THE FORMATION OF DEFORMATION-INDUCED FERRITE DURING MECHANICAL TESTING

The effects of austenite grain size, level of undercooling, and strain and strain rate in compression on the austenite-to-ferrite transforma tion were investigated in a 0.1% C, 1.4% Mn steel. The influence of th is transformation on the hot ductility was then examined. Straining wa s found to raise the effective Ar-3 temperature almost to the Ae(3), a nd to accelerate the transformation significantly in both fine ( simil ar to 25 mu m) and coarse (similar to 200 mu m) grained samples. At re latively low levels of undercooling ( similar to 40 degrees C), deform ation induced ferrite only formed in regions that were significantly a ffected by the applied strain. In tension, it was observed that, if th in bands of grain boundary ferrite were present in the microstructure, the ductility decreased significantly and failure always occurred in th is second phase. Increasing the strain rate significantly reduced t he depth of the ductility trough across its entire width. It is conclu ded that, for the steel in question, unbending after continuous castin g should be performed at strain rates in excess of 3 x 10(-2) s(-1) to ensure good ductility.