Influence of small additions of copper and niekel on hot ductility of steels

Abstract

The influence of small additions of Cu and Ni on the hot ductility of C–Mn–Al–Nb and C–Mn–Al steels has been examined by tensile testing specimens in the temperature range 750–1000°C at a low strain rate (~10−3 S−l). On solution treating at 1330°C and cooling to the test temperature, no significant influence ofCu could befound on ductility, independent of whether or not testing was carried out in air or in a protective atmosphere of Ar. However, samples tested in an Ar atmosphere gave improved ductility over samples tested in air. Tensile samples cast directly after melting and tested in a protective Ar atmosphere were again found to be uninfluenced by compositional changes. In contrast, samples melted and tested in air showed a deterioration in ductility on the addition of Cu, but the deleterious effect on ductility of Cu could be prevented by a similar addition of Ni. No evidence for thin films of Cu rich phases penetrating along the intergranular boundaries taken by surface cracks could be found, as in conventional hot shortness. It is suggested that the observed behaviour is due to the formation of fine copper sulphide or possibily oxysulphide precipitates as a result of oxidation and the presence of Cu.MST/3014