Hot Deformation of Austenite in a Plain Carbon Steel

Abstract

Sy nopsis H igh tem/Jerature tellsile deformatioll of a 0. / 6°o C steel was st1ldied over a wide rallge of straill rates from 18 to 2.73 x /0-• sec-I ill the austellite ral/ge. From metallographic obsenatiol/s al/d flow stress measuremel/ls it was revealed that the first flow stress maximum, a~I' the shape of the a-e curves, alld tne deformed structure ill high strail/s were unique .functiolls of the Z eller-Hollom on parameter, Z, which was calculated 01/ all activatioll energy for deformation (68.5 kcal/mol). The distillct structural challges occurred ill the initial hardenil/g stage below tlte strain at aM, al/d the r grain structures for high strail/s were of a mixture of fill e grains alld comparatively coarse graills, and the grain boul/daries of the latter were wavy on the whole regardless of z. 1t was cOl/sidered then that the deformatioll if a 0. 1 6~o C steel ill the r ral/ge was cOl/trolled ~Y the dynamic recrystallization p rocess assiJted by the migration of vacal/cies. al/d that this fact was closely related to the shape of the a-e curves, I/otably a sharp stress maximum or stress oscillatiol/s in low strain region followed by steady-state deformatioll in high strain region. I,Vhether a a-e curve was the stress peak type or the stress oscillation type depel/ded critica lljl 01/ the relative difference between tlze il/itial r grain size b~rore d,!/ormaliol/ al/d that dynamically rerrystallized under a high strain.

Application of Cellular Automata Simulations to Modelling of Dynamic Recrystallization

“…These overlapping waves are not synchronized, and therefore, they produce one sole peak on the flow stress curve. These characteristics of the single and the multiple peak behaviour are consistent with the experimental work of Sakui et al [14].…”

“…1 (b) for the same initial grain sizesD 0 = 2.9 (solid lines) and 7.0 (dashed lines). The multiple or single peak behaviour is produced at high or low temperature, respectively (what is consistent with experimental results [14]). The peak stress σ p is shifted upwards and to the right with an increase of the initial grain size.…”

“…The reason of this discrepancy could lay in the fact that exper-imental results are not in situ measurements but post mortem one (cf. details of [14]).…”

Model for Strain-Induced Precipitation Kinetics in Microalloyed Steels

“…The good approximation of the activation energy (Q d ) to the energy for self-diffusion in Fe  indicates that the mechanism which governs the plastic flow of austenite is principally the climb of edge dislocations, which depends in turn on the diffusion of vacancies. [15] The activation energy for the self-diffusion of iron in austenite varied with the presence of solutes, and the value of this variation depends on the atomic fraction of each solute, on its atomic volume, and on its heat sublimation. [16] Therefore it seems logical to imagine that an increase in Q d would also raise the value of t 0.05 .…”

Static recrystallization characteristics and kinetics of high-silicon steels for direct quenching and partitioning

“…2a) and at 1 150-1 200 8C in the case of 3Mn-1.5Si ( Fig. 2b) steels, where the critical strain for the initiation of dynamic recrystallization (DRX) e c might be exceeded (e c is about 0.8 times peak strain e p [21,36]). The peak strain was, however, not determined.…”