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US20200340073A1 - Steel section having a thickness of at least 100mm and method of manufacturing the same - Google Patents

Steel section having a thickness of at least 100mm and method of manufacturing the same Download PDF

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Publication number
US20200340073A1
US20200340073A1 US16/762,078 US201816762078A US2020340073A1 US 20200340073 A1 US20200340073 A1 US 20200340073A1 US 201816762078 A US201816762078 A US 201816762078A US 2020340073 A1 US2020340073 A1 US 2020340073A1
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Prior art keywords
steel section
precipitates
steel
vanadium
recited
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Christophe HOUYOUX
Valerie RINALDI
Boris Donnay
Liudmila WEBBER
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ArcelorMittal SA
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ArcelorMittal SA
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Assigned to ARCELORMITTAL reassignment ARCELORMITTAL ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HOUYOUX, Christophe, RINALDI, VALERIE, DONNAY, BORIS, WEBBER, Liudmila
Publication of US20200340073A1 publication Critical patent/US20200340073A1/en
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • 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
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
    • 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
    • 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
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • 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
    • C22C38/002—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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C3/00—Structural elongated elements designed for load-supporting
    • E04C3/02—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces
    • E04C3/04—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces of metal
    • 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
    • C21D2211/004—Dispersions; Precipitations
    • 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
    • C21D2211/008—Martensite
    • 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
    • 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
    • C21D2221/00—Treating localised areas of an article
    • C21D2221/10—Differential treatment of inner with respect to outer regions, e.g. core and periphery, respectively
    • E—FIXED CONSTRUCTIONS
    • E04—BUILDING
    • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
    • E04C3/00—Structural elongated elements designed for load-supporting
    • E04C3/02—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces
    • E04C3/04—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces of metal
    • E04C2003/0404—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces of metal beams, girders, or joists characterised by cross-sectional aspects
    • E04C2003/0443—Joists; Girders, trusses, or trusslike structures, e.g. prefabricated; Lintels; Transoms; Braces of metal beams, girders, or joists characterised by cross-sectional aspects characterised by substantial shape of the cross-section
    • E04C2003/0452—H- or I-shaped

Definitions

  • the present invention deals with a steel section comprising a web central portion connected on each side to a flange portion having a thickness above 100 mm.
  • the steel section according to the invention is particularly well suited for the manufacture of columns for high-rise buildings, long span, transfer and belt trusses, outriggers and bridge girders.
  • Another object of the present invention is to provide a method of manufacturing of a steel section comprising the following steps:
  • FIG. 1 shows an electron micrograph illustrating randomly distributed precipitates in the core of the flange of the heavy section
  • FIG. 2 shows an electron micrograph illustrating precipitates, arranged in regularly spaced bands
  • FIG. 3 shows schematically the web portion and flanges of the steel section.
  • carbon plays an important role in the formation of the microstructure and reaching of the targeted mechanical properties. Its main role is to provide strengthening through hardening of the martensite/bainite phases but also through formation of carbides and/or carbo-nitrides of metallic elements of the steel.
  • the carbon content of the grade according to the invention is between 0.06 and 0.16% weight. Carbon content below 0.06% will not result in a sufficient level of mechanical resistance, leading to yield strengths value below 485 MPa. On the opposite, carbon contents above 0.16% would result in reducing ductility and the weldability of the steel.
  • the carbon content is between 0.08 and 0.14%, so as to obtain sufficient strength and weldability.
  • Manganese is an element which increases hardenability.
  • the manganese content of the grade according to the invention is between 1.10 and 2.00%. Manganese content below 1.10% will not result in a sufficient level of mechanical resistance. On the opposite side of the range, manganese content above 2.00% would result in decreased weldability or would promote the formation of hard martensite-austenite constituents, also negatively impacting the toughness of the steel.
  • Silicon is a deoxidizing element and contributes to improving strength. Silicon content below 0.10% will not result in a sufficient level of mechanical resistance nor a good deoxidation. On the opposite side of the range, silicon contents above 0.40% would result in the formation of oxides, reducing welding properties of the steel.
  • Copper is an element contributing to improving the strength of the steel by hardenability improvement and precipitation strengthening. Copper content below 0.001% will not result in a sufficient level of mechanical resistance. On the opposite side of the range, copper contents above 0.50% would result in increasing the carbon equivalent and thus deteriorating the weldability or impacting the hot shortness of the steel during hot deformation, caused by penetration of the Cu-enriched phase into grain boundaries.
  • Nickel is an element contributing to improving the strength and toughness of the steel. Nickel content below 0.001% will not result in a sufficient level of mechanical resistance. On the opposite side of the range, nickel contents above 0.30% would lead to high alloying costs.
  • Chromium is an element contributing to improving the strength of the steel by improving hardenability through solution hardening but also through precipitation hardening. Chromium content below 0.001% will not result in a sufficient level of mechanical resistance. On the opposite side of the range, chromium contents above 0.50% would result in generating coarse chromium carbides or carbo-nitrides that may deteriorate the toughness of the steel
  • Molybdenum is an element contributing to improving the strength of the steel by improving hardenability. Molybdenum content below 0.001% will not result in a sufficient level of mechanical resistance. On the opposite side of the range, molybdenum contents above 0.20% would result in reducing the toughness of the steel.
  • Vanadium is an important element that is used to achieve hardening and strengthening by precipitation of nitrides, carbo-nitrides or carbides but also through grain refining.
  • the formation of vanadium precipitation limits the austenite grain coarsening, by resulting in ferrite grain decrease and improved strength by precipitation in ferrite phase.
  • Vanadium would also prevent the chromium and manganese migration in the cementite, resulting in their application in small precipitation formation.
  • Vanadium content below 0.06% will not result in a sufficient level of mechanical resistance.
  • vanadium contents above 0.12% would result in a risk that an excessive precipitation may cause a reduction in toughness, which has to be avoided.
  • vanadium addition is limited to 0.09% to improve further the toughness of the steel.
  • Nitrogen is an important element to form nitrides and carbo-nitrides of metallic elements like vanadium, niobium aluminum and titanium. Their size, distribution density and stability have a significant effect to mechanical strengthening. Nitrogen content below 0.0050% will not result in a sufficient level precipitation and grain size control. To further improve those properties, a minimum level of 0.0060%, or even of 0.0070% or even better of 0.0080% is preferred. On the opposite side of the range, nitrogen contents above 0.0200% would result in the presence of free nitrogen in the steel, which is known as having a negative impact on toughness in the Heat Affected Zone after welding.
  • the precipitation strengthening can be enhanced by optimizing the vanadium to nitrogen ratio in the steels section to approach the stoichiometric ratio of 4:1.
  • the ratio of V to N is comprised between 2.5 and 7, and even comprised between 3 and 5.
  • Aluminium can be added in the steel for deoxidizing effect and removing of the oxygen from the steel. If other deoxidizing elements are added in the steel, the aluminum content is 0.005% and lower. Otherwise, the aluminum content is between 0.005% and 0.040%. If the aluminum content is too high, the formation of AlN will occur in preference to VN, and AlN being bigger in size than VN, it will be not as efficient for pinning of austenite grain boundaries as VN.
  • Sulfur and phosphorus are impurities that embrittle the grain boundaries and lead to the formation of center and micro-segregation. Their respective contents must not exceed 0.030 and 0.040% so as to maintain sufficient hot ductility and to avoid deterioration in welding properties.
  • Niobium is an element that may optionally be used to achieve hardening and strengthening by precipitation of nitrides, carbo-nitrides or carbides. It suppresses the growth of austenite grains during rolling, by refining them, thus resulting in improvement of strength and low-temperature toughness. However, when its amount is above 0.05%, could deteriorate toughness in the Heat Affected Zone due to martensite hardening. On the other hand, when niobium amount is 0.05% and higher, it will pin to available nitrogen and thus impairing nitrogen from forming vanadium precipitates that assures the strengthening of the ductile core of the section.
  • Titanium is an element that may optionally be used to achieve hardening and strengthening by precipitation of nitrides, carbo-nitrides or carbides. However, when its amount is above or equal to 0.005%, there is a risk of TiN formation rather than VN. Moreover, TiN being cuboids particles may react as stress concentrators thus negatively impacting the toughness and fatigue properties of the steel. In a preferred embodiment, the maximum amount of titanium is set to 0.003% and even to 0.001%.
  • the carbon, manganese, chromium, molybdenum, vanadium, nickel and copper contents of the grade are such that
  • Respecting these values ensures that the hardenability of the steel section will be in suitable ranges through sufficient formation of bainite, while maintaining a good weldability of the steel sections.
  • the reduced carbon equivalent allows avoiding weld processing steps such as preheating (when acceptable) and also results in reduction of fabrication costs.
  • CEV ⁇ 0.5%.
  • the steel section comprises a web central portion 100 connected on each side to a flange portion 102 , 104 , as shown schematically in FIG. 3 .
  • the thickness of the flange of the steel section according to the invention is set above 100 mm, allowing the use of such beam for high-rise building structures, notably. Its thickness is preferably below 140 mm as a sufficient cooling rate to ensure the requested tensile and toughness properties is difficult to obtain.
  • the web and the flanges of the heavy section are composed of a hardened zone, resulting from the water cooling of the surface and a non-hardened zone, in the core of the product.
  • Each zone of the steel section can have a specific microstructure that can include one or more phases among tempered martensite, bainite, ferrite and pearlite. Ferrite can be present under the form of acicular ferrite or of regular ferrite.
  • microstructure of each zone depends on the steel section thickness and on the thermal path it is subjected to.
  • the microstructure of the flanges portions include, from surface to core, a first zone comprising tempered martensite and possibly bainite and a second zone comprising ferrite and pearlite.
  • the first zone can, for example, extend up to 10 mm under the surface of the flange portion.
  • An essential characteristic of the invention is the presence, in the steel section microstructure, of at least one kind of vanadium precipitates possibly comprising also one or more metal chosen among chromium, manganese and iron, said precipitates being chosen among nitrides, carbides, carbo-nitrides or any combination of them, more than 70% of such precipitates and preferably more than 80%, having a mean diameter below 6 nm.
  • the mean diameter determination was done in the following way: the surface of each detected precipitate was measured and applied to the corresponding circle, from which the diameter was extracted, giving then the mean diameter size for all detected precipitates.
  • the mean density of those precipitates is of at least 500 precipitates per mm 2 , preferably of at least 1000 precipitates per mm 2 .
  • Those precipitates have a beneficial effect on strength, known as being increased with precipitates size decrease and precipitates content increase.
  • Such precipitates are preferably present in the core zone of the flange of the section, mainly in the ferrite phase. At least 70% of such precipitates and preferably at least 80%, have a mean diameter below 6 nm. The reduced size of such precipitates increases their hardening effect and hence the tensile strength of the steel section.
  • two types of precipitates are preferably present in the core of the flange of the steel section:
  • the randomly distributed precipitated are bigger than the one arranged in regularly spaced bands.
  • such regularly spaced precipitates include at least vanadium and chromium.
  • more than 80% of the randomly distributed precipitates have a mean diameter between 3.5 and 6 nm.
  • Such precipitates preferably include at least vanadium, chromium and iron.
  • the steel section according to the invention can be produced by any appropriate manufacturing method and one of skill in the art can define one. It is however advisable to use a process ending by an accelerated cooling, in that case quenching and self-tempering of the surface layer after hot-rolling step.
  • the method according to the invention comprises the following steps:
  • the steel sections according to the present invention are preferably produced through a method in which a semi product made of a steel according to the present invention having the composition described above, is cast, the cast input stock is heated to a temperature above 1000° C., preferably above 1050° C. and more preferably above 1100° C. or 1150° C. or used directly at such a temperature after casting, without intermediate cooling. Such temperatures allow full dissolution of vanadium carbonitrides, which will further participate in precipitation strengthening mechanism.
  • the final hot-rolling step is performed at a temperature above 850° C.
  • the end-of-rolling temperature is above or equal to 850° C. in order to assure the austenite grains refining and thus the formation of a thinner microstructure after transformation, which is known to enhance the toughness and strength properties.
  • the aim is to create fine grained microstructure by grain refinement during the subsequent recristallization during rolling.
  • the hot-rolled product obtained by the process described above is then cooled using preferably a quenching and self-tempering process.
  • the so-called quenching and self-tempering process consists in subjecting a hot rolled steel section emerging from the finishing stand of the rolling mill to cooling by means of a fluid so as to produce martensitic and/or bainitic quenching of the surface layer of all or part of the product. Moreover, at the outlet of the fluid cooling zone, the non-quenched portion of the rolled product is at a temperature high enough to permit, during subsequent air cooling, tempering of the surface layer of martensite and/or bainite to take place.
  • the cooling fluid employed for carrying out the quenching and self tempering step is usually water with or without conventional additives, or aqueous of mineral salts, for example.
  • the fluid may be a mist, for example obtained by suspending water in a gas, or it may be a gas, such as steam.
  • desired cooling of the rolled products depends on the cooling devices used, and on suitable choice of the length and the flow rate characteristics of the cooling means.
  • the dimensions of the product are known as well as the composition of the steel, and thus its continuous cooling transformation diagram, making it possible to determine the conditions to apply for an adequate treatment of the steel section, among which, the temperature at which martensite is formed and the maximum time available for performing surface quenching to the desired depth.
  • the amount of heat to be removed can be as well as the characteristics of the cooling devices and the flow rates of the fluid applied by the cooling devices.
  • the evolutions of the skin temperature of the steel section starting from the end of the martensitic and/or bainitic quenching are being measured. After quenching, the skin temperature rises while the temperature at the core continuously decreases after the section has emerged from the last stand of the rolling mill.
  • the skin temperature and the core temperature in a given cross-section converge towards a time from where the two curves continue substantially parallel to one another. The skin temperature at this point is called the “equalization temperature”.
  • Trial 1 is a comparative example and trial 2 is an example according to the invention.
  • phase percentages of the microstructures of the obtained steel section were determined:
  • section no 1 The phase percentages in both zones, especially in the core zone, of section no 1 are quite similar to section no 2, showing that the impact of the vanadium precipitation strengthening is observed at smaller microstructural scale.
  • Precipitation analysis done by TEM examination of carbon extraction replicas taken from the core zone of the flange thickness of the section, showed the presence of vanadium precipitates. Fine precipitates analysis was performed through TEM thin foil method, which allowed quantifying the mean size and the density of the precipitates.
  • FIG. 1 shows the vanadium precipitates mostly having spherical shape, with bigger or smaller size.
  • the bigger size precipitates typically size about 6 nm in diameter
  • the fine precipitates typically size about 3 nm in diameter
  • FIG. 2 shows the microstructure consists of parallel sheets densely populated with vanadium particles. The sheets appear with a regular spacing.
  • Steel sections according to the present invention show excellent values of high strength, toughness and good weldability, which is nowadays not easily achievable.
  • design and construction teams involved in large-scale construction projects can benefit from more efficient structural solutions.
  • the steel section's higher yield strength enables weight savings and lower transportation and fabrication costs than other commonly-used structural steel grades. And thus, the present invention makes an extremely significant contribution to construction industry.

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US16/762,078 2017-12-18 2018-12-12 Steel section having a thickness of at least 100mm and method of manufacturing the same Pending US20200340073A1 (en)

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PCT/IB2018/059909 WO2019123115A1 (fr) 2017-12-18 2018-12-12 Profilé en acier d'une épaisseur d'au moins 100 mm et son procede de fabrication

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KR20200081486A (ko) 2020-07-07
WO2019122949A1 (fr) 2019-06-27
CN111356780A (zh) 2020-06-30
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FI3728672T3 (fi) 2024-12-30
UA124482C2 (uk) 2021-09-22
CA3083365A1 (fr) 2019-06-27
BR112020007981A2 (pt) 2020-10-20
ZA202002399B (en) 2021-04-28
RU2750752C1 (ru) 2021-07-02
ES3012754T3 (en) 2025-04-10
CA3083365C (fr) 2022-07-26
JP2025004102A (ja) 2025-01-14
KR102513656B1 (ko) 2023-03-24
JP2021507091A (ja) 2021-02-22
MA51301B1 (fr) 2024-12-31
HUE069485T2 (hu) 2025-03-28
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MA51301A (fr) 2021-03-24
BR112020007981B1 (pt) 2023-11-28

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