High carbon steel sheet superior in fatiugue lifeand manufacturing method thereof

Abstract

The present invention relates to a high carbon steel sheet that is superior in fatigue life and a method of manufacturing the high carbon steel sheet. The high carbon steel sheet includes about 0.75 wt % to about 0.95 wt % of carbon, smaller than about 1.8 wt % of silicon, about 0.1 wt % to about 1.5 wt % of manganese, about 0.1 wt %˜1.0 wt % of chromium, smaller than about 0.02 wt % of phosphorus, smaller than about 0.02 wt % of sulfur, a residual amount of iron, and inevitable impurities. A layer interval between laminar carbides included in the high carbon steel sheet is smaller than about 0.5 μm. The high carbon steel sheet may include a fine pearlite having a lamellar structure. The fine pearlite included in the high carbon steel sheet may have a volume percentage of larger than about 90%. A ratio of length to width of the lamellar structure may be larger than about 10:1.

1 . A high carbon steel sheet comprising
 about 0.75 wt % to about 0.95 wt % of carbon, smaller than about 1.8 wt % of silicon, about 0.1 wt % to about 1.5 wt % of manganese, about 0.1 wt %˜1.0 wt % of chromium, smaller than about 0.02 wt % of phosphorus, smaller than about 0.02 wt % of sulfur, a residual amount of iron, and inevitable impurities,   wherein a layer interval between laminar carbides included in the high carbon steel sheet is smaller than about 0.5 μm.   
   
   
       2 . The high carbon steel sheet of  claim 1 , wherein the high carbon steel sheet includes a fine pearlite having a lamellar structure. 
   
   
       3 . The high carbon steel sheet of  claim 2 , wherein the fine pearlite included in the high carbon steel sheet has a volume percentage of larger than about 90%. 
   
   
       4 . The high carbon steel sheet of  claim 2 , wherein a ratio of length to width of the lamellar structure is larger than about 10:1. 
   
   
       5 . The high carbon steel sheet of  claim 1 , further comprising about 0.05 wt % to about 0.25 wt % of at least one selected from the group consisting of vanadium, niobium, molybdenum, titanium, tungsten, and copper. 
   
   
       6 . The high carbon steel sheet of  claim 5 , further comprising about 30 ppm to about 120 ppm of nitrogen. 
   
   
       7 . A method of manufacturing a high carbon steel sheet, the method comprising:
 forming a steel member including about 0.75 wt % to about 0.95 wt % of carbon, smaller than about 1.8 wt % of silicon, about 0.1 wt % to about 1.5 wt % of manganese, about 0.1 wt % to about 1.0 wt % of chromium, smaller than about 0.02 wt % of phosphorus, smaller than about 0.02 wt % of sulfur, a residual amount of iron, and inevitable impurities;   performing a hot rolling process, a cold rolling process and an annealing process to allow the steel member to have a spheroidized cementite and an initial ferrite; and   performing a patenting annealing process to the heated steel member after heating the steel member, the patenting annealing process being performed using a solder pot having a maintained temperature of about 500° C. to about 530° C. for over about 60 seconds.   
   
   
       8 . The method of  claim 7 , wherein the steel member is heated before the patenting annealing process at a temperature of about 800° C. to about 1100° C. 
   
   
       9 . The method of  claim 7 , wherein the steel member further includes about 0.05 wt % to about 0.25 wt % of at least one selected from the group consisting of vanadium, niobium, molybdenum, titanium, tungsten, and copper. 
   
   
       10 . The method of  claim 9 , wherein the steel member further includes about 30 ppm to about 120 ppm of nitrogen. 
   
   
       11 . The method of  claim 7 , further comprising:
 performing a cooling process after the patenting annealing process; and   performing a cold rolling process such that a reduction ratio of the cold rolling process is over about 85%.   
   
   
       12 . A method of manufacturing a high carbon steel sheet, the method comprising:
 forming a steel member including about 0.75 wt % to about 0.95 wt % of carbon, smaller than about 1.8 wt % of silicon, about 0.1 wt % to about 1.5 wt % of manganese, about 0.1 wt % to about 1.0 wt % of chromium, smaller than about 0.02 wt % of phosphorus, smaller than about 0.02 wt % of sulfur, a residual amount of iron, and inevitable impurities;   performing a hot rolling process, a cold rolling process, and an annealing process to allow the steel member to have spheroidized cementite and initial ferrite; and   performing a patenting annealing process to the heated steel member after heating the steel member, the patenting annealing process being performed using a solder pot having a maintained temperature of about 500° C. to about 530° C. for over about 20 seconds.   
   
   
       13 . The method of  claim 12 , wherein the steel member is heated before the patenting annealing process at a temperature of about 800° C. to about 1100° C. 
   
   
       14 . The method of  claim 12 , wherein the steel member further includes about 0.05 wt % to about 0.25 wt % of at least one selected from the group consisting of vanadium, niobium, molybdenum, titanium, tungsten, and copper. 
   
   
       15 . The method of  claim 14 , wherein the steel member further includes about 30 ppm to about 120 ppm of nitrogen. 
   
   
       16 . The method of  claim 12 , further comprising:
 performing a cooling process after the patenting annealing process; and   performing a cold rolling process such that a reduction ratio of the cold rolling process is over about 85%.