Surface Attack in Chromium-Iron Alloys

Welchner and Roush
¹
used the term “surface attack” to describe supposed grain-boundary oxide deposits which they observed at and immediately beneath the surface of case-carburized steel parts. Hultgren and Hägglund
²
proposed that grain-boundary oxides could form during carburizing, provided certain alloying elements (such as chromium) having a greater affinity than iron for oxygen were present. The formation of iron or alloy nitrides
³
and the formation of certain hydrogen compounds
⁴
have been held responsible for the appearance of surface attack during gas carbonitriding.