Abstract
Powder liquid coating is applied as an aluminization technique for carbon steel (JIS S45C), and subsequent plasma nitriding for tool steel (SKD61). In this process, Fe2Al5 forms initially on S45C, and the intermetallic compound decomposes into α-Fe during heat treatment at 1273 K, excluding C atoms from the aluminized layer (α-Fe) to the substrate (γ-Fe). Aluminized layer of α-Fe including vanadium carbide particles is formed on SKD61 by heating at 1303 K, and the substrate transforms into martensite during N2 gas flow cooling after heat treatment. By plasma nitriding of aluminized SKD61, hardness of HV1200-1600 is achieved at previously aluminized layer, exhibiting no detectable aluminium nitride but Fe3N, Fe4N, and highly strained α-Fe matrix in its surface XRD. Although the hardening mechanism of the modified layer is not clarified, it is suggested from XRD that the hardness is attributed to precipitation hardening by nitrides (ε-Fe3N, γ'-Fe4N) as well as solid solution hardening by Al.
