High carbon steel sheet superior in tensile strength and elongation and method for manufacturing the same

A method for manufacturing a high carbon steel sheet, comprising:

• i) preparing a high carbon steel sheet comprising 0.2 to 1.0 wt % carbon (C), greater than about 1 wt % and less than or equal to 3.0 wt % silicon (Si), greater than 0 wt % and less than or equal to 3.0 wt % manganese (Mn), greater than 0 wt % and less than or equal to 3.0 wt % chromium (Cr), greater than 0 wt % and less than or equal to 3.0 wt % nickel (Ni), greater than 0 wt % and less than or equal to 0.5 wt % molybdenum (Mo), greater than about 1 wt % and less than or equal to 3.0 wt % aluminum (Al), greater than 0 wt % and less than or equal to 0.01 wt % boron (B), greater than 0 wt % and less than or equal to 0.5 wt % titanium (Ti), and the remainder substantially being iron (Fe) and inevitable impurities;
• ii) austenitizing the high carbon steel sheet;
• iii) cooling the high carbon steel sheet while maintaining the austenite structure;
• and
• iv) isothermally transforming the austenitized high carbon steel sheet in a temperature range from 150° C. below the bainite transformation starting temperature to the bainite transformation starting temperature,
• wherein the contents of carbon, manganese, chromium, and nickel satisfy the following Equation 1, and the silicon and the aluminum satisfy the following Equation 2, and the carbon (C), manganese (Mn), chromium (Cr), nickel (Ni), and aluminum (Al) satisfy the following Equation 3:
• (3.0−2.5×C)wt %≦(Mn+Cr+Ni/2)≦8.5 wt % (Equation 1)
• Si+Al> about 2.0 wt % (Equation 2),
• Log 10 [50% transformation time (sec)]=−2.742+3.561×C+0.820×Mn+0.416×Cr+0.402×Ni−0.332×Al+1330/(T+273)≦Log10[3×3600] (Equation 3),
• wherein T is a temperature in degrees Celsius and represents a transformation temperature, and 50% transformation time is a minimum time required for 50% transformation into bainite.