WO2018186273A1 - Élément en acier, tôle d'acier laminée à chaud destinée à cet élément en acier, et procédés de production associés - Google Patents

Élément en acier, tôle d'acier laminée à chaud destinée à cet élément en acier, et procédés de production associés Download PDF

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WO2018186273A1
WO2018186273A1 PCT/JP2018/013076 JP2018013076W WO2018186273A1 WO 2018186273 A1 WO2018186273 A1 WO 2018186273A1 JP 2018013076 W JP2018013076 W JP 2018013076W WO 2018186273 A1 WO2018186273 A1 WO 2018186273A1
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steel
hot
temperature
less
steel member
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PCT/JP2018/013076
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Japanese (ja)
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俊介 豊田
杉本　一郎
修司 川村
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Ｊｆｅスチール株式会社
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Priority to MX2019011941A priority Critical patent/MX2019011941A/es
Priority to CN201880023595.9A priority patent/CN110494582B/zh
Priority to KR1020197028866A priority patent/KR102319579B1/ko
Priority to US16/500,613 priority patent/US20200190618A1/en
Priority to JP2018536532A priority patent/JP6631715B2/ja
Priority to CA3057814A priority patent/CA3057814C/fr
Publication of WO2018186273A1 publication Critical patent/WO2018186273A1/fr

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    • 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
    • B21B1/22—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 plates, strips, bands or sheets of indefinite length
    • B21B1/24—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 plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process
    • B21B1/26—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 plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process by hot-rolling, e.g. Steckel hot mill
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C37/00—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape
    • B21C37/06—Manufacture of metal sheets, bars, wire, tubes or like semi-manufactured products, not otherwise provided for; Manufacture of tubes of special shape of tubes or metal hoses; Combined procedures for making tubes, e.g. for making multi-wall tubes
    • B21C37/08—Making tubes with welded or soldered seams
    • 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
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • 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
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
    • 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
    • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—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
    • C22C38/14—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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/24—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
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • 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

Definitions

  • the present invention relates to a steel member, a hot-rolled steel sheet for the steel member, and a method for producing them. More specifically, the present invention relates to a steel member having excellent fatigue resistance in a plastic strain region, a hot-rolled steel sheet for the steel member, and a method for producing them.
  • the present invention relates to a welded steel pipe for coiled tubing, a welded steel pipe for line pipe, and a welded steel pipe for structural members for automobiles, which are required to have high strength and fatigue resistance in the plastic strain region, and in particular, welding for coiled tubing.
  • the present invention relates to a steel pipe and relates to an improvement in fatigue life in the plastic strain region of these steel members.
  • Patent Document 1 as a high-strength structural member and a driving force transmission member for an automobile or the like, or an oil-welded pipe for washing an oil well pipe, the yield strength after pipe forming is 700 MPa or more, the tensile strength is 800 MPa or more, and the elongation is 15% or more.
  • a method of manufacturing a high-strength electric resistance welded steel pipe having the following ductility is disclosed. According to this method, 0.09 to 0.18% C and a predetermined amount of Cu, Ni, Cr, and Mo alloy elements are contained, so that high-strength electric sewing that does not cause softening of the weld heat affected zone is achieved.
  • a steel pipe can be obtained.
  • a steel tube for coiled tubing that is required for fatigue use, in particular, fatigue resistance in the plastic strain region, has a problem of low durability life in repeated use.
  • Patent Document 2 discloses a steel strip for coiled tubing excellent in material uniformity and a method for manufacturing the same. According to this method, variation in yield strength in the coil width direction and the longitudinal direction is achieved by containing a predetermined amount of 0.10 to 0.16% C and an alloy element of Cr, Cu, Ni, Mo, Nb, and Ti. A steel strip for coiled tubing with a small diameter can be obtained. However, the fatigue resistance property in the plastic strain region is not sufficient, and there is a problem that the durability life in repeated use is low.
  • Patent Document 3 discloses a quenched and tempered steel pipe having excellent fatigue life for a steel pipe for a machine structure such as an automobile, particularly for a hollow stabilizer for an automobile. According to this method, a steel pipe having a high fatigue life can be obtained by containing a predetermined chemical component, setting the average particle size of the precipitated carbide to 0.5 ⁇ m or less, and setting the hardness at the center of the thickness to 400 HV.
  • the fatigue life level obtained with this steel pipe is a low stress-high cycle elastic region fatigue characteristic with a life of tens of thousands of cycles.
  • coiled tubing is used several hundred times while being repeatedly inserted and recovered into the well.
  • An object of the present invention is to provide a steel member having excellent fatigue resistance in a plastic strain region, a hot-rolled steel sheet as a raw material thereof, and a method for producing them.
  • the hot-rolled steel sheet used as the material of the steel member of the present invention is also referred to as “material hot-rolled steel sheet”.
  • the steel member of the present invention include steel pipes such as welded steel pipes and molded parts such as automobile structural members.
  • Examples of the welded steel pipe include a welded steel pipe for coiled tubing, a welded steel pipe for line pipes, and a welded steel pipe for structural members for automobiles.
  • the present inventors have made various changes in the chemical composition and production conditions of the hot-rolled steel sheet used as a material. Experiments were conducted. As a result, a steel having a specific chemical component is hot-rolled under a specific temperature processing condition or formed into a steel pipe shape and then heat-treated under a specific condition, thereby achieving high strength and an excellent plastic strain region. It has been found that a steel member that simultaneously satisfies fatigue resistance can be obtained.
  • the present invention has been completed based on such findings, and has the following configurations [1] to [9].
  • a steel member that contains 0.031 to 0.200% Ti by mass%, and 0.005% or more of Ti is precipitated as a precipitate having a particle size of 20 nm or less in the structure.
  • the steel member is, by mass%, C: 0.19 to 0.50%, Si: 0.002 to 1.5%, Mn: 0.4 to 2.5%, Al: 0.01 To 0.19%, Cr: 0.001 to 0.90%, B: 0.0001 to 0.0050%, Ti: 0.031 to 0.200%, P: 0.019% or less (0% S): 0.015% or less (including 0%), N: 0.008% or less (including 0%), O: 0.003% or less (including 0%), Sn: 0.10 % Or less (including 0%), the steel member according to [1] having a composition in which the balance is composed of Fe and inevitable impurities.
  • Nb 0.001 to 0.15%
  • V 0.001 to 0.15%
  • W 0.001 to 0.15%
  • Mo 0 by mass% 0.001 to 0.45%
  • Cu 0.001 to 0.45%
  • Ni 0.001 to 0.45%
  • Ca 0.0001 to 0.005%
  • Sb 0.0001 to 0.10
  • a method for producing a hot-rolled steel sheet for a steel member wherein the temperature range is cooled at an average cooling rate of 10 ° C./s or more and wound at a temperature of T Ti ⁇ 500 ° C. or less.
  • the steel member excellent in the fatigue resistance characteristic of a plastic strain area can be provided.
  • the hot-rolled steel sheet of the present invention is particularly suitable as a material for the steel member.
  • ADVANTAGE OF THE INVENTION According to this invention, the steel member which can make compatible the characteristic which is the strength and the fatigue-resistant characteristic in a plastic strain area at a high level can be provided. Therefore, as the steel member of the present invention, a welded steel pipe for coiled tubing, a welded steel pipe for line pipes, and a welded steel pipe for automotive structural members, which are particularly required to have high strength and fatigue resistance in the plastic strain region, are suitable. In particular, a welded steel pipe for coiled tubing is suitable.
  • the steel member of the present invention is obtained by subjecting a hot-rolled steel sheet (raw material hot-rolled steel sheet) produced by hot rolling under specific temperature processing conditions to a heat treatment under specific conditions.
  • a hot-rolled steel sheet raw material hot-rolled steel sheet
  • the heat treatment performed after forming the raw hot-rolled steel sheet is also referred to as “post-heat treatment”.
  • Ti 0.031 to 0.200% Ti precipitates as carbonitride in the hot rolling process, and suppresses recovery / recrystallization grain growth in the hot rolling process.
  • Ti By containing Ti, there is an effect that a desired fine ferrite phase particle size (1 to 50 ⁇ m) can be obtained in the structure (microstructure) of the hot-rolled steel sheet.
  • the refinement of the microstructure at the hot-rolled steel sheet stage leads to the refinement of the microstructure after heat treatment after subsequent forming (cold working) such as pipe forming and part forming, and excellent plasticity. Fatigue resistance in the strain range is obtained.
  • Tanaka et al. Proposed a model in which dislocations pile up irreversibly on the slip surface due to fatigue cycles, and when the stress generated at this time exceeds the critical stress, an initial crack occurs (reference: K. Tanaka and T. Mura: J Appl Mech., Vol. 48, p.97-103 (1981)).
  • G transverse elastic constant
  • Ws fracture energy per unit area
  • ⁇ Poisson's ratio
  • ⁇ decomposition shear stress range on the sliding surface
  • k dislocation frictional force on the sliding surface, etc.
  • the fatigue crack generation cycle Nc of each crystal grain becomes longer as the slip surface length d is shorter, that is, as the crystal grain size is smaller. Due to such a mechanism, it is considered that the refined microstructure material of the present invention is delayed in fatigue crack generation and exhibits excellent fatigue resistance characteristics in the plastic strain region.
  • Ti is strengthened by precipitation strengthening the matrix as a carbide, solid solution strengthening as a solid solution element, and strengthening transformation structure strengthening as a hardenability improving element, and after heat treatment after forming processing such as pipe making and part forming
  • This is an essential element that improves the strength of the steel and significantly improves the fatigue strength.
  • Such an effect is obtained when the Ti content is in the range of 0.031 to 0.200%, and when the Ti content is less than the lower limit of the above range, the effect is 0. 005% or more of Ti exists as solute Ti, and the heat treatment after the molding process cannot precipitate 0.005% or more of Ti as fine precipitates having a particle diameter of 20 nm or less, and the above effect is obtained.
  • the Ti content is in the range of 0.031 to 0.200%.
  • the Ti content is preferably more than 0.120%. Further, the Ti content is preferably 0.150% or less.
  • 0.005% or more of Ti is precipitated as a precipitate having a particle size of 20 nm or less.
  • the present inventors need a fatigue resistance property in a plastic strain region after a heat treatment (post heat treatment) performed after a forming process such as pipe making or part forming using a hot-rolled steel sheet as in the present invention. In that case, it is found that by applying post-heat treatment, 0.005% or more of Ti is precipitated as fine precipitates having a particle size of 20 nm or less, so that excellent fatigue resistance characteristics in the plastic strain region can be obtained. did.
  • C 0.19 to 0.50%
  • C is post-heat-treated under specific conditions to ensure high strength, and further binds to Ti during post-heat treatment, in particular, precipitates fine precipitates in the surface layer portion to cause fatigue resistance in the plastic strain region. It is an element that improves the characteristics.
  • the C content is less than 0.19%, it becomes difficult to obtain the desired strength (YS ⁇ 770 MPa) and fatigue resistance in the plastic strain region.
  • the C content exceeds 0.50%, the toughness and weldability of a steel member, for example, a steel pipe, cannot be ensured, so this is the upper limit. More preferably, the C content is more than 0.28%. More preferably, the C content is 0.30% or less.
  • Si 0.002 to 1.5%
  • Si is an element that improves fatigue resistance in the plastic strain region while ensuring a desired strength by solid solution strengthening. If the Si content is less than 0.002%, the strength is insufficient. On the other hand, if the content exceeds 1.5%, weldability deteriorates. Therefore, the Si content is preferably limited to 0.002 to 1.5%. More preferably, the Si content is 0.05% or more. More preferably, the Si content is 0.35% or less.
  • Mn 0.4 to 2.5%
  • Mn has a function of ensuring a desired strength by strengthening at low temperature during post-heat treatment and improving fatigue resistance in the plastic strain region. If the Mn content is less than 0.4%, this effect is not sufficiently exhibited. On the other hand, if the Mn content exceeds 2.5%, the weldability deteriorates. Therefore, the Mn content is preferably limited to 0.4 to 2.5%. More preferably, the Mn content is 1.09% or more. More preferably, the Mn content is 1.99% or less.
  • Al 0.01 to 0.19%
  • Al is a deoxidizing element during steel making, suppresses the growth of austenite grains in the hot rolling process, makes the crystal grains fine, and obtains a desired ferrite grain size (1 to 50 ⁇ m) after post-heat treatment, It has the function of improving fatigue resistance in the plastic strain region. If the Al content is less than 0.01%, these effects cannot be obtained, and the ferrite grain size becomes coarse. On the other hand, if the Al content exceeds 0.19%, the weldability deteriorates and the oxide type intervening The fatigue resistance tends to decrease due to the increase in the number of objects. More preferably, the Al content is 0.041% or more. More preferably, the Al content is 0.080% or less.
  • Cr 0.001 to 0.90% Cr has a function of securing a desired strength by strengthening at low temperature transformation during post-heat treatment and improving fatigue resistance in a plastic strain region. If the Cr content is less than 0.001%, this effect is not sufficiently exhibited. On the other hand, if the Cr content exceeds 0.90%, the weldability deteriorates. Therefore, the Cr content is preferably limited to 0.001 to 0.90%. More preferably, the Cr content is 0.001 to 0.19%.
  • B 0.0001 to 0.0050%
  • B has a function of ensuring a desired strength by strengthening at low temperature transformation during post-heat treatment and improving fatigue resistance in a plastic strain region. If the B content is less than 0.0001%, this effect is not sufficiently exhibited. On the other hand, if the B content exceeds 0.0050%, the fatigue resistance tends to decrease. Therefore, the B content is preferably limited to 0.0001 to 0.0050%. More preferably, the B content is 0.0005% or more. More preferably, the B content is 0.0035% or less.
  • P 0.019% or less (including 0%) P deteriorates fatigue resistance in the plastic strain region and deteriorates electroweldability through solidification co-segregation with Mn. If the P content exceeds 0.019%, the adverse effect becomes remarkable, so 0.019% is preferable as the upper limit.
  • S 0.015% or less (including 0%) S exists as an inclusion in steel as MnS or the like, and lowers fatigue resistance as a starting point of fatigue cracks in the plastic strain region.
  • the S content exceeds 0.015%, this adverse effect becomes significant, so it is preferable to set the upper limit at 0.015%. More preferably, the S content is 0.005% or less.
  • N 0.008% or less (including 0%) N forms Ti and TiN, precipitates as coarse precipitates, and consumes solid solution Ti.
  • N is added in the form of hot-rolled steel sheet at the raw material stage so that 0.005% or more of Ti is present as solute Ti, and heat treatment after forming is performed so that 0.005% or more of Ti is finely grained with a particle size of 20 nm or less. It precipitates as a good precipitate and reduces the effect of obtaining excellent fatigue resistance characteristics in the plastic strain region. If the N content exceeds 0.008%, this adverse effect becomes significant, so it is preferable to set the upper limit to 0.008%. More preferably, the N content is 0.0049% or less.
  • O 0.003% or less (including 0%) O exists as oxide inclusions and reduces the fatigue resistance of steel. If the content of O exceeds 0.003%, this adverse effect becomes remarkable, so 0.003% is preferably set as the upper limit. More preferably, the O content is 0.002% or less.
  • Sn 0.10% or less (including 0%) Sn exists as a solid solution element and reduces the hot ductility of steel. If the Sn content exceeds 0.10%, this adverse effect becomes significant, so it is preferable to set the upper limit to 0.10%. More preferably, the Sn content is 0.03% or less.
  • the balance is Fe and inevitable impurities.
  • the following elements can be further added for the purpose of improving the effects of the present invention.
  • Nb 0.001 to 0.15% Nb precipitates as a carbide, suppresses recovery / recrystallization grain growth in the hot rolling process, and has the effect of obtaining a desired ferrite grain size (1 to 50 ⁇ m), and can be contained as needed. If the Nb content is less than 0.001%, these effects cannot be obtained. On the other hand, when the content of Nb exceeds 0.15%, coarse precipitates are deposited on the surface layer portion due to strain-induced precipitation during hot rolling, and fine precipitates on the surface layer portion are reduced. Since fatigue resistance is reduced, the upper limit is made 0.15%. Therefore, when Nb is contained, the Nb content is set to 0.001 to 0.15%. More preferably, the Nb content is 0.001 to 0.009%.
  • V 0.001 to 0.15%
  • V precipitates as a carbide, suppresses recovery / recrystallization grain growth in the hot rolling process, and has the effect of obtaining a desired ferrite grain size (1 to 50 ⁇ m), and can be contained as necessary. If the V content is less than 0.001%, these effects cannot be obtained.
  • the content of V exceeds 0.15%, coarse precipitates are deposited on the surface layer portion due to strain-induced precipitation during hot rolling, and fine precipitates on the surface layer portion are reduced, and in the plastic strain region.
  • the upper limit is 0.15% because the fatigue resistance is reduced. Therefore, when V is contained, the content of V is set to 0.001 to 0.15%. More preferably, the V content is 0.001 to 0.049%.
  • W 0.001 to 0.15% W precipitates as carbide, suppresses recovery / recrystallization grain growth in the hot rolling process, supplements the effect of obtaining the desired ferrite grain size (1 to 50 ⁇ m), and is contained if necessary it can. If the W content is less than 0.001%, these effects cannot be obtained. On the other hand, when the content of W exceeds 0.15%, coarse precipitates are deposited on the surface layer portion due to strain-induced precipitation during hot rolling, and fine precipitates on the surface layer portion are reduced. The upper limit is 0.15% because the fatigue resistance is reduced. Therefore, when W is contained, the W content is set to 0.001 to 0.15%. More preferably, the W content is 0.001 to 0.049%.
  • Mo 0.001 to 0.45%
  • Mo has a function of securing a desired strength by low-temperature transformation strengthening or precipitation strengthening during post-heat treatment and complementing the effect of improving fatigue resistance in the plastic strain region, and can be contained as necessary. If the Mo content is less than 0.001%, this effect does not appear. On the other hand, if the Mo content exceeds 0.45%, the weldability deteriorates. Therefore, when Mo is contained, the Mo content is set to 0.001 to 0.45%. More preferably, the Mo content is 0.001 to 0.30%.
  • Cu and Ni are elements that have a function of complementing the effect of improving the fatigue strength of Mn, and at the same time, have the effect of increasing the corrosion resistance of the steel material, and can contain Cu and Ni as needed. These effects are manifested when the content of Cu and Ni is 0.001% or more. However, when the content exceeds 0.45% for Cu and Ni, the upper limit is 0.45% for lowering weldability. Therefore, when Cu is contained, the Cu content is set to 0.001 to 0.45%. When Ni is contained, the Ni content is set to 0.001 to 0.45%. More preferably, any element is 0.35% or less.
  • Ca 0.0001 to 0.005%
  • Ca has a so-called form control effect in which expanded MnS is granular Ca (Al) S (O), has the effect of suppressing fatigue cracking and improving fatigue resistance, and can be contained if necessary. .
  • This effect is manifested with a content of 0.0001% or more.
  • the content exceeding 0.005% is limited to 0.005% because the fatigue resistance is lowered by the increase of nonmetallic inclusions. Therefore, when Ca is contained, the content of Ca is set to 0.0001 to 0.005%.
  • Sb 0.0001 to 0.10%
  • Sb preferentially segregates on the surface, suppresses the intrusion of N from the atmosphere in the hot rolling process or the post heat treatment process, and functions to suppress a decrease in the effect of adding B due to the formation of BN.
  • This effect is manifested at a content of 0.0001% or more, but even if it exceeds 0.10%, the effect is saturated, so 0.10% is made the upper limit. Therefore, when Sb is contained, the Sb content is set to 0.0001 to 0.10%. More preferably, the Sb content is 0.0001 to 0.030%.
  • the average crystal grain size of the ferrite phase from the surface after post heat treatment to the plate thickness direction of 200 ⁇ m is 1 to 50 ⁇ m, and the particle size of 1 in the ferrite phase from the surface to the plate thickness direction of 200 ⁇ m.
  • the difference between the average hardness from the surface to the thickness direction of 200 ⁇ m and the average hardness in the vicinity of the thickness center excluding the central segregation part (absolute value) has a structure in which Ti carbide of 0.0 to 20 nm is precipitated.
  • the hardness (HV) is desirably ⁇ HV 50 points or less.
  • the microstructure of the steel member, the precipitation state of the precipitates, and the cross-sectional hardness are important for ensuring fatigue resistance in an excellent plastic strain region. If the average crystal grain size of the ferrite phase from the surface after post-heat treatment to the plate thickness direction of 200 ⁇ m exceeds 50 ⁇ m, the initial fatigue cracks are early and large, making it difficult to ensure fatigue resistance characteristics in a desired plastic strain region. On the other hand, since it is difficult industrially and economically to make the average crystal grain size of the ferrite phase less than 1 ⁇ m after the post heat treatment, this is set as the lower limit.
  • ferrite phase refers to the body phase iron of a body-centered cubic lattice, so-called polygonal ferrite, acicular ferrite, Widmanstatten ferrite, bainitic ferrite, bainite, and low carbon (C content of 1% or less). Includes a martensite organization.
  • the second phase other than the ferrite phase include austenite, carbide, pearlite, and high carbon martensite (C content exceeding 1%).
  • the structure of the steel member of the present invention preferably has the ferrite phase as a main phase.
  • the main phase refers to a phase occupying 51% or more by volume ratio, preferably 80% or more, and may be 100%.
  • the Ti carbide dimension in the ferrite phase from the surface to the plate thickness direction of 200 ⁇ m is important for ensuring the surface hardness and the fatigue resistance in a high plastic strain region.
  • the precipitation of 1.0 to 20 nm Ti carbide in the ferrite phase from the surface to the thickness direction of 200 ⁇ m suppresses the occurrence of initial fatigue cracks, reduces the size, and provides excellent resistance to plastic strain. The fatigue characteristics can be further improved.
  • the precipitation amount of Ti carbide of 1.0 to 20 nm is not particularly defined here. In addition to Ti carbide having a thickness of 1.0 to 20 nm, it is allowed to deposit Ti carbides having different dimensions.
  • the difference between the average hardness from the surface to the thickness direction of 200 ⁇ m and the average hardness in the vicinity of the thickness center excluding the center segregation part is ⁇ HV50 points or less, in order to ensure excellent fatigue resistance in the plastic strain region. is important.
  • the difference between the average hardness from the surface to the thickness direction of 200 ⁇ m and the average hardness in the vicinity of the center of the plate thickness excluding the center segregation part exceeds ⁇ HV50 points, the initial fatigue cracks occur quickly and greatly, and in the desired plastic strain region It is difficult to ensure the fatigue resistance characteristics. For this reason, it is desirable that the difference between the average hardness from the surface to the plate thickness direction of 200 ⁇ m and the average hardness in the vicinity of the plate thickness center excluding the center segregation portion is ⁇ HV 50 points or less.
  • the difference between the average hardness from the surface to the thickness direction of 200 ⁇ m and the average hardness in the vicinity of the thickness center excluding the center segregation part is the micro Vickers hardness at a pitch of 25 ⁇ m in the thickness direction between 50 and 200 ⁇ m in the thickness direction.
  • HV (0.1) averaged 7 points HV (0.1) S , avoiding the center segregation around the center of the plate thickness
  • HV (0.1 average value HV (0.1) the difference in C) was measured 7 points was measured as HV (0.1) C -HV (0.1 ) S.
  • the hot-rolled steel sheet (raw material hot-rolled steel sheet) for steel members of the present invention is particularly suitable for obtaining the steel member of the present invention.
  • the material hot-rolled steel sheet of the present invention contains 0.031 to 0.200% Ti by mass%, and 0.005% or more of Ti exists in the structure as solute Ti. Thereby, after performing a predetermined heat treatment after forming, 0.005% or more of Ti can be precipitated as fine precipitates having a particle size of 20 nm or less in the structure of the steel member, and in the plastic strain region It is possible to obtain a steel member that is excellent in fatigue resistance and also excellent in strength characteristics.
  • the composition of the material hot-rolled steel sheet of the present invention is the same as the composition of the steel member.
  • the thickness of the tip and tail ends, which are both ends in the longitudinal direction is 5 compared to the thickness of the intermediate portion (longitudinal central portion) other than both ends in the longitudinal direction.
  • it is ⁇ 50% thick.
  • the temperature is the surface temperature of a steel slab or the like.
  • a steel slab obtained by casting steel having the above composition is used as a starting material.
  • the production method of the starting material is not particularly limited.
  • the molten steel having the above composition is melted by a conventional melting method such as a converter, and a steel slab is obtained by a normal casting method such as a continuous casting method. Is mentioned.
  • the material hot-rolled steel sheet of the present invention can be manufactured by hot rolling a steel slab containing 0.031 to 0.200% Ti under predetermined conditions.
  • the amount of dissolved Ti is less than 0.005%, and the fatigue resistance characteristics in the plastic strain region that are remarkably excellent after post-heat treatment cannot be obtained.
  • T Ti equilibrium solid solution temperature
  • the slab extraction temperature is preferably 1620 K or less from the viewpoint of preventing the crystal grain size from becoming coarse, and the slab leveling is ensured from the viewpoint of ensuring uniformity of the solid solution state of Ti and sufficient solid solution time.
  • the heat time time for holding the slab at a temperature higher than the equilibrium solid solution temperature T Ti ) is preferably 10 min or more.
  • T Ti -400 ° C or higher finish rolling temperature When hot rolling finish rolling temperature is lower than T Ti -400 ° C, strain induced precipitation due to additional shear strain by upper and lower rolls near the surface or heat removal by rolls and cooling water.
  • the amount of solid solution Ti present in the vicinity of the front surface is less than 0.005% at the stage of the raw hot-rolled steel sheet, and fatigue resistance in a plastic strain region that is remarkably excellent after post-heat treatment Characteristics are not obtained.
  • 0.005% or more of Ti including the vicinity of the surface is present as solute Ti at the stage of the raw hot rolled steel sheet, and it is reduced to 0 by heat treatment after forming.
  • 0.005% or more of Ti can be precipitated as fine precipitates having a particle size of 20 nm or less, and a particularly excellent fatigue resistance property in a plastic strain region can be obtained.
  • Ti including the vicinity of the surface is solidified at the stage of the hot rolled steel sheet. It exists as molten Ti, and 0.005% or more of Ti can be precipitated as fine precipitates with a particle size of 20 nm or less by heat treatment after forming, and has excellent fatigue resistance characteristics in the plastic strain region. can get.
  • Winding temperature of T Ti ⁇ 500 ° C. or lower When the winding temperature exceeds T Ti ⁇ 500 ° C., precipitation of Ti precipitates is promoted before coil cooling, and solid solution Ti present at the stage of the raw hot rolled steel sheet The amount is less than 0.005%, and the fatigue resistance property in the plastic strain region which is remarkably excellent after post heat treatment cannot be obtained.
  • T Ti ⁇ 500 ° C. or less By setting the winding temperature to T Ti ⁇ 500 ° C. or less, 0.005% or more of Ti including the vicinity of the surface is present as solute Ti at the stage of the raw hot-rolled steel sheet.
  • the finish rolling temperature and the coiling temperature are surface temperatures at the center of the coil width, and the average cooling rate is obtained from the surface temperature.
  • a hot-rolled steel sheet (raw material hot-rolled steel sheet) in which 0.005% or more of Ti exists as a solid solution Ti in the structure is obtained.
  • the steel member of the present invention is manufactured by subjecting the material hot-rolled steel sheet to a predetermined heat treatment after forming.
  • a predetermined heat treatment for example, if a steel member is a steel pipe, a pipe making process will be mentioned. If the steel member is a welded steel pipe, the welding process may be performed after the pipe making process.
  • the steel member is a molded part such as a structural member for an automobile, press working or the like can be given. After forming, heat treatment is performed under the following conditions.
  • the solid solution Ti is not precipitated as fine precipitates having a thickness of 20 nm or less, and the remarkably excellent fatigue resistance property in the plastic strain region cannot be obtained.
  • the heating temperature exceeds 1050 ° C.
  • the particle size of the ferrite phase exceeds 50 ⁇ m, and it becomes difficult to obtain fatigue resistance characteristics in a plastic strain region that is remarkably excellent. If the cooling rate in the temperature range of 550 to 400 ° C. is less than 10 ° C./s, sufficient strength (YS ⁇ 770 MPa) cannot be obtained.
  • the heating temperature is more preferably in the range of 700 to 1000 ° C.
  • the raw hot-rolled steel sheet is left as it is, or, if necessary, pickling, cold rolling, annealing, plating, or a plurality of After processing, slitting to a predetermined plate width, one or more coils are welded and joined in the longitudinal direction, formed into a roughly circular cross-section by roll forming or press forming, and the end is subjected to high-frequency electric seam welding, laser Joined by welding, etc., and heated online or offline to a temperature exceeding 550 ° C. and below 1050 ° C., cooling the temperature range of 550 to 400 ° C. at an average cooling rate of 10 ° C./s or more to form a coil.
  • the raw hot-rolled steel sheet is left as it is, or after performing any one or more of pickling, cold rolling, annealing, plating as necessary.
  • 0.005% or more of Ti precipitates as fine precipitates having a particle size of 20 nm or less, and the fatigue resistance characteristics in the plastic strain region that are remarkably excellent are obtained.
  • Example 1 A steel slab having the composition shown in Table 1 (steel types C to L) was extracted from a heating furnace at a slab surface temperature of about 1220 ° C and a slab center temperature of about 1210 ° C, and finish rolling reduction: 91%, coil width center finish rolling temperature of about 860 ° C., coil width direction minimum finish rolling temperature of about 850 ° C., and cooled at an average cooling rate of T Ti -400 ° C. from T Ti -500 temperature range of about 20 ° C.
  • sheet thickness: about 5 mm, the thickness of the front and rear end portions is about 10% thicker than the longitudinal center portion was obtained by hot rolling at a temperature of 0 ° C. (No. 3 to 12).
  • a raw hot-rolled steel sheet was obtained in the same manner as above ( No.
  • a welded steel pipe having an outer diameter of 50.8 mm and a thickness of about 5 mm was obtained.
  • the whole welded steel pipe is continuously heated at high frequency, heated at a heating temperature of 920 ° C and a holding time of about 5 seconds, then cooled with water from the outer surface, and the temperature range of 550 to 400 ° C is an average of about 50 ° C / s.
  • a heat treatment for cooling at a cooling rate was performed.
  • Specimens were collected from these welded steel pipes and subjected to a structure observation test, a precipitate, a quantitative test of the solid solution amount, a tensile test, a plastic strain region fatigue test, and a low temperature toughness test.
  • the test method was as follows.
  • Microstructure observation test Samples of microstructural observation specimens were collected so that the circumferential cross section of these welded steel pipes became the observation surface, polished, nital-corroded, and observed with a scanning electron microscope (3000 times).
  • the average grain size of the ferrite phase was determined by an EBSD (Electron BackScatter Diffraction) method with an inclination angle of 15 ° or more with adjacent grains as a grain boundary.
  • the average particle diameter from the surface to the plate thickness direction of 200 ⁇ m was measured by averaging three points at a pitch of 50 ⁇ m between the plate thickness directions of 50 to 200 ⁇ m and the center segregation portion around the plate thickness center, Values obtained by measuring and averaging three points at a pitch of 50 ⁇ m in the plate thickness direction were obtained.
  • the precipitate was peeled from the sample piece and extracted into an aqueous SHMP solution.
  • the SHMP aqueous solution containing the precipitate is filtered using a filter in the order of hole diameters of 100 nm and 20 nm, and the residue and filtrate on the filtered filter are analyzed using an ICP emission spectroscopic analyzer.
  • the absolute amount of Ti in the residue and the filtrate is measured, and the absolute amount of Ti contained in precipitates having a particle size of more than 100 nm, precipitates having a particle size of 100 nm or less and more than 20 nm, and precipitates having a particle size of 20 nm or less. , Tisp was obtained respectively.
  • the electrolytic mass was calculated
  • the electrolytic solution after electrolysis was used as an analysis solution, and the concentration of Ti and Ti as a comparative element in the solution was measured using ICP mass spectrometry. Based on the obtained concentration, the concentration ratio of Ti to Fe was calculated, and the content ratio of Ti in a solid solution state was determined by multiplying the content ratio of Fe in the sample. In addition, the content rate of Fe in a sample can be calculated
  • the quantitative test of the precipitate and the solid solution amount was also performed on the welded steel pipe before the post-heat treatment.
  • the average hardness (HV (0.1) S ) from the surface to the thickness direction of 200 ⁇ m and the average hardness near the center of the plate thickness (HV (0.1) C ) excluding the central segregation part are measured by the above method.
  • a difference ⁇ HV (HV (0.1) C ⁇ HV (0.1) S ) between the average hardness in the thickness direction of 200 ⁇ m and the average hardness in the vicinity of the thickness center excluding the center segregation portion was determined. The obtained results are shown in Table 2.
  • the number of cycles in the above-described plastic strain region fatigue test is 1000 cycles or more, and the fatigue resistance property in the plastic strain region is excellent.
  • YS is 770 MPa or more and excellent in strength characteristics.
  • the Charpy fracture surface transition temperature is ⁇ 30 ° C. or lower, and the low temperature toughness is excellent.
  • the composition of steel does not satisfy the scope of the present invention, and Ti deposited as a precipitate having a particle size of 20 nm or less is less than 0.005%.
  • steel component composition does not meet the scope of the present invention.
  • No. 13 does not provide fatigue resistance characteristics in the desired plastic strain region.
  • Example 2 A steel slab having the composition of steel types A, B, and C shown in Table 1 is subjected to hot rolling under the conditions shown in Table 3 and a hot-rolled steel sheet (thickness: about 5 mm, the thickness at the front and rear ends is the longitudinal center) About 10% thicker).
  • a hot-rolled steel sheet thickness: about 5 mm, the thickness at the front and rear ends is the longitudinal center
  • the open pipe is electro-welded by high-frequency resistance welding, and the width drawing ratio is 4%.
  • a welded steel pipe having an outer diameter of 50.8 mm and a thickness of about 5 mm was obtained.
  • the entire welded steel pipe was continuously heated at a high frequency and heat treated under the conditions shown in Table 3.
  • Specimens were collected from these welded steel pipes, and subjected to a structure observation test, a precipitate, a quantitative test of the solid solution amount, a tensile test, a plastic strain region fatigue test, a low temperature toughness test, and a Vickers hardness measurement.
  • No. for No. 23 the hot-rolled steel sheet was pickled, blanked to a predetermined size, and subjected to a heat treatment under the conditions shown in Table 3 for a molded part by pressing. And the test piece was extract
  • Table 4 shows the obtained results. In Tables 3 and 4, the above No. Results 1 to 3 are also shown.
  • the number of cycles in the plastic strain region fatigue test is 1000 cycles or more, and the fatigue resistance property in the plastic strain region is excellent.
  • YS is 770 MPa or more and excellent in strength characteristics.
  • the Charpy fracture surface transition temperature is ⁇ 30 ° C. or lower, and the low temperature toughness is excellent.
  • the amount of Ti deposited as a precipitate having a particle size of 20 nm or less is outside the scope of the present invention. In Nos. 14 to 20, fatigue resistance characteristics in a desired plastic strain region cannot be obtained.

Abstract

L'objectif de la présente invention est de fournir un élément en acier présentant d'excellentes caractéristiques de résistance à la fatigue dans la plage de déformation plastique, une tôle d'acier laminée à chaud en tant que matériau destiné à cet élément, ainsi que des procédés de production associés. Un élément en acier, qui contient de 0,031 à 0,200 % en masse de Ti et dans la structure duquel au moins 0,005 % en masse de ce Ti est précipité sous la forme de précipités ayant une dimension de particule de 20 nm ou moins. Une tôle d'acier laminée à chaud, destinée à cet élément en acier qui contient 0,031 à 0,200 % en masse de Ti et dans la structure de laquelle au moins 0,005 % en masse de ce Ti est présent sous la forme d'une solution solide de Ti. L'invention concerne un procédé de production de l'élément en acier consistant, après moulage de la tôle d'acier laminée à chaud, à effectuer un traitement thermique dans lequel l'élément est chauffé à une température supérieure à 550 °C et ne dépassant pas 1050 °C, puis refroidi à une vitesse de refroidissement moyenne d'au moins 10 °C/s pour la plage de température de 550 à 400 °C. L'invention concerne également un procédé de production de la tôle d'acier laminée à chaud dans lequel une brame d'acier contenant de 0,031 à 0,200 % en masse de Ti est extraite dans des conditions d'une température supérieure à la température de solution solide d'équilibre T Ti T déterminée à partir d'une formule spécifiée, après quoi le laminage de finition est effectué à une température d'au moins T Ti -400 °C , et la tôle est refroidie à une vitesse de refroidissement moyenne d'au moins 10 °C/s pour la plage de température allant de T Ti -400 °C à T Ti -500 °C , et est enroulée à une température de T Ti -500 °C ou moins.
PCT/JP2018/013076 2017-04-07 2018-03-29 Élément en acier, tôle d'acier laminée à chaud destinée à cet élément en acier, et procédés de production associés WO2018186273A1 (fr)

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CN201880023595.9A CN110494582B (zh) 2017-04-07 2018-03-29 钢构件、所述钢构件用的热轧钢板和它们的制造方法
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US16/500,613 US20200190618A1 (en) 2017-04-07 2018-03-29 Steel member, hot-rolled steel sheet for steel member, and production method therefor
JP2018536532A JP6631715B2 (ja) 2017-04-07 2018-03-29 鋼部材、前記鋼部材用の熱延鋼板およびこれらの製造方法
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CA3057814A1 (fr) 2018-10-11
CA3057814C (fr) 2022-07-12
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