| A study has been made of the aluminization of low carbon steel in packs of powder mixtures composed of aluminum or ferroaluminum, alumina and ammonium chloride. In packs of low aluminum content, in which the weight ratio of Al:Al₂O₃:NH₄Cl was 5:93:2 and that of Fe-50%Al:Al₂O₃:NH₄Cl was 10:88:2, the concentration of aluminum in the surface layer tended to decrease with increasing time at the calorizing temperature of 870 to 1010℃. In packs of higher aluminum content, in which the weight ratio of Fe-50%Al:Al₂O₃:NH₄Cl was 20:78:2, the surface composition was almost time-invariant and a steady state appeared to exist at the pack-coating interface. The apparent activation energy for diffusion in the solid phase (250kJ/mole) calculated on the assumption of constant surface concentration in a solid solution system was comparable with that of the interdiffusion in the Fe-Al system. The hardness of the pack-aluminized steel reached a maximum value of about 300 in the Vickers number on the surface, decreasing with increasing diffusion depth. |
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