Abstract:
Although the austenitic stainless steels 304 and 321 are often treated nominally as equivalents in their
hot rolling characteristics, the question remains whether any subtle differences between the two allow
further optimisation of their respective hot rolling schedules. The hot workability of these two types of
austenitic stainless steels were compared through single-hit Gleeble simulated thermomechanical processing
between 800 C and 1200 C while the strain rate was varied between 0.001 s 1 and 5 s 1. It
was found that the constants for the hyperbolic sine equation for hot working of 321 steel are
Q = 465 kJ/mol, A3 = 9.76 1017 MPa 1 s 1, a = 0.009 MPa 1 and n = 6.1 while for 304 steel the constants
are Q = 446 kJ/mol, A3 = 2.14 1017 MPa 1 s 1, a = 0.008 MPa 1 and n = 6.1. It is shown that the occurrence
of dynamic recrystallisation starts when the Zener Hollomon parameter Z 6.4 1017 s 1 for both
steels but that the differences in the values of Q and A3 (the structure factor) between the two steels does
lead to consistently lower steady state stresses for the steel 321 than is found in the steel 304 at the same
Z values. This may, therefore, offer some scope for further optimisation of the hot rolling schedules and in
particular in the mill loads of these two respective steels.
