Aluminizing of high-carbon steel by explosive welding and subsequent heat treatment

Abstract

A carbon steel plate containing 0.87 mass% C 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 973-1 273 K for up to 7.2 ks in the air to investigate reactions between molten aluminum and high-carbon steel from the viewpoint of aluminide coating. An aluminized layer was basically composed of Fe2Al5, FeAl, Fe3Al containing carbon (Fe3Al(C)), and ferrite stabilized by aluminum diffusion (α-Fe(Al)). FeAl2was detected with Fe2Al5 at heating temperatures of more than 1 223 K, whereas FeAl had two layers due to its chemical composition. In addition, defects like a crack and a void were observed in the vicinity of the FeAl/α-Fe(Al) interface after heating at 1 273 K for 3.6 ks. To reduce brittle Fe2Al5 and FeAl2 in the aluminized layer, the steel coated with aluminum with a thickness of 50 μm was prepared and then heat-treated under the same conditions. At 1 173 K, the region consisting of FeAl, Fe3Al(C), and α-Fe(Al) accounted for a large part of the aluminized layer. This aluminized steel was subjected to quenching and tempering on the basis of features of the used bare steel. As a result, the hardness near the surface of the aluminized layer was approximately equal to that of the steel substrate.