The sulphide capacity and the solubility limit of CaS in CaO-Al 2 O 3 and CaO-Al 2 O 3 -CaF 2 slags have been studied at the temperatures from 1 823 to 1 923 K by the equilibrium measurement of gas-slag reaction. The sulphide capacity and the solubility of CaS in these two slag systems increase with increasing CaO content and decreasing ratio of N Al 2 O 3 /N CaF 2 . The sulphur in CaO-Al 2 O 3 -CaF 2 slag negatively deviated from Henry's law in the high concentration range of sulphur in slag, and the activity coefficient of sulphur in slag varies with sulphur content, slag composition and temperature. It was confirmed that the sulphide capacity was unable to be applied as a real measure of the slag basicity theoretically.

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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.

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