EP3533893A1 - H-stahl und verfahren zur herstellung davon - Google Patents

H-stahl und verfahren zur herstellung davon Download PDF

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Publication number
EP3533893A1
EP3533893A1 EP17885325.5A EP17885325A EP3533893A1 EP 3533893 A1 EP3533893 A1 EP 3533893A1 EP 17885325 A EP17885325 A EP 17885325A EP 3533893 A1 EP3533893 A1 EP 3533893A1
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Prior art keywords
steel
less
rolling
flange
ferrite
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English (en)
French (fr)
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EP3533893A4 (de
Inventor
Masaki Mizoguchi
Kazutoshi Ichikawa
Hirokazu Sugiyama
Tetsuya Seike
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Nippon Steel Corp
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Nippon Steel Corp
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
    • 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
    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • 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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • 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
    • 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • 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
    • 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
    • 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
    • C21D2211/001—Austenite
    • 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

Definitions

  • the present invention relates to a thick H section, which has excellent strength and low temperature toughness, and a method for manufacturing the same.
  • Priority is claimed on Japanese Patent Application No. 2016-248181, filed on December 21, 2016 , the content of which is incorporated herein by reference.
  • Patent Document 1 a technology of ensuring the toughness by utilizing an effect of refining prior austenite grains due to a Ca-Al-based oxide and obtaining a steel, in which high strength is ensured by applying accelerated cooling, is proposed.
  • Patent Document 2 a technology of ensuring the toughness by utilizing the effect of refining prior austenite grains due to a Mg-S-based inclusion and obtaining a steel, in which high strength is ensured by applying accelerated cooling, is proposed.
  • H sections are unique in shape. Universal rolling and the like are applied to form a steel piece into an H-shape. However, rolling conditions (temperature and rolling reduction) are limited in universal rolling. Therefore, in a case where an H section is manufactured, particularly in a case where a thick H section having a thickness of a flange of 20 mm or more is manufactured, it is not easy to control mechanical properties compared to general thick steel plates (thick steel plates).
  • Patent Documents 3 and 4 methods of ensuring homogeneous mechanical properties of a steel piece by performing natural cooling after hot rolling of the steel piece, in which the amount of C is reduced and B is added, are proposed.
  • Patent Documents 5 to 8 methods for manufacturing a thick H section or an H section for the purpose of high strength, high toughness, and the like are disclosed.
  • thick H sections having a thickness of a flange of 20 mm or more, it has not been easy to control mechanical properties. Therefore, such thick H sections have been required to satisfy toughness no more than at room temperature or at 0°C.
  • thick H sections are required to have excellent toughness at a lower temperature.
  • thick H sections are also required to have yield stress (specifically, yield strength or 0.2% proof stress) of 385 MPa or more.
  • the present invention has been made in consideration of such circumstances, and an object thereof is to provide a thick H section, which has excellent strength and low temperature toughness, and a method for manufacturing the same.
  • the gist of the present invention is as follows.
  • thick H sections having a thickness of a flange of 20 mm or more have been required to satisfy toughness no more than at room temperature or at 0°C.
  • thick H sections are required to have excellent toughness at a lower temperature, such as approximately -20°C.
  • thick H sections are also required to have yield stress (specifically, yield strength or 0.2% proof stress) of 385 MPa or more.
  • a thick H section (there may hereinafter be a case where it is disclosed as a steel), particularly in regard to a flange which is an important portion in the structure of an H section, the inventors have found the following knowledge by investigating a steel composition (a chemical composition of a steel) affecting the strength and the low temperature toughness, and the influence of a steel structure (a metallographic structure of a steel).
  • strength means tensile yield stress and the maximum tensile strength
  • low temperature toughness means absorbed energy in a Charpy test at -20°C.
  • an excessively increase in hardenability caused by adding an alloying element encourages the generation of a martensite-austenite mixed structure (hereinafter, it will be disclosed as an MA) in a steel, and which leads to deterioration in low temperature toughness.
  • an MA martensite-austenite mixed structure
  • B in an alloying element noticeably tends to encourage the generation of an MA, it is effective that B is not actively added and is limited to the level of impurities or less.
  • Nb is added. Since Nb increases the strength of a steel through precipitation strengthening, there is no need to excessively increase the hardenability, and strength of a steel can be increased without encouraging the generation of an MA. In addition, Nb has effects of suppressing recrystallization of austenite during hot rolling, accumulating strain in a steel caused through rolling, and bringing grain refinement of ferrite after transformation.
  • V has effects of being precipitated as carbonitride (VC, VN, or a composite thereof), functioning as a nucleation site of ferrite, and bringing grain refinement of ferrite.
  • both the yield stress and the low temperature toughness can be achieved by optimally controlling the steel composition and manufacturing conditions.
  • the C content is 0.05% to 0.160%
  • B is not added and is limited to the level of impurities or less
  • Nb and V are actively added
  • the amounts of the alloying elements such as Mn, Ti, and N are appropriately controlled
  • a carbon equivalent Ceq is controlled to be a range of 0.30 to 0.48.
  • the area fraction of ferrite, the area fraction of MA, the average grain size of ferrite, and the like are elaborated by optimally controlling the manufacturing conditions. As a result, a thick H section having excellent strength and low temperature toughness can be obtained.
  • the H section according to the present embodiment includes, as a chemical composition, base elements and includes optional elements as necessary.
  • the remainder includes Fe and impurities.
  • C, Si, Mn, Nb, V, Ti, and N are the base elements (main alloying elements).
  • the lower limit for the C content is set to 0.05%.
  • the lower limit for the C content is set to 0.060%, 0.070%, or 0.080%.
  • the upper limit for the C content is set to 0.160%.
  • the upper limit for the C content is preferably set to 0.140%, 0.130%, or 0.120%.
  • the lower limit for the Si content is set to 0.01%.
  • the lower limit for the Si content is set to 0.05%, 0.10%, or 0.15%.
  • the upper limit for the Si content is set to 0.60%. In order to further improve the low temperature toughness, the upper limit for the Si content is preferably set to 0.40% or 0.30%.
  • the lower limit for the Mn content is set to 0.80%.
  • the lower limit for the Mn content is preferably set to 1.0%, 1.1%, or 1.2%.
  • the upper limit for the Mn content is set to 1.70%.
  • the upper limit for the Mn content is set to 1.60% or 1.50%.
  • Nb (Niobium) is an element which suppresses recrystallization of austenite at the time of hot rolling, contributes to grain refinement of ferrite by accumulating work strain in a steel, and contributes to improvement of strength through precipitation strengthening. Therefore, the lower limit for the Nb content is set to 0.005%. Preferably, the lower limit for the Nb content is set to 0.010%, more than 0.020%, 0.025%, or 0.030%. However, when the Nb content exceeds 0.050%, and which may lead to significant deterioration in low temperature toughness. Therefore, the upper limit for the Nb content is set to 0.050%. Preferably, the upper limit for the Nb content is set to 0.045%, 0.043%, or 0.040%. In a case where Nb is not intentionally added, the Nb content included as an impurity is set to less than 0.005%. In order to set the Nb content to 0.005% or more, Nb is intentionally included in a steel.
  • V (Vanadium) is an element which has effects of being precipitated as carbonitride inside grains of austenite, acting as transformation nuclei with respect to ferrite, and refining ferrite grains. Therefore, the lower limit for the V content is set to 0.05%. Preferably, the lower limit for the V content is set to more than 0.05%, 0.06%, or 0.07%. However, when the V content exceeds 0.120%, the low temperature toughness may be impaired by coarsening precipitates. Therefore, the upper limit for the V content is set to 0.120%. Preferably, the upper limit for the V content is set to 0.110% or 0.100%.
  • Ti is an element which forms TiN and fixes N in a steel. Therefore, the lower limit for the Ti content is set to 0.001%. In order to further refine austenite due to a pinning effect of TiN, the lower limit for the Ti content is preferably set to 0.005%, 0.007%, or 0.010%. On the other hand, when the Ti content exceeds 0.025%, coarse TiN is generated and the low temperature toughness is impaired. Therefore, the upper limit for the Ti content is set to 0.025%. Preferably, the upper limit for the Ti content is set to 0.020%, 0.015%, or 0.012%.
  • N is an element which forms TiN or VN and contributes to grain refinement of a structure or precipitation strengthening. Therefore, the lower limit for the N content is set to 0.0001%. Preferably, the lower limit for the N content is set to 0.0020%, 0.0035%, more than 0.0050%, or 0.0060%. However, when the N content exceeds 0.0120%, the low temperature toughness is deteriorated, and surface cracking at the time of casting or material defect due to strain aging of a manufactured steel is caused. Therefore, the upper limit for the N content is set to 0.0120%. Preferably, the upper limit for the N content is set to 0.0110%, 0.0100%, or 0.0090%.
  • the H section according to the present embodiment contains impurities as a chemical composition.
  • impurities indicate elements incorporated from ore or scrap as a raw material, or the manufacturing environment, when a steel is industrially manufactured.
  • impurities mean elements such as Al, B, P, S, and O.
  • Al and B are limited as follows in order to sufficiently exhibit the effects of the present embodiment.
  • the amounts of impurities are small, there is no need to limit the lower limit value, and the lower limit value for impurities may be 0%.
  • Al is an element used as a deoxidizing element.
  • the Al content exceeds 0.10%, oxide is coarsened and becomes origins of brittle fracture, so that low temperature toughness is deteriorated. Therefore, the upper limit for the Al content is limited to 0.10%.
  • Ti serves as the deoxidizing element, and Ti oxide is precipitated in a steel. This Ti oxide functions as a nucleation site of V carbonitride, refines the grain size of ferrite, and contributes to improvement of low temperature toughness.
  • the upper limit for the Al content may be limited to less than 0.003%, 0.002%, or 0.001% in a case of including Al as impurities, instead of using Al as a deoxidizing element.
  • Al is intentionally included in a steel.
  • B (Boron) increases the hardenability, encourages the generation of an MA, and deteriorates the low temperature toughness. Therefore, in the present embodiment, B is not actively added and is limited to the level of impurities or less.
  • the upper limit for the B content is limited to 0.0003%. Preferably, the upper limit for the B content is limited to less than 0.0003%, 0.0002%, or 0.0001%. Generally, in order to set the B content to more than 0.0003%, B is intentionally included in a steel.
  • P Phosphorus
  • S Sulfur
  • O Oxygen
  • P and S encourage the weld cracking through solidifying segregation and deteriorates the low temperature toughness.
  • the upper limit for the P content is limited to 0.03%, 0.02%, or 0.01%.
  • the upper limit for the S content is limited to 0.02% or 0.01%.
  • O deteriorates the low temperature toughness by being solid-solubilized in a steel, and deteriorates the low temperature toughness through coarsening of oxide particles.
  • the upper limit for the O content is limited to 0.005%, 0.004%, or 0.003%.
  • the H section according to the present embodiment may contain optional elements.
  • optional elements instead of a part of Fe which is the remainder as described above, Cr, Mo, Ni, Cu, W, Ca, Zr, Mg, and/or REM may be contained as optional elements. These optional elements may be contained in accordance with their purpose. Thus, there is no need to limit the lower limit values for these optional elements, and the lower limit values may be 0%. In addition, even if these optional elements are contained as impurities, the foregoing effects are not impaired.
  • Cr Chromium is an element which contributes to improvement of strength.
  • the Cr content may be 0% to 0.30%.
  • the lower limit for the Cr content is preferably set to 0.01%, 0.05%, or 0.10%.
  • the upper limit for the Cr content is set to 0.30%, 0.25%, or 0.20%.
  • Mo Mo is an element which is solid-solubilized in a steel and contributes to improvement of strength.
  • the Mo content may be 0% to 0.20%.
  • the lower limit for the Mo content is preferably set to 0.01%, 0.05%, or 0.10%.
  • the upper limit for the Mo content is preferably set to 0.20%, 0.17%, or 0.15%.
  • Ni Ni (Nickel) is an element which is solid-solubilized in a steel and contributes to improvement of strength.
  • the Ni content may be 0% to 0.50%.
  • the lower limit for the Ni content is preferably set to 0.01%, 0.05%, or 0.10%.
  • the upper limit for the Ni content is preferably set to 0.50%, 0.30%, or 0.20%.
  • Cu Copper is an element which contributes to improvement of strength.
  • the Cu content may be 0% to 0.35%.
  • addition of Cu may encourage the generation of an MA and may deteriorate the low temperature toughness. Therefore, preferably, the Cu content is limited to 0.30% or less, 0.20% or less, or 0.10% or less.
  • the Cu content may be limited to less than 0.03% or less than 0.01% which is the level of impurities.
  • W is an element which is solid-solubilized in a steel and contributes to improvement of strength.
  • the W content may be 0% to 0.50%.
  • the lower limit for the W content is set to 0.001%, 0.01%, or 0.10%.
  • the upper limit for the W content is set to 0.50%, 0.40%, or 0.30%.
  • the W content included as an impurity is set to less than 0.001%. In order to set the W content to 0.001% or more, W is intentionally included in a steel.
  • Ca is an element which is effective for controlling the form of sulfide, suppresses generation of coarse MnS, and contributes to improvement of low temperature toughness.
  • the Ca content may be set 0% to 0.0050%.
  • the lower limit for the Ca content is set to 0.0001%, 0.0005%, or 0.0010%.
  • the upper limit for the Ca content is set to 0.0050%, 0.0040%, or 0.0030%.
  • Zr Ziirconium
  • the Zr content may be set 0% to 0.0050%.
  • the lower limit for the Zr content is set to 0.0001%, 0.0005%, or 0.0010%.
  • the upper limit for the Zr content is set to 0.0050%, 0.0040%, or 0.0030%.
  • the Zr content included as an impurity is set to less than 0.0001%. In order to set the Zr content to 0.0001% or more, Zr is intentionally included in a steel.
  • Mg Magnetic
  • REM rare earth metal
  • the Mg content may be 0% to 0.0050%
  • the REM content may be 0% to 0.0050%
  • the lower limit for the Mg content is set to 0.0005%, 0.0010%, or 0.0020%
  • the lower limit for the REM content is set to 0.0005%, 0.0010%, or 0.0020%
  • the upper limit for the Mg content is set to 0.0040%, 0.0030%, or 0.0025%
  • the upper limit for the REM content is set to 0.0040%, 0.0030%, or 0.0025%.
  • the carbon equivalent Ceq is controlled.
  • the Ceq is set as the following Expression 1
  • the lower limit for Ceq is set to 0.32%, 0.34%, or 0.35%.
  • the upper limit for Ceq is set to 0.48.
  • the upper limit for Ceq is set to 0.45%, 0.43%, or 0.40%.
  • the Ceq may be calculated by substituting 0 for the value in Expression 1, for an element in which the amount in a steel is equal to or less than a detection limit.
  • Ceq C + Mn / 6 + Cr + Mo + V / 5 Ni + Cu / 15
  • the steel composition described above may be measured by a general analysis method for a steel.
  • the steel composition may be measured by using ICP-AES (inductively coupled plasma-atomic emission spectrometry).
  • C and S may be measured by using a combustion-infrared absorption method
  • N may be measured by using an inert gas fusion-thermal conductivity method
  • O may be measured by using an inert gas fusion-non dispersive infrared absorption method.
  • the steel structure includes ferrite of 60% to less than 100% by area fraction, a mixed structure MA of martensite and austenite being limited to 3.0% or less, and a structure other than ferrite and the MA being limited to 37% or less.
  • the average grain size of ferrite is set to 1 ⁇ m or more and 30 ⁇ m or less.
  • Ferrite is a main constituent phase in the steel structure of the H section according to the present embodiment. If the area fraction of ferrite is less than 60%, low temperature toughness is deteriorated. Therefore, the lower limit for the ferrite fraction is set to 60%. Preferably, the lower limit for the ferrite fraction is set to 65%, 70%, or 75%. On the other hand, controlling the area fraction of ferrite to 100% is physically difficult because it involves formation of pearlite or bainite. Therefore, the upper limit for the ferrite fraction is set to less than 100%. In order to preferably control the strength and the low temperature toughness, the upper limit for the ferrite fraction is preferably set to 90%, 85%, or 80%.
  • the MA fraction is limited to 3.0% or less.
  • the upper limit for the MA fraction is set to 2.5%, 2.0%, or 1.5%. The smaller the MA fraction, the more preferable. Therefore, the lower limit for the MA fraction may be 0%.
  • the steel structure of the H section according to the present embodiment includes bainite, pearlite, and the like as structures other than the ferrite and the MA, as described above. If a structure other than ferrite and an MA is excessively included, low temperature toughness is deteriorated. Therefore, the area fraction of a structure other than ferrite and an MA (the remainder of ferrite and an MA, as described above) is limited to 37% or less. Preferably, the fraction of a structure other than ferrite and an MA is set to 35% or less, 30% or less, or 25% or less. The smaller the fraction of a structure other than ferrite and an MA, the more preferable. Therefore, the lower limit therefor may be 0%.
  • an average grain size of ferrite is refined.
  • the upper limit for the grain size of ferrite is set to 30 ⁇ m.
  • the upper limit for the grain size of ferrite is set to 25 ⁇ m, 22 ⁇ m, or 18 ⁇ m.
  • the lower limit for the grain size of ferrite is set to 1 ⁇ m.
  • the lower limit for the grain size of ferrite is set to 3 ⁇ m, 5 ⁇ m, or 10 ⁇ m.
  • FIG. 1 is a schematic cross-sectional view orthogonal to a rolling direction of an H section.
  • the steel structure is observed by setting a portion in the vicinity of an evaluation portion 7 illustrated in FIG. 1 as an observed section.
  • the steel structure is observed by setting a portion in the vicinity of the evaluation portion 7 at a position of (1/6)F from an end surface 5a of a flange in a width direction and a position of (1/4)t 2 from an outer surface 5b of the flange in a thickness direction, as the observed section.
  • This observed section is a section parallel to the end surface 5a of the flange in the width direction.
  • the steel structure is observed by polishing and etching the observed section described above. Polishing is performed until the observed section becomes a specular section, and etching is performed by using an etching solution suitable for identifying the constituent phase. For example, if the observed section finished to be a specular section is etched with a nital solution such that the steel structure is manifested, pearlite or bainite is colored. Therefore, ferrite, martensite, and austenite can be identified. In addition, if the observed section finished to be a specular section is etched with a Le Pera solution such that the steel structure is manifested, the constituent phases other than martensite and austenite are colored black. Therefore, the mixed structure MA of martensite and austenite can be identified.
  • the fractions of ferrite and an MA are obtained from the nital-etched observed section, and the remainder is regarded as the fractions of the structures of pearlite and bainite.
  • the MA fraction is obtained from the Le Pera-etched observed section. Specifically, on a photograph of an optical microscope of 200 magnifications (as necessary, a plurality of visual fields) captured in the nital-etched observed section, measurement points are disposed in a lattice shape having one side of 25 ⁇ m, and it is discriminated whether or not the structure is ferrite or an MA at not less than 1,000 measurement points. The value obtained by dividing the number of measurement points determined to be ferrite or an MA by the number of all of the measurement points is regarded as the fraction of ferrite or an MA.
  • measurement points are disposed in a lattice shape having one side of 25 ⁇ m, and it is discriminated whether or not the structure is an MA at not less than 1,000 measurement points.
  • the value obtained by dividing the number of measurement points determined to be an MA by the number of all of the measurement points is regarded as the MA fraction.
  • the fraction of ferrite is obtained by subtracting the total fraction of pearlite, bainite, and the MA fraction obtained as above from 100%.
  • the average grain size of ferrite is obtained by an intercept method in conformity with JIS G 0551 (2013) using the photograph of an optical microscope of 200 magnifications captured in the nital-etched observed section described above.
  • test pieces are collected from a region including the evaluation portion 7 illustrated in FIG. 1 , as a position at which the average mechanical properties (strength and low temperature toughness) can be obtained, and mechanical properties are evaluated.
  • FIG. 1 is a schematic cross-sectional view orthogonal to the rolling direction of an H section.
  • an X-axis direction is defined as the width direction of the flange
  • a Y-axis is defined as the thickness direction of the flange
  • a Z-axis direction is defined as the rolling direction.
  • the center of the evaluation portion 7 is at the position of (1/6)F from the end surface of the flange in the width direction and the position of (1/4)t 2 from the outer surface of the flange in the thickness direction.
  • the outer surface of the flange in the thickness direction is a surface on one side in the thickness direction of the flange, is a surface on a side which does not come into contact with a web 6, and is the surface 5b illustrated in FIG. 1 .
  • the end surface of the flange in the width direction is the end surface 5a illustrated in FIG. 1 .
  • a test piece used when low temperature toughness is evaluated through the Charpy test is collected at the position of the evaluation portion 7 such that the longitudinal direction of the test piece becomes parallel to the rolling direction.
  • a surface on which a notch is formed in the test piece is any of surfaces parallel to the end surface 5a of the flange in the width direction.
  • the test piece may be collected at any position as long as it is the position of (1/6)F from the end surface 5a of the flange in the width direction and the position of (1/4)t 2 from the outer surface 5b of the flange in the thickness direction.
  • a test piece used when yield stress (yield strength or 0.2% proof stress) and tensile strength (maximum tensile strength) are evaluated through a tension test is collected such that the position of (1/6)F from the end surface 5a of the flange in the width direction becomes the center of the test piece in the thickness direction, in FIG. 1 .
  • the longitudinal direction of the test piece may be parallel to the rolling direction such that the entirety of the flange in the thickness direction is cut out.
  • the test piece may be collected at any position as long as it is the position of (1/6)F from the end surface 5a of the flange in the width direction.
  • the yield stress at a normal temperature becomes 385 MPa or more
  • the tensile strength becomes 490 MPa or more
  • the Charpy absorbed energy at -20°C becomes 100 J or greater.
  • the upper limit for the yield stress is preferably set to 530 MPa and the upper limit for the tensile strength is preferably set to 690 MPa.
  • the upper limit for the Charpy absorbed energy at - 20°C may be set to 500 J.
  • a normal temperature indicates 20°C.
  • the tension test is performed in conformity with JIS Z 2241 (2011), and the Charpy test is performed in conformity with JIS Z 2242 (2005).
  • yield strength is obtained as the yield stress.
  • no yielding phenomenon is recognized in the stress-strain curve, 0.2% proof stress is obtained as the yield stress.
  • the thickness t 2 of the flange is 20 mm to 140 mm.
  • the lower limit for the thickness of the flange is set to 20 mm.
  • the lower limit for the thickness of the flange is set to 25 mm, 40 mm, or 56 mm.
  • the upper limit for the thickness of the flange is set to 140 mm.
  • the upper limit for the thickness of the flange is set to 125 mm, 89 mm, or 77 mm.
  • the thickness t 2 of the flange is 25 mm to 140 mm.
  • the thickness t 1 of the web of an H section is not particularly regulated. However, it is preferable that the thickness t 1 of the web of an H section is 20 mm to 140 mm, and it is more preferable that the thickness t 1 of the web of an H section is 25 mm to 140 mm.
  • the ratio (t 2 /t 1 ) of thickness of flange / thickness of web is 0.5 to 2.0. If the ratio (t 2 /t 1 ) of thickness of flange / thickness of web exceeds 2.0, the web may be deformed into a wavy shape. On the other hand, in a case where the ratio (t 2 /t 1 ) of thickness of flange / thickness of web is less than 0.5, the flange may be deformed into a wavy shape.
  • the H section according to the present embodiment is a thick H section having a thickness of a flange of 20 mm or more, the steel composition and the steel structure are optimally controlled. Therefore, it is possible to achieve both the strength and the low temperature toughness.
  • the method for manufacturing an H section according to the present embodiment includes steelmaking, casting, heating, hot rolling, and cooling.
  • the chemical composition of a molten steel is adjusted to obtain the steel composition described above.
  • a molten steel manufactured by performing converter refining or secondary refining may be used, or a molten steel melted in an electric furnace may be used as a raw material.
  • deoxidation processing or vacuum degassing may be performed.
  • a steel piece is obtained by casting a molten steel after the steelmaking. Casting is performed by a continuous casting method, an ingot method, or the like. From the viewpoint of productivity, it is preferable to adopt continuous casting. It is preferable that the shape of a steel piece is a beam blank having a shape close to that of an H section to be manufactured, but the shape thereof is not particularly limited. In addition, from the viewpoint of productivity, it is preferable that the thickness of a steel piece is 200 mm or more. In consideration of reduction of segregation or homogeneity in the heating temperature before hot rolling is performed, it is preferable that the thickness thereof is 350 mm or less.
  • the heating a steel piece after the casting is heated to 1,100°C to 1,350°C. If the heating temperature of a steel piece is less than 1,100°C, deformation resistance at the time of finish rolling is increased. Therefore, the lower limit for the heating temperature is set to 1,100°C. In order to sufficiently solid-solubilize elements which forms carbide or nitride, such as Nb, the lower limit for the heating temperature is preferably set to 1,150°C. On the other hand, if the heating temperature exceeds 1,350°C, scale on a steel piece surface is liquefied, so that manufacturing is hindered. Therefore, the upper limit for the heating temperature is set to 1,350°C. In the heating, a steel piece which is not cooled to the room temperature after the casting may be used.
  • hot rolling rough rolling, intermediate rolling, and finish rolling are performed with respect to a steel piece after the heating.
  • forming is performed such that the shape seen in a cut section orthogonal to the rolling direction becomes a substantial H-shape.
  • hot rolling in which the surface temperature of the steel is a temperature range of more than 900°C and 1,100°C or less and the cumulative rolling reduction is 20% or more, is performed.
  • hot rolling in which the surface temperature of the steel is a temperature range of 730°C to 900°C and the cumulative rolling reduction is 15% or more, is performed.
  • forming is performed such that the shape seen in the foregoing cut section ultimately becomes an H-shape.
  • the cumulative rolling reduction is set to 20% or more.
  • the lower limit for the cumulative rolling reduction in the temperature range of more than 900°C and 1,100°C or less is set to 25%, 30%, or 35%.
  • the upper limit for the cumulative rolling reduction in the temperature range of more than 900°C and 1,100°C or less may be set to 60%.
  • the cumulative rolling reduction is set to 15% or more.
  • the lower limit for the cumulative rolling reduction in the temperature range of 730°C to 900°C is set to 20%, 25%, or 30%.
  • the upper limit for the cumulative rolling reduction in the temperature range of 730°C to 900°C may be set to 50%.
  • a finish temperature of rolling is set to 730°C or more on the surface temperature of a steel.
  • the upper limit for the finish rolling temperature is set to 750°C.
  • rough rolling, intermediate rolling, and finish rolling are performed.
  • rolling at the temperature range of more than 900°C to 1,100°C may be performed by any of rough rolling, intermediate rolling, and finish rolling.
  • rolling at the temperature range of 730°C to 900°C may be performed by any of rough rolling, intermediate rolling, and finish rolling.
  • the cumulative rolling reduction in the foregoing temperature range may be controlled.
  • the cumulative rolling reduction in the foregoing temperature range is obtained with reference to the thickness of the flange at a position corresponding to (1/6)F from the end surface 5a of the flange in the width direction illustrated in FIG. 1 .
  • the cumulative rolling reduction in the temperature range of more than 900°C and 1,100°C or less is set to the rolling reduction calculated from the difference between the thickness of the flange at the time when the surface temperature of a steel is 1,100°C and the thickness of the flange immediately before the temperature reaches 900°C.
  • the cumulative rolling reduction in the temperature range of 730°C to 900°C is set to the rolling reduction calculated from the difference between the thickness of the flange at the time when the surface temperature of a steel is 900°C and the thickness of the flange at the time when the surface temperature of a steel is 730°C.
  • the methods for rough rolling, intermediate rolling, and finish rolling are not particularly limited.
  • breakdown rolling is performed as the rough rolling
  • universal rolling or edging rolling is performed as the intermediate rolling
  • universal rolling is performed as the finish rolling, so that the shape seen in a cut section orthogonal to the rolling direction may be formed into an H-shape.
  • water cooling may be performed between rolling passes.
  • Water cooling performed between the rolling passes is cooling performed for the purpose of controlling temperature in a temperature range which is more than the temperature at which austenite is phase-transformed. Bainite or an MA is not generated in a steel due to water cooling performed between the rolling passes.
  • Dual heat rolling means a rolling method in which a steel piece is cooled to a temperature of 500°C or less after primary rolling, and then, the steel piece is heated to 1,100°C to 1,350°C and secondary rolling is performed again.
  • dual heat rolling the plastic deformation amount is reduced in hot rolling, and the decrease in temperature in the rolling also becomes small. Therefore, a second heating temperature can be lowered.
  • a hot rolled material after the hot rolling is cooled.
  • a hot rolled material is subjected to natural cooling in the atmosphere as it is after ending of the hot rolling.
  • the average cooling rates of a surface of a steel and inside thereof from 800°C to 500°C become 1 °C/sec or less. Since the cooling rates of a surface of a steel and inside thereof are uniform by performing natural cooling on a hot rolled material in the atmosphere, unevenness in mechanical properties depending on the portions of a steel is suppressed.
  • natural cooling means that cooling is performed in the atmosphere without forcibly performing cooling until the temperature of a steel reaches to 400°C or less from immediately after hot rolling.
  • a hot rolled material has been subjected to accelerated cooling in order to achieve both the strength and the toughness. Accordingly, unevenness in mechanical properties has been caused between a surface of a steel and inside thereof.
  • the steel composition and the steel structure are optimally controlled. Therefore, it is possible to achieve both the strength and the low temperature toughness without causing unevenness in mechanical properties between a surface of a steel and inside thereof.
  • the method for manufacturing an H section according to the present embodiment does not require an advanced steelmaking technology or accelerated cooling, it is possible to reduce a manufacturing load and to shorten a construction period. Therefore, the H section according to the present embodiment can improve reliability of a large building without impairing economic feasibility.
  • FIG. 2 illustrates processes for manufacturing an H section.
  • Hot rolling of a steel piece heated by a heating furnace 1 was performed in a universal rolling apparatus array including a rough rolling mill 2a, an intermediate rolling mill 2b, and a finish rolling mill 2c.
  • a hot rolled material was subjected to natural cooling as it is until the temperature reached to 400°C or less after ending of hot rolling. Both the average cooling rates of a surface of the hot rolled material and inside thereof from an ending temperature of hot rolling to 500°C were 1 °C/sec or less.
  • spray cooling of an outer surface of the flange was performed by using water cooling apparatuses 3 provided in the front and the rear of the intermediate universal rolling mill (intermediate rolling mill) 2b. In this case, reverse rolling was performed.
  • Table 4 to Table 6 show the manufacturing conditions and the manufactured results.
  • the rolling reductions at the time of hot rolling shown in Table 4 to Table 6 are cumulative rolling reductions in the temperature ranges at a position corresponding to (1/6)F from the end surface 5a of the flange in the width direction illustrated in FIG. 1 .
  • the Charpy test was performed at-20°C by using the test piece collected from the evaluation portion 7 illustrated in FIG. 1 , and the low temperature toughness was evaluated.
  • the tension test was performed at a normal temperature (20°C) by using the test piece in which the position of (1/6)F from the end surface 5a of the flange in the width direction became the center in the thickness direction, and the tensile properties were evaluated.
  • the structure was observed by using the sample having a portion in the vicinity of the evaluation portion 7 illustrated in FIG. 1 as the observed section, and the steel structure was evaluated.
  • the tension test was performed in conformity with JIS Z 2241 (2005). In the case where the stress-strain curve of the tension test indicated yielding behavior, a yield point was regarded as the yield stress. In the case where no yielding behavior was indicated, 0.2% proof stress was regarded as the yield stress.
  • a Charpy impact test was performed in conformity with JIS Z 2242 (2005). The Charpy impact test was performed at -20°C.
  • the structure was observed by using the method described above, and the ferrite fraction, the MA fraction, and the fraction of a structure other than the ferrite and the MA was measured by using a photograph of an optical microscope.
  • the structure other than the ferrite and the MA was bainite or pearlite.
  • the average grain size of ferrite was obtained by an intercept method in conformity with JIS G 0551 (2013) using a photograph of an optical microscope.
  • a steel having yield stress (YS) at a normal temperature of 385 MPa or more and tensile strength (TS) of 490 MPa or more was determined as PASSED.
  • a steel having Charpy absorbed energy at -20°C (vE-20) of 100 J or greater was determined as PASSED.
  • Serial No. 9 was an example in which rolling reduction within more than 900°C and 1,100°C or less was insufficient. Therefore, the ferrite fraction in the steel structure became insufficient and the fraction of the structure other than the ferrite and the MA became excessive, so that the Charpy absorbed energy at -20°C became insufficient.
  • Serial No. 10 was an example in which rolling reduction within 730°C to 900°C was insufficient. Therefore, grain size of ferrite was coarsened, so that the Charpy absorbed energy at -20°C became insufficient.
  • Serial No. 19 was an example in which rolling reduction within more than 900°C and 1,100°C or less was insufficient. Therefore, the fraction ferrite became insufficient, the MA fraction became excessive, and the fraction of the structure other than the ferrite and the MA became excessive, so that the Charpy absorbed energy at - 20°C became insufficient.
  • Serial No. 20 was an example in which the C content was large.
  • Serial No. 25 was an example in which the Nb content was large.
  • Serial No. 26 was an example in which the V content was large.
  • Serial No. 28 was an example in which the Al content was large.
  • Serial No. 29 was an example in which the Ti content was large.
  • Serial No. 30 was an example in which the N content was large.
  • Serial No. 31 was an example in which Ceq was excessive. Therefore, the Charpy absorbed energy at - 20°C became insufficient in these examples.
  • Serial No. 21 was an example in which the C content was small.
  • Serial No. 24 was an example in which the Mn content was small.
  • Serial No. 32 was an example in which Ceq was insufficient.
  • Serial No. 46 was an example in which the Si content was small. Therefore, YS and TS became insufficient in these examples.
  • Serial No. 22 was an example in which the Si content was large.
  • Serial No. 23 was an example in which the Mn content was large and MA fraction was excessive. Therefore, the Charpy absorbed energy at -20°C became insufficient in these examples.
  • Serial No. 27 was an example in which the V content was small, so that grain size of ferrite is coarsened. Therefore, the Charpy absorbed energy at -20°C became insufficient.
  • Serial No. 33 was an example in which the B content was excessive and Ceq was excessive.
  • Serial No. 49 was an example in which the B was large, so that the MA fraction became excessive. Therefore, the Charpy absorbed energy at -20°C became insufficient in these examples.
  • Serial No. 44 and Serial No. 45 were examples in which the V content was small, so that grain size of ferrite was coarsened. Therefore, the Charpy absorbed energy at -20°C became insufficient in these examples.
  • Serial No. 47 was an example in which the Nb content was small, so that grain size of ferrite was coarsened. Therefore, YS and TS became insufficient and the Charpy absorbed energy at -20°C became insufficient.
  • Serial No. 48 was an example in which the Ti content was small, so that grain size of ferrite was coarsened. Therefore, the Charpy absorbed energy at -20°C became insufficient.
  • Serial No. 50 was an example in which the finish rolling temperature was low. Therefore, the Charpy absorbed energy at -20°C became insufficient.
  • Table 1 Serial No. Composition No. Chemical composition [mass%] (remainder of Fe and impurities) Ceq C Si Mn Nb V Al Ti N Cr Mo Ni Cu W B Ca Zr 1 1 0.158 0.55 0.82 0.045 0.098 0.095 0.024 0.0005 0.314 2 2 0.157 0.54 0.84 0.046 0.051 0.091 0.022 0.0007 0.307 3 3 0.131 0.38 1.55 0.047 0.099 0.032 0.012 0.0023 0.40 0.0018 0.409 4 4 0.130 0.09 1.59 0.041 0.102 0.028 0.010 0.0030 0.415 5 5 0.121 0.40 1.40 0.045 0.110 0.037 0.011 0.0070 0.20 0.20 0.403 6 6 0.119 0.44 0.95 0.040 0.115 0.031 0.012 0.0042 0.18 0.336 7 7 0.110 0.29

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EP3533893A4 (de) 2020-06-24
CN109715842A (zh) 2019-05-03
JP6468408B2 (ja) 2019-02-13
WO2018117228A1 (ja) 2018-06-28
US20190203309A1 (en) 2019-07-04
JPWO2018117228A1 (ja) 2019-04-04
KR20190032625A (ko) 2019-03-27
CN109715842B (zh) 2020-03-06
PH12019500350A1 (en) 2019-11-11

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