Medium manganese cold-rolled steel intermediate product having a reduced carbon content, and method for providing such a steel intermediate product

{
  "publication_number": "US2022002847A1",
  "country": "US",
  "kind": "A1",
  "title": "Medium manganese cold-rolled steel intermediate product having a reduced carbon content, and method for providing such a steel intermediate product",
  "abstract": "A medium manganese cold-rolled steel intermediate product having an improved fts value is disclosed, the alloy having a carbon fraction within the range 0.003 wt %<C<0.12 wt %, a manganese fraction (Mn) within the range 3.5 wt %<Mn<12 wt %, a silicon fraction (Si) and/or an aluminium fraction (Al) as alloy fractions, where Si wt %+Al wt %<1, optionally further alloy fractions, optional microalloy fractions, in particular a titanium fraction (Ti) and/or a niobium fraction (Nb) and/or vanadium fraction (V), and the remainder of the alloy has iron (Fe) and unavoidable impurities of a melt. A method is also disclosed having the following step that is carried out after the cold-rolling step performing an intercritical box annealing process at a maximum annealing temperature of 684° C.−(517° C.*the carbon fraction in wt %).",
  "claims": [
    "1. A method for providing a medium-manganese cold strip steel intermediate product, its alloy comprising: a carbon content (C) in the range 0.003 wt. %≤C≤0.12 wt. %, a manganese content (Mn) in the range 3.5 wt. %≤Mn≤12 wt. %, a silicon component (Si) and/or an aluminum component (Al) as alloy components, with Si wt. %+Al wt. %<1, optional further alloy components, optional micro-alloy components, in particular a titanium content (Ti) and/or a niobium content (Nb) and/or a vanadium content (V), and where the rest of the alloy comprises iron (Fe) and unavoidable impurities in a melt, where said method comprises the following step, which us executed after a cold-rolling step: performing an intercritical box annealing (S. 2. 1, S. 2. 2) with a maximum annealing temperature (T 2) of 684° C.−(517° C.*the carbon content in wt. %). 2. The method according to claim 1, characterized in that the intercritical box annealing process (S. 2. 1, S. 2. 2) comprises a heating step (E 2), a holding phase (H 2) with a holding period (Δ 2) and a cooling process (Ab 2), whereby the holding period (Δ 2) lasts more than 1000 and less than 6000 minutes and preferably less than 5000 minutes. 3. The method of claim 1, characterized in that the cold strip steel intermediate product shows an fts value which is at least 40%, by choosing an annealing temperature (T 2) which is dependent on the carbon content in wt. % and which is smaller than the maximum annealing temperature. 4. The method according to claim 1, characterized in that the cold strip steel intermediate product shows an fts value, which is at least 104*e (−0001*Rm) at a minimum uniform elongation (A g) of 10% and with a tensile strength (R m) in the range from 590 MPa to 1350 MPa, by choosing an annealing temperature (T 2) which is dependent on the carbon content in wt. % and which is lower than the maximum annealing temperature, whereby this fts value is determined on a non-notched flat tensile sample of the cold strip steel intermediate product. 5. The method according to claim 1, characterized in that a single-step annealing process (GR 1) is applied, in which only the mentioned box annealing method (S. 2. 1) with an intercritical annealing temperature (T 2) is performed that lies above the A c1 -temperature and below a maximum annealing temperature defined by the equation 648° C.−(352° C.*the carbon content in wt. %). 6. The method according to claim 1, characterized in that a two-step annealing process (GR 2) is applied where prior to the intercritical box annealing (S. 2. 2) a fully austenitic annealing (S. 1) is applied. 7. The method according to claim 6, characterized in that the fully austenitic annealing process (S. 1) is carried out with an annealing temperature (T 1) which is above the Ac3-temperature, where the annealing temperature (T 1) is preferably held during a holding period (Δ 1) which is at least 10 seconds and preferably between 10 seconds and 6000 minutes. 8. The method according to claim 6, characterized in that a two-step annealing process (GR 2) is applied, in which first a fully austenitic annealing (S. 1) above the A c3 -temperature and then the intercritical box annealing method (S. 2. 2) is carried out with an intercritical annealing temperature which is above the A c1 -temperature and below the maximum annealing temperature. 9. The method according to claim 1, characterized in that the carbon content (C) is in the range 0.003 wt. %≤C≤0.08 wt. %. 10. The method according to claim 1, characterized in that the manganese content (Mn) lies in the range 4 wt. %≤Mn≤10 wt. %, in particular in the range 5 wt. %≤Mn≤8 wt. %. 11. The method according to claim 1, characterized in that the alloy comprises a silicon content (Si) in the range 0 wt. %≤Si≤1 wt. %, in particular in the range 0.2 wt. %≤Si≤0.9 wt. %. 12. The method according to claim 1, characterized in that the alloy comprises an aluminum content (Al) in the range of 0 wt. %≤Al<1 wt. %, in particular in the range 0.01 wt. %≤Al≤0.7 wt. %. 13. The method according to claim 1, characterized in that the alloy comprises a chromium content (Cr) in the range 0 wt. %≤Cr≤1 wt. %. 14. The method according to claim 1, characterized in that the alloy comprises a sulfur content (S) which is less than 60 ppm. 15. The method according to claim 1, characterized in that the alloy comprises one or more than one of the following micro-alloy components: titanium content (Ti), niobium content (Nb), vanadium content (V). 16. The method according to claim 15, characterized in that the micro-alloy components together have a maximum proportion of 0.15 wt. %. 17. A steel intermediate product provided in accordance with the method of claim 1, characterized in that it has a microstructure with the following proportions: a residual austenite content in the range ≥10% and ≤60%, and preferably in the range ≥10% and ≤40%, an alpha-ferrite content in the range ≥20% and ≤90%, and preferably in the range of ≥50% and ≤80%, and a cementite content in the range ≥0% and ≤5%. 18. The steel intermediate product provided in accordance with the method of claim 6, characterized in that it comprises a microstructure with the following proportions: a martensite content in the range ≥0% and ≤20%, and preferably in the range ≥0% and ≤10%, a residual austenite content in the range ≥10% and ≤60%, and preferably in the range ≥10% and ≤40%, an alpha-ferrite content in the range ≥20% and ≤90%, and preferably in the range of ≥50% and ≤80%, and a cementite content in the range ≥0% and ≤5%."
  ],
  "description_excerpt": "The present invention relates to a method for providing a medium-manganese cold strip steel intermediate product with reduced carbon content and medium-manganese cold strip steel intermediate products with reduced carbon content.\n\nBoth the composition, respectively alloy as well as the heat treatment in the manufacturing process do have a significant influence on the properties of steel products.\n\nA major component of today's steel-alloys is manganese (Mn). The content of manganese in weight % is often in the range between 3 and 12%. These steels are therefore so-called median-manganese steels, which are also referred to as a medium-manganese steels.\n\nMedium manganese steels are characterized, for example, by a structure that consists of a ferritic matrix and retained austenite. The content of ferrite in medium manganese steels usually has a maximum at 90 volume %. The austenite content, however, is usually in the range of about 30 vol. %.\n\nFerrite (also alpha- or α-mixed crystal) is the metallurgic designation of a body-centered cubic iron mixed crystal, in the lattice of which carbon (i.e., in intermediate positions of the lattice) is dissolved interstitially. A pure ferritic structure possesses a low strength but a high ductility. The strength can be improved by adding carbon, whereby this is at the expense of the ductility.\n\nAn austenite structure (also called gamma- or γ-mixed crystal) is a face-centered cubic iron mixed crystal which can form in a steel product.",
  "cpc": [
    "C22C 38/38",
    "C21D 1/26",
    "C21D 2211/001",
    "C21D 2211/003",
    "C21D 2211/005",
    "C21D 2211/008",
    "C21D 6/005",
    "C21D 9/46",
    "C21D 9/52",
    "C22C 38/02",
    "C22C 38/04",
    "C22C 38/06",
    "C22C 38/12",
    "C22C 38/14",
    "C22C 38/18",
    "C22C 38/24",
    "C22C 38/26",
    "C22C 38/28"
  ],
  "ipc": [
    "C21D 9/52",
    "C22C 38/02",
    "C22C 38/06",
    "C22C 38/38",
    "C21D 1/26",
    "C22C 38/04"
  ],
  "assignees": [
    "Voestalpine Stahl GmbH"
  ],
  "inventors": [
    "Daniel Krizan",
    "Katharina STEINDEDER",
    "Reinhold Schneider"
  ],
  "filing_date": "2019-07-04",
  "publication_date": "2022-01-06",
  "priority_date": "2018-07-13",
  "application_number": "US-201917258398-A",
  "family_id": "63012806",
  "cited_by_count": 3,
  "citations": [
    "US20140338800A1",
    "WO2017162450A1",
    "US20190071748A1"
  ]
}