It is by the continual melting galvanize line non aging it is good production manner null of the processability melting galvanize cold rolling

摘要

PURPOSE:To produce a hot dip galvanized steel sheet having non-ageing characteristic and baking hardenability and excellent in press formability and superior surface characteristics by subjecting a low carbon Al-killed steel sheet hot-rolled and cold-rolled under respectively specified conditions to heat treatment under specific conditions and then to hot dip galvanizing treatment or Zn-Fe alloying plating treatment. CONSTITUTION:A slab of a low carbon Al-killed steel having a composition containing, by weight, 0.01-0.02% C, 0.3% Si, 0.03-0.15% Mn, 0.02% P, 0.015% S, 0.04-0.10% Al, and 0.003% N is soaked at a temp. ST represented by an inequality, hot-rolled at =Ar3 finishing temp. and 600-700 deg.C coiling temp., and cold-rolled into a steel strip, and this steel strip is heated up to a temp. of the recrystallization temp. or above and further the surface is reduced in a reducing atmosphere. Subsequently, the steel strip is cooled from =600 deg.C down to 200-300 deg.C at =30 deg.C/sec cooling rate, held at the above temp. for =10sec, heated up to 430-500 deg.C at =10 deg.C/sec temp.-rise rate, and immersed into a molten Zn bath to undergo galvanizing, and, after Zn is subjected, if necessary, to Zn-Fe alloying treatment, the steel strip is cooled down to =370 deg.C and finally subjected to overageing treatment at 250-320 deg.C for =40sec.