Sulfur-added graphite steel wire rod, steel wire and graphite steel, which have excellent cutting performance, and manufacturing methods therefor

Abstract

The disclosure relates to a graphite steel wire rod, steel wire, graphite steel and manufacturing methods therefor to which sulfur is added and which have excellent cutting performance to that conventional free-cutting steel. Specifically, the disclosure relates to a graphite steel wire rod and steel wire, and manufacturing methods therefor, the rod and the wire comprising, by wt %, 0.60-0.90% of carbon (C), 2.0-2.5% of silicon (Si), 0.1-0.6% of manganese (Mn), 0.015% or less of phosphorus (P) (excluding 0), 0.031-0.3% of sulfur (S), 0.10-0.05% of aluminum (Al), 0.005-0.02% of titanium (Ti), 0.005-0.0020% of boron (B), 0.0030-0.0150% of nitrogen (N), and the balance of Fe and inevitable impurities. In addition, the present invention relates to graphite steel and a manufacturing method therefor, the steel comprising is same as above, having, as a microstructure, graphite grains distributed in a ferrite matrix, having a degree of graphitization of 90% or more, and containing 5% or less of MnS inclusions and pearlite in total.

1 . A graphite steel wire rod having superior cutting performance, the graphite steel wire rod comprising:
 in percent by weight, 0.60 to 0.90% of carbon (C), 2.0 to 2.5% of silicon (Si), 0.1 to 0.6% of manganese (Mn), 0.015% or less (except 0) of phosphorus (P), 0.031 to 0.3% of sulfur (S), 0.01 to 0.05% of aluminum (Al), 0.005 to 0.02% of titanium (Ti), 0.0005 to 0.0020% of boron (B), 0.0030 to 0.0150% of nitrogen (N) and the remainder having Fe and unavoidable impurities.   
     
     
         2 . The graphite steel wire rod of  claim 1 , wherein an area fraction of pearlite is at least 95%. 
     
     
         3 . A method of manufacturing the graphite steel wire rod with superior cutting performance of  claim 1 , the method comprising:
 manufacturing a billet including, in percent by weight, 0.60 to 0.90% of carbon (C), 2.0 to 2.5% of silicon (Si), 0.1 to 0.6% of manganese (Mn), 0.015% or less (except 0) of phosphorus (P), 0.031 to 0.3% of sulfur (S), 0.01 to 0.05% of aluminum (Al), 0.005 to 0.02% of titanium (Ti), 0.0005 to 0.0020% of boron (B), 0.0030 to 0.0150% of nitrogen (N) and the remainder having Fe and unavoidable impurities; and   heating the billet;   hot-rolling the heated billet to be manufactured into a wire rod; and   cooling the wire rod.   
     
     
         4 . The method of  claim 3 , wherein the heating comprises performing heat treatment by maintaining at a range of 1050±100° C. for at least 60 minutes. 
     
     
         5 . The method of  claim 3 , wherein the hot-rolling for manufacturing the wire rod comprises hot-rolling at a temperature range of 900 to 1150° C. 
     
     
         6 . The method of  claim 3 , wherein the cooling comprises cooling down to 500° C. at a cooling rate of 0.1 to 10.0° C./s. 
     
     
         7 . The method of  claim 3 , further comprising: air-cooling after the cooling. 
     
     
         8 . A graphite steel wire having superior cutting performance, the graphite steel wire comprising:
 in percent by weight, 0.60 to 0.90% of carbon (C), 2.0 to 2.5% of silicon (Si), 0.1 to 0.6% of manganese (Mn), 0.015% or less (except 0) of phosphorus (P), 0.031 to 0.3% of sulfur (S), 0.01 to 0.05% of aluminum (Al), 0.005 to 0.02% of titanium (Ti), 0.0005 to 0.0020% of boron (B), 0.0030 to 0.0150% of nitrogen (N) and the remainder having Fe and unavoidable impurities.   
     
     
         9 . A graphite steel with superior cutting performance, the graphite steel comprising:
 in percent by weight, 0.60 to 0.90% of carbon (C), 2.0 to 2.5% of silicon (Si), 0.1 to 0.6% of manganese (Mn), 0.015% or less (except 0) of phosphorus (P), 0.031 to 0.3% of sulfur (S), 0.01 to 0.05% of aluminum (Al), 0.005 to 0.02% of titanium (Ti), 0.0005 to 0.0020% of boron (B), 0.0030 to 0.0150% of nitrogen (N) and the remainder having Fe and unavoidable impurities,   wherein as a microstructure, graphite grains are distributed in a ferrite matrix, a graphitization rate is at least 95%, and a total of 5% or less of MnS inclusions and pearlite are included.   
     
     
         10 . A method of manufacturing the graphite steel having superior cutting performance of  claim 9 , the method comprising:
 manufacturing a wire rod including, in percent by weight, 0.60 to 0.90% of carbon (C), 2.0 to 2.5% of silicon (Si), 0.1 to 0.6% of manganese (Mn), 0.015% or less (except 0) of phosphorus (P), 0.031 to 0.3% of sulfur (S), 0.01 to 0.05% of aluminum (Al), 0.005 to 0.02% of titanium (Ti), 0.0005 to 0.0020% of boron (B), 0.0030 to 0.0150% of nitrogen (N) and the remainder having Fe and unavoidable impurities; and   performing graphitization heat treatment on the manufactured wire rod.   
     
     
         11 . The method of  claim 10 , wherein the performing graphitization heat treatment comprises performing heat treatment at a temperature range of 700 to 800° C. for at least 5 hours.