GB1118294A - Method for producing highly ductile metallic coated sheet and strip - Google Patents

Abstract

A process for producing a metallic-coated ferrous-base metal strip (e.g. of cold-reduced, rimmed, capped or killed, steel coated with Zn, Zn alloy, Al, Al alloy, terne or Sn) having greatly enhanced drawability comprises the steps of forming a strip of the base metal into an opened coil and decarburizing the base metal to a carbon content of 0.015% or less by weight, thereafter cleaning the surface of the base metal in preparation for coating, the cleaning step comprising heating the base metal to a temperature in the range of between 1350 DEG F. and the A3 critical point of the base metal in a reducing atmosphere and then passing the base metal into a bath of molten coating metal without re-exposing the base metal to air. The cleaning may include initially heating the strip in an oxidizing furnace to 700 to 900 DEG F. so as to burn oil or grease. Alternatively to this initial heating, the strip may be acid pickled or alkali cleaned. Thus steel strip may be 1) temper rolled, 2) decarburized in open coil form at between 1100 DEG F. and the A3 critical temperature (e.g. 1300 DEG F. to 1500 DEG F.) in a H2 bearing atmosphere (e.g. dissociated NH3) to which steam is introduced, 3) cooled, 4) temper rolled, 5) heated in the oxidizing furnace, 6) heated in the reducing atmosphere at 1350 DEG F. up to the A3 critical temperature (e.g. 1350 to 1575 DEG F.), 7) cooled in a neutral or reducing atmosphere to the temperature of the coating metal, 8) passed beneath the surface of the molten metal and 9) temper rolled.