Papers by Keyword: Deformation-Induced Ferrite

Abstract: Recent observations regarding the transformation of deformed austenite are reviewed. It is shown that superequilibrium ferrite and pearlite can be formed at temperatures well above the Ae₃ and Ae₁, respectively. The role of the stored energy associated with the introduction of the dislocations introduced by the deformation is discussed. It is shown that the forward dynamic transformation into ferrite and pearlite is several orders of magnitude faster than the reverse static transformation back into austenite. The retarding effect of alloying additions such as niobium is also outlined. The results are interpreted in terms of the effect of deformation on the modified phase diagrams pertaining to the transformation of deformed austenite.

Abstract: Recent observations regarding the transformation of deformed austenite are reviewed. It is shown that superequilibrium ferrite and pearlite can be formed at temperatures well above the Ae₃ and Ae₁, respectively. The role of the stored energy associated with the introduction of the dislocations introduced by the deformation is discussed. It is shown that the forward dynamic transformation into ferrite and pearlite is several orders of magnitude faster than the reverse static transformation back into austenite. The retarding effect of alloying additions such as niobium is also outlined. The results are interpreted in terms of the effect of deformation on the modified phase diagrams pertaining to the transformation of deformed austenite.

Abstract: A 0.21% C plain carbon steel was deformed in torsion to strains of ε = 0.15-3.0 at a strain rate of ε ̇= 4.5 s^-1 over the temperature range 722-822°C in a 5%H₂-Ar gas atmosphere. The experimental parameters were varied in order to study the formation of ferrite and pearlite by dynamic transformation (DT) in the intercritical region. This transformation was observed right up to the highest experimental temperature (822°C). The pearlite formed by DT contained cementite spheroids whose size distribution evolved during isothermal holding after deformation. In the first stage, corresponding to the first 800 s of holding, spheroid coarsening took place. When the holding time exceeded 800 s, the spheroids dissolved and the pearlite reverted into the original parent austenite. The results indicate that pearlite can form by DT at temperatures well above the Ae₁ and that the reverse static transformation is much slower than the forward dynamic transformation.

Abstract: A 0.45% C steel was deformed in torsion over the temperature range 762-872°C in a 5%H₂-Ar gas atmosphere. Strains of 0.25-3.0 were applied at a strain rate of ε^. = 4 s^-1. The experimental parameters were varied in order to study the effects of strain and temperature on the formation of ferrite by dynamic transformation (DT) at temperatures above the Ae₃. The critical strain for ferrite formation by DT was about 0.2 and its volume fraction increased with strain. The average ferrite grain sizes were about 1 to 2 µm and were fairly independent of temperature. It was observed that the deformation-induced ferrite remained fairly stable during 800 s of isothermal holding. In general, the experiments showed that DT takes place at temperatures above the Ae₃ and that the reverse static transformation is much slower than the forward dynamic transformation.