Preliminary analysis of hot ductility curve in simple C-Mn steels

An attempt has been made to predict the tensile hot ductility curves for simple C-Mn steels heated into the austenite phase to produce a coarse grain size and cooled to test temperatures in the range 700-1100 degrees C. The depth of the trough can be calculated from a knowledge of the inclusion volume fraction and the volume fraction of the ferrite films surrounding the gamma grains. The temperature at which ductility recovers at the high temperature end can also be determined from the point at which the base of the trough intersects the curve of peak strain v. temperature. This temperature is that at which dynamic recrystallisation becomes possible. Full recovery in ductility at the low temperature end of the trough occurs when large amounts of ferrite are formed; this is either 30-40 K below the Ar-3 (undeformed) or the Ae(3) depending on whether ferrite is present before or forms during deformation. The relevance of the hot ductility curve to the problem of transverse cracking is also discussed.