High Strength Steel Alloys With Ductility Characteristics

Abstract

A new class of advanced high strength steel alloys with ductility characteristics such as high impact toughness and improved resistance to penetration, crack resistance and crack propagation.

1 . A method to achieve a strength/ductility characteristic in a metal comprising:
 a. supplying a metal alloy comprising at least 70 atomic percent Fe, at least 9.0 atomic percent Mn, at least 0.4 atomic percent Al, and at least two elements selected from Cr, Si or C, melting and cooling at a rate of ≤250 K/s to a thickness of 25.0 mm to 500.0 mm;   b. processing said alloy into sheet by heating and reducing said thickness to form to a thickness of 1.5 mm to 8.0 mm wherein the sheet exhibits an ultimate tensile strength (TS) of 650 MPa to 1500 MPa, a yield strength (YS) at 0.2% offset of 200 MPa to 1,000 MPa and an elongation (E) from 10% to 70%, wherein the alloy further indicates a strength ductility product (TS×E) in the range of 15,000 MPa % to 75,000 MPa %.   
     
     
         2 . The method of  claim 1  wherein the alloy in (a) contains 70 to 80 at. % Fe, 9.0 to 17.0 at. % Mn, and 0.4 to 6.7 at. % Al. 
     
     
         3 . The method of  claim 1  wherein Cr is selected and is present at a level of 0.2 at. % to 6.3 at. %. 
     
     
         4 . The method of  claim 1  wherein Si is selected and is present at a level of 0.3 at. % to 6.3 at. %. 
     
     
         5 . The method of  claim 1  wherein C is selected and is present at a level of 0.3 at. % to 2.7 at. %. 
     
     
         6 . The method of  claim 1  wherein said alloy is substantially free of nickel and copper such that nickel and copper are present at a level of 0 to 5000 ppm. 
     
     
         7 . The method of  claim 1  wherein the alloy in (a) indicates a solidus temperature from 1300° C. to 1450° C., a liquidus temperature from 1400° C. to 1550° C., and a liquidus to solidus gap from 30° C. to 150° C. 
     
     
         8 . The method of  claim 1  wherein the alloy sheet in (b) has a density from 7.3 g/cm3 to 7.9 g/cm3. 
     
     
         9 . The method of  claim 1  wherein said alloy sheet in (b) indicates an area under a stress-strain curve up to fracture in the range of from 150 to 600 N/mm2. 
     
     
         10 . The method of  claim 1  wherein the alloy sheet in (b) exhibits a Charpy V-notched toughness of 10 J to 150 J. 
     
     
         11 . The method of  claim 1  wherein the alloy sheet in (b) exhibits a thickness normalized Charpy V-Notched toughness from 5 to 25 J/mm. 
     
     
         12 . The method of  claim 1  wherein the alloy sheet in (b) exhibits a bulk fracture toughness from 10 to 400 J. 
     
     
         13 . The method of  claim 1  wherein the alloy sheet in (b) exhibits a thickness normalized bulk fracture toughness from 5 to 50 J/mm. 
     
     
         14 . The method of  claim 1  wherein the alloy sheet in (b) exhibits a drop impact toughness of 100 J to 1250 J. 
     
     
         15 . The method of  claim 1  wherein the alloy sheet in (b) exhibits a thickness normalized drop impact toughness from 75 J/mm to 160 J/mm. 
     
     
         16 . The method of  claim 1  wherein said alloy sheet in (b) is positioned in a storage tank, freight car, or railway tank car. 
     
     
         17 . The method of  claim 1  wherein said alloy sheet formed in (b) is positioned in a vehicular frame, vehicular chassis, or vehicular panel. 
     
     
         18 . A method to achieve a strength/ductility characteristic in a metal comprising:
 a. supplying a metal alloy comprising at least 70 atomic percent Fe, at least 9.0 atomic percent Mn, at least 0.4 atomic percent Al, and at least two elements selected from Cr, Si or C, melting and cooling at a rate of ≤250 K/s to a thickness of 25.0 mm to 500.0 mm;   b. processing said alloy into sheet by heating and reducing said thickness to form to a thickness of 1.5 mm to 8.0 mm;   c. processing said alloy into sheet by reducing said thickness without heating to form to a thickness of 0.5 mm to 3.0 mm wherein the sheet exhibits an ultimate tensile strength (TS) of 650 MPa to 1500 MPa, a yield strength (YS) at 0.2% offset of 200 MPa to 1000 MPa and an elongation (E) from 10.0% to 90.0%, wherein the alloy further indicates a strength ductility product (TS×E) in the range of 10,000 MPa % to 80,000 MPa %.   
     
     
         19 . The method of  claim 18  wherein the alloy in (a) contains 70 to 80 at. % Fe, 9.0 to 17.0 at. % Mn, and 0.4 to 6.7 at. % Al. 
     
     
         20 . The method of  claim 18  wherein Cr is selected and is present at a level of 0.2 at. % to 6.3 at. %. 
     
     
         21 . The method of  claim 18  wherein Si is selected and is present at a level of 0.3 at. % to 6.3 at. %. 
     
     
         22 . The method of  claim 18  wherein C is selected and is present at a level of 0.3 at. % to 2.7 at. %. 
     
     
         23 . The method of  claim 18  wherein said alloy is substantially free of nickel and copper such that nickel and copper are present at a level of 0 to 5000 ppm. 
     
     
         24 . The method of  claim 18  wherein the alloy in (a) indicates a solidus temperature from 1300° C. to 1450° C., a liquidus temperature from 1400° C. to 1550° C., and a liquidus to solidus gap from 30° C. to 150° C. 
     
     
         25 . The method of  claim 18  wherein the alloy sheet in (b) has a density from 7.3 g/cm3 to 7.9 g/cm3. 
     
     
         26 . The method of  claim 18  wherein the alloy sheet in (c) may be annealed from 600° C. up to the solidus temperature. 
     
     
         27 . The method of  claim 18  wherein said alloy sheet in (c) indicates an area under a stress-strain curve up to fracture in the range of from 100 to 700 N/mm2. 
     
     
         28 . The method of  claim 18  wherein the alloy sheet in (c) exhibits a Charpy V-Notched toughness of 0.5 to 75 J. 
     
     
         29 . The method of  claim 18  wherein the alloy sheet in (c) exhibits a thickness normalized Charpy V-Notched toughness from 0.5 J/mm to 25 J/mm. 
     
     
         30 . The method of  claim 18  wherein the impacted alloy sheet in (c) exhibits a bulk fracture toughness from 2 J to 175 J. 
     
     
         31 . The method of  claim 18  wherein the alloy sheet in (c) exhibits a thickness normalized bulk fracture toughness from 1 to 60 J/mm. 
     
     
         32 . The method of  claim 18  wherein the impacted alloy sheet in (c) exhibits a drop impact toughness of 40 J to 700 J. 
     
     
         33 . The method of  claim 18  wherein the alloy sheet in (c) exhibits a thickness normalized drop impact toughness from 75 J/mm to 250 J/mm. 
     
     
         34 . The method of  claim 18  wherein said alloy sheet in (c) is positioned in a storage tank, freight car, or railway tank car. 
     
     
         35 . The method of  claim 18  wherein said alloy sheet formed in (c) is positioned in a vehicular frame, vehicular chassis, or vehicular panel.