Abstract
The experiments were carried out to determine the composition of an important phase in alloy layer which give superior effect to heat resistance of hot dip aluminized steel. The tests were made on microstructure, microhardness and X-ray analysis. The results obtained were as follows:
(1) The composition of an important phase in the intermediate layer is Fe2Al5(η). The excellent heat resistance of aluminized steel depends upon the presence of η.
(2) In the as aluminized, η phase appears clearly in coating layer, but it is not possible to deny the presence of θ phase at all. It is difficult to confirm θ phase in what happened when aluminized sample was given a 2 hour diffusion heat-treatment at 800°C.
(3) As a result of diffusion heat-treatment at 800°C, the microstructure of the coated layer appears to be a five-zone, except Fe layer. The higher the carbon content of base steel, the greater the tendency for apperance of various zones. The hardest phase in those zones is η, and its value is Hv 900-1000. When the aluminized sample is given one hour diffusion heat-treatment at 500°C, it is impossible to confirm those zones by microscope, and the hardeness value of intermediate layer is Hv 700-800. In the as aluminized, that value is Hv 550-600.
