WO2021199629A1 - 鋼板およびその製造方法 - Google Patents

鋼板およびその製造方法 Download PDF

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WO2021199629A1
WO2021199629A1 PCT/JP2021/002892 JP2021002892W WO2021199629A1 WO 2021199629 A1 WO2021199629 A1 WO 2021199629A1 JP 2021002892 W JP2021002892 W JP 2021002892W WO 2021199629 A1 WO2021199629 A1 WO 2021199629A1
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ferrite
temperature
toughness
steel sheet
steel
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PCT/JP2021/002892
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English (en)
French (fr)
Japanese (ja)
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竜平 竹下
亮 荒尾
植田　圭治
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Ｊｆｅスチール株式会社
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Priority to KR1020227019101A priority Critical patent/KR20220092977A/ko
Priority to JP2021524994A priority patent/JP7276443B2/ja
Priority to CN202180015241.1A priority patent/CN115135787A/zh
Publication of WO2021199629A1 publication Critical patent/WO2021199629A1/ja

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Definitions

  • the present invention has a thickness capable of ensuring high toughness even in steel plates used for ships, marine structures, mid-to-high-rise buildings, bridges, tanks, etc., particularly in weld heat-affected zones (hereinafter, also referred to as HAZ) when welding is performed. It is about steel plates.
  • Patent Document 1 As a method for improving the toughness of HAZ (hereinafter, also referred to as high heat-affected zone HAZ) by high heat-affected zone, for example, in Patent Document 1 and Patent Document 2, coarsening of austenite grains is suppressed by a pinning effect of TiN, Al oxide, etc. A method has been proposed. Further, Patent Document 3, Patent Document 4 and Patent Document 5 show a technique for refining the structure in crystal grains by allowing a large number of ferrite transformation nuclei to exist in austenite grains. Specifically, by using TiN, MnS, Ti oxide and the like as ferrite transformation nuclei, the microstructure in the crystal grains is miniaturized and the low temperature toughness of HAZ is improved. Further, in Patent Document 6, the HAZ toughness is improved by utilizing the solid solution B and suppressing the ratio of the grain boundary ferrite. In Patent Document 7, the reproduced HAZ structure is improved by making the bainite structure in the grain finer by using the compound B.
  • the inventors focused on a coarse ferrite side plate, which is a low toughness structure produced by high heat input welding.
  • the coarse ferrite side plate (hereinafter referred to as FSP) is a structure formed by extending ferrite into grains starting from the coarse grain boundary ferrite generated from the coarse austenite grain boundaries as described above.
  • the roughness of this FSP structure is the main factor of low toughness. Therefore, the inventors considered that by refining the coarse grain boundary ferrite, the formation of coarse FSP is suppressed and the low temperature toughness of the large heat-affected zone HAZ is improved.
  • the SB defined by the following equation (1) satisfies the predetermined conditions, and the temperature obtained by the following equation (2) is from Ar 3 points (transformation start temperature). It was found that by designing the component composition so that the temperature becomes high, grain boundary ferrite is nucleated from the BN precipitated at the grain boundary, and the grain boundary ferrite can be miniaturized. By refining the grain boundary ferrite, it is possible to obtain the low temperature toughness of the large heat-affected zone HAZ, which is superior to the conventional one.
  • SB [B] -0.77 x [N] + 0.22 x [Ti] ... (1)
  • T (° C.) 12000 / (4.63-log ([B] ⁇ ([N]-[Ti] /3.42)))-273 ... (2)
  • B, N, and Ti are the contents (mass%) of each element.
  • the present invention has been made based on the above findings, and its gist structure is as follows. 1. 1. By mass% C: 0.03 to 0.15%, Si: 0.01-0.50%, Mn: 1.20 to 2.00%, P: 0.020% or less, S: 0.0005 to 0.0100%, Al: 0.005 to 0.100%, Ti: 0.004 to 0.030%, B: 0.0020 to 0.0050% and N: 0.0035 to 0.0100% Is contained in the range where SB represented by the following formula (1) is ⁇ 0.0010 or more and 0.0002 or less and the temperature T represented by the following formula (2) is more than 3 points of Ar, and the balance is Fe and A steel sheet having a component composition that is an unavoidable impurity and having a metal structure having a volume fraction of processed ferrite of 50% or more.
  • each element in the formula shows the content (mass%) of the element.
  • composition of the components is further increased by mass%.
  • the steel material of the present invention is suitably used for structures such as low-temperature storage tanks for liquefied gas constructed by large heat input such as electrogas welding, submerged arc welding, and electroslag welding, and ships operated in a low temperature environment. Be done.
  • C 0.03 to 0.15% C must contain 0.03% or more in order to obtain the required strength. However, if the content exceeds 0.15%, island-like martensite increases and the toughness of the weld heat-affected zone decreases, so the upper limit is set to 0.15%.
  • the lower limit is preferably 0.045%. Further, it is preferably less than 0.10%.
  • Si 0.01-0.50% Si is a component necessary for ensuring the strength of the base material, deoxidizing, etc., and is added in an amount of 0.01% or more.
  • the upper limit is set to 0.50%.
  • the preferred lower limit is 0.10% and the preferred upper limit is 0.30%.
  • Mn 1.20 to 2.00% Mn is required to be 1.20% or more in order to secure the strength of the base material, and if it exceeds 2.00%, not only the weldability deteriorates but also the steel material cost increases. Therefore, the range of Mn is 1.20 to 2.00%.
  • the lower limit is preferably 1.40%.
  • the upper limit is preferably 1.60%.
  • P 0.020% or less
  • P is an impurity that is inevitably mixed in, and if the content exceeds 0.020%, the toughness of the base metal and welds will decrease, so the upper limit is set to 0.020%. .. In order to obtain good toughness, 0.010% or less is preferable, and 0.007% or less is more preferable. By the way, although it is not necessary to limit the lower limit, it is preferable to set it to 0.001% or more because the cost increases by performing the ultra-low P treatment.
  • S 0.0005 to 0.0100%
  • S is required to be 0.0005% or more in order to generate the required MnS in the nucleus of the composite inclusion required for ferrite nucleation, and CaS when Ca is added.
  • S is less than 0.0005%, MnS and further CaS are not sufficiently formed, and the toughness of HAZ is lowered.
  • the upper limit is preferably 0.0090%.
  • the lower limit is preferably 0.0010%.
  • Al 0.005 to 0.100% Al needs to be 0.005% or more, preferably 0.010% or more in terms of deoxidation of steel. On the other hand, if it is contained in excess of 0.100%, the toughness of the base metal is lowered and the toughness of the weld metal is deteriorated.
  • the upper limit is preferably 0.08%.
  • Ti 0.004 to 0.030% Ti precipitates as TiN during solidification of steel, and contributes to suppressing coarse-grained austenite in the weld heat-affected zone (HAZ) and becoming ferrite transformation nuclei to increase toughness. If Ti is less than 0.004%, its effect is small, while if it exceeds 0.030%, the expected effect cannot be obtained due to the coarsening of TiN particles. Therefore, the Ti content is in the range of 0.004 to 0.030%. The lower limit is preferably 0.008%. The upper limit is preferably 0.020%.
  • B 0.0020-0.0050% B is an important element for refining grain boundary ferrite and improving HAZ toughness, and is added at least 0.0020% in order to precipitate at a ferrite transformation temperature or higher. However, if a large amount is added, the toughness of the base metal deteriorates, so the upper limit is set to 0.0050%.
  • the lower limit is preferably 0.0025%.
  • the upper limit is preferably 0.0040%.
  • N 0.0035-0.0100% N is added in an amount of 0.0035% or more in order to combine with Ti to form TiN and to combine with B to form BN. That is, when N is below the lower limit of 0.0035%, BN is not formed and sufficient HAZ toughness cannot be secured. On the other hand, when the content of N increases, the solid solution N increases and the HAZ toughness decreases, so the upper limit is 0.0100%.
  • the lower limit is preferably 0.0040%.
  • the upper limit is preferably 0.0090%.
  • the steel sheet of the present invention contains each of the above components, and the balance has a component composition of Fe and unavoidable impurities.
  • B, N and Ti are contained in the above formulas (1) and (2) so as to satisfy the above-mentioned formulas (1) and (2), so that the heat cycle received by the steel sheet during large heat input welding (hereinafter, also referred to as a welding heat cycle). ), TiN remains without solidification, and BN is deposited at an early stage with this TiN as a nucleus.
  • FIG. 1 an observation image of a sample in which a steel sheet having the above-mentioned composition composition is subjected to a welding reproduction heat cycle equivalent to 10 kJ / mm of heat input is shown. It can be seen that BN is precipitated in. That is, BN is more likely to precipitate from the high temperature region.
  • the size of the composite precipitate of TiN and BN becomes larger than the size of TiN alone.
  • Increasing the size of the precipitate facilitates nucleation of ferrite.
  • the size of the core TiN is usually 15 nm or more and 200 nm or less, and when BN precipitates on TiN, the size of the BN-coated precipitate becomes 50 nm or more and 600 nm or less.
  • the fact that ferrite is easily nucleated means that many ferrite nuclei are formed at the grain boundaries, and many ferrites are formed at the grain boundaries. Since these ferrites are nucleated from different BNs and therefore have different orientations, the crystal orientations of the ferrites are randomized.
  • the grain boundary ferrite is miniaturized, and the ferrite side plate generated from the grain boundary ferrite is also miniaturized. Therefore, the HAZ toughness is improved by satisfying the formulas (1) and (2).
  • the above formula (2) shows the precipitation temperature T when BN is deposited around TiN as shown in FIG. 1, and when this T becomes Ar 3 points or less, ferrite having BN as a core is shown. As a result of difficulty in formation, miniaturization of grain boundary ferrite is not realized.
  • the heat-affected zone structure near the bond is the density of grain boundary ferrite generated at the old ⁇ grain boundaries. Is 20 pieces / mm or more.
  • the grain boundary ferrite formation density of the old ⁇ grain boundaries is measured by performing quenching treatment immediately after the start of ferrite transformation during cooling in a thermal cycle simulation simulating welding and using EBSD (electron backscatter diffraction method). Can be done.
  • the curve length along the adjacent 3 to 3 priority grain boundaries of the old ⁇ grain boundary is defined as the old ⁇ grain boundary length, and the crystals of adjacent ferrite grains generated on the old ⁇ grain boundary are used.
  • the number of ferrite grains with an orientation difference of 15 degrees or more is defined as the number of ferrites on the old ⁇ grain boundaries, and the density of grain boundary ferrites is defined by (number of ferrites on the old ⁇ grain boundaries) / (former ⁇ grain boundary length). do.
  • the density of grain boundary ferrites formed on the old ⁇ grain boundaries in the heat-affected zone structure near the bond becomes 20 grains / mm or more when the above-mentioned large heat-immersive welding is performed. Therefore, it is possible to suppress the formation of coarse ferrite side plates and realize excellent low temperature toughness in HAZ.
  • the heat-affected zone structure in the vicinity of the bond refers to a region from the boundary of the weld metal with the base steel plate to a position within about 0.5 mm on the steel plate side of the base material.
  • the density of grain boundary ferrite generated at the old ⁇ grain boundaries is determined by controlling the addition amounts of N, B and Ti within the specified range according to the above formulas (1) and (2), for example, the heat input amount is 5 kJ / mm.
  • the density of grain boundary ferrites when the above-mentioned large heat input welding is performed can be 20 pieces / mm or more. That is, the formation of coarse ferrite side plates is suppressed, and excellent toughness can be obtained in the heat-affected zone.
  • the metal structure of the steel sheet according to the present invention has a volume fraction of 50% or more of processed ferrite in the structure.
  • the processed ferrite refers to a ferrite having a dislocation density ⁇ of 1.0 ⁇ 10 14 m- 2 or more, which is determined by X-ray diffraction (XRD). That is, in the processed ferrite, high-density dislocations are introduced, and the dislocations interact with each other to hinder each other's movements, thereby increasing the strength. Then, by setting the volume fraction of the processed ferrite to 50% or more, the strength is increased.
  • the volume fraction of processed ferrite in the metal structure is preferably 60% or more.
  • the upper limit of the amount of processed ferrite is not particularly limited and may be 100%, but from the viewpoint of the capacity of the rolling mill, it is preferably 90% or less.
  • the remaining structure at that time is preferably one or more hard phases of pearlite, bainite and martensite.
  • two or more kinds can be arbitrarily contained.
  • Cu 0.01-0.50%
  • Cu is an element that enhances the hardenability of steel, and contributes to the improvement of functions such as toughness, high temperature strength, and weather resistance in addition to the improvement of the strength of the base metal after rolling. These effects are exhibited by the content of 0.01% or more. On the other hand, excessive content deteriorates the toughness and weldability of the base metal. Therefore, the Cu content is preferably 0.01 to 0.50%.
  • Ni 0.01-1.50%
  • Ni is an element that enhances the hardenability of steel, and contributes to the improvement of functions such as toughness, high temperature strength, and weather resistance in addition to the improvement of the strength of the base metal after rolling. These effects are exhibited by the content of 0.01% or more. On the other hand, excessive content deteriorates the toughness and weldability of the base metal, and also increases the cost of the alloy. Therefore, the Ni content is preferably 0.01 to 1.50%.
  • Nb 0.005 to 0.040%
  • Nb is an element effective for ensuring the strength, toughness and joint strength of the base metal. The effect is exhibited when the content is 0.005% or more. On the other hand, if it is contained in excess of 0.040%, the toughness deteriorates due to the formation of island-shaped martensite in the weld heat affected zone. Therefore, when Nb is contained, the Nb content is preferably 0.005 to 0.040%.
  • V acts as a ferrite nucleation nucleus as a VN and improves the strength and toughness of the base metal. This effect is exhibited by containing 0.005% or more of V. On the other hand, if V is contained in an amount of more than 0.100%, the toughness of the base metal is rather lowered. Therefore, when V is contained, the V content is preferably 0.005 to 0.100%.
  • Cr 0.01-0.50%
  • Cr is an element that enhances the hardenability of steel, and contributes to the improvement of functions such as toughness, high temperature strength, and weather resistance in addition to the improvement of the strength of the base metal after rolling. These effects are exhibited by the content of 0.01% or more. On the other hand, excessive content deteriorates the toughness and weldability of the base metal. Therefore, the Cr content is preferably 0.01 to 0.50%.
  • Mo 0.01-0.50%
  • Mo is an element that enhances the hardenability of steel, and contributes to the improvement of functions such as toughness, high temperature strength, and weather resistance in addition to the improvement of the strength of the base metal after rolling. These effects are exhibited by the content of 0.01% or more. On the other hand, excessive content deteriorates the toughness and weldability of the base metal. Therefore, the Mo content is preferably 0.01 to 0.50%.
  • Ca 0.0005 to 0.0030% Ca is an element useful for improving the toughness of the base metal by fixing S, but the effect is saturated when the content exceeds 0.0030%, so Ca should be contained at 0.0030% or less. .. On the other hand, if the content is less than 0.0005%, the fixation of S becomes insufficient. Therefore, the Ca content is preferably 0.0005% or more and 0.0030% or less.
  • Mg 0.0002 to 0.0050% REM: 0.0010 to 0.1000%
  • Both Mg and REM have a strong deoxidizing power in molten steel and have a function of assisting the formation of fine oxides, and therefore are added as necessary.
  • the addition amounts showing the deoxidizing effect are Mg: 0.0002% or more and REM: 0.0010% or more, respectively.
  • Mg 0.0002% or more
  • REM 0.0010% or more
  • a steel material having the above composition is heated to a temperature of 1050 ° C. or higher and 1200 ° C. or lower, cooled to a temperature of 900 ° C. or lower at a cooling rate of 7 ° C./s or lower, and then cooled to 850 ° C. or lower.
  • Hot rolling is performed in which the cumulative reduction rate of ferrite-austenite in the two-phase temperature range is 60% or more and the finishing temperature is 650 ° C. or more.
  • the heating temperature of the steel material for example, the slab, needs to be 1050 ° C. or higher and 1200 ° C. or lower.
  • the reason for this is that heating below 1050 ° C. may leave coarse inclusions that adversely affect the toughness produced during solidification undissolved.
  • the precipitates formed by controlling the cooling rate described later may be redissolved.
  • 1200 ° C. or lower is sufficient as the heating temperature in the sense of completing the phase transformation. It should be noted that the coarsening of crystal grains that is considered to occur at that time can also be prevented in advance by the pinning effect of TiN described above. From the above, the heating temperature was limited to 1050 ° C. or higher and 1200 ° C. or lower.
  • the cooling rate is preferably 1 ° C./s or higher from the viewpoint of production efficiency.
  • the cumulative reduction rate in the two-phase temperature range is 60% or more, dislocations are added to the ferrite in the two-phase temperature range, and as a result, the strength can be improved.
  • the cumulative reduction rate is 60% or more, the rolled texture of ferrite develops, which contributes to the improvement of low temperature toughness.
  • the cumulative reduction rate of ferrite + austenite in the two-phase temperature range of 850 ° C. or lower was limited to 60% or more.
  • the cumulative rolling reduction ratio is preferably 90% or less from the viewpoint of rolling functional force.
  • the finishing temperature in hot rolling is set to 650 ° C. or higher. This is because if the finish rolling is performed at a temperature lower than 650 ° C., the ferrite produced by the phase transformation is distorted more than necessary, and the toughness is lowered.
  • cooling from a temperature of 650 ° C. or higher to a temperature range of 600 ° C. or lower and 300 ° C. or higher at a cooling rate of 5 ° C./s or higher is used to increase the strength of the base metal.
  • the steel material is cooled from a temperature of 650 ° C. or higher to a cooling rate of 5 ° C./s or higher to a temperature range of 600 ° C. or lower and 300 ° C. or higher after hot rolling is completed at 650 ° C. or higher. That is, the reason for cooling from 650 ° C.
  • cooling is started at a temperature lower than 650 ° C., the hardenability becomes insufficient and the required strength may not be obtained. Further, if the cooling rate is less than 5 ° C./s, it becomes difficult to obtain a steel having a uniform microstructure. Further, it is preferable to cool to a temperature range of 600 ° C. or lower and 300 ° C. or higher. This is because it is difficult to secure sufficient strength from the viewpoint of hardenability when cooling is stopped at a temperature exceeding 600 ° C. In addition, stopping cooling at a temperature of less than 300 ° C. does not significantly change the characteristics of the steel material, so that only the operational load increases.
  • the steel pieces are cooled from a temperature of 650 ° C. or higher to a cooling rate of 5 ° C./s or higher to 600 ° C. or lower and 300 ° C. or higher after completing hot ductility at 650 ° C. or higher.
  • the cooling rate is preferably 50 ° C./s or higher from the viewpoint of ensuring the toughness of the base material.
  • the cooling rate during slab casting is set to 0.3 m / min or more and 1.0 m / min or less. If the casting speed is less than 0.3 m / min, the size of TiN of the base metal (steel plate) becomes large. As the TiN size increases, the TiN density of the base material (steel plate) may decrease and the amount of BN composite precipitates may decrease. As a result, the ferrite cannot be sufficiently miniaturized, and the HAZ toughness may deteriorate.
  • the size of the core TiN is 15 nm or more and 200 nm or less.
  • the steel sheet thus produced has a structure having a volume fraction of processed ferrite of 50% or more in addition to the above-mentioned component composition.
  • the main phase contains a soft phase made of ferrite, and the balance is a structure made of one or more hard phases of pearlite, bainite and martensite.
  • the main phase when the main phase is ferrite, it means that ferrite has a volume fraction of 60% or more. That is, the ferrite may be 100%, but it is preferably 90% or less from the viewpoint of rollability.
  • the remaining portion at that time does not need to be particularly limited, and is as described above, for example. What is important here is the ratio of processed ferrite to the structure among the ferrites, and the ratio should be 50% or more in terms of volume fraction. Therefore, ferrites other than processed ferrites, that is, ferrites having a dislocation density ⁇ of less than 1.0 ⁇ 10 14 m- 2 may be contained.
  • the yield stress is 325 MPa or more. Further, it is desirable that the Charpy impact absorption energy of the base material at ⁇ 70 ° C. is 200 J or more. Further, it is desirable that the Charpy impact absorption energy at ⁇ 70 ° C. of the joint subjected to the large heat input welding is 80 J or more.
  • a steel slab (steel material) adjusted to the composition shown in Table 1 is cooled after heating the slab according to various conditions shown in Table 2, and then hot-rolled and cooled to obtain a thick steel sheet having a thickness of 20 mm. And said.
  • Tensile test pieces conforming to JIS Z2241 were collected from each of the thick steel sheets thus obtained, and a tensile test conforming to JIS Z2241 was performed to measure the yield stress.
  • JIS Z2242 compliant test pieces are collected from each thick steel plate, V groove is processed on each test piece, and a Charpy impact test compliant with JIS Z2242 is performed to measure Charpy impact absorption energy at -70 ° C. bottom.
  • a test piece for welding a welded joint was collected from each of the obtained thick steel plates, a V groove was machined on the test piece, and a welded joint was manufactured by submerged arc welding (welding heat input: 102 kJ / cm).
  • a JIS No. 4 impact test piece having a notch position as a bond portion was collected from these welded joints, a Charpy impact test was carried out, and the Charpy impact absorption energy at ⁇ 70 ° C. was measured.

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PCT/JP2021/002892 2020-03-30 2021-01-27 鋼板およびその製造方法 WO2021199629A1 (ja)

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Application Number Priority Date Filing Date Title
KR1020227019101A KR20220092977A (ko) 2020-03-30 2021-01-27 강판 및 그 제조 방법
JP2021524994A JP7276443B2 (ja) 2020-03-30 2021-01-27 鋼板およびその製造方法
CN202180015241.1A CN115135787A (zh) 2020-03-30 2021-01-27 钢板及其制造方法

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WO2023276516A1 (ja) * 2021-07-02 2023-01-05 Ｊｆｅスチール株式会社 高強度鋼板およびその製造方法
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