Dr Steel Sheet and Manufacturing Method Thereof

Abstract

This DR steel sheet includes the following steel components: C: 0.02 to 0.06 mass %, Si: equal to or less than 0.03 mass %, Mn: 0.05 to 0.5 mass %, P: equal to or less than 0.02 mass %, S: equal to or less than 0.02 mass %, Al: 0.02 to 0.10 mass %, and N: 0.008 to 0.015 mass %. The amount of solute N (Ntotal−NasAlN) in the steel sheet containing a residual iron and inevitable impurities, is equal to or more than 0.006%; and the total stretchability in a rolling direction after aging is equal to or more than 10%, total stretchability in a sheet width direction after aging is equal to or more than 5%, and an average Lankford value after aging is equal to or less than 1.0.

1 . A DR steel sheet comprising the following steel components:
 C: 0.02 to 0.06 mass %,   Si: equal to or less than 0.03 mass %,   Mn: 0.05 to 0.5 mass %,   P: equal to or less than 0.02 mass %,   S: equal to or less than 0.02 mass %,   Al: 0.02 to 0.10 mass %, and   N: 0.008 to 0.015 mass %,   wherein: the amount of solute N (Ntotal−NasAlN) in the steel sheet containing a residual iron and inevitable impurities, is equal to or more than 0.006%; and   the total stretchability in a rolling direction after aging is equal to or more than 10%, total stretchability in a sheet width direction after aging is equal to or more than 5%, and an average Lankford value after aging is equal to or less than 1.0.   
   
   
       2 . A manufacturing method of a DR steel sheet including the following steel components:
 C: 0.02 to 0.06 mass %,   Si: equal to or less than 0.03 mass %,   Mn: 0.05 to 0.5 mass %,   P: equal to or less than 0.02 mass %,   S: equal to or less than 0.02 mass %,   Al: 0.02 to 0.10 mass %, and   N: 0.008 to 0.015 mass %,   wherein: the amount of solute N (Ntotal−NasAlN) in the steel sheet containing a residual iron and inevitable impurities, is equal to or more than 0.006%; and   the total stretchability in a rolling direction after aging is equal to or more than 10%, total stretchability in a sheet width direction after aging is equal to or more than 5%, and an average Lankford value after aging is equal to or less than 1.0, the manufacturing method comprising:   heating a steel work piece at equal to or more than 1200° C., and then hot-rolling the steel work piece at a finishing temperature of equal to or more than an Ar3 transformation point;   forming a winding hot-rolled steel sheet at a winding temperature of equal to or less than 600° C.;   subjecting a cold rolling to the wind hot-rolled steel sheet with a rolling rate of equal to or more than 80% after acid washing;   subjecting annealing to the cold-rolled steel sheet at a temperature of equal to or more than a recrystallization temperature and equal to or less than an Ac1 transformation point; and   subjecting DR rolling to the annealed steel sheet with a tempering rolling rate of 6% to 15%.