WO2022185632A1 - Ｈ形鋼 - Google Patents

Ｈ形鋼 Download PDF

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Publication number
WO2022185632A1
WO2022185632A1 PCT/JP2021/043489 JP2021043489W WO2022185632A1 WO 2022185632 A1 WO2022185632 A1 WO 2022185632A1 JP 2021043489 W JP2021043489 W JP 2021043489W WO 2022185632 A1 WO2022185632 A1 WO 2022185632A1
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less
mass
content
steel
toughness
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PCT/JP2021/043489
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English (en)
French (fr)
Japanese (ja)
Inventor
佳祐 安藤
浩文 大坪
進一 三浦
直人 中村
和彦 塩谷
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Ｊｆｅスチール株式会社
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Priority to JP2022514552A priority Critical patent/JP7405246B2/ja
Priority to KR1020237025670A priority patent/KR20230125287A/ko
Priority to CN202180092151.2A priority patent/CN116802333A/zh
Publication of WO2022185632A1 publication Critical patent/WO2022185632A1/ja

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
    • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
    • B05D7/50—Multilayers
    • B05D7/56—Three layers or more
    • 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
    • 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
    • C22C38/02—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
    • C22C38/08—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
    • C22C38/16—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
    • C22C38/40—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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D2504/00—Epoxy polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D2506/00—Halogenated polymers
    • B05D2506/10—Fluorinated polymers

Definitions

  • the present invention relates to H-section steel, which is mainly used in land and outdoor atmospheric corrosive environments such as construction, civil engineering, and bridges. It is related to the H-section steel that is used.
  • H-section steel which is frequently used as a structural member
  • weathering steel is often used in an environment with a small amount of airborne salt, for example.
  • the surface is covered with a highly protective rust layer in which alloy elements such as Cu, P, Cr, and Ni are concentrated, which greatly reduces the corrosion rate.
  • alloy elements such as Cu, P, Cr, and Ni are concentrated, which greatly reduces the corrosion rate.
  • It is a steel material that has been It is known that bridges using such weather-resistant steel can withstand several decades of service without painting in an environment with a small amount of airborne salt.
  • the H-section steel with excellent corrosion resistance that can reduce the frequency of painting and the maintenance cost of structures, especially the H-section steel with excellent painting durability. development is desired.
  • Patent Document 1 Cr and Cu are added to ensure corrosion resistance, and by precisely controlling rolling and cooling conditions, red-hot embrittlement caused by molten Cu is also suppressed.
  • a method for manufacturing an H-beam is disclosed.
  • Patent Document 2 discloses H-section steel with excellent weather resistance, which has excellent corrosion resistance even in coastal areas where the airborne salt content is 0.05 mdd or more, by adjusting the added amounts of Mo and Ni. ing.
  • Patent Documents 3 to 7 in addition to the above alloy elements, by adding predetermined amounts of Sn and Sb, corrosion resistance in severe corrosive environments such as the sea and near the coast is greatly improved. is disclosed.
  • H-shaped steel described in Patent Documents 1 and 2 did not consider coating durability, and there was a problem that the weather resistance in a high airborne salt environment was not sufficient.
  • H-section steel which requires heating at 1200 ° C. or higher during hot working, tends to have coarser grains than thick steel plates.
  • the element is contained excessively, it becomes difficult to ensure toughness.
  • the present invention has been made in view of the above circumstances, and aims to provide H-shaped steel that is excellent in coating durability and strength-toughness balance.
  • Excellent strength-toughness balance means that the tensile strength is 400 MPa or more, the yield strength is 235 MPa or more, and the impact absorption energy at 0°C is 27 J or more.
  • the present inventors produced H-shaped steel with varying contents of C, Si, Mn, P, S, Cu, Ni, W and Mo, and diligently investigated the coating durability, tensile properties and toughness.
  • excellent coating durability and strength can be achieved.
  • H-section steel with excellent toughness balance can be obtained.
  • the present invention is based on the above findings, and the gist and configuration thereof are as follows.
  • C 0.05 to 0.20% by mass
  • Si 0.05 to 1.00% by mass
  • Mn 0.50 to 2.00% by mass
  • P 0.003 to 0.035% by mass
  • S 0.035% by mass or less
  • Cu 0.01 to 0.50% by mass
  • Ni 0.01 to 0.50% by mass
  • W 0.005 to 0.30% by mass
  • Mo 0.005 to 0.50% by mass, containing one or two selected from and having a steel composition containing Cu, P, W, and Mo within a range that satisfies the following formula (1), with the balance being Fe and unavoidable impurities, H-section steel having a tensile strength of 400 MPa or more, a yield strength of 235 MPa or more, and an impact absorption energy of 27 J or more at 0°C.
  • [%Cu], [%P], [%W] and [%Mo] in the formula (1) are respectively the contents of Cu, P, W and Mo in the steel (% by mass). , 0 if not contained.
  • the steel composition further includes Cr: 1.00% by mass or less, Sn: 0.200% by mass or less, Sb: 0.200% by mass or less, Al: 0.100% by mass or less, Nb: 0.50% by mass or less, V: 0.50% by mass or less, Ti: 0.50% by mass or less, B: 0.0100% by mass or less, Zr: 0.100% by mass or less, Ca: 0.100% by mass or less,
  • the coating film has an anticorrosion undercoat layer, an undercoat layer, an intermediate coat layer and a topcoat layer, wherein the anticorrosion undercoat layer is an inorganic zinc-rich paint, the undercoat layer is an epoxy resin paint, and the intermediate coat layer is a fluorine resin.
  • the cycle of repainting can be extended.
  • H-section steel that can reduce the frequency of painting and has excellent painting durability and strength-toughness balance.
  • the present invention it is possible to stably produce H-shaped steel having excellent coating durability and strength-toughness balance, and it is possible to produce H-shaped steel in an outdoor atmospheric corrosion environment such as a bridge, especially at sea where there is a large amount of airborne salt. Even when used in severely corrosive environments such as near the coast or near the coast, it is possible to obtain H-shaped steel with excellent coating durability at low cost, which can extend the recoating cycle and reduce the coating frequency. can. Then, the H-shaped steel of the present invention, which has excellent coating durability, can be used for bridges and other structures that are used in outdoor atmospheric corrosive environments such as bridges, especially in severe corrosive environments such as the sea or near the coast where there is a large amount of airborne salt. By suitably using it for a structure, it becomes possible to reduce the maintenance cost of such a structure, and by extension, the life cycle cost.
  • C 0.05-0.20% C is an element necessary for ensuring the strength of the base material, and should be added in an amount of at least 0.05%. However, the addition of C exceeding 0.20% not only lowers the toughness of the base metal, but also lowers the weldability. Therefore, in the present invention, the C content is made 0.05 to 0.20%.
  • the C content is preferably 0.07% or more, more preferably 0.09% or more, still more preferably 0.11% or more. Also, the C content is preferably 0.18% or less, more preferably 0.15% or less.
  • Si 0.05-1.00%
  • Si also has the effect of forming a dense rust layer and improving the coating durability of the H-section steel.
  • the Si content is set to 0.05 to 1.00%.
  • the Si content is preferably 0.10% or more, more preferably 0.15% or more, still more preferably 0.20% or more.
  • the Si content is preferably 0.60% or less, more preferably 0.45% or less.
  • Mn 0.50-2.00%
  • Mn is an element effective in increasing the hardenability and ensuring the strength of the base material.
  • the Mn content is set to 0.50 to 2.00%.
  • the Mn content is preferably 0.60% or more, more preferably 0.80% or more, and still more preferably 1.20% or more.
  • the Mn content is preferably 1.80% or less, more preferably 1.60% or less.
  • P 0.003-0.035%
  • P is an element with high solid-solution strengthening ability, and since it reduces the toughness through hardening of ferrite, the P content in the steel is made 0.035% or less in the present invention.
  • P is an element that contributes to the improvement of coating durability, it is necessary to add at least 0.003% of P. Therefore, in the present invention, the P content is made 0.003 to 0.035%.
  • the P content is preferably 0.005% or more, more preferably 0.008% or more, and still more preferably 0.010% or more. Also, the P content is preferably 0.025% or less, more preferably 0.020% or less.
  • S 0.035% or less S exists in steel mainly in the form of A-based inclusions. It greatly reduces toughness in order to generate Therefore, in the present invention, the S content is made 0.035% or less.
  • the S content is preferably 0.020% or less, more preferably 0.010% or less, still more preferably 0.008% or less.
  • the lower the S content the better, so the lower limit of the S content is not particularly limited, and may be 0%. may be greater than 0%.
  • the S content is preferably 0.002% or more.
  • Cu 0.01-0.50%
  • Cu is an important element in the H-section steel of the present invention, which has excellent coating durability. It has the effect of suppressing the permeation of ions into the base iron.
  • the synergistic effect with these elements greatly improves the coating durability of the steel material. Such an effect is obtained when the Cu content is 0.01% or more.
  • the Cu content exceeds 0.50%, not only does the alloy cost rise, but Cu cracks are likely to occur during hot working. Furthermore, since the hardenability of the steel increases, the toughness also decreases. Therefore, in the present invention, the Cu content is set to 0.01 to 0.50%.
  • the Cu content is preferably 0.03% or more, more preferably 0.05% or more, and still more preferably 0.07% or more.
  • the Cu content is preferably 0.30% or less, more preferably 0.20% or less.
  • Ni forms a dense rust layer by refining the rust grains of the rust layer, suppressing the permeation of oxygen and chloride ions, which are factors that promote corrosion, into the base steel, and also suppresses Cu cracking. have.
  • the synergistic effect with these elements greatly improves the coating durability of the steel material.
  • the Ni content is set to 0.01 to 0.50%.
  • the Ni content is preferably 0.03% or more, more preferably 0.05% or more, still more preferably 0.07% or more.
  • the Ni content is preferably 0.30% or less, more preferably 0.20% or less.
  • the W content when W is contained, is set to 0.005 to 0.30%.
  • the W content is preferably 0.01% or more, more preferably 0.03% or more, still more preferably 0.05% or more.
  • the W content is preferably 0.30% or less, more preferably 0.20% or less.
  • Mo 0.005-0.50% Mo is eluted with the anodic reaction of the steel material and distributed as MoO 4 2- in the rust layer, thereby preventing chloride ions, which are corrosion-promoting factors, from penetrating the rust layer and reaching the base iron. do.
  • a compound containing Mo precipitates on the surface of the steel material, thereby suppressing the anode reaction of the steel material.
  • the Mo content is 0.005% or more.
  • the content exceeds 0.50%, the upper bainite transformation is accelerated and the toughness is lowered. Therefore, in the present invention, when Mo is contained, the Mo content is set to 0.005 to 0.50%.
  • the Mo content is preferably 0.02% or more, more preferably 0.05% or more, still more preferably 0.07% or more. Also, the Mo content is preferably 0.40% or less, more preferably 0.30% or less. In the present invention, it is preferable to contain W among the above-mentioned W and Mo, and it is more preferable to contain W and Mo.
  • [%Cu], [%P], [%W] and [%Mo] in the formula (1) are respectively the contents of Cu, P, W and Mo in the steel (% by mass). , 0 if not contained.
  • the inventors have evaluated coating durability and strength-toughness balance using various H-section steels having steel components within the content ranges described above. is within the above content range, and it is important to control the content of Cu, P, W and Mo within specific ranges.
  • the value calculated by the above formula (1) which is a parameter based on the contents of Cu, P, W and Mo (2.6 ⁇ [% Cu] + 0.8 ⁇ [% P] + 4.2 x [% W] + 1.1 x [% Mo]) is 0.25 or more and 1.30 or less, so that excellent coating durability and strength-toughness balance can be stably obtained. can be done.
  • the value calculated by the formula (1) is less than 0.25, it is difficult to stably form a dense rust layer that suppresses permeation of oxygen and chloride ions, which are corrosion-promoting factors, into the steel substrate. As a result, the coating durability is lowered.
  • the value calculated by the formula (1) exceeds 1.30, the increase in hardenability due to Cu, W and Mo and the superimposition of ferrite hardening due to P become significant, resulting in a decrease in toughness.
  • the range of values calculated by the above formula (1) should be 0.40 or more and 1.20 or less, that is, the contents of Cu, P, W and Mo should satisfy the following formula (2). is more preferred.
  • the value calculated by the above formula (1) (value calculated by 2.6 ⁇ [% Cu] + 0.8 ⁇ [% P] + 4.2 ⁇ [% W] + 1.1 ⁇ [% Mo]) is , is preferably 0.40 or more, more preferably 0.50 or more. Moreover, the value calculated by the above formula (1) is preferably 1.20 or less, more preferably 1.10 or less.
  • the steel composition of the H-section steel of the present invention is, for the purpose of further improving coating durability, strength, ductility, and toughness, Cr: 1.00% or less, Sn: 0.200% or less, Sb: 0.200% or less, Al: 0.100% or less, Nb: 0.50% or less, V: 0.50% or less, Ti: 0.50% or less, B: 0.0100% or less, Zr: One or more selected from 0.100% or less, Ca: 0.100% or less, Mg: 0.100% or less, and REM: 0.100% or less may optionally be contained.
  • Cr 1.00% or less
  • Cr is an element capable of further increasing the strength of steel through solid-solution strengthening. In order to sufficiently obtain such effects, it is preferable to contain 0.01% or more of Cr. However, when the content exceeds 1.00%, the upper bainite transformation is accelerated and the toughness is lowered. Therefore, when Cr is contained, the Cr content is made 1.00% or less.
  • the Cr content is more preferably 0.05% or more, still more preferably 0.10% or more. Also, the Cr content is preferably 0.50% or less, more preferably 0.30% or less.
  • Sn 0.200% or less Sn exists in the rust layer near the surface of the base iron, and by refining the rust particles, chloride ions, which are corrosion-promoting factors, permeate the rust layer and reach the base iron. to prevent Also, Sn suppresses the anode reaction on the surface of the steel material. Further, Sn is added together with Cu and Ni, and further together with Cu, Ni and W, to greatly improve the coating durability of the steel due to the synergistic effect with these elements. In order to sufficiently obtain such effects, it is preferable to contain 0.005% or more of Sn. However, when the content exceeds 0.200%, ductility and toughness are lowered. Therefore, when Sn is contained, the Sn content shall be 0.200% or less. The Sn content is more preferably 0.010% or more, still more preferably 0.020% or more. Also, the Sn content is preferably 0.100% or less, more preferably 0.080% or less.
  • Sb 0.200% or less Sb exists in the rust layer near the surface of the base iron, and by refining the rust particles, chloride ions, which are corrosion-promoting factors, permeate the rust layer and reach the base iron. to prevent Moreover, Sb suppresses the anode reaction on the surface of the steel material. Further, Sb is added together with Cu, Ni, and further together with Cu, Ni, and W in a composite manner, so that the synergistic effect with these elements greatly improves the coating durability of the steel material. In order to sufficiently obtain such effects, it is preferable to contain 0.005% or more of Sb. However, when the content exceeds 0.200%, ductility and toughness are lowered.
  • the Sb content shall be 0.200% or less.
  • the Sb content is more preferably 0.010% or more, still more preferably 0.020% or more.
  • the Sb content is preferably 0.100% or less, more preferably 0.080% or less.
  • Al 0.100% or less
  • Al is an element that can be added as a deoxidizing agent. In order to sufficiently obtain such effects, it is preferable to contain 0.001% or more of Al. However, when the Al content exceeds 0.100%, a large amount of oxide-based inclusions are generated in the steel due to the high bonding strength of Al with oxygen, resulting in a decrease in ductility of the steel. Therefore, when Al is contained, the Al content shall be 0.100% or less.
  • the Al content is more preferably 0.010% or more, still more preferably 0.020% or more. Also, the Al content is preferably 0.080% or less, more preferably 0.050% or less.
  • Nb 0.50% or less
  • Nb is an element that has the effect of improving tensile strength and yield point by precipitating as a carbonitride. In order to sufficiently obtain such effects, it is preferable to contain 0.005% or more of Nb. However, if the content exceeds 0.50%, in addition to promoting precipitation embrittlement, upper bainite transformation is promoted, resulting in a decrease in toughness. Therefore, when Nb is contained, the Nb content should be 0.50% or less.
  • the Nb content is more preferably 0.010% or more, still more preferably 0.020% or more. Also, the Nb content is preferably 0.20% or less, more preferably 0.10% or less.
  • V 0.50% or less
  • V is an element that precipitates in austenite as VN during rolling or during cooling after rolling, becomes ferrite transformation nuclei, and has the effect of refining crystal grains.
  • V also has a role of increasing the strength of the base material by precipitation strengthening, and is an element useful for ensuring tensile strength and toughness. In order to sufficiently obtain such effects, it is preferable to contain 0.005% or more of V. However, if the content exceeds 0.50%, excessive precipitation strengthening tends to lower the toughness of the base material. Therefore, when V is contained, the V content should be 0.50% or less.
  • the V content is more preferably 0.010% or more, still more preferably 0.020% or more. Also, the V content is preferably 0.20% or less, more preferably 0.10% or less.
  • Ti 0.50% or less
  • Ti is an element that not only forms TiN to refine austenite grains, but also refines the microstructure by promoting intragranular ferrite transformation with TiN as the nucleus, and is effective in improving toughness. is.
  • the Ti content should be 0.50% or less.
  • the Ti content is more preferably 0.010% or more, still more preferably 0.020% or more.
  • the Ti content is preferably 0.20% or less, more preferably 0.10% or less.
  • B 0.0100% or less
  • B is an element that segregates at grain boundaries in steel and has the effect of improving grain boundary strength.
  • it is an element effective in improving toughness by forming composite precipitates with TiN that serve as nucleation sites for intragranular ferrite and refining the microstructure.
  • it is preferable to contain 0.0001% or more of B.
  • the B content shall be 0.0100% or less.
  • the B content is more preferably 0.0010% or more, still more preferably 0.0020% or more.
  • the B content is preferably 0.0050% or less, more preferably 0.0040% or less.
  • Zr 0.100% or less
  • Zr is an element that can further increase the strength of steel. In order to sufficiently obtain this effect, it is preferable to contain 0.005% or more of Zr. However, when the content exceeds 0.100%, the effect of increasing the strength is saturated and the toughness is also lowered. Therefore, when Zr is contained, the Zr content shall be 0.100% or less.
  • the Zr content is more preferably 0.010% or more, still more preferably 0.015% or more. Also, the Zr content is preferably 0.050% or less, more preferably 0.040% or less.
  • Ca 0.100% or less
  • Ca has the effect of transforming the oxides and sulfides in the sulfide-based inclusions into those with high stability at high temperatures and granulating the sulfide-based inclusions.
  • the effect of controlling the morphology of inclusions by this Ca can improve the toughness and ductility of the steel.
  • the Ca content shall be 0.100% or less.
  • the Ca content is more preferably 0.0010% or more, still more preferably 0.0020% or more.
  • the Ca content is preferably 0.0100% or less, more preferably 0.0050% or less.
  • Mg 0.100% or less Mg has the effect of transforming the oxides and sulfides in the sulfide-based inclusions into those with high stability at high temperatures and granulating the sulfide-based inclusions.
  • the effect of controlling the shape of inclusions by this Mg makes it possible to improve the toughness and ductility of the steel.
  • Mg content when the Mg content exceeds 0.100%, the cleanliness is lowered and the toughness is lowered. Therefore, when Mg is contained, the Mg content shall be 0.100% or less.
  • the Mg content is more preferably 0.0010% or more, still more preferably 0.0020% or more.
  • the Mg content is preferably 0.0100% or less, more preferably 0.0050% or less.
  • REM 0.100% or less REM (rare earth metal) has the effect of transforming oxides and sulfides in sulfide-based inclusions into those with high stability at high temperatures, and granulating the sulfide-based inclusions. have The effect of controlling the morphology of inclusions by this REM makes it possible to improve the toughness and ductility of the steel. In order to sufficiently obtain such effects, it is preferable to contain 0.0001% or more of REM. However, when the REM content exceeds 0.100%, the cleanliness is lowered and the toughness is lowered. Therefore, when REM is contained, the REM content shall be 0.100% or less.
  • the REM content is more preferably 0.0010% or more, still more preferably 0.0020% or more.
  • the REM content is preferably 0.0100% or less, more preferably 0.0050% or less.
  • REM is a general term for Sc, Y, and 15 elements from lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71, and the REM content here is the total content of these elements. quantity.
  • Unavoidable impurities are impurities that exist in raw materials or are unavoidably mixed in during the manufacturing process, and are originally unnecessary, but are allowed to be contained because they are trace amounts and do not affect characteristics. means Examples of unavoidable impurities include N, O, etc. N can be contained up to 0.0150%, and O can be contained up to 0.005%.
  • the H-section steel of the present invention is usually used with the steel surface painted, in which case it has a coating film on the surface.
  • the coating film on the steel surface includes, for example, a coating film having an anticorrosion base layer, an undercoat layer, an intermediate coating layer and a top coating layer in this order from the steel surface.
  • the anti-corrosion base layer is an inorganic zinc-rich paint (e.g., Kansai Paint Co., Ltd.: SD Zinc 1500), the undercoat layer is an epoxy resin paint (e.g., Kansai Paint Co., Ltd.: EPOMARINE HB (K)), and the intermediate coating layer is Intermediate paint for fluororesin topcoat paint (e.g., Kansai Paint Co., Ltd.: Ceratect F middle coat), and the topcoat layer is formed using a fluororesin topcoat paint (e.g., Kansai Paint Co., Ltd.: Ceratect F (K) topcoat). preferably.
  • the method for manufacturing the H-section steel of the present invention will be explained.
  • the method of melting and casting the steel material slab or beam blank
  • any conventionally known method is suitable.
  • hot rolling conditions for forming the H-shaped steel from the steel material a steel material having a predetermined chemical composition is heated to a predetermined heating temperature and rolled at a predetermined finish rolling temperature. After that, there is hot rolling in which cooling is performed at a predetermined cooling rate.
  • the heating temperature of the steel material during hot rolling is preferably 1150 to 1350°C. If the heating temperature is lower than 1150° C., the deformation resistance in hot rolling increases and the load on the rolling rolls increases, resulting in difficulty in hot rolling. On the other hand, if the heating temperature exceeds 1350° C., the steel material is partially melted and internal defects are generated. In addition, the austenite grain size becomes coarse. It becomes easy to form, and a fall of toughness occurs. Therefore, it is preferable to set the heating temperature to 1150 to 1350.degree.
  • finish rolling it is preferable to set the finish rolling temperature (finish rolling end temperature) to 720°C or higher from the viewpoint of ensuring toughness. If the finish rolling temperature is less than 720° C., the rolling reduction in the ferrite+austenite two-phase region becomes large, and the rolling distortion reduces the toughness. On the other hand, the upper limit of the finishing temperature is not particularly limited.
  • the average cooling rate from the cooling start temperature to 500 ° C. after the finish rolling is less than 0.1 ° C./sec, it becomes difficult to ensure predetermined tensile properties and toughness, so the average cooling rate. is preferably 0.1° C./sec or more.
  • the average cooling rate exceeds 30° C./sec, the formation of bainite or martensite causes a decrease in toughness. Therefore, the average cooling rate is preferably in the range of 0.1 to 30°C/sec.
  • the average cooling rate is more preferably 30.0° C./sec or less, and even more preferably 20.0° C./sec or less.
  • the cooling start temperature is, for example, the finish rolling end temperature. Moreover, the above temperature means the surface temperature of the steel material.
  • the tensile strength TS is 400 MPa or more
  • the yield strength (yield point YP or 0.2% proof stress) is 235 MPa or more
  • vE0 is preferably 47 J or more.
  • the tensile strength, yield strength, and impact absorption energy at 0° C. can be determined by the methods described in Examples.
  • the tensile strength TS is preferably 490 MPa or higher, more preferably 520 MPa or higher. Moreover, although the upper limit of the tensile strength TS is not particularly limited, it is preferably 640 MPa or less.
  • the yield strength is preferably 325 MPa or higher, more preferably 355 MPa or higher. Moreover, although the upper limit of the yield strength is not particularly limited, it is preferably 475 MPa or less. More preferably, vE0 is 100 J or more.
  • a beam blank having a cross section of 400 mm ⁇ 560 mm ⁇ length of 8000 mm is made from steel having the chemical composition shown in Table 1 by a continuous casting machine, and hot rolled under the hot rolling conditions shown in Table 2.
  • An H-beam 1 was produced with a cross-sectional shape, namely a shape having a web 3 and a pair of flanges 2 arranged at opposite ends of the web.
  • the cross-sectional dimensions (web height ⁇ flange width ⁇ web thickness ⁇ flange thickness) were 900 mm ⁇ 300 mm ⁇ 18 mm ⁇ 34 mm, and the H-section steel was manufactured.
  • the average cooling rate after finish rolling is obtained by measuring the temperature of the flange surface with a radiation thermometer, and converting the temperature change from the cooling start temperature (finish rolling end temperature) to 500 ° C. per unit time (second). Thus, the average cooling rate (°C/sec) was calculated.
  • the resulting H-shaped steel was subjected to paint durability evaluation, tensile test, and Charpy impact test. Details of each evaluation are described below.
  • a test piece of 70 mm x 50 mm x 5 mm was taken from a 1/4t part (t/4 part) (t is the flange thickness) from the rear surface of the flange 1/6B part (B/6 part) 4 shown in Fig. 1 .
  • the surface of this test piece was shot-blasted so that the surface roughness was ISO Sa 2.5, ultrasonically degreased in acetone for 5 minutes, and air-dried.
  • one side of the test piece was used as a coated surface, and an inorganic zinc-rich paint (thickness: 75 ⁇ m) was applied as an anticorrosion base, an epoxy resin paint (thickness: 120 ⁇ m) was applied as a primer, and then a fluorine resin was applied as an intermediate coating. Apply an intermediate paint (thickness: 30 ⁇ m) for a topcoat, then apply a fluororesin topcoat paint (thickness: 25 ⁇ m) as a topcoat, consisting of an anticorrosion base layer, an undercoat layer, an intermediate coat layer and a topcoat layer. A coating was formed. The other side and the end face of the test piece were sealed with a solvent type epoxy resin paint and further coated with a silicon-based sealing agent.
  • each transition time from condition 1 to condition 2 and from condition 2 to condition 1 is set to 1 hour, and a cycle of a total of 8 hours is set as one cycle, and this cycle is repeated 1200 times to conduct a corrosion test.
  • the artificial sea salt was applied once a week. After the corrosion test was completed, the bulging area (painting bulge area) from the initial defective part in the coating was measured to evaluate the coating durability. In this evaluation, those with a blistering area of 480 mm 2 or less were judged to be excellent in coating durability.
  • ⁇ Tensile test> From the flange 1/6B portion 4 shown in FIG. 1, a JIS No. 1A full-thickness tensile test piece specified in JIS Z2201, in which the tensile direction is the length direction of the H-shaped steel, is taken, and a tensile test is performed according to JIS Z2241. was performed, and the yield strength (yield point YP or 0.2% yield strength) and tensile strength TS were measured.
  • Table 2 shows the above survey results.
  • the H-section steels (Test Nos. 1 to 18, 41, 42, 44, and 45 in Table 2) manufactured using compatible steel satisfying the steel composition of the present invention have excellent paint durability and the desired (tensile strength TS: 400 MPa or more, yield strength: 235 MPa or more, impact absorption energy vE0 at 0° C.: 27 J or more), and the strength-toughness balance was excellent.
  • H-shaped steel 2 Flange 3: Web 4: Flange 1/6B part (specimen sampling position)

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