WO2020096271A1 - Combination structure of metal sheets for automobile by using trip steel and method for manufacturing the same - Google Patents

Combination structure of metal sheets for automobile by using trip steel and method for manufacturing the same Download PDF

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Publication number
WO2020096271A1
WO2020096271A1 PCT/KR2019/014586 KR2019014586W WO2020096271A1 WO 2020096271 A1 WO2020096271 A1 WO 2020096271A1 KR 2019014586 W KR2019014586 W KR 2019014586W WO 2020096271 A1 WO2020096271 A1 WO 2020096271A1
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WO
WIPO (PCT)
Prior art keywords
steel sheet
coating layer
zinc
plated steel
aluminum
Prior art date
Application number
PCT/KR2019/014586
Other languages
French (fr)
Inventor
Heesang SHIN
Geonyong LEE
Baekhyun KIM
Sungwon Cho
Original Assignee
Renault-Samsung Motors Co., Ltd.
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Publication date
Priority claimed from KR1020190053388A external-priority patent/KR20200053392A/en
Application filed by Renault-Samsung Motors Co., Ltd. filed Critical Renault-Samsung Motors Co., Ltd.
Publication of WO2020096271A1 publication Critical patent/WO2020096271A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D29/00—Superstructures, understructures, or sub-units thereof, characterised by the material thereof
    • B62D29/007—Superstructures, understructures, or sub-units thereof, characterised by the material thereof predominantly of special steel or specially treated steel, e.g. stainless steel or locally surface hardened steel
    • 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
    • B23K11/163—Welding of coated materials
    • 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
    • B23K11/166—Welding of coated materials of galvanized or tinned 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
    • B32B15/012—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of aluminium or an aluminium alloy
    • 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
    • B32B15/013—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D25/00—Superstructure or monocoque structure sub-units; Parts or details thereof not otherwise provided for
    • B62D25/20—Floors or bottom sub-units
    • 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
    • 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
    • B23K2101/00—Articles made by soldering, welding or cutting
    • B23K2101/34—Coated articles, e.g. plated or painted; Surface treated articles
    • 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
    • B32B37/00—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding
    • B32B37/0076—Methods or apparatus for laminating, e.g. by curing or by ultrasonic bonding characterised in that the layers are not bonded on the totality of their surfaces
    • B32B37/0084—Point bonding

Definitions

  • the present invention relates to a combination structure of metal sheets for automobiles and a method for manufacturing the same, and more particularly, to a combination structure of metal sheets for automobiles by using TRIP steel and a method for manufacturing the same.
  • a high-strength steel sheet in particular, a giga-grade steel material (with tensile strength of at least 980 MPa) is used for the vehicle bodies (BIW, body in white).
  • Dual phase (DU) steel, complex phase (CP) steel, hot press forming (HPF) steel, transformation induced plasticity (TRIP) steel, twinning induced plasticity (TWIP) steel, or the like is being used as the giga-grade steel material.
  • the transformation induced plasticity (TRIP) steel among the giga-grade steel materials has both high strength and high elongation, and thus has recently been more spotlighted.
  • Zinc is widely used as a corrosion resistant coating agent for most steel materials, because the melting point of zinc is relatively low (about 420°C) and is easily processed in melt plating, and zinc has a sacrificial corrosion protection property to a steel base material and thus exhibits an excellent effect.
  • the TRIP steel has a problem of causing a crack when subjected to corrosion-resistant coating with zinc, because a liquid metal embrittlement (LME) phenomenon occurs in which zinc melted during spot welding flows into a base material along grain boundaries.
  • FIG. 1 illustrates a cross-sectional view in which spot welding is performed on zinc-plated TRIP steel, and it can be found that cracks occur in a base material due to the occurrence of liquid metal embrittlement (LME). From the standpoint of an automobile maker, since these cracks have risks of critical accidents, non-plated steel materials are exclusively used without corrosion-resistant coating when using TRIP steel for a vehicle body, or limitedly used through a post-heat treatment process or the like after welding.
  • aluminum melt plating to the corrosion-resistant coating of TRIP steel may be considered, but this is also difficult to actually use. That is, aluminum used as a coating agent has a relatively high melting point (about 670°C), and when the TRIP steel is heated to about 450°C or higher, inherent physical properties of the TRIP steel is weakened or disappeared while residual austenite phases inside the steel material are transformed into cementite, ferrite, pealite, etc. even in a short time.
  • An object to be addressed by the present invention is to provide, in applying TRIP steel to a vehicle body, a combination structure of metal sheets for automobiles which is capable of reinforcing the anti-corrosion property while maintaining the high-strength and high-elongation properties inherent in the TRIP steel, and which is capable of preventing liquid metal embrittlement even during spot welding with another steel sheet.
  • Another object to be addressed by the present invention is to provide a method for manufacturing the combination structure of metal sheets for automobiles.
  • a combination structure for automobiles using TRIP steel includes: an aluminum-plated steel sheet having an aluminum coating layer formed on a surface of a first steel sheet made of the TRIP steel, and the aluminum-plated steel sheet being formed by cold working at a temperature no higher than a recrystallization temperature of the TRIP steel; a zinc-plated steel sheet having a zinc coating layer formed on a surface of a second steel sheet which is not made of the TRIP steel, the zinc-plated steel sheet being formed; and a spot welding region created by spot welding of the aluminum-plated steel sheet and the zinc-plated steel sheet in a state in which the aluminum coating layer and the zinc coating layer abut each other.
  • the TRIP steel may have at least 5% of elongation (EL) and at least 980 MPa of tensile strength (TS), and a product of elongation (EL) x tensile strength (TS) may be 10 to 45 GPa ⁇ %
  • the aluminum coating layer may be formed through a physical vapor deposition process.
  • the aluminum-plated steel sheet may be used for a front cross member in a vehicle underbody.
  • a combination structure for automobiles using TRIP steel includes: a complex coating layer-plated steel sheet in which a lower coating layer made of a metal having a higher melting point than zinc is formed on a surface of a first steel sheet made of the TRIP steel and a zinc coating layer is formed on the lower coating layer, the complex coating layer-plated steel sheet being formed by cold working at a temperature of no higher than a recrystallization temperature of the TRIP steel; a zinc-plated steel sheet having a zinc coating layer formed on a surface of a second steel sheet not made of the TRIP steel, the zinc-plated steel sheet being formed; and a spot welding region created by spot welding of the complex coating layer-plated steel sheet and the zinc-plated steel sheet in a state in which the zinc coating layer of the complex coating layer-plated steel sheet and the zinc coating layer of the zinc-plated steel sheet abut each other.
  • the lower coating layer may include aluminum, magnesium, copper, or a combination thereof.
  • a method for manufacturing a combination structure of metal sheets for automobiles using TRIP steel includes: forming an aluminum coating layer on a surface of a first steel sheet made of the TRIP steel to prepare an aluminum-plated steel sheet; forming the aluminum-plated steel sheet by cold working at a temperature of no higher than the recrystallization temperature of the TRIP steel; forming a zinc coating layer on a surface of a second steel sheet not made of the TRIP steel to prepare a zinc-plated steel sheet; and completing the combination structure of metal sheets by spot welding of the aluminum-plated steel sheet and the zinc-plated steel sheet in a state in which the aluminum coating layer and the zinc coating layer abut each other.
  • the TRIP steel may have at least 5% of elongation (EL) and at least 980 MPa of tensile strength (TS), and a product of elongation (EL) x tensile strength (TS) may be 10 to 45 GPa ⁇ %.
  • the aluminum coating layer may be formed through a physical vapor deposition process.
  • the aluminum-plated steel sheet may be used for a front cross member in a vehicle underbody.
  • a method for manufacturing a combination structure of metal sheets for automobiles using TRIP steel includes: forming a lower coating layer made of a metal having a higher melting point than zinc on a surface of a first steel sheet made of the TRIP steel, and forming a zinc coating layer on the lower coating layer to prepare a complex coating layer-plated steel sheet; forming the complex coating layer-plated steel sheet by cold working at a temperature of no higher than the recrystallization temperature of the TRIP steel; forming a zinc coating layer on a surface of a second steel sheet not made of the TRIP steel to prepare a zinc-plated steel sheet; and completing the combination structure of metal sheets by spot welding of the complex coating layer-plated steel sheet and the zinc-plated steel sheet in a state in which the zinc coating layer of the complex coating layer-plated steel sheet and the zinc coating layer of the zinc-plated steel sheet abut each other.
  • the lower coating layer may include aluminum, magnesium, copper, or a combination thereof.
  • the TRIP steel is formed by cold working, so that the inherent high-strength and high-elongation properties of the TRIP steel can be maintained as it is.
  • an aluminum-plated steel sheet since coating is performed by using physical vapor deposition which is a relatively low temperature process while using aluminum as a corrosion-resistant coating agent on a TRIP steel sheet, degradation of the basic physical properties (high strength and high elongation) of the TRIP steel can be prevented. Furthermore, even when a zinc-plated steel sheet in which a zinc coating layer is formed on a steel sheet not made of TRIP steel is subjected to spot welding with an aluminum-plated TRIP steel sheet, an aluminum coating layer protects the TRIP steel sheet and thus, the occurrence of liquid metal embrittlement (LME) due to zinc can be prevented on the TRIP steel sheet.
  • LME liquid metal embrittlement
  • a complex coating layer-plated steel sheet uses a complex coating layer including a lower coating layer and an upper coating layer, so that zinc which can be economically coated compared to other metals is used for the upper coating layer, thereby capable of securing anti-corrosion performance, and a lower coating layer made of a metal other than zinc is interposed between TRIP steel and the upper zinc coating layer, thereby capable of preventing the occurrence of liquid metal embrittlement due to zinc on the TRIP steel sheet.
  • the lower coating layer is configured from a metal (for example, aluminum, magnesium, copper, or a combination thereof) having a higher melting point than zinc, so that zinc melted from the upper zinc coating layer can be effectively prevented from infiltrating into a TRIP steel base material during spot welding.
  • a metal for example, aluminum, magnesium, copper, or a combination thereof
  • FIG. 1 is a cross-sectional view of cracks due to liquid metal embrittlement (LME) that may occur during spot welding on a zinc-plated TRIP steel.
  • LME liquid metal embrittlement
  • FIG. 2 is a cross-sectional view illustrating a combination structure of metal sheets for automobiles in accordance with an embodiment of the present invention.
  • FIG. 3 is a flowchart sequentially illustrating a method for manufacturing the combination structure of metal sheets for automobiles.
  • FIG. 4 is a cross-sectional view illustrating a combination structure of metal sheets for automobiles in accordance with another embodiment of the present invention.
  • FIG. 5 is a cross-sectional view illustrating a combination structure of metal sheets for automobiles in accordance with still another embodiment of the present invention.
  • FIG. 6 is a flowchart sequentially illustrating a method for manufacturing the combination structure, in FIG. 5, of metal sheets for automobiles.
  • FIG. 7 is a view illustrating a vehicle underbody to which a combination structure of metal sheets of the present invention is applied.
  • FIG. 2 is a cross-sectional view illustrating a combination structure of metal sheets for automobiles in accordance with an embodiment of the present invention.
  • a combination structure 2 of metal sheets for automobiles according to the present invention includes an aluminum-plated steel sheet 100, a zinc-plated steel sheet 200, and a spot welding region 50 created by spot welding of these steel sheets.
  • the aluminum-plated steel sheet 100 includes a first steel sheet 110 made of TRIP steel and an aluminum coating layer 120 formed on a surface of the first steel sheet 110.
  • the transformation induced plasticity (TRIP) steel constituting the first steel sheet 110 has excellent processiblility due to a high-elongation behavior caused by transformation induced plasticity of residual austenite.
  • the TRIP steel is residual austenite steel having a phase structure mixed in three phases of austenite, ferrite and bainite by causing the austenite present at a high temperature to remain at room temperature.
  • austenite remains at room temperature, and the residual austenite is a metastable phase and is transformed into martensite when receiving deformation from the outside.
  • the TRIP steel When transformation occurs as such due to working, the TRIP steel has a high work hardening index unlike general steel, has increased necking resistance, and thus has excellent workability.
  • the TRIP steel of the present invention which is used for an underbody of a vehicle, has elongation EL of at least 5%, a tensile strength TS of at least 980 MPa, and the product of elongation EL x tensile strength TS is 10 to 45 GPa ⁇ %.
  • the aluminum coating layer 120 is a corrosion-resistant agent and may be formed at least on one surface of the first steel sheet 110. Since the melting point (about 670oC) of aluminum is relatively high, when an aluminum coating layer is formed on the first steel sheet 110 by general melt plating, the high-strength and high-elongation properties, which are inherent properties of the TRIP steel, are weakened because residual austenite structures present inside the TRIP steel disappear. Accordingly, in the present invention, the aluminum coating layer 120 is formed on the surface of the first steel sheet 110 through a physical vapor deposition (PVD). However, the embodiment of the present invention is not limited thereto, and the aluminum coating layer may also be formed by electroplating on the first steel sheet 110.
  • PVD physical vapor deposition
  • the zinc-plated steel sheet 200 includes a second steel sheet 210 made of a steel material other than TRIP steel and a zinc coating layer 220 formed on a surface of the second steel sheet 210.
  • the second steel sheet 210 may be formed of an arbitrary steel material, but may favorably be formed of a steel material other than the TRIP steel that has a risk of liquid metal embrittlement to zinc.
  • the zinc coating layer 220 may also be formed by using melt plating or electroplating.
  • the spot welding region 50 is a region created by spot welding of the aluminum-plated steel sheet 100 and the zinc-plated steel sheet 200 in a state in which the aluminum coating layer 120 and the zinc coating layer 220 abut each other.
  • the spot welding region 50 may include a martensite phase.
  • the aluminum coating layer 120 formed on the first steel sheet 110 may prevent the TRIP steel from being subjected to liquid metal embrittlement (LME) by zinc in spot welding with the zinc-plated steel sheet 200.
  • LME liquid metal embrittlement
  • FIG. 3 is a flowchart sequentially illustrating a method for manufacturing the combination structure, in FIG. 2, of metal sheets for automobiles.
  • an aluminum coating layer 120 is formed on a surface of a first steel sheet 110 made of TRIP steel (S10). Specifically, the aluminum coating layer 120 is formed by using physical vapor deposition on a first surface of the first steel sheet 110, and an aluminum coating layer 120 is formed by using physical vapor deposition on a second surface of the first steel sheet 110, thereby preparing an aluminum-plated steel sheet 100.
  • a continuous vacuum deposition device for physical vapor deposition may be configured to include a vacuum chamber, an aluminum target, a power supply device, a steel sheet feeding part, and the like.
  • the physical vapor deposition can be performed in a low-temperature process, and since the internal structure of the TRIP steel is not changed while depositing the aluminum coating layer 120 on the first steel sheet 110, the high-strength and high-elongation physical properties inherent in the TRIP steel may be nonetheless maintained. Aside from the physical vapor deposition, since the electroplating can also be performed in a low-temperature process, the aluminum coating layer 120 may also be formed without changing the internal structure of the TRIP steel.
  • the aluminum-plated steel sheet 100 is formed by cold working of the aluminum-plated steel sheet 100 at a temperature no higher than recrystallization temperature of the TRIP steel (S12). According to the present embodiment, a low temperature state is maintained while performing coating and forming processes on the first steel sheet 110 made of the TRIP steel, so that the inherent physical property of the TRIP steel may be maintained.
  • a zinc coating layer 220 is formed on a surface of a second steel sheet 210 made of a steel material other than the TRIP steel, thereby preparing a zinc-plated steel sheet 200 (S20).
  • the zinc coating layer 220 may be formed through various known existing methods. For example, zinc melt plating or zinc electroplating may be used.
  • the zinc-plated steel sheet 200 is formed through various known methods, thereby preparing a metal sheet for an automobile (S22).
  • a spot welding region 50 formed between the aluminum-plated steel sheet 100 and the zinc-plated steel sheet 200 by the spot welding may include a martensite phase.
  • FIG. 4 is a cross-sectional view illustrating a combination structure of metal sheets for automobiles in accordance with another embodiment of the present invention.
  • FIG. 4 a member having the same function as each of the members illustrated in the drawing (FIG. 2) of the previous embodiment, and the description thereon will be omitted, and differences therebetween will be mainly described.
  • a combination structure 3 of metal sheets according to the present embodiment includes: an aluminum-plated steel sheet 100 made of TRIP steel; a first zinc-plated steel sheet 200 coupled to one surface of the aluminum-plated steel sheet 100; a second zinc-plated steel sheet 300 coupled to the other surface of the aluminum-plated steel sheet 100; and a spot welding region 50 created by the spot welding therebetween.
  • the second zinc-plated steel sheet 300 includes a third steel sheet 310 formed of a steel material other than the TRIP steel and a zinc coating layer 320 formed on a surface of the third steel sheet 310.
  • FIG. 5 is a cross-sectional view illustrating a combination structure of metal sheets for automobiles in accordance with still another embodiment of the present invention.
  • a member having the same function as each of the members illustrated in the drawing (FIG. 2) of the previous embodiment is referred to as the same reference numerals, and the description thereon will be omitted, and differences therebetween will be mainly described.
  • a combination structure 4 of metal sheets for automobiles includes a complex coating layer-plated steel sheet 101, a zinc-plated steel sheet 200, and a spot welding region 50 generated by spot welding of the steel sheets.
  • the complex coating layer-plated steel sheet 101 is configured from a first steel sheet 110 made of TRIP steel and complex coating layers 121 and 131 formed on a surface of the first steel sheet 110 as corrosion-resistant agents.
  • the complex coating layers 121 and 131 are formed on the surface of the first steel sheet 110, and has a laminated structure of a lower coating layer 121 made of a metal having a higher melting point than zinc and a zinc coating layer 131 formed on the lower coating layer 121.
  • the lower coating layer 121 may be formed of aluminum, magnesium, copper, or a combination thereof, and may favorably be formed of aluminum.
  • the lower coating layer 121 may be formed in a thickness of about 0.1 to 3 ⁇ m, and be formed on the surface of the first steel sheet 110 through physical vapor deposition.
  • the embodiment of the present invention is not limited thereto, and the lower coating layer 121 may also be formed by electroplating on the first steel sheet 110.
  • the upper coating layer 131 is made of zinc. Since zinc has a lower melting point and higher vapor pressure than other metals and thus has lower energy required to form a coating layer, and a heat treatment temperature is low when performing post-heat treatment for controlling the physical properties of the coating layer, degradation in physical properties due to thermal deformation of a giga-grade high-elongation steel sheet base material can be minimized.
  • the zinc coating layer 131 directly contacts the TRIP steel sheet, liquid metal embrittlement may occur, and thus, in the present embodiment, the liquid metal embrittlement is prevented by interposing the lower coating layer 121 between the zinc coating layer 131 and the first steel sheet 110.
  • the zinc coating layer 131 may be formed in a thickness of about 5 to 15 ⁇ m and be formed on the surface of the lower coating layer 121 through physical vapor deposition.
  • the embodiment of the present invention is not limited thereto, and the zinc coating layer may also be formed by using melt plating or electroplating.
  • FIG. 6 is a flowchart sequentially illustrating a method for manufacturing the combination structure, in FIG. 5, of metal sheets for automobiles.
  • a first coating layer or a lower coating layer 121 is formed by physical vapor deposition, electroplating or the like on a surface of a first steel sheet 110 made of TRIP steel (S110).
  • a second coating layer or a zinc coating layer 131 is formed by physical vapor deposition, melt plating, electroplating or the like on the lower coating layer 121, thereby preparing a complex coating layer-plated steel sheet 101 (S112).
  • the lower coating layer 121 made of aluminum is formed on the first steel sheet 110 through physical vapor deposition and the zinc coating layer 131 may be formed through electroplating on the lower coating layer 121.
  • the thickness of the zinc coating layer 131 is maintained at 50-90% of the total thickness of the complex coating layer, so that anti-corrosion performance may be secured by using zinc which can be more economically coated than other metals, and liquid metal embrittlement may be prevented by interposing the lower coating layer 121 between the zinc coating layer 131 and the TRIP steel sheet 110.
  • the complex coating layer-plated steel sheet 101 is formed by performing cold working at a temperature no higher than the recrystallization temperature of the TRIP steel (S114). According to the present embodiment, a low temperature state is maintained while performing coating and forming processes on the first steel sheet 110 made of the TRIP steel, and thus, the inherent physical property of the TRIP steel may be maintained.
  • a zinc coating layer 220 is formed on a surface of a second steel sheet 210 made of a steel material other than the TRIP steel, thereby preparing a zinc-plated steel sheet 200 (S120).
  • the zinc-plated steel sheet 200 is formed through various known methods, thereby preparing a metal sheet for an automobile (S122).
  • spot welding is performed in a state in which the zinc coating layer 131 and the zinc-coating layer 220 abut each other, thereby completing the combination structure 4 for metal sheets (S130).
  • FIG. 7 is a view illustrating a vehicle underbody to which a combination structure of metal sheets of the present invention is applied.
  • An aluminum-plated steel sheet 100 or a complex coating layer-plated steel sheet 101 may be used as a front cross member 10 in a vehicle underbody 1, and a zinc-plated steel sheet 200 may be used for a side seal 20, a front floor 30 and the like.
  • the combination structure for metal sheets may be a spot welding coupling structure between, for example, the front cross member 10 and the side seal 20, or a spot welding coupling structure between the front cross member 10 and the front floor 30.
  • the embodiment of the present invention is not limited thereto, and may be applied to all of spot welding coupling structures between an aluminum-plated steel sheet (or complex coating layer-plated steel sheet) using TRIP steel and zinc-plated steel sheet not made of the TRIP steel.

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Abstract

Provided is a combination structure of metal sheets for automobiles which is capable of reinforcing the anti-corrosion property while maintaining the high-strength and high-elongation properties inherent in TRIP steel, in applying the TRIP steel to a vehicle body. This combination structure of metal sheets for automobiles includes: an aluminum-plated steel sheet having an aluminum coating layer formed on a surface of a first steel sheet made of TRIP steel, the aluminum-plated steel sheet being formed by cold working at a temperature no higher than the recrystallization temperature of the TRIP steel; a zinc-plated steel sheet having a zinc coating layer formed on a surface of a second steel sheet, the zinc-plated steel sheet being formed; and a spot welding region created by spot welding of the aluminum-plated steel sheet and the zinc-plated steel sheet in a state in which the aluminum coating layer and the zinc coating layer abut each other.

Description

COMBINATION STRUCTURE OF METAL SHEETS FOR AUTOMOBILE BY USING TRIP STEEL AND METHOD FOR MANUFACTURING THE SAME
The present invention relates to a combination structure of metal sheets for automobiles and a method for manufacturing the same, and more particularly, to a combination structure of metal sheets for automobiles by using TRIP steel and a method for manufacturing the same.
In automobile industry, it is continuously required to increase mileage by reducing the weight of a vehicle and secure the passenger's safety upon collision. In order to satisfy such requirements, there have recently been increasing cases in which a high-strength steel sheet, in particular, a giga-grade steel material (with tensile strength of at least 980 MPa) is used for the vehicle bodies (BIW, body in white). Dual phase (DU) steel, complex phase (CP) steel, hot press forming (HPF) steel, transformation induced plasticity (TRIP) steel, twinning induced plasticity (TWIP) steel, or the like is being used as the giga-grade steel material. The transformation induced plasticity (TRIP) steel among the giga-grade steel materials has both high strength and high elongation, and thus has recently been more spotlighted.
Zinc is widely used as a corrosion resistant coating agent for most steel materials, because the melting point of zinc is relatively low (about 420℃) and is easily processed in melt plating, and zinc has a sacrificial corrosion protection property to a steel base material and thus exhibits an excellent effect. However, the TRIP steel has a problem of causing a crack when subjected to corrosion-resistant coating with zinc, because a liquid metal embrittlement (LME) phenomenon occurs in which zinc melted during spot welding flows into a base material along grain boundaries. FIG. 1 illustrates a cross-sectional view in which spot welding is performed on zinc-plated TRIP steel, and it can be found that cracks occur in a base material due to the occurrence of liquid metal embrittlement (LME). From the standpoint of an automobile maker, since these cracks have risks of critical accidents, non-plated steel materials are exclusively used without corrosion-resistant coating when using TRIP steel for a vehicle body, or limitedly used through a post-heat treatment process or the like after welding.
As an alternative to these problems, aluminum melt plating to the corrosion-resistant coating of TRIP steel may be considered, but this is also difficult to actually use. That is, aluminum used as a coating agent has a relatively high melting point (about 670℃), and when the TRIP steel is heated to about 450℃ or higher, inherent physical properties of the TRIP steel is weakened or disappeared while residual austenite phases inside the steel material are transformed into cementite, ferrite, pealite, etc. even in a short time.
An object to be addressed by the present invention is to provide, in applying TRIP steel to a vehicle body, a combination structure of metal sheets for automobiles which is capable of reinforcing the anti-corrosion property while maintaining the high-strength and high-elongation properties inherent in the TRIP steel, and which is capable of preventing liquid metal embrittlement even during spot welding with another steel sheet.
Another object to be addressed by the present invention is to provide a method for manufacturing the combination structure of metal sheets for automobiles.
Various objects to be addressed by the present invention are not limited to the aforesaid, but other objects not described herein will be clearly understood by those skilled in the art from descriptions below.
In accordance with an embodiment of the present invention, a combination structure for automobiles using TRIP steel, includes: an aluminum-plated steel sheet having an aluminum coating layer formed on a surface of a first steel sheet made of the TRIP steel, and the aluminum-plated steel sheet being formed by cold working at a temperature no higher than a recrystallization temperature of the TRIP steel; a zinc-plated steel sheet having a zinc coating layer formed on a surface of a second steel sheet which is not made of the TRIP steel, the zinc-plated steel sheet being formed; and a spot welding region created by spot welding of the aluminum-plated steel sheet and the zinc-plated steel sheet in a state in which the aluminum coating layer and the zinc coating layer abut each other.
The TRIP steel may have at least 5% of elongation (EL) and at least 980 MPa of tensile strength (TS), and a product of elongation (EL) x tensile strength (TS) may be 10 to 45 GPa·%
The aluminum coating layer may be formed through a physical vapor deposition process.
The aluminum-plated steel sheet may be used for a front cross member in a vehicle underbody.
In accordance with another embodiment of the present invention, a combination structure for automobiles using TRIP steel, includes: a complex coating layer-plated steel sheet in which a lower coating layer made of a metal having a higher melting point than zinc is formed on a surface of a first steel sheet made of the TRIP steel and a zinc coating layer is formed on the lower coating layer, the complex coating layer-plated steel sheet being formed by cold working at a temperature of no higher than a recrystallization temperature of the TRIP steel; a zinc-plated steel sheet having a zinc coating layer formed on a surface of a second steel sheet not made of the TRIP steel, the zinc-plated steel sheet being formed; and a spot welding region created by spot welding of the complex coating layer-plated steel sheet and the zinc-plated steel sheet in a state in which the zinc coating layer of the complex coating layer-plated steel sheet and the zinc coating layer of the zinc-plated steel sheet abut each other.
The lower coating layer may include aluminum, magnesium, copper, or a combination thereof.
In accordance with still another embodiment of the present invention, a method for manufacturing a combination structure of metal sheets for automobiles using TRIP steel, includes: forming an aluminum coating layer on a surface of a first steel sheet made of the TRIP steel to prepare an aluminum-plated steel sheet; forming the aluminum-plated steel sheet by cold working at a temperature of no higher than the recrystallization temperature of the TRIP steel; forming a zinc coating layer on a surface of a second steel sheet not made of the TRIP steel to prepare a zinc-plated steel sheet; and completing the combination structure of metal sheets by spot welding of the aluminum-plated steel sheet and the zinc-plated steel sheet in a state in which the aluminum coating layer and the zinc coating layer abut each other.
The TRIP steel may have at least 5% of elongation (EL) and at least 980 MPa of tensile strength (TS), and a product of elongation (EL) x tensile strength (TS) may be 10 to 45 GPa·%.
The aluminum coating layer may be formed through a physical vapor deposition process.
The aluminum-plated steel sheet may be used for a front cross member in a vehicle underbody.
In accordance with yet another embodiment of the present invention, a method for manufacturing a combination structure of metal sheets for automobiles using TRIP steel, includes: forming a lower coating layer made of a metal having a higher melting point than zinc on a surface of a first steel sheet made of the TRIP steel, and forming a zinc coating layer on the lower coating layer to prepare a complex coating layer-plated steel sheet; forming the complex coating layer-plated steel sheet by cold working at a temperature of no higher than the recrystallization temperature of the TRIP steel; forming a zinc coating layer on a surface of a second steel sheet not made of the TRIP steel to prepare a zinc-plated steel sheet; and completing the combination structure of metal sheets by spot welding of the complex coating layer-plated steel sheet and the zinc-plated steel sheet in a state in which the zinc coating layer of the complex coating layer-plated steel sheet and the zinc coating layer of the zinc-plated steel sheet abut each other.
The lower coating layer may include aluminum, magnesium, copper, or a combination thereof.
Specific matters of other embodiments are included in the detailed description and drawings.
As described above, according to a combination structure of metal sheets for automobiles using TRIP steel and a method for manufacturing the same, the TRIP steel is formed by cold working, so that the inherent high-strength and high-elongation properties of the TRIP steel can be maintained as it is.
In the case of an aluminum-plated steel sheet according to an embodiment of the present invention, since coating is performed by using physical vapor deposition which is a relatively low temperature process while using aluminum as a corrosion-resistant coating agent on a TRIP steel sheet, degradation of the basic physical properties (high strength and high elongation) of the TRIP steel can be prevented. Furthermore, even when a zinc-plated steel sheet in which a zinc coating layer is formed on a steel sheet not made of TRIP steel is subjected to spot welding with an aluminum-plated TRIP steel sheet, an aluminum coating layer protects the TRIP steel sheet and thus, the occurrence of liquid metal embrittlement (LME) due to zinc can be prevented on the TRIP steel sheet.
In addition, a complex coating layer-plated steel sheet according to another embodiment of the present invention uses a complex coating layer including a lower coating layer and an upper coating layer, so that zinc which can be economically coated compared to other metals is used for the upper coating layer, thereby capable of securing anti-corrosion performance, and a lower coating layer made of a metal other than zinc is interposed between TRIP steel and the upper zinc coating layer, thereby capable of preventing the occurrence of liquid metal embrittlement due to zinc on the TRIP steel sheet. In addition, the lower coating layer is configured from a metal (for example, aluminum, magnesium, copper, or a combination thereof) having a higher melting point than zinc, so that zinc melted from the upper zinc coating layer can be effectively prevented from infiltrating into a TRIP steel base material during spot welding.
FIG. 1 is a cross-sectional view of cracks due to liquid metal embrittlement (LME) that may occur during spot welding on a zinc-plated TRIP steel.
FIG. 2 is a cross-sectional view illustrating a combination structure of metal sheets for automobiles in accordance with an embodiment of the present invention.
FIG. 3 is a flowchart sequentially illustrating a method for manufacturing the combination structure of metal sheets for automobiles.
FIG. 4 is a cross-sectional view illustrating a combination structure of metal sheets for automobiles in accordance with another embodiment of the present invention.
FIG. 5 is a cross-sectional view illustrating a combination structure of metal sheets for automobiles in accordance with still another embodiment of the present invention.
FIG. 6 is a flowchart sequentially illustrating a method for manufacturing the combination structure, in FIG. 5, of metal sheets for automobiles.
FIG. 7 is a view illustrating a vehicle underbody to which a combination structure of metal sheets of the present invention is applied.
Advantages and features of the present invention, and implementation methods thereof will be clarified through following embodiments described with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. Further, the present invention is only defined by scopes of claims. Like reference numerals refer to like elements throughout.
FIG. 2 is a cross-sectional view illustrating a combination structure of metal sheets for automobiles in accordance with an embodiment of the present invention. A combination structure 2 of metal sheets for automobiles according to the present invention includes an aluminum-plated steel sheet 100, a zinc-plated steel sheet 200, and a spot welding region 50 created by spot welding of these steel sheets.
The aluminum-plated steel sheet 100 includes a first steel sheet 110 made of TRIP steel and an aluminum coating layer 120 formed on a surface of the first steel sheet 110.
The transformation induced plasticity (TRIP) steel constituting the first steel sheet 110 has excellent processiblility due to a high-elongation behavior caused by transformation induced plasticity of residual austenite. The TRIP steel is residual austenite steel having a phase structure mixed in three phases of austenite, ferrite and bainite by causing the austenite present at a high temperature to remain at room temperature. When the TRIP steel is heat treated after adding C, Si, Mn and the like which are austenite reinforcing elements, austenite remains at room temperature, and the residual austenite is a metastable phase and is transformed into martensite when receiving deformation from the outside. When transformation occurs as such due to working, the TRIP steel has a high work hardening index unlike general steel, has increased necking resistance, and thus has excellent workability. Favorably, the TRIP steel of the present invention, which is used for an underbody of a vehicle, has elongation EL of at least 5%, a tensile strength TS of at least 980 MPa, and the product of elongation EL x tensile strength TS is 10 to 45 GPa·%.
The aluminum coating layer 120 is a corrosion-resistant agent and may be formed at least on one surface of the first steel sheet 110. Since the melting point (about 670ºC) of aluminum is relatively high, when an aluminum coating layer is formed on the first steel sheet 110 by general melt plating, the high-strength and high-elongation properties, which are inherent properties of the TRIP steel, are weakened because residual austenite structures present inside the TRIP steel disappear. Accordingly, in the present invention, the aluminum coating layer 120 is formed on the surface of the first steel sheet 110 through a physical vapor deposition (PVD). However, the embodiment of the present invention is not limited thereto, and the aluminum coating layer may also be formed by electroplating on the first steel sheet 110.
The zinc-plated steel sheet 200 includes a second steel sheet 210 made of a steel material other than TRIP steel and a zinc coating layer 220 formed on a surface of the second steel sheet 210. The second steel sheet 210 may be formed of an arbitrary steel material, but may favorably be formed of a steel material other than the TRIP steel that has a risk of liquid metal embrittlement to zinc. The zinc coating layer 220 may also be formed by using melt plating or electroplating.
The spot welding region 50 is a region created by spot welding of the aluminum-plated steel sheet 100 and the zinc-plated steel sheet 200 in a state in which the aluminum coating layer 120 and the zinc coating layer 220 abut each other. The spot welding region 50 may include a martensite phase.
In the present invention, since the surface of the first steel sheet 110 made of the TRIP steel is coated with the aluminum coating layer 120, a basically excellent anti-corrosion effect can be obtained. In addition, the aluminum coating layer 120 formed on the first steel sheet 110 may prevent the TRIP steel from being subjected to liquid metal embrittlement (LME) by zinc in spot welding with the zinc-plated steel sheet 200.
Hereinafter, referring to FIG. 3, a method for manufacturing a combination structure of metal sheets for automobiles in accordance with an embodiment of the present invention will be described. FIG. 3 is a flowchart sequentially illustrating a method for manufacturing the combination structure, in FIG. 2, of metal sheets for automobiles.
First, an aluminum coating layer 120 is formed on a surface of a first steel sheet 110 made of TRIP steel (S10). Specifically, the aluminum coating layer 120 is formed by using physical vapor deposition on a first surface of the first steel sheet 110, and an aluminum coating layer 120 is formed by using physical vapor deposition on a second surface of the first steel sheet 110, thereby preparing an aluminum-plated steel sheet 100. A continuous vacuum deposition device for physical vapor deposition may be configured to include a vacuum chamber, an aluminum target, a power supply device, a steel sheet feeding part, and the like. Since the physical vapor deposition can be performed in a low-temperature process, and since the internal structure of the TRIP steel is not changed while depositing the aluminum coating layer 120 on the first steel sheet 110, the high-strength and high-elongation physical properties inherent in the TRIP steel may be nonetheless maintained. Aside from the physical vapor deposition, since the electroplating can also be performed in a low-temperature process, the aluminum coating layer 120 may also be formed without changing the internal structure of the TRIP steel.
Subsequently, the aluminum-plated steel sheet 100 is formed by cold working of the aluminum-plated steel sheet 100 at a temperature no higher than recrystallization temperature of the TRIP steel (S12). According to the present embodiment, a low temperature state is maintained while performing coating and forming processes on the first steel sheet 110 made of the TRIP steel, so that the inherent physical property of the TRIP steel may be maintained.
Subsequently, a zinc coating layer 220 is formed on a surface of a second steel sheet 210 made of a steel material other than the TRIP steel, thereby preparing a zinc-plated steel sheet 200 (S20). The zinc coating layer 220 may be formed through various known existing methods. For example, zinc melt plating or zinc electroplating may be used. Subsequently, the zinc-plated steel sheet 200 is formed through various known methods, thereby preparing a metal sheet for an automobile (S22).
As such, after preparing the aluminum-plated steel sheet 100 and the zinc-plated steel sheet 200, spot welding is performed in a state in which the aluminum coating layer 120 and the zinc coating layer 220 abut each other, thereby completing a combination structure 2 for metal sheet materials (S30). A spot welding region 50 formed between the aluminum-plated steel sheet 100 and the zinc-plated steel sheet 200 by the spot welding may include a martensite phase.
Hereinafter, referring to FIG. 4, a combination structure for metal sheets for automobiles according to another embodiment of the present invention will be described. FIG. 4 is a cross-sectional view illustrating a combination structure of metal sheets for automobiles in accordance with another embodiment of the present invention. For convenience of description, a member having the same function as each of the members illustrated in the drawing (FIG. 2) of the previous embodiment, and the description thereon will be omitted, and differences therebetween will be mainly described.
A combination structure 3 of metal sheets according to the present embodiment includes: an aluminum-plated steel sheet 100 made of TRIP steel; a first zinc-plated steel sheet 200 coupled to one surface of the aluminum-plated steel sheet 100; a second zinc-plated steel sheet 300 coupled to the other surface of the aluminum-plated steel sheet 100; and a spot welding region 50 created by the spot welding therebetween. Here, the second zinc-plated steel sheet 300 includes a third steel sheet 310 formed of a steel material other than the TRIP steel and a zinc coating layer 320 formed on a surface of the third steel sheet 310.
In the present embodiment, even when the zinc-plated steel sheets 200 and 300 are placed on both sides of the aluminum-plated steel sheet 100 and spot welding is performed, substantially the same effect as the previous embodiment may be obtained.
Hereinafter, referring to FIG. 5, a combination structure of metal sheets for automobiles according to still another embodiment of the present invention will be described. FIG. 5 is a cross-sectional view illustrating a combination structure of metal sheets for automobiles in accordance with still another embodiment of the present invention. For convenience of description, a member having the same function as each of the members illustrated in the drawing (FIG. 2) of the previous embodiment is referred to as the same reference numerals, and the description thereon will be omitted, and differences therebetween will be mainly described.
A combination structure 4 of metal sheets for automobiles according to the present embodiment includes a complex coating layer-plated steel sheet 101, a zinc-plated steel sheet 200, and a spot welding region 50 generated by spot welding of the steel sheets.
The complex coating layer-plated steel sheet 101 is configured from a first steel sheet 110 made of TRIP steel and complex coating layers 121 and 131 formed on a surface of the first steel sheet 110 as corrosion-resistant agents. The complex coating layers 121 and 131 are formed on the surface of the first steel sheet 110, and has a laminated structure of a lower coating layer 121 made of a metal having a higher melting point than zinc and a zinc coating layer 131 formed on the lower coating layer 121.
The lower coating layer 121 may be formed of aluminum, magnesium, copper, or a combination thereof, and may favorably be formed of aluminum. The lower coating layer 121 may be formed in a thickness of about 0.1 to 3㎛, and be formed on the surface of the first steel sheet 110 through physical vapor deposition. However, the embodiment of the present invention is not limited thereto, and the lower coating layer 121 may also be formed by electroplating on the first steel sheet 110.
The upper coating layer 131 is made of zinc. Since zinc has a lower melting point and higher vapor pressure than other metals and thus has lower energy required to form a coating layer, and a heat treatment temperature is low when performing post-heat treatment for controlling the physical properties of the coating layer, degradation in physical properties due to thermal deformation of a giga-grade high-elongation steel sheet base material can be minimized. When the zinc coating layer 131 directly contacts the TRIP steel sheet, liquid metal embrittlement may occur, and thus, in the present embodiment, the liquid metal embrittlement is prevented by interposing the lower coating layer 121 between the zinc coating layer 131 and the first steel sheet 110. The zinc coating layer 131 may be formed in a thickness of about 5 to 15㎛ and be formed on the surface of the lower coating layer 121 through physical vapor deposition. However, the embodiment of the present invention is not limited thereto, and the zinc coating layer may also be formed by using melt plating or electroplating.
Hereinafter, referring to FIG. 6, a method for manufacturing a combination structure of metal sheets for automobiles of the present invention will be described in detail. FIG. 6 is a flowchart sequentially illustrating a method for manufacturing the combination structure, in FIG. 5, of metal sheets for automobiles.
First, a first coating layer or a lower coating layer 121 is formed by physical vapor deposition, electroplating or the like on a surface of a first steel sheet 110 made of TRIP steel (S110). Subsequently, a second coating layer or a zinc coating layer 131 is formed by physical vapor deposition, melt plating, electroplating or the like on the lower coating layer 121, thereby preparing a complex coating layer-plated steel sheet 101 (S112).
In a preferred embodiment, the lower coating layer 121 made of aluminum is formed on the first steel sheet 110 through physical vapor deposition and the zinc coating layer 131 may be formed through electroplating on the lower coating layer 121. At this point, the thickness of the zinc coating layer 131 is maintained at 50-90% of the total thickness of the complex coating layer, so that anti-corrosion performance may be secured by using zinc which can be more economically coated than other metals, and liquid metal embrittlement may be prevented by interposing the lower coating layer 121 between the zinc coating layer 131 and the TRIP steel sheet 110.
Subsequently, the complex coating layer-plated steel sheet 101 is formed by performing cold working at a temperature no higher than the recrystallization temperature of the TRIP steel (S114). According to the present embodiment, a low temperature state is maintained while performing coating and forming processes on the first steel sheet 110 made of the TRIP steel, and thus, the inherent physical property of the TRIP steel may be maintained.
Subsequently, a zinc coating layer 220 is formed on a surface of a second steel sheet 210 made of a steel material other than the TRIP steel, thereby preparing a zinc-plated steel sheet 200 (S120). The zinc-plated steel sheet 200 is formed through various known methods, thereby preparing a metal sheet for an automobile (S122).
After preparing the complex coating layer-plated steel sheet 101 and the zinc-plated steel sheet 200, spot welding is performed in a state in which the zinc coating layer 131 and the zinc-coating layer 220 abut each other, thereby completing the combination structure 4 for metal sheets (S130).
FIG. 7 is a view illustrating a vehicle underbody to which a combination structure of metal sheets of the present invention is applied.
An aluminum-plated steel sheet 100 or a complex coating layer-plated steel sheet 101 may be used as a front cross member 10 in a vehicle underbody 1, and a zinc-plated steel sheet 200 may be used for a side seal 20, a front floor 30 and the like. Accordingly, the combination structure for metal sheets may be a spot welding coupling structure between, for example, the front cross member 10 and the side seal 20, or a spot welding coupling structure between the front cross member 10 and the front floor 30. However, the embodiment of the present invention is not limited thereto, and may be applied to all of spot welding coupling structures between an aluminum-plated steel sheet (or complex coating layer-plated steel sheet) using TRIP steel and zinc-plated steel sheet not made of the TRIP steel.
So far, embodiments of the present invention have been described with reference to the accompanying drawings, but those skilled in the art to which the present invention belongs could understand that the present invention may be implemented in other specific forms without changing the spirit or characteristics thereof. Thus, the above-disclosed embodiments are to be considered illustrative and not restrictive.

Claims (10)

  1. A combination structure for automobiles using TRIP steel, the combination structure comprising:
    an aluminum-plated steel sheet having an aluminum coating layer formed on a surface of a first steel sheet made of the TRIP steel, the aluminum-plated steel sheet being formed by cold working at a temperature no higher than a recrystallization temperature of the TRIP steel;
    a zinc-plated steel sheet having a zinc coating layer formed on a surface of a second steel sheet which is not made of the TRIP steel, the zinc-plated steel sheet being formed; and
    a spot welding region created by spot welding of the aluminum-plated steel sheet and the zinc-plated steel sheet in a state in which the aluminum coating layer and the zinc coating layer abut each other.
  2. The combination structure of claim 1, wherein the TRIP steel has at least 5% of elongation (EL) and at least 980 MPa of tensile strength (TS), and a product of elongation (EL) x tensile strength (TS) is 10 to 45 GPa·%.
  3. The combination structure of claim 1, wherein the aluminum coating layer is formed through a physical vapor deposition process or electroplating.
  4. A combination structure for automobiles using TRIP steel, the combination structure comprising:
    a complex coating layer-plated steel sheet in which a lower coating layer made of a metal having a higher melting point than zinc is formed on a surface of a first steel sheet made of the TRIP steel and a zinc coating layer is formed on the lower coating layer, the complex coating layer-plated steel sheet being formed by cold working at a temperature of no higher than the recrystallization temperature of the TRIP steel;
    a zinc-plated steel sheet having a zinc coating layer formed on a surface of a second steel sheet not made of the TRIP steel, the zinc-plated steel sheet being formed; and
    a spot welding region created by spot welding of the complex coating layer-plated steel sheet and the zinc-plated steel sheet in a state in which the zinc coating layer of the complex coating layer-plated steel sheet and the zinc coating layer of the zinc-plated steel sheet abut each other.
  5. The combination structure of claim 4, wherein the lower coating layer comprises aluminum, magnesium, copper, or a combination thereof.
  6. A method for manufacturing a combination structure of metal sheets for automobiles using TRIP steel, the method comprising:
    forming an aluminum coating layer on a surface of a first steel sheet made of the TRIP steel to prepare an aluminum-plated steel sheet;
    forming the aluminum-plated steel sheet by cold working at a temperature of no higher than the recrystallization temperature of the TRIP steel;
    forming a zinc coating layer on a surface of a second steel sheet not made of the TRIP steel to prepare a zinc-plated steel sheet; and
    completing the combination structure of metal sheets by spot welding of the aluminum-plated steel sheet and the zinc-plated steel sheet in a state in which the aluminum coating layer and the zinc coating layer abut each other.
  7. The method of claim 6, wherein the TRIP steel has at least 5% of elongation (EL) and at least 980 MPa of tensile strength (TS), and a product of elongation (EL) x tensile strength (TS) is 10 to 45 GPa·%.
  8. The method of claim 6, wherein the aluminum coating layer is formed through a physical vapor deposition process or electroplating.
  9. A method for manufacturing a combination structure of metal sheets for automobiles using TRIP steel, the method comprising:
    forming a lower coating layer made of a metal having a higher melting point than zinc on a surface of a first steel sheet made of the TRIP steel, and forming a zinc coating layer on the lower coating layer to prepare a complex coating layer-plated steel sheet;
    forming the complex coating layer-plated steel sheet by cold working at a temperature of no higher than the recrystallization temperature of the TRIP steel;
    forming a zinc coating layer on a surface of a second steel sheet not made of the TRIP steel to prepare a zinc-plated steel sheet; and
    completing the combination structure of metal sheets by spot welding of the complex coating layer-plated steel sheet and the zinc-plated steel sheet in a state in which the zinc coating layer of the complex coating layer-plated steel sheet and the zinc coating layer of the zinc-plated steel sheet abut each other.
  10. The method of claim 9, wherein the lower coating layer comprises aluminum, magnesium, copper, or a combination thereof.
PCT/KR2019/014586 2018-11-08 2019-10-31 Combination structure of metal sheets for automobile by using trip steel and method for manufacturing the same WO2020096271A1 (en)

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Citations (5)

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Publication number Priority date Publication date Assignee Title
US20090050608A1 (en) * 2004-10-26 2009-02-26 Noboru Hayashi Method for joining iron member and aluminum member
US20130125607A1 (en) * 2010-05-12 2013-05-23 Voestalpine Stahl Gmbh Method for producing a structural part from an iron-manganese steel sheet
US20130189539A1 (en) * 2010-10-11 2013-07-25 Tata Steel Ijmuiden B.V. Steel strip composite and a method for making the same
US20170298482A1 (en) * 2014-10-30 2017-10-19 Jfe Steel Corporation High-strength steel sheet and method for manufacturing same
US20180079026A1 (en) * 2015-03-30 2018-03-22 Nippon Steel & Sumitomo Metal Corporation Method of spot welding

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20090050608A1 (en) * 2004-10-26 2009-02-26 Noboru Hayashi Method for joining iron member and aluminum member
US20130125607A1 (en) * 2010-05-12 2013-05-23 Voestalpine Stahl Gmbh Method for producing a structural part from an iron-manganese steel sheet
US20130189539A1 (en) * 2010-10-11 2013-07-25 Tata Steel Ijmuiden B.V. Steel strip composite and a method for making the same
US20170298482A1 (en) * 2014-10-30 2017-10-19 Jfe Steel Corporation High-strength steel sheet and method for manufacturing same
US20180079026A1 (en) * 2015-03-30 2018-03-22 Nippon Steel & Sumitomo Metal Corporation Method of spot welding

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