High strength high ductility high copper low alloy thin cast strip product and method for making the same

Abstract

A high copper carbon alloy steel sheet made by preparing a molten melt producing an as-cast carbon alloy steel sheet including, (i) by weight, between 0.15 and 0.50% carbon, less than 1.0% chromium, between 3.0 and 9.0% manganese, between 0.2 and 3.5% silicon, more than 0.5% copper, less than 0.01% aluminum, a total oxygen level of at least 50 or 100 ppm; (ii) nickel in levels below 0.5%; (iii) the remainder iron and impurities resulting from melting; solidifying and cooling the molten melt into a sheet less than 10 mm in thickness in a non-oxidizing atmosphere to below 1080° C. at a cooling rate between 1000 and 2000° C./s, hot rolling the as-cast sheet to between 10 and 50% reduction to form a sheet with microstructure providing a tensile strength of at least 900 MPa and an elongation of at least 15%.

What is claimed is: 
     
         1 . A high copper carbon alloy steel sheet made by the steps comprising:
 (a) preparing a molten melt producing an as-cast carbon alloy steel sheet comprising:
 (i) by weight, between 0.15% and 0.50% carbon, less than 1.0% chromium, between 3.0% and 9.0% manganese, between 0.2% and 3.5% silicon, more than 0.5% copper, less than 0.01% aluminum, a total oxygen level of at least 50 ppm; 
 (ii) nickel in levels below 0.5%; 
 (iii) the remainder iron and impurities resulting from melting; 
   (b) solidifying and cooling the molten melt into a sheet less than 10 mm in thickness in a non-oxidizing atmosphere to below 1080° C. at a cooling rate between 1000 and 2000° C./s; and   (c) hot rolling the as-cast carbon alloy steel sheet to between 10% and 50% reduction to form a sheet with a microstructure providing a tensile strength of at least 900 MPa and an elongation of at least 15%.   
     
     
         2 . The high copper carbon alloy steel sheet as claimed in  claim 1 , where the as-cast carbon alloy steel sheet further comprises by weight between 1.0% and 3.5% silicon. 
     
     
         3 . The high copper carbon alloy steel sheet as claimed in  claim 1 , where the molten melt is solidified and cooled into a sheet less than 10 mm in thickness in a non-oxidizing atmosphere to below 1080° C. at a cooling rate between 1200 and 1700° C./s. 
     
     
         4 . The high copper carbon alloy steel sheet as claimed in  claim 1 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing by volume at least 10% bainite, at least 2% ferrite and at least 15% retained austenite. 
     
     
         5 . The high copper carbon alloy steel sheet as claimed in  claim 1 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing a tensile strength of 900 MPa or more and an elongation of at least 25%. 
     
     
         6 . The high copper carbon alloy steel sheet as claimed in  claim 1 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing a tensile strength of 1200 MPa or more and an elongation of at least 20%. 
     
     
         7 . The high copper carbon alloy steel sheet as claimed in  claim 1 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing a tensile strength of 1500 MPa or more and an elongation of at least 15%. 
     
     
         8 . The high copper carbon alloy steel sheet as claimed in  claim 1 , where after the solidifying and hot rolling steps the steel sheet has a thickness of less than 1.6 mm. 
     
     
         9 . The high copper carbon alloy steel sheet as claimed in  claim 1  wherein the molten melt has a free oxygen content between 5 and 70 ppm. 
     
     
         10 . The high copper carbon alloy steel sheet as claimed in  claim 1  comprising the additional steps of:
 (d) annealing the hot rolled sheet to a temperature to obtain a microstructure providing by volume at least 70% austenite; and then 
 (e) rapidly cooling to obtain a microstructure providing by volume at least 20% austenite and at least 50% martensite. 
 
     
     
         11 . The high copper carbon alloy steel sheet as claimed in  claim 1  comprising the additional step of:
 (d) cold rolling the hot rolled sheet up to 5% strain to obtain a microstructure providing by volume at least 20% austenite and at least 50% martensite. 
 
     
     
         12 . The high copper carbon alloy steel sheet as claimed in  claim 1  comprising the additional step of:
 (d) annealing the hot rolled cast sheet with a soak at between 550 and 800° C. for between 5 and 100 hours. 
 
     
     
         13 . The high copper carbon alloy steel sheet as claimed in  claim 12 , where the annealing soak is between 5 and 25 hours. 
     
     
         14 . The high copper carbon alloy steel sheet as claimed in  claim 1  comprising the additional step of:
 (d) continuously annealing the hot rolled cast sheet, where the annealing is in-line. 
 
     
     
         15 . The high copper carbon alloy steel sheet as claimed in  claim 1  comprising the additional step of:
 (d) coating the hot rolled cast sheet in a hot bath of molten metal selected from the group consisting of zinc, aluminum and alloys thereof. 
 
     
     
         16 . The high copper carbon alloy steel sheet as claimed in  claim 1  comprising the additional step of:
 (d) quenching and partitioning the hot rolled cast sheet. 
 
     
     
         17 . The high copper carbon alloy steel sheet as claimed in  claim 1 , where after the solidifying step the steel sheet has more than 50% MnSiO 2  and MnS inclusions with less than 5 μm in size. 
     
     
         18 . A high copper carbon alloy steel sheet made by the steps comprising:
 (a) preparing a molten melt producing an as-cast carbon alloy steel sheet comprising:
 (i) by weight, between 0.15% and 0.50% carbon, less than 1.0% chromium, between 3.0% and 9.0% manganese, between 0.2% and 3.5% silicon, more than 0.5% copper, less than 0.01% aluminum, a total oxygen level of at least 100 ppm; 
 (ii) nickel in levels below 0.5% found in steel scrap used in steelmaking; 
 (iii) the remainder iron and impurities resulting from melting; 
   (b) solidifying and cooling the molten melt into a sheet less than 10 mm in thickness in a non-oxidizing atmosphere to below 1080° C. at a cooling rate between 1000 and 2000° C./s; and   (c) hot rolling the as-cast sheet to between 10% and 50% reduction to form a sheet with a microstructure providing a tensile strength of at least 900 MPa and an elongation of at least 15%.   
     
     
         19 . The high copper carbon alloy steel sheet as claimed in  claim 18 , where the as-cast carbon alloy steel sheet further comprises by weight between 1.0% and 3.5% silicon. 
     
     
         20 . The high copper carbon alloy steel sheet as claimed in  claim 18 , where the molten melt is solidified and cooled into a sheet less than 10 mm in thickness in a non-oxidizing atmosphere to below 1080° C. at a cooling rate between 1200 and 1700° C./s. 
     
     
         21 . The high copper carbon alloy steel sheet as claimed in  claim 18 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing by volume at least 10% bainite, at least 2% ferrite and at least 15% retained austenite. 
     
     
         22 . The high copper carbon alloy steel sheet as claimed in  claim 18 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing a tensile strength of 900 MPa or more and an elongation of at least 25%. 
     
     
         23 . The high copper carbon alloy steel sheet as claimed in  claim 18 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing a tensile strength of 1200 MPa or more and an elongation of at least 20%. 
     
     
         24 . The high copper carbon alloy steel sheet as claimed in  claim 18 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing a tensile strength of 1500 MPa or more and an elongation of at least 15%. 
     
     
         25 . The high copper carbon alloy steel sheet as claimed in  claim 18 , where after the solidifying and hot rolling steps the steel sheet has a thickness of less than 1.6 mm. 
     
     
         26 . The high copper carbon alloy steel sheet as claimed in  claim 18  wherein the molten melt has a free oxygen content between 5 and 70 ppm. 
     
     
         27 . The high copper carbon alloy steel sheet as claimed in  claim 18  comprising the additional steps of:
 (d) annealing the hot rolled sheet to a temperature to obtain a microstructure providing by volume at least 70% austenite; and then 
 (e) rapidly cooling to obtain a microstructure providing by volume at least 20% austenite and at least 50% martensite. 
 
     
     
         28 . The high copper carbon alloy steel sheet as claimed in  claim 18  comprising the additional step of:
 (d) cold rolling the hot rolled sheet up to 5% strain to obtain a microstructure providing by volume at least 20% austenite and at least 50% martensite. 
 
     
     
         29 . The high copper carbon alloy steel sheet as claimed in  claim 18  comprising the additional step of:
 (d) annealing the hot rolled cast sheet with a soak at between 550 and 800° C. for between 5 and 100 hours. 
 
     
     
         30 . The high copper carbon alloy steel sheet as claimed in  claim 29 , where the annealing soak is between 5 and 25 hours. 
     
     
         31 . The high copper carbon alloy steel sheet as claimed in  claim 18  comprising the additional step of:
 (d) continuously annealing the hot rolled cast sheet, where the annealing is in-line. 
 
     
     
         32 . The high copper carbon alloy steel sheet as claimed in  claim 18  comprising the additional step of:
 (d) coating the hot rolled cast sheet in a hot bath of molten metal selected from the group consisting of zinc, aluminum and alloys thereof. 
 
     
     
         33 . The high copper carbon alloy steel sheet as claimed in  claim 18  comprising the additional step of:
 (d) quenching and partitioning the hot rolled cast sheet. 
 
     
     
         34 . The high copper carbon alloy steel sheet as claimed in  claim 18 , where after the solidifying step the steel sheet has more than 50% MnSiO 2  and MnS inclusions with less than 5 μm in size. 
     
     
         35 . A method of making a high copper carbon alloy steel sheet comprising the steps of:
 (a) preparing a molten melt producing an as-cast carbon alloy steel sheet comprising:
 (i) by weight, between 0.15% and 0.50% carbon, less than 1.0% chromium, between 3.0% and 9.0% manganese, between 0.2% and 3.5% silicon, more than 0.5% copper, less than 0.01% aluminum, and a total oxygen level of at least 50 ppm; 
 (ii) nickel in levels below 0.5%; 
 (iii) the remainder iron and impurities resulting from melting; 
   (b) forming the melt into a casting pool supported on casting surfaces of a pair of cooled casting rolls having a nip there between;   (c) counter rotating the casting rolls to form a thin cast sheet of less than 10 mm in thickness extending downwardly from the nip;   (d) cooling the cast sheet to below 1080° C. at a cooling rate between 1000 and 2000° C./s in a non-oxidizing atmosphere; and   (e) hot rolling the thin cast sheet to between 10% and 50% reduction to form a thin cast sheet with a microstructure providing a tensile strength of at least 900 MPa and an elongation of at least 15%.   
     
     
         36 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 35 , where the as-cast carbon alloy steel sheet further comprises by weight between 1.0% and 3.5% silicon. 
     
     
         37 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 35 , where the molten melt is solidified and rolled into a sheet less than 10 mm in thickness in a non-oxidizing atmosphere to below 1080° C. at a cooling rate between 1200 and 1700° C./s. 
     
     
         38 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 35 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing by volume at least 10% bainite, at least 2% ferrite and at least 15% retained austenite. 
     
     
         39 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 35 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing a tensile strength of 900 MPa or more and an elongation of at least 25%. 
     
     
         40 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 35 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing a tensile strength of 1200 MPa or more and an elongation of at least 20%. 
     
     
         41 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 35 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing a tensile strength of 1500 MPa or more and an elongation of at least 15%. 
     
     
         42 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 35 , where after the solidifying and hot rolling steps the steel sheet has a thickness of less than 1.6 mm. 
     
     
         43 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 35  wherein the molten melt has a free oxygen content between 5 and 70 ppm. 
     
     
         44 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 35  comprising the additional steps of:
 (d) annealing the hot rolled sheet to a temperature to obtain a microstructure providing by volume at least 70% austenite; and 
 (e) rapidly cooling to obtain a microstructure providing by volume at least 20% austenite and at least 50% martensite. 
 
     
     
         45 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 35  comprising the additional step of:
 (d) cold rolling the hot rolled sheet up to 5% strain to obtain a microstructure providing by volume at least 20% austenite and at least 50% martensite. 
 
     
     
         46 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 35  comprising the additional step of:
 (d) annealing the hot rolled cast sheet with a soak at between 550 and 800° C. for between 5 and 100 hours. 
 
     
     
         47 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 46 , where the annealing soak is between 5 and 25 hours. 
     
     
         48 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 35  comprising the additional step of:
 (d) continuously annealing the hot rolled cast sheet, where the annealing is in-line. 
 
     
     
         49 . The method of making the high copper carbon alloy steel sheet as claimed in  claim 35  comprising the additional step of:
 (d) coating the hot rolled cast sheet in a hot bath of molten metal selected from the group consisting of zinc, aluminum and alloys thereof. 
 
     
     
         50 . The method of making the high copper carbon alloy steel sheet as claimed in  claim 35  comprising the additional step of:
 (d) quenching and partitioning the hot rolled cast sheet. 
 
     
     
         51 . The method of making high copper carbon alloy steel sheet as claimed in  claim 35 , where after the solidifying and hot rolling steps the steel sheet has more than 50% MnSiO 2  and MnS inclusions less than 5 μm in size. 
     
     
         52 . A method of making a high copper carbon alloy steel sheet comprising the steps of:
 (a) preparing a molten melt producing an as-cast carbon alloy steel sheet comprising:
 (i) by weight, between 0.15% and 0.50% carbon, less than 1.0% chromium, between 3.0% and 9.0% manganese, between 0.2% and 3.5% silicon, more than 0.5% copper, less than 0.01% aluminum, and a total oxygen level of at least 100 ppm; 
 (ii) nickel at a level below 0.5%; 
 (iii) the remainder iron and impurities resulting from melting; 
   (b) forming the melt into a casting pool supported on casting surfaces of a pair of cooled casting rolls having a nip there between;   (c) counter rotating the casting rolls to form a thin cast sheet of less than 10 mm in thickness extending downwardly from the nip;   (d) cooling the cast sheet to below 1080° C. at a cooling rate between 1000 and 2000° C./s in a non-oxidizing atmosphere; and   (e) hot rolling the thin cast sheet to between 10% and 50% reduction to form a thin cast sheet with a microstructure providing a tensile strength of at least 900 MPa and an elongation of at least 15%.   
     
     
         53 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 52 , where the as-cast carbon alloy steel sheet further comprises by weight between 1.0% and 3.5% silicon. 
     
     
         54 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 52 , where the molten melt is solidified and rolled into a sheet less than 10 mm in thickness in a non-oxidizing atmosphere to below 1080° C. at a cooling rate between 1200 and 1700° C./s. 
     
     
         55 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 52 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing by volume at least 10% bainite, at least 2% ferrite and at least 15% retained austenite. 
     
     
         56 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 52 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing a tensile strength of 900 MPa or more and an elongation of at least 25%. 
     
     
         57 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 52 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing a tensile strength of 1200 MPa or more and an elongation of at least 20%. 
     
     
         58 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 52 , where after the solidifying and hot rolling steps the steel sheet has a microstructure providing a tensile strength of 1500 MPa or more and an elongation of at least 15%. 
     
     
         59 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 52 , where after the solidifying and hot rolling steps the steel sheet has a thickness of less than 1.6 mm. 
     
     
         60 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 52  wherein the molten melt has a free oxygen content between 5 and 70 ppm. 
     
     
         61 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 52  comprising the additional steps of:
 (d) annealing the hot rolled sheet to a temperature to obtain a microstructure providing by volume at least 70% austenite; and 
 (e) rapidly cooling to obtain a microstructure providing by volume at least 20% austenite and at least 50% martensite. 
 
     
     
         62 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 52  comprising the additional step of:
 (d) cold rolling the hot rolled sheet up to 5% strain to obtain a microstructure providing by volume at least 20% austenite and at least 50% martensite. 
 
     
     
         63 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 52  comprising the additional step of:
 (d) annealing the hot rolled cast sheet with a soak at between 550 and 800° C. for between 5 and 100 hours. 
 
     
     
         64 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 63 , where the annealing soak is between 5 and 25 hours. 
     
     
         65 . The method of making a high copper carbon alloy steel sheet as claimed in  claim 52  comprising the additional step of:
 (d) continuously annealing the hot rolled cast sheet, where the annealing is in-line. 
 
     
     
         66 . The method of making the high copper carbon alloy steel sheet as claimed in  claim 52  comprising the additional step of:
 (d) coating the hot rolled cast sheet in a hot bath of molten metal selected from the group consisting of zinc, aluminum and alloys thereof. 
 
     
     
         67 . The method of making the high copper carbon alloy steel sheet as claimed in  claim 52  comprising the additional step of:
 (d) quenching and partitioning the hot rolled cast sheet. 
 
     
     
         68 . The method of making high copper carbon alloy steel sheet as claimed in  claim 52 , where after the solidifying step the steel sheet has more than 50% MnSiO 2  and MnS inclusions less than 5 μm in size.