THIN STEEL PLATE OF HIGH RECTANGULAR TUBE DRAWABILITY AND METHOD OF MANUFACTURING THE SAME

摘要

A thin steel sheet having excellent rectangular drawability is produced by completing roughing rolling of steel containing C: 0.02 wt% or less, Si: 0.5 wt% or less, Mn: 1.0 wt% or less, P: 0.15 wt% or less, S: 0.02 wt% or less, Al: 0.01 to 0.10 wt%, N: 0.008 wt% or less, at least one of Ti: 0.001 to 0.20 wt% and Nb: 0.001 to 0.15 wt%, the balance comprising Fe, and inevitable impurities, in the temperature region of 950 DEG C to the Ar3 transformation temperature: performing finish rolling at a reduction of over 70% under lubrication in the temperature region of the Ar3 transformation temperature to 500 DEG C; pickling the sheet; annealing the resultant hot rolled sheet under conditions which satisfy the equations (1) and (2) below: $$ $ wherein\; T:\; hot\; rolled\; sheet\; annealing\; temperature\; (\; DEG\; C)\; t:\; hot\; rolled\; sheet\; annealing\; time\; (sec);\; cold\; rolling\; at\; a\; reduction\; of\; 50\; to\; 95\%;\; and\; then\; recrystallization\; annealing;\; to\; satisfy\; the\; following\; relations:$ $ $ wherein\; rL\; :\; Lankford\; value\; in\; the\; rolling\; direction,\; rD\; :\; Lankford\; value\; in\; the\; direction\; at\; 45\; DEG\; with\; the\; rolling\; direction,\; and\; rC\; :\; Lankford\; value\; in\; the\; direction\; perpendicular\; to\; the\; rolling\; direction.\mathop{\mathrm{image}}$$$$$$