Tailor-rolled blank for use in hot stamping automotive parts, and method of making hot stamped automotive parts

Abstract

A tailor-rolled blank for use in hot stamping automotive parts made from an alloy comprising between from about 0.05 to about 0.35 wt % carbon, about 0.5 to about 5.0 wt % manganese, about 0.5 to about 2.0 wt % silicon, about 0.6 to about 4.0 wt % chromium, optionally about 0.02-0.05 wt % niobium, and optionally about 0.03 to about 0.3 wt % yttrium and/or cerium, and the balance being iron and impurities. The blank is cold rolled to have at least one of these geometrical features (a) the maximum thickness difference greater than about 0.8 mm and less than about 2.0 mm; (b) a maximum ratio of the thickest area the thinnest greater than about 1.2 and less than about 2.5; and (c) at least one transition zone between adjacent areas of different thickness with a length greater than 10 times and less than 80 times the difference in thickness between the areas.

What is claimed is: 
     
         1 . A tailor-rolled blank for use in hot stamping automotive parts, the blank made from an alloy comprising between from about 0.05 to about 0.35 wt % carbon, about 0.5 to about 5.0 wt % manganese, about 0.5 to about 2.0 wt % silicon, about 0.6 to about 4.0 wt % chromium, optionally about 0.02-0.05 wt % niobium, and optionally about 0.03 to about 0.3 wt % yttrium and/or cerium, and the balance being iron and impurities, the tailor-rolled blank being cold rolled to have one or more of these geometrical features:
 a maximum thickness difference between the thinnest area of the blank and the thickest area of the blank greater than about 0.8 mm and less than about 2.0 mm;   a maximum ratio of the thickest area of the blank to the thinnest area of the blank greater than about 1.2 and less than about 2.5; and   at least one transition zone between adjacent areas the blank of different thickness with a length that is less than 80 times the difference in thickness between the areas, but greater than 10 times the difference in thickness between the areas.   
     
     
         2 . The tailor-rolled blank according to  claim 1  comprising about 0.02 to 0.05 wt % niobium. 
     
     
         3 . The tailor-rolled blank according to  claim 2  comprising about 0.03 to about 0.3 wt % yttrium and/or cerium. 
     
     
         4 . The tailor-rolled blank according to  claim 1  comprising about 0.03 to about 0.3 wt % yttrium and/or cerium. 
     
     
         5 . A structural part for an automobile, made by hot stamping a tailor-rolled blank according to  claim 1 . 
     
     
         6 . The structural part for an automobile according to  claim 5  wherein the part has an ultimate tensile strength greater than about 1500 MPa. 
     
     
         7 . The structural part for an automobile according to  claim 6  wherein the part has a hardness between about 400 and 560 HV. 
     
     
         8 . The structural part for an automobile according to  claim 5  wherein the part has a hardness above about 400 and 560 HV. 
     
     
         9 . A method of manufacturing a structural part for an automobile comprising:
 forming a tailor-rolled blank for use in hot stamping automotive parts, by cold rolling a blank made from an alloy comprising between from about 0.05 to about 0.35 wt % carbon, about 0.5 to about 5.0 wt % manganese, about 0.5 to about 2.0 wt % silicon, about 0.6 to about 4.0 wt % chromium, optionally about 0.02-0.05 wt % niobium, and optionally about 0.03 to about 0.3 wt % yttrium and/or cerium, the tailor-rolled blank being cold rolled to have one or more of these geometrical features: (a) a maximum thickness difference between the thinnest area of the blank and the thickest area of the blank greater than about 0.8 mm and less than about 2.0 mm; (b) a maximum ratio of the thickest area of the blank to the thinnest area of the blank greater than about 1.2 and less than about 2.5; and (c) at least one transition zone between adjacent areas the blank of different thickness areas of the blank with a length less than 80 times the difference in thickness between the areas, but greater than 10 times the difference in thickness between the areas; and   hot stamping the tailor-rolled blank to form the structural part for an automobile.   
     
     
         10 . The method of manufacturing a structural part for an automobile according to  claim 9  where the blank is made from an alloy comprising about 0.02-0.05 wt % niobium. 
     
     
         11 . The method of manufacturing a structural part for an automobile according to  claim 10  where the blank is made from an alloy comprising about 0.03 to about 0.3 wt % yttrium and/or cerium. 
     
     
         12 . The method of manufacturing a structural part for an automobile according to  claim 9  where the blank is made from an alloy comprising about 0.03 to about 0.3 wt % yttrium and/or cerium.