then enter LF furnace, VD/VOD furnace or RH furnace for refining.
  • the non-oxidizing gas is CO 2 obtained by sublimation of N 2 , Ar or dry ice.
  • the gas-water ratio of the gas atomization cooling is 15:1-10:1, the air pressure is 0.5-0.8 MPa, and the water pressure is 1.0-1.5 MPa.
  • air-water ratio refers to the flow ratio of compressed air and water, and the unit of flow is m 3 /h.
  • the winding adopts a double-winding machine form or a Carrosel winding form.
  • the cooled hot-rolled steel strip is directly coiled into a coil after being cut by a cutting head to remove the poor quality head.
  • the cooling rate in step 5) is 20-35°C/s.
  • Smelting is made by electric furnace, and 100% of the raw materials can be smelted from scrap; smelting is made by converter, and scrap is added to the converter at a ratio of more than 20% of the smelting raw materials, and no pre-screening is required. This maximizes the ratio of converter scrap and greatly reduces production costs. ; Then enter LF furnace, VD/VOD furnace or RH furnace for refining.
  • MnO-SiO 2 -Al 2 O 3 ternary inclusions As shown in the shaded area in Figure 5, MnO-SiO 2 -Al 2 O 3 ternary inclusions
  • the MnO/SiO 2 in the composition is controlled within 0.5-2, preferably 1-1.8.
  • O in steel is an essential element for the formation of oxidized inclusions.
  • the present invention requires the formation of low-melting ternary inclusions of MnO-SiO 2 -Al 2 O 3 , which requires steel
  • the free oxygen [O] Free range in water is: 0.0005 to 0.005%.
  • thermodynamic equations of boron and nitrogen, aluminum and nitrogen in ⁇ -Fe in steel are as follows:
  • the initial precipitation temperature of BN in steel is about 1280°C
  • the precipitation of BN tends to balance at 980°C
  • the precipitation of AlN has just begun (the precipitation temperature of AlN is about 980°C).
  • the precipitation of BN has priority over AlN.
  • the present invention uses reasonable process control means to complete the combination of B and N in the lower sealed chamber, thereby preferentially precipitating BN particles in high-temperature austenite to inhibit the precipitation of AlN, weaken the pinning effect of AlN on the grain boundary, and increase the grain size
  • the growth ability of the austenite can make the austenite grains more uniform; in addition, the combination of B and N can effectively prevent the appearance of the low melting point phase B 2 O 3 at the grain boundary.
  • the strip steel after online hot rolling is cooled after rolling.
  • the cooling method adopts gas atomization cooling method.
  • the gas atomization cooling method can effectively reduce the thickness of the surface oxide scale of the strip steel, improve the temperature uniformity of the strip steel, and improve the surface quality and quality of the strip steel. Reaming performance.
  • the gas-water ratio of gas atomization cooling is 15:1 ⁇ 10:1, the air pressure is 0.5 ⁇ 0.8MPa, and the water pressure is 1.0 ⁇ 1.5MPa. After the gas is atomized, high-pressure water mist is sprayed on the surface of the steel strip. On the one hand, it can reduce the temperature of the steel strip. On the other hand, the water mist will form a dense gas film covering the surface of the steel strip, which can prevent the strip from being oxidized.
  • This cooling method can avoid the problems caused by traditional spraying or laminar cooling, make the surface temperature of the strip drop uniformly, improve the uniformity of the strip temperature, and achieve the effect of homogenizing the internal microstructure; at the same time, the uniform cooling can improve the strip The shape quality and performance stability of the steel; effectively reduce the thickness of the oxide scale on the surface of the strip.
  • the cooling rate range of gas atomization cooling is ⁇ 20°C/s, and the strip is cooled to 550-650°C, so that the high-temperature austenite after rolling is transformed into a mixed microstructure of ferrite + a small amount of bainite, as shown in Figure 7. Shown.
  • converter steelmaking to provide molten steel requires manufacturers to have the conditions to provide molten iron. Under normal circumstances, blast furnace ironmaking or non-blast furnace ironmaking equipment is required, which belongs to the current long-process steel production mode. However, today with increasingly rich scrap steel resources, the country is advocating to increase the converter scrap ratio, so as to achieve the purpose of energy saving, consumption reduction and cost reduction.
  • the average level of converter scrap ratio in the past was about 8%. Now and in the future, the target of converter scrap ratio It is 15-25%.
  • Scrap steel As the main raw material.
  • Traditional processes such as die casting or thick plate continuous casting have a solidification and cooling rate of only 10 -1 -10°C/s. These residual elements in the scrap will solidify Grain boundary segregation occurs during the process, which deteriorates the performance and quality of the steel. In severe cases, cracks and fractures occur directly. Therefore, in the traditional process, these harmful elements must be strictly controlled.
  • some pre-screening is required.
  • some special treatments are required in the steelmaking process, such as adding some concentrates for dilution, etc., which undoubtedly increase the cost of production operations. Due to the need to control the composition of steel, there are certain quality requirements for the used scrap raw materials.
  • the scrap steel needs to be pre-screened and classified.
  • some domestic electric furnace steel plants will choose to add refined materials such as purchased sponge iron and iron carbide to the raw material composition to dilute the harmful elements that are difficult to remove in the scrap and improve the quality of molten steel.
  • Some domestic steel mills that have both blast furnaces and electric furnaces use self-produced molten iron into the electric furnace as raw materials to improve the production efficiency of the electric furnace, thereby greatly shortening the tapping time of the electric furnace, and the hot metal blending ratio in the electric furnace can reach 30-50% .
  • twin-roll thin strip continuous casting technology is a typical sub-rapid solidification process.
  • the solidification cooling rate is as high as 10 2 -10 4 °C/s.
  • Some harmful residual elements in the scrap such as Cu, Sn, P, etc., can be maximized
  • the ground solid dissolves into the steel matrix without causing grain boundary segregation. Therefore, 100% all scrap smelting can be realized in the electric furnace steelmaking, without pre-screening, which greatly reduces the cost of raw materials; in the converter steelmaking, the scrap smelting is accounted for More than 20% of the raw materials are added to the converter without pre-screening, which maximizes the scrap ratio of the converter and greatly reduces the production cost.
  • Cast Ability of Strip Casting refers to the feasibility of double-roll casting for a steel grade.
  • Good castability means that there will be no restrictive problems that affect the inability of the casting process or the quality of the cast product cannot meet the requirements during the casting process; poor castability means that there are often problems such as molten steel during the casting process. Poor fluidity, agglomeration and bridging of the molten pool, severe belt breaks, surface cracks and surface slag inclusions, etc., have caused the production to be unable to proceed normally and stably or the product quality does not meet the requirements.
  • the steel grades involved in the present invention control from carbon content (avoid the peritectic zone to solve uneven solidification shrinkage); basicity control, Als control, free oxygen total oxygen control, and low melting point MnO-SiO 2 -Al 2 O 3 Ternary inclusion control (improving the uniformity of interface heat transfer to solve the uniformity of solidification); Mn/S control (avoiding hot brittleness) and other aspects, strictly meet the castability of thin strip continuous casting.
  • Traditional continuous casting also uses spray cooling, but the area and temperature are different.
  • the casting slab is spray-cooled at the exit fan-shaped area of the casting mold. At this time, the temperature of the casting slab is higher, which is shown in the phase diagram. Look at the high-temperature austenite single-phase region.
  • the main purpose of spray cooling in this area is to control the position of the solidification end, accelerate the surface cooling of the cast slab, refine the surface austenite grain structure, increase the surface strength of the cast slab, improve the surface quality of the cast slab, and avoid the occurrence of cracks.
  • the present invention sprays and cools the ultra-thin steel strip after the on-line hot rolling of the cast strip. The temperature is relatively low.
  • the phase diagram From the phase diagram, it is in the solid phase transformation zone where high-temperature austenite transforms to ferrite.
  • spray cooling by adjusting the spray cooling intensity, the type of microstructure after solid phase transformation can be effectively controlled, and the performance requirements of the final product can be achieved.
  • the present invention preferably adopts the Carrousel coiling method, which can realize the co-coiling of the hot-rolled steel coil, ensure the uniformity of the coiling temperature, and greatly improve the stability of the product performance of the steel coil.
  • the Carrosel coiler is widely used in the cold rolling field. Its main advantage is that it can realize thinner strip coiling, and it has a small footprint, which can greatly shorten the length of the production line. Due to the low temperature of the strip steel, it is relatively easy to realize.
  • the present invention proposes to adopt the Carrousel coiling method in the field of ultra-thin hot-rolled steel strip coiling, taking into account the high temperature resistance of the equipment, and realizes the coiling of ultra-thin hot-rolled steel strip.
  • the coiling method is more advanced than the coiling method of the Casttrip thin strip continuous casting production line of Nucor in the United States.
  • the most obvious feature of the present invention which is different from the existing thin strip continuous casting technology is the roll diameter of the crystallizing roll and the corresponding flow distribution method.
  • the technical feature of EUROSTRIP is ⁇ 1500mm large diameter crystallizing roller, large crystallizing roller, large molten steel capacity in molten pool, easy flow distribution, high cost of crystallizing roller manufacturing and operation and maintenance.
  • the technical feature of CASTRIP is the ⁇ 500mm small diameter crystallizing roller, the crystallizing roller is small, the molten steel volume is small, and the flow distribution is very difficult, but the cost of manufacturing and operation and maintenance of the casting machine is low.
  • CASTRIP adopts a three-stage molten steel distribution system (tundish + transition bag + flow distributor).
  • the use of a three-stage flow distribution system directly leads to an increase in the cost of refractory materials; more importantly, the three-stage flow distribution system makes the path of molten steel flow longer and the temperature drop of molten steel is also greater.
  • the tapping temperature needs to be greatly increased. The increase in the tapping temperature will cause problems such as increased steelmaking costs, increased energy consumption, and shortened life of refractory materials.
  • the molten steel flowing out of the distributor forms different distribution patterns along the roller surface and the two end surfaces, and flows in two paths without interfering with each other. Due to the use of a two-stage flow distribution system, compared with a three-stage flow system, the cost of refractory materials is greatly reduced; the shortening of the molten steel flow path reduces the temperature drop of the molten steel, which can lower the tapping temperature, compared with the three-stage flow system , The tapping temperature can be reduced by 30-50°C.
  • the lowering of the tapping temperature can effectively reduce the cost of steelmaking, save energy and extend the life of refractory materials.
  • the invention is matched with a crystallizing roller with a roller diameter of ⁇ 800mm and adopts a two-stage molten steel distribution system, which not only realizes the requirement of stable molten steel distribution, but also realizes the goals of simple structure, convenient operation and low processing cost.
  • Chinese patent CN101353757 uses low-carbon microalloy components to produce 440MPa tensile strength reamed steel, with a small amount of Nb:0-0.25% and Ti:0-0.03% added to the composition. Due to the 600°C coiling temperature, this patent adopts the traditional Continuous casting + traditional hot rolling process. For carbon-manganese steel hot-rolled sheets, there is often a band structure, which leads to a decrease in the plate hole expansion rate. At the same time, a variety of microalloys are added, which increases the cost of steelmaking.
  • the invention is obviously different from the patent in the production process.
  • the invention adopts the thin strip continuous casting process to produce, which can greatly shorten the production process, and can avoid the band structure. At the same time, it can save the amount of microalloys and only need to add a small amount of microalloys. The same or even better performance can be achieved.
  • Chinese patent CN101928881 discloses a hot-rolled high-expanded steel sheet with a tensile strength of 590MPa and its manufacturing process.
  • the patent composition adds a small amount of Nb:0-0.10% and Ti:0-0.04%, using traditional continuous casting + traditional heat It is produced by rolling process.
  • the finished steel plate is cooled to 600-750°C at a cooling rate of 50°C/s ⁇ 100°C/s, and then cooled in air at a cooling rate of 5°C/s ⁇ 15°C/s for 3 ⁇ After 10 seconds, the steel plate is again cooled to 350-500°C at a cooling rate of 70°C/s-150°C/s and coiled, and then air-cooled to room temperature.
  • the subsequent cooling adopts complicated three-stage cooling, the coiling temperature fluctuates greatly, the performance fluctuation of the coil head, middle and tail will be relatively large, and the hole expansion rate fluctuates also.
  • the invention adopts the thin strip continuous casting process to produce, greatly simplifies the production process, and does not need to use complicated three-stage cooling, and has obvious advancement.
  • Japanese patent JP2006063394 discloses a hot-rolled high-expansion steel with a carbon content of 0.20 ⁇ 0.48%, its tensile strength ⁇ 440MPa, and its addition of Cr alloy elements, but its hole expansion rate is only ⁇ 70%, and after hot rolling An annealing treatment at 640°C is also required.
  • the carbon content design of the invention has reached the range of medium and high carbon steel, which is obviously higher than the low carbon design of the invention.
  • the hot-rolled high-strength steel sheet disclosed in Japanese patent JP2006305700 adopts the composition design of C-Si-Mn+Ti to obtain a tensile strength of more than 780MPa and a hole expansion rate of only 68% or more.
  • Japanese patent JP2003/016614 discloses a hot-rolled high-expansion steel with carbon content of 0.02 ⁇ 0.10%, Si ⁇ 0.5%, and its tensile strength ⁇ 590MPa, but it contains a lot of alloys such as Nb, Ti, V, Cr, RE, etc. Element, steelmaking costs are relatively high, and good surface paintability is the main goal.
  • the present invention adopts a simple alloy composition system and a thin strip continuous casting process to realize the performance of high-expansion steel.
  • the present invention has the characteristics of simplicity and high efficiency.
  • the hot-rolled steel sheet disclosed in US Patent US2006096678 has a strength of 780MPa or more, an elongation rate of 22% or more, and a hole expansion rate of 60% or more.
  • the hot-rolled steel sheet disclosed in US Patent No. 4,415,376 has a yield strength of 80 ksi (550 MPa) or more, a hole expansion rate of 58% or more, and is strengthened by Nb and V.
  • the production processes used in these patents are all traditional continuous casting + traditional hot rolling production processes, which are different from the production process of the present invention, and the product hole expansion rate is low.
  • the present invention uses thin strip continuous casting technology to produce high-expansion steel containing tin (Sn), copper (Cu)/tin (Sn), copper (Cu), and boron (B). There have been no reports so far.
  • Sn tin
  • Cu copper
  • Cu copper
  • B boron
  • the present invention eliminates the need for complex processes such as slab heating and multi-pass repeated hot rolling. Through double-roll thin strip continuous casting + one online hot rolling process, the production process is shorter, the efficiency is higher, and the investment cost of the production line is reduced. The production cost is greatly reduced.
  • the present invention eliminates many complicated intermediate steps in the production of traditional high-expansion steel. Compared with traditional high-expansion steel, the energy consumption and CO 2 emission of production are greatly reduced, and it is a green and environmentally friendly product.
  • thin strip continuous casting Due to the advantages of the natural process flow of thin strip continuous casting, compared with the traditional hot rolling process, thin strip continuous casting is easy to generate bainite type microstructure during the cooling process after rolling, and it is easy to produce excellent products. The reaming performance.
  • the present invention adopts the thin strip continuous casting process to produce high-reamed steel.
  • the thickness of the cast strip itself is relatively thin.
  • the purpose of supplying hot-rolled sheets of specifications can significantly improve the cost-effectiveness of sheets and strips.
  • the invention adopts the addition of a trace amount of boron to preferentially precipitate BN particles in high-temperature austenite, thereby inhibiting the precipitation of AlN, weakening the pinning effect of fine AlN on grain boundaries, improving the growth ability of grains, and homogenizing the austenite Bulk grains are conducive to the development of high hole expansion performance of strip steel.
  • the smelted raw materials can be smelted in a real sense of 100% all scrap steel, without pre-screening, which greatly reduces the cost of raw materials; if the converter steelmaking is used, the scrap steel accounts for more than 20% of the smelting raw materials It is added to the converter in a proportion and does not require pre-screening, which maximizes the scrap ratio of the converter and greatly reduces smelting costs and energy consumption.
  • the present invention uses scrap steel containing Cu and Sn to "turn harms into benefits" for Cu and Sn in the steel, and realizes the full use of existing scrap steel or low-quality inferior mineral resources (high tin ore, high copper ore) Utilize, promote the recycling of scrap steel, reduce production costs, and realize the sustainable development of the steel industry.
  • the present invention adopts the strip steel gas atomization cooling method after rolling, which can avoid the problems caused by traditional spraying or laminar cooling, so that the surface temperature of the strip can be uniformly lowered, and the uniformity of the strip temperature can be improved, thereby achieving uniform internal micro
  • the effect of the structure; at the same time, the cooling is uniform, which can improve the strip quality and the stability of the hole reaming performance; effectively reduce the thickness of the oxide scale on the surface of the strip.
  • the precipitation of alloying elements occurs during the cooling process of the traditional slab.
  • the utilization rate of the alloying elements is often reduced due to insufficient re-dissolution of the alloying elements.
  • the high-temperature cast strip is directly hot-rolled, and the added alloy elements mainly exist in a solid solution state, which can improve the alloy utilization rate.
  • the present invention uses a hot-rolled steel strip Carrousel coiler, which effectively shortens the length of the production line; at the same time, co-coiling can greatly improve the control accuracy of the coiling temperature and improve the stability of product performance.
  • Figure 1 is a schematic diagram of the process layout of the twin-roll thin strip continuous casting process
  • Figure 2 is a schematic diagram of the influence of Cu on the interface heat flow
  • Figure 3 is a schematic diagram of the relationship between Sn content and average heat flux
  • Figure 4 is a schematic diagram of the relationship between the Sn content and the surface roughness of the cast strip
  • Figure 5 is a ternary phase diagram of MnO-SiO 2 -Al 2 O 3 (shaded area: low melting point area);
  • Figure 6 is a schematic diagram of the thermodynamic curves of BN and AlN precipitation
  • Figure 7 is a photo of the microstructure of the steel in the example of the present invention.
  • the molten steel in accordance with the chemical composition design of the present invention is directly poured in a large ladle 1, through a ladle nozzle 2, a tundish 3, an immersion nozzle 4, and a distributor 5, which is rotated by two relative to each other and can quickly
  • the molten steel solidifies on the rotating circumferential surface of the crystallizing rollers 8a, 8b, and then forms a solidified shell and gradually grows on the two crystallizing rollers
  • a 1.5-3mm thick cast belt 11 is formed at the smallest gap (nip point).
  • the diameter of the crystallizing roller described in this embodiment is between 500-1500mm, and the inside is cooled by water; depending on the thickness of the casting strip, the casting speed of the casting machine ranges from 60-150m/min.
  • the temperature of the casting belt is between 1420 and 1480 °C, and it directly enters the lower closed chamber 10, and the lower closed chamber 10 protects the strip with non-oxidizing gas to realize the oxidation prevention of the strip. Protection, the atmosphere for anti-oxidation protection can be N 2 , Ar, or other non-oxidizing gases, such as CO 2 gas obtained by sublimation of dry ice, etc.
  • the oxygen concentration in the lower closed chamber 10 is controlled to be ⁇ 5%; The lower airtight chamber 10 protects the cast strip 11 from oxidation to the entrance of the rolling mill 13.
  • the temperature of the cast strip at the outlet of the lower closed chamber 10 is between 1150-1300°C; then the cast strip is sent to the hot rolling mill 13 through the swinging guide plate 9, the pinch roll 12, and the roller table 15.
  • a 0.8-2.5mm hot rolling is formed Strip
  • the rolled strip is cooled by the gas atomization rapid cooling device 14 to improve the temperature uniformity of the strip; after being cut by the flying shear device 16, the cut head falls along the flying shear guide plate 17 In the flying shear pit 18, the cut hot-rolled strip enters the coiler 19 for coiling.
  • the steel coil is removed from the coiler, it is naturally cooled to room temperature; the finally produced steel coil can be used directly as a hot-rolled sheet, or it can be used after pickling and leveling.
  • the chemical composition of the embodiment of the present invention is shown in Table 1, and the balance of the composition is Fe and other unavoidable impurities.
  • the process parameters are shown in Table 2, and the properties of the final product obtained are shown in Table 3.
  • the method for measuring the hole expansion rate is carried out in accordance with the international standard ISO16630:2009 or the Chinese standard GB/T24524-2009.
  • the present invention utilizes the thin strip continuous casting process and combines the steel grade composition to design and manufacture high-expansion steel with yield strength ⁇ 290MPa, tensile strength ⁇ 440MPa, elongation ⁇ 29%, and hole expansion rate ⁇ 110%.
  • Table 1 The chemical composition of the example steel (wt.%)
  • Example 1 0.04 0.25 1.45 0.008 0.004 0.0074 0.0093 0.0009 0.33 0.024 0.003 0.003
  • Example 2 0.01 0.22 0.90 0.013 0.003 0.0061 0.0110 0.0006 0.15 0.005 0.002 0.001
  • Example 3 0.03 0.35 1.28 0.015 0.004 0.0058 0.0150 0.0004 0.10 — 0.003 0.004
  • Example 4 0.03 0.28 1.10 0.013 0.003 0.0077 0.0130 0.0008 0.55 0.040 0.004 0.006
  • Example 5 0.05 0.34 0.85 0.009 0.002 0.0052 0.0120 0.0007 0.44 0.014 0.005 0.003
  • Example 6 0.04 0.43 0.80 0.012 0.002 0.0046 0.0070 0.0008 — 0.025 0.001 0.005
  • Example 7 0.03 0.20 0.95 0.015 0.003 0.0040 0.0100 0.0005 0.37 0.035 0.002 0.003
  • Example 8 0.

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Abstract

Sont divulgués un acier à forte expansion de trou obtenu par coulée continue en bandes minces et un procédé pour le fabriquer. Les constituants chimiques de l'acier sont les suivants, en pourcentages en poids : 0,01 à 0,05 % de C, 0,2 à 0,6 % de Si, 0,8 à 1,5 % de Mn, 0,02 % ou moins de P, 0,005 % ou moins de S, 0,008 % ou moins de N, moins de 0,001 % d'Als, 0,0050 % ou moins de Ca, 0,001 à 0,006 % de B, un rapport Mn/S étant supérieur à 250, 0,007 à 0,020 % d'oxygène total [O]T, le reste étant du Fe et des impuretés inévitables, et l'acier comprenant 0,1 à 0,6 % de Cu et/ou 0,005 à 0,04 % de Sn. Dans la présente invention, les éléments résiduels, tels que Sn et Cu, dans la ferraille d'acier sont utilisés pour la fusion, et des éléments de micro-alliage, tels que B, sont ajoutés de manière sélective ; la basicité du laitier, le type et le point de fusion des inclusions dans l'acier, la teneur en oxygène libre dans l'acier fondu et la teneur en aluminium soluble dans l'acide pendant le processus de fusion sont commandés, et une bande est obtenue par coulée continue en bandes minces à deux cylindres, après quoi la bande entre directement dans une chambre inférieure fermée après avoir quitté un cylindre de cristallisation et entre dans un laminoir en ligne pour un laminage à chaud dans des conditions fermées puis, après le laminage, la bande d'acier est refroidie par atomisation d'air et, pour finir, enroulée.
PCT/CN2020/115960 2019-09-19 2020-09-17 Acier à forte expansion de trou obtenu par coulée continue en bandes minces et procédé pour le fabriquer WO2021052431A1 (fr)

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