High-carbon hot-rolled steel sheet having excellent surface quality and manufacturing method therefor

Abstract

The present invention relates to a hot-rolled steel sheet suitable for construction, tools, vehicle parts, and the like and, more particularly to a high-carbon hot-rolled steel sheet having an excellent surface quality and a manufacturing method therefor.

1 . A high-carbon hot-rolled steel sheet having an excellent surface quality, comprising: 0.3 wt % to 1.3 wt % of carbon (C), 0.01 wt % to 0.5 wt % of silicon (Si), 0.3 wt % to 2.0 wt % of manganese (Mn), 0.1 wt % or less, excluding 0 wt % of aluminum (Al), 5.0 wt % or less, excluding 0 wt % of chromium (Cr), further comprising: one or more selected from the group consisting of 2.0 wt % or less of molybdenum (Mo), 0.005 wt % to 0.1 wt % of antimony (Sb), 0.5 wt % or less of vanadium (V), 0.5 wt % or less of copper (Cu), and 2.0 wt % or less of nickel (Ni), and comprising: the balance of iron (Fe) and other inevitable impurities,
 wherein a hardenability index (HI) value, represented by Relation 1, is 0 or more, and Relation 2 is satisfied,
   (HI)=−5.69+(4.43×C)+(3.71×Mn)−(4.5×Si)+(1.77×Ni)+(6.18×Cr)+(12.0×Mo)−(43.6×Cu)+(48.1×V)≥0   [Relation 1]
 
   Mo+(10×Sb)−(0.1×Cr)≥0.14   [Relation 2]
 
   where the content of each element means weight %.   
     
     
         2 . The high-carbon hot-rolled steel sheet having an excellent surface quality of  claim 1 , wherein the hot-rolled steel sheet comprises 0.03 wt % or less of phosphorous (P), 0.02 wt % or less of sulfur (S), and 0.01 wt % or less of nitrogen (N). 
     
     
         3 . The high-carbon hot-rolled steel sheet having an excellent surface quality of  claim 1 , wherein the hot-rolled steel sheet includes a ferrite and pearlite composite structure as a microstructure. 
     
     
         4 . The high-carbon hot-rolled steel sheet having an excellent surface quality of  claim 1 , wherein the hot-rolled steel sheet has an area fraction of an oxide, located within 10 μm in a thickness direction from a surface, is 5% or less. 
     
     
         5 . A method for manufacturing a high-carbon hot-rolled steel sheet having an excellent surface quality, comprising:
 reheating a steel slab in a temperature range of 1100° C. to 1300° C., the steel slab comprising: 0.3 wt % to 1.3 wt % of carbon (C), 0.01 wt % to 0.5 wt % of silicon (Si), 0.3 wt % to 2.0 wt % of manganese (Mn), 0.1 wt % or less, excluding 0 wt % of aluminum (Al), 5.0 wt % or less, excluding 0 wt % of chromium (Cr), further comprising: one or more selected from the group consisting of 2.0 wt % or less of molybdenum (Mo), 0.005 wt % to 0.1 wt % of antimony (Sb), 0.5 wt % or less of vanadium (V), 0.5 wt % or less of copper (Cu), and 2.0 wt % or less of nickel (Ni), and comprising: the balance of iron (Fe) and other inevitable impurities, and in which an HI value, represented by Relation 1, is 0 or more and Relation 2 is satisfied;   producing a hot-rolled steel sheet by rough rolling and finish rolling the reheated steel slab; and   coiling the hot-rolled steel sheet in a temperature range of 500° C. to 710° C. after cooling,
   (HI)=−5.69+(4.43×C)+(3.71×Mn)−(4.5×Si)+(1.77×Ni)+(6.18×Cr)+(12.0×Mo)−(43.6×Cu)+(48.1×V)≥0   [Relation 1]
 
   Mo+(10×Sb)−(0.1×Cr)≥0.14   [Relation 2]
 
   where the content of each element means weight %.   
     
     
         6 . The method for manufacturing a high-carbon hot-rolled steel sheet having an excellent surface quality of  claim 5 , wherein the steel slab includes: 0.03 wt % or less of phosphorous (P), 0.02 wt % or less of sulfur (S), and 0.01 wt % or less of nitrogen (N). 
     
     
         7 . The method for manufacturing a high-carbon hot-rolled steel sheet having an excellent surface quality of  claim 5 , wherein the finish rolling is performed in a temperature range, in which an inlet temperature is 900° C. to 1100° C. and an outlet temperature is 800° C. to 950° C. 
     
     
         8 . The method for manufacturing a high-carbon hot-rolled steel sheet having an excellent surface quality of  claim 5 , wherein an area fraction of an oxide, located within 10 μm in a thickness direction from a surface of the hot-rolled steel sheet after the coiling, is 5% or less.