| 摘要 |
A steel strip contg. more than 0.5 wt.% Cr is subjected to continuous hot dip aluminising in an Al bath by: (a) box annealing in 100% H2 of dew pt. below -60[deg]C at 675-786[deg]C, to give surfaces with an Fe:Cr ratio above 3; (b) maintaining the box-annealed surfaces after the box anneal; (c) heating the strip to at least the bath temp. in an aluminising furnace contg. a non-oxidising atmos., (d) maintaining the surfaces in this furnace until the strip is admitted to the bath; (e) delivering the strip to the bath at at least the temp. of the bath; and (f) hot dip aluminising the strip to provide an Al-coated strip contg. Cr. The atmos. in the aluminising furnace is N2 and/or H2 with a dew pt. below -18[deg]C. The dew pt. of the box annealing atmos. is below -62, pref. below -65[deg]C. The steel contains at least 6, pref. at least 8 and most pref. 10-30 wt.% Cr, in addn. to (wt.%): at least 0.1 Ti and 0.01-0.1 Al. The box anneal may be carried out in a gas-tight enclosed base and a high convection bell furnace, e.g. with a wholly metallic cover enclosing internal base insulation, or in an Ebner HlCON/H2 (RTM) furnace. The Fe:Cr ratio on the box-annealed surfaces is pref. at least 5. |
