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WO2018115945A1 - A method for the manufacture of a galvannealed steel sheet - Google Patents

A method for the manufacture of a galvannealed steel sheet Download PDF

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Publication number
WO2018115945A1
WO2018115945A1 PCT/IB2017/001279 IB2017001279W WO2018115945A1 WO 2018115945 A1 WO2018115945 A1 WO 2018115945A1 IB 2017001279 W IB2017001279 W IB 2017001279W WO 2018115945 A1 WO2018115945 A1 WO 2018115945A1
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WO
WIPO (PCT)
Prior art keywords
steel sheet
anyone
coating
zinc
iron
Prior art date
Application number
PCT/IB2017/001279
Other languages
French (fr)
Inventor
Anirban Chakraborty
Hassan GHASSEMI-ARMAKI
Original Assignee
Arcelormittal
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Arcelormittal filed Critical Arcelormittal
Publication of WO2018115945A1 publication Critical patent/WO2018115945A1/en
Priority to BR112020006461-0A priority Critical patent/BR112020006461B1/en
Priority to CA3076464A priority patent/CA3076464C/en
Priority to PCT/IB2018/058158 priority patent/WO2019082038A1/en
Priority to JP2020522914A priority patent/JP7062058B2/en
Priority to US16/754,589 priority patent/US11578378B2/en
Priority to KR1020207011205A priority patent/KR102383618B1/en
Priority to ES18797150T priority patent/ES2982286T3/en
Priority to CN201880069224.4A priority patent/CN111279007B/en
Priority to HUE18797150A priority patent/HUE067484T2/en
Priority to PL18797150.2T priority patent/PL3701058T3/en
Priority to MX2020004313A priority patent/MX2020004313A/en
Priority to MA50453A priority patent/MA50453B1/en
Priority to RU2020113209A priority patent/RU2738130C1/en
Priority to UAA202003016A priority patent/UA125978C2/en
Priority to FIEP18797150.2T priority patent/FI3701058T3/en
Priority to EP18797150.2A priority patent/EP3701058B1/en
Priority to US18/094,503 priority patent/US12091724B2/en

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Classifications

    • 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
    • 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
    • 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
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • 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
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments
    • 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
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • 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
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • 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
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/02—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material
    • C23C28/023—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material only coatings of metal elements only
    • C23C28/025—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D only coatings only including layers of metallic material only coatings of metal elements only with at least one zinc-based layer
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/76—Adjusting the composition of the atmosphere

Definitions

  • the present invention relates to a method for the manufacture of a galvannealed steel sheet.
  • the invention is particularly well suited for the manufacture of automotive vehicles.
  • Zinc based coatings are generally used because they allow for a protection against corrosion, thanks to barrier protection and cathodic protection.
  • the barrier effect is obtained by the application of a metallic coating on steel surface.
  • the metallic coating prevents the contact between steel and corrosive atmosphere.
  • the barrier effect is independent from the nature of the coating and the substrate.
  • sacrificial cathodic protection is based on the fact that zinc is a metal less noble that steel. Thus, if corrosion occurs, zinc is consumed preferentially as compared to steel. Cathodic protection is essential in areas where steel is directly exposed to corrosive atmosphere, like cut edges where surrounding zinc will be consumed before steel.
  • zinc coated steel sheets are alloyed at high temperature in order to obtain a galvannealed steel sheet.
  • This steel sheet is more resistance to LME than a zinc coated steel sheet because an alloy comprising Fe and Zn is formed which has higher melting point and forms less liquid during spot welding as compared to pure Zinc.
  • the object of the invention is to provide a galvannealed steel sheet which does not have LME issues. It aims to make available, in particular, an easy to implement method in order to obtain an assembly which does not have LME issues after the forming and/or the welding.
  • the object is achieved by providing a method according to claim 1 .
  • the method can also comprise any characteristics of claims 2 to 18.
  • the steel sheet can also comprise any characteristics of claims 20 to 26.
  • spot welded joint can also comprise characteristics of claim according to claim 30.
  • steel or “steel sheet” means a steel sheet, a coil, a plate having a composition allowing the part to achieve a tensile strength up to 2500 MPa and more preferably up to 2000MPa.
  • the tensile strength is above or equal to 500 MPa, preferably above or equal to 980 MPa, advantageously above or equal to 1180 MPa and even above or equal 1470 MPa.
  • the invention relates to a method for the manufacture of a galvannealed steel sheet comprising the following steps:
  • the first coating comprising iron and nickel is deposited by any deposition method known by the man skilled in the art. It can be deposited by vacuum deposition or electro-plating method. Preferably, it is deposited by electro-plating method.
  • the first coating comprises from 10% to 75%, more preferably between 25 to 65% and advantageously between 40 to 60% by weight of iron.
  • the first coating comprises from 25.0 to 90%, preferably from 35 to 75% and advantageously from 40 to 60% by weight of nickel.
  • the first coating consists of iron and nickel.
  • the first coating has a thickness equal or above 0.5 pm. More preferably, the first coating has a thickness between 0.8 and 5.0pm and advantageously between 1.0 and 2.0pm.
  • the thermal treatment is a continuous annealing.
  • the continuous annealing comprises a heating, a soaking and a cooling step. It can further comprise a pre-heating step.
  • the thermal treatment is performed in an atmosphere comprising from 1 to 30% of H 2 at a dew point between -10 and -60°C.
  • the atmosphere comprises from 1 to 10% of H 2 at a dew point between - 40°C and -60°C.
  • the second layer comprises above 70%, more preferably above 80% of zinc and advantageously above 85% of zinc.
  • the second layer can be deposited by any deposition method known by the man skilled in the art. It can be done by hot-dip coating, by vacuum deposition or by electro- galvanizing.
  • the coating based on zinc comprises between 0.01 and0.18 wt.% Al, optionally 0.2-8.0% Mg, the remainder being Zn.
  • the coating based on zinc is deposited by hot-dip galvanizing method.
  • the molten bath can also comprise unavoidable impurities and residuals elements from feeding ingots or from the passage of the steel sheet in the molten bath.
  • the optionally impurities are chosen from Sr, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Zr or Bi, the content by weight of each additional element being inferior to 0.3% by weight.
  • the residual elements from feeding ingots or from the passage of the steel sheet in the molten bath can be iron with a content up to 5.0%, preferably 3.0%, by weight.
  • the second layer consists of zinc.
  • the percentage of Aluminum is comprised between 0.10 and 0.18 wt.% in the bath.
  • step D) the alloying treatment is performed by heating the coated steel sheet obtained in step C) at a temperature between 460 and 550 °C for 5 to 40 seconds.
  • step D is performed at 500°C for 20 seconds.
  • a galvannealed steel sheet is obtained with a first layer comprising iron and nickel directly topped by a second layer based on zinc, the first and second layers being alloyed through diffusion such that the second alloy layer comprising from 5 to 15wt.% of iron, from 0 to 15wt.% and preferably from 1 to 15wt.% of nickel, the balance being zinc.
  • the steel sheet has a microstructure comprising from 1 to 50% of residual austenite, from 1 to 60% of martensite and optionally at least one element chosen from: bainite, ferrite, cementite and pearlite.
  • the martensite can be tempered or untempered.
  • the steel sheet has a microstructure comprising from 5 to 25 % of residual austenite.
  • the steel sheet has a microstructure comprising from 1 to 60% and more preferably between 10 to 60% of tempered martensite.
  • the steel sheet has a microstructure comprising from 10 to 40% of bainite, such bainite comprising from 10 to 20% of lower bainite, from 0 to 15% of upper bainite and from 0 to 5% of carbide free bainite.
  • the steel sheet has a microstructure comprising from 1 to 25% of ferrite.
  • the steel sheet has a microstructure comprising from 1 to 15% untempered martensite.
  • the welding is performed with an effective intensity is between 3kA and 15kA and the force applied on the electrodes is between 150 and 850 daN with said electrode active face diameter being between 4 and 10mm.
  • a spot welded joint of at least two metal sheets, comprising the coated steel sheet according to the present invention is obtained, such said joint containing less than 3 cracks having a size above 100pm and wherein the longest crack has a length below 400 ⁇ .
  • the second metal sheet is a steel sheet or an aluminum sheet. More preferably, the second metal sheet is a steel sheet according to the present invention.
  • the spot welded joint comprises a third metal sheet being a steel sheet or an aluminum sheet.
  • the third metal sheet is a steel sheet according to the present invention.
  • the steel sheet or the spot welded joint according to the present invention can be used for the manufacture of parts for automotive vehicle.
  • Trial 1 to 4 were prepared by deposited a first coating comprising 55% and
  • Trial 5 was prepared by depositing a zinc coating by electro-galvanizing after the continuous annealing of the above steel sheet.
  • Trials according to the present invention show an excellent resistance to LME compared to Trial 5. Indeed, the number of cracks of Trials according to the present invention is very low, even nonexistent, compared to Trial 5.
  • Trials according to the present invention show an excellent resistance to LME as compared to Trial 5.
  • Trials 1 to 4 were bent at a 90° angle followed. An adhesive tape was then applied and removed to verify the coating adhesion with the substrate steel. The coating adhesion of those Trials was excellent.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Coating With Molten Metal (AREA)

Abstract

The present invention relates a method for the manufacture of a galvannealed steel sheet.

Description

A method for the manufacture of a galvannealed steel sheet
The present invention relates to a method for the manufacture of a galvannealed steel sheet. The invention is particularly well suited for the manufacture of automotive vehicles.
Zinc based coatings are generally used because they allow for a protection against corrosion, thanks to barrier protection and cathodic protection. The barrier effect is obtained by the application of a metallic coating on steel surface. Thus, the metallic coating prevents the contact between steel and corrosive atmosphere. The barrier effect is independent from the nature of the coating and the substrate. On the contrary, sacrificial cathodic protection is based on the fact that zinc is a metal less noble that steel. Thus, if corrosion occurs, zinc is consumed preferentially as compared to steel. Cathodic protection is essential in areas where steel is directly exposed to corrosive atmosphere, like cut edges where surrounding zinc will be consumed before steel.
However, when heating steps are performed on such zinc coated steel sheets, for example hot press hardening or welding, cracks are observed in steel which spread from the steel/coating interface. Indeed, occasionally, there is a reduction of metal mechanical properties due to the presence of cracks in the coated steel sheet after the above operation. These cracks appear with the following conditions: high temperature; contact with a liquid metal having a low melting point (such as zinc) in addition to the presence of tensile stress; heterogeneous diffusion of molten metal with substrate grain and grain boundaries. The designation for such phenomenon is known as liquid metal embrittlement (LME), also called liquid metal assisted cracking (LMAC).
Sometimes, zinc coated steel sheets are alloyed at high temperature in order to obtain a galvannealed steel sheet. This steel sheet is more resistance to LME than a zinc coated steel sheet because an alloy comprising Fe and Zn is formed which has higher melting point and forms less liquid during spot welding as compared to pure Zinc.
However, although galvannealed steel sheets are more resistance to LME, when heating steps are performed, some cracks can appear because the resistance to LME is not sufficient enough. Thus, the object of the invention is to provide a galvannealed steel sheet which does not have LME issues. It aims to make available, in particular, an easy to implement method in order to obtain an assembly which does not have LME issues after the forming and/or the welding.
This object is achieved by providing a method according to claim 1 . The method can also comprise any characteristics of claims 2 to 18.
Another object is achieved by providing a steel sheet according to claim 19. The steel sheet can also comprise any characteristics of claims 20 to 26.
Another object is achieved by providing a spot welded joint according to claim 27. The spot welded joint can also comprise characteristics of claim according to claim 30.
Finally, another object is achieved by providing the use of the steel sheet or the assembly according to claim 31.
Other characteristics and advantages of the invention will become apparent from the following detailed description of the invention.
The designation "steel" or "steel sheet" means a steel sheet, a coil, a plate having a composition allowing the part to achieve a tensile strength up to 2500 MPa and more preferably up to 2000MPa. For example, the tensile strength is above or equal to 500 MPa, preferably above or equal to 980 MPa, advantageously above or equal to 1180 MPa and even above or equal 1470 MPa.
The invention relates to a method for the manufacture of a galvannealed steel sheet comprising the following steps:
A. the provision of a pre-coated steel sheet coated with a first coating comprising iron and nickel, such steel sheet having the following chemical composition in weight percent:
0.10 < C < 0.40%,
1 .5 < Mn < 3.0%,
0.7 < Si < 2.0%,
0.05 < AI < 1 .0%
0.75 < (Si+AI) < 3.0 %
and on a purely optional basis, one or more elements such as
Nb < 0.5 %, B < 0.005%,
Cr < 1.0%,
Mo < 0.50%,
Ni≤ 1.0%,
Ti < 0.5%,
the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration,
B. the thermal treatment of such pre-coated steel sheet at a temperature between 600 to 1000°C,
C. the hot-dip coating of the steel sheet obtained in step B) with a second coating based on zinc and
D. an alloying treatment to form a galvannealed steel sheet. Without willing to be bound by any theory, it seems that during the thermal treatment, on the one hand, Ni diffuses towards the steel sheet allowing a Fe-Ni alloy layer. On the other hand, some amount of Ni is still present at the interface between the steel and the coating interface which preventing liquid zinc penetration into steel during any heating steps being for example a welding. Moreover, the presence of iron in the first coating allows for the formation of the Fe-Zn alloy during step D).
The first coating comprising iron and nickel is deposited by any deposition method known by the man skilled in the art. It can be deposited by vacuum deposition or electro-plating method. Preferably, it is deposited by electro-plating method.
Preferably, in step A), the first coating comprises from 10% to 75%, more preferably between 25 to 65% and advantageously between 40 to 60% by weight of iron.
Preferably, in step A), the first coating comprises from 25.0 to 90%, preferably from 35 to 75% and advantageously from 40 to 60% by weight of nickel.
In a preferred embodiment, in step A), the first coating consists of iron and nickel. Preferably, in step A), the first coating has a thickness equal or above 0.5 pm. More preferably, the first coating has a thickness between 0.8 and 5.0pm and advantageously between 1.0 and 2.0pm.
Preferably, in step B), the thermal treatment is a continuous annealing. For example, the continuous annealing comprises a heating, a soaking and a cooling step. It can further comprise a pre-heating step.
Advantageously, the thermal treatment is performed in an atmosphere comprising from 1 to 30% of H2 at a dew point between -10 and -60°C. For example, the atmosphere comprises from 1 to 10% of H2 at a dew point between - 40°C and -60°C.
Advantageously, in step C), the second layer comprises above 70%, more preferably above 80% of zinc and advantageously above 85% of zinc. The second layer can be deposited by any deposition method known by the man skilled in the art. It can be done by hot-dip coating, by vacuum deposition or by electro- galvanizing.
For example, the coating based on zinc comprises between 0.01 and0.18 wt.% Al, optionally 0.2-8.0% Mg, the remainder being Zn.
Preferably, the coating based on zinc is deposited by hot-dip galvanizing method. In this embodiment, the molten bath can also comprise unavoidable impurities and residuals elements from feeding ingots or from the passage of the steel sheet in the molten bath. For example, the optionally impurities are chosen from Sr, Sb, Pb, Ti, Ca, Mn, Sn, La, Ce, Cr, Zr or Bi, the content by weight of each additional element being inferior to 0.3% by weight. The residual elements from feeding ingots or from the passage of the steel sheet in the molten bath can be iron with a content up to 5.0%, preferably 3.0%, by weight.
In a preferred embodiment, the second layer consists of zinc. In this case, when the coating is deposited by hot-dip galvanizing, the percentage of Aluminum is comprised between 0.10 and 0.18 wt.% in the bath.
Preferably, in step D), the alloying treatment is performed by heating the coated steel sheet obtained in step C) at a temperature between 460 and 550 °C for 5 to 40 seconds. For example, step D is performed at 500°C for 20 seconds. With the method according to the present invention, a galvannealed steel sheet is obtained with a first layer comprising iron and nickel directly topped by a second layer based on zinc, the first and second layers being alloyed through diffusion such that the second alloy layer comprising from 5 to 15wt.% of iron, from 0 to 15wt.% and preferably from 1 to 15wt.% of nickel, the balance being zinc.
Preferably, the steel sheet has a microstructure comprising from 1 to 50% of residual austenite, from 1 to 60% of martensite and optionally at least one element chosen from: bainite, ferrite, cementite and pearlite. In this case, the martensite can be tempered or untempered.
In a preferred embodiment, the steel sheet has a microstructure comprising from 5 to 25 % of residual austenite.
Preferably, the steel sheet has a microstructure comprising from 1 to 60% and more preferably between 10 to 60% of tempered martensite.
Advantageously, the steel sheet has a microstructure comprising from 10 to 40% of bainite, such bainite comprising from 10 to 20% of lower bainite, from 0 to 15% of upper bainite and from 0 to 5% of carbide free bainite.
Preferably, the steel sheet has a microstructure comprising from 1 to 25% of ferrite.
Preferably, the steel sheet has a microstructure comprising from 1 to 15% untempered martensite.
After the manufacture of a steel sheet, in order to produce some parts of a vehicle, it is known to assembly by welding two metal sheets. Thus, a spot welded joint is formed during the welding of at least two metal sheets, said spot being the link between the at least two metal sheets.
To produce a spot welded joint according to the invention, the welding is performed with an effective intensity is between 3kA and 15kA and the force applied on the electrodes is between 150 and 850 daN with said electrode active face diameter being between 4 and 10mm.
Thus, a spot welded joint of at least two metal sheets, comprising the coated steel sheet according to the present invention, is obtained, such said joint containing less than 3 cracks having a size above 100pm and wherein the longest crack has a length below 400μηι. Preferably, the second metal sheet is a steel sheet or an aluminum sheet. More preferably, the second metal sheet is a steel sheet according to the present invention.
In another embodiment, the spot welded joint comprises a third metal sheet being a steel sheet or an aluminum sheet. For example, the third metal sheet is a steel sheet according to the present invention.
The steel sheet or the spot welded joint according to the present invention can be used for the manufacture of parts for automotive vehicle.
The invention will now be explained in trials carried out for information only. They are not limiting.
Example
For all samples, steel sheets used have the following composition in weight percent: C=0.37%, Mn=1 .9%, Si=1 .9%, Cr=0.35% and Mo=0.1 %.
Trial 1 to 4 were prepared by deposited a first coating comprising 55% and
75% of Ni, the balance being Fe. Then, a continuous annealing was performed in an atmosphere comprising 5% of H2 and 95% of N2 at a dew point of -45°C. The pre-coated steel sheet was heated at a temperature of 900°C. A zinc coating was deposited by hot-dip galvanizing, the zinc bath comprising 0.2% of Al. The bath temperature was of 460°C. Finally, an alloying treatment was performed at 500°C for 20 seconds in order to obtain a galvannealed steel sheet.
For comparison purpose, Trial 5 was prepared by depositing a zinc coating by electro-galvanizing after the continuous annealing of the above steel sheet.
The resistance to LME of Trials 1 to 5 was evaluated. To this end, for each Trial, two coated steel sheets were welded together by resistance spot welding. The type of the electrode was ISO Type B with a diameter of 16mm; the force of the electrode was of 5kN and the flow rate of water of was 1.5g/min. The welding cycle was cycle is reported in Table 1 . Table 1. Welding Schedule
Figure imgf000008_0001
The number of cracks above Ι ΟΌμηι was then evaluated using an optical as well as SEM (Scanning Electron Microscopy) as reported in Table 2.
Table 2. LME crack details after spot welding (2 layer stack-up condition)
Figure imgf000008_0002
*: according to the present invention.
Trials according to the present invention show an excellent resistance to LME compared to Trial 5. Indeed, the number of cracks of Trials according to the present invention is very low, even nonexistent, compared to Trial 5.
For each Trial, three coated steel sheets were also welded together by resistance spot welding under three layer stack-up configuration. The number of cracks above 100pm was then evaluated using an optical as well as SEM (Scanning Electron Microscopy) as reported in Table 3. Table 3. LME crack details after spot welding (3 layer stack-up condition)
Figure imgf000009_0001
*: according to the present invention.
Trials according to the present invention show an excellent resistance to LME as compared to Trial 5.
Finally, Trials 1 to 4 were bent at a 90° angle followed. An adhesive tape was then applied and removed to verify the coating adhesion with the substrate steel. The coating adhesion of those Trials was excellent.

Claims

Claims
Method for the manufacture of a galvannealed steel sheet comprising the following steps:
A. the provision of a pre-coated steel sheet coated with a first coating comprising iron and nickel, such steel sheet having the following chemical composition in weight percent:
0.10 < C < 0.40%,
1.5 < Mn < 3.0%,
0.7 < Si < 2.0%,
0.05 < AI < 1.0%
0.75 < (Si+AI) < 3.0 %
and on a purely optional basis, one or more elements such as
Nb < 0.5 %,
B < 0.005%,
Cr < 1.0%,
Mo < 0.50%,
Ni < 1.0%,
Ti < 0.5%,
the remainder of the composition making up of iron and inevitable impurities resulting from the elaboration,
B. the thermal treatment of such pre-coated steel sheet at a temperature between 600 to 1000°C,
C. the hot-dip coating of the steel sheet obtained in step B) with a second coating based on zinc and
D. an alloying treatment to form a galvannealed steel sheet.
Method according to claim 1 , wherein in step A), the first coating comprises from 10% to 75% by weight of iron.
Method according to claim 2, wherein in step A), the first coating comprises from 25.0 to 65.0% by weight of iron.
4. Method according to anyone of claims 1 to 3, wherein in step A), the first coating comprises from 40 to 60% of weight of iron.
5. Method according to anyone of claims 1 or 2, wherein in step A), the first coating comprises from 25 to 90% by weight of nickel.
6. Method according to claim 1 or 3, wherein in step A), the first coating comprises from 35 to 75% by weight of nickel. 7. Method according to claim 1 or 4, wherein in step A), the first coating comprises from 40 to 60% by weight of nickel.
8. Method according to anyone of claims 1 to 7, wherein in step A), the first coating consists of iron and nickel.
9. Method according to anyone of claims 1 to 8, wherein in step A), the first coating has a thickness equal or above 0.5 pm.
10. Method according to claim 9, wherein in step A), the first coating has a thickness between 0.8 and 5.0 pm.
1 1 . Method according to claim 10, wherein in step A), the first coating has a thickness between 1.0 and 2.0pm. 12. Method according to anyone of claims 1 to 1 1 , wherein in step C), the second layer comprises above 70% of zinc.
13. Method according to claim 12, wherein in step C), the second layer comprises above 80% of zinc.
14. Method according to claim 13, wherein in step C), the second layer comprises above 85 % of zinc.
15. Method according to claim 14, wherein in step C), the second layer consists of zinc.
16. Method according to anyone of claims 1 to 15, wherein in step B), the thermal treatment is a continuous annealing.
17. Method according to anyone of claims 1 to 16, wherein in step B), the thermal treatment is performed in an atmosphere comprising from 1 to 10% of H2 at a dew point between -30 and -60°C.
18. Method according to anyone of claims 1 to 17, wherein in step D), the alloying treatment is performed by heating the coated steel sheet obtained in step C) at a temperature between 460 and 550 °C.
19. A galvannealed steel sheet obtainable from the method according to anyone of claim 1 to 18 coated with a first layer comprising iron and nickel directly topped by a second layer based on zinc, the first and second layers being alloyed through diffusion such that the second alloy layer comprising from 5 to 15wt.% of iron, from 0 to 15wt.% of nickel, the balance being zinc.
20. A galvannealed steel sheet according to claim 19, wherein the second alloy layer comprising from 1 to 15% by weight of nickel.
21 . A galvannealed steel sheet according to claim 20, wherein the steel microstructure comprising from 1 to 50% of residual austenite, from 1 to 60% of martensite and optionally at least one element chosen from: bainite, ferrite, cementite and pearlite.
22. A galvannealed steel sheet according to claim 21 , wherein the microstructure comprises from 5 to 25 % of residual austenite.
23. A galvannealed steel sheet according to claim 21 or 22, wherein the microstructure comprises from 1 to 60% of tempered martensite.
24. A galvannealed steel sheet according to anyone of claims 21 to 23, wherein the microstructure comprises from 10 to 40% of bainite.
25. A galvannealed steel sheet according to anyone of claims 21 to 24, wherein the microstructure comprises from 1 to 25% of ferrite.
26. A galvannealed steel sheet according to anyone of claims 21 to 25, wherein the microstructure comprises from 1 to 15% of untempered martensite.
27. Spot welded joint of at least two metal sheets comprising at least a steel sheet according to anyone of claims 19 to 26 or obtainable from the method according to anyone of claims 1 to 18, said joint containing less than 3 cracks having a size above 100pm and wherein the longest crack has a length below 400μηι.
28. Spot welded joint according to claim 27, wherein the second metal sheet is a steel sheet or an aluminum sheet.
29. Spot welded joint according to claim 28, wherein the second metal sheet is a steel sheet according to anyone of claims 20 to 26 or obtainable from the method according to claims 1 to 19.
30. Spot welded joint according to anyone of claims 27 to 29, comprising a third metal sheet being a steel sheet or an aluminum sheet.
31. Use of a galvannealed steel sheet according to anyone of claims 19 to 26 or a spot welded joint according to anyone of claims 27 to 30, for the manufacture of automotive vehicle.
PCT/IB2017/001279 2016-12-21 2017-10-24 A method for the manufacture of a galvannealed steel sheet WO2018115945A1 (en)

Priority Applications (17)

Application Number Priority Date Filing Date Title
EP18797150.2A EP3701058B1 (en) 2017-10-24 2018-10-19 A method for the manufacture of a galvannealed steel sheet
ES18797150T ES2982286T3 (en) 2017-10-24 2018-10-19 A process for manufacturing a galvanised steel sheet
PL18797150.2T PL3701058T3 (en) 2017-10-24 2018-10-19 A method for the manufacture of a galvannealed steel sheet
PCT/IB2018/058158 WO2019082038A1 (en) 2017-10-24 2018-10-19 A method for the manufacture of a galvannealed steel sheet
JP2020522914A JP7062058B2 (en) 2017-10-24 2018-10-19 Manufacturing method of alloyed hot-dip galvanized steel sheet
US16/754,589 US11578378B2 (en) 2017-10-24 2018-10-19 Method for the manufacture of a galvannealed steel sheet
KR1020207011205A KR102383618B1 (en) 2017-10-24 2018-10-19 Method for manufacturing hot-dip galvanized steel sheet
BR112020006461-0A BR112020006461B1 (en) 2017-10-24 2018-10-19 METHOD FOR MANUFACTURING A GALVANIZED AND ANNEATED STEEL SHEET
CN201880069224.4A CN111279007B (en) 2017-10-24 2018-10-19 Method for manufacturing zinc-plated diffusion-annealed steel sheet
HUE18797150A HUE067484T2 (en) 2017-10-24 2018-10-19 A method for the manufacture of a galvannealed steel sheet
CA3076464A CA3076464C (en) 2017-10-24 2018-10-19 A method for the manufacture of a galvannealed steel sheet
MX2020004313A MX2020004313A (en) 2017-10-24 2018-10-19 A method for the manufacture of a galvannealed steel sheet.
MA50453A MA50453B1 (en) 2017-10-24 2018-10-19 METHOD FOR MANUFACTURING A GALVANIZED STEEL SHEET
RU2020113209A RU2738130C1 (en) 2017-10-24 2018-10-19 Method of making galvanized and annealed steel sheets
UAA202003016A UA125978C2 (en) 2017-10-24 2018-10-19 A method for the manufacture of a galvannealed steel sheet
FIEP18797150.2T FI3701058T3 (en) 2017-10-24 2018-10-19 A method for the manufacture of a galvannealed steel sheet
US18/094,503 US12091724B2 (en) 2017-10-24 2023-01-09 Galvannealed steel sheet coated with an iron and nickel layer topped by a zinc-based layer

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KR20120074144A (en) * 2010-12-27 2012-07-05 주식회사 포스코 High manganese and aluminium galvannealed steel sheet having excellent powdering resistance and method for manufacturing the same
EP2631319A1 (en) * 2010-10-21 2013-08-28 Posco Galvanized steel sheet having excellent coatability, coating adhesion, and spot weldability, and method for manufacturing same
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Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2004124187A (en) * 2002-10-03 2004-04-22 Sumitomo Metal Ind Ltd High strength galvanized steel sheet with excellent adhesion and weldability
EP2631319A1 (en) * 2010-10-21 2013-08-28 Posco Galvanized steel sheet having excellent coatability, coating adhesion, and spot weldability, and method for manufacturing same
KR20120074144A (en) * 2010-12-27 2012-07-05 주식회사 포스코 High manganese and aluminium galvannealed steel sheet having excellent powdering resistance and method for manufacturing the same
US20160082701A1 (en) * 2013-05-20 2016-03-24 Nippon Steel & Sumitomo Metal Corporation Galvannealed steel sheet and manufacturing method thereof

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