WO2013099318A1 - 脆性亀裂伝播停止特性に優れた構造用高強度厚鋼板およびその製造方法 - Google Patents

脆性亀裂伝播停止特性に優れた構造用高強度厚鋼板およびその製造方法 Download PDF

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WO2013099318A1
WO2013099318A1 PCT/JP2012/063409 JP2012063409W WO2013099318A1 WO 2013099318 A1 WO2013099318 A1 WO 2013099318A1 JP 2012063409 W JP2012063409 W JP 2012063409W WO 2013099318 A1 WO2013099318 A1 WO 2013099318A1
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rolling
plate thickness
steel plate
crack propagation
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PCT/JP2012/063409
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English (en)
French (fr)
Japanese (ja)
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佳子 竹内
長谷　和邦
三田尾　眞司
善明 村上
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Ｊｆｅスチール株式会社
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Priority to KR1020147017473A priority Critical patent/KR101588258B1/ko
Priority to BR112014015779-0A priority patent/BR112014015779B1/pt
Priority to CN201280065286.0A priority patent/CN104024462B/zh
Priority to EP12863408.6A priority patent/EP2799584B1/de
Publication of WO2013099318A1 publication Critical patent/WO2013099318A1/ja

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—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
    • C21D8/0205—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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—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
    • 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
    • C21D2201/00—Treatment for obtaining particular effects
    • C21D2201/05—Grain orientation
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite

Definitions

  • the present invention relates to a high-strength thick steel plate and a manufacturing method thereof excellent in brittle crack propagation arresting characteristics and particularly for a ship. It relates to a plate thickness of 50 mm or more.
  • Ni steel is used on a commercial scale in liquefied natural gas storage tanks.
  • TMCP Thermo-Mechanical Control Process
  • TMCP Thermo-Mechanical Control Process
  • Method fine graining can be achieved, low temperature toughness can be improved, and excellent brittle crack propagation stopping characteristics can be imparted.
  • Patent Document 1 proposes a steel material in which the structure of the surface layer portion is ultrafinely refined in order to improve brittle crack propagation stopping characteristics without increasing the alloy cost.
  • the steel material excellent in the brittle crack propagation stopping characteristics described in Patent Document 1 has an effect of improving the brittle crack propagation stopping characteristics due to shear lip (plastic deformation region shear-lips) generated in the steel layer when the brittle crack propagates.
  • shear lip plastic deformation region shear-lips
  • it is characterized in that the propagation energy possessed by the propagating brittle crack is absorbed by refining the crystal grains of the shear lip portion.
  • the surface layer portion is cooled to below A r3 transformation point (transformation point) by controlled cooling after hot rolling, then controlled cooling (Controlled Cooling)
  • the Stop recuperator the surface layer portion to the transformation point or higher (Recuperate ) Is repeated one or more times, and during this time, the steel material is subjected to reduction, and repeatedly transformed or processed and recrystallized, so that a superfine ferrite structure or bainite structure is formed on the surface layer portion. Is described.
  • both surface portions of the steel material have an equivalent circular particle diameter (cycle-equalent average grain). size): 5 ⁇ m or less, aspect ratio (aspect ratio of the grains): a layer having a ferrite structure having 50% or more of ferrite grains having two or more ferrite grains, and it is important to suppress variations in the ferrite grain size, and to suppress variations
  • a maximum rolling reduction per pass during finish rolling is set to 12% or less to suppress a local recrystallization phenomenon.
  • the steel materials excellent in brittle crack propagation stopping characteristics described in Patent Documents 1 and 2 are obtained by recooling only the steel surface layer part and then recovering the heat, and by applying processing during the recuperation, a specific structure is obtained.
  • control is not easy, and in particular, a thick material with a plate thickness exceeding 50 mm is a process with a heavy load on the rolling and cooling equipment.
  • Patent Document 3 attention is paid not only to the refinement of ferrite crystal grains but also to subgrains formed in ferrite crystal grains, and a technique on the extension of TMCP that improves brittle crack propagation stop characteristics. Is described.
  • the (110) plane X-ray intensity ratio in the (110) plane showing a texture developing degree) is set to 2 or more by controlled rolling, and the equivalent diameter of the circle (diameter equivalent).
  • the equivalent diameter of the circle is improved by making coarse particles of 20 ⁇ m or more 10% or less.
  • Patent Document 5 is characterized in that, as a welded structural steel having excellent brittle crack propagation stopping performance in a joint part, the (100) plane X-ray plane strength ratio in the rolled surface inside the plate thickness is 1.5 or more.
  • a steel sheet is disclosed. It is described that it has excellent brittle crack propagation stoppage properties due to the difference in angle between the stress loading direction and the crack propagation direction due to the texture development.
  • Japanese Patent Publication No. 7-100814 JP 2002-256375 A Japanese Patent No. 3467767 Japanese Patent No. 3548349 Japanese Patent No. 2659661
  • Non-Patent Document 1 evaluates the brittle crack propagation stopping performance of a steel plate having a thickness of 65 mm, and reports a result that the brittle crack does not stop in a large-scale brittle crack propagation stopping test of the base material.
  • Kca Kca ( ⁇ 10 ° C.)
  • the value of Kca at the use temperature of ⁇ 10 ° C. (hereinafter also referred to as Kca ( ⁇ 10 ° C.)) is less than 3000 N / mm 3/2 .
  • the results are shown, and it is suggested that in the case of a hull structure to which a steel plate having a thickness exceeding 50 mm is applied, ensuring safety is an issue.
  • Patent Documents 1 to 5 are mainly applied to manufacturing conditions and disclosed experimental data up to a plate thickness of about 50 mm, and applied to thick materials exceeding 50 mm. In this case, it is unclear whether a predetermined characteristic can be obtained, and the characteristics against crack propagation in the plate thickness direction necessary for the hull structure have not been verified at all.
  • the present invention provides a high-strength thick steel plate having excellent brittle crack propagation stopping characteristics that can be stably produced by an industrially simple process that optimizes rolling conditions and controls the texture in the thickness direction, and a method for producing the same The purpose is to provide.
  • FIGS. 1A and 1B schematically show that the crack 3 that has entered from the notch 2 of the standard ESSO test piece 1 has stopped propagating at the tip shape 4 in the base material 5.
  • a steel structure mainly composed of bainite having a packet or the like inside is more advantageous than a steel structure mainly composed of ferrite. It is also effective to accumulate the (100) plane, which is a cleavage plane, obliquely with respect to the rolling direction or the plate width direction, which is the crack propagation direction. 3.
  • the fracture surface of the standard ESSO test it is effective to improve the arrest performance by controlling the material of the central part of the plate thickness that becomes the tip of the crack. In particular, it is effective to satisfy the following formula (1) as an index relating to the toughness and texture of the central portion of the plate thickness.
  • vTrs (1 / 2t) ⁇ 12 ⁇ I RD // (110) [1 / 2t] ⁇ ⁇ 70
  • vTrs (1 / 2t) Fracture surface transition temperature at the thickness center (° C)
  • I RD // (110) [1 / 2t] Degree of integration of RD // (110) plane at the center of the plate thickness t: Plate thickness (mm) 4).
  • the structure is refined by carrying out rolling with a cumulative rolling reduction of 20% or more in a state where the temperature is in the austenite recrystallization temperature range. Thereafter, the cumulative rolling reduction is set to 40% or more in a state in the austenite non-recrystallization temperature region.
  • the texture at the center of the plate thickness can be controlled, and the above-described structure can be realized.
  • the present invention has been made by further study based on the obtained knowledge. That is, the present invention 1.
  • the metal structure is mainly bainite, and has a texture with an accumulation degree I of RD // (110) plane (Rolling Direction parallel to (110) plane) at the center of the plate thickness of 1.5 or more, and a surface layer portion and A structural high-strength thick steel plate excellent in brittle crack propagation stop characteristics, characterized in that the Charpy fracture surface transition temperature at the center of the plate thickness is vTrs ⁇ ⁇ 40 ° C. 2.
  • Steel composition is mass%, C: 0.03-0.20%, Si: 0.03-0.5%, Mn: 0.5-2.5%, Al: 0.005-0.08 %, P: 0.03% or less, S: 0.01% or less, N: 0.0050% or less, Ti: 0.005-0.03%, with the balance being Fe and inevitable impurities 3.
  • the steel composition is further mass%, Nb: 0.005 to 0.05%, Cu: 0.01 to 0.5%, Ni: 0.01 to 1.0%, Cr: 0.01 to 0 0.5%, Mo: 0.01 to 0.5%, V: 0.001 to 0.10%, B: 0.0030% or less, Ca: 0.0050% or less, REM: 0.010% or less 3.
  • Nb 0.005 to 0.05%
  • Cu 0.01 to 0.5%
  • Ni 0.01 to 1.0%
  • Cr 0.01 to 0 0.5%
  • Mo 0.01 to 0.5%
  • V 0.001 to 0.10%
  • B 0.0030% or less
  • Ca 0.0050% or less
  • REM 0.010% or less 3.
  • the structural high-strength thick steel plate having excellent brittle crack propagation stopping characteristics as described in 3 above, containing at least one of them.
  • the steel material (slab) having the composition described in either 5.3 or 4 is heated to a temperature of 1000 to 1200 ° C., and the sum of the cumulative reduction ratios in the austenite recrystallization temperature range and the austenite non-recrystallization temperature range is Roll 65% or more.
  • the cumulative rolling reduction is 20% or more in a state where the center portion of the plate thickness is in the austenite recrystallization temperature region.
  • the cumulative rolling reduction is 40% or more, and the first rolling in the state where the plate thickness central portion is in the austenite non-recrystallization temperature range Rolling is performed within a difference of 40 ° C.
  • the figure which shows typically the fracture surface form of the standard ESSO test of the thick steel plate exceeding 50 mm in thickness (a) is the figure which observed the test piece from the plane side, (b) is the figure which shows the fracture surface of a test piece.
  • Toughness and texture at the center of the plate thickness Define the metallographic structure. 1. Toughness and texture
  • the toughness and RD at the center of the sheet thickness are improved. // The degree of integration I on the (100) plane is appropriately defined according to the desired brittle crack propagation stop characteristics.
  • the Charpy fracture surface transition temperature in the surface layer part and the center part of the plate thickness is specified to be ⁇ 40 ° C. or lower. To do.
  • board thickness center part is -50 degrees C or less.
  • the cleaved surface is accumulated obliquely with respect to the main crack direction, and the effect of stress relaxation at the brittle crack tip by generating fine crack branching causes brittle cracks. Propagation stop performance is improved.
  • a brittle crack propagation stopping performance which is a target for ensuring structural safety, is a thick material exceeding 50 mm thick that has been used for hull outer plates such as recent container ships and bulk carriers: Kca ( ⁇ 10 In order to obtain (° C.) ⁇ 6000 N / mm 3/2 , it is necessary that the integration degree I of the RD // (110) plane at the central portion of the plate thickness is 1.5 or more, preferably 1.7 or more.
  • the degree of integration I of the RD // (110) plane in the central portion of the plate thickness indicates the following.
  • a sample having a thickness of 1 mm is collected from the central portion of the plate thickness, and a specimen parallel to the plate surface is mechanically polished / electrolytic polished to prepare a test piece for X-ray diffraction.
  • an X-ray diffraction measurement (X-ray diffraction measurement) was performed using a Mo ray source, and (200), (110) and (211) positive figures (pole figures) were obtained, A three-dimensional crystal orientation density function is calculated from the obtained positive pole figure by the Bunge method.
  • the integrated value is obtained by integrating the values of the three-dimensional crystal orientation density function of the orientation.
  • a value obtained by dividing the integrated value by the number of integrated directions is referred to as an integration degree I of the RD // (110) plane.
  • the Charpy toughness value at the center of the plate thickness and the degree of integration I on the RD // (110) plane satisfy the following expression (1) in addition to the above-mentioned base material toughness and texture definition.
  • the following formula (1) further excellent brittle crack propagation stopping performance can be obtained.
  • the metal structure is mainly composed of bainite.
  • the fact that the metal structure is mainly bainite means that the area fraction of the bainite phase is 80% or more of the whole. The balance is 20% or less of the total area fraction of ferrite, martensite (including island martensite), pearlite, and the like.
  • martensite including island martensite
  • pearlite and the like.
  • it is effective to transform into bainite after performing controlled rolling in the austenite non-recrystallization temperature range.
  • the desired toughness When transforming from austenite to ferrite after rolling, the desired toughness can be obtained, but because there is sufficient transformation time when transforming from austenite to ferrite, the resulting texture becomes random, and the target
  • the degree of integration I on the RD // (110) plane is not more than 1.5, preferably not less than 1.7.
  • the transformation time is not sufficient, and a so-called variant is selected in which a texture with a specific orientation is preferentially formed. Is performed, it is possible to obtain an integration degree I of RD // (110) plane of 1.5 or more, preferably 1.7 or more. For this reason, the metal structure obtained after rolling and cooling is mainly bainite.
  • C is an element that improves the strength of steel. In the present invention, it is necessary to contain 0.03% or more in order to ensure a desired strength, but if it exceeds 0.20%, the weldability deteriorates. As well as adversely affecting toughness. For this reason, C is preferably specified in the range of 0.03 to 0.20%. More preferably, it is 0.05 to 0.15%.
  • Si 0.03-0.5% Si is effective as a deoxidizing element and as a strengthening element for steel, but if its content is less than 0.03%, it has no effect. On the other hand, if it exceeds 0.5%, not only the surface properties of the steel are impaired, but also the toughness is extremely deteriorated. Therefore, the addition amount is preferably 0.03% or more and 0.5% or less.
  • Mn 0.5 to 2.5% Mn is added as a strengthening element. If the content is less than 0.5%, the effect is not sufficient. If the content exceeds 2.5%, the weldability is deteriorated and the steel material cost is increased.
  • Al acts as a deoxidizer, and for this purpose, it needs to contain 0.005% or more. However, if it contains more than 0.08%, it reduces the toughness and, when welded, weld metal Reduce the toughness of the part. Therefore, Al is preferably specified in the range of 0.005 to 0.08%, more preferably 0.02 to 0.04%.
  • N 0.0050% or less N combines with Al in the steel to form AlN, thereby adjusting the crystal grain size during rolling and strengthening the steel, but if it exceeds 0.0050%, the toughness Since it deteriorates, it is preferable to make it 0.0050% or less.
  • P, S P and S are inevitable impurities in the steel. However, if P exceeds 0.03%, the toughness deteriorates when S exceeds 0.01%. % Or less is desirable, and 0.02% or less and 0.005% or less are more desirable, respectively.
  • Ti 0.005 to 0.03%
  • Ti has the effect of forming nitrides, carbides, or carbonitrides by adding a small amount, and refining crystal grains to improve the base material toughness. The effect is obtained by addition of 0.005% or more, but inclusion exceeding 0.03% lowers the toughness of the base metal and the weld heat affected zone, so Ti is 0.005 to 0.03%. The range is preferable.
  • the above is the basic component composition of the present invention, but in order to further improve the characteristics, it is possible to contain one or more of Nb, Cu, Ni, Cr, Mo, V, B, Ca, and REM.
  • Nb 0.005 to 0.05%
  • Nb precipitates as NbC at the time of ferrite transformation or reheating, and contributes to the increase in strength.
  • Nb has the effect of expanding the non-recrystallization temperature region in rolling in the austenite region, and contributes to the fine graining of the bainite packet, which is also effective in improving toughness.
  • the effect is exhibited by addition of 0.005% or more, but if added over 0.05%, coarse NbC precipitates and conversely causes a decrease in toughness, so the upper limit is made 0.05%. Is preferred.
  • Cu, Ni, Cr, Mo Cu, Ni, Cr, and Mo are all elements that enhance the hardenability of steel. While contributing directly to strength enhancement after rolling, it can be added to improve functions such as toughness, high-temperature strength, or weather resistance, since these effects are exhibited by containing 0.01% or more, When contained, the content is preferably 0.01% or more. However, when it contains excessively, toughness and weldability will deteriorate, when containing, upper limit is 0.5% for Cu, 1.0% for Ni, 0.5% for Cr, and 0.5% for Mo. % Is preferable.
  • V 0.001 to 0.10%
  • V is an element that improves the strength of the steel by precipitation strengthening as V (C, N). In order to exhibit this effect, 0.001% or more may be contained, but if it exceeds 0.10%, toughness is reduced. For this reason, when it contains V, it is preferable to set it as 0.001 to 0.10% of range.
  • B 0.0030% or less B may be added as an element that enhances the hardenability of steel in a small amount. However, if it exceeds 0.0030%, the toughness of the welded portion is lowered. Therefore, when B is contained, the content is preferably 0.0030% or less.
  • Ca 0.0050% or less
  • REM 0.010% or less Ca
  • REM is necessary because it refines the structure of the heat affected zone and improves toughness, and even if added, the effect of the present invention is not impaired. It may be added accordingly. However, if it is excessively contained, coarse inclusions are formed and the toughness of the base material is deteriorated. Therefore, when it is included, the upper limit of Ca is preferably 0.0050% and REM is preferably 0.010%. .
  • manufacturing conditions it is preferable to define the heating temperature, hot rolling conditions, cooling conditions, and the like of the steel material (slab).
  • the heating temperature, hot rolling conditions, cooling conditions, and the like of the steel material (slab) it is preferable to define the cumulative rolling reduction for each of the cases in the temperature range and the rolling temperature conditions in a state where the plate thickness center portion is in the austenite non-recrystallized region.
  • the toughness at the surface layer portion and the central portion of the plate thickness, the RD // (110) integration degree I at the central portion of the plate thickness, and the strength at 1 ⁇ 4 portion of the plate thickness can be obtained as desired.
  • the molten steel having the above composition is melted in a converter or the like, and is made into a steel material by continuous casting or the like.
  • the steel material is heated to a temperature of 1000 to 1200 ° C. and then hot rolled.
  • the heating temperature is less than 1000 ° C., sufficient time for rolling in the austenite recrystallization temperature region cannot be secured. If the temperature exceeds 1200 ° C., the austenite grains become coarse, leading to a decrease in toughness, as well as significant oxidation loss and a decrease in yield. Therefore, the heating temperature is preferably 1000 to 1200 ° C. A more preferable heating temperature range is from 1000 to 1150 ° C. from the viewpoint of toughness.
  • the integration degree I of the RD // (110) plane can be 1.5 or more, preferably 1.7 or more.
  • the hot rolling first, it is preferable to perform rolling with a cumulative reduction ratio of 20% or more in a state where the central portion of the plate thickness is in the austenite recrystallization temperature region.
  • a cumulative reduction ratio of 20% or more in a state where the central portion of the plate thickness is in the austenite recrystallization temperature region.
  • the cumulative reduction ratio in this temperature range is 40% or more, the texture at the central portion of the plate thickness is sufficiently developed, and the integration degree I of the RD // (110) plane at the central portion of the plate thickness is 1.5. As mentioned above, Preferably it can be 1.7 or more.
  • the rolling temperature refers to the temperature at the center of the plate thickness of the steel just before rolling.
  • the temperature at the center of the plate thickness is obtained by simulation calculation or the like from the plate thickness, surface temperature, thermal history, and the like. For example, the temperature at the center of the plate thickness of the steel sheet is obtained by calculating the temperature distribution in the plate thickness direction using the difference method.
  • the cumulative rolling reduction is preferably 65% or more as a whole by combining the austenite recrystallization temperature range and the austenite non-recrystallization temperature range.
  • the overall rolling reduction is small, the rolling of the structure is not sufficient, and the toughness and strength cannot achieve the target values. This is because by setting the total cumulative rolling reduction to 65% or more, a sufficient rolling reduction can be ensured for the structure, and the toughness and strength can achieve the target values.
  • the austenite recrystallization temperature range and the austenite non-recrystallization temperature range can be grasped by conducting a preliminary experiment in which the steel having the component composition is given a heat / working history with varying conditions.
  • finish temperature of hot rolling is not specifically limited, From a viewpoint of rolling efficiency, it is preferable to complete
  • the rolled steel sheet is cooled to 450 ° C. or lower at a cooling rate of 4 ° C./s or higher.
  • the cooling rate 4 ° C./s or more the structure is not coarsened, and by suppressing the ferrite transformation, a fine-grained bainite structure is obtained, and the excellent excellent toughness and texture are obtained. Strength can be obtained.
  • the cooling rate is less than 4 ° C./s, coarsening of the structure and ferrite transformation proceed at each plate thickness position, so that not only a desired structure cannot be obtained but also the strength of the steel sheet is lowered.
  • the cooling stop temperature to 450 ° C.
  • the bainite transformation can be sufficiently advanced, and a metal structure having desired toughness and texture can be obtained. If the cooling stop temperature is higher than 450 ° C., the bainite transformation does not proceed sufficiently, and a structure such as ferrite or pearlite is also produced, and the bainite-based structure intended by the present invention cannot be obtained.
  • these cooling rate and cooling stop temperature be the temperature of the plate
  • a tempering temperature can be made not to impair the desired structure obtained by rolling and cooling by implementing as steel sheet average temperature below AC1 point.
  • the AC1 point (° C.) is obtained by the following equation.
  • a C1 point 751-26.6C + 17.6Si-11.6Mn-169Al-23Cu-23Ni + 24.1Cr + 22.5Mo + 233Nb-39.7V-5.7Ti-895B
  • each element symbol is the content (% by mass) in steel, and 0 if not contained.
  • the average temperature of the steel sheet can also be obtained by simulation calculation or the like from the sheet thickness, surface temperature, cooling conditions, etc., similarly to the temperature at the center of the sheet thickness.
  • Molten steel (steel symbols A to O) of each composition shown in Table 1 is melted in a converter, made into a steel material (slab thickness 250 mm) by a continuous casting method, hot-rolled to a sheet thickness of 50 to 90 mm, and then cooled. No. 1-30 test steels were obtained.
  • Table 2 shows hot rolling conditions and cooling conditions.
  • a JIS 14A test piece having a diameter of 14 mm was collected from a 1/4 part of the plate thickness so that the longitudinal direction of the test piece was perpendicular to the rolling direction, and a tensile test was performed, yield point (Yield Strength). Tensile Strength was measured.
  • a JIS No. 4 impact test piece was taken from 1/2 part of the plate thickness so that the direction of the longitudinal axis of the test piece was parallel to the rolling direction, and a Charpy impact test was conducted to determine the fracture surface transition temperature.
  • the impact test piece of the surface layer part is assumed to have a surface closest to the surface at a depth of 1 mm from the steel sheet surface.
  • the degree of integration I of the RD // (110) plane at the central portion of the plate thickness was determined as follows. First, a sample having a plate thickness of 1 mm was collected from the central portion of the plate thickness, and a test piece for X-ray diffraction was prepared by mechanically polishing and electrolytic polishing a surface parallel to the plate surface. Using this test piece, X-ray diffraction measurement was performed using a Mo ray source, and (200), (110) and (211) positive electrode dot diagrams were obtained. A three-dimensional crystal orientation density function was calculated from the obtained positive electrode dot diagram by the Bunge method.
  • the integrated value was obtained by integrating the values of the three-dimensional crystal orientation density function of the orientation to be.
  • a value obtained by dividing the integrated value by the integrated number of azimuths 19 was defined as an integration degree I of the RD // (110) plane.
  • Table 3 shows the results of these tests.
  • Kca ( ⁇ 10 ° C.) is 6000 N / mm 3/2 or more. Excellent brittle crack propagation stopping performance was demonstrated.
  • the equation (1) is A higher Kca ( ⁇ 10 ° C.) value was obtained as compared with the test steel plates (Product Nos. 27 to 30) which were not satisfied.
  • the component composition of the steel sheet is within the preferable range of the present invention
  • the steel sheet (manufacturing numbers 21 to 26) whose heating and rolling conditions in the manufacturing conditions of the steel sheet deviate from the preferable range of the present invention is Kca ( ⁇ 10 ° C.). The value did not reach 6000 N / mm 3/2 .
  • the texture of the steel plate does not satisfy the provisions of the present invention.
  • the toughness of the steel sheets did not satisfy the provisions of the present invention, and the value of Kca ( ⁇ 10 ° C.) was 6000 N / It did not reach mm 3/2 .
  • Kca ( ⁇ 10 ° C.) is 6000 N / mm 3 / 2 was not reached.

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PCT/JP2012/063409 2011-12-27 2012-05-18 脆性亀裂伝播停止特性に優れた構造用高強度厚鋼板およびその製造方法 WO2013099318A1 (ja)

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KR1020147017473A KR101588258B1 (ko) 2011-12-27 2012-05-18 취성 균열 전파 정지 특성이 우수한 구조용 고강도 후강판 및 그의 제조 방법
BR112014015779-0A BR112014015779B1 (pt) 2011-12-27 2012-05-18 Método para produzir uma placa de aço espessa de alta resistência para uso estrutural
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EP12863408.6A EP2799584B1 (de) 2011-12-27 2012-05-18 Herstellungsverfahren für eine hochfeste dicke stahlplatte zur konstruktion mit hervorragenden magnetischen eigenschaften zur verhinderung der diffusion von spröden rissen

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JP2018504523A (ja) * 2014-12-24 2018-02-15 ポスコＰｏｓｃｏ 脆性亀裂伝播抵抗性に優れた高強度鋼材及びその製造方法
JP2018504524A (ja) * 2014-12-24 2018-02-15 ポスコＰｏｓｃｏ 脆性亀裂伝播抵抗性に優れた構造用極厚鋼材及びその製造方法
JP2018504520A (ja) * 2014-12-24 2018-02-15 ポスコＰｏｓｃｏ 脆性亀裂伝播抵抗性に優れた高強度鋼材及びその製造方法
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JP6245352B2 (ja) 2014-03-31 2017-12-13 Ｊｆｅスチール株式会社 高張力鋼板およびその製造方法
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JP2018503744A (ja) * 2014-12-24 2018-02-08 ポスコＰｏｓｃｏ 脆性亀裂伝播抵抗性に優れた高強度鋼材及びその製造方法
JP2018504523A (ja) * 2014-12-24 2018-02-15 ポスコＰｏｓｃｏ 脆性亀裂伝播抵抗性に優れた高強度鋼材及びその製造方法
JP2018504524A (ja) * 2014-12-24 2018-02-15 ポスコＰｏｓｃｏ 脆性亀裂伝播抵抗性に優れた構造用極厚鋼材及びその製造方法
JP2018504520A (ja) * 2014-12-24 2018-02-15 ポスコＰｏｓｃｏ 脆性亀裂伝播抵抗性に優れた高強度鋼材及びその製造方法
US10822671B2 (en) 2014-12-24 2020-11-03 Posco High-strength steel having superior brittle crack arrestability, and production method therefor
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