Resistance spot welded joint comprising a zinc coated AHSS steel sheet

{
  "publication_number": "US12337405B2",
  "country": "US",
  "kind": "B2",
  "title": "Resistance spot welded joint comprising a zinc coated AHSS steel sheet",
  "abstract": "A resistance spot welded joint of at least two steel sheets and a method of producing a resistance spot welded joint of at least two steel sheets, wherein at least one of the steel sheets is provided with a Zn containing layer, the steel sheet has a tensile strength of at least 980 MPa, a multiphase microstructure comprising bainite, bainitic ferrite and tempered martensite in a total amount of at least of 75 volume % and retained austenite in an amount of 3-20 volume % and wherein the steel sheet provided with the Zn containing layer has a composition consisting of (in wt. %): C 0.1-0.3; Si 0.2-3.0; Mn 1.0-3.0; Cr≤2.0; Mo≤0.5; Al≤2.0; Nb≤0.2; V≤0.2; Ti 0.01-0.15; B 0.0005-0.01; and balance Fe apart from impurities, wherein the heat affected zone in the spot welded joint is free from cracks having a length of more than 500 μm.",
  "claims": [
    "1. A resistance spot welded joint between at least a first steel sheet and a second steel sheet, wherein the first steel sheet is provided with a Zn containing layer, wherein the first steel sheet has a tensile strength of at least 980 MPa, a multiphase microstructure comprising bainite, bainitic ferrite and tempered martensite in a total amount of at least of 75 volume % and retained austenite in an amount of 3.5-20 volume %, and wherein the first steel sheet has a composition consisting of, in weight %: C 0.1-0.3 Si 0.2-3.0 Mn 1.0-3.0 Cr ≤2.0 Mo ≤0.5 Al ≤2.0 Nb ≤0.2 V ≤0.2 Ti 0.01-0.15 B 0.0005-0.01, and balance Fe apart from impurities, wherein a heat affected zone in the resistance spot welded joint is free from cracks having a length of more than 500 μm, and wherein the multiphase microstructure comprises, in volume %: bainitic ferrite ≥55, polygonal ferrite ≤4, and tempered martensite >0 and ≤30.",
    "2. The resistance spot welded joint according to claim 1, wherein the first steel sheet has the composition fulfilling at least one of the following requirements, in weight %: C 0.15-0.25 Si 0.6-2.0 Mn 2.2-2.8 Cr 0.01-0.8 Mo ≤0.2 Al 0.03-1.0 Nb ≤0.04 V ≤0.04 Ti 0.02-0.06 B 0.001-0.007 wherein the composition also fulfils at least one of the following requirements with respect to impurity content, in weight %: Cu ≤0.15 Ni ≤0.15 P ≤0.02 S ≤0.005 N 0.003-0.005, and wherein the heat affected zone in the resistance spot welded joint is free from cracks having a length of more than 200 μm.",
    "3. The resistance spot welded joint according to claim 1, wherein the first steel sheet fulfils at least one of the requirements a), b), c) and d): a) the composition consisting of, in weight %: C 0.15-0.25 Si 0.7-1.6 Mn 2.2-2.8 Cr 0.01-0.8 Mo ≤0.2 Al 0.03-1.0 Ti 0.02-0.04 B 0.001-0.005 Ti/B 5-30 wherein the composition fulfils at least one of the following requirements with respect to the impurities: Cu ≤0.08 Ni ≤0.08 Nb ≤0.005 V ≤0.01 P ≤0.01 S ≤0.003 N 0.003-0.005 Sn ≤0.015 Zr ≤0.006 As ≤0.012 Ca ≤0.005 H ≤0.0003 O ≤0.0020 b) the multiphase microstructure comprising at least one of, in volume %: bainitic ferrite ≥50 tempered martensite ≤30 fresh martensite ≤20 retained austenite 4-20 polygonal ferrite ≤10 c) at least one of the following mechanical properties; tensile strength (R m) 1100-1350 MPa yield strength (R p0.2) 780-1100 MPa total elongation (A 50) ≤7% hole expansion ratio (λ) ≤20%, and d) wherein the heat affected zone in the resistance spot welded joint is free from cracks having a length of more than 50 μm.",
    "4. The resistance spot welded joint according to claim 1, wherein the multiphase microstructure comprises at least one of, in volume %: bainitic ferrite ≥60 tempered martensite ≤20 fresh martensite ≤10 retained austenite 5-20, or polygonal ferrite ≤6.",
    "5. The resistance spot welded joint according to claim 1, wherein the multiphase microstructure comprises bainite, bainitic ferrite and tempered martensite in a total amount of at least of 80 volume % and at least one of, in volume %: bainitic ferrite ≥65 tempered martensite ≤15 fresh martensite ≤5 retained austenite 6-20, or polygonal ferrite ≤5.",
    "6. The resistance spot welded joint according to claim 1, wherein the first steel sheet fulfils the requirements of: a) the composition consisting of, in weight %: C 0.15-0.25 Si 0.7-1.6 Mn 2.2-2.8 Cr 0.01-0.8 Mo <0.2 Al 0.03-1.0 Ti 0.02-0.04 B 0.001-0.005 Ti/B 5-30 V ≤0.01, wherein the composition fulfils the following requirements with respect to the impurities: Cu ≤0.08 Ni ≤0.08 Nb ≤0.005 P ≤0.01 S ≤0.003 N 0.003-0.005 Sn ≤0.015 Zr ≤0.006 As ≤0.012 Ca ≤0.005 H ≤0.0003 O ≤0.0020, b) the multiphase microstructure comprising, in volume %: fresh martensite ≤20 retained austenite 4-20, c) the following mechanical properties: tensile strength (R m) 1100-1350 MPa yield stregnth (R p0.2) 780-1100 MPa total elongation (A 50) ≥7% hole expansion ratio (λ) ≥20%, and d) wherein the heat affected zone in the resistance spot welded joint is free from cracks having a length of more than 50 μm.",
    "7. The resistance spot welded joint according to claim 2, wherein the first steel sheet has the composition consisting of, in weight %: C 0.15-0.25 Si 0.6-2.0 Mn 2.2-2.8 Cr 0.05-0.8 Mo ≤0.2 Al 0.03-1.0 Nb ≤0.04 V ≤0.04 Ti 0.02-0.06 B 0.001-0.007 Cu ≤0.15 Ni ≤0.15 P ≤0.02 S ≤0.005 N 0.003-0.005, and wherein the heat affected zone in the resistance spot welded joint is free from cracks having a length of more than 100 μm.",
    "8. The resistance spot welded joint according to claim 2, wherein the first steel sheet has the composition fulfilling the following requirements, in weight %: C 0.15-0.25 Si 0.6-2.0 Mn 2.2-2.8 Cr 0.01-0.8 Mo ≤0.2 Al 0.03-1.0 Nb ≤0.04 V ≤0.04 Ti 0.02-0.06 B 0.001-0.007, wherein the composition also fulfils the following requirements with respect to impurity content, in weight %: Cu ≤0.15 Ni ≤0.15 P ≤0.02 S ≤0.005 N 0.003-0.005, and wherein the heat affected zone in the resistance spot welded joint is free from cracks having a length of more than 200 μm.",
    "9. The resistance spot welded joint according to claim 2, wherein the first steel sheet has the composition consisting of, in weight %: C 0.15-0.25 Si 0.6-2.0 Mn 2.2-2.8 Cr 0.05-0.8 Mo ≤0.2 Al 0.03-1.0 Nb ≤0.04 V ≤0.04 Ti 0.02-0.06 B 0.001-0.007 Cu ≤0.15 Ni ≤0.15 P ≤0.02 S ≤0.005 N 0.003-0.005, and wherein the heat affected zone in the resistance spot welded joint is free from cracks having a length of more than 100 μm.",
    "10. A method of producing the resistance spot welded joint according to claim 1, comprising the steps of: (i) providing a hot rolled strip having the composition of the first steel sheet; (ii) batch annealing the strip at 450-650° C. for a total time of 2 to 20 hours; (iii) cold rolling the batch annealed strip with a thickness reduction of at least 50%; (iv) continuously annealing the cold rolled strip at a temperature of 800-1000° C. for 30 to 160 seconds; (v) cooling the strip to a temperature of 200 to 500° C. for 50 to 500 seconds; (vi) providing the strip with the Zn containing layer; (vii) cutting the strip to obtain the first steel sheet provided with the Zn containing layer; and (viii) resistance spot welding the first steel sheet to a second steel sheet.",
    "11. A method of claim 10 wherein the Zn containing layer is formed by means of hot dip galvanizing, galvannealing or electrolytically galvanizing.",
    "12. The method of producing the resistance spot welded joint according to claim 10, wherein the batch annealing is for a total time of 5 to 10 hours."
  ],
  "description_excerpt": "The present invention relates to a resistance spot welded (RSW) joint of at least two steel sheets suitable for applications in automobiles, wherein at least one of the steel sheets is an Advanced High Strength Steel (AHSS). In particular, the invention relates to a RSW joint wherein the AHSS steel sheet has a tensile strength of at least 980 MPa, a multiphase microstructure comprising bainite, bainitic ferrite and tempered martensite in a total amount of at least of 75 volume % and retained austenite in an amount of 3-20 volume % and wherein the steel sheet provided with the Zn containing layer wherein the heat affected zone in the spot welded joint is free from cracks having a length of more than 500 μm.\n\nFor a great variety of applications increased strength levels are a pre-requisite for light-weight constructions in particular in the automotive industry, since car body mass reduction results in reduced fuel consumption. Various AHSS steels have therefore been used in order to reduce the body-in-white (BIW) weight of the vehicles. However, welding defects such as surface cracking may occur in RSW joints of Zn-coated steels. A state-of-the-art review on the surface crack evolution due to liquid metal embrittlement during spot welding is given in the recent article: Diptak Bhattacharya (2018), Liquid metal embrittlement during resistance spot welding of Zn-coated high-strength steels, Materials Science and Technology, 34:15, 1809-1829, DOI: 10.1080/02670836.2018.1461595.",
  "cpc": [
    "B23K 11/20",
    "B23K 11/11",
    "B23K 11/16",
    "B32B 15/011",
    "C21D 1/26",
    "C21D 2211/00",
    "C21D 2211/005",
    "C21D 6/005",
    "C21D 6/008",
    "C22C 18/00",
    "C22C 38/02",
    "C22C 38/04",
    "C22C 38/06",
    "C22C 38/12",
    "C22C 38/14",
    "C22C 38/18",
    "C22C 38/22",
    "C22C 38/24",
    "C22C 38/26",
    "C22C 38/28",
    "C22C 38/32",
    "C22C 38/34",
    "C22C 38/38",
    "C23C 2/06",
    "C23C 2/40"
  ],
  "ipc": [
    "F16B 5/08",
    "B23K 11/11",
    "B23K 11/20",
    "B23K 11/16",
    "B32B 15/01",
    "C21D 1/26",
    "C21D 6/00",
    "C22C 38/02",
    "C22C 38/04",
    "C22C 38/06",
    "C22C 38/12",
    "C22C 38/14",
    "C22C 38/18",
    "C22C 38/22",
    "C22C 38/24",
    "C22C 38/26",
    "C22C 38/28",
    "C22C 38/32",
    "C23C 2/06"
  ],
  "assignees": [
    "Voestalpine Stahl GmbH"
  ],
  "inventors": [
    "Florian WINKELHOFER",
    "Thomas Hebesberger",
    "Martin Gruber"
  ],
  "filing_date": "2019-11-28",
  "publication_date": "2025-06-24",
  "grant_date": "2025-06-24",
  "priority_date": "2018-11-30",
  "application_number": "US-201917289569-A",
  "family_id": "68848225",
  "cited_by_count": 0,
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}