溶融Alと鋼板の短時間反応に及ぼすめっき浴中Siの影響

抄録

Low-carbon rimmed steel sheets were dipped into pure Al and Al-Si alloys by a gas reduction type aluminizing instrument to study the effects of Si on the reaction between steel sheets and molten Al under short time dipping. The growth of an alloy layer at steel-coating interface, the phase change of intermetallic compounds in the alloy layer and the wetting characteristics between steel sheets and molten metals were investigated by means of an observation of cross-sectional microstructure, an X-ray diffraction technique, an X. M. A. and a meniscograph measurement. The results obtained are as follows. 1) The alloy layer in aluminizing with pure Al bath was composed of η-phase (Al₅Fe₂) and θ-phase (Al₃Fe). Increase of the alloy layer thickness with dipping time was devided into two parabolic growth steps. It was considered that the growth of the alloy layer is controlled by an internal diffusion of Al through θ-phase in the first step and through η-phase in the second step respectively. 2) When the steel was dipped in Al-2.5%Si bath, the alloy layer was composed of η-phase, θ-phase and (Al, Fe, Si) H-phase. The growth rate of the alloy layer with Al-2.5 %Si was much lower than that with pure Al bath. 3) The alloy layer formed by dipping into Al-8%Si bath was composed of only (Al, Fe, Si) H-phase and it did not grow for dipping time up to 30 seconds. 4) The wetting force between steel sheets and pure molten Al in which the alloy layer formation was vigorous, was as high as 400 dyn/cm, but that between steel sheets and molten Al-8% Si in which the growth of the alloy layer was not detected, was as low as about 50 dyn/cm. From these results, it was considered that the (Al, Fe, Si) H-phase, an outermost alloy layer, has the inhibition effects on the reaction between steel sheets and molten Al.