WO2020136776A1 - 溶接構造体 - Google Patents
溶接構造体 Download PDFInfo
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- WO2020136776A1 WO2020136776A1 PCT/JP2018/047974 JP2018047974W WO2020136776A1 WO 2020136776 A1 WO2020136776 A1 WO 2020136776A1 JP 2018047974 W JP2018047974 W JP 2018047974W WO 2020136776 A1 WO2020136776 A1 WO 2020136776A1
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- joining member
- plate thickness
- distance
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- thickness direction
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
- B23K9/23—Arc welding or cutting taking account of the properties of the materials to be welded
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
- B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
- B23K35/24—Selection of soldering or welding materials proper
- B23K35/30—Selection of soldering or welding materials proper with the principal constituent melting at less than 1550 degrees C
- B23K35/3053—Fe as the principal constituent
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K9/00—Arc welding or cutting
- B23K9/02—Seam welding; Backing means; Inserts
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2101/00—Articles made by soldering, welding or cutting
- B23K2101/04—Tubular or hollow articles
- B23K2101/12—Vessels
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2101/00—Articles made by soldering, welding or cutting
- B23K2101/18—Sheet panels
- B23K2101/185—Tailored blanks
Definitions
- the present invention relates to a welded structure used in a container ship or the like.
- Hatch large container vessels that carry a large amount of cargo have a large opening (hatch) formed in the upper deck (upper deck) for loading and unloading cargo.
- a hatchside combing is provided on the upper deck so as to surround the hatch to prevent the inflow of seawater.
- the upper deck and the hatch side combing are each constructed by welding a plurality of steel plates. Hatchside combing is also welded on the upper deck.
- each of the hatchside combing and the upper deck has a structure in which a plurality of steel plates are welded.
- the hatchside combing and the upper deck are formed with a plurality of welds for welding the steel plates to each other.
- the crack generated in the weld easily propagates along the weld. Therefore, for example, when a crack occurs in the hatch side combing weld, the crack propagates toward the upper deck side along the weld, and the propagated crack propagates to the weld in the upper deck. There are cases. Therefore, in order to sufficiently improve the strength of the hull, the hatchside combing and the upper deck must have the characteristics (brittle crack propagation stopping characteristics) that can stop the crack growth as described above.
- Patent Documents 1 and 2 disclose welded structures relating to brittle crack propagation arresting properties.
- a crack may be generated from the upper deck and propagated toward the hatchside combing side. Then, according to the results of the verification test carried out in the joint research between the Japan Maritime Association and the Japan Welding Association, in order to stop the propagation of cracks that occur in the upper deck and propagate toward the hatchside combing side, It has been found that it is necessary to use a thick steel plate having an extremely high Kca value of 8,000 N/mm 1.5 or more.
- the present invention has been made to solve such a problem, and an object thereof is to provide a welded structure having excellent brittle crack propagation arresting properties.
- the gist of the present invention is the following welded structure.
- the joining member has a first surface and a second surface perpendicular to the plate thickness direction of the joining member,
- the plate thickness t (mm) of the joining member satisfies the following formula (i)
- a distance in the plate thickness direction of the joining member between the highest point of the first heat-affected zone of the first welded portion formed on the first surface side and the first surface is a distance h 1 (mm)
- the second When the distance in the plate thickness direction of the joining member between the highest point of the second heat-affected zone of the second welded portion formed on the surface side and the second surface is a distance h 2 (mm),
- the acute angle ⁇ 2 (°) formed by and the partial penetration d 2 (mm) of the joint in the plate thickness direction and the distance s 2 (mm) between the toe on the joined member side and the second surface are as follows. Satisfies the equations (iv) to (ix), The welded structure according to (1) or (2) above.
- the yield stress of the joining member is 400 to 580 MPa, and the tensile strength is 510 to 750 MPa.
- the welded structure according to any one of (1) to (5) above.
- a welded structure having excellent brittle crack propagation arresting properties can be obtained.
- the structure is such that the crack entry area is limited to only the surface layer area of the thick steel plate used for hatchside combing. If it is possible to improve the brittle crack propagation stopping property in the surface layer region of the thick steel plate, it becomes possible to stop the crack growth. As a result, it becomes possible to improve the brittle crack propagation arresting property of the entire welded structure at low cost.
- FIG. 1 is a perspective view showing a welding structure according to an embodiment of the present invention.
- the welding structure 10 according to this embodiment includes a joining member 11 and a joined member 12.
- the joining member 11 is plate-shaped and has a first surface 11a and a second surface 11b that are perpendicular to the plate thickness direction.
- the member 12 to be joined is plate-shaped, and has a face 12a to be joined with which the end surface 11c of the joining member 11 abuts.
- the welded structure 10 has a T joint portion in which the joining member 11 is partially welded to both sides of the joined member 12 in a state where the end surface 11c is in contact with the joined surface 12a. ..
- the above-mentioned welded structure having the T-joint portion includes, for example, structures having the shapes shown in FIGS. 2 and 3.
- joining member 11 and the joined member 12 may be joined by fillet welding, but from the viewpoint of joining strength, the joining member 11 is provided with a groove and is joined by groove welding. Is preferred.
- a thick joining member is targeted, and specifically, when the plate thickness of the joining member 11 is t (mm), the following formula (i) is satisfied.
- the plate thickness t (mm) of the joining member 11 preferably satisfies the following equation (xi).
- the upper limit of t need not be specified in particular, but can be set to 200 mm, 150 mm, or 120 mm, for example. t ⁇ 50.0 (i) t>80.0 (xi)
- the plate thickness of the members to be joined is not particularly limited, but like the joined members, it is preferably 50.0 mm or more, and more preferably more than 80.0 mm.
- the welded structure 10 has a first welded portion 13a formed on the first surface 11a side and a second welded portion 13b formed on the second surface 11b side.
- FIG. 4 is a cross-sectional view of the welded structure 10 perpendicular to the first surface 11a and the surface 12a to be joined. In FIG. 4, hatching is not added in order to avoid making the drawing complicated.
- a first weld metal 14a is formed on the first surface 11a side of the joining portion of the joining member 11 and the joined member 12.
- a first heat-affected zone 15a is formed at the boundary between the first weld metal 14a and the joining member 11 and the joined member 12.
- the second weld metal 14b is formed on the second surface 11b side, and the second heat-affected zone 15b is formed at the boundary between the second weld metal 14b and the joining member 11 and the joined member 12.
- the welded portion means a portion in which the weld metal and the heat affected zone are combined. That is, the area where the first weld metal 14a and the first heat-affected zone 15a are combined is the first weld zone 13a, and the area where the second weld metal 14b and the second heat-affected zone 15b are combined is the second weld zone. 13b.
- the highest peak of the first welding portion 13a from the first surface 11a In order to limit the penetration region of the crack generated from the member to be joined 12 and propagating to the joining member 11 to only the surface layer side of the joining member 11, the highest peak of the first welding portion 13a from the first surface 11a. And the depth from the second surface 11b to the apex of the second weld 13b need to be controlled.
- the distance h 2 (mm) in the plate thickness direction between the highest point and the second surface 11b preferably satisfies the following formulas (ii) and (iii). h 1 ⁇ t/4 (ii) h 2 ⁇ t/4 (iii)
- the lower limits of the distance h 1 and the distance h 2 need not be particularly limited, but even when the joining member 11 and the joined member 12 are joined by fillet welding, thermal influence is exerted up to a depth of about 1 mm. Parts are formed. Therefore, 1 mm is the practical lower limit of the distance h 1 and the distance h 2 .
- the highest point of the first heat-affected zone 15a means the tip in the plate thickness direction of the first heat-affected zone 15a
- the highest point of the second heat-affected zone 15b means the second heat-affected zone 15b.
- the distance h 1 is a distance between the first surface 11a and a virtual surface 11d that is parallel to the first surface 11a and passes through the tip of the first heat-affected zone 15a in the plate thickness direction.
- the distance h 2 is a distance between the second surface 11b and a virtual surface 11e that is parallel to the second surface 11b and passes through the tip of the second heat-affected zone 15b in the plate thickness direction.
- the acute angle ⁇ 2 (°) formed by the line L 2 passing through the toe and the route on the side of the joining member 11 and the joined surface 12a in 13b may satisfy the following equations (iv) and (v), respectively. preferable. 45.0 ⁇ 1 ⁇ 70.0 (iv) 45.0 ⁇ 2 ⁇ 70.0 (v)
- the toe of the first welded portion 13a on the joining member 11 side means the intersection A 1 between the outer edge of the first weld metal 14a and the first surface 11a.
- the route on the joining member 11 side in the first welded portion 13a means the intersection B 1 between the outer edge of the first welded metal 14a and the end surface 11c.
- the bonding member 11 side of the toe at the second weld portion 13b means an intersection A 2 between the outer edge and the second surface 11b of the second weld metal 14b
- the bonding member 11 side in the second welding portion 13b Means the intersection B 2 between the outer edge of the second weld metal 14b and the end surface 11c.
- the partial penetration d 1 (mm) of the joint in the plate thickness direction of the first welded portion 13a and the partial penetration d 2 (mm) of the joint in the plate thickness direction of the second welded portion 13b are respectively the following (vi) It is preferable to satisfy the formulas and the formula (vii).
- the values calculated on the left side of the following equations (vi) and (vii) represent the effective throat thicknesses Td 1 (mm) and Td 2 (mm), respectively.
- the partial penetration d 1 of the joint is a virtual surface that passes through the first surface 11a and the end on the plate thickness center side of the first weld metal 14a parallel to the first surface 11a and in the plate thickness direction of the joining member 11. It is the distance from 11f.
- the partial penetration d 2 of the joint is an imaginary line that passes through the second surface 11b and the end portion of the second weld metal 14b in the plate thickness direction of the joining member 11 on the plate thickness center side in parallel with the second surface 11b. This is the distance from the flat surface 11g.
- the distance s 1 (mm) between the toe on the joined member 12 side and the first surface 11a and the toe on the joined member 12 side in the second welded portion 13b preferably satisfies the following equations (viii) and (ix), respectively. s 1 ⁇ d 1 (sec( ⁇ 1 )-1) (viii) s 2 ⁇ d 2 (sec( ⁇ 2 ) ⁇ 1) (ix)
- the distance s 1 and the distance s 2 are the weld leg lengths in the plate thickness direction of the first welded portion 13a and the second welded portion 13b, respectively.
- the distance s 1 is an imaginary line passing through the first surface 11a and an end portion that is parallel to the first surface 11a and that is opposite to the plate thickness center of the first weld metal 14a in the plate thickness direction of the joining member 11. This is the distance from the target surface 11h.
- the distance s 2 is a virtual surface that passes through the second surface 11b and an end portion that is parallel to the second surface 11b and that is opposite to the plate thickness center of the second weld metal 14b in the plate thickness direction of the joining member 11. It is the distance from 11i.
- first weld metal 14a and the second weld metal 14b and the joining member 11 can be easily visually identified. Also, the tip positions of the first heat-affected zone 15a and the second heat-affected zone 15b can be easily determined by exposing them by nital corrosion.
- Bainite 70-95% Ferrite: 5-30%
- the reason for using bainite as the main phase at the above depth position is to secure the strength of the joint member.
- ferrite is the main phase, it is difficult to secure high strength.
- all of bainite is used, the toughness is significantly deteriorated. Therefore, the inclusion of ferrite as the second phase suppresses the deterioration of the toughness.
- bainite and ferrite have the above area ratio as the metal structure at the above-mentioned depth position, in addition to that, for example, pearlite and/or island-like martensite (MA: Martensite-Austenite-Constituent) may be included. Good. However, pearlite is preferably 5% or less from the viewpoint of ensuring strength, and island martensite is preferably 5% or less from the viewpoint of ensuring toughness.
- pearlite is preferably 5% or less from the viewpoint of ensuring strength
- island martensite is preferably 5% or less from the viewpoint of ensuring toughness.
- Average crystal grain size 12.0 ⁇ m or less
- a boundary having a crystal orientation difference of 15° or more is defined as a crystal grain boundary
- a circle equivalent diameter of a region surrounded by the crystal grain boundary is defined as a crystal grain size.
- the metallographic structure at the center of the plate thickness of the joint member may include bainite: 70 to 95%, ferrite: 5 to 30%, pearlite: 5% or less, and MA: 5% or less.
- the average particle size is also not particularly limited, but it is technically difficult to reduce the particle size to the center of the plate thickness, which may lead to an increase in cost. Therefore, it is preferable that the average crystal grain size in the plate thickness center portion of the joining member is more than 12.0 ⁇ m.
- the preferable upper limit of the average particle size in the central part of the plate thickness is 40.0 ⁇ m.
- the area ratio and average crystal grain size of each structure are measured as follows. First, using a crystal orientation measuring device (OIM of TSL Co.) attached to a scanning electron microscope, an area of 500 ⁇ m ⁇ 500 ⁇ m at a predetermined depth position of a joining member is 0.5 ⁇ m by an EBSP (Electron Back Scattering Pattern) method. Measure in pitch.
- OIM crystal orientation measuring device
- EBSP Electro Back Scattering Pattern
- the boundary where the crystal orientation difference with the adjacent grain is 15° or more is defined as the grain boundary, and the GAM (Grain Average Misorientation) value that is the average value of the misorientation between the adjacent measurement points in the grain is obtained.
- a crystal grain having a GAM value of 1° or less is defined as a ferrite phase, and an average value of the area ratio of the ferrite phase at each position is obtained.
- a grain boundary map having a crystal orientation difference of 15° or more with adjacent grains is created, and the equivalent circle diameter of the crystal grains at that time is determined by image analysis.
- the steel plate sample was subjected to nital corrosion, and the microstructure was photographed at each depth position with a magnification of 500 times with an optical microscope, and the lumpy region visually recognized in black was defined as a pearlite phase, and each position was analyzed by image analysis. The average value of the area ratio of the pearlite phase with respect to the entire visual field area measured in step 1 is obtained.
- the steel plate sample was subjected to repeller corrosion, the microstructure was photographed at a magnification of 500 times at each depth position with an optical microscope, and the region visually recognized in white was defined as an island martensite phase.
- the average value of the area ratio of the island martensite phase with respect to the entire visual field measured at the position is obtained.
- the area ratios of the ferrite phase, the pearlite phase, and the island-like martensite phase are obtained, and the value obtained by subtracting the sum of them is defined as the area ratio of the bainite phase.
- Chemical composition of joining member The chemical composition of the joining member used in the welded structure of the present invention is not particularly limited, but in order to exhibit excellent brittle crack propagation arresting properties, it may have the following chemical composition. preferable.
- the reasons for limiting each element are as follows. In the following description, “%” regarding the content means “mass %”.
- C 0.030 to 0.100%
- C is an element that has the effect of ensuring the strength and toughness of the steel sheet by improving the hardenability.
- the C content is preferably 0.030% or more.
- the C content is preferably 0.030 to 0.100%.
- the C content is more preferably 0.060% or more, and even more preferably 0.090% or less.
- Si 0.01 to 0.30%
- Si is an element effective as a deoxidizing element and a strengthening element.
- the Si content is preferably 0.01% or more.
- the Si content is more preferably 0.10% or less.
- Mn 1.40 to 2.50%
- Mn is an element that has the action of ensuring the strength of the steel sheet and reducing the Ar 3 point. To obtain this effect, the Mn content is preferably 1.40% or more. On the other hand, if the Mn content exceeds 2.50%, the weldability and joint toughness may decrease. Therefore, the Mn content is preferably 1.40 to 2.50%. The Mn content is more preferably 1.50% or more, and more preferably 2.00% or less.
- P 0.015% or less
- P is an impurity element and reduces weldability and joint toughness, so it is preferable to reduce its content to 0.015% or less. More preferably, the P content is 0.010% or less.
- S 0.0100% or less
- S is an impurity element and causes a decrease in toughness and weldability due to the formation of MnS. Therefore, it is preferable to reduce the content thereof to 0.0100% or less. More preferably, the S content is 0.0050% or less.
- Nb 0.005 to 0.030%
- Nb is an element that suppresses the recrystallization temperature, contributes to the refinement of the structure and increases the strength of the steel sheet.
- the Nb content is preferably 0.005% or more.
- the Nb content is preferably 0.005 to 0.030%.
- the Nb content is more preferably 0.008% or more, and even more preferably 0.015% or less.
- Ti is an element that forms TiN and finely disperses TiN to improve the toughness and joint toughness of the steel sheet. To obtain this effect, the Ti content is preferably 0.005% or more. On the other hand, if the Ti content exceeds 0.030%, the toughness and joint toughness of the steel sheet may decrease. Therefore, the Ti content is preferably 0.005 to 0.030%. The Ti content is more preferably 0.008% or more, and even more preferably 0.015% or less.
- N 0.0005 to 0.0050%
- N is an element having the action of improving the toughness and joint toughness of the steel sheet by forming TiN in the steel material.
- the N content is preferably 0.0005% or more.
- the N content is preferably 0.0050% or less.
- the N content is more preferably 0.0020% or more, and even more preferably 0.0040% or less.
- Al 0.001 to 0.080%
- Al is an element that plays a role of deoxidizing and has a function of reducing O which is an impurity element.
- the free N in the steel is made AlN to be harmless.
- the Al content is preferably 0.001% or more.
- the Al content is preferably 0.001 to 0.080%.
- the Al content is more preferably 0.010% or more, and further preferably 0.040% or less.
- Cu 0.10 to 0.50%
- Cu is an element that has the effect of improving strength and lowering the Ar 3 point.
- the Cu content is preferably 0.10% or more.
- the Cu content is preferably 0.10 to 0.50%.
- the Cu content is more preferably 0.20% or more.
- Ni 0.15 to 2.00%
- Ni is an element that has the effects of improving strength and lowering the Ar 3 point.
- the Ni content is preferably 0.15% or more.
- the Ni content is more preferably 0.30% or more, and even more preferably 1.00% or less.
- the Cr content is preferably 0.50% or less, more preferably 0.20% or less. In order to obtain the above effect, the Cr content is preferably 0.10% or more.
- Mo 0 to 0.50% Mo has the effect of improving the hardenability and increasing the strength of the steel sheet due to the combined effect of B and B, so Mo may be contained if necessary. However, if its content exceeds 0.50%, the toughness and joint toughness of the steel sheet may be reduced. Therefore, the Mo content is preferably 0.50% or less, more preferably 0.40% or less, further preferably 0.30% or less, and 0.25% or less. Particularly preferred. In order to obtain the above effects, the Mo content is preferably 0.03% or more, more preferably 0.05% or more, and further preferably 0.08% or more.
- V 0 to 0.100% V has the effect of increasing the strength due to precipitation strengthening, so it may be contained if necessary. However, if the content exceeds 0.100%, the joint toughness may decrease. Therefore, the V content is preferably 0.100% or less, and more preferably 0.050% or less. In order to obtain the above effects, the V content is preferably 0.020% or more.
- B 0 to 0.0030% B has the effect of increasing the strength of the steel sheet by improving the hardenability, so it may be contained if necessary. However, if the content exceeds 0.0030%, the toughness and weldability may decrease. Therefore, the B content is preferably 0.0030% or less, and more preferably 0.0020% or less. When it is desired to obtain the above effects, the B content is preferably 0.0005% or more, more preferably 0.0010% or more.
- Ca 0 to 0.0050% Since Ca has the effect of improving the joint toughness, it may be contained if necessary. However, if the content exceeds 0.0050%, the joint toughness may decrease. Therefore, the Ca content is preferably 0.0050% or less, and more preferably 0.0030% or less. In order to obtain the above effect, the Ca content is preferably 0.0003% or more.
- Mg 0 to 0.0050% Mg forms MgS and contributes to the refinement of the base metal structure and the improvement of the joint toughness, so it may be contained if necessary. However, if the content exceeds 0.0050%, the joint toughness may decrease. Therefore, the Mg content is preferably 0.0050% or less, more preferably 0.0030% or less. In order to obtain the above effect, the Mg content is preferably 0.0003% or more.
- REM 0 to 0.0050% REM (rare earth element) has the effect of improving the joint toughness, so it may be contained if necessary. However, if the content exceeds 0.0050%, the joint toughness may decrease. Therefore, the REM content is preferably 0.0050% or less, and more preferably 0.0030% or less. In order to obtain the above effect, the REM content is preferably 0.0003% or more.
- REM means a total of 17 elements of Sc, Y and lanthanoid, and the content of REM means the total content of these elements.
- the lanthanoid is industrially added in the form of misch metal.
- the balance is Fe and impurities.
- impurities are components that are mixed by ores, raw materials such as scrap, and various factors of the manufacturing process when the steel sheet is industrially manufactured, and are allowed within a range that does not adversely affect the present invention. Means something.
- the chemical composition of the bonding member it is preferable to adjust the components so that the Ar 3 point (° C.) represented by the following formula (x) is 600 to 740° C.
- Ar 3 940-310 ⁇ C+40 ⁇ Si-90 ⁇ Mn-40 ⁇ Cu-60 ⁇ Ni-15 ⁇ Cr-80 ⁇ Mo (x)
- the element symbol in the above formula represents the content (mass %) of each element.
- the Ar 3 point is less than 600° C., the hardenability becomes excessive and the strength becomes excessive, which may deteriorate the toughness. In particular, the toughness at the center of the plate thickness of the joining member is likely to deteriorate.
- the Ar 3 point exceeds 740° C., the surface layer portion of the joined member will undergo two-phase region rolling during rolling at a low temperature, coarse work ferrite will be generated, and the brittle crack propagation arresting property may deteriorate.
- the Ar 3 point is more preferably 650° C. or higher. Further, the Ar 3 point is more preferably 720° C. or lower, and further preferably 700° C. or lower.
- the mechanical properties of the joining member used in the welded structure of the present invention there is no particular limitation on the mechanical properties of the joining member used in the welded structure of the present invention. However, when the welded structure is used in a container ship or the like, the yield stress of the joining member is preferably 400 to 580 MPa, and the tensile strength is preferably 510 to 750 MPa.
- the manufacturing method of the joining member is not particularly limited, but the steel sheet used as the joining member can be manufactured by, for example, the following procedure.
- the molten steel adjusted to the appropriate chemical composition described above is melted by a commonly known melting method such as a converter, and made into a steel slab that is a steel material by a commonly known casting method such as continuous casting.
- the steel slab is heated to 950 to 1100° C. to form an austenite single phase. If the heat extraction temperature is lower than 950°C, austenitization may be insufficient and a coarse structure may be formed. On the other hand, if the temperature exceeds 1100° C., the austenite grains may be coarsened and the grain size may not be reduced.
- Hot-rolling is performed on the heat-extracted steel slab to produce a steel plate having a plate thickness of, for example, 80 to 100 mm with a reduction ratio of 50% or more in finish rolling.
- the starting temperature of finish rolling on the surface is set to Ar 3 point to 740° C.
- the finish rolling is a rolling process performed by a finish rolling mill, and rough rolling may be performed before the finish rolling to adjust the plate thickness at the start of the finish rolling.
- the reduction ratio means the reduction ratio of the cumulative in finish rolling, the thickness of the finish rolling start t 0, when the sheet thickness after the finish rolling completing (product thickness) and t, (t 0 - It can be calculated by t)/t 0 ⁇ 100.
- the austenite grains may not be sufficiently stretched, resulting in insufficient grain refinement.
- the rolling reduction is preferably 55% or more, more preferably 60% or more.
- the upper limit of the rolling reduction is not particularly limited, but if the rolling reduction exceeds 75%, the number of rolling passes increases and the productivity decreases, so the rolling reduction is preferably 75% or less.
- the starting temperature of finish rolling on the surface is less than Ar 3 point, coarse processed ferrite that is elongated in the rolling direction is generated in the vicinity of the surface layer portion, and the brittle crack propagation stopping property may be deteriorated.
- the temperature exceeds 740° C. the ledges formed in the austenite grain boundaries or the dislocations introduced into the austenite and the deformation zone become insufficient, the number density of fine crystal grains decreases, and the brittle crack propagation arresting property deteriorates.
- the surface temperature at the start of finish rolling is set to Ar 3 point to 740° C. From the viewpoint of suppressing the formation of work ferrite, the surface temperature at the start of finish rolling is preferably above Ar 3 points +30°C.
- the surface temperature at the start of finish rolling is preferably 720°C or lower.
- the austenite in order to reduce the grain size of the steel sheet, rolling is carried out at the lowest possible temperature below the non-recrystallization temperature range.
- the austenite can be stretched in a non-recrystallized state, and the density of the former austenite grain boundaries, which becomes the nucleation site of ferrite, can be increased, and at the same time, ledges (stepwise unevenness) are formed in the austenite grain boundaries.
- ledges stepwise unevenness
- dislocations and deformation zones that become ferrite nucleation sites are also introduced into the austenite grains.
- the ferrite itself is fine, and bainite can be finely divided, so that the crystal grain size can be made finer.
- the finish rolling start temperature at the 1/4 position of the plate thickness is set to 800°C or lower.
- the finish rolling start temperature at the 1/4 position of the plate thickness exceeds 800°C, the ledges formed at the austenite grain boundaries in that part or the dislocations and deformation zones introduced into the austenite become insufficient and the grain size becomes coarse. Will turn into.
- the preferable finish rolling start temperature at the 1/4 position of the plate thickness is 760°C or lower.
- the lower limit is Ar 3 points, but normally the temperature at the 1/4 position of the plate thickness does not fall below the surface temperature, and there is no problem if the surface temperature is controlled to be Ar 3 points or higher.
- the temperature of the surface of the steel sheet can be reduced by descaling (the step of spraying high-pressure water on the steel sheet to remove the scale), but the temperature inside the sheet has little effect of descaling, and It strongly depends on the time elapsed from the heat extraction to the start of rolling. Therefore, in order to satisfy both the surface temperature and the temperature inside the plate thickness, it is necessary to perform an operation in which both descaling and elapsed time are properly controlled.
- the starting temperature of finish rolling is 3 points or more of Ar
- coarse work ferrite formation can be suppressed, and the austenite grains can be stretched to increase the austenite grain boundary density, which becomes the nucleation site of ferrite
- rapid cooling water cooling in a continuous cooling process (CLC: Continuous on Line Control Process)
- bainite is used as a main phase, A structure in which fine ferrite is dispersed can be formed.
- cooling After the hot rolling is completed, cooling is started at a surface temperature of 3 points or more of Ar, the cooling rate at a position 5 mm deep from the surface is set to 25.0° C./s or more, and the cooling is performed at a surface temperature of 400° C. or less. finish.
- the cooling start temperature is lower than Ar 3 point, coarse ferrite is generated before the start of cooling, and the crystal grain size cannot be reduced.
- a cooling rate of 25.0° C./s or more is required at a depth of 5 mm from the surface.
- the cooling stop temperature is set to 400° C. or lower.
- tempering Further, it is desirable to perform tempering heat treatment at a temperature of 400 to 600° C. after cooling to adjust the strength and toughness of the steel sheet. If the tempering temperature exceeds 600°C, the strength decreases. On the other hand, if the temperature is less than 400°C, the improvement in toughness due to strain removal is insufficient.
- the steel sheet thus manufactured can have a yield stress of 400 to 580 MPa and a tensile strength of 510 to 750 MPa.
- the manufacturing method of the welded structure is also not particularly limited, but for example, welding is performed along the end surface of the above-mentioned joined member with the end surface of the joined member abutting against each other. It can be manufactured by At this time, it is desirable that the joining member side of the joining member be groove processed. The groove processing may be performed over the entire end surface of the joining member, or may be performed only at the joining portion with the joined member.
- the welding method is also not particularly limited, and a known method such as CO 2 welding or covered arc welding (SMAW) may be adopted.
- SMAW covered arc welding
- the No. 4 tensile test piece described in JIS Z 2241 was sampled in a direction perpendicular to the rolling direction from the 1/4 position of the thickness of each steel sheet obtained, and a tensile test was performed in accordance with JIS Z 2241 to yield stress. (YS), tensile strength (TS) and total elongation (EL) were measured. The results are also shown in Table 2.
- the manufactured steel plate was used as a test plate (bonding member 11), and the structural model arrest test body shown in FIG. 5 was produced and tested.
- a welded joint in which a steel plate having a plate thickness of 100 mm was joined by CO 2 welding was used as a run-up welding joint (joined member 12), and the welded structure 10 was produced by CO 2 welding or covered arc welding (SMAW) under the conditions shown in Table 3. ..
- the notch 16b was introduced into the fusion line portion 16a of the welded structure 10. Then, the welded structure 10 is cooled to a ship design temperature of ⁇ 10° C., a test stress of 257 MPa corresponding to the design stress of EH40 is applied, and only the vicinity of the notch is rapidly cooled to about ⁇ 50° C. An impact was applied through the wedge to generate and propagate a brittle crack.
- the area of 500 ⁇ m ⁇ 500 ⁇ m was measured by 0.5 ⁇ m pitch by the EBSP method. Then, a boundary having a crystal orientation difference of 15° or more with an adjacent grain is defined as a grain boundary, and a GAM value which is an average value of misorientation between adjacent measurement points in the crystal grain is obtained.
- the crystal grain of was defined as a ferrite phase, and the average value of the area ratio of the ferrite phase at each position was obtained. Further, a grain boundary map having a crystal orientation difference of 15° or more with adjacent grains was created, and the equivalent circle diameter of the crystal grains at that time was determined by image analysis.
- each test piece was subjected to nital corrosion, the microstructure was photographed at each depth position with a magnification of 500 times with an optical microscope, and the massive region visually recognized in black was defined as a pearlite phase. The average value of the area ratio of the pearlite phase with respect to the entire visual field region measured at the position was obtained.
- each test piece was subjected to repeller corrosion, the microstructure was photographed at each depth position with a magnification of 500 times with an optical microscope, and the white visible region was defined as an island martensite phase.
- the average value of the area ratio of the island martensite phase with respect to the entire visual field region measured at the position was calculated.
- the area ratios of the ferrite phase, pearlite phase, and island martensite phase were obtained, and the value obtained by subtracting the sum thereof from 100% was taken as the area ratio of the bainite phase.
- Table 4 shows the average crystal grain size at each depth position and the phase fraction (area%) of each structure. Table 4 also shows the results of the test using the above structural model arrest specimen. When the brittle crack stopped at the test plate, it was judged as stopped, and when the test plate was broken, it was judged as broken.
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Abstract
Description
前記接合部材は、前記接合部材の板厚方向に垂直な第1表面および第2表面を有し、
前記接合部材の板厚t(mm)が、下記(i)式を満足し、
前記第1表面側に形成された第1溶接部の第1熱影響部の最頂点と前記第1表面との前記接合部材の板厚方向の距離を距離h1(mm)とし、前記第2表面側に形成された第2溶接部の第2熱影響部の最頂点と前記第2表面との前記接合部材の板厚方向の距離を距離h2(mm)とした時に、
前記接合部材の、前記第1表面から前記板厚方向に2mmの深さ位置、前記第2表面から前記板厚方向に2mmの深さ位置、前記距離h1が2mmを超える場合には、前記第1表面から前記板厚方向にh1(mm)の深さ位置、および前記距離h2が2mmを超える場合には、前記第2表面から前記板厚方向にh2(mm)の深さ位置における金属組織が、
面積%で、ベイナイト:70~95%、およびフェライト:5~30%を含有し、かつ、
平均結晶粒径が12.0μm以下である、
溶接構造体。
t≧50.0 ・・・(i)
上記(1)に記載の溶接構造体。
h1≦t/4 ・・・(ii)
h2≦t/4 ・・・(iii)
前記第1溶接部における、前記接合部材側の止端とルートとを通る線と前記被接合面とがなす鋭角α1(°)、前記板厚方向における継手の部分溶込みd1(mm)および前記被接合部材側の止端と前記第1表面との距離s1(mm)、ならびに、前記第2溶接部における、前記接合部材側の止端とルートとを通る線と前記被接合面とがなす鋭角α2(°)、前記板厚方向における継手の部分溶込みd2(mm)および前記被接合部材側の止端と前記第2表面との距離s2(mm)が、下記(iv)~(ix)式を満足する、
上記(1)または(2)に記載の溶接構造体。
45.0≦α1≦70.0 ・・・(iv)
45.0≦α2≦70.0 ・・・(v)
d1・sec(α1)・cos(α1/2)≧0.35t ・・・(vi)
d2・sec(α2)・cos(α2/2)≧0.35t ・・・(vii)
s1≧d1(sec(α1)-1) ・・・(viii)
s2≧d2(sec(α2)-1) ・・・(ix)
C:0.030~0.100%、
Si:0.01~0.30%、
Mn:1.40~2.50%、
P:0.015%以下、
S:0.0100%以下、
Nb:0.005~0.030%、
Ti:0.005~0.030%、
N:0.0005~0.0050%、
Al:0.001~0.080%、
Cu:0.10~0.50%、
Ni:0.15~2.00%、
Cr:0~0.50%、
Mo:0~0.50%、
V:0~0.100%、
B:0~0.0030%、
Ca:0~0.0050%、
Mg:0~0.0050%、
REM:0~0.0050%、
残部:Feおよび不純物であり、
下記(x)式で表わされるAr3が600~740である、
上記(1)から(3)までのいずれかに記載の溶接構造体。
Ar3=940-310×C+40×Si-90×Mn-40×Cu-60×Ni-15×Cr-80×Mo ・・・(x)
但し、上記式中の元素記号は各元素の含有量(質量%)を表す。
上記(1)から(4)までのいずれかに記載の溶接構造体。
t>80.0 ・・・(xi)
上記(1)から(5)までのいずれかに記載の溶接構造体。
図1は、本発明の一実施形態に係る溶接構造体を示す斜視図である。図1に示すように、本実施形態に係る溶接構造体10は、接合部材11および被接合部材12を備えている。接合部材11は板状であり、板厚方向に垂直な第1表面11aおよび第2表面11bを有する。また、被接合部材12は板状であり、接合部材11の端面11cが当接される被接合面12aを有する。
t≧50.0 ・・・(i)
t>80.0 ・・・(xi)
h1≦t/4 ・・・(ii)
h2≦t/4 ・・・(iii)
45.0≦α1≦70.0 ・・・(iv)
45.0≦α2≦70.0 ・・・(v)
d1・sec(α1)・cos(α1/2)≧0.35t ・・・(vi)
d2・sec(α2)・cos(α2/2)≧0.35t ・・・(vii)
s1≧d1(sec(α1)-1) ・・・(viii)
s2≧d2(sec(α2)-1) ・・・(ix)
上述のように、接合部材の全厚にわたって脆性き裂伝播停止特性を向上させるためには、例えば、Kca値が8000N/mm1.5以上の鋼板を接合部材として用いる必要があり、そのような特性を有する鋼板の確保が困難であるという問題がある。しかしながら、少なくとも接合部材のき裂が突入する領域の脆性き裂伝播停止特性を向上させれば、き裂の進展を停止することが可能になる。
フェライト:5~30%
上記の深さ位置においてベイナイトを主相とする理由は、接合部材の強度を確保するためである。フェライトが主相では、高い強度を確保することが困難である。ただし、全てがベイナイトでは、靭性が大きく劣化してしまうため、第二相としてフェライトを含有することで靭性の劣化を抑制している。
被接合部材からのき裂の突入部分である上記の深さ位置において、細粒な組織とすることによって、き裂の進展を停止することが可能になる。ここで、本発明においては、結晶方位差が15°以上の境界を結晶粒界と定義し、当該結晶粒界によって囲まれた領域の円相当直径を結晶粒径と定義する。
本発明の溶接構造体に用いられる接合部材の化学組成については特に限定されないが、優れた脆性き裂伝播停止特性を発揮するためには、以下に示す化学組成を有することが好ましい。各元素の限定理由は下記のとおりである。なお、以下の説明において含有量についての「%」は、「質量%」を意味する。
Cは、焼入れ性向上により鋼板の強度と靭性を確保する作用を有する元素である。この効果を得るため、C含有量を0.030%以上とするのが好ましい。一方、C含有量が0.100%を超えると溶接性および継手靭性(HAZ靭性)が低下するおそれがある。そのため、C含有量は0.030~0.100%とするのが好ましい。C含有量は0.060%以上であるのがより好ましく、0.090%以下であるのがより好ましい。
Siは、脱酸元素および強化元素として有効な元素である。この効果を得るため、Si含有量を0.01%以上とするのが好ましい。一方、Si含有量が0.30%を超えると継手靭性が低下し、また、Ar3点が過剰に上昇するおそれがある。そのため、Si含有量は0.01~0.30%とするのが好ましい。Si含有量は0.10%以下であるのがより好ましい。
Mnは鋼板の強度を確保し、また、Ar3点を低下させる作用を有する元素である。この効果を得るため、Mn含有量を1.40%以上とするのが好ましい。一方、Mn含有量が2.50%を超えると溶接性および継手靭性が低下するおそれがある。そのため、Mn含有量は1.40~2.50%とするのが好ましい。Mn含有量は1.50%以上であるのがより好ましく、2.00%以下であるのがより好ましい。
Pは、不純物元素であり、溶接性および継手靭性を低下させるため、その含有量を0.015%以下に低減するのが好ましい。P含有量は0.010%以下であるのがより好ましい。
Sは、不純物元素であり、MnS生成による靭性の低下、溶接性の低下を招くため、その含有量を0.0100%以下に低減するのが好ましい。S含有量は0.0050%以下であるのがより好ましい。
Nbは、再結晶温度を抑制し、組織細粒化へ寄与し、鋼板の強度を上昇させる作用を有する元素である。この効果を得るため、Nb含有量を0.005%以上とするのが好ましい。一方、Nb含有量が0.030%を超えると溶接性が低下するおそれがある。そのため、Nb含有量は0.005~0.030%とするのが好ましい。Nb含有量は0.008%以上であるのがより好ましく、0.015%以下であるのがより好ましい。
Tiは、TiNを形成し、TiNを微細分散にさせることより鋼板の靭性と継手靭性を向上させる作用を有する元素である。この効果を得るため、Ti含有量を0.005%以上とするのが好ましい。一方、Ti含有量が0.030%を超えると鋼板の靭性および継手靭性が低下するおそれがある。そのため、Ti含有量は0.005~0.030%とするのが好ましい。Ti含有量は0.008%以上であるのがより好ましく、0.015%以下であるのがより好ましい。
Nは、鋼材中にTiNを形成させることより鋼板の靭性および継手靭性を向上させる作用を有する元素である。この効果を得るため、N含有量を0.0005%以上とするのが好ましい。一方、スラブ疵の抑制のため、N含有量を0.0050%以下とするのが好ましい。N含有量は0.0020%以上であるのがより好ましく、0.0040%以下であるのがより好ましい。
Alは、脱酸を担い、不純物元素であるOを低減する作用を有する元素である。また、鋼中のフリーNをAlNとし無害化する。この効果を得るため、Al含有量を0.001%以上とするのが好ましい。一方、Al含有量が0.080%を超えると、継手靭性が低下するおそれがある。そのため、Al含有量は0.001~0.080%とするのが好ましい。Al含有量は0.010%以上であるのがより好ましく、0.040%以下であるのがより好ましい。
Cuは、強度を向上させ、また、Ar3点を低下させる作用を有する元素である。この効果を得るため、Cu含有量を0.10%以上とするのが好ましい。一方、Cu含有量が0.50%を超えると溶接性および継手靭性が低下するおそれがある。そのため、Cu含有量は0.10~0.50%とするのが好ましい。Cu含有量は0.20%以上であるのがより好ましい。
Niは、強度を向上させ、また、Ar3点を低下させる作用を有する元素である。この効果を得るため、Ni含有量を0.15%以上とするのが好ましい。一方、Ni含有量が2.00%を超えると溶接性および継手靭性が低下するおそれがある。また、Niは高価であり過剰な添加はコスト高を招く。そのため、Ni含有量は0.15~2.00%とするのが好ましい。Ni含有量は0.30%以上であるのがより好ましく、1.00%以下であるのがより好ましい。
Crは、鋼板の強度を上昇させる効果を有するため、必要に応じて含有させてもよい。しかしながら、その含有量が0.50%を超えると溶接性および継手靭性が低下するおそれがある。そのため、Cr含有量は0.50%以下であるのが好ましく、0.20%以下であるのがより好ましい。上記の効果を得たい場合には、Cr含有量は0.10%以上であるのが好ましい。
Moは、Bとの複合効果により焼入れ性を向上させ、鋼板の強度を上昇させる効果を有するため、必要に応じて含有させてもよい。しかしながら、その含有量が0.50%を超えると鋼板の靭性および継手靭性が低下するおそれがある。そのため、Mo含有量は0.50%以下であるのが好ましく、0.40%以下であるのがより好ましく、0.30%以下であるのがさらに好ましく、0.25%以下であるのが特に好ましい。上記の効果を得たい場合には、Mo含有量は0.03%以上であるのが好ましく、0.05%以上であるのがより好ましく、0.08%以上であるのがさらに好ましい。
Vは、析出強化による強度上昇の効果を有するため、必要に応じて含有させてもよい。しかしながら、その含有量が0.100%を超えると継手靭性が低下するおそれがある。そのため、V含有量は0.100%以下であるのが好ましく、0.050%以下であるのがより好ましい。上記の効果を得たい場合には、V含有量は0.020%以上であるのが好ましい。
Bは、焼入れ性向上により鋼板の強度を上昇させる効果を有するため、必要に応じて含有させてもよい。しかしながら、その含有量が0.0030%を超えると靭性および溶接性が低下するおそれがある。そのため、B含有量は0.0030%以下であるのが好ましく、0.0020%以下であるのがより好ましい。上記の効果を得たい場合には、B含有量は0.0005%以上であるのが好ましく、0.0010%以上であるのがより好ましい。
Caは、継手靭性を向上させる効果を有するため、必要に応じて含有させてもよい。しかしながら、その含有量が0.0050%を超えると継手靭性が低下するおそれがある。そのため、Ca含有量は0.0050%以下であるのが好ましく、0.0030%以下であるのがより好ましい。上記の効果を得たい場合には、Ca含有量は0.0003%以上であるのが好ましい。
Mgは、MgSを形成し、母材組織の細粒化および継手靭性の向上に寄与するため、必要に応じて含有させてもよい。しかしながら、その含有量が0.0050%を超えると継手靭性が低下するおそれがある。そのため、Mg含有量は0.0050%以下であるのが好ましく、0.0030%以下であるのがより好ましい。上記の効果を得たい場合には、Mg含有量は0.0003%以上であるのが好ましい。
REM(希土類元素)は、継手靭性を向上させる効果を有するため、必要に応じて含有させてもよい。しかしながら、その含有量が0.0050%を超えると継手靭性が低下するおそれがある。そのため、REM含有量は0.0050%以下であるのが好ましく、0.0030%以下であるのがより好ましい。上記の効果を得たい場合には、REM含有量は0.0003%以上であるのが好ましい。
Ar3=940-310×C+40×Si-90×Mn-40×Cu-60×Ni-15×Cr-80×Mo ・・・(x)
但し、上記式中の元素記号は各元素の含有量(質量%)を表す。
本発明の溶接構造体に用いられる接合部材の機械的特性についても特に制限は設けない。しかし、溶接構造体をコンテナ船等において利用する場合においては、接合部材の降伏応力は400~580MPaであるのが好ましく、引張強さが510~750MPaであるのが好ましい。
接合部材の製造方法について、特に制限は設けないが、例えば以下に示す手順により、接合部材として用いられる鋼板を製造することができる。
まず、鋳造時の冷却途中または冷却後に鋼片を950~1100℃に加熱し、オーステナイト単相化する。加熱抽出温度が950℃未満ではオーステナイト化が不十分となり粗大組織を形成するおそれがある。一方、1100℃超ではオーステナイト粒が粗大化して、結晶粒径を微細化することができない場合がある。
加熱抽出された鋼片に熱間圧延を行い、仕上げ圧延における圧下率を50%以上として、板厚が例えば80~100mmの鋼板を製造する。この時、表面における仕上げ圧延の開始温度をAr3点~740℃とする。なお、仕上げ圧延とは、仕上げ圧延機で行う圧延工程であり、仕上げ圧延の前に粗圧延を行い、仕上げ圧延開始時の板厚を調整してもよい。また、圧下率とは、仕上げ圧延中の累積の圧下率を意味し、仕上げ圧延開始時の板厚をt0、仕上げ圧延完了後の板厚(製品厚)をtとすると、(t0-t)/t0×100により計算することができる。
熱間圧延の終了後、Ar3点以上の表面温度で冷却を開始して、表面から深さ5mmの位置における冷却速度を25.0℃/s以上とし、400℃以下の表面温度で冷却を終了する。冷却の開始温度がAr3点未満では、冷却開始前に粗大なフェライトが生成し、結晶粒径を微細化することができない。ベイナイトを微細化させるためには冷却速度を大きくしてできるだけ低温で変態させる必要があり、そのためには表面から深さ5mmの位置で25.0℃/s以上の冷却速度が必要である。また、十分なベイナイト組織を得るために、冷却停止温度を400℃以下とする。
また、冷却後に400~600℃の温度で焼戻し熱処理を行い、鋼板の強度および靭性を調節することが望ましい。焼戻しの温度が600℃を超えると強度が低下する。一方、400℃未満ではひずみ除去による靭性改善が不十分である。
溶接構造体の製造方法についても、特に制限は設けないが、例えば、上述の被接合部材の被接合面に接合部材の端面を突き合わせた状態で、端面に沿って溶接することで製造することができる。この際、接合部材の被接合部材側を開先加工しておくことが望ましい。開先加工は、接合部材の端面全体にわたって施してもよいが、被接合部材との接合箇所にのみ施してもよい。
11 接合部材
11a 第1表面
11b 第2表面
11c 端面
11d~i 仮想的な面
12 被接合部材
12a 被接合面
13a 第1溶接部
13b 第2溶接部
14a 第1溶接金属
14b 第2溶接金属
15a 第1熱影響部
15b 第2熱影響部
16a フュージョンライン部
16b ノッチ
Claims (6)
- 板状の接合部材の端面が板状の被接合部材の被接合面に当接した状態で、前記接合部材が前記被接合部材に両側部分溶込み溶接されたT継手部を有する溶接構造体であって、
前記接合部材は、前記接合部材の板厚方向に垂直な第1表面および第2表面を有し、
前記接合部材の板厚t(mm)が、下記(i)式を満足し、
前記第1表面側に形成された第1溶接部の第1熱影響部の最頂点と前記第1表面との前記接合部材の板厚方向の距離を距離h1(mm)とし、前記第2表面側に形成された第2溶接部の第2熱影響部の最頂点と前記第2表面との前記接合部材の板厚方向の距離を距離h2(mm)とした時に、
前記接合部材の、前記第1表面から前記板厚方向に2mmの深さ位置、前記第2表面から前記板厚方向に2mmの深さ位置、前記距離h1が2mmを超える場合には、前記第1表面から前記板厚方向にh1(mm)の深さ位置、および前記距離h2が2mmを超える場合には、前記第2表面から前記板厚方向にh2(mm)の深さ位置における金属組織が、
面積%で、ベイナイト:70~95%、およびフェライト:5~30%を含有し、かつ、
平均結晶粒径が12.0μm以下である、
溶接構造体。
t≧50.0 ・・・(i) - 前記接合部材の板厚t(mm)、前記距離h1(mm)および前記距離h2(mm)が、下記(ii)式および(iii)式を満足する、
請求項1に記載の溶接構造体。
h1≦t/4 ・・・(ii)
h2≦t/4 ・・・(iii) - 前記第1表面および前記被接合面に垂直な断面において、
前記第1溶接部における、前記接合部材側の止端とルートとを通る線と前記被接合面とがなす鋭角α1(°)、前記板厚方向における継手の部分溶込みd1(mm)および前記被接合部材側の止端と前記第1表面との距離s1(mm)、ならびに、前記第2溶接部における、前記接合部材側の止端とルートとを通る線と前記被接合面とがなす鋭角α2(°)、前記板厚方向における継手の部分溶込みd2(mm)および前記被接合部材側の止端と前記第2表面との距離s2(mm)が、下記(iv)~(ix)式を満足する、
請求項1または請求項2に記載の溶接構造体。
45.0≦α1≦70.0 ・・・(iv)
45.0≦α2≦70.0 ・・・(v)
d1・sec(α1)・cos(α1/2)≧0.35t ・・・(vi)
d2・sec(α2)・cos(α2/2)≧0.35t ・・・(vii)
s1≧d1(sec(α1)-1) ・・・(viii)
s2≧d2(sec(α2)-1) ・・・(ix) - 前記接合部材の化学組成が、質量%で、
C:0.030~0.100%、
Si:0.01~0.30%、
Mn:1.40~2.50%、
P:0.015%以下、
S:0.0100%以下、
Nb:0.005~0.030%、
Ti:0.005~0.030%、
N:0.0005~0.0050%、
Al:0.001~0.080%、
Cu:0.10~0.50%、
Ni:0.15~2.00%、
Cr:0~0.50%、
Mo:0~0.50%、
V:0~0.100%、
B:0~0.0030%、
Ca:0~0.0050%、
Mg:0~0.0050%、
REM:0~0.0050%、
残部:Feおよび不純物であり、
下記(x)式で表わされるAr3が600~740である、
請求項1から請求項3までのいずれかに記載の溶接構造体。
Ar3=940-310×C+40×Si-90×Mn-40×Cu-60×Ni-15×Cr-80×Mo ・・・(x)
但し、上記式中の元素記号は各元素の含有量(質量%)を表す。 - 前記接合部材の板厚t(mm)が下記(xi)式を満足する、
請求項1から請求項4までのいずれかに記載の溶接構造体。
t>80.0 ・・・(xi) - 前記接合部材の降伏応力が400~580MPaであり、引張強さが510~750MPaである、
請求項1から請求項5までのいずれかに記載の溶接構造体。
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JP2013129885A (ja) * | 2011-12-22 | 2013-07-04 | Jfe Steel Corp | 脆性亀裂伝播停止特性に優れた高強度厚鋼板の製造方法 |
JP2018039052A (ja) * | 2015-03-12 | 2018-03-15 | Jfeスチール株式会社 | 溶接構造体 |
JP2018069323A (ja) * | 2016-11-02 | 2018-05-10 | 新日鐵住金株式会社 | 溶接継手の作製方法、および溶接継手の改修方法 |
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