WO2011148755A1 - 溶接構造用高強度鋼板の製造方法 - Google Patents

溶接構造用高強度鋼板の製造方法 Download PDF

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WO2011148755A1
WO2011148755A1 PCT/JP2011/060341 JP2011060341W WO2011148755A1 WO 2011148755 A1 WO2011148755 A1 WO 2011148755A1 JP 2011060341 W JP2011060341 W JP 2011060341W WO 2011148755 A1 WO2011148755 A1 WO 2011148755A1
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rolling
less
temperature
toughness
plate thickness
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PCT/JP2011/060341
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English (en)
French (fr)
Japanese (ja)
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浩幸 白幡
龍治 植森
明彦 児島
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新日本製鐵株式会社
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Priority to BR112012029698-1A priority Critical patent/BR112012029698B1/pt
Priority to JP2011543021A priority patent/JP4897127B2/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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • 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
    • C22C38/02—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
    • C22C38/12—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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals

Definitions

  • the present invention relates to a method for producing a high-strength steel sheet having excellent toughness, particularly applied to welded structures such as ships, buildings, bridges, tanks, and marine structures. Further, the steel sheet of the present invention may be distributed as a secondary processed product processed into a steel pipe, a column or the like, and these are also targeted.
  • TMCP Thermo-Mechanical Control Process
  • This is a method of refining the structure of a steel sheet by a combination of appropriate heating, hot rolling, cooling, and heat treatment processes, as shown in Non-Patent Document 1, for example.
  • hot rolling CR (Controlled Rolling) performed in a temperature range in which austenite ( ⁇ ) does not recrystallize, and ACC (Accelerated Cooling) that generates fine ferrite ( ⁇ ) grains are particularly important.
  • Non-Patent Document 2 a technique for examining the effect of suppressing ⁇ grain growth on various nitrides, carbides, oxides, sulfides and the like generated in steel.
  • a technique for examining the effect of suppressing ⁇ grain growth on various nitrides, carbides, oxides, sulfides and the like generated in steel can be mentioned.
  • fine particles of TiN are generated in the steel, and ⁇ grain growth in the HAZ of the high heat input welded joint can be effectively suppressed (for example, Non-Patent Document 2).
  • the present invention is excellent in toughness of the base material and HAZ in which the process conditions are defined in order to precisely control the sequential change of the microstructure in the heating, rolling, cooling, and heat treatment processes in consideration of the influence of TiN.
  • a method for producing high-strength steel for welded structures is provided.
  • the strength of the steel sheet may be, for example, a yield strength of 315 MPa or more and 580 MPa or less, a tensile strength of 440 MPa or more and 720 MPa or less, a yield strength of 550 MPa or less, and a tensile strength of 470 MPa or more, 490 MPa or more, or 650 MPa or less or 620 MPa or less.
  • the plate thickness is, for example, 10 to 100 mm, the lower limit may be 12 mm, 20 mm, or 30 mm, and the upper limit may be 70 mm or 50 mm.
  • the gist of the present invention is as follows.
  • the said slab is mass%, Cu: 1.5% or less, Cr: 0.5% or less, Mo: 0.5% or less, Ni: 2.0% or less, V: 0.10% or less, B: 0.0030% Mg: 0.0050% or less, Ca: 0.0030% or less, REM: The manufacturing method of the high-strength steel sheet for welded structures as described in said (1)-(5) characterized by including 1 type or 2 types or less of 0.010% or less.
  • Nb amount and Ti amount, and appropriate heating conditions It is a figure which shows the relationship between Nb amount and suitable rough rolling conditions. It is a figure which shows the relationship between Nb amount and the lower limit of the time between passes of rough rolling. It is a figure which shows Nb amount and appropriate finish rolling conditions. It is a figure which shows the relationship between Nb amount and the upper limit of the time between passes of finishing rolling. It is a figure which shows the relationship between product thickness and the cumulative reduction rate of finish rolling.
  • a manufacturing method is important for improving the strength and toughness of a steel sheet.
  • heat the slab perform hot rolling at a high temperature that promotes recrystallization, and recrystallize repeatedly to refine the crystal grain size. be able to.
  • TMCP is applied when the plate thickness of the steel plate is large or when extremely excellent toughness is required.
  • TMCP TMCP
  • the slab is heated, and after rough rolling, generally, finish rolling is generally performed, followed by accelerated cooling.
  • Rough rolling is rolling in a high temperature range in order to refine the structure in a temperature range where ⁇ recrystallizes ( ⁇ recrystallization temperature range).
  • Finish rolling is performed in a temperature range ( ⁇ non-recrystallization temperature range) in which ⁇ does not recrystallize, and is a rolling in a low temperature range for sufficiently stretching ⁇ grains and accumulating strain, and controlled rolling (CR ).
  • ACC accelerated cooling
  • fine ferrite ( ⁇ ) grains are generated from ⁇ grains with accumulated strain.
  • the basic guidelines for obtaining a fine structure can be summarized as follows.
  • hot rolling in the ⁇ recrystallization temperature region is defined as rough rolling
  • hot pressure in the ⁇ non-recrystallization temperature region is defined as finish rolling.
  • Nb produces precipitates such as carbides and nitrides, has the effect of delaying recrystallization and increasing the non-recrystallization temperature range, and contributes to precipitation strengthening. Therefore, a part of the present inventors, according to Patent Document 2, controls the rolling temperature and rolling reduction of each pass of finish rolling according to the amount of Nb added in order to improve the strength and toughness of the steel sheet. (Refer to Patent Document 2).
  • TiN particles and oxide / sulfide particles such as Ti, Ca and Mg are used to suppress ⁇ grain coarsening and promote intragranular ⁇ transformation. Is common. Among these, TiN is easily finely dispersed in steel as compared with oxides and sulfides, and can also be used for controlling the structure of the base material.
  • TiN promotes or delays recrystallization to affect the toughness of the base material, and also acts as pinning particles to affect the HAZ toughness. Therefore, in order to improve the base metal and the HAZ toughness, it is necessary to control the heating temperature of hot rolling, the conditions of rough rolling, and further the conditions of finish rolling in consideration of the precipitation behavior of TiN.
  • the present inventors pay attention to the precipitation behavior of TiN, which is useful for preventing the coarsening of the HAZ structure and can also be used for the structure control of the base material, and details the sequential microstructural changes from the heating to the heat treatment process.
  • the present invention was completed by clarifying the conditions of each process, particularly the heating conditions of hot rolling, the rolling reduction and the time between passes, in order to refine the structure and secure TiN that contributes to pinning. I let you.
  • the production conditions of the present invention will be described in detail.
  • the heating temperature and holding time of hot rolling are extremely important for securing TiN that solidifies Nb having a large influence on the recrystallization behavior and improves HAZ toughness.
  • the heating temperature and holding time of hot rolling are very important for controlling the microstructure of the steel, and in order to ensure the toughness of the steel sheet (base material), a uniform and fine ⁇ structure is used. There is a need.
  • the important points in the heating process are the temperature and holding time that do not completely dissolve TiN, which is effective in suppressing the coarsening of ⁇ grains, while sufficiently dissolving Nb that contributes to increasing the non-recrystallization temperature range and increasing strength. It is to do.
  • the present inventors conducted various experiments and thermodynamic calculations on the precipitation behavior of Nb and Ti, and derived the following equations (3) and (4) based on the results.
  • Functional form of P h is in the tempering parameters used to carry out the conversion of the tempering temperature and time of the reference.
  • the left side of the inequality is the lower limit of the heating condition that changes according to the amount of Nb
  • the right side of the inequality is the upper limit of the heating condition that changes according to the amount of Ti.
  • Each coefficient was experimentally determined from the limit conditions for generating coarse ⁇ and the limit conditions for securing the amount of solute Nb.
  • the holding time was set to 30 minutes or more, which is for uniformly dissolving a trace alloy element such as Nb.
  • the holding time is defined as the time from when the temperature reaches 20 ° C. lower than the set furnace temperature until extraction, and the heating temperature is defined as the average temperature during that time.
  • FIG. 1 shows the lower limit of the heating conditions when Nb: 0.005% and 0.03%, and the upper limit of the heating conditions when Ti: 0.005% and 0.03%. If the lower limit of the heating temperature and holding time changes according to the Nb content, and slab heating is performed within a range that satisfies the conditions shown in FIG. Further, the upper limit of the heating temperature and holding time varies depending on the Ti content, and when the Ti amount is 0.005 to 0.03%, if slab heating is performed within the range shown in FIG. The coarsening can be suppressed. When the Ti amount is 0.003%, the curve indicated by the solid line in FIG. 1 moves downward, and when the Ti amount reaches 0.05%, the curve indicated by the dotted line in FIG. (Curve) moves upward.
  • the left side of the formula (5) represents the lower limit temperature at which recrystallization occurs
  • the right side represents the upper limit temperature at which recrystallization ⁇ does not grow. That is, in the function type of the equation (5), the distortion of each path, that is, the term of “ ⁇ ln (1-R j )” is larger, and the smaller the Nb amount, the easier the recrystallization occurs. This reflects the tendency that the recrystallized ⁇ grains become smaller and the grains grow more easily if the strain of ⁇ increases.
  • the coefficient of each term in the formula (5) was experimentally determined from the limit conditions for causing recrystallization and grain growth.
  • the left side of the formula (6) represents the lower limit time necessary for completing the recrystallization
  • the right side represents the upper limit time necessary for preventing the grain growth.
  • the function type of the equation (6) expresses the tendency that the larger the strain, the higher the temperature, and the smaller the Nb, the faster the recrystallization is completed and the easier the grain growth.
  • the coefficient of each term in the equation (6) was also experimentally determined.
  • FIG. 2 shows the rough rolling temperature, the lower limit and the upper limit of the rolling reduction when Nb is 0.005% and 0.03%.
  • FIG. 3 shows the minimum inter-path time for each Nb amount described above.
  • the steel sheet is thick or when extremely excellent toughness is required, it is preferable to perform finish rolling subsequent to rough rolling.
  • finish rolling After rough rolling, as described above, the structure has been refined to some extent, and since the temperature is low and the cooling rate increases as the plate thickness decreases, grain growth and coarsening of TiN are suppressed. The Therefore, the time until the finish rolling is started after the rough rolling is not particularly defined, but it takes 30 s to 180 s as the time for adjusting the temperature of the finish rolling (cooling time until the finish rolling temperature is reached). There is a case. Air cooling may be performed from the completion of rough rolling to the start of finish rolling, but water cooling may be performed in order to shorten the temperature waiting time from the viewpoint of productivity and to prevent recrystallization ⁇ grain growth. .
  • the finish rolling process introduces a processing structure such as dislocations and deformation bands that become nucleation sites for ⁇ transformation in ⁇ , and promotes transformation in the subsequent accelerated cooling, thereby significantly improving toughness.
  • a processing structure such as dislocations and deformation bands that become nucleation sites for ⁇ transformation in ⁇ , and promotes transformation in the subsequent accelerated cooling, thereby significantly improving toughness.
  • it is effective to increase the cumulative rolling reduction as much as possible under the condition that no recovery or recrystallization occurs between passes. Therefore, it is preferable to increase the rolling reduction ratio of the rolling pass at a low temperature.
  • the finish rolling time becomes long, and thus the productivity is impaired.
  • the present inventors investigated in detail the relationship between the rolling temperature, rolling ratio, holding time, recrystallization and flatness of ⁇ grains in the case of performing finish rolling after rough rolling, and further considered productivity.
  • the plate thickness before finish rolling may be referred to as transfer thickness
  • the plate thickness after finish rolling may be referred to as product thickness.
  • the unit of the plate thickness before finish rolling and the plate thickness after finish rolling is mm. By multiplying the right side of ⁇ R k by 100, the cumulative rolling reduction of finish rolling is substantially the cumulative rolling reduction in% units.
  • Equation (8) represents the upper limit of the time between passes necessary for recrystallization not to start. Note that the shorter the time between passes in the finish rolling process, the more advantageous is the suppression of recrystallization and the improvement of productivity. Therefore, it is not necessary to define the lower limit, and it is determined from the specifications of the rolling apparatus and the length of the steel plate. In a reverse rolling mill, since it is not easy to make the time between passes shorter than 1 s, the lower limit may be set to 1 s.
  • Formulas (7) and (8) are also experimentally adopted in consideration of the effects of temperature, rolling reduction, and Nb amount on the recrystallization behavior, adopting a functional type according to formulas (5) and (6).
  • the coefficient was determined.
  • FIG. 4 shows the finish rolling temperature, the lower limit of the rolling reduction, and the temperature and the upper limit of the rolling reduction when Nb: 0.005% and 0.03%.
  • FIG. 5 shows the maximum inter-path time for each Nb amount described above.
  • Equations (9) and (10) are necessary conditions for improving productivity while ensuring the strength and toughness of the steel sheet. This region is shown in FIG. If the relationship between the product thickness and the cumulative rolling reduction falls below this region, the amount of ⁇ nucleation sites introduced into ⁇ is insufficient, and the base material toughness is not improved. On the other hand, if the relationship between the product thickness and the cumulative rolling reduction is deviated above the region shown in FIG. 6, the strength and toughness are improved, but the productivity of finish rolling is significantly reduced, and the shape of the thin material is also deteriorated. Also, between the finishing rolling passes, air cooling is usually sufficient, but water cooling may be performed.
  • Accelerated cooling is performed after rough rolling or finish rolling. By performing accelerated cooling after rough rolling, growth of crystal grains and coarsening of precipitates can be prevented, and a decrease in toughness can be suppressed.
  • Accelerated cooling after finish rolling is the process of generating a large number of ⁇ grains from ⁇ (work hardening ⁇ ) flattened by finish rolling and strain accumulated by increasing the driving force of transformation. Very important from.
  • the time until the accelerated cooling is performed after the finish rolling is not particularly defined, but it may take 30 to 90 s for transportation from the rolling equipment to the cooling equipment. It is preferable to shorten the time from the finish rolling to the start of accelerated cooling as short as possible in order to suppress dislocation recovery and recrystallization and improve productivity. If necessary, a lower limit of the cooling start temperature such as Ar3, Ar3-10 ° C or Ar3 + 10 ° C may be provided.
  • the cooling rate In order to improve the toughness of the steel sheet, it is necessary to perform accelerated cooling at a cooling rate of 5 ° C./s or more on the average sheet thickness.
  • the cooling rate is less than 5 ° C./s, not only the strength is insufficient, but the structure is not sufficiently refined, and the base material toughness is lowered.
  • the cooling rate has a limit depending on the thickness of the steel sheet and the capacity of the apparatus, and it is difficult to set the cooling rate above 100 ° C./s.
  • the upper limit of the cooling rate may be limited to 75 ° C./s, 50 ° C./s, or 30 ° C./s.
  • the cooling stop temperature is not necessarily limited in the present invention, and may be determined according to the required characteristics of the steel sheet. In order to suppress the growth of crystal grains and precipitates and improve productivity, it is preferable to set the cooling stop temperature of accelerated cooling to 600 ° C. or lower. More preferably, it is 550 degrees C or less. Moreover, if the accelerated cooling is stopped at less than 200 ° C., the time required for the accelerated cooling becomes long and the productivity may be impaired. Therefore, the cooling stop temperature is preferably set to 200 ° C. or higher. The lower limit of the cold stop temperature may be set to 300 ° C., 400 ° C., or 450 ° C. in order to improve the strength.
  • heat treatment may be performed at a temperature of 650 ° C. or lower in order to adjust strength and toughness.
  • the temperature of heat processing shall be 400 degreeC or more. It may be 490 ° C. or higher for further improvement of toughness.
  • the rolling productivity (ton / hr) depends not only on the dimensions of the rolled steel sheet such as the product thickness but also on the equipment specifications of the heating furnace, rolling mill, and accelerated cold speed apparatus. For this reason, in this invention, the target of rolling productivity cannot be defined clearly.
  • % for a component means mass%.
  • C is an essential element for increasing the strength, and 0.03% or more is added.
  • the addition amount increases, it becomes difficult to ensure the HAZ toughness of the high heat input welded joint, so 0.16% is made the upper limit of the C amount.
  • the lower limit of C may be 0.05%, 0.06%, or 0.07%.
  • the upper limit of C may be 0.14%, 0.13%, or 0.12%.
  • Si is an inexpensive deoxidizing element and contributes to solid solution strengthening, so 0.03% or more is added.
  • the upper limit is made 0.5%.
  • the lower limit of Si may be 0.05%, 0.08%, or 0.12%.
  • the upper limit of Si may be 0.40%, 0.35%, or 0.30%.
  • Mn is effective as an element for improving the strength and toughness of the base material, so 0.3% or more is added.
  • the lower limit of the amount of Mn is preferably 0.5% or 0.7%. More preferably, 0.9% or more or 1.0% or more is added.
  • the amount of Mn is preferably 1.8% or less, and more preferably 1.6% or less.
  • the upper limit is 0.020% for P and 0.010% for S.
  • the upper limit of P may be 0.017% or 0.015%, and the upper limit of S may be 0.008%, 0.006%, or 0.004%. The smaller the contents of P and S, the better.
  • the lower limit may be 0.001% for P and 0.0001% for S.
  • Nb is an element that contributes to the refinement of structure, transformation strengthening, and precipitation strengthening by adding a small amount.
  • 0.005% or more of Nb is added to ensure the strength of the base material.
  • the content may be 0.008% or more or 0.010% or more.
  • Nb is added excessively, the HAZ hardens and deteriorates toughness, so 0.030% or less is made the upper limit.
  • a more preferable upper limit of the Nb amount is 0.020%.
  • Al is an important deoxidizing element, 0.002% or more is added. In order to perform deoxidation reliably, it is good also as 0.008% or more or 0.012% or more. However, excessive addition of Al impairs the surface quality of the slab and forms inclusions harmful to toughness, so the upper limit is made 0.10%.
  • the upper limit with preferable Al amount is 0.07% or 0.05%.
  • Ti is an extremely important element in the present invention, and is effective for improving the strength and toughness of the base metal and the HAZ toughness by refinement of the structure, precipitation strengthening, and formation of fine TiN when added in a small amount.
  • a preferable lower limit of the amount of Ti is 0.005% or more, and more preferably 0.008% or more of Ti is added.
  • Ti is added excessively, the HAZ toughness is remarkably deteriorated, so 0.050% is made the upper limit.
  • a preferable upper limit of the Ti amount is 0.040%. The upper limit may be 0.030%, 0.025%, or 0.020%.
  • N is added in an amount of 0.0020% or more in order to form a nitride with Ti and improve the HAZ toughness.
  • a preferable lower limit of the N amount is 0.0030% or more, and more preferably 0.0035% or more.
  • the content is limited to 0.0100% or less. In order to prevent embrittlement, it may be 0.0080% or less or 0.0060% or less.
  • C, Mn, and Nb are elements that contribute to hardenability, and the amount added must satisfy the following formula (1) from the viewpoint of securing the strength of the base metal and HAZ toughness.
  • one or more of Cu, Cr, Mo, Ni, V, B, Mg, Ca, and REM may be added.
  • Cu, Cr, and Mo are all elements that improve hardenability.
  • Cu, Cr, and Mo may be added in an amount of 0.05% or more in order to increase the strength of the base material and prevent softening of the HAZ.
  • the upper limit is 1.5% for Cu and 0.5% for Cr and Mo.
  • the upper limit of Cu is 0.5% or less, 0.35% or 0.20%, the upper limit of Cr is 0.3%, 0.2% or 0.1%. May be limited to 0.2%, 0.1%, and 0.08%.
  • Ni is effective for securing strength, arrestability, and improving HAZ toughness, and may be added by 0.05% or more.
  • an increase in the amount of Ni increases the alloy cost, so the upper limit is made 2.0%.
  • the upper limit of Ni may be set to 0.8%, 0.6%, or 0.4%.
  • V may contribute 0.005% or more because it contributes to strength increase by precipitation strengthening.
  • the upper limit is preferably made 0.10% or less. More preferably, it is 0.080% or less, More preferably, 0.05% or less is good.
  • B is an element that improves hardenability, and 0.0002% or more may be added to increase the strength of the steel. On the other hand, excessive addition of B impairs weldability, so the upper limit of B is made 0.0030%. It is good also as 0.0020% or 0.0015%.
  • Mg, Ca, and REM are elements that contribute to improving HAZ toughness by forming fine oxides and sulfides.
  • Mg is 0.0003% or more
  • Ca is 0.0005% or more
  • REM is 0.0005% or more. May be added.
  • the upper limit of Mg amount is 0.0050% or less
  • the upper limit of Ca amount is 0.0030% or less
  • the upper limit of REM is 0.010. % Or less is preferable.
  • REM is a rare earth metal such as La or Ce.
  • Table 2 is the heating conditions of hot rolling, M L is 56000 / Calculated (1.2-0.18 ⁇ log [Nb]) , P h is the (T + 273) ⁇ (log (t) +25) calc, M U is the calculated value of 91000 / (1.9-0.18 ⁇ log [Ti ]).
  • [X] element addition amount (mass%)
  • T heating temperature (° C.)
  • t heating holding time (min) (where t ⁇ 30).
  • Table 3 shows the thickness of the slab, the thickness (transfer thickness) of the steel plate after rough rolling (before finish rolling), the thickness (product thickness) of the steel plate after product (finish rolling), between rolling passes and rough rolling. The presence or absence of water cooling between the steel and finish rolling, and the cumulative rolling reduction of finish rolling are shown. When accelerated cooling is performed after rough rolling, the transfer thickness is equal to the product thickness.
  • Table 4 shows the sheet thickness on the exit side of each rolling pass, and from the sheet thickness shown in Table 4, the rolling reduction rate of each rolling pass and the cumulative rolling reduction rate of finish rolling were obtained and shown in Table 5.
  • Table 6 and Table 7 show the rolling temperature of each pass of rough rolling, and the calculated values of the left side and the right side of Equation (5).
  • Tables 8 and 9 show the rolling temperature of each pass of finish rolling, The calculated values of the left side and the right side of Equation (6) are shown.
  • Tables 10 and 11 show the time between rolling passes of each pass of rough rolling and finish rolling, the calculated values of the left side and the right side of Equation (7), and the calculated value of the right side of Table (8).
  • Table 12 shows accelerated cooling conditions and heat treatment temperatures.
  • Table 13 shows the strength, toughness, HAZ toughness, and rolling productivity of the base material.
  • a No. 1A full thickness test piece (thickness of 40 mm or less) described in JIS Z 2201 or a No. 4 round bar test piece (thickness of more than 40 mm; thickness center) is taken in the direction perpendicular to the rolling direction.
  • the tensile test was conducted in accordance with the procedure of JIS Z 2241, and the evaluation was made by measuring the yield strength (YP) and the tensile strength (TS).
  • the base metal toughness was obtained by taking a 2 mm V notch Charpy test piece in the rolling direction from the center of the plate thickness of the steel sheet, performing a Charpy impact test at various temperatures, and then performing a fracture surface transition temperature (vTrs ) Was evaluated.
  • the base material toughness was set to be ⁇ 50 ° C. or less in vTrs.
  • HAZ toughness For HAZ toughness, submerged arc welding or electrogas welding was performed under conditions of a heat input of about 100 to 300 kJ / cm, and a Charpy specimen with a notch in HAZ 1 mm away from the melt line at the center of the plate thickness was collected. The test was performed and evaluated by vTrs. The target value of HAZ toughness was set to ⁇ 40 ° C. or less in vTrs. The rolling productivity was evaluated by a value (Ton / h) obtained by dividing the rolling weight by the rolling time (here, the time from the start of rough rolling to the end of finish rolling). Rolling productivity generally decreases as the plate thickness increases.
  • the productivity target is 240, 230, 220, 210, 200, 190, 180, and 170 Ton when the plate thickness is 15 mm or less, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, and 50 mm, respectively. / H or more.
  • Nos. 1 to 16 have chemical components within a predetermined range and were manufactured under predetermined conditions, and as shown in Table 13, all have a sufficient strength as a steel having a tensile strength of 440 MPa or higher in a thickness range of 12 to 50 mm.
  • the base metal toughness was ⁇ 50 ° C. or less in vTrs and the high heat input HAZ toughness was ⁇ 40 ° C. or less in vTrs, both of which were good and the rolling productivity also satisfied the target value.
  • no. 17 to 36 as shown in Tables 1 to 12, since any one of the chemical components and production conditions deviated from the scope of the present invention, as shown in Table 13, the base material strength, base material toughness, HAZ Either toughness or productivity has fallen.
  • No. 20, 22, and 30 are comparative examples in which the heating conditions for hot rolling are out of the scope of the present invention.
  • No. 20 since the Ph exceeded the upper limit, the heating ⁇ was coarsened, a fine structure was not obtained, and the base material toughness was lowered.
  • No. No. 22 had a Ph of less than the lower limit, so that the solid solution of Nb was insufficient and the chemical components were the same. Compared with 7 and 8, the strength is reduced and the base metal toughness is also insufficient.
  • No. 30 had a short heating and holding time, the solution of the alloy element became insufficient, and the base material toughness was lowered.
  • No. Reference numerals 17, 19, 23, and 26 are comparative examples in which the rough rolling conditions are out of the scope of the present invention.
  • No. No. 17 has a longer time between 1 and 2 passes of rough rolling and between 2 and 3 passes.
  • No. 19 has a high rolling temperature of 2 passes and 3 passes, so that the recrystallization ⁇ is coarsened and the toughness of the base material is lowered.
  • No. No. 23 has a short inter-pass time between 1-2 passes and 2-3 passes. In No. 26, the rolling temperature of 8 pass and 9 pass was low, so that recrystallization was not completed and a mixed grain structure was formed, so that the toughness was lowered.
  • No. 18, 21, 24, 25, 28 and 31 are comparative examples in which the finish rolling conditions are outside the scope of the present invention.
  • No. 24 since the rolling temperature was high, ⁇ was partly recrystallized to form a mixed grain structure and toughness was reduced.
  • No. 28 the time between passes was long, and recrystallization ⁇ occurred, resulting in a decrease in toughness.
  • No. 21 has a low rolling temperature in the third pass and the fourth pass. Since No. 18 had a large cumulative rolling reduction, the base metal toughness was good, but the rolling productivity decreased.
  • No. 25 the rolling temperature was too low and excessive two-phase rolling occurred, so that both the base metal toughness and productivity decreased.
  • No. 31 had a small cumulative rolling reduction, so that a fine structure was not obtained and toughness was lowered.
  • No. 32 to 36 are comparative examples in which the chemical components are outside the scope of the present invention.
  • No. 32 since the index Ceq ′ composed of C, Mn, and Nb exceeded the upper limit value, the center segregation became remarkable, and the HAZ toughness particularly decreased.
  • No. 33 the index Ceq 'was less than the lower limit value, so the base material strength decreased.
  • No. 34 had high Ti / N, coarse Ti oxide remained, and particularly HAZ toughness was lowered.
  • No. 35 had a low Ti / N ratio, the HAZ toughness particularly deteriorated due to the effect of solid solution N.
  • No. Since 36 had a large amount of C the strength increased, and the base metal and the HAZ toughness decreased.

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  • Physics & Mathematics (AREA)
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  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
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CN102766806A (zh) * 2012-07-11 2012-11-07 莱芜钢铁集团有限公司 一种超宽薄规格桥梁用结构钢板及其生产方法
WO2013099179A1 (ja) * 2011-12-27 2013-07-04 Ｊｆｅスチール株式会社 脆性き裂伝播停止特性に優れた高強度厚鋼板およびその製造方法
JP2014074194A (ja) * 2012-10-03 2014-04-24 Kobe Steel Ltd 歪時効前後の靭性変化が少ない厚鋼板
JP2016507649A (ja) * 2012-12-27 2016-03-10 ポスコ 極低温靱性に優れ低降伏比特性を有する高強度鋼板及びその製造方法
JP2016509129A (ja) * 2013-01-22 2016-03-24 宝山鋼鉄股▲分▼有限公司 高強度鋼板及びその製造方法
JP2016079449A (ja) * 2014-10-15 2016-05-16 新日鐵住金株式会社 鋼管の製造方法及び鋼管
JP2017150067A (ja) * 2016-02-25 2017-08-31 新日鐵住金株式会社 脆性き裂伝播停止特性に優れた鋼板およびその製造方法
JP2018076573A (ja) * 2016-11-11 2018-05-17 新日鐵住金株式会社 脆性き裂伝播停止特性に優れた鋼板およびその製造方法
JP2018095904A (ja) * 2016-12-12 2018-06-21 Ｊｆｅスチール株式会社 低降伏比角形鋼管用熱延鋼板の製造方法および低降伏比角形鋼管の製造方法
WO2019001464A1 (zh) * 2017-06-27 2019-01-03 南京钢铁股份有限公司 一种超细晶粒宽厚管线钢板的生产工艺
CN109365529A (zh) * 2018-10-08 2019-02-22 鞍钢股份有限公司 一种奥氏体不锈钢中厚板的生产方法
CN115404328A (zh) * 2022-09-23 2022-11-29 鞍钢股份有限公司 一种基于叠加轧制宽厚管线钢板低温韧性调控的方法
CN115433874A (zh) * 2022-08-31 2022-12-06 马鞍山钢铁股份有限公司 一种屈服强度460MPa级耐-20℃热轧角钢及其生产方法
CN115558851A (zh) * 2022-09-23 2023-01-03 鞍钢股份有限公司 一种370MPa级别工程结构用热轧钢板及其制造方法
CN115558849A (zh) * 2022-09-23 2023-01-03 鞍钢股份有限公司 一种345MPa级别工程结构用热轧钢板及其制造方法

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WO2013099179A1 (ja) * 2011-12-27 2013-07-04 Ｊｆｅスチール株式会社 脆性き裂伝播停止特性に優れた高強度厚鋼板およびその製造方法
JPWO2013099179A1 (ja) * 2011-12-27 2015-04-30 Ｊｆｅスチール株式会社 脆性き裂伝播停止特性に優れた高強度厚鋼板およびその製造方法
CN102766806A (zh) * 2012-07-11 2012-11-07 莱芜钢铁集团有限公司 一种超宽薄规格桥梁用结构钢板及其生产方法
JP2014074194A (ja) * 2012-10-03 2014-04-24 Kobe Steel Ltd 歪時効前後の靭性変化が少ない厚鋼板
JP2016507649A (ja) * 2012-12-27 2016-03-10 ポスコ 極低温靱性に優れ低降伏比特性を有する高強度鋼板及びその製造方法
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JP2016509129A (ja) * 2013-01-22 2016-03-24 宝山鋼鉄股▲分▼有限公司 高強度鋼板及びその製造方法
JP2016079449A (ja) * 2014-10-15 2016-05-16 新日鐵住金株式会社 鋼管の製造方法及び鋼管
JP2017150067A (ja) * 2016-02-25 2017-08-31 新日鐵住金株式会社 脆性き裂伝播停止特性に優れた鋼板およびその製造方法
JP2018076573A (ja) * 2016-11-11 2018-05-17 新日鐵住金株式会社 脆性き裂伝播停止特性に優れた鋼板およびその製造方法
JP2018095904A (ja) * 2016-12-12 2018-06-21 Ｊｆｅスチール株式会社 低降伏比角形鋼管用熱延鋼板の製造方法および低降伏比角形鋼管の製造方法
WO2019001464A1 (zh) * 2017-06-27 2019-01-03 南京钢铁股份有限公司 一种超细晶粒宽厚管线钢板的生产工艺
CN109365529A (zh) * 2018-10-08 2019-02-22 鞍钢股份有限公司 一种奥氏体不锈钢中厚板的生产方法
CN115433874A (zh) * 2022-08-31 2022-12-06 马鞍山钢铁股份有限公司 一种屈服强度460MPa级耐-20℃热轧角钢及其生产方法
CN115433874B (zh) * 2022-08-31 2023-08-25 马鞍山钢铁股份有限公司 一种屈服强度460MPa级耐-20℃热轧角钢及其生产方法
CN115404328A (zh) * 2022-09-23 2022-11-29 鞍钢股份有限公司 一种基于叠加轧制宽厚管线钢板低温韧性调控的方法
CN115558851A (zh) * 2022-09-23 2023-01-03 鞍钢股份有限公司 一种370MPa级别工程结构用热轧钢板及其制造方法
CN115558849A (zh) * 2022-09-23 2023-01-03 鞍钢股份有限公司 一种345MPa级别工程结构用热轧钢板及其制造方法

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