2023 年 109 巻 1 号 p. 42-50
A carbon tool steel plate was coated with an aluminum foil with a thickness of 100 μm by explosive welding. This aluminum-coated steel was heat-treated in the temperature range of 973−1273 K for up to 3.6 ks in the atmosphere to form a Fe-Al alloy layer on the steel surface. The alloy layer was basically composed of Fe2Al5, two kinds of FeAl (Al-rich FeAl and Fe-rich FeAl), Fe3Al containing carbon (Fe3Al(C)) and ferrite stabilized by aluminum diffusion (α-Fe(Al)). FeAl2 was also detected together with Fe2Al5 at more than 1223 K. At 1273 K, island-shaped Fe3Al(C) was produced in α-Fe(Al), and the Fe-rich FeAl/α-Fe(Al) interface became indistinct. In addition, defects like a crack and a void were observed in the vicinity of Fe-rich FeAl. The purpose of the present study is to investigate the reason for the defect formation. Various heat treatments were conducted for the aluminum-coated steel, and it was found that a temperature-rising step was responsible for the defect formation. This consideration got support from the results of two-step heat treatment, which was a heating process at 1273 K immediately after holding for 600 s near the eutectoid temperature in the Fe-C binary system.
