Effect of Small Amounts of Cu on Nitrocarburizing Characteristics for Medium-Carbon Steels

Abstract

Copper, of which small amounts are usually contained in steel scraps, has been the target of the elimination from automotive or machine-grade carbon steels for a long time. However recently its effectiveness on steel's mechanical properties has been revealed and application to commercial products has begun. In this paper, the effect of Cu up to 1.0 mass% on the nitrocarburizing characteristics for 0.35 mass% C steels has been studied. (1) Mechanical properties of Cu-bearing samples showed Cu has an effect on the 0.2 % proof stresses both before and after nitrocarburizing treatment. This is possibly caused by the high increase of ferrite hardness for Cu-bearing samples even after nitrocarburizing. (2) Compound layers of Cu-bearing steels are thinner than steels bearing less amounts of Cu. This phenomenon can be explained by the occurrence of an increasing of ' (Fe 4 N) phase in the compound layers of Cu-bearing steels because the rate of ' layer formation is slower than that of (Fe 2-3 N) layer.