Effect of sulfur on the properties of copper

However, with an increase in sulfur content from 0 to 0.5% the mechanical properties of copper are almost unchanged, even such asensitive property as necking [6], and only with an increase in sulfur content in copper to 1% are they reduced. It was shown in [7] that with a content of 2-3% S (by weight) copper in fact becomes brittle. The widespread opinion in recent years that sulfur in small amounts causes copper embrittlement is based on the fact that sulfur was detected at the fracture surface of specimens on whose tensile curves there was a drop in ductility. On the basis of this it was concluded that embrittlement of copper is caused by sulfur impurity located at grain boundaries [8]. It was established in [2] that with a content of less than 0.0018% S in copper, in order to avoid cracking it is necessary to carry out prolonged annealing so that sulfur is transferred into solid solution. Sulfur in copper is in the form of copper sulfide Cu2S globules [9]. It is also well known that sulfur is added to copper in an amount up to 0.03% in order to improve cuttability. In view of this contradictory data it is of interest to study the effect of sulfur on the properties of copper. The effect of sulfur on the mechanical properties of copper M1 and MIR was determined. For this purpose sulfur was added to molten copper MOO in different forms; pure sulfur, copper sulfate containing water, and anhydrous copper sulfate (after roasting). Roasting of copper sulfate was carried out at 140°C for 20-30 h in order to obtain almost constant weight. Anhydrous copper sulfate, which is white in color, rapidly absorbs water, and therefore melting was carried out on the same day when the weight of copper sulfate became almost constant. Copper sulfate was charged in amounts corresponding to the sulfur content in copper (0.030.04%). Melting was carried out under a layer of carbon with deoxidation by phosphorus and ~ without it. A copper--phosphorus master alloy (9% P) was used for deoxidation, calculated on the basis of 0.04% P in copper. Metal pouring was carried out into a horizontal copper mold. In those cases when sulfur (in any form) was added to copper without phosphorus, during solidification swelling of the ingot was observed with an increase in its volume by about a factor of two. Ingots were machined on all sides for complete removal of the rough surface. In order to obtain circular blanks 80 mm in diameter for pressing they were cut from the flat ingots.