Le. Cepeda et al., INFLUENCE OF COMPOSITION AND THERMAL HISTORY ON THE DYNAMIC RECRYSTALLIZATION AND SUBSEQUENT HOT DUCTILITY OF MILD STEELS, ISIJ international, 33(7), 1993, pp. 799-806
Torsion tests at strain rates of 1 x 10(-3), 1.6 x 10(-1) and 1 s-1 an
d at temperatures between 850 and 1 100-degrees-C were carried out (1)
on Al and Al-Ti mild steels after heating directly to the testing tem
perature, (2) on Al steel soaking for 30 min at 1 200-degrees-C, then
cooling the specimen to the testing temperature and (3) after soaking,
cooling to 700-degrees-C and then heating to the testing temperature.
Both steels showed a clear trough in ductility between 850 and 1 050-
degrees-C, the ductility being lowest for the directly heated Al treat
ed steel and the soaked, cooled below A1 and heated again, highest for
the 1 200-degrees-C soaked steel and intermediate for the directly he
ated Al-Ti steel. The lowest ductilities are associated with the inhib
iting effect of AlN and TiN exerted on grain boundary migration and pr
eventing the completion of dynamic recrystallisation, as shown also by
their effect of increasing the peak strain and making the reaching of
equilibrium dynamic recrystallised grain size difficult, which would
markedly improve ductility. Soaking at 1 200-degrees-C, by dissolving
and/or coarsening the AlN precipitates has the marked effect of increa
sing ductility. The present results can be explained in terms of the d
rag exerted by the dispersed particles making dynamic recrystallisatio
n and grain growth difficult.