EP2899289B1 - Feuille d'acier épaisse ayant une excellente ténacité dans la zone affectée thermiquement par le soudage - Google Patents

Feuille d'acier épaisse ayant une excellente ténacité dans la zone affectée thermiquement par le soudage Download PDF

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EP2899289B1
EP2899289B1 EP13838421.9A EP13838421A EP2899289B1 EP 2899289 B1 EP2899289 B1 EP 2899289B1 EP 13838421 A EP13838421 A EP 13838421A EP 2899289 B1 EP2899289 B1 EP 2899289B1
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titanium nitride
equivalent circle
circle diameter
particles
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EP2899289A4 (fr
EP2899289A1 (fr
Inventor
Hidenori Nako
Hitoshi Hatano
Yoshitomi Okazaki
Akira Ibano
Tetsushi Deura
Masaki Shimamoto
Takashi SUGITANI
Sei Kimura
Shinsuke Sato
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Kobe Steel Ltd
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Kobe Steel Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • 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
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
    • 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
    • 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
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations

Definitions

  • the present invention generally relates to steel plates (thick steel plates) to be applied to welded structures such as bridges, high-rise buildings, ships (marine vessels), and line pipes. More specifically, the present invention relates to a steel plate having excellent toughness in a heat affected zone after high heat input welding.
  • the heat affected zone is hereinafter also simply referred to as HAZ.
  • the HAZ upon high heat input welding is held in the high-temperature austenite ( ⁇ ) region for a long time upon heating and then gradually cooled. This often causes the coarsening of the microstructure typically by growth of austenite grains upon heating and formation of coarse ferrite ( ⁇ ) grains during the cooling process. This in turn causes the HAZ to have lower toughness upon high heat input welding. To prevent this, demands have been made to develop a technique for maintaining the toughness of HAZ stably at high level upon high heat input welding.
  • the toughness of HAZ is hereinafter also referred to as "HAZ toughness".
  • Proposed techniques to ensure the HAZ toughness at certain level include techniques relating to austenite grain growth pinning by inclusion particles, and to microstructure refinement by intragranular ferrite formation occurring at such inclusion particles.
  • the inclusions are exemplified by oxides, nitrides, and sulfides.
  • Such proposed techniques include techniques described in Patent Literature (PTL) and PTL 2.
  • PTL 1 and PTL 2 disclose that fine titanium nitride particles, when dispersed and precipitated as austenite grain growth pinning particles in a steel, inhibit the coarsening of austenite grains formed in the HAZ upon high heat input welding and inhibit the HAZ toughness from deteriorating.
  • the titanium nitride particles readily disappear with a higher welding heat input, and there is a need for a special scheme in order to obtain stable HAZ toughness.
  • the present inventors have also proposed a technique of precisely controlling the size and number (number density) of fine titanium nitride particles so as to improve HAZ toughness upon high heat input welding in PTL 3.
  • the assumed heat input in this technique is at most 55 kJ/mm, and there is a need for further improvements so as to support further higher welding heat input.
  • PTL 4 to 7 have proposed techniques of utilizing oxide inclusions as austenite grain growth pinning particles, where the oxide inclusions are stable at high temperatures.
  • the oxide inclusions are few in number as compared with titanium-containing nitrides and fail to provide a sufficient pinning effect. The techniques therefore fail to support high heat input welding sufficiently, and there is a need for still further improvements.
  • PTL 4 describes that the presence of oxides containing rare-earth elements (REM) and/or Zr gives good HAZ properties. However, the assumed heat input in the technique remains still low, and the technique is not considered to always provide good HAZ properties upon high heat input welding.
  • PTL 5 describes a technique of using oxides containing REM and/or Zr as with PTL 4. In this technique, the HAZ toughness is evaluated as Charpy absorbed energy (Charpy impact energy). It is considered, however, that not only the average, but also the minimum of this parameter should be maintained or secured at high level from the viewpoint of material reliability.
  • Charpy absorbed energy Charpy impact energy
  • PTL 6 describes a technique of using both oxide inclusions and titanium-containing inclusions as austenite grain growth pinning particles to give high HAZ toughness.
  • the HAZ toughness is evaluated by a thermal cycle test that simulates high heat input welding. The test is performed at a highest heating temperature of 1400°C at which part of titanium-containing nitrides remains. In actual, however, the highest heating temperature in the HAZ partially becomes as high as greater than 1450°C, and this still further promotes the disappearance of titanium-containing nitrides. Accordingly, a high heat input welding test is desirably actually performed so as to accurately evaluate the HAZ toughness upon high heat input.
  • the present inventors have proposed a technique using the austenite grain growth pinning effect of fine oxide inclusions in PTL 7. This technique also utilizes the inhibition of reprecipitation of fine manganese sulfide particles and requires complicated control of determining amounts of alloy elements to be added based on the dissolved oxygen amount and dissolved sulfur amount.
  • PTL 8 describes a technique of utilizing MnS (manganese sulfide) and complex oxides containing Ti and REM.
  • MnS manganese sulfide
  • the present inventors have proposed a technique of controlling the form of inclusions to promote the intragranular ferrite formation in PTL 9.
  • These techniques have been made on the assumption that inclusions having a low interfacial energy between intragranular ferrite and the inclusions are effective in intragranular ferrite formation.
  • the techniques have not yet reached sufficient HAZ toughness upon high heat input. This is because the intragranular ferrite formation is largely affected also by the interfacial energy between intragranular ferrite and austenite, and is not sufficiently obtained merely by decreasing the interfacial energy between intragranular ferrite and inclusions.
  • the present inventors have developed a technique to provide high HAZ toughness using intragranular ferrite formation occurring at oxi-sulfides and have proposed in PTL 10.
  • PTL 10 in return for the high HAZ toughness, there is a need for dispersing relatively large-sized oxi-sulfide particles having a size of 2 pm or more.
  • this technique has also not yet reached sufficient HAZ toughness upon high heat input.
  • the technique described in PTL 8 employs a small heat input as assumed; whereas the techniques described in PTL 9 and PTL 10 provide, in Charpy absorbed energy, a high average, but a minimum that is susceptible to improvements under present circumstances.
  • the technique described in PTL 11 controls the amount of Ca to be added based on the amount of dissolved oxygen before the addition of Ca so as to provide predetermined oxide particle form. This technique, however, should be performed so that the time from the Ti addition to the Ca addition falls within the range of 3 to 20 minutes and may increase the operator's burden.
  • the technique described in PTL 12 requires holding of the work for a time of 40 minutes to 90 minutes in a period of time from the Ca addition to casting (pouring) and is still susceptible to improvements in productivity.
  • PTL 13 discloses a thick steel plate having excellent heat affected zone toughness. PTL 13 is silent about the size and distribution of the titanium nitride particles.
  • the present invention has been made under the circumstances of the conventional techniques and has an object to provide a steel plate that can have not only a higher average, but also a higher minimum charpy impact value in HAZ toughness even upon high heat input welding, has excellent heat affected zone toughness, and exhibits excellent productivity.
  • the present invention provides, according to a first embodiment, a steel plate having excellent heat affected zone toughness, the steel plate having a thickness of 50 mm or more.
  • the steel plate contains, in mass percent, C in a content of 0.03% to 0.12%, Si in a content of 0.10% to 0.25%, Mn in a content of 1.0% to 2.0%, P in a content of 0.03% or less (excluding 0%), S in a content of 0.015% or less (excluding 0%), Al in a content of 0.004% to 0.05%, Ti in a content of 0.010% to 0.050%, at least one rare-earth element (REM) in a content of 0.0003% to 0.02%, Zr in a content of 0.0003% to 0.02%, Ca in a content of 0.0005% to 0.010%, N in a content of 0.002% to 0.010%; and optionally at least one element selected from the group consisting of Ni in a content of 0.05% to 1.50%; Cu in a content of 0.05% to 1.5
  • the steel plate includes oxide particles that contain constituent elements excluding oxygen in contents, in mass percent, meeting conditions as follows: 2% ⁇ Ti ⁇ 40%, 5% ⁇ Al ⁇ 30%, 5% ⁇ Ca ⁇ 40%, 5% ⁇ REM ⁇ 50%, 2% ⁇ Zr ⁇ 30%, and 1.0 ⁇ REM/Zr.
  • oxide particles having an equivalent circle diameter of less than 2 ⁇ m are present in a number density of 300 or more per square millimeter, and oxide particles having an equivalent circle diameter of 2 ⁇ m or more are present in a number density of 100 or less per square millimeter.
  • the steel plate includes titanium nitride particles.
  • titanium nitride particles having an equivalent circle diameter of 1 ⁇ m or more are present in a number density of 7 or less per square millimeter, and titanium nitride particles having an equivalent circle diameter of 20 nm or more are present in a number density of 1.0x 10 6 or more per square millimeter.
  • the steel plate has df and da meeting a condition specified by the relational expression:
  • the da represents an average equivalent circle diameter of the titanium nitride particles having an equivalent circle diameter of 20 nm to less than 500 nm.
  • equivalent circle diameter refers to the diameter of an assumed circle having an equivalent area to the size (area) of an oxide particle or a titanium nitride particle in question.
  • the equivalent circle diameter may be determined by observation under a transmission electron microscope (TEM) or a scanning electron microscope (SEM).
  • the steel plate having excellent heat affected zone toughness may include specific oxides in a number density of 300 or more per square millimeter, where the specific oxides include constituent elements excluding oxygen in contents, in mass percent, meeting conditions as follows: 2% ⁇ Ti ⁇ 40%, 5% ⁇ Al ⁇ 30%, 5% ⁇ Ca ⁇ 40%, 5% ⁇ REM ⁇ 50%, 2% ⁇ Zr ⁇ 30%, and 1.5 ⁇ REM/Zr.
  • the present invention provides a steel plate that can have a higher average and a higher minimum in HAZ toughness not only upon low to moderate heat input welding, but also even upon high heat input welding, has such excellent heat affected zone toughness, and still exhibits excellent productivity.
  • the present inventors have made searches for ways to allow a steel plate to have better HAZ toughness upon high heat input under production conditions with relatively high productivity. As a result, the present inventors have found as follows. Assume that intragranular ferrite formation occurring at oxides is ensured, coarse titanium nitride particles acting as an inhibitory factor to HAZ toughness are inhibited to be formed, and titanium nitride particles are dispersed in an appropriately controlled form. This allows a steel plate to have productivity and HAZ toughness upon high heat input both at satisfactory levels. Specifically, the present inventors have findings as follows. Assume that the oxides are controlled appropriately in their chemical compositions. This ensures intragranular ferrite formation.
  • titanium nitride particles are appropriately controlled in size and number to inhibit coarsening of prior austenite grains. This enables the refinement of grain-boundary ferrite grains that are formed at prior austenite grain boundaries. Thus, a steel plate having excellent HAZ toughness upon high heat input is provided.
  • the present inventors have verified as follows. Assume that, of the oxides, those having an equivalent circle diameter of less than 2 pm are dispersed in a number density of 300 or more per square millimeter, but those having an equivalent circle diameter of 2 ⁇ m or more are controlled to be dispersed in a number density of 100 or less per square millimeter. This provides excellent HAZ toughness.
  • the present invention has been made based on the above-mentioned findings.
  • the individual elements and conditions are specified for reasons as follows.
  • oxide particles meeting the conditions of constituent elements excluding oxygen in contents, in mass percent: 2% ⁇ Ti ⁇ 40%, 5% ⁇ Al ⁇ 30%, 5% ⁇ Ca ⁇ 40%, 5% ⁇ REM ⁇ 50%, 2% ⁇ Zr ⁇ 30%, and 1.0 ⁇ REM/Zr, and having an equivalent circle diameter of less than 2 ⁇ m are present in a number density of 300 or more per square millimeter.
  • oxide particles are controlled to have an equivalent circle diameter of less than 2 ⁇ m. Such fine oxide particles promote intragranular ferrite formation to improve the HAZ toughness. In contrast, oxide particles having an equivalent circle diameter of 2 ⁇ m or more may lower the barrier energy upon formation of coarse titanium nitride particles to increase the amount of formed coarse titanium nitride particles. Oxide particles, if having a chemical composition, in mass percent, not meeting the conditions of 2% ⁇ Ti ⁇ 40%, 5% ⁇ Al ⁇ 30%, 5% ⁇ Ca ⁇ 40%, 5% ⁇ REM ⁇ 50%, 2% ⁇ Zr ⁇ 30%, and 1.0 ⁇ REM/Zr, may fail to contribute to sufficient intragranular ferrite formation.
  • the ratio (in mass percent) of REM to Zr in the oxide particles may be controlled to 1.5 or more. This further reduces the amount of coarsely formed titanium nitride particles in the surface of the oxide particles in molten steel to achieve still further excellent HAZ toughness.
  • oxide particles having an equivalent circle diameter of 2 ⁇ m or more are present in a number density of 100 or less per square millimeter.
  • oxide particles meeting the chemical composition as above those having an equivalent circle diameter of 2 ⁇ m or more cause deterioration in HAZ toughness and are preferably minimized. From this viewpoint, the number density of oxide particles having an equivalent circle diameter of 2 ⁇ m or more is controlled to 100 or less per square millimeter in the present invention.
  • the form of titanium nitride (particles) is specified in detail.
  • the titanium nitride inhibits austenite grain coarsening upon HAZ high-temperature heating, reduces the sizes of grain-boundary ferrite grains formed during cooling, and thereby contributes to better HAZ toughness. To sufficiently inhibit austenite grain coarsening, a large number of titanium nitride particles should naturally be dispersed.
  • the present inventors have found that the titanium nitride particles are dissolved at a lower dissolution rate upon HAZ high-temperature heating with more uniformized sizes of the particles; and that appropriate control of the size and number of the titanium nitride particles can effectively inhibit austenite grain coarsening even upon high heat input welding.
  • the steel plate when meeting two conditions as follows, can exhibit satisfactory HAZ toughness upon high heat input.
  • titanium nitride particles having an equivalent circle diameter of 1 ⁇ m or more are controlled to be present in a number density of 7 or less per square millimeter.
  • the titanium nitride particles having an equivalent circle diameter of 1 ⁇ m or more, if present in a number density of greater than 7 per square millimeter, may cause the steel plate to have inferior HAZ toughness.
  • Such titanium nitride particles have a rectangular parallelepiped shape, still have remarkably high hardness as compared with the steel, and cause stress concentration to significantly impair the HAZ toughness. Accordingly, the coarse titanium nitride particles should be more strictly controlled as compared with coarse oxide particles.
  • titanium nitride particles having an equivalent circle diameter of 20 nm or more are present in a number density of 1.0x 10 6 or more per square millimeter.
  • the titanium nitride particles having an equivalent circle diameter of 20 nm or more may fail to sufficiently act as titanium nitride particles necessary in inhibition of austenite grain coarsening.
  • Ultrafine titanium nitride particles having an equivalent circle diameter of less than 20 nm disappear in a short time in high-temperature heating upon high heat input welding, thereby little contribute to the inhibition of austenite grain coarsening, and do not require special control.
  • Titanium nitride particles are energetically unstable with a decreasing size thereof. Specifically, titanium nitride particles more readily disappear upon HAZ high-temperature heating with a smaller (decreasing) size as compared to the average size of all titanium nitride particles. For this reason, particles that contribute to austenite grain coarsening inhibition are substantially present in an increasing number with an increasing number of titanium nitride particles having a larger size than the average size, or having a size smaller than, but relatively near to, the average size.
  • the present inventors have found herein as follows.
  • the size and number of the particles are preferably controlled so that the difference between the average size and a size in which the largest number of titanium nitride particles is recorded becomes small. This increases the number of the substantially contributive titanium nitride particles and achieves highly effective inhibition of austenite grain coarsening.
  • the control may be performed that the difference between values df and da becomes small.
  • the df is defined as follows.
  • the titanium nitride particles having an equivalent circle diameter of 20 nm or more are classified into ranges of equivalent circle diameter from 20 nm up to 500 nm every 5 nm in an increasing order, in which particles in each of the ranges have an equivalent circle diameter of (di-5) to less than di, where di is 25, 30, 35,...500, and the di in a range having a largest number of titanium nitride particles present in the range is defined as the df.
  • the da represents the average equivalent circle diameter of the titanium nitride particles having an equivalent circle diameter of 20 nm to less than 500 nm. This control increases the number of substantially contributive titanium nitride particles and achieves highly effective inhibition of austenite grain coarsening.
  • the average equivalent circle diameter of titanium nitride particles was calculated in the following manner. Specifically, a sample was subjected to transmission electron microscopic (TEM) observation under conditions mentioned below in experimental examples. The areas of individual titanium nitride particles in the observation view field were measured by image analysis, from which equivalent circle diameters of the individual titanium nitride particles were calculated Of the particles, titanium nitride particles having an equivalent circle diameter of 20 nm to less than 500 nm were selected, and the arithmetic mean of the equivalent circle diameters of the selected particles was determined.
  • TEM transmission electron microscopic
  • titanium nitride particles even if present in a large number, may fail to sufficiently inhibit austenite grain coarsening and fail to provide satisfactory HAZ toughness upon high heat input.
  • the steel plate according to the present invention meets the above-mentioned conditions.
  • the steel plate contains oxide particles including constituent elements excluding oxygen in contents, in mass percent, meeting conditions: 2% ⁇ Ti ⁇ 40%, 5% ⁇ Al ⁇ 30%, 5% ⁇ Ca ⁇ 40%, 5% ⁇ REM ⁇ 50%, 2% ⁇ Zr ⁇ 30%, and 1.0 ⁇ REM/Zr.
  • oxide particles having an equivalent circle diameter of less than 2 ⁇ m are present in a number density of 300 or more per square millimeter; and oxide particles having an equivalent circle diameter of 2 ⁇ m or more are present in a number density of 100 or less per square millimeter.
  • titanium nitride particles contained in the steel plate titanium nitride particles having an equivalent circle diameter of 1 ⁇ m or more are present in a number density of 7 or less per square millimeter, and titanium nitride particles having an equivalent circle diameter of 20 nm or more are present in a number density of 1.0x 10 6 or more per square millimeter.
  • the steel plate meets the conditions as specified by the relational expression of
  • the steel plate is preferably produced under production conditions as follows.
  • the preferred production conditions are as follows.
  • the dissolved oxygen content in the molten steel is controlled to the range of 0.002% to 0.01% (in mass percent) by deoxidation typically using Mn and Si.
  • Al, Ti, (REM, Zr), and Ca are added in the specified order in such a controlled manner that a time t1 from the REM or Zr addition to the Ca addition be 5 minutes or longer.
  • a cooling time t2 in the temperature range of 1500°C to 1450°C upon casting may be set within 300 seconds
  • a cooling time t3 in the temperature range of 1300°C to 1200°C upon casting may be set within 680 seconds.
  • the mass ratio [REM]/[Zr] of the REM content [REM] to the Zr content [Zr] may be controlled to 1.8 or more, and the time t1 may be controlled to 10 minutes or longer. This may provide more an appropriate oxide particle form and reduce the amount of coarsely formed titanium nitride particles in the surface of the oxide particles to give still better HAZ toughness.
  • (REM, Zr) refers to that REM and Zr may be added simultaneously or non-simultaneously in any order.
  • the dissolved oxygen content in the molten steel is controlled to the range of 0.002% to 0.01% by deoxidation typically using Mn and Si.
  • the dissolved oxygen if present in a content less than 0.002%, may fail to provide a necessary amount of oxide particles having such an appropriate chemical composition as to induce intragranular ferrite formation.
  • the dissolved oxygen if present in a content greater than 0.01%, may cause the formation of a larger amount of coarse oxide particles having an equivalent circle diameter of 2 ⁇ m or more to cause the steel plate to have inferior HAZ toughness.
  • the time t1 from the addition of REM or Zr to the addition of Ca is controlled to 5 minutes or longer.
  • the oxides specified in the present invention effectively promote intragranular ferrite formation and hardly function as nucleation sites for coarse titanium nitride particles.
  • an oxide formation reaction of REM or Zr preferably proceeds sufficiently before the addition of Ca that acts as a strong deoxidizing element.
  • the time t1 from the addition of REM or Zr to the addition of Ca is preferably controlled to 5 minutes or longer. This can give oxide particles that are present in a predetermined number density and meet the condition: REM/Zr ⁇ 1.0.
  • oxide particles meeting the condition: REM/Zr ⁇ 1.0 may be formed insufficiently.
  • the mass ratio [REM]/[Zr] of the REM content [REM] to the Zr content [Zr] is controlled to 1.8 or more, and the time t1 is controlled to 10 minutes or longer. This can give oxide particles that are present in a predetermined number density and meet the condition: REM/Zr ⁇ 1.5.
  • the elements Al, Ti, (REM, Zr), and Ca are added in the specified order in ingot making. This is because these elements, if added in a order other than the specified order, may fail to ensure a sufficient number of oxide particles having such an appropriate chemical composition as to act as nucleation sites of intragranular ferrite.
  • Ca is a strong deoxidizing element and has extremely strong deoxidation power and, if added prior to Ti and Al, may significantly reduce the amount of oxygen to be combined with Ti and Al.
  • the cooling time t2 in the temperature range of 1500°C to 1450°C upon casting is controlled within 300 seconds.
  • cooling time t2 in the temperature range of 1500°C to 1450°C upon casting is longer than 300 seconds, coarse oxide particles may be increased, or coarse titanium nitride particles may be formed due to component segregation upon solidification, to cause the steel plate to have inferior HAZ toughness.
  • the cooling time t3 in the temperature range of 1300°C to 1200°C upon casting is controlled within 680 seconds.
  • Titanium nitride particles formed upon casting are classified into A, B, and C as follows.
  • the titanium nitride particles A are those formed in the molten steel.
  • the titanium nitride particles B are those formed in a solidification segregation portion of the solidified steel.
  • the titanium nitride particles are those formed in a non-solidification-segregation portion of the solidified steel.
  • the titanium nitride particles A, B, and C are formed in the specified order and have sizes (particle diameters) in decreasing order (A > B > C). In contrast, the titanium nitride particles A, B, and C are present in increasing order of number (A ⁇ B ⁇ C).
  • titanium nitride particles having sizes corresponding to the df are the titanium nitride particles C.
  • the titanium nitride particles A are present in a smaller number as compared with the titanium nitride particles B and C and little affect the average equivalent circle diameter da of titanium nitride particles. It is therefore considered that, to control the value specified by
  • the titanium nitride particles B grow prior to the formation of the titanium nitride particles C and may cause the specific titanium nitride particles to have a larger average equivalent circle diameter da, to probably cause the value specified by
  • the steel plate according to the present invention includes individual chemical compositions (elements) in contents out of appropriate ranges.
  • the base metal steel plate
  • the steel plate according to the present invention includes chemical compositions in contents within ranges as described below.
  • the contents of elements constituting oxides, such as Al, Ca, and Ti, among the chemical compositions, are contents as including part of the elements constituting the oxides.
  • the contents (%) of the chemical compositions are all in mass percent.
  • Carbon (C) element is essential for ensuring the strength of the steel plate. Carbon, if present in a content less than 0.03%, may fail to provide a necessary strength. In contrast, carbon, if present in an excessively high content, may cause the formation of a large amount of hard martensite-austenite constituent (MA) to cause the base metal to have inferior toughness. To prevent this, the carbon content may be controlled to 0.12% or less. Of the carbon content, the lower limit is preferably 0.04%, and the upper limit is preferably 0.10%.
  • Silicon (Si) element allows titanium (Ti) to have higher activity and may be added as appropriate to provide the predetermined titanium nitride particle form.
  • Si if added in an amount of less than 0.10%, may fail to allow the titanium nitride particles having an equivalent circle diameter of 20 nm or more to be present in a number density of 1.0x 10 6 per square millimeter or more.
  • Si if added in an amount of greater than 0.25%, may readily cause the formation of coarse titanium nitride particles and the formation of a hard MA phase, to fail to provide a predetermined HAZ toughness.
  • the lower limit is preferably 0.12% and more preferably 0.14%
  • the upper limit is preferably 0.22% and more preferably 0.20%.
  • Mn element is useful in ensuring the strength of the steel plate.
  • Mn is preferably present in a content of 1.0% or more.
  • Mn if present in an excessively high content of greater than 2.0%, may cause the HAZ to have an excessively high strength and to have inferior toughness.
  • the Mn content is preferably 2.0% or less.
  • the lower limit is preferably 1.4%
  • the upper limit is preferably 1.8%.
  • Phosphorus (P) element is an impurity element that readily causes grain boundary fracture and adversely affects the toughness. To prevent this, the phosphorus content is preferably minimized. From the viewpoint of ensuring the HAZ toughness, the phosphorus content is controlled to 0.03% or less, and preferably 0.02% or less. However, it is difficult to industrially control the phosphorus content in the steel to 0%.
  • S Sulfur (S) element forms manganese sulfide at the prior austenite grain boundary in the HAZ and causes the steel plate to have inferior HAZ toughness.
  • the sulfur content is preferably minimized.
  • the sulfur content is controlled to 0.015% or less, and preferably 0.010% or less.
  • Aluminum (Al) element forms oxides that act as nucleation sites for intragranular ferrite.
  • Al if present in a content of less than 0.004%, may fail to provide the predetermined oxide form and fail to sufficiently promote intragranular transformation to cause the steel plate to have inferior HAZ toughness.
  • Al if present in an excessively high content, may cause the formation of coarse oxide particles to cause the steel plate to have inferior HAZ toughness.
  • the Al content may be controlled to 0.05% or less.
  • the lower limit is preferably 0.007%, and the upper limit is preferably 0.04%.
  • Titanium (Ti) element forms titanium nitride and, when added prior to REM, Zr, and Ca, enables fine dispersion of oxides that effectively promote intragranular ferrite formation.
  • Ti may be contained in a content of 0.010% or more. However, Ti, if present in an excessively high content, may cause the formation of a larger amount of coarse titanium nitride particles to cause the steel plate to have inferior HAZ toughness. To prevent this, the Ti content may be controlled to 0.050% or less. Of the Ti content, the lower limit is preferably 0.012%, and the upper limit is preferably 0.035% and more preferably 0.025%.
  • Rare-earth elements (REM) and zirconium (Zr) element when added after the addition of Ti but before the addition of Ca, form oxides that are effective in intragranular ferrite formation. These oxides, when compositively precipitated with titanium nitride, more suitably act as intragranular ferrite formation sites.
  • the elements exhibit these effects increasingly with increasing contents.
  • REM and Zr may be present each in a content of 0.0003% or more. However, these elements, if present in an excessively high content, may cause the oxides to be coarsened to cause the steel plate to have inferior HAZ toughness. To prevent this, the contents of REM and Zr may be each controlled to 0.02% or less. Of the contents of these elements, the lower limit is more preferably 0.0005%, and the upper limit is more preferably 0.015%.
  • Ca element when added 5 minutes or longer after the addition of REM and Zr (in any order), forms oxides that are effective in intragranular ferrite formation and inhibit the formation of coarse titanium nitride particles.
  • Ca may be contained in a content of 0.0005% or more.
  • Ca if present in an excessively high content, may form coarse oxide particles to cause the steel plate to have inferior HAZ toughness.
  • the Ca content may be controlled to 0.010% or less.
  • the lower limit is preferably 0.0008%
  • the upper limit is preferably 0.008%.
  • Nitrogen (N) element when forming fine titanium nitride particles, is useful in ensuring the HAZ toughness. Nitrogen, if present in a content of 0.002% or more, may provide the desired titanium nitride particles. However, nitrogen, if present in an excessively high content, may promote the formation of coarse titanium nitride particles. To prevent this, the nitrogen content may be controlled to 0.010% or less. Of the nitrogen content, the lower limit is preferably 0.003%, and the upper limit is preferably 0.008%.
  • the above-mentioned elements are essential elements specified in the present invention, with the remainder being iron and inevitable impurities.
  • inevitable impurities Sn, As, Pb, and other elements may be contained, where the elements are brought into the steel under circumstances of raw materials, facility materials, and production facilities. It is also effective to actively add any of elements as follows. This may allow the steel plate to have further better property or properties depending on the type of the chemical composition (element) to be added.
  • At least one element selected from the group consisting of Ni of 0.05% to 1.50%, Cu of 0.05% to 1.50%, Cr of 0.05% to 1.50%, and Mo of 0.05% to 1.50% may be added.
  • Nickel (Ni), copper (Cu), Chromium (Cr), and molybdenum (Mo) elements are each effective in allowing the steel plate to have a higher strength. These elements exhibit increasing effects with increasing contents. To allow the elements to exhibit such effects effectively, the elements are preferably contained each in a content of 0.05% or more. However, the elements, if present in an excessively high content, may cause the steel plate to have an excessively high strength and to have inferior HAZ toughness. To prevent this, the contents of the elements are each preferably controlled to 1.50% or less. Of each of the contents of the elements, the lower limit is more preferably 0.10%, and the upper limit is more preferably 1.20%.
  • At least one of Nb of 0.002% to 0.10% and V of 0.002% to 0.10% may be added.
  • Niobium (Nb) and vanadium (V) elements precipitate as carbonitrides, inhibit the coarsening of austenite grains, and are effective in allowing the base metal to have good toughness. These elements exhibit increasing effects with increasing contents. To allow the elements to exhibit such effects effectively, the elements are preferably contained each in a content of 0.002% or more. However, the elements, if contained in excessively high contents, may cause the coarsening of the HAZ microstructure to cause the steel plate to have inferior HAZ toughness. To prevent this, the contents of the elements are each preferably controlled to 0.10% or less. Of each of the contents of the elements, the lower limit is more preferably 0.005%, and the upper limit is more preferably 0.08%.
  • B of 0.0005% to 0.0050% may be added
  • Boron (B) element inhibits the formation of coarse grain boundary ferrite and effectively allows the steel plate to have better HAZ toughness.
  • the element exhibits an increasing effect as above with an increasing content thereof.
  • the element is preferably contained in a content of 0.0005% or more.
  • the boron content is more preferably 0.0010% or more, and furthermore preferably 0.0015% or more.
  • boron if present in an excessively high content, may promote the formation of a coarse bainite packet at prior austenite grain boundaries to cause the steel plate to have inferior HAZ toughness contrarily.
  • the upper limit is preferably 0.0045%, more preferably 0.0040%, and furthermore preferably 0.0035%.
  • the steel plate it is effective for the steel plate to contain at least one element selected from the group consisting of Ni, Cu, Cr, and Mo.
  • the contents (in mass percent) of these elements preferably meet the condition: [Ni]+[Cu]+[Cr]+[Mo] ⁇ 2.5%, where [Ni], [Cu], [Cr], and [Mo] are contents (in mass percent) respectively of Ni, Cu, Cr, and Mo.
  • Coarse titanium nitride particles are formed in a liquid phase in a solidification stage of the molten steel, where Ti and N are enriched in the liquid phase due to solidification segregation.
  • the elements when present in a total content ([Ni]+[Cu]+[Cr]+[Mo]) of greater than 2.5%, may cause the solidification temperature to be lowered This may cause the liquid phase to remain even cooled down to a low temperature. At such low temperatures, the driving force for the formation of coarse titanium nitride particles becomes large to cause the formation of a larger amount of the coarse titanium nitride particles.
  • /da is a parameter that relates to the number of titanium nitride particles contributing to austenite grain coarsening inhibition upon HAZ high-temperature heating. If the value is greater than 0.35, the austenite grains are not sufficiently inhibited from coarsening and fail to provide predetermined HAZ toughness.
  • the upper limit of the value is preferably 0.30 and more preferably 0.25.
  • the present invention relates to steel plates.
  • the term "steel plate” refers to a steel sheet having a thickness of 3.0 mm or more as defined in Japanese Industrial Standards (JIS).
  • JIS Japanese Industrial Standards
  • the steel plate according to the present invention has been invented as targeting the welding of steel plates having a thickness of 50 mm or more.
  • the target steel sheets herein may be considered to be steel sheets (steel plates) having a thickness of 50 mm or more.
  • steel plates were produced in the following manner. Initially, molten steels having chemical compositions given in Tables 1 and 2 were prepared using a vacuum induction furnace (VIF: 150 kg). The molten steels were cast to give slabs (150 mm by 250 mm in section). The slabs were subjected to hot rolling and yielded hot-rolled plates having a thickness of 80 mm. The hot rolling was performed under conditions as follows. Prior to rolling, heating was performed at 1100°C for 3 hours. Then the hot rolling was performed at a finish rolling temperature of 780°C or higher, an average cooling rate down to 450°C of 6°C/s, and a cooling stop temperature of 450°C.
  • the controlled conditions are the dissolved oxygen content [Of] (in mass percent) in the molten steel before the addition of Al (Ti); the order of the additions of Al, Ti, REM, Zr, and Ca; the time t1 from the addition of REM or Zr to the addition of Ca; the mass ratio [REM]/[Zr] of the REM content [REM] to the Zr content [Zr], where this ratio is indicated as "REM/Zr" in the tables; the cooling time t2 in the temperature range of 1500°C to 1450°C upon casting; and the cooling time t3 in the temperature range of 1300°C to 1200°C upon casting.
  • REM as in Tables 1 and 2 was added in the form of a misch metal containing, in mass percent, about 50% of Ce and about 25% of La.
  • the symbol "-" in Tables 1 and 2 refers to that an element in question was not added.
  • the hot-rolled plates (steel plates) produced under the conditions as above were each subjected to measurements of number densities N1, NA, N2, N3, and N4, the value
  • the number density N1 refers to the number density of oxide particles having an equivalent circle diameter of less than 2 pm, containing Ti, Al, Ca, REM, and Zr in contents within the predetermined ranges, and having a ratio [REM]/[Zr] of equal to or greater than 1.0.
  • the number density NA refers to the number density of oxide particles having an equivalent circle diameter of less than 2 pm, containing Ti, Al, Ca, REM, and Zr in contents within the predetermined ranges, and having a ratio [REM]/[Zr] of equal to or greater than 1.5.
  • the number densityN2 refers to the number density of oxide particles having an equivalent circle diameter of 2 ⁇ m or more.
  • the number density N3 refers to the number density of titanium nitride particles having an equivalent circle diameter of 1 ⁇ m or more.
  • the number density N4 refers to the number density of titanium nitride particles having an equivalent circle diameter of 20 nm or more. The measurement results are indicated in Tables 5 and 6.
  • Test specimens were cut out from the steel plates in a position at a depth of one-fourth the thickness from the surface so that the axis of the test specimen passed through the position at a depth of one-fourth the thickness.
  • the test specimens were observed in a cross section in parallel with the rolling direction and thickness direction using the field emission scanning electron microscope SUPRA35 (trade name) supplied by Carl Zeiss AG.
  • the field emission scanning electron microscope is hereinafter also simply referred to as FE-SEM.
  • the observation was performed at 5000-fold magnification in an observation area of 0.048 mm 2 .
  • the areas of individual oxide particles in the observation view field were measured by image analysis, and based on which the equivalent circle diameters of the oxide particles were calculated.
  • oxide particles having chemical compositions meeting the conditions was determined using an energy dispersive X-ray spectrometer (EDX)).
  • EDX energy dispersive X-ray spectrometer
  • the chemical composition measurement using the EDX was performed at an acceleration voltage of 15 kV for a measurement time of 100 seconds.
  • the numbers (N1, NA) of oxide particles having an equivalent circle diameter of less than 2 ⁇ m were determined each as a number density per square millimeter. However, oxide particles having an equivalent circle diameter of 0.2 ⁇ m or less did not have sufficient reliability in EDX analysis and were excluded from the analysis.
  • Test specimens were cut out from the steel plates in a position at a depth of one-fourth the thickness from the surface so that the axis of the test specimen passed through the position at a depth of one-fourth the thickness.
  • the test specimens were observed in a cross section in parallel with the rolling direction and thickness direction using the FE-SEM. The observation was performed at 1000-fold magnification in an observation view field of 0.06 mm 2 at 20 points. The areas of individual oxide particles in the observation view field were measured by image analysis, and based on which the equivalent circle diameters of the oxide particles were calculated. Whether the oxide particles had chemical compositions meeting the conditions was determined using an energy dispersive X-ray spectrometer (EDX)). The chemical composition measurement using the EDX was performed at an acceleration voltage of 15 kV for a measurement time of 100 seconds. The number (N2) of oxide particles having an equivalent circle diameter of 2 ⁇ m or more was determined as a number density per square millimeter.
  • EDX energy dispersive X-ray spect
  • Test specimens were cut out from the steel plates in a position at a depth of one-fourth the thickness from the surface so that the axis of the test specimen passed through the position at a depth of one-fourth the thickness.
  • the test specimens were observed in a cross section in parallel with the rolling direction and thickness direction, and images of 20 view fields in the cross section were taken using an optical microscope at 200-fold magnification.
  • the number of coarse titanium nitride particles was counted and converted into a number density (N3) per square millimeter.
  • the measured images have an area of 0.148 mm 2 per view field and an area of 2.96 mm 2 per test specimen. Titanium nitride particles were identified based on shape and color.
  • titanium nitride particles Vivid orange, angular inclusions were considered as titanium nitride particles.
  • the equivalent circle diameters of the titanium nitride particles were calculated using an analysis software. A coarse titanium nitride particle often forms with an oxide as a nucleation site. In this case, the oxide in the titanium nitride was excluded from the object for the measurement of equivalent circle diameter.
  • Specimens were cut out from the steel plates in a position at a depth of one-fourth the thickness.
  • the cross sections of the specimens in parallel with the rolling direction and thickness direction were treated to give replica TEM test specimens.
  • the replica TEM test specimens were observed with a transmission electron microscope (TEM) at 15000-fold magnification in 4 view fields each having an area of 6.84 ⁇ m by 8.05 pm, based on which particles containing Ti and N were identified using an energy dispersive X-ray fluorescence spectrometer (EDX) and treated as titanium-containing nitrides.
  • TEM transmission electron microscope
  • EDX energy dispersive X-ray fluorescence spectrometer
  • the areas of titanium-containing nitrides in the view fields were measured by image analysis and converted into equivalent circle diameters.
  • the number of titanium-containing nitride particles having an equivalent circle diameter of 20 nm or more was determined and converted into a value per square millimeter to give the number density (N4).
  • df and da were determined as follows.
  • the titanium nitride particles having an equivalent circle diameter of 20 nm or more were classified into ranges of equivalent circle diameter from 20 nm up to 500 nm every 5 nm in an increasing order, in which particles in each of the ranges had an equivalent circle diameter of (di-5) to less than di, where di is 25, 30, 35,...500, and the di in a range having a largest number of titanium nitride particles present in the range was defined as the df.
  • the da was defined as the average equivalent circle diameter of titanium nitride particles having an equivalent circle diameter of 20 nm to less than 500 nm.
  • /da was calculated.
  • Specimens for weld joint was sampled from the steel plates, processed to have a V groove, and subjected to electrogas arc welding with a heat input of 50 kJ/mm.
  • Each three Charpy impact test specimens (V-notched test specimens prescribed in JIS Z 2242) were sampled from the specimens, where the test specimens had notches in a heat affected zone (HAZ) adjacent to the weld line (bond) in a position at a depth of one-fourth the thickness from the surface of the steel plate.
  • the Charpy impact test specimens were subjected to Charpy impact tests at -40°C to measure absorbed energy (vE -40 ). Of the measured absorbed energy, the average and minimum were determined A specimen having an average vE -40 of greater than 180 J and a minimum vE -40 of greater than 120 J was evaluated as having excellent HAZ toughness.
  • the steel plates of Nos. 36 to 55 are comparative examples not meeting at least one of the conditions specified in the present invention.
  • the data demonstrate that these steel plates failed to meet the criterion in either one of the HAZ toughness (average and minimum) with a heat input of 50 kJ/mm and the HAZ toughness (average) with a heat input of 60 kJ/mm.
  • the steel plate according to the present invention has excellent toughness in a heat affected zone after high heat input and is useful in welded structures such as bridges, high-rise buildings, ships, and line pipes.

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Claims (2)

  1. Feuille d'acier ayant une excellente ténacité dans une zone affectée thermiquement, la feuille d'acier ayant une épaisseur de 50 mm ou plus et étant constituée de
    en pourcentage en masse,
    C en une teneur allant de 0,03 % à 0,12 % ;
    Si en une teneur allant de 0,10 % à 0,25 % ;
    Mn en une teneur allant de 1,0 % à 2,0 % ;
    P en une teneur de 0,03 % ou moins, excluant 0 % ;
    S en une teneur de 0,015 % ou moins, excluant 0 % ;
    Al en une teneur allant de 0,004 % à 0,05 % ;
    Ti en une teneur allant de 0,010 % à 0,050 % ;
    au moins un élément de terres rares (REM) en une teneur allant de 0,0003 % à 0,02 % ;
    Zr en une teneur allant de 0,0003 % à 0,02 % ;
    Ca en une teneur allant de 0,0005 % à 0,010 % ;
    N en une teneur allant de 0,002 % à 0,010 % ; et
    éventuellement au moins un élément sélectionné parmi le groupe constitué de
    Ni en une teneur allant de 0,05 % à 1,50 % ;
    Cu en une teneur allant de 0,05 % à 1,50 % ;
    Cr en une teneur allant de 0,05 % à 1,50 % ;
    Mo en une teneur allant de 0,05 % à 1,50 % ;
    Nb en une teneur allant de 0,002 % à 0,10 % ;
    V en une teneur allant de 0,002 % à 0,10 % ; et
    B en une teneur allant de 0,0005 % à 0,0050 %,
    le reste étant constitué de fer et d'impuretés inévitables,
    la feuille d'acier comprenant des particules d'oxyde, les particules d'oxyde comprenant des éléments constitutifs sans tenir compte de l'oxygène présent, en pourcentage en masse, respectant les conditions suivantes : 2 % < Ti < 40 % ;
    Figure imgb0030
     5 % < Al < 30 % ;
    Figure imgb0031
     5 % < Ca < 40 % ;
    Figure imgb0032
     5 % < REM < 50 % ;
    Figure imgb0033
     2 % < Zr < 30 % ;
    Figure imgb0034
     et 1,0 ≤ REM / Zr ,
    Figure imgb0035
     des particules d'oxyde,
    des particules d'oxyde avec un diamètre de cercle équivalent inférieur à 2 µm étant présentes en une densité en nombre de 300 ou plus par millimètre carré ; et
    des particules d'oxyde avec un diamètre de cercle équivalent de 2 µm ou plus étant présentes en une densité en nombre de 100 ou moins par millimètre carré,
    la feuille d'acier comprenant des particules de nitrure de titane, de particules de nitrure de titane contenues dans la feuille d'acier,
    des particules de nitrure de titane avec un diamètre de cercle équivalent de 1 µm ou plus étant présentes en une densité en nombre de 7 ou moins par millimètre carré ; et
    des particules de nitrure de titane avec un diamètre de cercle équivalent de 20 nm ou plus étant présentes en une densité en nombre de 1,0 x 106 ou plus par millimètre carré,
    la feuille d'acier ayant da et df respectant une condition spécifiée par l'expression relationnelle : | da − df | / da ≤ 0,35
    Figure imgb0036
     dans laquelle le df est défini de sorte que les particules de nitrure de titane ayant un diamètre de cercle équivalent de 20 nm ou plus soient classées dans des plages de diamètres de cercle équivalent allant de 20 nm jusqu'à 500 nm tous les 5 nm dans un ordre croissant, dans lequel des particules dans chacune des plages ont un diamètre de cercle équivalent de (di-5) à moins de di, où di est égal à 25, 30, 35,...500, et le di dans une plage ayant un nombre maximal de particules de nitrure de titane présentes dans la plage est défini en tant que le df, et
    dans laquelle le da représente un diamètre de cercle équivalent moyen des particules de nitrure de titane ayant un diamètre de cercle équivalent de 20 nm à moins de 500 nm.
  2. Feuille d'acier ayant une excellente ténacité dans une zone affectée thermiquement selon la revendication 1,
    dans laquelle la feuille d'acier comprend des particules d'oxyde ayant un diamètre de cercle équivalent inférieur à 2 µm et comprenant des éléments constitutifs sans tenir compte de l'oxygène présent, en pourcentage en masse, respectant les conditions suivantes : 2 % < Ti < 40 % ;
    Figure imgb0037
     5 % < Al < 30 % ;
    Figure imgb0038
     5 % < Ca < 40 % ;
    Figure imgb0039
     5 % < REM < 50 % ;
    Figure imgb0040
     2 % < Zr < 30 % ;
    Figure imgb0041
     et 1,5 ≤ REM / Zr ,
    Figure imgb0042
     les particules d'oxyde étant présentes en une densité en nombre de 300 ou plus par millimètre carré.
EP13838421.9A 2012-09-19 2013-08-29 Feuille d'acier épaisse ayant une excellente ténacité dans la zone affectée thermiquement par le soudage Not-in-force EP2899289B1 (fr)

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JP5883369B2 (ja) 2016-03-15
EP2899289A4 (fr) 2016-06-01
WO2014045829A1 (fr) 2014-03-27
KR101659245B1 (ko) 2016-09-22
KR20150038664A (ko) 2015-04-08
EP2899289A1 (fr) 2015-07-29
JP2014058734A (ja) 2014-04-03
CN104603314A (zh) 2015-05-06

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