WO2024053669A1 - Joint soudé - Google Patents

Joint soudé Download PDF

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Publication number
WO2024053669A1
WO2024053669A1 PCT/JP2023/032519 JP2023032519W WO2024053669A1 WO 2024053669 A1 WO2024053669 A1 WO 2024053669A1 JP 2023032519 W JP2023032519 W JP 2023032519W WO 2024053669 A1 WO2024053669 A1 WO 2024053669A1
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WIPO (PCT)
Prior art keywords
steel plate
less
base steel
welded joint
plating layer
Prior art date
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PCT/JP2023/032519
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English (en)
Japanese (ja)
Inventor
卓哉 光延
卓史 横山
浩史 竹林
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日本製鉄株式会社
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Publication of WO2024053669A1 publication Critical patent/WO2024053669A1/fr

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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
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/10—Spot welding; Stitch welding
    • B23K11/11—Spot welding
    • 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
    • B23K11/00—Resistance welding; Severing by resistance heating
    • B23K11/16—Resistance welding; Severing by resistance heating taking account of the properties of the material to be welded
    • 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
    • C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
    • C21D3/02—Extraction of non-metals
    • C21D3/04—Decarburising
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C18/00—Alloys based on zinc
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C18/00—Alloys based on zinc
    • C22C18/04—Alloys based on zinc with aluminium as the next major constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon

Definitions

  • the present invention relates to a welded joint. More specifically, the present invention relates to a welded joint that suppresses LME cracking during manufacturing.
  • LME cracking is thought to occur when the surface layer of the steel plate transforms into austenite during welding, molten zinc intrudes into the grain boundaries and embrittles the steel plate, and furthermore, tensile stress is applied to the steel plate during welding.
  • Non-Patent Document 1 it is known that ferrite phase grain boundaries have lower LME susceptibility than austenite grain boundaries with respect to LME cracking.
  • Patent Document 2 discloses that, as a steel sheet that suppresses LME cracking and improves weldability, Si oxide particles with a particle size of 20 nm or more are contained in a number density of 3000 to 6000 pieces/mm 2 in the surface layer of the steel sheet. A steel sheet having a grain size distribution is disclosed.
  • the present inventors have diligently studied means for solving the above problems. As a result, by containing a large amount of Si and Al in the steel plate to be spot welded and subjecting the steel plate to an appropriate surface condition and subjecting it to high dew point annealing, the area around the weld is decarburized and the ferrite ( ⁇ ) phase is stabilized. It was discovered that LME can be suppressed by covering the surface layer of a steel plate with a ferrite phase with a low solid solution amount of C, and by maintaining the ferrite phase in a stable state even during the production of welded joints.
  • the present invention has been made based on the above findings and further studies, and the gist thereof is as follows.
  • a plurality of superimposed steel plates a nugget that joins the plurality of steel plates, a spot weld having a pressure weld and a heat affected zone formed around the nugget, and a separation formed around the pressure weld.
  • one or more of the plurality of steel plates is a plated steel plate including a base steel plate and a plating layer, and the plating layer is at least on the overlapping surface of the plurality of steel plates.
  • the plated steel sheet is formed on the corresponding surface and contains Zn, the tensile strength of the plated steel sheet is 780 MPa or more, and the chemical composition of the base steel sheet is C: 0.05 to 0.40% in mass%.
  • Si 0.7 to 3.0%
  • Mn 0.1 to 5.0%
  • sol. Al 0.7-2.0%
  • P 0.0300% or less
  • S 0.0300% or less
  • N 0.0100% or less
  • B 0-0.010%
  • the total content of Al is 1.8% or more, and in the non-heat-affected zone of the welded joint, the base steel plate starts from the interface between the plating layer of the plated steel plate and the base steel plate.
  • the depth at which the C concentration measured by GDS is 0.05% or less is 10 ⁇ m or more, and the roughness of the interface between the plating layer of the plated steel sheet and the base steel sheet is Ra 3. 0 ⁇ m or less, and at a position 500 ⁇ m outward from the end of the press-welded portion, a ferrite phase is formed in the depth direction of the base steel plate starting from the interface between the plating layer of the plated steel plate and the base steel plate.
  • a welded joint characterized in that the layer having an area ratio of 90% or more has a thickness of 15 ⁇ m or more.
  • the C concentration measured by GDS in the depth direction of the base steel plate starting from the interface between the plating layer of the plated steel plate and the base steel plate is 0.
  • the C concentration measured by GDS in the depth direction of the base steel plate starting from the interface between the plating layer of the plated steel plate and the base steel plate is 0. .05% or less
  • the base material has a depth of 15 ⁇ m or more, and is located at a position 500 ⁇ m outward from the end of the press-welded portion, starting from the interface between the plating layer of the plated steel sheet and the base steel sheet.
  • the roughness of the interface between the plating layer of the plated steel sheet and the base steel sheet in the non-heat affected zone is 2.0 ⁇ m or less in terms of Ra. Any welded fittings.
  • FIG. 1 is a diagram schematically showing an example of a welded joint of the present invention.
  • FIG. 3 is a diagram showing a layered ferrite ( ⁇ ) phase formed around a welded portion of a welded joint of the present invention. It is a figure explaining LME resistance evaluation in an example.
  • the present invention will be explained below.
  • the present invention is not limited to the following embodiments.
  • First, an outline of improving the LME resistance during manufacturing in the welded joint of the present invention will be explained.
  • LME cracking occurs when the surface layer of a steel plate is heated during spot welding, the steel plate structure in the surface layer transforms into austenite, and the grain boundaries become brittle as hot-dip plating enters the steel plate structure along the austenite grain boundaries. It is caused by doing. It is thought that LME cracking occurs because tensile stress is applied to the steel plate during welding.
  • the welded joint of the present invention improves LME resistance during manufacture of the welded joint due to the structure formed on the surface layer of the steel plate. Note that in this specification, the surface layer of a steel plate refers to the range from the outermost surface of the steel plate to a depth of 100 ⁇ m.
  • the C element is contained in the surface layer of a steel sheet, LME cracking is likely to occur, so keeping the C concentration in the surface layer of the steel sheet low is effective in preventing LME cracking.
  • the C concentration measured by GDS is measured in the depth direction of the base metal starting from the interface between the plating layer of the plated steel plate constituting the welded joint and the base steel plate.
  • a strong strain is applied to the surface layer of the base steel plate without increasing the surface roughness, and the steel plate is annealed at a high dew point. This allows oxygen to diffuse into the steel sheet and form internal oxides, making it possible to suppress the formation of external oxides. This reduces the C concentration in the surface layer of the base steel plate.
  • the area of the ferrite phase is The thickness of the layer with a ratio of 90% or more is 15 ⁇ m or more. That is, the ferrite phase stably exists even around the heat affected zone.
  • the term "heat affected zone” refers to an unmolten part of a steel plate whose structure, metallurgical properties, mechanical properties, etc. have changed due to welding heat. The heat affected zone can be confirmed by observing a cross section in the plate thickness direction using an SEM. Note that the "non-heat-affected zone” refers to a portion other than the heat-affected zone. Furthermore, Si and sol. It is thought that the effect of adding Al in combination can stabilize ferrite.
  • the welded joint of the present invention has Si and sol. Due to the combined effects of high Al content, applying strain to the surface layer before annealing, and controlling the dew point during annealing, the surface layer of the plated steel sheet has a low C concentration even when affected by the heat from welding, and furthermore, ferrite By forming a layer with a high area ratio of , it is possible to improve the LME resistance during the manufacture of welded joints.
  • the welded joint of the present invention is manufactured by spot-welding a plurality (two in FIG. 1) of steel plates 1 using a welding electrode A, as shown in FIG. 1(a). An overlapping surface 6 is formed on the surface where the plurality of steel plates 1 are in contact with each other.
  • Figure 1(b) shows a welded joint in which two steel plates are welded together by spot welding.
  • the welded joint of the present invention includes a plurality of superimposed steel plates 1 and a nugget 2 that joins the plurality of steel plates.
  • the nugget 2 is a portion where steel components and plating layer components are melted and solidified by spot welding.
  • a pressure welding portion 3 is formed around the nugget 2, in which two steel plates 1 are pressed together.
  • a separation portion 4 exists around the pressure contact portion 3 .
  • the separation portion 4 is a portion where welding or pressure welding by spot welding has not occurred, and is a portion where the two steel plates 1 are not in direct contact.
  • end of the press-contact portion refers to the position of the press-contact portion 3 that is closest to the separation portion 4 .
  • the term “outside” from the end of the pressure contact portion refers to the direction from the end of the pressure contact portion 3 toward the open portion of the separation portion 4 .
  • a heat affected zone 5 is formed in which the structure, metallurgical properties, mechanical properties, etc. have changed due to the welding heat.
  • the plurality of steel plates constituting the welded joint of the present invention may include both a plated steel plate having a base steel plate and a plating layer, and a non-plated steel plate that is not plated, but one or more of the plurality of steel plates is a plated steel plate.
  • the plating layer is formed at least on a surface corresponding to the overlapping surface 6 of the steel plates.
  • the tensile strength of the plated steel sheet is 780 MPa or more.
  • LME cracking occurs when molten zinc plating is present on the surface of a high-strength (tensile strength of 780 MPa or more) steel plate during welding. Therefore, for example, when considering a welded joint made up of two steel plates, if one of the two steel plates is a high-strength plated steel plate, LME cracking may occur.
  • the welded joint of the present invention includes a high-strength plated steel plate in the steel plates constituting the welded joint, and can suppress LME cracking during manufacture of the welded joint.
  • C (carbon) is an element that ensures the strength of steel.
  • the C content was reduced to 0, taking into account the balance with weldability, and to prevent the C concentration in the surface layer of the base steel plate from becoming too high. .05 to 0.40%. If the C content is too large, the C concentration in the surface layer of the base steel sheet will not be reduced even by high dew point annealing, which will be described later.
  • the content of C may be 0.07% or more, 0.10% or more, or 0.12% or more.
  • the content of C may be 0.35% or less, 0.30% or less, or 0.25% or less.
  • Si Si: 0.7-3.0%, sol.Al: 0.7-2.0%, Si+sol.Al ⁇ 1.8%)
  • Si silicon
  • Al 0.7 to 2.0% is contained, and Si and sol.
  • the total value of Al content is 1.8% or more.
  • sol. Al refers to acid-soluble Al that is not converted into oxides such as Al 2 O 3 and is soluble in acids, and was measured by subtracting the insoluble residue on the filter paper that is generated during the Al analysis process. Required as Al.
  • the content of Si may be 0.8% or more, 0.9% or more, or 1.0% or more.
  • the content of Si may be 2.8% or less, 2.5% or less, or 2.0% or less.
  • the Al content may be 0.8% or more, 0.9% or more, or 1.0% or more. sol.
  • the Al content may be 1.8% or less, 1.6% or less, or 1.5% or less.
  • the total content of Al may be 1.9% or more, 2.0% or more, or 2.2% or more.
  • Mn manganese
  • Mn manganese
  • Mn content is set to 0.1 to 5.0%.
  • the Mn content may be 0.5% or more, 1.0% or more, or 1.5% or more.
  • the Mn content may be 4.5% or less, 4.0% or less, or 3.5% or less.
  • P 0.0300% or less
  • P phosphorus
  • the content of P may be 0.0200% or less, 0.0100% or less, or 0.0050% or less. It is preferable that P is not contained, and the lower limit of the P content is 0%. From the viewpoint of dephosphorization cost, the P content may be more than 0%, 0.0001% or more, or 0.0005% or more.
  • S sulfur
  • S is an impurity generally contained in steel. If the S content exceeds 0.0300%, weldability will decrease, and furthermore, the amount of MnS precipitated may increase, leading to a possibility that workability such as bendability will decrease. Therefore, the S content is set to 0.0300% or less.
  • the S content may be 0.0100% or less, 0.0050% or less, 0.0030% or less, 0.0020% or less, or 0.0010% or less. It is preferable that S is not contained, and the lower limit of the S content is 0%. From the viewpoint of desulfurization cost, the S content may be more than 0%, 0.0001% or more, or 0.0005% or more.
  • N nitrogen
  • nitrogen is an impurity generally contained in steel. If the N content exceeds 0.0100%, weldability may deteriorate. Therefore, the N content is set to 0.0100% or less.
  • the content of N may be 0.0080% or less, 0.0050% or less, 0.0030% or less, 0.0020% or less, or 0.0010% or less. It is preferable that N is not contained, and the lower limit of the N content is 0%. From the viewpoint of manufacturing cost, the N content may be more than 0%, 0.0001% or more, 0.0002% or more, 0.0003% or more, or 0.0005% or more.
  • B (boron) is an element that increases hardenability and contributes to improvement of strength, and also segregates at grain boundaries to strengthen grain boundaries and improve toughness, so it may be included as necessary. . Since B is not an essential element, the lower limit of the content of B is 0%. Although this effect can be obtained even when B is contained in a trace amount, it is preferable that the content of B is 0.0001% or more.
  • the content of B may be 0.0002% or more, 0.0003% or more, 0.0005% or more, 0.0007% or more, or 0.0010% or more.
  • the B content is set to 0.010% or less.
  • the content of B may be 0.0080% or less, 0.0060% or less, 0.0050% or less, 0.0040% or less, or 0.0030% or less.
  • Ti titanium
  • Ti titanium
  • Ti titanium
  • the lower limit of the content of Ti is 0%.
  • the content of Ti is preferably 0.0001% or more.
  • the content of Ti may be 0.0002% or more, 0.0003% or more, 0.0005% or more, 0.0007% or more, or 0.0010% or more.
  • coarse TiN may be generated and toughness may be impaired, so the content of Ti is set to 0.150% or less.
  • the Ti content is 0.1000% or less, 0.0500% or less, 0.0300% or less, 0.0200% or less, 0.0100% or less, 0.0050% or less, or 0.0030% or less. good.
  • Nb 0-0.150% Since Nb (niobium) is an element that contributes to improving strength through improving hardenability, it may be included as necessary. Since Nb is not an essential element, the lower limit of the content of Nb is 0%. Although this effect can be obtained even with a trace amount of Nb, the content of Nb is preferably 0.001% or more. The Nb content may be 0.002% or more, 0.003% or more, 0.005% or more, or 0.008% or more. On the other hand, from the viewpoint of ensuring sufficient toughness, the Nb content is set to 0.150% or less. The Nb content may be 0.100% or less, 0.060% or less, 0.050% or less, 0.040% or less, or 0.030% or less.
  • V vanadium
  • V vanadium
  • the lower limit of the content of V is 0%.
  • the content of V is set to 0.150% or less.
  • the V content may be 0.100% or less, 0.060% or less, 0.050% or less, 0.040% or less, 0.030% or less, or 0.020% or less.
  • Cr 0-2.00% Cr (chromium) is effective in improving the hardenability of steel and increasing the strength of steel, and therefore may be contained as necessary. Since Cr is not an essential element, the lower limit of the content of Cr is 0%. Although this effect can be obtained even with a trace amount of Cr, the content of Cr is preferably 0.001% or more. The content of Cr may be 0.01% or more, 0.02% or more, 0.03% or more, 0.05% or more, or 0.08% or more. On the other hand, if it is contained excessively, a large amount of Cr carbide will be formed, and the hardenability may be adversely affected, so the content of Cr is set to 2.00% or less. The Cr content is 1.80% or less, 1.50% or less, 1.20% or less, 1.00% or less, 0.70% or less, 0.50% or less, or 0.30% or less. good.
  • Ni nickel
  • Ni nickel
  • the lower limit of the Ni content is 0%.
  • the Ni content may be 0.01% or more, or 0.02% or more.
  • the Ni content is set to 2.00% or less.
  • the Ni content is 1.80% or less, 1.50% or less, 1.20% or less, 1.00% or less, 0.80% or less, 0.50% or less, 0.30% or less, 0.20 % or less, 0.10% or less, or 0.05% or less.
  • Cu (Cu: 0-2.00%) Cu (copper) is effective in improving the hardenability of steel and increasing the strength of steel, and therefore may be contained as necessary. Since Cu is not an essential element, the lower limit of the content of Cu is 0%. Although this effect can be obtained even with a trace amount of Cu, the content of Cu is preferably 0.0001% or more. The content of Cu may be 0.0002% or more, 0.0003% or more, or 0.0005% or more. On the other hand, from the viewpoint of suppressing a decrease in toughness and cracking of the slab after casting, the content of Cu is set to 2.00% or less.
  • the Cu content is 1.8000% or less, 1.5000% or less, 1.2000% or less, 1.0000% or less, 0.5000% or less, 0.1000% or less, 0.0500% or less, 0.0100 % or less, 0.0050% or less, 0.0030% or less, or 0.0020% or less.
  • Mo mobdenum
  • Mo mobdenum
  • the lower limit of the content of Mo is 0%.
  • the content of Mo is preferably 0.001% or more.
  • the Mo content may be 0.01% or more, 0.02% or more, 0.03% or more, 0.05% or more, or 0.08% or more.
  • the Mo content is set to 1.00% or less.
  • the Mo content may be 0.90% or less, 0.70% or less, 0.50% or less, or 0.30% or less.
  • W 0-1.00% W (tungsten) is effective in improving the hardenability of steel and increasing the strength of steel, and therefore may be included as necessary. Since W is not an essential element, the lower limit of the content of W is 0%. Although this effect can be obtained even when a small amount of W is included, it is preferable that the content of W is 0.001% or more. The content of W may be 0.002% or more, 0.005% or more, or 0.01% or more. On the other hand, from the viewpoint of suppressing a decrease in toughness, the content of W is set to 1.00% or less. The content of W is 0.90% or less, 0.70% or less, 0.50% or less, 0.30% or less, 0.10% or less, 0.05% or less, or 0.03% or less. good.
  • Ca (Ca: 0-0.100%)
  • Ca (calcium) is an element that contributes to control of inclusions, particularly fine dispersion of inclusions, and has the effect of increasing toughness, and therefore may be contained as necessary. Since Ca is not an essential element, the lower limit of the content of Ca is 0%. Although this effect can be obtained even with a trace amount of Ca, the content of Ca is preferably 0.0001% or more. The content of Ca may be 0.0002% or more. On the other hand, since excessive Ca content may cause deterioration of surface properties, the Ca content is set to 0.100% or less.
  • the content of Ca is 0.0800% or less, 0.0500% or less, 0.0100% or less, 0.0050% or less, 0.0030% or less, 0.0020% or less, 0.0010% or less, 0.0008 % or less, or 0.0005% or less.
  • Mg manganesium
  • Mg is an element that contributes to control of inclusions, particularly to fine dispersion of inclusions, and has the effect of increasing toughness, and therefore may be contained as necessary. Since Mg is not an essential element, the lower limit of the Mg content is 0%. Although this effect can be obtained even with a trace amount of Mg, it is preferable that the Mg content is 0.0001% or more.
  • the content of Mg may be 0.0002% or more, 0.0003% or more, 0.0005% or more, or 0.0008% or more.
  • the content of Mg is set to 0.100% or less.
  • the Mg content may be 0.090% or less, 0.080% or less, 0.050% or less, 0.010% or less, 0.005% or less, or 0.003% or less.
  • Zr zirconium
  • Zr zirconium
  • Zr zirconium
  • Zr zirconium
  • the content of Zr may be 0.002% or more, 0.003% or more, 0.005% or more, or 0.010% or more.
  • the Zr content is set to 0.100% or less.
  • the content of Zr may be 0.080% or less, 0.050% or less, 0.040% or less, or 0.030% or less.
  • Hf (hafnium) is an element that contributes to inclusion control, particularly fine dispersion of inclusions, and has the effect of increasing toughness, and therefore may be contained as necessary. Since it is not an essential element, the lower limit of the content of Hf is 0%. Although this effect can be obtained even with a trace amount of Hf, it is preferable that the Hf content is 0.0001% or more.
  • the Hf content may be 0.0002% or more, 0.0003% or more, 0.0005% or more, or 0.0008% or more.
  • the content of Hf is set to 0.100% or less.
  • the Hf content may be 0.050% or less, 0.030% or less, 0.010% or less, 0.005% or less, or 0.003% or less.
  • REM 0-0.100%
  • REM rare earth element
  • the lower limit of the content of REM is 0%.
  • the content of REM is preferably 0.0001% or more.
  • the content of REM may be 0.0003% or more, or 0.0005% or more.
  • the content of REM is set to 0.100% or less.
  • the content of REM may be 0.0500% or less, 0.0300% or less, 0.0100% or less, 0.0050% or less, 0.0030% or less, or 0.0020% or less.
  • REM is an abbreviation for Rare Earth Metal, and refers to an element belonging to the lanthanide series. REM is usually added as a misch metal.
  • the remainder other than the above chemical components consists of Fe and impurities.
  • impurities are components that are mixed in due to various factors in the manufacturing process, including raw materials such as ore and scrap when manufacturing steel sheets industrially, and are components that are mixed in due to various factors in the manufacturing process, including raw materials such as ore and scrap. It means a substance that does not have an adverse effect on LME resistance.
  • the chemical components of the base steel plate may be analyzed using elemental analysis methods known to those skilled in the art, such as inductively coupled plasma mass spectrometry (ICP-MS). However, C and S may be measured using the combustion-infrared absorption method, and N may be measured using the inert gas melting-thermal conductivity method. These analyzes may be performed using samples taken from the base steel plate using a method compliant with JIS G0417:1999.
  • ICP-MS inductively coupled plasma mass spectrometry
  • One or more of the plurality of steel plates constituting the welded joint of the present invention is a plated steel plate comprising a base steel plate and a plating layer.
  • the plating layer contains Zn. Further, the plating layer is formed on at least a surface corresponding to the overlapping surface of the plurality of steel plates.
  • the plating layer is not particularly limited as long as it contains Zn. As an example, Zn-0.2%Al, Zn-0.5%Al, Zn-1.5%Al-1.5%Mg, Zn-20%Al-7%Mg, Zn-30%Al-10 %Mg.
  • the plating layer may be formed on surfaces other than those corresponding to the overlapping surfaces of the plurality of steel plates.
  • the chemical composition of the plating layer is determined by dissolving the plating layer in an acid solution containing an inhibitor that suppresses the corrosion of the base steel sheet, and measuring the resulting solution using ICP (inductively coupled plasma) emission spectroscopy. be able to.
  • the thickness of the plating layer may be, for example, 3 to 50 ⁇ m. Further, the amount of the plating layer deposited is not particularly limited, but may be, for example, 10 to 170 g/m 2 per side. In the present invention, the amount of the plating layer deposited is determined by dissolving the plating layer in an acid solution containing an inhibitor that suppresses corrosion of the base steel plate, and from the change in weight of the plating layer before and after pickling and peeling. The thickness of the plating layer may be 5 ⁇ m or more, 10 ⁇ m or more, 15 ⁇ m or more, or 20 ⁇ m or more. The thickness of the plating layer may be 40 ⁇ m or less, or 30 ⁇ m or less.
  • the amount of the plating layer deposited on one side may be 20 g/m 2 or more, 30 g/m 2 or more, 40 g/m 2 or more, or 50 g/m 2 or more.
  • the amount of the plating layer deposited per side may be 150 g/m 2 or less, 130 g/m 2 or less, 120 g/m 2 or less, or 100 g/m 2 or less.
  • the thickness of the plated steel plate constituting the welded joint of the present invention is not particularly limited. For example, it can be 0.6 to 3.2 mm.
  • the plate thickness may be 0.8 mm or more, or 1.0 mm or more.
  • the plate thickness may be 3.0 mm or less, 2.6 mm or less, 2.4 mm or less, 2.2 mm or less, 2.0 mm or less, or 1.8 mm or less.
  • the C concentration measured by GDS in the depth direction of the base steel plate starting from the interface between the plating layer of the plated steel plate and the base steel plate is 0.05%.
  • the depth is 10 ⁇ m or more.
  • the heat-affected zone is a part where the material properties have changed due to heat during the spot welding process, and can be confirmed by SEM observation.
  • the non-heat affected zone is a portion other than the heat affected zone. Any position 5 mm or more away from the outer edge of the spot weld may be considered a non-heat-affected zone, so measurements are performed at a position 5 mm or more away from the outer edge of the spot weld.
  • Such a structure can be obtained by changing the chemical composition of the base steel plate of the plated steel plate to one containing a large amount of Si and Al as described above, subjecting it to the heat treatment described below, and spot welding.
  • the depth at which the C concentration is 0.05% or less is 10 ⁇ m or more, the effect of suppressing LME during manufacturing can be obtained, so the upper limit of the depth is not particularly limited, and the depth is, for example, 50 ⁇ m or less. , 40 ⁇ m or less, or 30 ⁇ m or less.
  • the depth at which the C concentration is 0.05% or less is preferably 25 ⁇ m or more.
  • the GDS measurement is performed five times in the thickness direction, and the average value of these measurements is taken as the C concentration.
  • the measurement conditions are as follows.
  • the starting point of "depth” is the interface between the base steel sheet and the plating layer.
  • the interface between the base steel plate and the plating layer is located at a position where the Fe concentration measured by GDS measurement is 93% of the Fe concentration at a depth of 150 ⁇ m.
  • the roughness of the interface between the plating layer of the plated steel plate and the base steel plate in the non-heat affected zone is 3.0 ⁇ m or less as an arithmetic mean height Ra defined by JIS B0601:2013.
  • the interface between the plating layer and the base steel sheet means the actual interface between the plating layer and the base steel sheet.
  • the roughness of the interface between the plating layer and the base steel plate may be 2.5 ⁇ m or less, or 2.0 ⁇ m or less in Ra.
  • the surface roughness of the base steel plate measured after removing the plating may be regarded as the roughness of the interface between the plating layer and the base steel plate.
  • the plating is removed by dissolving the plating layer in an acid solution containing an inhibitor that inhibits corrosion of the steel plate.
  • FIG. 2 shows an example of a microstructure photograph taken by SEM around the welded part of the welded joint of the present invention.
  • FIG. 2 shows the vicinity of the pressure welding part and the separation part of the welded joint, and the black part in the upper right corner is the separation part.
  • a layer in which the area ratio of ferrite ( ⁇ ) phase is 90% or more is formed on the surface layer of the lower steel plate.
  • the interior of the steel plate is martensite (M), and some ferrite ( ⁇ ) may also be present. Further, a heat affected zone (HAZ) whose structure has changed due to welding heat is formed near the pressure welded portion.
  • Non-Patent Document 1 It is known that ferrite phase grain boundaries have lower LME susceptibility than ⁇ (austenite) grain boundaries (for example, Non-Patent Document 1). Therefore, by forming the periphery of the welded joint of the welded joint into a structure in which the ferrite phase is stable even during welding, it is possible to improve the LME suppression effect during the production of the welded joint.
  • Such a surface structure can be obtained by changing the chemical composition of the base steel plate to one containing a large amount of Si and Al as described above, subjecting it to the heat treatment described below, and then spot welding.
  • the thickness of the layer in which the area ratio of the ferrite phase is 90% or more is 15 ⁇ m or more, the effect of improving LME resistance can be obtained, so the upper limit of the thickness is not particularly limited, and the thickness is, for example, 100 ⁇ m.
  • the thickness may be less than or equal to 80 ⁇ m or less than or equal to 60 ⁇ m.
  • the thickness of the layer in which the area ratio of the ferrite phase is 90% or more may be 20 ⁇ m or more, or 30 ⁇ m or more.
  • the thickness of the layer in which the area ratio of the ferrite phase is 90% or more can be determined by nital-etching a cross section of the welded joint perpendicular to the steel plate surface and observing it with SEM. etc., and find them.
  • the area ratio of the ferrite phase refers to the area ratio determined by observing a cross section cut perpendicular to the surface of the steel plate. Even if there is a local part in the thickness direction where the area ratio of ferrite phase is less than 90% when observing a cross section cut parallel to the steel sheet surface, vertical There is no problem as long as the area ratio of the ferrite phase in the cross section cut is 90% or more.
  • a more specific measurement method is as follows.
  • the ferrite area ratio is determined by cutting a cross section of the steel plate in the thickness direction perpendicular to the rolling direction, mirror polishing, revealing the steel structure with nital liquid, and taking a secondary electron image using a field emission scanning electron microscope. ,demand.
  • the observation position is 500 ⁇ m outward from the end of the press-welded part, and five observation positions are set at equal intervals at arbitrary positions in the rolling direction (direction perpendicular to the plane of the paper in FIG. 1(b)) for observation.
  • the ferrite area ratio is the average value of 5 fields of view.
  • the fraction of each tissue is calculated by the point counting method. More specifically, first, a grid of equal intervals is drawn on the tissue photograph.
  • each lattice point corresponds to tempered martensite, pearlite, ferrite, fresh martensite, retained austenite, or bainite.
  • the fraction of each tissue can be measured. The larger the total number of grid points, the more accurately the volume fraction can be determined.
  • the grid spacing is 2 ⁇ m ⁇ 2 ⁇ m, and the total number of grid points is 1500 points.
  • tempered martensite, pearlite, ferrite, fresh martensite, retained austenite, or bainite are shown below.
  • a region that has a substructure (lath boundary, block boundary) within the grain and in which carbides are precipitated in a plurality of variants is determined to be tempered martensite.
  • a region where cementite is precipitated in a lamellar shape is determined to be pearlite.
  • a region with low brightness and no underlying structure is determined to be ferrite.
  • a region where the brightness is high and the underlying structure is not exposed by etching is determined to be fresh martensite or retained austenite. Areas that do not fall under any of the above are determined to be bainite. Simply speaking, the area ratio of the ferrite phase can be determined by distinguishing between ferrite and other structures.
  • the plated steel plates constituting the welded joints have high strength, and specifically have a tensile strength of 780 MPa or more.
  • the upper limit of the tensile strength is not particularly limited, but from the viewpoint of ensuring toughness, the tensile strength may be, for example, 2000 MPa or less.
  • the tensile strength may be measured in accordance with JIS Z 2241:2011 by taking a JIS No. 5 tensile test piece whose longitudinal direction is perpendicular to the rolling direction.
  • the tensile strength may be 880 MPa or more, 980 MPa or more, 1080 MPa or more, or 1180 MPa or more.
  • the tensile strength may be 1900 MPa or less, or 1800 MPa or less.
  • the hardness of the plated steel plate in the non-heat-affected zone located at a distance of 5 mm or more from the outer edge of the spot weld may be used. (Vickers hardness) and estimate the value of tensile strength from the correlation formula below (Correlation between static strength parameters, Norihiko Hasegawa, Junichi Arai, Michishichi Tanaka, "Materials" Vol. 39, No. 442, P859-863).
  • Hv 0.301 ⁇ TS+5.701 (However, Hv is Vickers hardness and TS is tensile strength (unit: MPa))
  • the tensile strength can be considered to be 780 MPa or more.
  • the hardness of the plated steel plate is measured at 1/2 depth at a position that is the non-heat affected zone of the plated steel plate that constitutes the welded joint. Hardness measurement is performed in accordance with JIS Z 2244:2009. The measurement load is 200gf.
  • the hardness of the plated steel plate in the non-heat affected zone located at a distance of 5 mm or more from the outer end of the spot weld may be 245 Hv or more, 250 Hv or more, 260 Hv or more, 270 Hv or more, 300 Hv or more, or 340 Hv or more.
  • the base steel plate of the plated steel plate constituting the welded joint according to the present invention can be obtained, for example, by a casting process in which molten steel with adjusted chemical composition is cast to form a steel billet, and a hot rolled steel plate is obtained by hot rolling the steel billet.
  • the material may be pickled and then cold-rolled without being wound up after the hot-rolling process.
  • the conditions of the casting process are not particularly limited. For example, following melting in a blast furnace, electric furnace, etc., various secondary smelting may be performed, and then casting may be performed by a method such as ordinary continuous casting or ingot casting.
  • a hot rolled steel plate can be obtained by hot rolling a steel piece obtained by casting.
  • the hot rolling process is performed by directly or once cooling the cast steel billet, then reheating and hot rolling.
  • the heating temperature of the steel piece may be, for example, 1100 to 1250°C.
  • rough rolling and finish rolling are usually performed.
  • the temperature and reduction rate of each rolling may be changed as appropriate depending on the desired metal structure and plate thickness.
  • the end temperature of finish rolling may be 900 to 1050°C, and the reduction ratio of finish rolling may be 10 to 50%.
  • Hot-rolled steel sheets can be rolled up at a predetermined temperature.
  • the winding temperature may be changed as appropriate depending on the desired metal structure, etc., and may be, for example, 500 to 800°C.
  • the hot-rolled steel sheet may be subjected to a predetermined heat treatment by unwinding the hot-rolled steel sheet before or after winding.
  • the hot rolled steel sheet After pickling or the like is performed on the hot rolled steel sheet, the hot rolled steel sheet can be cold rolled to obtain a cold rolled steel sheet.
  • the rolling reduction ratio of cold rolling may be changed as appropriate depending on the desired metallographic structure and plate thickness, and may be, for example, 20 to 80%.
  • the material After the cold rolling process, the material may be cooled to room temperature by, for example, air cooling.
  • the C concentration measured by GDS in the depth direction of the base steel plate starting from the interface between the plating layer of the plated steel plate and the base steel plate is 0.05%.
  • the ferrite phase is In order to make the thickness of the layer with an area ratio of 90% or more 15 ⁇ m or more, it is necessary to perform a predetermined pretreatment before annealing the steel plate, and then perform the annealing.
  • the pretreatment includes grinding the surface of the cold rolled steel plate with a grinding brush (brush grinding process).
  • a grinding brush that can be used is M-33 manufactured by Hotani Corporation. Thereby, strain can be introduced without increasing the surface roughness.
  • the brush reduction amount is 0.5 to 10.0 mm and the rotation speed is 100 to 1000 rpm.
  • the cold rolled steel sheet is annealed.
  • Annealing is performed under a tension of 1 to 20 MPa. Applying tension during annealing makes it possible to more effectively introduce strain into the steel sheet, promoting decarburization of the surface layer.
  • the holding temperature in the annealing step is 750 to 900°C.
  • the holding temperature may be 770-870°C. By setting it within such a range, decarburization can be promoted, the C concentration in the surface layer can be reduced, and the ferrite phase can be stabilized.
  • the heating rate up to the holding temperature is not particularly limited, but may be 1 to 10° C./sec.
  • the holding time at the holding temperature in the annealing step is 20 to 300 seconds.
  • the holding time may be between 30 and 250 seconds.
  • the atmosphere in the annealing step has a dew point of -30 to 20°C.
  • the dew point may be -10 to 5°C.
  • the atmosphere may be, for example, N 2 -1 to 10 vol% H 2 or N 2 -2 to 4 vol% H 2 . If the dew point is too high or too low, a phase containing oxides such as Si, Mn, and Al is formed outside the steel sheet, which inhibits the mutual diffusion of the plating components and steel components, resulting in insufficient plating properties. There is.
  • the plated steel plate constituting the welded joint according to the present invention can be obtained by performing a plating process to form a plating layer containing Zn on the base steel plate manufactured as described above.
  • the plating treatment may be performed according to methods known to those skilled in the art.
  • the plating treatment may be performed, for example, by hot-dip plating or electroplating.
  • the plating process is performed by hot-dip plating.
  • the conditions for the plating treatment may be appropriately set in consideration of the chemical composition, thickness, amount of adhesion, etc. of the desired plating layer. For example, it may be immersed in a hot-dip galvanizing bath at 420 to 480° C. with adjusted chemical components for 1 to 10 seconds, and then pulled out at 20 to 200 mm/sec after immersion, and the amount of plating deposited may be controlled by N 2 wiping gas.
  • an alloying process may be performed.
  • the alloying treatment may be performed, for example, at 500 to 550° C. for 10 to 60 seconds.
  • spot welding process A plurality of steel plates including the above-mentioned plated steel plates are overlapped and spot welded to obtain a welded joint.
  • the conditions for spot welding are not particularly limited.
  • spot welding can be performed using a dome radius type welding electrode with a tip diameter of 6 to 8 mm, with a pressure of 1.5 to 6.0 kN, a current application time of 0.1 to 1.0 seconds, and a current of 4 to 15 kA. Can be done.
  • the welded joint according to the present invention suppresses LME cracking during manufacturing, it can be suitably used in a wide range of fields such as automobiles, home appliances, and building materials. It is particularly preferred to be used in the automotive field.
  • Example 1> (Preparation of plated steel sheet sample) No. of Table 1 Molten steel adjusted to have the chemical composition described in 1 was melted in a blast furnace and cast by continuous casting to obtain a steel billet. The obtained steel piece was heated to 1200°C and hot rolled at a finish rolling end temperature of 950°C and a finish rolling reduction of 30% to obtain a hot rolled steel plate. The obtained hot-rolled steel sheet was wound up at a winding temperature of 650° C., pickled, and then cold-rolled at a rolling reduction of 50% to obtain a cold-rolled steel sheet. The thickness of the cold-rolled steel plate was 1.6 mm.
  • the surface roughness of the steel plate was measured in accordance with JIS B 0601:2013. That is, 10 locations are randomly selected on the surface of the surface layer side, the surface profile at each location is measured using a contact type surface roughness meter, and the arithmetic mean roughness Ra is obtained by arithmetic averaging of the surface roughness at those locations. , was evaluated as follows.
  • Evaluation AA 2.0 ⁇ m or less Evaluation A: More than 2.0 ⁇ m, 3.0 ⁇ m or less Evaluation B: More than 3.0 ⁇ m
  • annealing was performed in a N 2 -4% H 2 gas atmosphere in a furnace with an oxygen concentration of 20 ppm or less at a dew point of 0° C., a holding temperature of 800° C., and a holding time of 100 seconds.
  • the temperature increase rate during annealing was 6.0°C/sec up to 500°C, and 2.0°C/sec from 500°C to the holding temperature.
  • the annealing treatment was performed under a tension of 15 MPa.
  • the steel plate was subjected to a plating treatment to obtain a hot-dip galvanized steel plate.
  • the plating treatment was performed by immersing the sample in a hot-dip galvanizing bath (Zn-0.2% Al) at 460° C. for 3 seconds. After dipping, it was pulled out at 100 mm/sec, and the coating weight was controlled to 50 g/m 2 using N 2 wiping gas, to obtain a plated steel sheet.
  • Examples 2 to 28, Comparative Examples 29 to 41> A plated steel sheet was prepared in the same manner as in Example 1, except that the chemical components were as shown in Table 1, the conditions for the pretreatment process and annealing process were as shown in Table 2, and the plating type was as shown in Table 3. was manufactured. In addition, No. In No. 40, the pretreatment of brush grinding was omitted. Also, No. In No. 41, a grinding brush D-100 manufactured by Hotani Co., Ltd. was used in the pretreatment (condition B in Table 2). D-100 is a brush with approximately twice the amount of grinding as M-33.
  • composition and bath temperature of the plating species shown in Table 3 are as follows. After the plating treatment, F was subjected to alloying treatment at 530° C. for 20 seconds to obtain alloyed hot-dip galvanizing.
  • Evaluation AAA 1180MPa or more Evaluation AA: 980MPa or more, less than 1180MPa Evaluation A: 780MPa or more, less than 980MPa
  • LME resistance was evaluated as follows using the length of the LME crack that occurred just outside the pressure welded part. Evaluation of LME resistance will be described with reference to FIG. 3.
  • LME resistance is the outer part of the pressure welded part 3 formed by overlapping two steel plates 1 and spot welding, and the LME that occurs immediately outside the pressure welded part, which is a position near the pressure welded part. Evaluation was made by measuring the crack length. The evaluation was made as follows based on the length of the crack 11 just outside the pressure welding part. In this example, if the evaluation was A or higher, it was determined that the LME resistance was excellent. If the evaluation was "A" or higher, it was determined that the LME resistance was excellent and the problem to be solved by the present invention was solved.
  • Evaluation AAA 0 ⁇ m Evaluation AA: More than 0 ⁇ m and less than 60 ⁇ m Evaluation A: More than 60 ⁇ m and less than 120 ⁇ m Evaluation B: More than 120 ⁇ m
  • the plating was removed using a 10 mass% hydrochloric acid solution containing 0.06 mass% inhibitor (manufactured by Asahi Chemical Co., Ltd., Ivit) at the position that would become the non-heat affected zone, and the surface of the exposed base steel sheet was removed.
  • the roughness was measured in the same manner as before annealing, and is shown in "Base material steel plate/plating interface roughness" in Table 3.
  • the thickness of the layer in which the area ratio of the ferrite phase is 90% or more was measured using the method described above. It is shown in " ⁇ phase thickness" in Table 3.
  • No. No. 29 is a comparative example in which the base steel plate of the plated steel plate has a high C content. It is thought that because the base steel plate had a high C content, decarburization in the surface layer did not proceed even with high dew point annealing. Therefore, the depth at which the C concentration is 0.05% or less in the non-heat-affected zone becomes small, and the layer where the area ratio of the ferrite phase is 90% or more at a position 500 ⁇ m outward from the end of the pressure welding part. thickness has become smaller. As a result, the LME resistance during manufacture of welded joints was inferior.
  • No. No. 30 has a low Si content in the base steel plate of the plated steel plate, and Si and sol.
  • This is a comparative example in which the sum of the Al contents is small. It is thought that because the Si content of the base steel sheet was low, decarburization did not proceed in the surface layer even when high dew point annealing was performed, and the ferrite was not stabilized. Therefore, the depth at which the C concentration is 0.05% or less in the non-heat-affected zone becomes small, and the layer where the area ratio of the ferrite phase is 90% or more at a position 500 ⁇ m outward from the end of the pressure welding part. thickness has become smaller. As a result, the LME resistance during manufacture of welded joints was inferior.
  • No. No. 31 is a comparative example in which the base steel plate of the plated steel plate has a high Si content. Because the base steel sheet had a high Si content, it is thought that even after high dew point annealing, external oxidation progressed and oxides (scale) were formed on the surface layer of the steel sheet, suppressing decarburization at the outermost surface. It will be done. Therefore, the depth at which the C concentration in the non-heat-affected zone is 0.05% or less has become smaller. As a result, the LME resistance during manufacture of welded joints was inferior.
  • No. 32 is the sol. of the base steel plate of the plated steel plate. This is a comparative example with a low Al content. Base material steel plate sol. It is thought that because the Al content was low, decarburization did not proceed in the surface layer even though high dew point annealing was performed, and the ferrite was not stabilized. Therefore, the depth at which the C concentration is 0.05% or less in the non-heat-affected zone becomes small, and the layer where the area ratio of the ferrite phase is 90% or more at a position 500 ⁇ m outward from the end of the pressure welding part. thickness has become smaller. As a result, the LME resistance during manufacture of welded joints was inferior.
  • No. 33 is the sol. of the base steel plate of the plated steel plate.
  • the content of Al is low, and the content of Si and sol.
  • This is a comparative example in which the sum of the Al contents is small.
  • the content of Al is low, and the content of Si and sol. It is considered that because the sum of the Al contents was small, decarburization did not progress in the surface layer even if high dew point annealing was performed, and the ferrite was not stabilized. Therefore, the depth at which the C concentration is 0.05% or less in the non-heat-affected zone becomes small, and the layer where the area ratio of the ferrite phase is 90% or more at a position 500 ⁇ m outward from the end of the pressure welding part. thickness has become smaller. As a result, the LME resistance during manufacture of welded joints was inferior.
  • No. 34 is the sol. of the base steel plate of the plated steel plate.
  • This is a comparative example with a high content of Al.
  • Base material steel plate sol It is thought that because the Al content was high, even if high dew point annealing was performed, external oxidation progressed and oxides (scale) were formed on the surface layer of the steel sheet, suppressing decarburization at the outermost surface. Therefore, the depth at which the C concentration in the non-heat-affected zone is 0.05% or less has become smaller. As a result, the LME resistance during manufacture of welded joints was inferior.
  • No. No. 35 is a comparative example in which the total content of Si and Al in the base steel plate of the plated steel plate is small. Si and sol. of base material steel plate. It is considered that because the sum of the Al contents was small, decarburization did not progress in the surface layer even if high dew point annealing was performed, and the ferrite was not stabilized. Therefore, the depth at which the C concentration is 0.05% or less in the non-heat-affected zone becomes small, and the layer where the area ratio of the ferrite phase is 90% or more at a position 500 ⁇ m outward from the end of the pressure welding part. thickness has become smaller. As a result, the LME resistance during manufacture of welded joints was inferior.
  • No. No. 37 had a high dew point during annealing during the manufacturing of the plated steel sheet, so a layer containing oxides such as Si, Mn, and Al was formed on the outside of the steel sheet during annealing, and during the plating process, the interaction between the plating components and the steel components occurred. It is thought that diffusion was inhibited. As a result, welded joints were not evaluated because appropriate plating could not be obtained.
  • No. No. 39 is a comparative example in which the annealing temperature during production of the plated steel sheet was high. It is thought that decarburization was not sufficiently promoted during annealing because the holding temperature during annealing was high. Therefore, the depth at which the C concentration is 0.05% or less in the non-heat-affected zone becomes small, and the layer where the area ratio of the ferrite phase is 90% or more at a position 500 ⁇ m outward from the end of the pressure welding part. thickness has become smaller. As a result, the LME resistance during manufacture of welded joints was inferior.
  • No. No. 40 is a comparative example in which the annealing time during production of the plated steel sheet is short. It is thought that decarburization was not sufficiently promoted during annealing because the holding time during annealing was short. Therefore, the depth at which the C concentration is 0.05% or less in the non-heat-affected zone becomes small, and the layer where the area ratio of the ferrite phase is 90% or more at a position 500 ⁇ m outward from the end of the pressure welding part. thickness has become smaller. As a result, the LME resistance during manufacture of welded joints was inferior.
  • Examples 1 to 28 are examples of the present invention, in which LME was suppressed during the production of welded joints.
  • the depth where the C concentration in the non-heat affected zone is 0.05% or less is large, and the thickness of the layer where the area ratio of the ferrite phase is 90% or more at a position 500 ⁇ m outward from the end of the pressure welding part is large.
  • the material had particularly excellent LME resistance.
  • the present invention it is possible to provide a welded joint in which LME cracking during manufacturing is suppressed, and the welded joint can be suitably used for applications such as automobiles, home appliances, and building materials, particularly for automobiles. Therefore, the present invention has extremely high industrial applicability.

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Abstract

La présente invention aborde le problème de la fourniture d'un joint soudé dans lequel la fissuration de LME pendant la fabrication est supprimée. Un joint soudé selon la présente invention est caractérisé en ce que : une tôle d'acier plaquée formant le joint soudé a une composition chimique prescrite ; lorsque la concentration en C est mesurée par GDS dans une partie thermiquement non affectée du joint soudé dans la direction de profondeur d'une tôle d'acier de base à partir de l'interface entre la tôle d'acier de base et une couche de placage de la tôle d'acier plaquée, la profondeur à laquelle la concentration en C est de 0,05 % ou moins est de 10 µm ou plus ; la rugosité exprimée en tant que Ra de l'interface entre la tôle d'acier de base et la couche de placage de la tôle d'acier plaquée dans la partie thermiquement non affectée est inférieure ou égale à 3,0 µm ; et, à une position distante de 500 µm d'une extrémité d'une partie soudée par pression du joint soudé, l'épaisseur d'une couche où le pourcentage de surface d'une phase de ferrite est de 90 % ou plus est d'au moins 15 µm dans la direction de profondeur de la tôle d'acier de base à partir de l'interface entre la tôle d'acier de base et la couche de placage de la tôle d'acier plaquée.
PCT/JP2023/032519 2022-09-06 2023-09-06 Joint soudé WO2024053669A1 (fr)

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KR20220019867A (ko) * 2020-08-10 2022-02-18 주식회사 포스코 우수한 점용접성, 강도 및 성형성을 갖는 냉연강판 및 그 제조방법
WO2022097738A1 (fr) * 2020-11-06 2022-05-12 Ｊｆｅスチール株式会社 FEUILLE D'ACIER ÉLECTROPLAQUÉE À BASE DE Fe, FEUILLE D'ACIER GALVANISÉE PAR IMMERSION À CHAUD ALLIÉE ET LEURS PROCÉDÉS DE FABRICATION
WO2022149511A1 (fr) * 2021-01-08 2022-07-14 日本製鉄株式会社 Joint soudé et composant d'automobile
WO2022149507A1 (fr) * 2021-01-08 2022-07-14 日本製鉄株式会社 Joint de soudure et composant d'automobile
WO2022149505A1 (fr) * 2021-01-08 2022-07-14 日本製鉄株式会社 Joint soudé et pièce de véhicule

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WO2020130631A1 (fr) * 2018-12-19 2020-06-25 주식회사 포스코 Tôle d'acier galvanisée à haute résistance ayant une excellente soudabilité par point de résistance électrique et son procédé de fabrication
KR20220019867A (ko) * 2020-08-10 2022-02-18 주식회사 포스코 우수한 점용접성, 강도 및 성형성을 갖는 냉연강판 및 그 제조방법
WO2022097738A1 (fr) * 2020-11-06 2022-05-12 Ｊｆｅスチール株式会社 FEUILLE D'ACIER ÉLECTROPLAQUÉE À BASE DE Fe, FEUILLE D'ACIER GALVANISÉE PAR IMMERSION À CHAUD ALLIÉE ET LEURS PROCÉDÉS DE FABRICATION
WO2022149511A1 (fr) * 2021-01-08 2022-07-14 日本製鉄株式会社 Joint soudé et composant d'automobile
WO2022149507A1 (fr) * 2021-01-08 2022-07-14 日本製鉄株式会社 Joint de soudure et composant d'automobile
WO2022149505A1 (fr) * 2021-01-08 2022-07-14 日本製鉄株式会社 Joint soudé et pièce de véhicule

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