Abstract:
This paper presents constitutive equations that describe the hot flow behaviour of Virgin (VG) X20 and
rejuvenated heat-treated creep exhaust (CE) X20 steels. The study provides a foundation for determining
the effect of rejuvenation heat treatment on CE steels by making comparisons to the VG steel. Hot
compression tests in the temperature range of 900°C to 1050°C, strain rate range of 0.1–10 s
− 1
to a total
strain of 0.6 and stress-strain curves were obtained. The flow stress curves of both steels exhibited
dynamic recovery (DRV) characteristics as the main softening mechanism. Constitutive constants of
steady-state stresses were determined. The stress exponents, n, were 6.62 (VG) and 5.58 (CE), and the
apparent activation energy values were 380.36 kJmol
− 1
(VG) and 435.70 kJmol
− 1
(CE). Analysis of the
activation energies showed that VG steel had better workability properties than CE steel and was easier to
deform at high temperatures. Constitutive equations for predicting the flow stress in the two steels were
established. This were verified by statistical tools: Pearson’s correlation coefficient (R) and Absolute
Average Relative Error (AARE). The results showed R-values were, 0.98 (VG) and 0.99 (CE), and the AARE
value for VG was 4.17% and 9.01% for CE. The statistical parameters indicated a good correlation
between the experimental and predicted values. The constitutive equations therefore adequately
described the flow stress behaviour of both steels and can therefore efficiently analyse industrial metal
forming schedules.
