METHOD FOR COATING OF FLAT ROLLED STEEL FROM HIGH-STRENGTH STEEL Russian patent published in 2010 - IPC C23C2/02 C23C2/06 C23C2/12 

FIELD: metallurgy.

SUBSTANCE: invention relates to method of coating with zinc and/or aluminium by dipping to molten metal of flat rolled steel made from high-strength steel containing various alloying components, namely Mn, Al, Si and/or Cr, by means of which steel band with optimum processed surface is obtained at RTF plant. In the method the flat rolled steel is first subject to heat treatment and then in heated state it is coated with metallic film in bath with molten metal, which contains in general at least 85 % of zinc and/or aluminium, by melt dipping method. Heat treatment includes the following steps: a) flat rolled steel is heated in reducing atmosphere with H₂ content at least of 2% to 8% to the temperature of above 750°C to 850°C, b) surface mainly consisting of pure iron by means of heat treatment taking about 1 to 10 sec of flat rolled steel at temperature of above 750°C to 850°C in reaction chamber with oxidation atmosphere, which is built in through-type furnace, with O₂ content of 0.01% to 1% is converted to iron oxide layer, c) then flat rolled steel is calcined in reducing atmosphere with H₂ content of 2% to 8% by means of heating maximum to 900°C at time interval which exceeds the duration of heat treatment (step b) performed for formation of iron oxide layer so that previously formed iron oxide layer is reduced at least on its surface to pure iron, d) after that flat rolled steel is cooled to the temperature of bath with molten metal.

EFFECT: increasing coating strength.

11 cl, 1 dwg