INFLUENCE OF CARBON CONTENT ON SUPERPLAST IC BEHAVIOR IN TI AND B-DOPED CR-MO STEELS

Superplasticity has been investigated in various ferrous alloys and st eels. However, in these materials, especially in the hypoeutectoid ste el bellow A(1) temperature, the relationship between the content of ca rbon and elongation to failure is not obvious. In the present investig ation, the influence of carbon content on superplastic behaviour is st udied using carbon steels based on Cr-Mo steel. In order to obtain the fine grain structure, a small amount of Ti and B were added and the c ontent of carbon was controlled to be in the range of 0.24% to 0.83%. The largest value of elongation to failure was 644% which was obtained by the tensile test of the specimen containing 0.58% carbon. The temp erature and strain rate at which the maximum value was obtained were 7 10 degrees C and 5 x 10(-4)s(-1), respectively. Of all the specimens, this; specimen had the minimum grain size. Moreover, the area fraction of carbide took the maximum value at the temperature where the larges t elongation value was obtained. These results show that the addition of carbon has an effect on grain refinement by formation of carbide, b ut excess amounts of carbons (>0.6%) bring about premature failure bec ause of coarse microstructure and larger carbide.