Ferrite Transformation during Deformation of Super-cooled Austenite

Abstract

The research results achieved by the Korean national project, HIPERS-21, on the ferrite transformation during the deformation of super-cooled low carbon austenite were summarized. Fine ferrite grains formed during the deformation of austenite, i.e. dynamically. The rate of ferrite nucleation was estimated to be accelerated several hundred times by the deformation of austenite. However, the grain refinement could not be explained by the accumulated strain alone. The application of stress during the ferrite transformation is known to effectively weaken the orientation relationship of the ferrite grains with austenite, making the coalescence of the grain difficult during the growth of ferrite and effectively increasing the nominal ferrite nucleation rate. The application of the dynamic ferrite transformation to industrial hot rolling or plate milling was also summarized. The multi-pass rolling technique was introduced to produce a fine ferrite grain structure and controlled cooling was adopted to produce a multi-phase structure in order to improve the work hardening rate of fine grained steels.

Small-scale mechanical property characterization of ferrite formed during deformation of super-cooled austenite by nanoindentation

“…This is in contrast to the reports showing that the transformation temperature of dynamic ferrite is higher than that of static ferrite. There are some reports showing that supersaturated carbon in dynamic ferrite forms very small cementite particles on the ferrite boundary [10,19]. This supersaturated carbon in dynamic ferrite is expected to be a strengthening mechanism.…”

“…The Strain-Induced Dynamic Transformation (SIDT) of super-cooled austenite has been highlighted as a process that can overcome the limitations of conventional ThermoMechanical Control Processing (TMCP). Both dynamically and statically transformed ferrites coexist in SIDTed steels due to the lower volume fraction of SIDTed ferrite in low carbon steel than the equilibrium ferrite fraction at a given processing temperature [5,7,10].…”

“…The key technology for producing ultrafine-grained ferritic steels is to impose heavy deformation to super-cooled austenite to induce a dynamic formation of ferrite grains [10]. The Strain-Induced Dynamic Transformation (SIDT) of super-cooled austenite has been highlighted as a process that can overcome the limitations of conventional ThermoMechanical Control Processing (TMCP).…”

Influence of strain reversal on dynamic transformation in microalloyed steels deformed above the Ae3 temperature

“…Dynamic strain-induced transformation (DSIT) have received considerable attention in the past decade from not just academia but also industry [1][2][3][4][5] due to its great potential as a relative simple processing route to produce steels containing ultrafine ferrite (UFF). However, despite considerable investments made to industrialise this process, the fundamental mechanism of DSIT is still not well understood.…”

Identification of dynamic ferrite formed during the deformation of super-cooled austenite by image-based analysis of an EBSD map

“…Grain refinement of carbon steels has been regarded as an effective method to improve strength and toughness simultaneously [1][2][3][4][5][6][7][8][9][10][11]. Recently, to overcome the limitations of conventional ThermoMechanical Control Processing (TMCP) and manufacture ultrafine-grained ferritic steels, the StrainInduced Dynamic Transformation (SIDT) of super-cooled austenite has been investigated.…”