Production manner null of the BH steel sheet for deep drawing which is superior in resistance dent Characteristic and resistance surface deformation

摘要

PURPOSE: To inexpensively produce a steel sheet which has been impossible to attain without the remarkable increase of the cost such as a double-layered steel sheet by specifying the atmosphere and annealing conditions in continuous annealing and the componental compsn. of the steel and gas carbonitriding conditions. ;CONSTITUTION: A steel having a compsn. of total ≥0.02% of Ti and/or Nb satisfying the conditions of, by weight, ≤0.005% C, ≤0.01% N, 1.5% Mn, ≤l.0% Si, ≤0.15% P, 0.005 to 0.2% Al, ≤0.02%. S and C/12+N/14+S/320.9(Ti/48+Nb/93), and the balance Fe is used. This is subjected to cold rolling, is thereafter subjected to recrystallization annealing in a continuous annealing atmosphere and is subsequently subjected to carbonitriding treatment under the conditions in which the product of the staying time (sec) at 600 to 850°C and the concentration (%) of NH₃ 15 regulated to 50 to 1000 in a carbonitriding atmosphere in which the equilibrium carbon concentration is controlled to 0.005 to 0.03%.;COPYRIGHT: (C)1995,JPO