WO2023000479A1 - 一种屈服强度420MPa级热轧耐低温H型钢及其制备方法 - Google Patents

一种屈服强度420MPa级热轧耐低温H型钢及其制备方法 Download PDF

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WO2023000479A1
WO2023000479A1 PCT/CN2021/118771 CN2021118771W WO2023000479A1 WO 2023000479 A1 WO2023000479 A1 WO 2023000479A1 CN 2021118771 W CN2021118771 W CN 2021118771W WO 2023000479 A1 WO2023000479 A1 WO 2023000479A1
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ladle
molten iron
iron
slag
dephosphorization
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PCT/CN2021/118771
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English (en)
French (fr)
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王中学
赵培林
刘洪银
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山东钢铁股份有限公司
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Priority to KR1020247001833A priority Critical patent/KR20240023136A/ko
Publication of WO2023000479A1 publication Critical patent/WO2023000479A1/zh

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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
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/08—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling structural sections, i.e. work of special cross-section, e.g. angle steel
    • B21B1/088—H- or I-sections
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/02—Dephosphorising or desulfurising
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/02—Dephosphorising or desulfurising
    • C21C1/025—Agents used for dephosphorising or desulfurising
    • 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
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • 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
    • 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
    • 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 belongs to the technical field of metallurgy. Specifically, the invention relates to a 420MPa grade hot-rolled low-temperature-resistant H-shaped steel and a preparation method thereof.
  • H-shaped steel production enterprises have successively developed H-shaped steels with different grades of yield strength above 345MPa, which are generally produced by composite microalloying and hot rolling. Different enterprises prepare products of different grades and comprehensive performance according to the level of equipment.
  • Patent application CN201510498771.2 discloses a 420MPa grade excellent low-temperature toughness hot-rolled H-beam and its production method, composition: C 0.06-0.12%, Si 0.20-0.40%, Mn 1.20-1.60%, P ⁇ 0.015%, S ⁇ 0.010%, V 0.050 ⁇ 0.070%, Ni 0.10 ⁇ 0.20%, N 0.0050 ⁇ 0.0100%, the rest is Fe and unavoidable impurities.
  • this patent Compared with the existing technology, this patent has developed a 420MPa hot-rolled H-shaped steel with excellent comprehensive performance through reasonable V, Ni, and N composition design, matching the appropriate controlled rolling and controlled cooling process; the yield strength ReH is 440-520MPa ; Tensile strength Rm is 550 ⁇ 650MPa, elongation A is A ⁇ 22%, -40°C low temperature impact toughness KV2 ⁇ 100J.
  • the patent controlled cooling adopts a two-stage method, the first stage of rapid cooling + the second stage of air cooling, which requires a special cooling device to meet the above preparation requirements.
  • the produced 420MPa grade excellent low-temperature toughness hot-rolled H-beam thickness direction property Z is 40-65%.
  • Patent application CN201510788520.8 discloses a 420MPa grade high-strength low-yield ratio H-shaped steel and its preparation method.
  • the chemical composition of the H-shaped steel is: C 0.11-0.15%, Si 0.20-0.35%, Mn 1.35-1.50%, P ⁇ 0.035%, S ⁇ 0.025%, Cu 0.25-0.30%, Cr 0.40-0.45, Ni 0.20-0.30%, Nb 0.20-0.30%, and the rest are iron and trace impurities.
  • This patent realizes the production of 420MPa grade low yield ratio H-beam through optimized composition design, yield strength greater than 427MPa, tensile strength greater than 641MPa, and yield ratio 0.64-0.67.
  • This patent adds Ni, Nb, Cu and other elements, which are used in specific high-corrosion-resistant environments; the preparation process is affected by Cu elements, and the probability of cracks in the legs of H-beams increases under high final rolling temperature conditions, and at the same time significantly increases preparation cost.
  • Patent application CN201510498771.2 discloses a 420MPa high-performance anti-seismic H-shaped steel and its preparation method, including the following weight percentages: C: 0.15-0.18wt%, Si: 0.30-0.45wt%, Mn: 1.35-1.55wt% , V: 0.070-0.090wt%, P: ⁇ 0.015wt%, S: ⁇ 0.020wt%, and the rest are Fe and unavoidable impurities.
  • the preparation method includes molten steel smelting, deoxidation alloying, molten steel LF furnace refining, molten steel casting, and post-treatment steps.
  • the patent smelting adopts nitrogen-enriched vanadium microalloying process, which can effectively refine the austenite grains, and increase the nitrogen content during smelting, which is conducive to the formation of vanadium carbonitrides to disperse at the grain boundaries and promote the austenite grains. Grain nucleation further refines austenite grains, and through rolling, controlled cooling, rapid cooling and other processes, it ensures the excellent shape and surface quality of H-beams and improves performance.
  • the patent obtained a strength index of 420MPa, but did not greatly improve the low temperature toughness.
  • the above three 420MPa grade H-beams and their preparation technologies all adopt micro-alloying and different cooling methods.
  • the products involved are larger in size, have higher strength and at the same time ensure a certain impact toughness, and have higher requirements for cooling equipment;
  • ordinary equipment is used for rolling, and the requirements for low-temperature toughness are relatively low. Therefore, it is necessary to re-design for small and medium-sized H-beam products to improve the strength under the condition of high-temperature normalizing rolling while further improving the impact toughness.
  • H-beams unlike plate rolling, H-beams have more stringent requirements on the process because of their complex cross-sections.
  • the dephosphorization link in the steelmaking process is generally completed in a converter, but the dephosphorization rate of a single converter is low, and it is difficult to stably control the phosphorus content in molten steel below 0.01%.
  • two converters are mostly used for deep dephosphorization using a dual process, which can stably control the phosphorus content in molten steel below 0.01%.
  • Phosphorus and decarburization requires a new dephosphorization furnace, and the smelting time is more than 40 minutes longer than that of a single converter, which has the disadvantages of large equipment investment and low production efficiency.
  • Some enterprises use converter double slag method for deep dephosphorization. However, since the dephosphorization slag cannot be completely drained once in the converter, the deep dephosphorization rate cannot be guaranteed, and it is difficult to stably control the phosphorus content in molten steel below 0.01%.
  • Some enterprises use the three dephosphorization processes (desiliconization, desulfurization, and dephosphorization) in the pretreatment of molten iron for dephosphorization.
  • the dephosphorization reaction is a reaction at the slag-steel interface, the reaction equation is shown in the following formula 1, phosphorus and oxygen
  • the reaction product P 2 O 5 of the element is very unstable. P 2 O 5 can only be removed when it enters the slag and reacts with CaO to form CaO ⁇ P 2 O 5.
  • H-shaped steel In order to meet the needs of high-strength, high-low temperature ductile steel in complex environments such as the Arctic and Antarctic, a hot-rolled low-temperature resistant H-shaped steel with a yield strength of 420MPa and its preparation method were designed and invented.
  • the H-shaped steel not only meets the extremely low temperature condition
  • the invention provides a low-temperature-resistant H-shaped steel with a yield strength of 420 MPa, the chemical composition of which is: C: 0.08%-0.10%, Si ⁇ 0.2%, Mn: 1.25%-1.45%, V: 0.03%-0.045 %, Ti: 0.015% ⁇ 0.025%, Cr: 0.15% ⁇ 0.30%, A1s: 0.02% ⁇ 0.04%, N: 0.007% ⁇ 0.01%, P ⁇ 0.008%, S ⁇ 0.005%, O ⁇ 0.004%, the rest For Fe and unavoidable impurities.
  • P and S elements in the present invention satisfy P+S ⁇ 0.01%.
  • the H-shaped steel prepared by meeting the requirements of this formula can better meet the impact toughness requirements at polar temperatures.
  • the invention is especially suitable for preparing small and medium-sized H-shaped steel products with a flange thickness of less than 15mm, but is not limited to the products of the above-mentioned specifications.
  • the matrix structure of the steel is ultra-fine flaky pearlite and flat ferrite, and at the same time, certain nano-scale vanadium-containing carbides are obtained.
  • the compression ratio is relatively large, combined with factors such as equipment capacity and difficulty in controlling the final rolling temperature, so the carbon content should not be too high, and should be controlled at 0.08% to 0.10%.
  • Mn can stabilize the austenite structure, increase the hardenability of the steel, and increase the strength of the steel.
  • Mn is also an element that is easy to segregate, and it is unevenly distributed in different parts of the steel structure, resulting in large performance differences.
  • too much addition of Mn will damage the low-temperature toughness, plasticity and other mechanical performance indicators, and it is not easy to add too much. Therefore, considering comprehensively, the Mn content in the steel of the present invention is controlled to be 1.25%-1.45%.
  • Si is a deoxidizing element, which helps to improve the strength, but too high Si will form a large amount of Si-containing Fe 2 SiO 4 Si on the surface of the steel, thereby increasing the viscosity of the steel, making it difficult to remove the oxide scale and affecting the surface quality.
  • the lower limit of the content is set to 0.20% or less.
  • Phosphorus As a harmful impurity in steel, phosphorus can significantly expand the two-phase region between the liquid phase and the solid phase, and is easy to segregate at the grain boundary, making the local structure of the steel abnormal, causing the steel to be "cold and brittle", and significantly reducing the low temperature of the steel. Impact toughness and temper brittleness, resulting in uneven mechanical properties; phosphorus can also cause corrosion fatigue and welding cracking. Therefore, proper control of P content in converter smelting has a significant effect on improving the low temperature toughness of H-beams. Considering the equipment capability, P ⁇ 0.008% in the present invention.
  • Sulfur As one of the five elements that inevitably exist in steel, it causes weld cracking and toughness decline due to solidification segregation. The intermittent inclusions brought about by the preparation process seriously deteriorate the low temperature toughness of steel, so their content should be reduced as much as possible. Sulfur easily forms MnS inclusions and becomes the origin of cracks to deteriorate the workability, and the S content is preferably limited to 0.005% or less.
  • the lower limit of P and S depends on the equipment capability and cost control, both of which can exceed 0%, and P+S ⁇ 0.010%.
  • Aluminum is used as a strong deoxidizing element in the preparation process of the H-shaped steel of the present invention. In order to ensure that the oxygen content in the steel is as low as possible and reduce the probability of spherical inclusions; some aluminum can also form AlN precipitates with nitrogen in the steel, which can increase the strength of the steel. Therefore, in the present invention, the content of aluminum is controlled at 0.02%-0.04%.
  • Titanium is a strong carbide forming element. A small amount of Ti is beneficial to fix N in the steel. At the same time, the fine TiN formed can inhibit the excessive growth of austenite grains when the billet is heated, thereby refining the original austenite grains. grain purpose. Ti can also generate TiC, TiS, Ti 4 C 2 S 2 and other compounds in steel, which can also prevent the grain growth of the heat-affected zone during welding, and can also improve the welding performance of the finished H-beam. Therefore, in the present invention, 0.015% to 0.025% of Ti is selected to be added.
  • Vanadium As a strong carbonitride forming element, the carbonitrides of V form nano-scale carbonitrides in the cooling stage of the post-rolling stage to play a significant role in precipitation strengthening; VN alloys can be used as nucleation points for ferrite and pearlite structures , contribute to the grain refinement of the organization. VC also plays the role of precipitation strengthening, and at the same time, the rolling deformation resistance of vanadium-containing steel is low, which plays a role in reducing the rolling load. For the yield strength level of 420MPa, the V content is controlled at 0.03% to 0.045%.
  • Chromium Adding a certain amount of Cr to steel can improve the strength, hardness and wear resistance of steel.
  • the addition of chromium to steel can significantly improve the hardenability of steel.
  • the hardenability of Cr element is weaker than that of Mo element, and it will not form a large amount of bainite structure at a lower cooling rate to deteriorate the toughness of steel.
  • too high or too low Cr content is unfavorable to the hardenability and delayed fracture of the steel, and easily causes defects.
  • Cr is controlled between 0.15% and 0.30%.
  • N element in steel forms TiN with Ti, and forms VN with V at the same time
  • VC alloy has a precipitation strengthening effect and improves strength. If the N content is too high, it is easy to induce defects in the surface quality of the slab and produce transverse cracks. Therefore, the present invention requires a nitrogen content of 0.007% to 0.010%.
  • Oxygen Appropriately reducing the oxygen content in the steel can avoid the formation of large particles of oxide inclusions with strong oxidizing elements, thereby ensuring the improvement of the toughness and plasticity of the steel.
  • the present invention requires the nitrogen content to be ⁇ 0.004%.
  • the yield strength of the H-shaped steel is ⁇ 420MPa, the tensile strength is ⁇ 520MPa, the elongation is ⁇ 20%, and the impact energy at -50°C is ⁇ 100J.
  • the present invention also provides a method for preparing the above-mentioned H-shaped steel with a yield strength of 420 MPa.
  • the preparation method includes the following steps: molten iron pretreatment + deep dephosphorization ⁇ converter smelting ⁇ ladle blowing argon ⁇ RH/LF refining ⁇ rectangular continuous casting slab casting ⁇ Slow cooling or hot delivery and hot charging in the slow cooling pit of continuous casting slab ⁇ semi-continuous rolling of section steel wire ⁇ intensive slow cooling in cooling bed; specifically, the following steps are included:
  • the molten iron in the blast furnace flows into the first ladle.
  • the dephosphorization agent is injected into the ladle for dephosphorization.
  • the liquid level in the ladle continues to rise, and the liquid level of the molten iron exceeds
  • the upper edge of the iron opening is 20 to 30 cm, open the iron opening, and the molten iron flows into the second ladle through the iron opening, and the injection dephosphorization operation is carried out again in the second ladle, and the second ladle is facing the slag interface of the iron ladle.
  • the side of the lower 20-30cm is also provided with an iron discharge hole, and the molten iron dephosphorized on the upper part of the second ladle flows downward through the iron discharge hole into the third molten iron ladle, and then circulates through the iron discharge hole and flows downward into the Nth molten iron ladle.
  • the molten iron is dephosphorized for N times, and the phosphorus content in the molten iron is removed to below 0.02%, wherein, 4 ⁇ N ⁇ 6;
  • the first ladle to the N-1th ladle have a nominal volume of 30-50t of molten iron, a depth of 1.5-2m, and are opened at the side wall of the ladle at a distance of 50-60cm from the top of the ladle.
  • There is an iron opening and the iron opening protrudes 20-30 cm outwards, and a slide plate is used to control the switch of the iron opening, and the volume of the Nth molten iron ladle matches the tonnage of the converter project.
  • the injection point of the dephosphorizing agent includes the injection point of the blast furnace molten iron to the first ladle and the injection point of the molten iron in the upper ladle to the lower ladle, that is, the injection point of the molten iron in the first ladle to the second ladle.
  • the molten iron is stirred violently, and the kinetic conditions of dephosphorization are good.
  • the dephosphorization agent is a mixture of sludge pellets and lime, the mass ratio of sludge pellets and lime is 1:1, and the mass percentage of components in sludge pellets includes: CaO: 2-8%, Fe 2 O 3 : 85-92%, SiO 2 : 1-5%, the mass percentages of ingredients in lime include: CaO: 85-90%, Fe 2 O 3 : 0-3%, SiO 2 : 0-10 %, MgO: 0-10%, and the addition amount of the dephosphorization agent in the ladle is 2-3kg/ton of iron ladle.
  • the carrier gas when spraying the dephosphorization agent is oxygen
  • the spraying pressure is 0.2-0.3Mpa
  • the spraying flow rate is 2-4m 3 /min.
  • the position of the next ladle is 60-70cm lower than that of the previous ladle.
  • the slag changing operation is as follows: the slag in the first ladle is poured out, the slag at the top of the second ladle is poured into the first ladle, and the slag at the top of the third ladle is poured into the second ladle , until the slag at the top of the N-1 ladle is poured into the N-2 ladle;
  • the first ladle to the top of the N-1th ladle are provided with slag outlets, the slag outlets protrude outwards by 20-30 mm, and the position difference between the slag outlet and the iron outlet on the ladle wall is is a quarter of a circle;
  • the first molten iron ladle to the N-1th molten iron ladle car are all equipped with hydraulic lifting devices and rotating devices, which can lift the molten iron ladle by 1-2m, and can rotate the molten iron by 90 degrees around the central axis.
  • rolling is divided into rough rolling and finish rolling, and rough rolling adopts reciprocating rolling generally 7 times.
  • the finishing rolling adopts 5 continuous rolling passes, and the water cooling between the finishing rolling stands is fully turned on.
  • the compression ratio of the last two passes of finishing rolling is 6% to 12%; the cooling after finishing rolling is sufficient to precipitate the carbon of V
  • the nitrides exert a precipitation strengthening effect.
  • the invention realizes the industrialized production of small and medium-sized 420MPa high-strength and tough H-shaped steel products through the design of low-carbon, low-phosphorous and vanadium-added micro-alloying process, combined with profile steel pass rolling.
  • the molten iron is subjected to multi-stage injection dephosphorization treatment, and the molten iron in the ladle is subjected to injection dephosphorization treatment.
  • the ladle slag interface is 20 to 30 cm below the side of the molten iron ladle, and the molten iron with sufficient dephosphorization in the upper part of the ladle flows into the next ladle through the ladle, and spraying dephosphorization is carried out again in the next ladle operation, and the side of the lower ladle steel slag interface is 20-30cm down, and there is also an iron outlet, and the molten iron with sufficient dephosphorization on the upper part of the next ladle can continue to flow downward through the iron outlet.
  • the molten iron ladle performs 4-6 dephosphorization operations on the molten iron in such a cycle.
  • the following will introduce the dephosphorization process of the molten iron by taking the 4 dephosphorization of the molten iron as an example. Since the slag in the upper level ladle cannot flow into the lower level ladle, only the molten iron will flow into the lower level ladle, and the phosphorus and slag in the lower level ladle will have a dephosphorization equilibrium reaction again, and the molten iron The phosphorus element is further removed, and after multiple dephosphorization treatments, the phosphorus element in the molten iron will be removed to an extremely low value.
  • Step 1) During the tapping process of the blast furnace, the molten iron in the blast furnace flows into the first ladle.
  • the nominal volume of the first ladle is 30-50t of molten iron, and the depth is 1.5-2m.
  • the iron discharge port When the molten iron level is 20-30cm higher than the upper edge of the iron discharge port, the iron discharge port is opened, and the molten iron flows into the second ladle through the iron discharge port.
  • the flow rate of the first ladle is the same, the liquid level of the molten iron is in a stable state of neither rising nor falling, the dephosphorization reaction continues at the steel slag interface of the first ladle, and the phosphorus content in the molten iron near the steel slag interface is continuously removed.
  • the molten iron with sufficient dephosphorization on the upper part of the ladle flows into the second ladle through the iron opening.
  • the position of the second molten iron ladle is 60-70cm lower than that of the first molten iron ladle, and the molten iron flows into the second molten iron ladle from the first molten iron ladle through the iron opening under the action of gravity.
  • Step 2) The ladle size parameters and dephosphorization process parameters of the second ladle, the third ladle, and the fourth ladle are exactly the same as those of the first ladle, and spraying is carried out in the second, third, and fourth ladles. Dephosphorization operation.
  • the molten iron with sufficient dephosphorization near the steel slag interface in the second ladle flows into the third ladle through the iron discharge hole under the action of gravity, and the molten iron with relatively sufficient dephosphorization near the steel slag interface in the third ladle passes through the iron discharge hole under the action of gravity Flow into the fourth ladle.
  • the molten iron with sufficient dephosphorization near the slag interface of the fourth ladle flows into the fifth ladle under the action of gravity through the iron opening.
  • the positions of the third ladle, the fourth ladle and the fifth ladle are 60-70cm lower than the positions of the second ladle, the third ladle and the fourth ladle respectively.
  • the fifth ladle is a large-volume ladle.
  • the volume of the fifth ladle matches the tonnage of the converter project.
  • the molten iron in the fifth ladle is transported to the KR station for desulfurization. After desulfurization, it is transported to the converter for normal smelting.
  • the phosphorus content at the end of smelting is controlled below 0.007%.
  • the first to fourth ladles are all subjected to a slag change operation.
  • the slag change process is that the slag in the first ladle is poured out, and the slag at the top of the second ladle is poured out. Pour into the first ladle, the slag from the top of the third ladle is poured into the second ladle, and the slag from the top of the fourth ladle is poured into the third ladle. Due to the multi-stage dephosphorization process, the next level of molten iron The phosphorus content in the ladle is lower than that of the upper ladle.
  • the distribution ratio of phosphorus in the iron slag is basically unchanged, that is, the phosphorus content in the slag of the next ladle will also be lower Therefore, after pouring the slag from the top of the lower ladle into the upper ladle, the slag can still exert a good dephosphorization effect.
  • the slag outlets are slag outlets on the top of the first to fourth ladles, and the slag outlets protrude outward by 20-30 mm, and the slag in the ladle can flow out through the slag outlets.
  • the position difference of the molten iron ladle wall is a quarter of a circle.
  • the first to fourth ladle cars are equipped with hydraulic lifting devices and rotating devices, which can lift the ladle by 1-2m and rotate the molten iron by 90 degrees around the central axis.
  • the rotating device on the ladle car when performing the slag change operation, first close the iron outlet, and then use the rotating device on the ladle car to rotate the upper-level molten iron ladle and the lower-level molten iron wrap around the central axis by 90 degrees to avoid touching the steel ladle when it is lifted. Put the iron hole, and then use the hydraulic lifting device to lower the upper ladle and raise the lower ladle until the lower ladle is higher than the upper ladle, and the slag in the lower ladle can be passed through When the slag mouth flows into the upper ladle, the slag outlet is opened, and the slag flows from the lower ladle into the upper ladle, and the slag outlet is closed after the slag flows completely.
  • the present invention combines the characteristics of thin flanges of small and medium-sized H-beams in rectangular billet rolling, adopts the design of low C content suitable for normalizing rolling and V microalloying components, and adds an appropriate amount of Cr element to control the cooling rate and avoid the occurrence of Wei's body and other abnormal structures, and deteriorate the low temperature impact toughness of steel. Therefore, a stable and controlled high-strength and tough hot-rolled H-beam above the 420MPa level can be obtained on the hot-rolled H-beam rolling mill.
  • the present invention adopts a low-phosphorus smelting process to control the P content below 0.008%, and at the same time, the P+S content is below 0.011%, which is conducive to improving the low-temperature toughness of the steel and maintaining a high level under the condition of -50°C.
  • the matrix structure of the H-shaped steel of the present invention is refined pearlite + proeutectoid ferrite, and the second phase particles are mainly V(C, N), which has better structure stability and is easier to obtain.
  • the present invention achieves fine-grain strengthening and precipitation strengthening through the refinement of the matrix structure, and achieves the good effect of obtaining 420MPa for H-shaped steel and obtaining low-temperature impact toughness greater than 100J under the condition of -50°C.
  • the molten iron is sprayed and dephosphorized four to six times through four to six small ladles.
  • the dephosphorization operation is a continuous operation with high production efficiency, and the total dephosphorization time is
  • the turnover time of molten iron in these four to six small iron ladles is only 20 to 30 minutes, which is much lower than the three dephosphorization treatment time, and the dephosphorization efficiency is high.
  • the iron outlet in the small ladle of the present invention is located near the interface of the steel slag in the ladle.
  • the dynamic conditions for dephosphorization at this position are good, and the dephosphorization reaction at the slag-steel interface is relatively sufficient, so the fully dephosphorized molten iron will flow into the next step.
  • Level iron ladle, the molten iron that has not undergone dephosphorization reaction at the bottom of the ladle rises to the slag-steel interface and continues to undergo dephosphorization reaction. This dephosphorization method has high dephosphorization efficiency.
  • the phosphorus enrichment amount of the slag in the next-level ladle of the present invention is lower than that of the slag in the upper-level ladle, so the molten iron flowing into the next-level ladle can continue to undergo dephosphorization reaction with the slag, which is equivalent to
  • the phosphorus content in the hot metal can be removed to less than 0.02%, and the dephosphorization rate of the hot metal is high, which is conducive to the stable production of low-phosphorus steel.
  • the phosphorus enrichment amount of the lower ladle slag of the present invention is lower than that of the upper ladle slag, so after the slag of the lower ladle flows into the upper ladle, it can still play a role in desorption.
  • the phosphorus effect is equivalent to the recycling of dephosphorization slag, which saves the consumption of dephosphorization materials and reduces the cost of dephosphorization.
  • Fig. 1 is the metallographic structure diagram ( ⁇ 200) of the yield strength 420MPa level high toughness low temperature resistant H-shaped steel prepared by embodiment 2 of the present invention
  • Fig. 2 is the multistage dephosphorization schematic diagram described in the application
  • Fig. 3 is a structural schematic diagram of a small ladle
  • Fig. 4 is a side view schematic diagram of a small ladle structure
  • the continuous casting slabs in the following examples are all prepared according to the following process flow: according to the set chemical composition range (Table 1), using blast furnace molten iron as raw material, through dephosphorization, KR dephosphorization and converter smelting in the blast furnace tapping process , Refining, adjust the content of C, Si, Mn, S, P, etc. and carry out microalloying. After the composition reaches the target value, carry out continuous casting, direct heating or soaking of the cast slab.
  • Table 1 set chemical composition range
  • section steel rolling includes two-stage rolling of rough rolling and finishing rolling.
  • the hot rolling process is mainly based on temperature control.
  • the final rolling temperature is detected on the outside of the flange, and the rolled material is naturally cooled in the cooling bed after rolling.
  • Table 1 The chemical composition and specific process of Examples 1-4 are shown in Table 1 below.
  • Example 1 0.08 0.15 1.30 0.007 0.002 0.28 0.03 0.015 0.025 0.008
  • Example 2 0.09 0.20 1.45 0.006 0.003 0.30 0.03 0.025 0.026 0.009
  • Example 3 0.08 0.20 1.28 0.006 0.004 0.25 0.04 0.018 0.03 0.008
  • Example 4 0.10 0.15 1.39 0.005 0.003 0.30 0.035 0.019 0.033 0.01
  • the specific dephosphorization process in blast furnace tapping process is:
  • Step 1 During the tapping process of the blast furnace, the molten iron in the blast furnace flows into the first ladle.
  • the nominal volume of the first ladle is 30t of molten iron, and the depth is 1.5m. Put the iron hole, the iron hole protrudes 20cm outward, and use the slide plate to control the switch of the iron hole.
  • dephosphorization is carried out by spraying dephosphorization agent in the ladle.
  • the molten iron level exceeds 20cm from the upper edge of the iron hole, the iron hole is opened, and the molten iron flows into the second ladle through the iron hole.
  • the flow rate of the ladle is the same, the molten iron level is in a stable state of neither rising nor falling, the dephosphorization reaction continues at the steel slag interface of the first ladle, and the phosphorus content in the molten iron near the steel slag interface is continuously removed, and the first ladle The molten iron with sufficient dephosphorization in the upper part flows into the second ladle through the iron outlet, as shown in Figure 2-4.
  • the injection point of the dephosphorizing agent includes the injection point of the blast furnace molten iron to the first ladle and the injection point of the molten iron in the upper ladle to the lower ladle, where the molten iron is stirred violently, and the dephosphorization kinetic conditions it is good.
  • the dephosphorization agent is a mixture of sludge pellets and lime, the amount of dephosphorization agent added in the first ladle is 2kg/ton of iron ladle, the mass ratio of sludge pellets to lime is 1:1, and the sludge pellets
  • the mass percentage of the ingredients in the lime is: CaO: 5%, Fe 2 O 3 : 88%, SiO 2 : 3%, and the rest is impurities.
  • the mass percentage of the ingredients in the lime is: CaO: 90%, Fe 2 O 3 : 1%, SiO 2 : 3%, MgO: 5%, and the balance is impurities.
  • the carrier gas when spraying the dephosphorization agent is oxygen, the injection pressure is 0.2Mpa, and the injection flow rate is 2m 3 /min.
  • Described second molten iron ladle is 60cm lower than the position of the first molten iron ladle, and molten iron flows into the second molten iron ladle from the first molten iron ladle by putting iron hole under the effect of gravity.
  • Step 2 the ladle size parameters of the second ladle, the third ladle, and the fourth ladle, and the dephosphorization process parameters are exactly the same as those of the first ladle, and spraying is carried out in the second, third, and fourth ladles. Dephosphorization operation.
  • the molten iron with sufficient dephosphorization near the steel slag interface in the second ladle flows into the third ladle through the iron discharge hole under the action of gravity, and the molten iron with relatively sufficient dephosphorization near the steel slag interface in the third ladle passes through the iron discharge hole under the action of gravity Flow into the fourth ladle.
  • the fully dephosphorized molten iron near the steel slag interface of the fourth ladle flows into the fifth ladle under the action of gravity through the tap hole.
  • the positions of the third ladle, the fourth ladle and the fifth ladle are 60cm lower than the positions of the second ladle, the third ladle and the fourth ladle respectively.
  • composition and temperature of the molten iron are detected, and the dephosphorization rate and temperature of the molten iron in the four small ladles are as follows:
  • the fifth ladle is a large-volume ladle.
  • the volume of the fifth ladle matches the tonnage of the converter project.
  • the molten iron in the fifth ladle is transported to the KR station for desulfurization. After desulfurization, it is transported to the converter for normal smelting.
  • the phosphorus content at the end of smelting is controlled below 0.007%.
  • the first to fourth ladles are all subjected to a slag replacement operation.
  • the slag replacement process is that the slag in the first ladle is poured out, and the slag on the top of the second ladle is poured into the second ladle.
  • One ladle, the slag at the top of the third ladle is poured into the second ladle, and the slag at the top of the fourth ladle is poured into the third ladle. Due to the multi-stage dephosphorization process, the slag in the next ladle The phosphorus content is lower than that of the upper ladle.
  • the distribution ratio of phosphorus in slag and iron is basically unchanged, that is to say, the phosphorus content in the lower ladle slag will also be lower than that of the previous one.
  • grade steel ladle the composition of ladle slag is detected, the composition of slag in four small ladles is as follows
  • the blast furnace slag 1st ladle 2nd ladle 3rd ladle 4th ladle CaO(%) 41 37 43 45 45 SiO 2 (%) 35 31 30 29 31 Al 2 O 3 (%) 14 11 7 5 5 MgO(%) 6 5 5 6 5
  • the slag outlets are on the top of the first to fourth ladles, and the slag outlets protrude outward by 20mm.
  • the slag in the ladle can flow out through the slag outlets.
  • the slag outlets and iron outlets are located on the wall of the ladle The difference is a quarter of a circle.
  • the first ladle to the fourth ladle car are equipped with hydraulic lifting devices and rotating devices, which can lift the ladle by 1.5m and rotate the molten iron around the central axis by 90 degrees.
  • the hydraulic lifting device to lower the upper-level ladle and raise the lower-level ladle until the lower-level ladle is higher than the upper-level ladle, and the slag in the lower-level ladle can flow into it through the slag discharge port
  • the slag outlet is opened, and the slag flows from the lower ladle into the upper ladle, and the slag outlet is closed after the slag flows out.
  • the hot rolling process conditions of Examples 1-4 are shown in Table 2.
  • the test method of yield strength, tensile strength and elongation refers to the standard ISO6892-1-2009 “Metal material room temperature tensile test method”
  • the impact energy test method refers to the standard ISO 148-1 "Charpy Pendulum Impact Test of Metal Materials", and the results are shown in Table 3.
  • the yield strength of Examples 1-4 of the present invention remains at the level of 440 MPa, has good elongation performance, and has a relatively high impact energy at -50°C. It can meet the use conditions of the preparation of marine engineering components in extremely low environments, and is suitable for the production of support structures with high low temperature toughness requirements such as offshore oil platforms and ocean-going transportation ships.
  • the structure of the present application is granular bainite + ferrite structure.
  • the reduction of P content can meet the strength and improve the toughness, especially the low temperature toughness.
  • the conventional technical knowledge in this field can be used for the contents not described in detail in the present invention.

Abstract

一种420MPa级热轧耐低温H型钢及其制备方法，所述H型钢化学成分组成按重量百分比为：C：0.08％～0.10％，Si≤0.2％，Mn：1.25％～1.45％，V：0.03％～0.045％，Ti：0.015％～0.025％，Cr：0.15％～0.30％，A1s：0.02％～0.04％，N：0.007％～0.01％，P≤0.008％，S≤0.005％，O≤0.004％，其余为Fe和不可避免杂质。所述制备方法结合矩形坯轧制中小规格H型钢翼缘薄的特点，采用适合正火轧制的低C含量配合V微合金化成分设计，添加适量的Cr元素控制冷却速度，避免出现魏氏体等异常组织，恶化钢的低温冲击韧性，从而在热轧H型钢轧机上得到稳定控制的420MPa级别以上高强韧性热轧H型钢。

Description

一种屈服强度420MPa级热轧耐低温H型钢及其制备方法
相关申请的交叉参考
该申请要求2021年7月20日提交的中国专利申请号为202110818559.5的专利申请的优先权，该专利申请在此被完全引入作为参考。
技术领域
本发明属于冶金技术领域，具体地，本发明涉及一种420MPa级热轧耐低温H型钢及其制备方法。
背景技术
随着能源开采向极寒等复杂区域发展，迫切需要综合性能更高的热轧H型钢替代目前低级别H型钢，在减轻重量的同时，保证具有较高的可靠性。同时为适应极寒等复杂地区服役环境，对钢材的低温冲击韧性，焊接性能，抗层状撕裂性能等提出了更高的要求，更高强度级别的热轧H钢需求逐渐增加。
目前我国的热轧H型钢生产企业已陆续开发出屈服强度345MPa以上不同级别的H型钢，一般采用复合微合金化配合热轧方法生产。不同企业根据装备水平制备出不同级别和不同综合性能的产品。
专利申请CN201510498771.2中中公开了一种420MPa级优异低温韧性热轧H型钢及其生产方法，成分：C 0.06～0.12％、Si 0.20～0.40％、Mn 1.20～1.60％、P≤0.015％、S≤0.010％、V 0.050～0.070％、Ni 0.10～0.20％、N 0.0050～0.0100％，其余为Fe及不可避免的杂质。与现有技术相比，该专利通过合理的V、Ni、N成分设计，匹配相适应的控轧控冷工艺，开发出了综合性能优异的420MPa热轧H型钢；屈服强度ReH为440～520MPa；抗拉强度Rm为550～650MPa，延伸率A为A≥22％，-40℃低温冲击韧性KV2≥100J。该专利控制冷却采用两段式，第一阶段快速冷却+第二阶段空冷，需要特殊冷却装置满足上述制备要求。所生产的420MPa级优异低温韧性热轧H型钢厚度方向性能Z为40～65％，是针对异型坯大规格产品进行的工艺设计，不适合中小规格薄翼缘H型钢产品制备。
专利申请CN201510788520.8中公开了一种420MPa级高强度低屈强比H型钢及其制备方法，所述H型钢的化学成分按重量百分数计为：C 0.11～0.15％、Si 0.20～0.35％、Mn 1.35～1.50％、P≤0.035％、S≤0.025％，Cu 0.25-0.30％，Cr 0.40-0.45，Ni 0.20-0.30％，Nb 0.20-0.30％，其余为铁和微量杂质。该专利通过优化成分设计实现了生产420MPa级低屈强比H型钢， 屈服强度大于427MPa，抗拉强度大于641MPa，屈强比0.64～0.67。该专利添加了Ni，Nb，Cu等元素，针对特定高耐蚀环境下使用；制备过程受到Cu元素的影响，在高终轧温度条件下H型钢腿部产生裂纹的几率提高，同时显著增加了制备成本。
专利申请CN201510498771.2中公开了一种420MPa级高性能抗震H型钢及其制备方法，包含下列重量百分比：C：0.15～0.18wt％，Si：0.30～0.45wt％，Mn：1.35～1.55wt％，V：0.070～0.090wt％，P：≤0.015wt％，S：≤0.020wt％，其余为Fe及不可避免的不纯物。制备方法钢水冶炼、脱氧合金化、钢水LF炉精炼、钢水浇铸、后处理步骤。该专利冶炼采用富氮钒微合金化工艺，有效细化奥氏体晶粒，冶炼时的增加氮含量，有利于形成钒的碳氮化物使其弥散分布于晶界处，促进奥氏体晶粒形核进一步细化奥氏体晶粒，经轧制、控冷、快速冷却等工艺，确保H型钢优良的外形及表面质量及提高性能。该专利获得强度指标达到420MPa，但是没有大幅度提升低温韧性。
上述三种420MPa级别H型钢及制备技术均采用微合金化配合不同冷却方式，涉及到的产品一方面规格较大，具有较高强度且同时保证一定的冲击韧性，对于冷却设备要求较高；另一方面采用普通设备轧制，低温韧性要求较低。因此，针对中小规格H型钢产品采用高温正火轧制条件下强度提升的同时进一步提高冲击韧性需要重新进行设计。另外，与板材轧制不同，H型钢因为具有复杂截面对工艺的要求更加苛刻。
目前炼钢流程中的脱磷环节普遍放在转炉中完成，但单转炉的脱磷率较低，很难稳定的将钢水中磷含量控制在0.01％以下，为提高脱磷率，目前公开的现有技术中多是采用两个转炉使用双联工艺来深脱磷，可稳定的将钢水中磷含量控制在0.01％以下，但由于双联工艺需要使用脱磷转炉和脱碳转炉分别进行脱磷和脱碳，需新建脱磷炉，且比单转炉的冶炼时间长40min以上，具有设备投资大、生产效率低的缺点。有部分企业采用转炉双渣法来深脱磷，但由于转炉一次脱磷渣无法完全倒净，深脱磷率无法保证，很难稳定的将钢水中磷含量控制在0.01％以下。
有部分企业采用铁水预处理中的三脱工艺(脱硅、脱硫、脱磷)来进行脱磷，但由于脱磷反应为渣钢界面的反应，反应方程式如下式①所示，磷元素和氧元素的反应生成物P 2O 5很不稳定，P 2O 5只有进入炉渣中与CaO反应生成CaO·P 2O 5才能除掉，只有与钢渣接触的钢水才能发生脱磷反应(铁水包中下部的钢水几乎不发生脱磷反应)，因此只有通过长时间的搅拌来促进钢渣与钢水的接触才能把铁水中P脱至要求范围(铁水中P含量0.03％以下)，铁水预处理效率低，整个三脱过程需进行150～200min，生产效率低且铁水温降大，给钢铁企业的效益带来严重不良影响，国内钢铁企业采用三脱进行铁水预处理的也越来越少。因此，需改进脱磷工艺，实现降低磷含量的目的，达到提升低温韧性的效果。
2[P]+5[O]+4(CaO)＝(4CaO·P 2O 5)①
发明内容
为了满足北极南极等极地高寒区域等复杂环境下高强、高低温韧性型钢的需求，设计发明一种屈服强度达到420MPa级热轧耐低温H型钢及其制备方法，该H型钢不仅满足极低温度条件陆地及海洋地区石油平台建设等建筑结构用钢需求，同时具有低成本制备优势，实现了建筑结构轻量化，为钢结构建筑提供便利。
本发明的技术方案如下：
本发明提供一种屈服强度420MPa级耐低温H型钢，其化学成分组成按重量百分比为：C：0.08％～0.10％，Si≤0.2％，Mn：1.25％～1.45％，V：0.03％～0.045％，Ti：0.015％～0.025％，Cr：0.15％～0.30％，A1s：0.02％～0.04％，N：0.007％～0.01％，P≤0.008％，S≤0.005％，O≤0.004％，其余为Fe和不可避免杂质。
作为优选的，本发明中P，S元素，满足P+S≤0.01％。满足该公式要求制备出的H型钢，可以更好的满足极地温度下冲击韧性要求。该发明尤其适合制备翼缘厚度15mm以下中小规格H型钢产品，但不仅限于上述规格产品。
本发明所述的高强度热轧H型钢中各化学元素设计原理如下：
碳：为获得热轧H型钢420MPa强度级别同时满足耐低温性能要求，钢的基体组织为超细片状珠光体和扁平状铁素体，同时获得一定的纳米级含钒碳化物。对于规格较小的H型钢压缩比较大，结合设备能力及终轧温度控制难度大等因素，因此碳的含量不能太高，控制在0.08％～0.10％。
锰：在热轧态钢中，Mn能够稳定奥氏体组织，增加钢的淬透性，提高钢的强度。同时Mn也是容易偏析元素，在钢的组织的不同部位分布不均匀，造成性能差异较大。为了保证强度优选将Mn含量设定为1.25％以上。同时为了控制裂纹敏感性，Mn添加过多损害低温韧性、塑性等力学性能指标也不易过多添加。因此，综合考虑，本发明钢中控制Mn含量1.25％～1.45％。
硅：Si是脱氧元素，有助于强度的提高，但是过高的Si将在钢的表面形成大量含Si的Fe 2SiO 4Si从而增加钢的粘度，造成氧化铁皮不易去除，影响表面质量。含量的下限设定为0.20％以下。
磷：磷作为钢中有害杂质，磷能显著扩大液相和固相之间的两相区，容易在晶界偏析，使钢的局部组织异常，造成钢材“冷脆”，显著降低钢材的低温冲击韧性及回火脆性，造成机械性能不均匀；磷还会引起腐蚀疲劳和焊接开裂。因此，转炉冶炼中适当控制P含量，对 于提高H型钢的耐低温韧性作用显著。考虑到设备能力本发明中P≤0.008％。
硫：作为钢中不可避免存在的五大元素之一，因凝固偏析而引起焊接开裂、韧性下降。制备过程带来的断续存在的夹杂物严重恶化钢的低温韧性，因此应该尽量减少其的含量。硫容易形成MnS夹杂，成为裂纹的起点而使加工性能恶化，S含量优选被限制为0.005％以下。P、S的下限值取决于设备能力和成本控制，均超过0％即可，P+S≤0.010％。
铝：Al在本发明H型钢的制备过程中作为强脱氧元素使用。为了保证钢中的氧含量尽可能地低，降低球形夹杂物产生几率；部分铝还可以和钢中的氮元素能形成AlN析出物，其能提高钢的强度。所以，在本发明中将铝的含量控制在0.02％～0.04％。
钛：Ti是强碳化物形成元素，微量Ti有利于固定钢中的N，同时形成的细小TiN能使钢坯加热时抑制奥氏体晶粒过分长大，从而起到细化原始奥氏体晶粒的目的。Ti在钢中还能生成TiC、TiS、Ti 4C 2S 2等化合物，在焊接时还可阻止热影响区晶粒长大，也能起到改善成品H型钢的焊接性能。因此，本发明中选择添加0.015％～0.025％的Ti。
钒：作为强碳氮化物形成元素，V的碳氮化物在轧制后期冷却阶段形成纳米级别碳氮化物起到显著的沉淀强化作用；VN合金可以作为铁素体和珠光体组织的形核质点，有助于组织的晶粒细化。VC也起到沉淀强化作用，同时含钒钢的轧制变形抗力低，起到降低轧制负荷的作用。对于屈服强度420MPa级别，V含量控制在0.03％～0.045％。
铬：钢中添加一定Cr可提高钢的强度和硬度以及耐磨性。铬加入钢中能显著提高钢的淬透性。实验证明，与Mo元素相比Cr元素淬透性弱一些，不至于在较低冷速下形成大量的贝氏体组织从而恶化钢的韧性。同时Cr含量太高或者太低对钢的淬透性、延迟断裂性不利，容易引起缺陷。考虑到避免异常组织的形成Cr控制在0.15％～0.30％之间。
氮：钢中的N元素，与Ti形成TiN，同时与V一起形成VN，VC合金起到沉淀强化效果，提高强度。N含量太高，容易诱发铸坯表面质量缺陷，产生横裂纹等，因此，本发明要求氮含量0.007％～0.010％。
氧：适当降低钢中的氧含量，可以避免与强氧化元素形成大颗粒的氧化物夹杂，从而保证钢的韧性和塑性提升，本发明要求氮含量≤0.004％。
所述H型钢屈服强度≥420MPa，抗拉强度≥520MPa，延伸率≥20％，-50℃冲击功≥100J。
本发明还提供了上述屈服强度420MPa级H型钢的制备方法，所述制备方法包括以下步骤：铁水预处理+深脱磷→转炉冶炼→钢包吹氩→RH/LF精炼→矩形连铸坯浇铸→连铸坯缓冷坑进行缓冷或者热送热装→型钢线半连续轧制→冷床密集缓冷；具体包括以下步骤：
1)铁水预处理、多次脱磷：
在高炉出铁过程中，高炉中铁水流入第一铁水包，随着高炉中铁水的持续注入，对铁水 包中喷吹脱磷剂进行脱磷，铁水包中液位不断上升，铁水液位超过放铁口上沿20～30cm时，开启放铁口，铁水经放铁口流入第二铁水包，在第二铁水包内再次进行喷吹脱磷操作，且第二铁水包在铁水包钢渣界面向下20～30cm处的侧面也开设有放铁口，第二铁水包上部脱磷的铁水通过放铁口向下流入第三铁水包，如此循环通过放铁口向下流入第N铁水包，对铁水进行N次脱磷操作，将铁水中磷含量脱至0.02％以下，其中，4≤N≤6；
每脱磷30到40min后，第一铁水包至第N-1铁水包都进行一次换渣操作；
2)转炉冶炼：终点磷含量控制在0.007％以下；
3)钢包吹氩、RH/LF精炼、矩形连铸坯浇铸、连铸坯缓冷坑进行缓冷或者热送热装、型钢线半连续轧制、冷床密集缓冷；其中，在轧制过程中，加热炉均热温度为1210～1250℃，铸坯在炉时间为140～180min；精轧开轧温度为1000～1050℃，精轧终轧温度为890～930℃。
优选的，所述步骤1)中第一铁水包至第N-1铁水包公称容积为30～50t铁水，深度为1.5～2m，在距离铁水包顶部50～60cm处的铁水包侧壁处开有放铁口，放铁口向外伸出20～30cm，采用滑板控制放铁口的开关，所述第N铁水包的容积与转炉工程吨位相匹配。
优选的，所述脱磷剂喷吹点包括高炉铁水向第一铁水包的注入点和上一级铁水包中铁水向下一级铁水包的注入点，即第一铁水包中铁水向第二铁水包的注入点、第二铁水包中铁水向第三铁水包的注入点，以此类推，第N-2铁水包中铁水向第N-1铁水包的注入点。此位置处铁液搅拌剧烈，脱磷动力学条件好。
优选的，所述脱磷剂为污泥球和石灰的混合物，污泥球和石灰的质量比为1:1，污泥球中成份的质量百分含量包括：CaO:2～8％，Fe 2O 3:85～92％，SiO 2:1～5％，石灰中成份的质量百分含量包括：CaO:85～90％，Fe 2O 3:0～3％，SiO 2:0～10％，MgO:0～10％，所述铁水包中脱磷剂的加入量为2～3kg/吨铁·铁水包。
作为优选，所述喷吹脱磷剂时的载气为氧气，喷吹压力为0.2～0.3Mpa，喷吹流量为2～4m 3/min。
优选的，所述铁水包中，下一个铁水包比上一个铁水包的位置低60-70cm。
优选的，所述换渣操作为：第一铁水包中的炉渣被倒出，第二铁水包顶部的炉渣被倒入第一铁水包，第三铁水包顶部的炉渣被倒入第二铁水包，直至第N-1铁水包顶部的炉渣被倒入第N-2铁水包；
优选的，所述第一铁水包至第N-1铁水包顶部均开有放渣口，放渣口向外伸出20～30mm，放渣口和放铁口在铁水包包壁的位置差为四分之一圆周；
第一铁水包至第N-1铁水包包车中均配置有液压升降装置和旋转装置，将铁水包升降1～2m，并可将铁水包绕中轴线旋转90度。在轧制过程中，轧制分为粗轧和精轧，粗轧采 用往复轧制一般为7道次。精轧采用连续轧制5道次，精轧机架间水冷全部开启，为保证终轧温度控制，精轧最后两道次压缩比为6％～12％；精轧后冷却充分利于析出V的碳氮化物发挥沉淀强化作用。
本发明通过低碳低磷加钒微合金化工艺设计，结合型钢孔型轧制，实现中小规格420MPa级别高强韧H型钢产品的工业化生产。
脱磷工艺：
在高炉出铁过程中对铁水进行多级喷吹脱磷处理，对铁水包内铁水进行喷吹脱磷处理，利用钢渣界面处的铁水脱磷动力学条件好、脱磷较充分的特点，在铁水包钢渣界面向下20～30cm处的侧面开设放铁口，铁水包上部脱磷较充分的铁水通过该放铁口流入下一级铁水包，在下一级铁水包内再次进行喷吹脱磷操作，且下一级铁水包钢渣界面向下20～30cm处的侧面也开设有放铁口，下一级铁水包上部脱磷较充分的铁水能继续通过放铁口向下流入更下一级铁水包，如此循环对铁水进行4-6次脱磷操作，以下具体以对铁水进行4次脱磷为例来介绍铁水脱磷工艺。由于上一级铁水包中的炉渣无法流入下一级铁水包中，只有铁水会流入下一级铁水包中，在下一级铁水包铁水中的磷与炉渣会再次发生脱磷平衡反应，铁水中磷元素进一步被脱除，经过多次脱磷处理后，铁水中磷元素会被脱至极低值。
该脱磷方法的具体实施工艺为：
步骤1)在高炉出铁过程中，高炉中铁水流入第一铁水包，第一铁水包的公称容积为30～50t铁水，深度为1.5～2m，在距离铁水包顶部50～60cm处的铁水包侧壁处开有放铁口，放铁口向外伸出20～30cm，采用滑板控制放铁口的开关。随着高炉中铁水的持续注入，第一铁水包中铁水容积达到50％以上时，对铁水包中喷吹脱磷剂进行脱磷，此时放铁口为关闭状态，铁水包中液位不断上升，铁水液位超过放铁口上沿20～30cm时，开启放铁口，铁水经放铁口流入第二铁水包，铁水由第一铁水包流入第二铁水包的流量速度与高炉铁水流入第一铁水包的流量速度相同，铁水液位处于不升不降的稳定状态，第一铁水包钢渣界面处持续的进行脱磷反应，钢渣界面附近处铁水中的磷含量被持续脱除，第一铁水包上部脱磷较充分的铁水通过放铁口流入第二铁水包。
所述第二铁水包比第一铁水包的位置低60-70cm，铁水在重力的作用下由第一铁水包由放铁口流入第二铁水包。
步骤2)第二铁水包、第三铁水包、第四铁水包的铁水包尺寸参数、脱磷工艺参数与第一铁水包完全相同，在第二、第三、第四铁水包内均进行喷吹脱磷操作。
第二铁水包钢渣界面附近处脱磷较充分的铁水通过放铁口在重力作用下流入第三铁水包，第三铁水包钢渣界面附近处脱磷较充分的铁水通过放铁口在重力作用下流入第四铁水包。第四铁水包钢渣界面附近处脱磷较充分的铁水通过放铁口在重力作用下流入第五铁水 包。
第三铁水包、第四铁水包、第五铁水包分别比第二铁水包、第三铁水包、第四铁水包的位置低60-70cm。
第五铁水包为大体积铁水包，第五铁水包的容积与转炉工程吨位相匹配，第五铁水包内的铁水被运入KR工位脱硫，脱硫完毕后运入转炉进行正常的冶炼，转炉冶炼终点磷含量控制在0.007％以下。
优选的，每正常脱磷30到40min后，第一至第四铁水包都进行一次换渣操作，其换渣工艺为第一铁水包中的炉渣被倒出，第二铁水包顶部的炉渣被倒入第一铁水包，第三铁水包顶部的炉渣被倒入第二铁水包，第四铁水包顶部的炉渣被倒入第三铁水包，由于采用了多级脱磷工艺，下一级铁水包中的磷含量都低于上一级铁水包，在充分脱磷的工艺条件下，磷在渣铁中的分配比基本不变，也即是下一级钢包渣中的磷含量也会低于上一级钢包，因此将下一级铁水包顶部的炉渣倒入上一级铁水包中后，炉渣仍能发挥较好的脱磷效果。
优先的，第一至第四铁水包顶部均开有放渣口，放渣口向外伸出20～30mm，铁水包内的炉渣可通过该放渣口流出，放渣口和放铁口在铁水包包壁的位置差为四分之一圆周。
优选的，第一至第四铁水包包车中均配置有液压升降装置和旋转装置，可将铁水包升降1～2m，并可将铁水包绕中轴线旋转90度。
优选的，进行换渣操作时，先关闭放铁口，然后利用铁水包车上的旋转装置使上一级铁水包和下一级铁水包绕中轴线旋转90度，以避免钢包升降时碰触到放铁口，然后使用液压升降装置使上一级铁水包降低、下一级铁水包上升，等下一级铁水包高于上一级铁水包，且下一级铁水包内的炉渣可通过放渣口流入上一级铁水包时，开启放渣口，炉渣由下一级铁水包流入上一级铁水包，待炉渣流净后，关闭放渣口。
本发明未提及的工序，均可采用现有技术。
本发明技术方案的优点在于：
1、本发明结合矩形坯轧制中小规格H型钢翼缘薄的特点，采用适合正火轧制的低C含量配合V微合金化成分设计，添加适量的Cr元素控制冷却速度，避免出现魏氏体等异常组织，恶化钢的低温冲击韧性。从而在热轧H型钢轧机上得到稳定控制的420MPa级别以上高强韧性热轧H型钢。
2、本发明采用低磷冶炼工艺，控制P含量在0.008％以下，同时P+S含量低于0.011％以下水平，有利于提高钢的耐低温韧性在-50℃条件下仍旧保持较高水平。
3、本发明H型钢基体组织为细化珠光体+先共析铁素体，第二相粒子主要是V(C，N)，组织稳定性更好，更加容易获得。
4、本发明通过基体组织细化实现细晶强化，沉淀强化，实现H型钢获得420MPa基础 上获得-50℃条件下低温冲击韧性大于100J的良好效果。
5、本发明在高炉出铁过程中，通过四-六个小型铁水包对铁水进行四-六次喷吹脱磷操作，该脱磷操作为连续式操作，生产效率高，脱磷总时间为铁水在这四-六个小铁水包内的流动周转时间，仅需20～30min，远低于三脱处理时间，脱磷效率高。
6、本发明小型铁水包中的放铁口位于铁水包钢渣界面附件，此位置处的脱磷动力学条件好，渣钢界面脱磷反应较充分，因此脱磷较充分的铁水会流入下一级铁水包，铁水包底部未发生脱磷反应的铁水上升至渣钢界面附件继续发生脱磷反应，此种脱磷方式的脱磷效率高。
7、本发明下一级铁水包中炉渣的磷富集量低于上一级铁水包中炉渣的磷富集量，因此流入下一级铁水包的铁水能继续与炉渣发生脱磷反应，相当于进行了换渣式脱磷操作，经过四-六次换渣式脱磷操作后，能将铁水中磷含量脱至0.02％以下，铁水脱磷率高，有利于低磷钢的稳定生产。
8、本发明下一级铁水包炉渣的磷富集量低于上一级铁水包炉渣的磷富集量，因此将下一级铁水包的炉渣流入上一级铁水包后，仍能发挥脱磷效果，相当于进行了脱磷渣的循环利用，节省了脱磷物料消耗，降低了脱磷成本。
附图说明
图1是本发明中实施例2制备的屈服强度420MPa级高韧性耐低温H型钢的金相组织图(×200)；
图2是本申请所述的多级脱磷示意图；
图3为小型铁水包结构示意图；
图4为小型铁水包结构侧视示意图；
附图标记：
1、高炉，2、第一铁水包，3、第二铁水包，4、第三铁水包，5、第四铁水包，6、第五铁水包，7、喷粉脱硫装置，8、放铁口，9、放渣口。
具体实施方式
以下列举具体实施例对本发明进行说明。需要指出的是，实施例只用于对本发明作进一步说明，不限制本发明的保护范围，其他人根据本发明做出的非本质的修改和调整，仍属于本发明的保护范围。
下述实施例中的连铸坯均按以下工艺流程制备：根据设定的化学成分范围(表1)，以 高炉铁水为原料，通过高炉出铁过程中的脱磷、KR脱磷、转炉冶炼、精炼，调整C、Si、Mn、S、P等的含量并进行微合金化，成分达到目标值后进行连铸、铸坯直接加热或者均热。
实施例1-4的制备步骤如下：
该钢经过高炉出铁过程中的脱磷、KR铁水预处理脱硫→转炉冶炼→钢包吹氩→精炼→连铸→型钢线轧制→在线冷却→冷床缓冷。其中，型钢线轧制包括粗轧和精轧两阶段轧制。热轧工序以控制温度为主，终轧温度检测翼缘外侧，轧后轧材在冷床自然冷却。实施例1-4的化学成分及具体工艺见下表1。
表1 化学成分(wt％，余量铁)
项目 C Si Mn P S Cr V Ti Al N
实施例1 0.08 0.15 1.30 0.007 0.002 0.28 0.03 0.015 0.025 0.008
实施例2 0.09 0.20 1.45 0.006 0.003 0.30 0.03 0.025 0.026 0.009
实施例3 0.08 0.20 1.28 0.006 0.004 0.25 0.04 0.018 0.03 0.008
实施例4 0.10 0.15 1.39 0.005 0.003 0.30 0.035 0.019 0.033 0.01
具体的高炉出铁过程中的脱磷工艺为：
步骤1、在高炉出铁过程中，高炉中铁水流入第一铁水包，第一铁水包的公称容积为30t铁水，深度为1.5m，在距离铁水包顶部50cm处的铁水包侧壁处开有放铁口，放铁口向外伸出20cm，采用滑板控制放铁口的开关。随着高炉中铁水的持续注入，第一铁水包中铁水容积达到50％以上时，对铁水包中喷吹脱磷剂进行脱磷，此时放铁口为关闭状态，铁水包中液位不断上升，铁水液位超过放铁口上沿20cm时，开启放铁口，铁水经放铁口流入第二铁水包，铁水由第一铁水包流入第二铁水包的流量速度与高炉铁水流入第一铁水包的流量速度相同，铁水液位处于不升不降的稳定状态，第一铁水包钢渣界面处持续的进行脱磷反应，钢渣界面附近处铁水中的磷含量被持续脱除，第一铁水包上部脱磷较充分的铁水通过放铁口流入第二铁水包，如图2-4所示。
所述脱磷剂喷吹点包括高炉铁水向第一铁水包的注入点和上一级铁水包中铁水向下一级铁水包的注入点，此位置处铁液搅拌剧烈，脱磷动力学条件好。
所述脱磷剂为污泥球和石灰的混合物，第一铁水包中的脱磷剂加入量为2kg/吨铁·铁水包，污泥球和石灰的质量比为1：1，污泥球中成份的质量百分含量为：CaO：5％，Fe 2O 3：88％，SiO 2：3％，余量为杂质，，石灰中成份的质量百分含量为：CaO：90％，Fe 2O 3：1％，SiO 2：3％，MgO：5％，余量为杂质。
所述喷吹脱磷剂时的载气为氧气，喷吹压力为0.2Mpa，喷吹流量为2m 3/min.
所述第二铁水包比第一铁水包的位置低60cm，铁水在重力的作用下从第一铁水包由放 铁口流入第二铁水包。
步骤2、第二铁水包、第三铁水包、第四铁水包的铁水包尺寸参数、脱磷工艺参数与第一铁水包完全相同，在第二、第三、第四铁水包内均进行喷吹脱磷操作。
第二铁水包钢渣界面附近处脱磷较充分的铁水通过放铁口在重力作用下流入第三铁水包，第三铁水包钢渣界面附近处脱磷较充分的铁水通过放铁口在重力作用下流入第四铁水包。第四铁水包钢渣界面附近处脱磷较充分的铁水通过放铁口在重力作用下流入第五铁水包。
第三铁水包、第四铁水包、第五铁水包分别比第二铁水包、第三铁水包、第四铁水包的位置低60cm。
对铁水进行成份和温度检测，四个小型铁水包内的脱磷率和铁水温度如下表：
表2 铁水包内的脱磷率和铁水温度
Figure PCTCN2021118771-appb-000001
由上表可看出，经过四个小型铁水包内脱磷后，铁水中磷含量由0.163％降低至0.017％，铁水脱磷率为89.6％，铁水脱磷率高，铁水温度由1520℃降低值1426℃，铁水温降为94℃，铁水温降小，脱磷后的铁水温度远高于入转炉温度要求(高于1250℃)。
第五铁水包为大体积铁水包，第五铁水包的容积与转炉工程吨位相匹配，第五铁水包内的铁水被运入KR工位脱硫，脱硫完毕后运入转炉进行正常的冶炼，转炉冶炼终点磷含量控制在0.007％以下。
每正常脱磷30到40min后，第一至第四铁水包都进行一次换渣操作，其换渣工艺为第一铁水包中的炉渣被倒出，第二铁水包顶部的炉渣被倒入第一铁水包，第三铁水包顶部的炉渣被倒入第二铁水包，第四铁水包顶部的炉渣被倒入第三铁水包，由于采用了多级脱磷工艺，下一级铁水包中的磷含量都低于上一级铁水包，在充分脱磷的工艺条件下，磷在渣铁中的分配比基本不变，也即是下一级钢包渣中的磷含量也会低于上一级钢包，对铁水包炉渣进行成份检测，四个小型铁水包内的炉渣成份如下表
表3 铁水包内炉渣成份
  高炉炉渣 第1铁水包 第2铁水包 第3铁水包 第4铁水包
CaO(％) 41 37 43 45 45
SiO 2(％) 35 31 30 29 31
Al 2O 3(％) 14 11 7 5 5
MgO(％) 6 5 5 6 5
S(％) 0.9 0.1 0.2 0.1 0.1
P 2O 5(％) 0.13 0.91 0.64 0.47 0.30
T.Fe(全铁)(％) 0.3 8 11 13 14
由上表可看出，下一级钢包炉渣中的磷含量均低于上一级炉渣中的磷含量，且碱度更高，氧化性更强(T.Fe可折算成FeO)，因此将下一级铁水包顶部的炉渣倒入上一级铁水包中后，炉渣仍能发挥较好的脱磷效果。
第一至四铁水包顶部均开有放渣口，放渣口向外伸出20mm，铁水包内的炉渣可通过该放渣口流出，放渣口和放铁口在铁水包包壁的位置差为四分之一圆周。
第一铁水包至第四铁水包包车中均配置有液压升降装置和旋转装置，可将铁水包升降1.5m，并可将铁水包绕中轴线旋转90度。
进行换渣操作时，先关闭放铁口，然后利用铁水包车上的旋转装置使上一级铁水包和下一级铁水包绕中轴线旋转90度，以避免钢包升降时碰触到放铁口，然后使用液压升降装置使上一级铁水包降低、下一级铁水包上升，等下一级铁水包高于上一级铁水包，且下一级铁水包内的炉渣可通过放渣口流入上一级铁水包时，开启放渣口，炉渣由下一级铁水包流入上一级铁水包，待炉渣流净后，关闭放渣口。
实施例1-4的热轧工艺条件见表2。按照标准为BS EN ISO 377-1997《力学性能试验试样的取样位置和制备》；屈服强度、抗拉强度、延伸率的试验方法参照标准ISO6892-1-2009《金属材料室温拉伸试验方法》；冲击功试验方法参照标准ISO 148-1《金属材料夏比摆锤冲击试验》，结果见表3。
表4 实施例热轧工艺
Figure PCTCN2021118771-appb-000002
表5 实施例力学性能试验结果
Figure PCTCN2021118771-appb-000003
Figure PCTCN2021118771-appb-000004
从表中可见，本发明实施例1-4屈服强度保持440MPa级别，具有良好的延伸性能，其-50℃冲击功较高。可以满足制备海洋工程构件在极低环境下的使用条件，适用于制作海洋石油平台、海洋远洋运输船舶等具有较高低温韧性要求的支撑结构件。
从图1可以看出本申请的组织为粒状贝氏体+铁素体组织。P含量降低对于420MPa级别强度的H型钢，满足强度的同时，韧性尤其是低温韧性得到提升。本发明未详细说明的内容均可采用本领域的常规技术知识。
最后所应说明的是，以上实施例仅用以说明本发明的技术方案而非限制。尽管参照实施例对本发明进行了详细说明，本领域的普通技术人员应当理解，对本发明的技术方案进行修改或者等同替换，都不脱离本发明技术方案的精神和范围，其均应涵盖在本发明的权利要求范围当中。

Claims (10)

  1. 一种屈服强度420MPa级耐低温H型钢，其特征在于，所述H型钢化学成分组成按重量百分比为：C：0.08％～0.10％，Si≤0.2％，Mn：1.25％～1.45％，V：0.03％～0.045％，Ti：0.015％～0.025％，Cr：0.15％～0.30％，A1s：0.02％～0.04％，N：0.007％～0.01％，P≤0.008％，S≤0.005％，O≤0.004％，其余为Fe和不可避免杂质。
  2. 根据权利要求1所述的屈服强度420MPa级耐低温H型钢，其特征在于，所述H型钢化学成分组成按重量百分比为：P+S≤0.01％。
  3. 一种屈服强度420MPa级耐低温H型钢的制备方法，包括以下步骤：
    1)铁水预处理、多次脱磷：
    在高炉出铁过程中，高炉中铁水流入第一铁水包，随着高炉中铁水的持续注入，对铁水包中喷吹脱磷剂进行脱磷，铁水包中液位不断上升，铁水液位超过放铁口上沿20～30cm时，开启放铁口，铁水经放铁口流入第二铁水包，在第二铁水包内再次进行喷吹脱磷操作，且第二铁水包在铁水包钢渣界面向下20～30cm处的侧面也开设有放铁口，第二铁水包上部脱磷的铁水通过放铁口向下流入第三铁水包，如此循环通过放铁口向下流入第N铁水包，对铁水进行N次脱磷操作，将铁水中磷含量脱至0.02％以下，其中，4≤N≤6；
    每脱磷30到40min后，第一铁水包至第N-1铁水包都进行一次换渣操作；
    2)转炉冶炼：终点磷含量控制在0.007％以下；
    3)钢包吹氩、RH/LF精炼、矩形连铸坯浇铸、连铸坯缓冷坑进行缓冷或者热送热装、型钢线半连续轧制、冷床密集缓冷；其中，在轧制过程中，加热炉均热温度为1210～1250℃，铸坯在炉时间为140～180min；精轧开轧温度为1000～1050℃，精轧终轧温度为890～930℃。
  4. 根据权利要求1所述的制备方法，其特征在于，所述步骤1)中第一铁水包至第N-1铁水包公称容积为30～50t铁水，深度为1.5～2m，在距离铁水包顶部50～60cm处的铁水包侧壁处开有放铁口，放铁口向外伸出20～30cm，采用滑板控制放铁口的开关，所述第N铁水包的容积与转炉工程吨位相匹配；所述步骤4)精轧最后两道次压缩比为6％～12％。
  5. 根据权利要求1所述的制备方法，其特征在于，所述脱磷剂喷吹点为高炉铁水向第一铁水包的注入点和上一级铁水包中铁水向下一级铁水包的注入点。
  6. 根据权利要求1所述的制备方法，其特征在于，所述脱磷剂为污泥球和石灰的混合物，污泥球和石灰的质量比为1:1，污泥球中成份的质量百分含量包括：CaO:2～8％，Fe 2O 3:85～92％，SiO 2:1～5％，石灰中成份的质量百分含量包括：CaO:85～90％，Fe 2O 3:0～3％，SiO 2:0～10％，MgO:0～10％，所述铁水包中脱磷剂的加入量为2～3kg/吨铁·铁水包。
  7. 根据权利要求1所述的制备方法，其特征在于，所述喷吹脱磷剂时的载气为氧气， 喷吹压力为0.2～0.3Mpa，喷吹流量为2～4m 3/min。
  8. 根据权利要求1所述的制备方法，其特征在于，所述铁水包中，下一个铁水包比上一个铁水包的位置低60-70cm。
  9. 根据权利要求1所述的制备方法，其特征在于，所述换渣操作为：第一铁水包中的炉渣被倒出，第二铁水包顶部的炉渣被倒入第一铁水包，第三铁水包顶部的炉渣被倒入第二铁水包，直至第N-1铁水包顶部的炉渣被倒入第N-2铁水包。
  10. 根据权利要求9所述的制备方法，其特征在于，所述第一铁水包至第N-1铁水包顶部均开有放渣口，放渣口向外伸出20～30mm，放渣口和放铁口在铁水包包壁的位置差为四分之一圆周；
    第一铁水包至第N-1铁水包包车中均配置有液压升降装置和旋转装置，将铁水包升降1～2m，并可将铁水包绕中轴线旋转90度。
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