Cold rolled steel sheet - for coachwork with slow ageing and improved extensibility and shapability by pressing

摘要

The cold-rolled steel sheet has not more than 0.1% C and not more than 0.30% Mn, and is such that 0.002 x N (ppm) - 0.03 = K; =0.17 + 0.002 x N (ppm) where K = Mn - 55/32 S - 55/16 O The cold-rolled steel sheet is made by passing a cold-rolled steel sheet containing not more than 0.1% C into a continuous annealing furnace consisting of (a) a zone of heating and hardening (or soaking or tempering) (b) a first cooling zone, (c) an overaging zone, and (d) a second cooling zone, in series. Heating and hardening (or soaking or tempering) are performed in (a) for 30 sec. to 5 min. at 650-900 degrees C, cooling to the starting temp. for overaging or below in (b), overaging in (c) starting at 400-500 degrees C and reducing to between 200-500 degrees C over 2-10 min., this overaging being completed between 200 and 350 degrees C.