Retention Of Mechanical Properties In Steel Alloys After Processing And In The Presence Of Stress Concentration Sites

Abstract

This invention is related to retention of mechanical properties in high strength steel at reduced thicknesses and which mechanical property performance is also retained at relatively high strain rates. These new steels can offer advantages for a myriad of applications where reduced sheet thickness is desirable. In addition, the alloys herein are those that retain useful mechanical properties after introduction of a geometric discontinuity and an accompanying stress concentration.

1 . A method to retain mechanical properties in a metallic sheet alloy at reduced thickness comprising:
 a. supplying a metal alloy comprising at least 70 atomic % iron and at least four or more elements selected from Si, Mn, Cr, Ni, Cu, or C, 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. processing said alloy into sheet form with thickness T 1  with the sheet having a total elongation of X 1  (%), an ultimate tensile strength of Y 1  (MPa), and a yield strength of Z 1  (MPa);   c. further processing said alloy into a second sheet with reduction in thickness T 2 <T 1  with the second sheet having a total elongation of X 2 =X 1 ±10%, an ultimate tensile strength of Y 2 =Y 1 ±50 MPa, and a yield strength of Z 2 =Z 1 ±100 MPa.   
     
     
         2 . The method of  claim 1  wherein said at least 70 atomic percent iron is combined with five or more elements that are selected from Si, Mn, Cr, Ni, Cu, or C. 
     
     
         3 . The method of  claim 1  wherein said at least 70 atomic percent iron is combined with all six elements: Si, Mn, Cr, Ni, Cu, and C. 
     
     
         4 . The method of  claim 1  wherein the levels of the four elements that are selected are as follows: Si (1.14 to 6.13 atomic percent), Mn (3.19 to 15.17 atomic percent), Cr (0.78 to 8.64 atomic percent); Ni (0.9 to 11.44 atomic percent), Cu (0.37 to 1.87 atomic percent). 
     
     
         5 . The method of  claim 1  wherein said alloy formed in step (b), exhibits X 1  (12% to 80%), Y 1  (700 MPa to 2100 MPa), and Z 1  (250 MPa to 1500 MPa). 
     
     
         6 . The method of  claim 1  wherein said alloy formed in step (b), exhibits a thickness from 1.2 mm to 10.0 mm. 
     
     
         7 . The method of  claim 1  wherein said alloy formed in step (c), exhibits X 2  (2 to 90%), Y 2  (650 MPa to 2150 MPa), and Z 2  (150 MPa to 1600 MPa). 
     
     
         8 . The method of  claim 1  wherein said alloy formed in step (c), exhibits a thickness from 0.2 mm to <1.2 mm. 
     
     
         9 . The method of  claim 1  wherein said alloy formed in step (c) is positioned in a vehicular frame, vehicular chassis, or vehicular panel. 
     
     
         10 . The method of  claim 1  wherein said alloy formed in step (c) is positioned in a storage tank, freight car, or railway tank car. 
     
     
         11 . A method to retain mechanical properties in a metallic sheet alloy at relatively high strain rates comprising:
 a. supplying a metal alloy comprising at least 70 atomic % iron and at least four or more elements selected from Si, Mn, Cr, Ni, Cu, or C and melting said alloy and cooling at a rate of <250 K/s and solidifying to a thickness of 25.0 mm up to 500 mm;   b. processing said alloy into sheet form with thickness from 1.2 mm to 10.0 mm with the sheet having a total elongation of X 1  (%), an ultimate tensile strength of Y 1  (MPa), and a yield strength of Z 1  (MPa) when tested at a strain rate S 1 ;   c. deforming the sheet from said alloy at a strain rate S 2 >S 1  with the sheet having a total elongation of X 3 =X 1 ±7%, ultimate tensile strength Y 3 =Y 1 ±200 MPa, and yield strength Z 3 =Z 1 ±50 MPa.   
     
     
         12 . The method of  claim 11  wherein said at least 70 atomic percent iron is combined with five or more elements that are selected from Si, Mn, Cr, Ni, Cu, or C. 
     
     
         13 . The method of  claim 11  wherein said at least 70 atomic percent iron is combined with all six elements: Si, Mn, Cr, Ni, Cu, and C. 
     
     
         14 . The method of  claim 11  wherein the levels of the four elements that are selected are as follows: Si (1.14 to 6.13 atomic percent), Mn (3.19 to 15.17 atomic percent), Cr (0.78 to 8.64 atomic percent); Ni (0.9 to 11.44 atomic percent), Cu (0.37 to 1.87 atomic percent). 
     
     
         15 . The method of  claim 11  wherein said alloy formed in step (b), exhibits X 1  (12% to 80%), Y 1  (700 MPa to 2100 MPa), and Z 1  (250 MPa to 1500 MPa). 
     
     
         16 . The method of  claim 11  wherein the strain rate S 1  is 0.007 s −1  to 0.0001 s −1 . 
     
     
         17 . The method of  claim 11  wherein said alloy formed in step (c), exhibits X 3  (5% to 87%), Y 3  (500 MPa to 2300 MPa), and Z 3  (200 MPa to 1550 MPa). 
     
     
         18 . The method of  claim 11  wherein the strain rate S 2  is >0.007 s −1  to 1200 s −1 . 
     
     
         19 . The method of  claim 11  wherein said processing in step (c) comprises roll forming, metal stamping or hydroforming. 
     
     
         20 . The method of  claim 11  wherein said alloy formed in step (c) is positioned in a vehicular frame, vehicular chassis, or vehicular panel. 
     
     
         21 . The method of  claim 11  wherein said alloy formed in step (c) is positioned in a storage tank, freight car, or railway tank car. 
     
     
         22 . The method of  claim 11  wherein said alloy formed in step (c) is positioned in body armor, shield, military vehicle, or armored vehicle. 
     
     
         23 . A method to retain mechanical properties in a metallic sheet alloy comprising:
 a. supplying a metal alloy comprising at least 70 atomic % iron and at least four or more elements selected from Si, Mn, Cr, Ni, Cu, or C and melting said alloy and cooling at a rate of <250 K/s and solidifying to a thickness of 25.0 mm up to 500 mm;   b. processing said alloy into sheet form with thickness from 1.2 mm to 10.0 mm with the sheet having a total elongation of X 1  (%), an ultimate tensile strength of Y 1  (MPa), and a yield strength of Z 1  (MPa);   c. introducing stress concentration sites and then deforming the sheet from said alloy with the sheet having a total elongation of X 4 ≥0.2X 1  (%), an ultimate tensile strength Y 4 ≥0.5Y 1  (MPa), and a yield strength Z 4 ≥0.6Z 1  (MPa).   
     
     
         24 . The method of  claim 23  wherein said at least 70 atomic percent iron is combined with five or more elements that are selected from Si, Mn, Cr, Ni, Cu, or C. 
     
     
         25 . The method of  claim 23  wherein said at least 70 atomic percent iron is combined with all six elements: Si, Mn, Cr, Ni, Cu, and C. 
     
     
         26 . The method of  claim 23  wherein the levels of the four elements that are selected are as follows: Si (1.14 to 6.13 atomic percent), Mn (3.19 to 15.17 atomic percent), Cr (0.78 to 8.64 atomic percent); Ni (0.9 to 11.44 atomic percent), Cu (0.37 to 1.87 atomic percent). 
     
     
         27 . The method of  claim 23  wherein said alloy formed in step (b), exhibits X 1  (12% to 80%), Y 1  (700 MPa to 2100 MPa), and Z 1  (250 MPa to 1500 MPa). 
     
     
         28 . The method of  claim 23  wherein said processing in step (c) comprises roll forming, metal stamping or hydroforming. 
     
     
         29 . The method of  claim 23  wherein said alloy formed in step (c) is positioned in a vehicular frame, vehicular chassis, or vehicular panel. 
     
     
         30 . The method of  claim 23  wherein said alloy formed in step (c) is positioned in a storage tank, freight car, or railway tank car. 
     
     
         31 . The method of  claim 23  wherein said alloy formed in step (c) is positioned in body armor, shield, military vehicle, or armored vehicle.