Machining steel superior in manufacturability

Abstract

The present invention provides machining steel superior in machinability, accompanied with little melt loss of plate refractories of continuous casting sliding nozzles, and superior in ductility in hot rolling and able to prevent deterioration of the surface properties due to hot rolling, containing, by mass %, C: 0.005 to 0.2%, Si: 0.001 to 0.5%, Mn: 0.3 to 3.0%, P: 0.001 to 0.2%, S: 0.30 to 0.60%, B: 0.0003 to 0.015%, O: 0.005 to 0.012%, Ca: 0.0001 to 0.0010%, and Al≦0.01%, having an N content satisfying N≧0.0020% and 1.3×B−0.0100≦N≦1.3×B+0.0034, and having a balance of Fe and unavoidable impurities, wherein, regarding the MnO in the steel, in a cross-section of the steel material perpendicular to the rolling direction, the area of MnO of a circle equivalent diameter of 0.5 μm or more being 15% or less of the area of the total Mn-based inclusions.

1 . Machining steel superior in manufacturability containing, by mass %,
 C: 0.005 to 0.2%   Si: 0.001 to 0.5%   Mn: 0.3 to 3.0%   P: 0.001 to 0.2%   S: 0.30 to 0.60%   B: 0.0003 to 0.015%   O: 0.005 to 0.012%   Ca: 0.0001 to 0.0010%, and   Al≦0.01%,   having an N content satisfying   N≧0.0020% and 1.3×B−0.0100≦N≦1.3×B+0.0034, and   having a balance of Fe and unavoidable impurities, wherein   further, regarding the MnO in the steel, in a cross-section of the steel material perpendicular to the rolling direction, the area of MnO of a circle equivalent diameter of 0.5 μm or more being 15% or less of the area of the total Mn-based inclusions.   
     
     
         2 . Machining steel superior in manufacturability as set forth in  claim 1 , wherein, regarding the sulfides mainly comprised of MnS, in a cross-section of the steel material perpendicular to the rolling direction, a density of sulfides of a circle equivalent diameter of 0.1 to 0.5 μm is 10000/mm 2  or more. 
     
     
         3 . Machining steel superior in manufacturability as set forth in  claim 1 , further containing, by mass %, one or more of
 V: 0.05 to 1.0%   Nb: 0.005 to 0.2%   Cr: 0.01 to 2.0%   Mo: 0.05 to 1.0%   W: 0.05 to 1.0%   Ni: 0.05 to 2.0%   Cu: 0.01 to 2.0%   Sn: 0.005 to 2.0%   Zn: 0.0005 to 0.5%   Ti: 0.0005 to 0.1%   Zr: 0.0005 to 0.1%   Mg: 0.0003 to 0.005%   Te: 0.0003 to 0.2%   Bi: 0.005 to 0.5%   Pb: 0.005 to 0.5%.