Abstract
Acoustic emission in two different TWIP/TRIP steels during thermally induced γ–ε martensitic phase transformation was investigated. Large asymmetry was observed: the noise activity was considerably larger for heating than cooling. This was explained by the plastic deformation and strain-induced martensite nucleation (which usually provides much lower acoustic emission signals) in the austenite during cooling. The amplitude and energy probability distribution functions for heating followed the power-law behavior, and the critical exponents were counted as well. The amplitude and energy exponents (α and ε, respectively) for the two different samples were the same within the errors (α = 2.4 ± 0.2, ε = 1.7 ± 0.1), indicating the universal character. The acoustic activity vs martensite volume faction showed a maximum at around 60 pct for heating, which is most probably related to the coming apart of the elastic fields of the martensite variants.
Highlights
TWINNING-INDUCED plasticity (TWIP) and transformation-induced plasticity (TRIP) steels are important because they exhibit high deformability and strength at the same time
The intermittent character of the martensitic transformation during heating leads to clear power law behavior of the probability density distributions of the amplitudes and energies of acoustic emission events
Surprising asymmetry is observed: the AE activity was considerably larger for heating than cooling
Summary
TWINNING-INDUCED plasticity (TWIP) and transformation-induced plasticity (TRIP) steels are important because they exhibit high deformability and strength at the same time In such steels the austenite is able to accommodate strain through both dislocation glide and twinning on the f111gch112ic slip system. TWIP steels exhibit rather low yield strength, but their ultimate tensile strength can exceed 1100 MPa. TWIP steels exhibit rather low yield strength, but their ultimate tensile strength can exceed 1100 MPa This is due to their high strain-hardening coefficient, which results in large uniform elongation (60 to 95 pct).[1,2,3,4,5,6] The high degree of strain-hardening is considered to be the result of the competition between the dislocation slip and e-martensite formation.[2,3,4,5,6] In
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