Classifications

• • 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
  • B23K11/163—Welding of coated materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B15/00—Layered products comprising a layer of metal
  • B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
  • B32B15/011—Layered products comprising a layer of metal all layers being exclusively metallic all layers being formed of iron alloys or steels
• • 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
  • B23K1/00—Soldering, e.g. brazing, or unsoldering
  • B23K1/20—Preliminary treatment of work or areas to be soldered, e.g. in respect of a galvanic coating
• • 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
• • 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
  • B23K11/30—Features relating to electrodes
• • 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
  • B23K11/34—Preliminary treatment
• • 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
  • B23K35/001—Interlayers, transition pieces for metallurgical bonding of workpieces
  • B23K35/004—Interlayers, transition pieces for metallurgical bonding of workpieces at least one of the workpieces being of a metal of the iron group
• • 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
  • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
  • B23K35/0255—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in welding
  • B23K35/0288—Welding studs
• • 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
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B15/00—Layered products comprising a layer of metal
  • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
• • 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
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B3/00—Ohmic-resistance heating
  • H05B3/02—Details
  • H05B3/03—Electrodes
• • 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
  • B23K2101/006—Vehicles
• • 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
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/02—Iron or ferrous alloys
  • B23K2103/04—Steel or steel alloys
• • B23K2203/04—
• • 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
  • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
  • B23K35/0205—Non-consumable electrodes; C-electrodes
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium

Definitions

• This disclosure relates to a steel sheet assembly obtained by joining a plurality of steel sheets by a joining method using a combination of an adhesive and welding, having excellent performance including high strength, high rigidity and the like and also relates to a method of joining the same.
• a resistance welding process typified by spot welding is a joining process which is low-cost and has high production efficiency and therefore is used in various industries including the automobile industry.
• a weld bond process using a combination of bonding and spot welding is being increasingly used. This is because changing a joint from those by spot joining to line joining, and further face joining increases the rigidity of members as well as joints.
• the weld bond process as compared to joining by bonding only, has an advantage that a joint improved in impact strength, high-temperature strength, creep resistance and the like can be formed. Furthermore, the weld bond process, as compared to joining by spot welding only, has advantages that fatigue properties, rigidity and the like are improved and corrosion resistance also is improved because sealing properties are imparted to a joint. Because of these advantages, the weld bond process is being increasingly used in steps of manufacturing automobiles.
• each material to be joined is joined through steps of such as application of an adhesive to a faying surface, lapping, spot welding, and curing an adhesive. Therefore, the materials to be joined are retained with a spot weld only until the adhesive becomes cured.
• thermal stress is induced in a joint because of the difference in thermal expansion coefficient from the material to be joined so that various stresses are applied to the joint until the adhesive is cured. Therefore, joints formed by spot welding need to have strength sufficient to withstand these stresses.
• the impact strength, high-temperature strength and the like of a weld-bond joint affect the strength of the spot weld and therefore the spot weld needs to have high strength.
• Japanese Unexamined Patent Application Publication No. 8-118031 proposes a method in which a good nugget is ensured and necessary bond strength is maintained such that a material to be welded is heated to 50° C. to 170° C. prior to the pressing operation of spot welding and then welded.
• Japanese Unexamined Patent Application Publication No. 8-118031 proposes a method in which a good nugget is ensured and necessary bond strength is maintained such that a material to be welded is heated to 50° C. to 170° C. prior to the pressing operation of spot welding and then welded.
• 8-206845 proposes a method in which conductivity during resistance spot welding is made good, melting failures are prevented, a good nugget is ensured, and sufficient joint strength is obtained by using an adhesive which is a thermosetting epoxy resin containing one or more additives such as conductive powdery, scaly, or flaky metals, metal oxides, metal carbides, metal nitrides, and metal silicides.
• JP '031 has a problem that the increase in number of steps causes cost increases because steel sheets need to be heated prior to welding.
• JP '845 although a weld having a stable nugget diameter can be obtained by ensuring conductivity, the reduction in number of welds and the effect of increasing the strength of a weld itself are not obtained because the strength of a weld is equivalent to that of a conventional one.
• the amount of C in a nugget can be increased by application of an adhesive and a carbon-supplying agent and by appropriately controlling the shape of the tip of an electrode and welding conditions during spot welding. This increases the strength of the nugget to enable the strength of a joint to be increased.
• the strength of a weld can be ensured by adding an appropriate amount of carbon to the weld even in such a state that strength due to bonding cannot be sufficiently obtained prior to adhesive curing in a manufacturing process of an assembly. Furthermore, the necessary strength of a structure can be maintained by the strength of the weld even in the case where the strength of the assembly in use and the bond strength of the adhesive are reduced by temporal changes.
• the strength of a weld is increased by supplying carbon to the weld through application of an adhesive and a carbon-supplying agent to a faying surface.
• a means of supplying carbon is not particularly limited. However, since the carbon-supplying agent is supplied to a melted portion, in a pressing step and a subsequent heating step in spot welding, the spot welding needs to be performed without completely discharging the adhesive from a melted portion-forming range, so as the adhesive and the carbon-supplying agent to be incorporated within the melted portion when the melted portion is grown.
• the steel sheet components need to contain C: 0.4% or less, Si: 3.0% or less, Al: 3.0% or less, Mn: 0.2% to 6.0%, P: 0.1% or less, and S: 0.07% or less on a mass basis, the remainder being Fe and inevitable impurities.
• the unit “%” used to express the content of each component refers to “mass percent.”
• the C content of each steel sheet is more than 0.4%, the weld becomes brittle and it is difficult to ensure the strength thereof in some cases. Therefore, the C content of the steel sheet is 0.4% or less.
• the C content of the steel sheet is preferably 0.3% or less and more preferably 0.25% or less.
• Si is a useful element contributing to increasing the strength of steel by solid solution strengthening.
• the Si content is 3.0% or less.
• the Si content is preferably 2.6% or less and more preferably 2.2% or less.
• the lower limit of Si is not particularly limited.
• Si is an element effective in suppressing the formation of carbides and is useful in increasing the strength due to the increase in amount of C in a melted portion. Therefore, the Si content is preferably 0.02% or more and more preferably 0.1% or more.
• Al 3.0% or less
• Al is an element effective in controlling the fraction of a microstructure. However, containing more than 3.0% increases the number of inclusions in the steel sheet to deteriorate the ductility. Thus, the content is 3.0% or less. The content is preferably 2.5% or less and more preferably 1.5% or less. The lower limit of the Al content is not particularly regulated, however, the reduction thereof is costly. Therefore, the Al content is preferably 0.01% or more and more preferably 0.02% or more.
• Mn is an element effective in strengthening steel and necessary to strengthen the weld and the melted portion.
• the Mn content is 0.2% or more.
• the Mn content is preferably 0.5% or more and more preferably 0.8% or more.
• the Mn content is 6.0% or less.
• the Mn content is preferably 5.2% or less and more preferably 4.7% or less.
• P is an element useful in strengthening steel.
• the P content is more than 0.1%, P segregates at solidification interfaces or the like to cause embrittlement and deteriorates the crashworthiness. Therefore, the effect of strengthening the weld by the increase in the amount of P as in that of C is not obtained. Therefore, the P content is 0.1% or less.
• the P content is preferably 0.05% or less.
• the P content is preferably minimized. However, reducing the P content to less than 0.005% causes a significant increase in cost. Therefore, the lower limit thereof is preferably about 0.005%.
• the S content is preferably minimized.
• the excessive reduction of the S content causes an increase in manufacturing cost. Therefore, the S content is 0.07% or less.
• the S content is preferably 0.05% or less and more preferably 0.02% or less. Incidentally, adjusting the S content to less than 0.0005% causes a large increase in manufacturing cost in a desulfurization step. Therefore, from the viewpoint of manufacturing cost, the lower limit of the S content is about 0.0005%.
• N is an element most significantly deteriorating the aging resistance of the steel sheet and the content is preferably reduced.
• the N content is more than 0.020%, the deterioration of the aging resistance is significant. Therefore, the N content is preferably 0.020% or less.
• adjusting the N content to less than 0.001% causes a large increase in manufacturing cost. Therefore, from the viewpoint of manufacturing cost, the lower limit of the N content is about 0.001%.
• components other than the above are Fe and inevitable impurities. Containing components other than the above, necessary to improve other properties is not refused unless the desired effects are impaired.
• Cr, V, Mo, Ni, and Cu may be added for the purpose of controlling the transformation of a second phase during cooling to control hardenability.
• Ti, Nb, B, and the like may be added for the purpose of controlling the precipitation behavior of carbides and nitrides in consideration of using precipitation hardening and the like.
• Ca and a REM may be added for the purpose of improving a negative influence of sulfides on the stretch-flange formability by spheroidizing sulfides.
• the additive amount (content) of each element is preferably as follows: Cr: 0.05% to 5.0%, V: 0.005% to 1.0%, Mo: 0.005% to 0.5%, Ni: 0.05% to 2.0%, Cu: 0.05% to 2.0%, Ti: 0.01% to 0.1%, Nb: 0.01% to 0.1%, B: 0.0003% to 0.0050%, Ca: 0.001% to 0.005%, and the REM: 0.001% to 0.005%. If the content of each element is below the lower limit of the above range the desired effects are not impaired. Therefore, even when the content of the element is less than the lower limit, the element is regarded as an inevitable impurity.
• the strength of the steel sheets is 1,470 MPa or less in terms of tensile strength.
• the steel sheets intended by a joining method include those having a surface galvanized, galvannealed, or electroplated with Zn, Al, Mg, or an alloy thereof and further chromate-treated or coated with a resin film.
• each steel sheet described above is lapped and the adhesive and the carbon-supplying agent are applied thereto, followed by welding.
• the thickness of each steel sheet is not particularly limited by the joining method and is usually 0.3 mm to 5.0 mm from the viewpoint of practical use. When the thickness thereof is less than 0.3 mm, it is difficult to ensure the strength of a member.
• a steel sheet with a thickness of more than 5.0 mm is rarely used in automobile bodies and is joined by a method other than resistance spot welding and weld bonding in general.
• the adhesive may be applied to a faying surface of either one of the two steel sheets to be lapped or faying surfaces of both of the steel sheets.
• the adhesive may be one such as an epoxy resin-based adhesive obtained by blending an epoxy resin widely used in the field of automotive and the like with a curing agent, filler, a modifier or the like, a modified acrylic adhesive, or a polyurethane-based adhesive, the type and components of the adhesive are not particularly limited as far as the required properties are satisfied.
• the components and the blending ratio thereof may be appropriately selected depending on required properties such as bond strength, durability, and cost.
• the spread of the adhesive may be arbitrarily selected depending on properties required of a faying surface and the weld. However, when the spread is too large, it is difficult to control formation of a nugget. Therefore, the spread is preferably 1.0 mm or less in terms of thickness and more preferably 0.5 mm or less. In contrast, when the spread is excessively small, there is a problem in that not only it is difficult to incorporate a necessary component in the melted portion but also the possibility of causing a region not applied with the adhesive is high because it is difficult to uniformly apply the adhesive. Therefore, the spread is preferably 0.01 mm or more and more preferably 0.03 mm or more.
• the carbon-supplying agent used may be a graphite powder or carbon black.
• the carbon-supplying agent may be provided on the adhesive applied to a surface of each steel sheet. Alternatively, a prepared mixture of the graphite powder and the adhesive as described above may be applied to the steel sheet.
• the amount of the carbon-supplying agent used is not particularly limited and may be determined such that the increase in amount of C is within an appropriate range as described below.
• a measure of the amount of the carbon-supplying agent used is 2 mass parts to 30 mass parts per 100 mass parts of the adhesive.
• TS MPa
• t all (mm) denotes the total thickness of the steel sheets (the sum of the thicknesses of the steel sheets).
• Conditions to cure the adhesive after spot welding may be selected on the basis of curing properties of the adhesive.
• a necessary heat treatment may be performed by charging welded members into a high-frequency heater or a furnace.
• the adhesive may be cured in association with heating during painting when bake painting is performed in a step after welding.
• a spot welding machine may be any type of welding machine such as a stationary welding machine or a gun-type welding machine as far as not departing from the gist of the present invention.
• a welding power supply can be selected from a single-phase alternating current power supply, a direct-current power supply, a three-phase rectifier-type power supply, a capacitor-type power supply and the like.
• the following method may be used: a control method in which the resistance, the voltage and the like are monitored during welding and the current or the heat time is varied depending on the change thereof.
• the nugget diameter is set to 2.8 ⁇ qt (mm) or more [t: the thickness of a thinner one of the steel sheets on both sides of a weld interface].
• the nugget diameter is preferably is 3.5 ⁇ t (mm) or more.
• the upper limit of the nugget diameter is not particularly limited, however, the upper limit is preferably 1.2 times or less the tip diameter of an electrode in consideration of the stability of occurrence of expulsion. A method described in an example is used to measure the nugget diameter.
• the weld is hardened by supplying carbon to the weld such that the strength of the joint is increased. This effect is obtained by increasing the increment of carbon in the weld by 0.02% by mass or more.
• the increment is preferably 0.03% by mass or more.
• the increment of carbon is preferably 1.3% by mass or less because the weld becomes brittle in the case of extremely increasing the increment of carbon. A method described in an example is used to measure the increment of carbon.
• the hardening value (the increment of hardness) of the weld along with the increment of C is preferably 20 or more in terms of Vickers hardness and more preferably 30 or more.
• the upper limit of the increment of Vickers hardness is not particularly limited, however, the increment is preferably 800 or less because of the suppression of significant embrittlement.
• Epoxy-based and graphite powder means that an adhesive used was an epoxy resin-based adhesive and a carbon-supplying agent used was a graphite powder (after the adhesive was applied to a steel sheet, the carbon-supplying agent was provided on the adhesive).
• Carbon-containing epoxy-based means that an adhesive used was an epoxy resin-based adhesive, a carbon-supplying agent used was carbon black, and carbon black was mixed with the epoxy resin-based adhesive in advance.
• Epoxy-based for No. 4 means that an adhesive used was an epoxy resin-based adhesive and no carbon-supplying agent was applied.
• a welding machine used was a direct-current resistance spot welding machine. Welding was performed such that the shape of the tip of each electrode, the weld force, the welding current, and the heat time were varied. After welding, a joint was vertically cut in the center of a weld, a cross section thereof was observed, and the diameter of a nugget was measured. The amount of carbon in the weld was determined in such a manner that five spots in a 200 ⁇ m ⁇ 200 ⁇ m region in the nugget were measured using an EPMA and the measurements were averaged. The quality of the joint was evaluated for rupture strength and failure mode by shear tensile testing in accordance with JIS Z 3136. The joint was evaluated depending on the tensile shear strength and the failure mode.
• the failure mode was “plug failure,” the strength of a weld was rated sufficient.
• the failure mode was “partial plug failure (partial plug in Table 2)” or “interface failure,” the strength of a weld was rated insufficient.
• the hardness of the weld was evaluated in terms of Vickers hardness. The average of measurements of five spots in the nugget measured under a test load of 300 gf was defined as the hardness of the weld. Results of the increment of hardness were shown in Table 2.

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• Materials Engineering (AREA)
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• Organic Chemistry (AREA)
• Resistance Welding (AREA)

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• 2016
  • 2016-01-22 EP EP16746280.3A patent/EP3254796B1/en active Active
  • 2016-01-22 US US15/545,757 patent/US20170348790A1/en not_active Abandoned
  • 2016-01-22 JP JP2016527488A patent/JP6048622B1/ja active Active
  • 2016-01-22 MX MX2017009932A patent/MX2017009932A/es unknown
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  • 2016-01-22 WO PCT/JP2016/000328 patent/WO2016125446A1/ja active Application Filing
  • 2016-01-22 KR KR1020177020691A patent/KR101960625B1/ko active IP Right Grant
• 2021
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