WO2011148754A1 - 厚鋼板の製造方法 - Google Patents
厚鋼板の製造方法 Download PDFInfo
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- WO2011148754A1 WO2011148754A1 PCT/JP2011/060337 JP2011060337W WO2011148754A1 WO 2011148754 A1 WO2011148754 A1 WO 2011148754A1 JP 2011060337 W JP2011060337 W JP 2011060337W WO 2011148754 A1 WO2011148754 A1 WO 2011148754A1
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 55
- 239000010959 steel Substances 0.000 title claims abstract description 55
- 238000004519 manufacturing process Methods 0.000 title claims description 18
- 238000000034 method Methods 0.000 title abstract description 26
- 230000008569 process Effects 0.000 title abstract description 9
- 238000001816 cooling Methods 0.000 claims abstract description 46
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- 239000000203 mixture Substances 0.000 claims abstract description 4
- 238000010438 heat treatment Methods 0.000 claims description 28
- 150000004767 nitrides Chemical class 0.000 claims description 13
- 239000012535 impurity Substances 0.000 claims description 3
- 238000003303 reheating Methods 0.000 claims 1
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 abstract description 47
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- 239000000126 substance Substances 0.000 abstract description 7
- 229910052758 niobium Inorganic materials 0.000 abstract description 5
- 229910052748 manganese Inorganic materials 0.000 abstract description 4
- 229910052757 nitrogen Inorganic materials 0.000 abstract description 4
- 229910052799 carbon Inorganic materials 0.000 abstract description 3
- 229910052761 rare earth metal Inorganic materials 0.000 description 14
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 3
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 3
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- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 2
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Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
- B22D11/059—Mould materials or platings
-
- 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
- C22C38/001—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
- C22C38/12—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
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/004—Dispersions; Precipitations
Definitions
- the present invention relates to a method for producing a thick steel plate excellent in toughness of a base material and a welded heat affected zone (HEAT Affected Zone: HAZ).
- the steel plate manufactured according to the present invention is suitable for welded structures such as ships, buildings, bridges, tanks, and marine structures.
- the thick steel plate manufactured by this invention may distribute
- Non-Patent Document 1 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 1).
- Patent Document 1 For oxides and sulfides, in steel containing 0.04 to 0.10% Al, 0.002 to 0.02% Ti, and 0.003 to 0.05% rare earth element (REM) A technique for improving HAZ toughness has been proposed (for example, Patent Document 1). This is a method in which sulfides and oxides of REM are used to prevent coarsening of the HAZ part during high heat input welding.
- REM rare earth element
- Patent Document 2 a Ti oxide having a particle diameter of 0.1 to 3.0 ⁇ m and a particle number of 5 ⁇ 10 3 to 1 ⁇ 10 7 particles / mm 3 , or Ti oxide A steel containing any one of a composite of Ti and nitride has been proposed (for example, Patent Document 2).
- This is a technology to improve the toughness by making particles such as Ti oxide or a composite of Ti oxide and Ti nitride act as ⁇ intragranular ferrite ( ⁇ ) transformation nuclei in HAZ, and refine the HAZ structure. is there.
- BN also acts as an ⁇ transformation nucleus, so 0.005 to 0.08% Al, 0.0003 to 0.0050% B, and at least one of Ti, Ca, and REM A steel containing 0.03% or less has been proposed (for example, Patent Document 3).
- This is a technique in which HAZ toughness is improved by forming BN in the cooling process starting from REM, Ca oxide, sulfide or TiN that is not dissolved in HAZ, and then generating ⁇ .
- Patent Document 4 This is a technique that improves the toughness of the base metal by efficiently miniaturizing the ⁇ grain size by rolling under a predetermined condition using a slab containing a predetermined size and number of oxide particles. is there.
- Kanazawa, Nakajima, Okamoto, Kanaya “Improvement of weld bond toughness by fine TiN and development of steel for high heat input welding”, Iron and Steel, Vol. 61 (1975), p. 2589
- Non-Patent Document 1 is only a general technique using TiN particles, and there is no detailed description regarding the control of components, particle diameters, and distributions. It is difficult to ensure good HAZ toughness in high heat input welding.
- Patent Document 1 uses REM sulfides and oxides, but it is usually difficult to finely disperse sulfides and oxides. Therefore, there is a limit to reducing the ⁇ particle size of the HAZ of the high heat input welded joint. Further, if coarse sulfides or oxides are present in the steel, the toughness may be lowered.
- Patent Document 2 utilizes Ti oxide or composite particles of Ti oxide and Ti nitride as ⁇ intragranular ferrite ( ⁇ ) transformation nuclei.
- ⁇ intragranular ferrite
- Patent Document 3 utilizes REM or Ca oxide, sulfide, or BN formed on TiN as an ⁇ transformation nucleus, but it is also effective in the case of coarse ⁇ grains.
- oxides and sulfides may be the starting point of destruction.
- Patent Document 4 uses oxide particles that are usually used for improving HAZ toughness to efficiently build base material toughness, but there is a coarse oxide. Then, HAZ toughness may decrease.
- the present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing a thick steel plate excellent in toughness of a base material and a weld heat affected zone, which can be applied as a large structural steel.
- the present invention pays attention to the Ti-containing nitride produced in the slab and the heating conditions for hot rolling, and a method for controlling the Ti-containing nitride that contributes to suppression of refinement of the base material and coarsening of the HAZ grain size And the manufacturing method for obtaining the thick steel plate excellent in the toughness of a base material and a welding heat affected zone is provided.
- the strength of the thick steel plate is, for example, a yield strength of 315 MPa to 580 MPa and a tensile strength of 440 MPa to 720 MPa.
- the yield strength may be 500 MPa or less, and the tensile strength may be 490 MPa or more or 620 MPa or less.
- the plate thickness is, for example, 10 to 100 mm, and the lower limit may be 12 mm or 20 mm, particularly preferably 30 mm. Further, the upper limit of the plate thickness may be 70 mm or 50 mm.
- the target of the toughness of the base material is to obtain a high value of 31J or more, 47J or more, or 100J or more with a Charpy absorbed energy value of ⁇ 50 ° C. or less, or ⁇ 40 ° C. in vTrs, for example.
- the target of the toughness of the weld heat affected zone is, for example, in a weld heat affected zone of a welded joint having a heat input of 200 kJ / cm or higher, vTrs of ⁇ 40 ° C. or lower, or a Charpy absorbed energy value of ⁇ 21 ° C. of 27 J or higher, It is to obtain a high value of 34J or higher or 70J or higher.
- the gist of the present invention is as follows.
- the steel is in 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% or less Mg: 0.0050% or less, Ca: 0.0030% or less, REM: The manufacturing method of the thick steel plate as described in said (1) or (2) characterized by containing 1 type or 2 types or more of 0.010% or less.
- the HAZ toughness is obtained when welding with a base metal toughness and heat input of about 200 to 500 kJ / cm with a steel plate having a tensile strength of 440 MPa class or more, a plate thickness of 10 mm or more, particularly 30 mm or more. Since a good thick steel plate can be provided by an efficient manufacturing method, the industrial effect is extremely large.
- FIG. 6 is a diagram showing the relationship between the TiN number density of 0.02 to 0.05 ⁇ m in the surface layer and the fracture surface transition temperature of the base material.
- FIG. 6 is a diagram showing the relationship between the TiN number density of 0.05 to 0.2 ⁇ m in the center and the fracture surface transition temperature of HAZ. It is a figure which shows the relationship between the cooling rate at the time of casting, and TiN number density. It is a figure which shows the heating condition range in this invention of the steel containing Nb: 0.02% and Ti: 0.01%.
- the ⁇ grain size becomes coarse in the weld heat affected zone (HAZ) heated to a temperature of 1400 ° C. or higher, and in the case of a highly hardenable component system, a martensite-austenite mixture ( A brittle phase called M-A) is formed, and the HAZ toughness is lowered. Therefore, in order to improve the HAZ toughness, it is basically necessary to combine the adjustment of chemical components and the inclusion control for HAZ microstructure refinement.
- HAZ weld heat affected zone
- alloy elements such as Mn are concentrated particularly in the center of the plate thickness, and the formation of MA is promoted, so that it is more difficult to ensure toughness.
- the stress state at the central portion of the plate thickness becomes the most severe. Therefore, it is necessary to make the structure at the central portion of the plate thickness as fine as possible by making full use of the structure control means.
- TMCP Thermo-Mechanical Control Process
- CR Controlled Rolling
- ACC Accelerated Cooling
- the temperature of the surface layer of the steel sheet tends to rise locally in the heating process, and the coarse ⁇ grains generated in such a part remain even after recrystallization in the rough rolling process, resulting in a non-uniform final structure. , Toughness may decrease. Therefore, in order to ensure the toughness of the steel sheet, it is necessary to suppress the formation of coarse ⁇ grains in the surface layer portion. Therefore, the present inventors considered that the Ti-containing nitride particles used for securing the HAZ toughness of the high heat input welded joint could be used for refining the surface layer portion of the base material, and conducted various studies. It was. In addition, although Ti containing nitride particle
- TiN is less stable at high temperatures than oxide, it can be relatively easily dispersed finely in steel. Moreover, since size distribution changes with thermal histories, it discovered that especially a heating process was very important among the casting process which manufactures a slab, and the process which manufactures a thick steel plate so that it may demonstrate below.
- the TiN distribution necessary for suppressing the formation of coarse ⁇ grains in the surface layer portion and ensuring toughness was examined.
- the TiN distribution necessary for suppressing the ⁇ grain growth in the central portion of the HAZ plate thickness and ensuring toughness was examined. Toughness was evaluated by the Charpy impact test and the fracture surface transition temperature (vTrs). Furthermore, based on these results, a detailed study was performed on the TiN distribution required for the surface layer portion and the center portion of the plate thickness of the slab. In addition, the size and density of TiN were measured using a transmission electron microscope by collecting samples from slabs, steel plates, and HAZ to produce extraction replicas.
- TiN having an equivalent circle diameter of 0.02 to 0.05 ⁇ m at a surface layer portion of the slab is 7.0 per mm 2 If it is set to x10 4 or more, the toughness of the surface layer part of a base material will become favorable.
- the density of TiN with an equivalent circle diameter of 0.02 to 0.05 ⁇ m If it is less than 0.02 ⁇ m, it dissolves during hot rolling, and if it exceeds 0.05 ⁇ m, the pinning effect This is because the effect of suppressing grain growth becomes insufficient.
- the upper limit of the TiN number density in the surface layer portion of the slab is not particularly specified, but if it is too large, surface defects may occur in the surface layer portion. Therefore, 0.02 to 0.05 ⁇ m of TiN in the surface layer portion is preferably 4.0 ⁇ 10 5 or less per 1 mm 2 .
- the thickness of the slab thickness of the slab is equal to or greater than 5.0 ⁇ 10 4 per mm 2 with 0.05 to 0.2 ⁇ m of equivalent circle diameter, HAZ toughness of the part becomes good. Attention was focused on the density of TiN with an equivalent circle diameter of 0.05 to 0.2 ⁇ m at the center of the plate thickness of the slab. This is because the effect becomes insufficient, and when the thickness exceeds 0.2 ⁇ m, the toughness of the base material decreases.
- the upper limit of the TiN number density in the center part of the slab thickness is not particularly specified, but if it is too large, the toughness of the center part of the base metal thickness may be lowered. Therefore, 0.05 to 0.2 ⁇ m of TiN in the central portion of the plate thickness is preferably 3.0 ⁇ 10 5 or less per 1 mm 2 .
- the present inventors have further studied, and the ratio (Ti / N) of each content (mass%) of Ti and N is 1.5 to 3.0, and a temperature of 1100 to 1300 ° C. corresponding to a precipitation nose.
- the knowledge that the cooling rate of the center part of the slab in the range is required to be 0.1 ° C./s or more was obtained.
- the surface layer of the slab is 7.0 equivalent to 0.02 to 0.05 ⁇ m in diameter with a circle equivalent diameter.
- ⁇ 10 4 pieces / mm 2 or more, and TiN having an equivalent circle diameter of 0.05 to 0.2 ⁇ m can be set to 5.0 ⁇ 10 4 pieces / mm 2 or more at the center of the plate thickness of the slab.
- the distribution of TiN is not necessarily uniform in the width direction and the longitudinal direction of the slab (slab), and there is a possibility of variation depending on the number density measurement method. For this reason, even when the cooling rate is 0.1 ° C./s or less, the number density of TiN in either the surface layer portion or the center portion of the plate thickness may satisfy the regulation.
- Specific means for increasing the cooling rate include increasing the pressure and water volume of the cooling zone in the continuous casting machine, reducing the mold thickness, and reducing the slab thickness by reducing the unsolidified layer of the slab.
- the upper limit of the cooling rate is not particularly defined, but it is difficult to exceed 1 ° C./s due to restrictions on the slab thickness (casting thickness) and equipment.
- the slab thickness at the time of casting is not particularly specified, most of the cast thickness at the time of manufacturing the thick steel plate is in the range of 150 mm to 400 mm.
- Functional form of P H is in the tempering parameters used in terms of temperature and time of tempering 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. 4 shows the Nb solid solution, ⁇ coarsening state, and heating condition range when Nb: 0.02% and Ti: 0.01%. If slab heating is performed within a range that satisfies this condition, solid solution Nb can be utilized to the maximum while suppressing the coarsening of ⁇ grains, so that the manufacturing load of subsequent processes such as hot rolling and accelerated cooling is not increased so much.
- the base material toughness can be improved.
- hot rolling performed at 900 ° C. or higher where recrystallization proceeds easily is defined as rough rolling
- hot rolling may be performed at a temperature higher than 880 ° C. and lower than 900 ° C., the influence on the structure and mechanical properties is not significant.
- Rough rolling is performed at a temperature of 900 ° C. or higher and a cumulative reduction ratio of 30% or higher. This is because if the temperature is less than 900 ° C. and the cumulative rolling reduction is less than 30%, the recrystallization of ⁇ does not proceed sufficiently to form a mixed grain structure and the material may become non-uniform.
- the upper limit of the rough rolling temperature is not defined, and is determined as appropriate according to the heating temperature of the slab and the start temperature of finish rolling.
- the upper limit of the cumulative rolling reduction is not specified, and is determined as appropriate according to the thickness of the cast slab, the thickness of the steel plate, and the cumulative rolling reduction of finish rolling.
- Finish rolling is performed at a temperature of Ar 3 or higher and 880 ° C. or lower and a cumulative rolling reduction of 40% or higher. If the temperature is lower than Ar 3 , processed ferrite is generated and the toughness may be reduced. When the temperature is higher than 880 ° C. and the cumulative rolling reduction is less than 40%, it is difficult to increase the dislocation density, and the structure cannot be sufficiently refined and the toughness is lowered.
- accelerated cooling is performed from a temperature of Ar 3 or higher to a temperature of 550 ° C. or lower at a cooling rate of 5 ° C./s or higher on the average thickness.
- the cooling rate is less than 5 ° C./s or the cooling stop temperature is higher than 550 ° C., not only the strength is insufficient, but the structure is not sufficiently refined and the base material toughness is lowered.
- the cooling rate of accelerated cooling is increased, a low temperature transformation structure that impairs toughness is not generated, and therefore the upper limit of the cooling rate is not specified.
- the cooling rate has a limit depending on the thickness of the thick steel plate and the capability 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 lower limit of the cooling stop temperature is not necessarily limited in the present invention, and may be determined according to the required characteristics of the thick steel plate. 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 550 ° C. or lower. 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 exceeds 650 ° C., cementite and crystal grains are coarsened to promote the occurrence of brittle fracture, and the toughness of the base material may be lowered.
- the temperature of heat processing shall be 400 degreeC or more. It may be 490 ° C. or higher for further improvement of toughness.
- a steel plate manufactured under a predetermined condition using a slab having a TiN distribution as described above has good toughness in the surface layer portion, and even when high heat input welding is performed, the TiN in the central portion of the HAZ plate thickness is completely Thus, a large amount of TiN of 0.05 ⁇ m or less that can effectively suppress the growth of ⁇ grains remains. Therefore, the coarsening of the structure of the center portion of the HAZ thickness of the high heat input welded joint can be suppressed to some extent.
- TiN in the surface layer portion of the base material is fine, most of it is dissolved due to the heat effect of high heat input welding. However, due to the effect of composite precipitates of TiN and MnS that re-precipitate during the cooling process, etc.
- % 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, 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 added amount needs to satisfy the following formula (1) from the viewpoint of securing the base metal strength and the HAZ toughness. 0.32 ⁇ [C] +0.15 [Mn] +3.8 [Nb] ⁇ 0.39 (1) In the above formula, [C], [Mn], and [Nb] are added amounts of each element. The coefficient was experimentally determined from the contribution to hardenability. If [C] +0.15 [Mn] +3.8 [Nb] is less than 0.32, the strength becomes insufficient.
- Mn and Nb are elements that are difficult to suppress center segregation, and when [C] +0.15 [Mn] +3.8 [Nb] exceeds 0.39, center segregation becomes significant.
- the HAZ toughness of the high heat input welded joint will decrease. 0.38 or 0.37 may be set as the upper limit for improving HAZ toughness, and 0.33 may be set as the lower limit for improving strength.
- 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%, 0.35% or 0.20%
- the upper limit of Cr is 0.3%, 0.2% or 0.1%.
- the upper limit 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.
- Ar3 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo + 0.35 + 0.35 (t-8)
- t is a plate thickness (mm).
- Tables 4 and 5 show the TiN number density of the slab, the strength and toughness of the base material, and the HAZ toughness.
- TiN number density is the surface layer part of the slab, specifically, an extraction replica sample is prepared from the slab surface at a position 1 / 20th of the slab thickness and the slab thickness center, and transmission electron microscope (TEM) is used.
- the TiN number density was calculated by taking 50 to 100 000 fields of view arbitrarily and measuring the size and number of TiN.
- Base material strength is JIS Z 2201 No. 4 tensile test specimen taken from the center of the plate thickness in the direction perpendicular to the rolling direction, and subjected to a tensile test according to JIS Z 2241, yield strength (YP). Evaluation was made by measuring the tensile strength (TS). Based on JIS Z 2242, the base material toughness is 2 mmV notch Charpy specimens taken in the rolling direction from the outermost layer of the steel sheet and the center of the sheet thickness, and after performing Charpy impact tests at various temperatures, the fracture surface transition Evaluation was made by calculating the temperature (vTrs). The base material toughness (center portion and surface layer portion) was set to be ⁇ 50 ° C. or less in terms of vTrs.
- HAZ toughness For HAZ toughness, electrogas welding (EGW) was performed under conditions of heat input of 200 to 450 kJ / cm, and a Charpy test piece with a notch in HAZ 1 mm away from the melt line at the center of the plate thickness was collected and tested. And evaluated with vTrs. In addition, the toughness (center portion) of HAZ was set to be ⁇ 40 ° C. or less in vTrs.
- No. of the present invention example. Nos. 1 to 15 have chemical components within a predetermined range and manufactured under predetermined conditions, and therefore satisfy a predetermined TiN number density, and all have sufficient strength as steel having a tensile strength of 440 MPa or more.
- the toughness was ⁇ 50 ° C. or less in vTrs, and the high heat input HAZ toughness was ⁇ 40 ° C. or less, both of which were good.
- No. with a plate thickness of 60 mm or more and a large amount of heat input. 5, 7, 13, 14 and 15 also show good toughness.
- any one of chemical components and production conditions was outside the scope of the present invention, and any of base material strength, base material toughness, and HAZ toughness was lowered.
- No. Nos. 16, 20, and 25 are examples in which TiN number density was insufficient due to a slow cooling rate during casting, and at least one of base metal toughness or HAZ toughness was lowered.
- No. No. 16 had a lack of TiN at the center of the plate thickness of the slab, and the HAZ ⁇ grains were coarsened, resulting in a decrease in toughness.
- No. 25 did not satisfy the predetermined number density in the surface layer portion and the center portion, the base material toughness and the HAZ toughness were lowered.
- both the surface layer portion of the slab and the plate thickness center portion do not satisfy the predetermined number density, the surface layer portion of the slab, and the plate thickness center.
- One of the parts may not satisfy a predetermined number density.
- No. Reference numerals 17, 19 and 23 are comparative examples in which the heating conditions for hot rolling are out of the scope of the present invention.
- No. No. 27 is a comparative example in which the rough rolling conditions were out of the scope of the present invention. Since the cumulative rolling reduction was small, the microstructure was not refined and the base metal toughness was lowered.
- No. 18, 21, and 26 are comparative examples in which the finish rolling conditions are out of the scope of the present invention.
- No. No. 18 had a finish rolling start temperature and finish temperature lower than Ar3, so that processing ⁇ was generated, and the base metal toughness, particularly the toughness of the surface layer portion, was significantly lowered.
- No. 21 since the start temperature and finish temperature of finish rolling were too high, the structure at the center of the plate thickness was particularly coarsened and the toughness was lowered.
- No. No. 26 is an example in which the cumulative rolling reduction of finish rolling is small, and the structure becomes coarse and the toughness decreases.
- No. 22 and 24 are comparative examples in which the conditions for accelerated cooling and heat treatment after hot rolling are outside the scope of the present invention.
- No. No. 24 was an example in which accelerated cooling was not performed, and the structure was not refined and the toughness was lowered.
- No. Reference numerals 28 to 32 are comparative examples in which chemical components are out of the scope of the present invention.
- the index Ceq ′ composed of C, Mn, and Nb exceeded the upper limit value, so that the center segregation became remarkable, and the HAZ toughness particularly decreased.
- the index Ceq ' was less than the lower limit value, so that the base material strength decreased.
- No. 30 had a high Ti / N ratio, coarse Ti oxide remained, and the HAZ toughness particularly decreased.
- TiN was low in No. 31, the HAZ toughness particularly deteriorated due to the effect of solute N.
- No. 32 had a large amount of C, the strength was excessive, and the HAZ toughness particularly decreased.
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Abstract
Description
C :0.03~0.16%、
Si:0.03~0.5%、
Mn:0.3~2.0%、
Nb:0.005~0.030%、
Ti:0.003~0.050%、
Al:0.002~0.10%、
N :0.0020~0.0100%
を含有し、
P :0.020%以下、
S :0.010%以下
に制限し、残部がFeおよび不可避的不純物からなり、かつ下記(1)、(2)式を満足する組成の鋼を、1100~1300℃の温度範囲における鋳片厚中心部の冷却速度が0.1℃/s以上となるように冷却して鋳造し、表層部において円相当径で0.02~0.05μmのTi含有窒化物が1mm2当たり7.0×104個以上、中心部において円相当径で0.05~0.2μmのTi含有窒化物が1mm2当たり5.0×104個以上存在する鋳片を製造し、該鋳片を、下記(3)、(4)式を満たす条件で加熱し、900℃以上の温度で累積圧下率30%以上の粗圧延を行い、さらにAr3以上880℃以下の温度で、累積圧下率40%以上の仕上圧延を行い、引き続きAr3以上の温度から、板厚平均で5℃/s以上の冷却速度で550℃以下の温度まで加速冷却を行うことを特徴とする厚鋼板の製造方法。
0.32≦[C]+0.15[Mn]+3.8[Nb]≦0.39 ・・・(1)
1.5≦[Ti]/[N]≦3.0 ・・・(2)
56000/(1.2−0.18×log[Nb])≦(T+273)×{log(t)+25}≦91000/(1.9−0.18×log[Ti]) ・・・(3)
t≧30 ・・・(4)
ただし、[X]:元素Xの添加量(質量%)、T:加熱温度(℃)、t:保持時間(分)
Cu:1.5%以下、
Cr:0.5%以下、
Mo:0.5%以下、
Ni:2.0%以下、
V:0.10%以下、
B:0.0030%以下
Mg:0.0050%以下、
Ca:0.0030%以下、
REM:0.010%以下
の1種または2種以上を含有することを特徴とする上記(1)又は(2)に記載の厚鋼板の製造方法。
56000/(1.2−0.18×log[Nb])≦PH≦91000/(1.9−0.18×log[Ti]) ・・・・・・・ (3)
ただし、PH=(T+273)×{log(t)+25}
t≧30 ・・・・・・・ (4)
ただし、[X]:元素Xの添加量(質量%)、T:加熱温度(℃)、t:保持時間(分)
0.32≦[C]+0.15[Mn]+3.8[Nb]≦0.39・・・(1)上式の[C]、[Mn]、[Nb]は、各元素の添加量(質量%)であり、係数は焼入れ性への寄与から実験的に求めた。[C]+0.15[Mn]+3.8[Nb]が0.32未満であると、強度が不十分になる。一方、特に、Mn、Nbは、中心偏析を抑制することが難しい元素であり、[C]+0.15[Mn]+3.8[Nb]が0.39を超えると中心偏析が顕著になり、大入熱溶接継手のHAZ靭性が低下してしまう。HAZ靭性の改善のため、0.38又は0.37を上限としてもよく、強度向上のため0.33を下限としてもよい。
1.5≦[Ti]/[N]≦3.0 ・・・(2)
上式の[Ti]、[N]は、各元素の添加量(質量%)である。
Ar3=910−310C−80Mn−20Cu−15Cr−55Ni−80Mo+0.35+0.35(t−8)
ここで、tは板厚(mm)である。また、表4および5に鋳片のTiN個数密度、母材の強度および靭性、HAZ靭性を示す。
Claims (3)
- 質量%で、
C :0.03~0.16%、
Si:0.03~0.5%、
Mn:0.3~2.0%、
Nb:0.005~0.030%、
Ti:0.003~0.050%、
Al:0.002~0.10%、
N :0.0020~0.0100%
を含有し、
P :0.020%以下、
S :0.010%以下
に制限し、残部がFeおよび不可避的不純物からなり、かつ下記(1)、(2)式を満足する組成の鋼を、1100~1300℃の温度範囲における鋳片厚中心部の冷却速度が0.1℃/s以上となるように冷却して鋳造し、表層部において円相当径で0.02~0.05μmのTi含有窒化物が1mm2当たり7.0×104個以上、中心部において円相当径で0.05~0.2μmのTi含有窒化物が1mm2当たり5.0×104個以上存在する鋳片を製造し、該鋳片を、下記(3)、(4)式を満たす条件で加熱し、900℃以上の温度で累積圧下率30%以上の粗圧延を行い、さらにAr3以上880℃以下の温度で、累積圧下率40%以上の仕上圧延を行い、引き続きAr3以上の温度から、板厚平均で5℃/s以上の冷却速度で550℃以下の温度まで加速冷却を行うことを特徴とする厚鋼板の製造方法。
0.32≦[C]+0.15[Mn]+3.8[Nb]≦0.39 ・・・(1)
1.5≦[Ti]/[N]≦3.0 ・・・(2)
56000/(1.2−0.18×log[Nb])≦(T+273)×{log(t)+25}≦91000/(1.9−0.18×log[Ti]) ・・・(3)
t≧30 ・・・(4)
ただし、[X]:元素Xの添加量(質量%)、T:再加熱温度(℃)、t:保持時間(分) - 前記加速冷却終了後、650℃以下の温度で熱処理することを特徴とする請求項1記載の厚鋼板の製造方法。
- さらに、前記鋼が質量%で、
Cu:1.5%以下、
Cr:0.5%以下、
Mo:0.5%以下、
Ni:2.0%以下、
V:0.10%以下、
B:0.0030%以下
Mg:0.0050%以下、
Ca:0.0030%以下、
REM:0.010%以下
の1種または2種以上を含有することを特徴とする請求項1又は2に記載の厚鋼板の製造方法。
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WO2014157215A1 (ja) * | 2013-03-29 | 2014-10-02 | 株式会社神戸製鋼所 | 耐水素誘起割れ性と溶接熱影響部の靭性に優れた鋼板およびラインパイプ用鋼管 |
KR20150119958A (ko) * | 2013-03-29 | 2015-10-26 | 가부시키가이샤 고베 세이코쇼 | 내수소유기균열성과 용접열영향부의 인성이 우수한 강판 및 라인 파이프용 강관 |
CN105074036A (zh) * | 2013-03-29 | 2015-11-18 | 株式会社神户制钢所 | 抗氢致裂纹性和焊接热影响部的韧性优异的钢板和管线钢管 |
CN103627980A (zh) * | 2013-11-25 | 2014-03-12 | 首钢总公司 | 低温大壁厚x80hd大变形管线钢及其生产方法 |
JP2019505676A (ja) * | 2015-12-23 | 2019-02-28 | ポスコPosco | 熱間抵抗性に優れた高強度構造用鋼板及びその製造方法 |
JP2022550795A (ja) * | 2019-10-01 | 2022-12-05 | ポスコ | 中心部における極低温変形時効衝撃靭性に優れた高強度極厚物鋼材及びその製造方法 |
JP7404520B2 (ja) | 2019-10-01 | 2023-12-25 | ポスコホールディングス インコーポレーティッド | 中心部における極低温変形時効衝撃靭性に優れた高強度極厚物鋼材及びその製造方法 |
JPWO2022097588A1 (ja) * | 2020-11-05 | 2022-05-12 | ||
WO2022097589A1 (ja) * | 2020-11-05 | 2022-05-12 | Jfeスチール株式会社 | 鋼板およびその製造方法 |
JP7099653B1 (ja) * | 2020-11-05 | 2022-07-12 | Jfeスチール株式会社 | 鋼板およびその製造方法 |
WO2022097588A1 (ja) * | 2020-11-05 | 2022-05-12 | Jfeスチール株式会社 | 鋼板および鋼板の製造方法 |
JP7243916B2 (ja) | 2020-11-05 | 2023-03-22 | Jfeスチール株式会社 | 鋼板および鋼板の製造方法 |
KR20230041045A (ko) | 2020-11-05 | 2023-03-23 | 제이에프이 스틸 가부시키가이샤 | 강판 및 그 제조 방법 |
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