Production manner null of the cold rolling steel sheet where normal temperature non-ageing properties and printing hardenability

摘要

PURPOSE:To obtain a cold rolled steel sheet having an excellent ordinary temp. non-aging property and high baking hardenability, by cold rolling a hot rolled steel sheet contg. one kind among Mo, Sn and Sb in addition to C, Mn, P, and Al, then heating the steel sheet at the temp. above the recrystallization temp. and below Ar3, cooling the sheet and subjecting such sheet to an overaging treatment in a prescribed temp. range. CONSTITUTION:The hot rolled steel sheet contg., by weight, 0.01-0.04% C, 0.05-0.4% Mn, =0.03% P, and 0.02-0.08% total Al, and in addition, one kind among 0.06-0.35% Mo, 0.01-0.1% Sn and 0.01-0.1% Sb is treated in the following manner: The hot rolled steel sheet is cold rolled preferably at =60% and is then heated in the temp. range above the recrystallization temp. and below Ar3 and is cooled preferably at =5 deg.C/sec cooling rate. The cold rolled steel sheet after the cooling is subjected to the overaging treatment in a 250-400 deg.C temp. range and is further subjected to temper rolling, by which the desired cold rolled steel sheet is obtd.