Composite steel plate

Abstract

A composite steel plate in which at least two steel sheets are rolled to form a plate. One of the sheets has a composition that varies in a depthwise direction between nanocrystalline and micron grained. The plate is made by treating a steel sheet to produce a composition in the sheet that varies in a depthwise direction of the sheet between nanocrystalline and micron grained, stacking the treated sheet with at least one other steel sheet and rolling the sheets to form the plate.

1 - 25 . (canceled) 
     
     
         26 . A rolled composite steel sheet having a crystalline grain structure that varies in a thickness direction of the sheet, between at least one region having a micro-grain or ultrafine-grain structure and a first nanocrystalline region having a nanocrystalline grain structure, wherein the nanocrystalline region has a mechanically-induced grain size of no more than 100 microns and a thickness in a range from 10 microns to 50 microns. 
     
     
         27 . The rolled composite steel sheet of  claim 26  including a second nanocrystalline region having the nanocrystalline grain structure, the first and second nanocrystalline regions being separated by the region having a micro-grain or ultrafine-grain structure. 
     
     
         28 . The rolled composite steel sheet of  claim 26 , wherein the grain structure of the composite steel sheet varies smoothly in the thickness direction of the composite steel sheet between the region having a micro-grain or ultrafine-grained structure and the first nanocrystalline region. 
     
     
         29 . The rolled composite steel sheet of  claim 27 , wherein the grain structure of the composite steel sheet varies smoothly in the thickness direction of the composite steel sheet between the region having a micro-grain or ultrafine-grained structure and the first and second nanocrystalline regions. 
     
     
         30 . The rolled composite steel sheet of  claim 26 , wherein
 the composite steel sheet has a first surface, a second surface, and a center between the first and second surfaces, and   the first nanocrystalline region is located at the center of the composite steel sheet.   
     
     
         31 . The rolled composite steel sheet of  claim 27 , wherein
 the composite steel sheet has a first surface, a second surface, and a center between the first and second surfaces, and   one of the first and second nanocrystalline regions is located at the center of the composite steel sheet.   
     
     
         32 . The rolled composite steel sheet of  claim 26 , wherein
 the composite steel sheet has a first surface, a second surface, and a center between the first and second surfaces, and   the first nanocrystalline region is located at one of the first and second surfaces and the micro-grain or ultrafine-grain structure is at located at the center.   
     
     
         33 . The rolled composite steel sheet of  claim 32 , wherein surface roughness of the first and second surfaces varies between 0.05 microns and 10 (Ra). 
     
     
         34 . The rolled composite steel sheet of  claim 32 , wherein the grain structure of the composite steel sheet varies smoothly in the thickness direction, between the first surface and the center, and varies smoothly between the center and the second surface. 
     
     
         35 . The rolled composite steel sheet of  claim 27 , wherein
 the composite steel sheet has a first surface, a second surface, and a center between the first and second surfaces, and   the first nanocrystalline region is located at the first surface, the second nanocrystalline region is located at the second surface, and the micro-grain or ultrafine-grain structure is at located at the center.   
     
     
         36 . The rolled composite steel sheet of  claim 35 , wherein surface roughness of the first and second surfaces varies between 0.05 microns and 10 microns (Ra). 
     
     
         37 . The rolled composite steel sheet of  claim 35 , wherein the grain structure of the composite steel sheet varies smoothly in the thickness direction, between the first surface and the center, and varies smoothly between the center and the second surface. 
     
     
         38 . A rolled composite steel sheet having a crystalline grain structure that varies in a thickness direction of the composite steel sheet, between at least one microcrystalline region having a first grain size, and at least one nanocrystalline region having a mechanically-induced second grain size, wherein
 the second grain size is smaller than the first grain size,   the mechanically-induced second grain size does not exceed 100 microns, and   the nanocrystalline region has a thickness in a range from 10 microns to 50 microns.   
     
     
         39 . A rolled composite steel sheet comprising a first surface region having a mechanically-induced first grain size, a second surface region, opposite the first surface region, the second surface region having a mechanically-induced second grain size, and a center region, located between the first and second surface regions, wherein
 the third grain size is larger than the first and second grain sizes,   the first and second surface regions have a grain size not exceeding 100 microns, and a thickness in a range from 5 microns to 20 microns, and   grain size varies smoothly from the first and second surface regions to the center region of the composite steel sheet.   
     
     
         40 . The rolled composite steel sheet of  claim 39  including a fourth region located between the first surface region and the center region, wherein
 the fourth region has a mechanically induced fourth grain size, 
 the fourth grain size is larger than the first grain size and smaller than the third grain size, and 
 the fourth grain size is in a range from larger than 100 microns to 500 microns.