INFLUENCE OF SMALL ADDITIONS OF COPPER AND NICKEL ON HOT DUCTILITY OFSTEELS

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 spe cimens in the temperature range 750-1000 degrees C at a low strain rat e (similar to 10(-3) s(-1)). On solution treating at 1330 degrees C an d cooling to the test temperature, no significant influence of Cu coul d be found on ductility, independent of whether ol not testing was car ried out in air or in a protective atmosphere of Ar. However, samples tested in an Ar atmosphere gave improved ductility over samples tested in ail. Tensile samples cast directly after melting and tested in a p rotective Ar atmosphere were again found to be uninfluenced by composi tional changes. In contl ast, samples melted and tested in ail showed a deterioration in ductility on the addition of Cu, but the deleteriou s effect on ductility of Cu could be prevented by a similar addition o f Ni. No evidence for thin films of Cu rich phases penetrating along t he intergranular boundaries taken by surface cracks could be found, as in conventional hot shortness. It is suggested that the observed beha viour is due to the formation of fine copper sulphide or possibily oxy sulphide precipitates as a result of oxidation and the presence of Cu.