EP4100552A1 - Améliorations apportées à une bande chaude dans des alliages d'acier à haute résistance - Google Patents

Améliorations apportées à une bande chaude dans des alliages d'acier à haute résistance

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Publication number
EP4100552A1
EP4100552A1 EP21750872.0A EP21750872A EP4100552A1 EP 4100552 A1 EP4100552 A1 EP 4100552A1 EP 21750872 A EP21750872 A EP 21750872A EP 4100552 A1 EP4100552 A1 EP 4100552A1
Authority
EP
European Patent Office
Prior art keywords
alloy
tensile
alloy sheet
sheet
mpa
Prior art date
Legal status (The legal status 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 status listed.)
Pending
Application number
EP21750872.0A
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German (de)
English (en)
Other versions
EP4100552A4 (fr
Inventor
Daniel James Branagan
Grant G. Justice
Kurtis R. CLARK
Scott T. LARISH
Alla V. Sergueeva
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United States Steel Corp
Original Assignee
United States Steel Corp
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Publication date
Application filed by United States Steel Corp filed Critical United States Steel Corp
Publication of EP4100552A1 publication Critical patent/EP4100552A1/fr
Publication of EP4100552A4 publication Critical patent/EP4100552A4/fr
Pending legal-status Critical Current

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    • 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
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • C21D1/26—Methods of annealing
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • 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
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for drawing, e.g. for deep-drawing
    • C21D8/0421—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for drawing, e.g. for deep-drawing characterised by the working steps
    • C21D8/0426—Hot rolling
    • 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
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for drawing, e.g. for deep-drawing
    • C21D8/0447—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for drawing, e.g. for deep-drawing characterised by the heat treatment
    • C21D8/0463—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for drawing, e.g. for deep-drawing characterised by the heat treatment following hot rolling
    • 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
    • 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
    • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

  • This application deals with a new class of advanced high strength steel alloys with a combination of toughness and a Directional Toughness Ratio (DTR).
  • DTR Directional Toughness Ratio
  • a combination of yield strength and a Tensile Squareness Ratio (TSR) can be achieved by rolling of the hot band at ambient or identified elevated temperatures.
  • Toughness or resistance to fracture, is crucial in applications across many industries. Automotive manufacturers look for materials with high toughness to absorb energy during a crash event. Shipping industries such as rail need materials with high toughness to protect cargo during transport and in the event of a collision or derailment. Materials with high toughness are desirable in these applications to provide and improve efficiency and safety for both the public and cargo.
  • Toughness as an engineering property can be thought of in a simplified form as the work energy needed to cause failure in a material.
  • the higher the work required to cause failure by a method the higher the toughness of the material.
  • Toughness in materials is becoming increasingly important across many sectors, especially where tough materials can be used to improve safety.
  • high toughness materials are seeing use in so-called crumple zones to reduce the energy that enters the passenger compartment during a collision.
  • gauge thicknesses can be reduced in automobiles in parts where energy absorption is needed to protect passengers, increasing fuel efficiency without compromising safety.
  • These high toughness materials can also be used for road barriers to keep out-of-control vehicles from leaving the roadway or entering the opposing traffic by absorbing energy from the vehicle and safely stopping it.
  • Uniform or isotropic toughness in more than one plane or orientation is of great importance in real-world applications.
  • Designers can plan for specific impacts to best use anisotropic toughness in ideal cases, but this is difficult to achieve in an uncontrolled event.
  • dynamic events such as collisions, it is common for multiple impacts to occur throughout the event.
  • the first impact may start in a favorable manner and result in controlled material deformation.
  • Subsequent impacts in a complex event are likely to occur at different angles of incidence and may be in unfavorable orientations for a given material. These events can be more easily managed in materials where the toughness in different orientations are similar or uniform.
  • Multicomponent systems also pose potential complications for realizing high toughness in real-world applications.
  • the toughness of a multicomponent system is a sum of the energy absorption properties in the system, and the toughness of different pieces of a multicomponent system are often different.
  • a weak point will always exist within any multicomponent system, and this weak point will typically fail before the remainder of the system.
  • the other components in the system will deform and absorb energy until the system is compromised by the failure of the weak point.
  • the full toughness of a material will not be realized because the individual part may only see a partial strain until system failure, for example at 10, 20% or 30% strain.
  • a material that achieves high toughness as a result of high tensile elongation and moderate yield strength therefore may not contribute adequate energy absorption in the system during such an event. This is because a large portion of high toughness, moderate yield material energy absorption, likely occurs at strains greater than the failure strain of low toughness or low ductility materials which may be in the 10 to 30% strain range. Alternately, a material with similar toughness but with higher yield strength, ultimate tensile strength and possibly lower elongation might be expected to contribute more energy absorption prior to system failure in the 10 to 30% strain range. High yield and ultimate tensile strength are therefore desirable in multicomponent systems to provide high energy absorption as a result of high loads at low strain prior to the failure of the system at the weak point.
  • AHSS Advanced High Strength Steels
  • Conventional mild steel has a relatively simple ferritic microstructure; it typically has low carbon content and minimal alloying elements, is readily formed, and is especially sought for its ductility. Widely produced and used, mild steel often serves as a baseline for comparison of other materials.
  • IF interstitial free
  • BH bake hardened
  • HSLA high-strength low- alloy
  • IF internal free
  • BH bake hardened
  • HSLA high-strength low- alloy
  • DP dual phase
  • CP complex phase
  • TRIP transformation induced plasticity
  • High strength steels are those which exhibit a tensile strength of 750 MPa or greater.
  • the development of advanced high strengths steel has been a challenge since increased strength (i.e. > 750 MPa) often results in reduced ductility, cold formability, and toughness.
  • Fracture toughness is a material specific parameter that quantifies a material’s resistance to fracture under specific loading conditions.
  • fracture toughness is difficult to measure for many engineering materials due to the test requirements in order to achieve proper fracture without buckling or other unwanted plastic deformation.
  • other methods of quantifying toughness are regularly employed that are more appropriate to the desired final application and simulate real-world fracture conditions. Calculating the area under a tensile stress - tensile strain curve is one method and provides an approximation of the energy required to fracture a specimen under uniaxial tensile loading with a relatively constant strain rate.
  • Dynamic impact tests are another method used to quantify toughness, wherein rapid, dynamic strains are applied to the material during the test.
  • Charpy v-notch testing is a commonly used technique to measure a material’s resistance to fracture with a crack that was introduced prior to the test.
  • Drop impact tests can also be used to gauge toughness, as a measurement of the material’s ability to resist fracture caused by a moving mass without a previously introduced crack.
  • Results from toughness tests including but not limited to those mentioned previously do not provide a material parameter unlike fracture toughness testing, but rather a value specific to that test, material, and loading condition.
  • the values from each test can be compared to other materials in the same test when needed for materials selection.
  • steel grades with high ductility measured as a total elongation during tensile tests also demonstrate high toughness during impact testing. However, high ductility comes with decrease in strength characteristics including yield strength.
  • the present invention is directed at a method to achieve a combination of properties including toughness and a directional toughness ratio (DTR) in hot band from high strength steel alloys comprising: a. supplying a metal alloy comprising at least 65 at.% Fe with Mn, Cr, Si, and C, and optionally Ni and/or Cu; melting said alloy, cooling at a rate of ⁇ 250 K/s, and solidifying to a thickness of 25.0 mm up to 500 mm; b.
  • DTR directional toughness ratio
  • step (a) processing said alloy by heating and reducing said thickness by rolling the metal alloy in step (a) in a selected direction to form a sheet with thickness of 10.0 mm to 20.0 mm, optionally subjecting said alloy sheet to a temperature from 600 °C up to but not including Tm where T m is a melting point of said alloy, to produce said alloy sheet with a total elongation, El from 30 to 75%, a yield strength at 0.2% offset, Yl, from 250 to 525 MPa, an ultimate tensile strength, Ul, from 750 to 1400 MPa and a Tensile Squareness Ratio, TSR1, from 0.65 to 0.90, wherein:
  • a method to achieve a combination of properties including yield strength and a tensile squareness ratio (TSR) in hot band from steel alloys involving: a. supplying a metal alloy comprising at least 65 at.% Fe with Mn, Cr, Si, and C, and optionally Ni and/or Cu; melting said alloy, cooling at a rate of ⁇ 250 K/s, and solidifying to a thickness of 25.0 mm up to 500 mm; b.
  • TSR tensile squareness ratio
  • processing said alloy by heating and reducing said thickness to form a sheet with thickness of 10.0 mm to 20.0 mm, optionally subjecting said alloy sheet to a temperature from 600 °C up to but not including Tm, to produce said alloy sheet with a total elongation, El from 30 to 75%, a yield strength at 0.2% offset, Yl, from 250 to 525 MPa, an ultimate tensile strength, Ul, from 750 to 1400 MPa and a Tensile Squareness Ratio, TSR1, from 0.65 to 0.90; c.
  • FIG. 1 Summary of steps towards alloys herein to achieve novel combinations of properties including toughness and a Directional Toughness Ratio.
  • FIG. 2 Summary of steps towards alloys herein to achieve novel combinations of properties including yield strength and Tensile Squareness Ratio.
  • FIG. 3 Examples of engineering stress - strain curves with equal area under the curve
  • FIG. 4 Example engineering stress - strain curve showing two regions; A) Toughness calculation based on product of UTS multiplied by strain at UTS (rectangular region light shading), and B) Toughness calculation based on area under the curve up to UTS (dark shading). Note that the TSR is defined as a ratio of area with B/A.
  • FIG. 5 Diagram of V-notch Charpy sample orientations taken from the alloy sheet, to determine a Directional Toughness Ratio (DTR), which was calculated as the impact energy absorbed by a V-notch Charpy sample cut from said alloy sheet where said sample is notched perpendicular to a longitudinal-normal plane of the sheet divided by the impact energy absorbed by a V-notched Charpy sample cut from said alloy sheet where said sample is notched perpendicular to a transverse- longitudinal plane of said sheet.
  • DTR Directional Toughness Ratio
  • FIG. 6 Schematic illustration of the Charpy V-notched sample. Note that dimensions are in mm unless otherwise indicated.
  • FIG. 7 An image of the unbroken Alloy 80 sample in L-N orientation after Charpy testing.
  • FIG. 8 SEM image of the fracture surface of Alloy 66 sample in L-N orientation after Charpy testing.
  • FIG. 9 SEM image of the fracture surface of Alloy 66 sample in L-T orientation after Charpy testing.
  • FIG. 10 SEM image of the fracture surface of Alloy 80 sample in L-T orientation after Charpy testing.
  • FIG. 11 SEM image of the fracture surface of Alloy 84 sample in L-N orientation after Charpy testing.
  • FIG. 12 SEM image of the fracture surface of Alloy 84 sample in L-T orientation after Charpy testing.
  • FIG. 13 SEM micrograph of fracture surface of hot band from Alloy 2 before annealing.
  • FIG. 14 SEM micrograph of fracture surface of hot band from Alloy 2 after annealing at 600°C for 10 min.
  • FIG. 15 SEM micrograph of fracture surface of hot band from Alloy 3 before annealing.
  • FIG. 16 SEM micrograph of fracture surface of hot band from Alloy 3 after annealing at 600°C for 10 min.
  • FIG. 17 Types of material fracture behavior during Instrumented Charpy testing; a) Type I, b) Type II, c) Type III, and d) Type IV.
  • FIG. 18 Force-displacement curve for Alloy 18. Note that Alloy 18 shows Type IV behavior.
  • FIG. 19 Force-displacement curve for Alloy 32. Note that Alloy 32 shows Type IV behavior.
  • FIG. 20 Force-displacement curve for Alloy 37. Note that Alloy 37 shows Type IV behavior.
  • FIG. 21 Force-displacement curve for Alloy 44. Note that Alloy 44 shows Type IV behavior.
  • FIG. 22 Yield strength as a function of reduction during rolling at ambient temperature of hot band from Alloy 66.
  • FIG. 23 Yield strength as a function of reduction during rolling at ambient temperature of hot band from Alloy 80.
  • FIG. 24 Yield strength as a function of reduction during rolling at ambient temperature of hot band from Alloy 84.
  • FIG. 25 Tensile Squareness Ratio as a function of reduction during rolling at ambient temperature of hot band from Alloy 66.
  • FIG. 26 Tensile Squareness Ratio as a function of reduction during rolling at ambient temperature of hot band from Alloy 80.
  • FIG. 27 Tensile Squareness Ratio as a function of reduction during rolling at ambient temperature of hot band from Alloy 84.
  • FIG. 28 Yield strength as a function of reduction during rolling of hot band from Alloy 66 at 550°C.
  • FIG. 29 Yield strength as a function of reduction during rolling of hot band from Alloy 80 at 600°C.
  • FIG. 30 Yield strength as a function of temperature during rolling of hot band from Alloy 84 with 10% reduction.
  • FIG. 31 Tensile Squareness Ratio as a function of reduction during rolling of hot band from Alloy 66 at 550°C.
  • FIG. 32 Tensile Squareness Ratio as a function of reduction during rolling of hot band from Alloy 80 at 600°C.
  • FIG. 33 Tensile Squareness Ratio as a function of temperature during rolling of hot band from Alloy 84 with 10% reduction.
  • FIG. 34 Force-displacement curve for hot band from Alloy 88 with thickness of 11.9 mm. Note that it shows Type IV behavior.
  • FIG. 35 Force-displacement curve for hot band from Alloy 88 after rolling at ambient temperature with 3% reduction. Note that it shows Type IV behavior.
  • FIG. 36 Force-displacement curve for hot band from Alloy 88 after rolling at ambient temperature with 9% reduction. Note that it shows Type IV behavior.
  • FIG. 37 Force-displacement curve for hot band from Alloy 88 with thickness of 17.5 mm. Note that it shows Type IV behavior.
  • FIG. 38 Force-displacement curve for hot band from Alloy 88 after rolling with 20% reduction at 550°C. Note that it shows Type IV behavior.
  • FIG. 39 Force-displacement curve for hot band from Alloy 88 after rolling with 40% reduction at 550°C. Note that it shows Type IV behavior.
  • Alloys herein can be produced in a sheet or plate form by different methods of casting including but not limited to continuous casting, thin slab casting, thick slab and bloom casting with achievement of advanced property combinations by subsequent hot rolling and optionally heat treating. Additional rolling at ambient temperature or rolling at identified elevated temperature can be applied.
  • FIG. 1 and FIG. 2 illustrate a summary of steps towards alloys herein to achieve novel combinations of properties including toughness, yield strength, a Tensile Squareness Ratio (TSR), and a Directional Toughness Ratio (DTR) in a hot band with thickness of 2 mm to 20 mm.
  • TSR Tensile Squareness Ratio
  • DTR Directional Toughness Ratio
  • FIG. 1 illustrates a summary of steps towards alloys herein to achieve a combination of properties in high strength steel including toughness and a Directional Toughness Ratio (DTR).
  • high strength steel are those steel that exhibit a tensile strength of 750 MPa or greater.
  • the method applies to a hot band steel, which may be understood as a sheet of steel that has been hot-rolled to reduce the sheet thickness.
  • the starting condition is to supply a metal alloy Fe, Mn, Cr, Si and C, and additionally at least one element selected from Ni and Cu.
  • the alloy chemistry is melted, cooled at a rate of ⁇ 250 K/s, and solidified to a thickness of 25 mm and up to 500 mm.
  • the casting process can be done in a wide variety of processes including ingot casting, bloom casting, continuous casting, thin slab casting, thick slab casting, belt casting etc. Preferred methods would be continuous casting in sheet or plate form by thin slab casting or thick slab casting.
  • Step 2 in FIG. 1 corresponds to a hot band sheet or plate from the said alloy with thickness from 10.0 to 20.0 mm.
  • hot rolling in a selected direction is applied to a cast product (slab, bloom, etc.).
  • a cast product slab, bloom, etc.
  • the alloy would be cast going through a water cooled mold typically in a thickness range of 150 to 350 mm in thickness and typically processed through a roughing mill hot rolling into a transfer bar slab of 25 to 150 mm in thickness and through the finishing mill into a hot band with thickness of 10.0 to 20.0 mm.
  • the thickness of the alloy in Step 2 may be 10.0 mm to 15.0 mm, or even more preferably, the alloy thickness may be 10.0 mm, 11.0 mm, 12.0 mm, 13.0 mm, 14.0 mm, 15.0 mm, 16.0 mm, 17.0 mm, 18.0 mm, 19.0 mm or 20.0 mm.
  • Another example would be to preferably process the cast material through a thin slab casting process.
  • the newly formed slab goes directly to hot rolling and the strip is rolled into hot band coils with typical thickness from 10.0 to 20.0 mm.
  • bloom casting would be similar to the examples above, but higher thickness might be cast typically from 200 to 500 mm thick and initial breaker steps would be needed to reduce initial cast thickness to allow it to go through hot rolling.
  • Thin slab casting is another process route allowing to get to hot band product with thickness from 10.0 to 20.0 mm.
  • a relatively ductile micro structure develops providing a total elongation from 30 to 75% which exhibits a microvoid coalescence mechanism during fracture.
  • microvoid coalescence is a ductile failure mechanism involving nucleation, growth, and coalescence of microvoids and is preferable to other brittle fracture modes such as intergranular fracture or transgranular cleavage.
  • a hot band product can be subjected to temperature from 600°C to but not including T m , where T m is a melting point of said alloy, by annealing.
  • a hot band from alloys herein has a total elongation (El) from 30 to 75%, a yield strength (Yl) from 250 to 525 MPa, and a tensile strength (Ul) from 750 to 1400 MPa.
  • Some methods for material toughness evaluation are based on tensile testing, which is one of the most widely used methods for mechanical properties evaluation and generally performed by applying a tensile load to a sample with a reduced section by a moving crosshead until the sample fails.
  • the displacement rate of the crosshead in tensile testing is generally kept constant or near constant, resulting in a narrow range of strain rates throughout the test.
  • Tensile testing can provide a measure of toughness by calculating the integral of the engineering stress - engineering strain curve (an area under the curve) and corresponds to the work required to break the sample in tension (FIG. 3). Material behavior during tensile testing in Step 2 in FIG. 1 correspond to Material 1 in FIG.
  • TSR Tensile Squareness Ratio
  • the alloy sheet produced in step (2) is such that it may be positioned as all or part of a storage tank, freight car, railway tank car, vehicular frame, vehicular chassis, vehicular panel and/or the alloy sheet can be utilized in a battery exo-skeleton (i.e. the external skeleton that protects the battery from external damage), battery tray (i.e. a protective structure which may consist of upper and lower halves to prevent water or other corrosive agents from contacting the battery and to provide for improved thermal management), or battery cage (i.e. a structure designed to confine and protect individual batteries or multiple batteries).
  • the alloy sheet can be configured and utilized as all or a portion of any one of these aforementioned applications.
  • the impact energy absorbed by a V-notch in the sheet in the range of 150 J to 850 J is such that it would occur on any such alloy sheet positioned and utilized for these applications.
  • Hot band toughness from said alloy can be evaluated by Charpy V-notch impact testing.
  • Charpy impact testing is performed by the dynamic loading of a sample by a swinging hammer starting from a known height and distance from the center of rotation. The ends of the samples in Charpy impact testing are free and the loading of the sample is similar to a three-point bend test. The total energy of the moving hammer is known, and the energy lost in the impact event with the sample can be measured by the rotation angle of the hammer after impact.
  • the sample has a pre-machined stress concentration point at the V-notch tip which helps encourage crack nucleation.
  • the hammer strikes the side opposite the machined notch.
  • Charpy V-notch impact testing measures the work required to plastically deform the sample as well as crack nucleation and propagation.
  • Uniformity of the toughness in the sheet or plate from the alloys herein may be determined by a Directional Toughness Ratio (DTR).
  • DTR Directional Toughness Ratio
  • the alloys sheet herein may be described, as illustrated in FIG. 5, to have a longitudinal-normal plane, which as shown is the plane that otherwise defines the extended edge portion of the sheet. The longitudinal direction coincides with the rolling direction of the sheet.
  • the sheet may include a transverse-longitudinal plane, which as shown is a plane that otherwise defines the upper or lower surface of the sheet.
  • One may then cut a sample from said sheet and provide a notch that is perpendicular to the longitudinal-normal plane of the sheet and measure the Charpy impact for such first sample (L- N).
  • One may then also cut a sample from said sheet and provide a notch that is perpendicular to the transverse-longitudinal plane of the sheet and measure the Charpy impact for such second sample (L-T).
  • the value of DTR is then determined by dividing the Charpy impact result for such first sample (L-N) by the Charpy impact result for the second sample (L-T).
  • Hot band from alloys herein has Directional Toughness Ratio (DTR) from 0.8 to 1.5.
  • a hot band from alloys herein has Charpy V-notch toughness (Jl) from 150 J to 850 J.
  • FIG. 2 illustrates a summary of steps towards alloys herein to achieve novel combinations of properties including yield strength and a Tensile Squareness Ratio (TSR) in a hot band from alloys herein after rolling at ambient or intermediate temperature.
  • Step 1 and Step 2 are the same as in FIG. 1.
  • Step 3 in FIG. 2 a hot band from alloys herein is subjected to rolling at a first or second temperature range (described herein) when the sheet is passed through a set of rolls to further reduce the sheet thickness.
  • Rolling can be accomplished via a number of means, with mills of a myriad of configurations, including but not limited to reversing mills, tandem mills, and Sendzimir mills.
  • the hot band thickness is reduced by plastically deforming the material utilizing the deformation mechanisms that are available in the material at the first temperature range or second temperature range leading to a change in material properties and behavior.
  • Rolling of hot band from alloys herein preferably occurs at a first ambient temperature range (Tl) in a range from 15 °C to ⁇ 50 °C with reduction from 1 to 10% or at a second higher temperature range (T2) of 50 to 600°C with reduction in thickness from 10 to 40%. In either case, it results in the formation of the metal alloy sheet with an increase in yield strength of the material where Y2>Y 1 leading to higher Tensile Squareness Ratio TSR2>TSR1.
  • TSR2 is calculated to be in a range from 0.75 to 0.95 for the alloys herein.
  • Material behavior during tensile testing in Step 3 in FIG. 2 corresponds to Material 2 in FIG. 3.
  • three applied strain levels are defined and shown in FIG. 3 at strain levels of 10%, 20%, and 30%.
  • the area under the stress-strain curve related to the work require to strain the material to 10% (S2o .i > Slo .i ) is in a range from 5,500 to 10,500 MPa%, to strain to 20% (S2o .2 > S I0 . 2) is in a range from 13,000 to 21,000 MPa%, and to strain to 30% (S2o .3 > SI0 . 3) is in a range from 21,100 to 32,500 MPa%.
  • the alloy sheet produced in step (3) is such that it may be positioned as all or part of a storage tank, freight car, railway tank car, vehicular frame, vehicular chassis, vehicular panel and/or the alloy sheet can be utilized in a battery exo-skeleton, battery tray, or battery cage. Accordingly, the alloy sheet can be configured and utilized as all or a portion of any one of these aforementioned applications.
  • Fe is present at a level of greater than 65 at. % with Mn, Cr, Si, and C and one or two elements from the group of Ni and Cu to provide a formulation of elements that totals 100 atomic percent.
  • the alloys herein can be described as comprising, consisting essentially of, or consisting of the following elements at the indicated atomic percent (when present): Fe (65.0 to 80.0 at.%), Mn (9.5 to 17.5 at.%), Cr (1.0 to 10.0 at.%), Si (1.0 to 5.5 at.%), and C (0.5 to 1.5 at.%), and optionally Ni (0.2 to 4.0 at.%), and Cu (0.1 to 2.5 at.%).
  • the total level of impurities of other elements is in the range of 0 to 5,000 ppm. Accordingly, for an individual element to be defined as an impurity the total amount of the specific element is ⁇ 1,000 ppm. The level of all such selected elements may then be in combination be present to account for the 5,000 ppm impurity, such that the total of all elements present (selected elements and impurities) is 100 atomic percent.
  • the alloys herein were processed into a laboratory sheet by processing of laboratory slabs. Laboratory alloy processing is developed to mimic closely the commercial sheet production by continuous casting and hot rolling. Annealing might be applied depending on targeted properties.
  • Impurities can be present at various levels depending on the feedstock used. Impurity elements would commonly include the following elements; Co, Al, N, P, Ti,, W, Mo, Nb, V, Ga, Ge, Sb, Zr, O, Sn, Ca, B, and S which if present would be in the range from 0 to 5,000 ppm (parts per million) (0 to 0.5 wt%) at the expense of the desired elements noted previously. Preferably, the level of impurities is controlled to fall in the range of 0 to 3,000 ppm (0.3 wt%).
  • a sample of between 50 and 150 mg from each alloy herein was taken in the as-cast condition. This sample was heated to an initial ramp temperature between 900°C and 1300°C depending on alloy chemistry, at a rate of 40°C/min. Temperature was then increased at 10°C/min to a max temperature between 1425°C and 1510°C (maximum temperature limit for the used DSC equipment) depending on alloy chemistry. Once this maximum temperature was achieved, the sample was cooled at a rate of 10°C/min back to the initial ramp temperature before being reheated at 10°C/min to the maximum temperature.
  • DSC Differential Scanning Calorimetry
  • the density of the alloys herein was measured on samples from hot rolled material using the Archimedes method in a specially constructed balance allowing weighing in both air and distilled water.
  • the density of each alloy is tabulated in Table 3 and was found to be in the range from 7.74 to 7.91 g/cm 3 .
  • the accuracy of this technique is ⁇ 0.01 g/cm 3 .
  • the slabs were allowed to soak for 40 minutes prior to hot rolling to ensure they reach the target temperature and then pushed out of the tunnel furnace into a Fenn Model 061 2 high rolling mill.
  • the 50 mm casts were hot rolled for 5 to 10 passes though the mill before being allowed to air cool.
  • Final thickness after hot rolling ranges from 3.89 to 4.24 mm. Although this tensile testing was on such final thicknesses due to load limitations, it is reasonable to conclude that such tensile properties would be present at the range of 10.0 mm to 20.0 mm, since the hot band structure becomes sufficiently homogenized in this range.
  • Tensile specimens were cut from laboratory hot band using wire EDM (electrical discharge machining). Tensile properties were measured on an Instron mechanical testing frame (Model 3369) with hydraulic grips, utilizing Instron’ s Bluehill control and analysis software. Note that the load limits for the 3369 test frame is 150 kN with the hydraulic grips limited to a load of 120 kN. Due to the high strengths of the alloys within and load limit considerations, the maximum sample thickness that can be tensile tested until failure is 7 mm in thickness. To get tensile data then processing was continued to produce hot band of 4 mm thick and results for hot band samples (three to four specimens for each alloy) with thickness of 4 mm are listed in Table 4 including area under the stress - strain curve.
  • the ultimate tensile strength values of the annealed sheet from alloys herein are in a range from 784 to 1218 MPa, the yield strength at 0.2% offset varies from 257 to 391 MPa, the total elongation recorded in the range from 36.6 to 72.1%, and area under tensile stress-strain curve is in a range from 29,272 to 61,055 MPa%.
  • Strength ductility product is calculated as UTS multiplied by total tensile elongation varies from 41,800 to 73,600 MPa%.
  • a tensile squareness ratio (TSR) is determined as the area under stress - strain curve up to UTS divided by the product of UTS multiplied by strain at UTS (FIG. 4) and the calculated values are in a range from to 0.70 to 0.85.
  • An area under tensile curve for alloys herein after straining to 10%, 20%, and 30% is shown in Table 5.
  • the area under the stress- strain curve corresponding to the work required to strain the material to 10% (S10.1) is in a range from 4,791 to 5,973 MPa%, to strain to 20% (S10.2) is in a range from 10,949 to 13,556 MPa%, and to strain to 30% (S 10.3) is in a range from 17,933 to 23,256 MPa%.
  • S10.1 work required to strain the material to 10%
  • S10.2 strain to 20%
  • S 10.3 is in a range from 10,949 to 13,556 MPa%
  • S 10.3 is in a range from 17,933 to 23,256 MPa%.
  • Final thickness ranges after hot rolling from 2.37 to 2.60 mm The hot band in this thickness range is expected to have similar properties in the thickness range of 10 to 20 mm but hot band in this reduced thickness range was much faster to cut through wire EDM into tensile specimens.
  • the ultimate tensile strength values of the sheet from alloys herein are in a range from 902 to 1383 MPa, the yield strength at 0.2% offset (a valued determined by drawing a parallel line on the initial stress strain curve at a 0.2% offset with the resulting point of intersection recorded) varies from 267 to 504 MPa, the total elongation recorded in the range from 34.7 to 65.3 %, and area under tensile stress-strain curve is in a range from 30,497 to 64,399 MPa%.
  • Strength ductility product is calculated as UTS multiplied by total tensile elongation varies from 41,755 to 79,325 MPa%.
  • a tensile squareness ratio is determined as the area under stress - strain curve up to UTS divided by the product of UTS multiplied by strain at UTS (FIG. 4) and the calculated values are in a range from to 0.66 to 0.89.
  • An area under tensile curve for alloys herein after straining to 10%, 20%, and 30% is shown in Table 7.
  • the area under the stress-strain curve corresponding to the work required to strain the material to 10% (S lo .i ) is in a range from 5,521 to 6,861 MPa%
  • to strain to 20% (SI 0 . 2) is in a range from 13,676 to 15,310 MPa%
  • to strain to 30% (SI0 . 3) is in a range from 22,332 to 25,777 MPa%.
  • Table 6 and Table 7 properties correspond to Step 2 in FIG. 1 and FIG. 2.
  • Charpy V-notch samples were machined by wire EDM from hot rolled sheet. Charpy V-notch samples are machined in L- T (sample length in rolling direction, notch in transverse direction) and L-N (sample length in rolling direction, notch in normal direction to rolled surface) orientations as shown in FIG. 5.
  • Charpy V-notch samples were cut in accordance with ASTM E23-12c (10 mm x 55 mm x 10 mm) thickness with a centered 45° V-notch of 0.25 mm radius, 2 mm in depth with a surface finish Ra of less than 2.0 pm on notch and strike face).
  • An example of the Charpy V-notch specimen before testing and its schematic illustration are shown in FIG. 6.
  • Charpy V-notch samples are mounted using self-centering tongs to ensure the samples are centered on the anvil. Testing was done by using the Satec Systems S1-1K3 Pendulum Impact Tester. The arm of the Impact Tester is set to the high latch position with 66.6 lb weights configured for indicating dial maximum reading of -400 J. The latch is released and after contacting the sample, the reading of energy absorbed by the sample is recorded in joules.
  • Alloy 66, Alloy 80 and Alloy 84 hot band with a thickness of >10 mm was used for impact toughness testing.
  • Laboratory slab with thickness of 80 mm was cast from alloys according to the atomic ratios provided in Table 1 and laboratory processed by hot rolling as described in the Main Body section of the current application down to a thickness of ⁇ 12 mm.
  • V-notch Charpy samples were EDM cut from the laboratory produced hot band in different orientations as shown in FIG. 5.
  • V-notch Charpy samples used for impact testing were cut from the sheet in the hot rolled condition. The impact testing was conducted using an Instron SI- IB Charpy impact tester. The V-notch Charpy impact energy varies from 175 to 372 J and results are listed in Table 9. Based on the test results, two types of a Directional Toughness Ratio (DTR) were calculated as the ratio between toughness in the normal orientation of the Charpy impact in respect to hot band surface and toughness in the transverse orientation of the Charpy impact. For samples with longitudinal orientation, DTR (L-N/L-T) varies from 1.09 to 1.18. Note that the Table 9 properties correspond to Step 3 in FIG. 1.
  • Charpy test specimens were cut by wire EDM from the hot rolled material from selected alloys listed in Table 10. Specimens were cut with two orientations (L-N and L-T) as shown in FIG. 5. The test specimens are then wrapped in foil and placed in a pre -heated furnace at 600°C. Argon gas is injected into the furnace during the annealing process. After ten minutes the samples are removed from the furnace and placed under a fan to cool. Specimens are then cleaned with a Scotch-Brite pad and wire brush prior to testing.
  • This Case Example demonstrates that Charpy V-notch toughness of the hot band from alloys herein can be improved by annealing with high toughness in a range from 258 to 407 J and a Directional Toughness Ratio (DTR) from 0.91 to 1.28.
  • DTR Directional Toughness Ratio
  • V-notch Charpy samples were EDM cut from the Alloy 2 and Alloy 3 hot band. Half of the samples were annealed at 600°C for 10 m. Charpy testing was conducted on samples before and after the heat treatment. SEM analysis of the fracture surface was done using an EVO-MAIO scanning electron microscope manufactured by Carl Zeiss SMT Inc. Fracture surface of the hot band samples before and after annealing is shown in FIG. 13 though FIG. 16 for Alloy 2 and Alloy 3.
  • the fracture surface in the V-notch Charpy sample from Alloy 2 before annealing is shown in FIG. 19.
  • Ductile fracture characteristic of microvoid coalescence is seen in the fracture surface. After the annealing at 600°C for 10 m, the fracture is also characteristic of ductile type (FIG. 17). Even though the fracture toughness is improved after annealing, ductile fracture dominates in both cases. It suggests that higher energy absorption after the heat treatment might be caused by structure relaxation from the annealing, but the fracture surface does not show an obvious difference.
  • Fracture surface before and after annealing of Alloy 3 is shown in FIG. 15 and FIG. 16, respectively. Similar to Alloy 2, ductile fracture is seen before and after annealing in Alloy 3.
  • This Case Example shows that the fracture of the hot band material is of ductile nature exhibiting a microvoid coalescence fracture mechanism.
  • Alloy 18, Alloy 32, Alloy 37 and Alloy 44 hot band with a thickness of -10 mm was used for instrumented Charpy testing.
  • Laboratory slab with thickness of 80 mm was cast from alloys according to the atomic ratios provided in Table 1 and laboratory processed by hot rolling as described in the Main Body section of the current application down to a thickness of - 10 mm.
  • Type III fracture behavior is elastic plastic with unstable cleavage failure after stable crack extension.
  • Type IV is elastic plastic with stable crack extension. Note that Type IV is the most ductile fracture type characterized by ductile failure through microvoid coalescense. Force-displacement data were captured in addition to the total energy absorbed and corresponding curves are shown in FIG. 18 through FIG. 21 for each alloy tested.
  • a dynamic fracture toughness J0 . 2 was calculated based on test results and it is listed in Table 11 and varies from 120 to 274 J/cm 2 .
  • the fracture toughness values reported are for notched Charpy specimens.
  • the final fracture toughness values are reported with the subscript “0.2” to indicate the final recommended fracture toughness is the value of Ji dn at a crack extension of 0.2 mm.
  • Hot band with a final hot rolled thickness of ⁇ 11.9 mm was further cold rolled an additional 3% and 9%.
  • Charpy V-notch specimens were cut from the hot band before and after cold rolling by wire EDM and tested according to the procedures described in the Main Body of the current application. The results are listed in Table 12. Absorbed energy values during Charpy V-notch testing of alloys herein are in a range from 96 to 158 J with Directional Toughness Ratio (DTR) from 0.91 to 0.96.
  • DTR Directional Toughness Ratio
  • Hot band with a thickness of -17.5 mm was further processed to an intermediate band by rolling at 550°C an additional 20% and 40%.
  • Charpy V-notch specimens were cut from the hot band before and after cold rolling by wire EDM and tested according to the procedures described in the Main Body of the current application. The results are listed in Table 12. Absorbed energy values during Charpy V-notch testing of alloys herein are in a range from 89 to 171 J with Directional Toughness Ratio (DTR) from 0.94 to 1.20.
  • DTR Directional Toughness Ratio
  • This Case Example demonstrates that rolling of hot band from alloys herein at ambient and intermediate temperatures maintain toughness uniformity with a Directional Toughness Ratio (DTR) from 0.91 to 1.20.
  • DTR Directional Toughness Ratio
  • the Alloy 66 was processed into a laboratory hot band by hot rolling of laboratory cast slabs at high temperatures.
  • Laboratory alloy processing is developed to simulate the hot band production from slabs produced by continuous casting.
  • Industrial hot rolling is performed by heating a slab in a tunnel furnace to a target temperature, then passing it through either a reversing mill or a multi-stand mill or a combination of both to reach the target gauge. During rolling on either mill type, the temperature of the slab is steadily decreasing due to heat loss to the air and to the rolls, so the final hot band is formed at a reduced temperature. This is simulated in the laboratory by heating in a tunnel furnace to between 1100°C and 1250°C, then hot rolling.
  • the laboratory mill is slower than industrial mills causing greater loss of heat during each hot rolling pass so the slab is reheated for 4 minutes between passes to reduce the drop in temperature, the final temperature at target gauge when exiting the laboratory mill commonly is in the range from 800°C to 1000°C, depending on furnace temperature and final thickness.
  • Tensile specimens were cut from laboratory hot band using wire EDM. Since laboratory tensile testing machine is not capable of testing samples with >10 mm thickness, the hot band thick specimens were the “sliced” into multiple specimens with -1.6 mm thickness. Tensile properties were measured on an Instron mechanical testing frame (Model 3369), utilizing Instron’s Bluehill control and analysis software. Tensile testing results are listed in Table 13 representing the properties of the thick hot band.
  • the ultimate tensile strength values of the thick hot band are in a range from 914 to 1060 MPa, the yield strength at 0.2% offset varies from 276 to 340 MPa, the total elongation recorded in the range from 30.4 to 46.4%, and area under tensile stress-strain curve is in a range from 20,149 to 35,535 MPa%.
  • Strength ductility product is calculated as UTS multiplied by total tensile elongation varies from 27,959 to 49,174 MPa%.
  • a Tensile Squareness Ratio (TSR) is determined as the area under stress - strain curve up to UTS divided by the product of UTS multiplied by strain at UTS (FIG. 4) and the calculated values are in a range from 0.71 to 0.73. Note that the Table 13 properties correspond to Step 2 in FIG. 1 and FIG. 2.
  • This Case Example demonstrates tensile properties of the hot band from alloys here with thickness greater than 10 mm with a Tensile Squareness Ratio (TSR) from 0.71 to 0.73.
  • TSR Tensile Squareness Ratio
  • Tensile specimens were cut from laboratory hot band using wire EDM. Tensile properties were measured on an Instron mechanical testing frame (Model 3369), utilizing Instron’s Bluehill control and analysis software. Tensile testing results are listed in Table 14 (hot rolled condition). The yield strength at 0.2% offset varies from 307 to 320 MPa and a Tensile Squareness Ratio (TSR) is determined in a range from 0.72 to 0.82. The area under the stress-strain curve corresponding to the work require to strain the material to 10% (Slo .i ) is in a range from 4,936 to 8,446 MPa%, to strain to 20% (SI 0 . 2) is in a range from 11,618 to 18,193 MPa%, and to strain to 30% (SI 0 . 3) is in a range from 20,015 to 26,899 MPa%.
  • TSR Tensile Squareness Ratio
  • the hot band from each alloy was rolled at ambient temperature with reductions between 2 and 9%. Note that while no external heating was applied, there was some temperature rise depending on the amount of the reduction and the time between passes, so the temperature range was from 15 to up to 50°C. Due to the high thickness of the cold rolled material, the thickness was sliced to approximately 1.6 mm thick for tensile property testing. Between ten and twelve tensile specimens were cut from each cold rolled plate by wire EDM and tested according to the procedures described above. The average values of the measured 0.2% offset yield strength and Tensile Squareness Ratio in each condition is provided in Table 14. Both yield strength and Tensile Squareness Ratio increase with increasing cold rolling reduction.
  • the average yield strength (Y2) is in a range from 403 to 562 MPa and Y2>Y1.
  • the average Tensile Squareness Ratio (TSR2) is between 0.78 and 0.92 and TSR2>TSR1.
  • the area under the stress-strain curve corresponding to the work require to strain the material to 10% (S2o .i ) is in a range from 5,918 to 8,510 MPa%, to strain to 20% (S2o .2 ) is in a range from 13,159 to 18,721 MPa%, and to strain to 30% (S2O . 3) is in a range from 21,310 to 30,015 MPa%.
  • Yield strength (Y2) as a function of rolling reduction at ambient temperature is demonstrated in FIG. 22, FIG. 23 and FIG. 24 for Alloy 66, Alloy 80 and Alloy 84, respectively.
  • Tensile Squareness Ratio (TSR2) as a function of rolling reduction is shown in FIG. 25, FIG. 26 and FIG. 27 for Alloy 66, Alloy 80, and Alloy 84, respectively. Note that this data in the Table 14 correspond to Step 3 in FIG. 2.
  • This Case Example demonstrates that the yield strength of the hot band from alloys herein increases as a function of rolling reduction at ambient temperature forming alloys with yield strength Y2>Y1 and Tensile Squareness Ratio TSR2>TSR1, where Y1 and TSR1 are yield strength and Tensile Squareness Ratio in a hot band before rolling.
  • Hot band material from Alloy 66 was heated to 550°C for 40 minutes, then rolled at to approximately 10%, 20%, 30%, and 40% reductions. The thickness was sliced to approximately 1.6 mm thick for tensile property testing. Between ten and twelve reduced geometry tensile specimens were cut for each rolled condition by wire EDM and tested according to the procedures described above. Hot band material from Alloy 80 was heated to 600°C for 40 minutes, then rolled to approximately 10%, 20%, 30%, and 40% reductions. The thickness was sliced to approximately 1.6 mm thick for tensile property testing. Between ten and twelve reduced geometry tensile specimens were cut for each rolled condition by wire EDM and tested according to the procedures described above.
  • Hot band material from Alloy 84 was rolled with approximately 10% reduction at four intermediate temperatures (50, 150, 250 and 350°C). The thickness was sliced to approximately 1.6 mm thick for tensile property testing. Between ten and twelve reduced geometry tensile specimens were cut for each condition by wire EDM and tested according to the procedures described above. The average values of the measured 0.2% offset yield strength and Tensile Squareness Ratio in each condition are provided in Table 15 and Table 16.
  • the yield strength at 0.2% offset in hot rolled condition varies from 319 to 331 MPa and a Tensile Squareness Ratio (TSR) is determined in a range from 0.70 to 0.83.
  • the area under the stress- strain curve corresponding to the work require to strain the material to 10% (Slo .i ) is in a range from 4,882 to 4,998 MPa%, to strain to 20% (SI0 . 2) is in a range from 11,518 to 11,701 MPa%, and to strain to 30% (SI 0 . 3) is in a range from 19,194 to 19,831 MPa%.
  • the average yield strength (Y2) is in a range from 393 to 746 MPa and Y2>Y1.
  • the average Tensile Squareness Ratio (TSR2) is between 0.78 and 0.91 and TSR2>TSR1.
  • the area under the stress-strain curve corresponding to the work require to strain the material to 10% (S2o .i ) is in a range from 6,466 to 10,007 MPa%, to strain to 20% (S2o .2 ) is in a range from 14,754 to 20,762 MPa%, and to strain to 30% (S2o .3 ) is in a range from 23,962 to 32,102 MPa%. Note that this data in the Table 15 correspond to Step 3 in FIG. 2.
  • Table 16 Tensile Properties As A Function Of Rolling Temperature
  • Yield strength (Y2) as a function of rolling reduction is demonstrated in FIG. 28 and FIG. 29 for Alloy 66 and Alloy 80, respectively. Yield strength (Y2) as a function of rolling temperature is shown in FIG. 30 for Alloy 84.
  • Tensile Squareness Ratio (TSR2) as a function of rolling reduction is shown in FIG. 31 and FIG. 32 for Alloy 66 and Alloy 80, respectively.
  • Tensile Squareness Ratio (TSR2) as a function of rolling temperature is demonstrated in FIG. 33 for Alloy 84.
  • This Case Example demonstrates that the yield strength of the hot band from alloys herein increases as a function of a reduction during rolling at intermediate temperatures forming alloys with yield strength Y2>Y1 and Tensile Squareness Ratio TSR2>TSR1, where Y1 and TSR1 are yield strength and Tensile Squareness Ratio in hot band before rolling.
  • a yield strength at 0.2% offset varies from 268 to 319 MPa and a Tensile Squareness Ratio (TSR2), determined as the area under stress - strain curve up to UTS divided by the product of UTS multiplied by strain at UTS (FIG. 4), is in range from 0.77 to 0.82.
  • the area under the stress-strain curve corresponding to the work require to strain the material to 10% (Slo .i ) is in a range from 4,835 to 4,969 MPa%, to strain to 20% (SI0 . 2) is in a range from 11,499 to 11,787 MPa%, and to strain to 30% (SI0 . 3) is in a range from 19,439 to 19,880 MPa%.
  • Hot band with a final hot rolled thickness of -11.9 mm was further rolled at ambient temperature with additional 3% and 9% reduction. The thickness was also sliced to approximately 1.6 mm thick for tensile property testing. Tensile specimens were cut for each rolled condition by wire EDM and tested according to the procedures described above. Tensile properties were measured on an Instron mechanical testing frame (Model 3369), utilizing Instron’s Bluehill control and analysis software. Tensile properties are listed in Table 17.
  • a yield strength at 0.2% offset (Y2) varies from 327 to 801 MPa and a Tensile Squareness Ratio (TSR2), determined as the area under stress - strain curve up to UTS divided by the product of UTS multiplied by strain at UTS (FIG. 4), is in range from 0.82 to 0.93.
  • the area under the stress-strain curve corresponding to the work require to strain the material to 10% (S2o .i ) is in a range from 6,068 to 9,349 MPa%, to strain to 20% (S2o .2 ) is in a range from 13,891 to 19,555 MPa%, and to strain to 30% (S2o .3 ) is in a range from 22,782 to 30,305 MPa%.
  • Hot band with a thickness of -17.5 mm was further processed to an intermediate band by rolling at 550°C an additional 20% and 40%. The thickness was also sliced to approximately 1.6 mm thick for tensile property testing. Tensile specimens were cut for each rolled condition by wire EDM and tested according to the procedures described above. Tensile properties were measured on an Instron mechanical testing frame (Model 3369), utilizing Instron’s Bluehill control and analysis software. Tensile properties are listed in Table 17.
  • a yield strength at 0.2% offset (Y2) varies from 529 to 840 MPa and a Tensile Squareness Ratio (TSR2), determined as the area under stress - strain curve up to UTS divided by the product of UTS multiplied by strain at UTS (FIG. 4), is in range from 0.89 to 0.94.
  • the area under the stress- strain curve corresponding to the work require to strain the material to 10% (S2o .i ) is in a range from 7,624 to 8,174 MPa%, to strain to 20% (S2o .2 ) is in a range from 16,575 to 17,647 MPa%, and to strain to 30% (S2o .3 ) is in a range from 26,179 to 27,767 MPa%.
  • Standard V-notch Charpy specimens (FIG. 6) were cut by wire EDM for instrumented Charpy impact testing of the hot band before and after rolling at ambient and intermediate temperatures.
  • the Charpy machine used is instrumented with a small force sensor to record load and an encoder to record hammer velocity. The results are listed in Table 18. Based on material response to impact, its fracture behavior can be represented by four types with Type IV being most ductile (FIG. 17). Force-displacement data were captured in addition to the total energy absorbed and corresponding curves are shown in FIG. 34 through FIG. 39.
  • a V-notch Charpy impact energy of the material in the hot rolled condition is measured from 293 to 319 J and after rolling at ambient or intermediate temperatures it varies from 105 to 160 J.
  • a dynamic fracture toughness (J0 . 2) was calculated based on test results and it is listed in Table 18.
  • the fracture toughness values reported are for notched Charpy specimens.
  • the final fracture toughness values are reported with the subscript “0.2” to indicate the final recommended fracture toughness is the value of Ji dn at a crack extension of 0.2 mm.
  • the “Idn” subscript indicates Mode I loading, dynamic testing and a notch was used to initiate the crack.
  • This Case Example demonstrates that a hot band from Alloy 88 exhibits a ductile Type IV behavior in initial state as well as after rolling at ambient or intermediate temperatures. Both rolling at ambient temperature and rolling at intermediate temperature form alloys with yield strength, Y2>Y1, and a Tensile Squareness Ratio, TSR2>TSR1, (TSR) that and Tensile Squareness Ratio, where Y 1 and TSR1 are yield strength and Tensile Squareness Ratio in hot band before rolling.

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  • Mechanical Engineering (AREA)
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  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
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  • Heat Treatment Of Steel (AREA)
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Abstract

La présente invention concerne des alliages d'acier avancés à haute résistance combinant la ténacité et un rapport de ténacité directionnelle (DTR). Une combinaison d'une limite d'élasticité et d'un taux de rectangularité en traction (TSR) peut être obtenue par laminage de la bande chaude à des températures ambiantes ou à des températures élevées identifiées.
EP21750872.0A 2020-02-03 2021-02-03 Améliorations apportées à une bande chaude dans des alliages d'acier à haute résistance Pending EP4100552A4 (fr)

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PCT/US2021/070117 WO2021159142A1 (fr) 2020-02-03 2021-02-03 Améliorations apportées à une bande chaude dans des alliages d'acier à haute résistance

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JP (1) JP2023513091A (fr)
KR (1) KR20220156817A (fr)
CN (1) CN115812108A (fr)
AU (1) AU2021216446A1 (fr)
BR (1) BR112022015099A2 (fr)
CA (1) CA3169236A1 (fr)
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US3378360A (en) * 1964-09-23 1968-04-16 Inland Steel Co Martensitic steel
US4534805A (en) * 1983-03-17 1985-08-13 Armco Inc. Low alloy steel plate and process for production thereof
TW567233B (en) * 2001-03-05 2003-12-21 Kiyohito Ishida Free-cutting tool steel
ES2864636T3 (es) * 2013-10-28 2021-10-14 Nanosteel Co Inc Producción de acero metálico por fundición de planchones
JP6869178B2 (ja) * 2014-09-24 2021-05-12 ザ・ナノスティール・カンパニー・インコーポレーテッド 混合型ミクロ構成成分組織を有する高延性鋼合金
MX2018013869A (es) * 2016-05-10 2019-03-21 United States Steel Corp Productos de acero de alta resistencia y procesos de recocido para fabricar los mismos.
PL3481972T3 (pl) * 2016-07-08 2023-03-13 United States Steel Corporation Sposób wytwarzania stali o wysokiej granicy plastyczności
CN110382130A (zh) * 2017-02-21 2019-10-25 纳米钢公司 金属合金的改善的边缘可成形性
EP3645763A4 (fr) * 2017-06-30 2021-04-21 The Nanosteel Company, Inc. Rétention de propriétés mécaniques dans des alliages d'acier après traitement et en présence de sites de concentration de contraintes
WO2019240910A1 (fr) * 2018-06-14 2019-12-19 The Nanosteel Company, Inc. Alliages d'acier à haute résistance présentant des caractéristiques de ductilité

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CA3169236A1 (fr) 2021-08-12
EP4100552A4 (fr) 2024-02-21
AU2021216446A1 (en) 2022-09-22
WO2021159142A1 (fr) 2021-08-12
JP2023513091A (ja) 2023-03-30
MX2022009457A (es) 2022-09-29
KR20220156817A (ko) 2022-11-28
BR112022015099A2 (pt) 2022-11-08
CN115812108A (zh) 2023-03-17

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