Steel plate and steel plate coil

Abstract

In a steel plate having tensile strength of 1 GPa or more at the normal temperature, the steel plate is made, stress decrement (SD) after uniform elongation in the stress-strain diagram obtained by using a tabular specimen of which is not less than 1.8×10 2 MPa, yield ratio (YR) of which is preferably not lower than 0.7, further preferably not lower than 0.8, and matrix structure of which is composed of martensite or bainite, or mixture of martensite and bainite substantially without proeutectoid ferrite, whereby the tough-ductility is improved on a practically utilizable level, and the steel plate becomes possible to be supplied in large quantities by winding up into a coil.

1 . A steel plate characterized in that tensile strength is not lower than 1 GPa at the normal temperature, and stress decrement (SD) after uniform elongation in a stress-strain diagram obtained by a tensile test using a tabular specimen is not lower than 1.8×10 2  MPa. 
   
   
       2 . The steel plate as set forth in  claim 1 , yield ratio (YR) of which is not lower than 0.7. 
   
   
       3 . The steel plate as set forth in  claim 1 , yield ratio (YR) of which is not lower than 0.8. 
   
   
       4 . The steel plate as set forth in  claim 1 , matrix structure of which is composed of at least one of martensite and bainite, and does not substantially contain proeutectoid ferrite. 
   
   
       5 . A steel plate coil made by winding up the steel plate as set forth in  claim 1 . 
   
   
       6 .- 11 . (canceled) 
   
   
       12 . The steel plate as set forth in  claim 2 , the matrix structure of which is composed of at least one of martensite and bainite, and does not substantially contain proeutectoid ferrite. 
   
   
       13 . The steel plate as set forth in  claim 3 , the matrix structure of which is composed of at least one of martensite and bainite, and does not substantially contain proeutectoid ferrite. 
   
   
       14 . A steel plate coil made by winding up the steel plate as set forth in  claim 2 . 
   
   
       15 . A steel plate coil made by winding up the steel plate as set forth in  claim 3 . 
   
   
       16 . A steel plate coil made by winding up the steel plate as set forth in  claim 4 . 
   
   
       17 . A steel plate coil made by winding up the steel plate as set forth in  claim 12 . 
   
   
       18 . A steel plate coil made by winding up the steel plate as set forth in  claim 13 .