Continuously Cast Enameled Steel Sheet Remarkably Excellent in Fishscale Resistance and Method of Production of the Same

Abstract

The present invention provides a continuously cast enameled steel sheet with remarkably excellent fishscale resistance improving the ability to form spaces in the steel sheet so as to increase the hydrogen trap ability, and a method of production of the same, comprised of steel having as ingredients, by mass %, C: 0.010% or less, Mn: 0.03 to 1.30%, Si: 0.100% or less, Al: 0.030% or less, N: 0.0055% or less, P: 0.035% or less, S: 0.08% or less, O: 0.005 to 0.085%, and B: 0.0003 to 0.0250% and including in the steel sheet not integral or integral oxides differing in mass concentration of B or Mn. The ratio of the maximum concentration and minimum concentration is made 1.2 or more. When not integral, they are present with a straight line distance between centers of the oxides differing in concentration of 0.10 μm to 20 μm and with an angle of the line connecting the centers of the two oxides of within ±10° from the rolling direction.

1 . A continuously cast enameled steel sheet excellent in fishscale resistance characterized by being comprised of, by mass %,
 C: 0.010% or less,   Mn: 0.03 to 1.30%,   Si: 0.100% or less,   Al: 0.030% or less,   N: 0.0055% or less,   P: 0.035% or less,   S: 0.08% or less,   O: 0.005 to 0.085%,   B: 0.0003 to 0.0250%, and   
     a balance of Fe and unavoidable impurities and having, in complex oxides of 0.10 μm or more diameter comprised of Fe, Mn, Si, Al, B, or other oxides combined together in a unit observation field of 100 μm×100 μm in the sheet cross-section, any two complex oxides with different B mass concentrations and not contacting each other and with a ratio of a maximum concentration of a B mass concentration (Bmax %) and a minimum concentration of a B mass concentration (Bmin %) of Bmax/Bmin≧1.2. 
   
   
       2 . A continuously cast enameled steel sheet excellent in fishscale resistance as set forth in  claim 1 , characterized by having, in complex oxides of 0.10 μm or more diameter comprised of Fe, Mn, Si, Al, B, or other oxides combined together in a unit observation field of 100 μm×100 μm in the sheet cross-section, any two complex oxides with different Mn mass concentrations and not contacting each other and with a ratio of a maximum concentration of an Mn mass concentration (Mnmax %) and a minimum concentration of an Mn mass concentration (Mnmin %) of Mnmax/Mnmin≧1.2. 
   
   
       3 . A continuously cast enameled steel sheet excellent in fishscale resistance as set forth in  claim 1 , characterized by further containing, by mass %, one or both of
 Nb: less than 0.004% (including zero)   V: 0.003 to 0.15%.   
   
   
       4 . A continuously cast enameled steel sheet excellent in fishscale resistance as set forth in  claim 1 , characterized by further containing, by mass %, Cu: 0.01 to 0.500%. 
   
   
       5 . A continuously cast enameled steel sheet excellent in fishscale resistance as set forth in  claim 1 , characterized by further containing, by mass %, one or more of Cr, Ni, As, Ti, Se, Ta, W, Mo, Sn, Sb, La, Ce, Ca, and Mg in a total of 1.0% or less. 
   
   
       6 . A continuously cast enameled steel sheet excellent in fishscale resistance as set forth in  claim 1 , characterized by having, in complex oxides of 0.10 μm or more diameter comprised of Fe, Mn, Si, Al, B, or other oxides combined together in the steel sheet, a distribution of the B mass concentration and a ratio of the B mass concentration of the high concentration part (Bmax %) and the B mass concentration of the low concentration part (Bmin %) of Bmax/Bmin≧1.2. 
   
   
       7 . A continuously cast enameled steel sheet excellent in fishscale resistance as set forth in  claim 1 , characterized in one of the Fe, Mn, Si, Al, Nb, B, V, Cr, and other oxides in the steel sheet join together to form complex oxides in which the Mn concentration fluctuates, and a ratio of the Mn mass concentration of the high concentration part (Mnmax %) and the Mn mass concentration of the low concentration part (Mmmin %) is Mnmax/Mnmin≧1.2. 
   
   
       8 . A continuously cast enameled steel sheet excellent in fishscale resistance as set forth in  claim 1 , characterized by having separate complex oxides with a B mass concentration 1.2 times or more or 1/1.2 times or less of the B mass concentration (%) of the complex oxides comprised of the Fe, Mn, Si, Al, Nb, B, V, Cr, or other oxides combined together in the sheet with a straight line distance between centers of the two complex oxides of 0.10 μm to 20 μm and with an angle of the line connecting the centers of the two oxides of within ±10° from the rolling direction. 
   
   
       9 . A continuously cast enameled steel sheet excellent in fishscale resistance as set forth in  claim 1 , characterized by having separate complex oxides with an Mn mass concentration 1.2 times or more or 1/1.2 times or less of the Mn mass concentration (%) of the complex oxides comprised of the Fe, Mn, Si, Al, Nb, B, V, Cr, or other oxides combined together in the sheet with a straight line distance between centers of the two complex oxides of 0.10 μm to 20 μm and with an angle of the line connecting the centers of the two oxides of within ±100 from the rolling direction. 
   
   
       10 . A method of production of a continuously cast enameled steel sheet excellent in fishscale resistance characterized by making and casting steel comprising, by mass %
 C: 0.010% or less,   Mn: 0.03 to 1.3%,   Si: 0.100% or less,   Al: 0.030% or less,   N: 0.0055% or less,   P: 0.035% or less,   S: 0.08% or less,   O: 0.005 to 0.085%,   B: 0.0003 to 0.0250%, and   
     a balance of Fe and unavoidable impurities, during which adding the Mn and B into the molten steel in the order of adding Mn in a total amount of addition of 80% or more, then allowing 1 minute or more to elapse, adding B in a total amount of addition of 80% or more, and casting within 60 minutes. 
   
   
       11 . A method of production of a continuously cast enameled steel sheet excellent in fishscale resistance as set forth in  claim 10 , characterized by further including, by mass %, one or both of
 Nb: less than 0.004% (including zero) and   V: 0.003 to 0.15%   
   
   
       12 . A method of production of a continuously cast enameled steel sheet excellent in fishscale resistance as set forth in  claim 10 , characterized by further including, by mass %, Cu: 0.01 to 0.500%. 
   
   
       13 . A method of production of a continuously cast enameled steel sheet excellent in fishscale resistance as set forth in  claim 10 , characterized by further including, by mass %, one or more of Cr, Ni, As, Ti, Se, Ta, W, Mo, Sn, Sb, La, Ce, Ca, and Mg in a total of 1.0% or less. 
   
   
       14 . A method of production of continuously cast enameled steel sheet excellent in fishscale resistance as set forth in  claim 10 , characterized by casting by the cooling rate at the time of solidification of ≦10° C./sec at ¼ the sheet thickness of the slab. 
   
   
       15 . A method of production of continuously cast enameled steel sheet excellent in fishscale resistance as set forth in  claim 10 , characterized by hot rolling a slab with oxides of an average diameter of 1.0 μm or more and with a thickness of 50 mm or more at 600° C. or more during which rolling under conditions of 1000° C. or more and a strain rate of 1/sec or more to a total of the true strain of 0.4 or more, then rolling under conditions of 1000° C. or less and a strain rate of 10/sec or more to a total of the true strain of 0.7 or more.