Papers by Keyword: Ultra Fine Ferrite

Abstract: In the current study, a novel approach was employed to produce a unique combination of ultrafine ferrite grains and low temperature bainite in a low carbon steel with a high hardenability. The thermomechanical route included warm deformation of supercooled austenite followed by reheating in the ferrite region and then cooling to bainitic transformation regime (i.e. 400-250°C). The resultant microstructure was ultrafine ferrite grains (i.e. <4μm) and very fine bainite consisting of bainitic ferrite laths with high dislocation density and retained austenite films. This microstructure offers a unique combination of ultimate tensile strength and elongation due to the presence of ductile fine ferrite grains and hard low temperature bainitic ferrite laths with retained austenite films. The microstructural characteristics of bainite were studied using optical microscopy in conjunction with scanning and transmission electron microscopy techniques.

Abstract: The ferrite transformation kinetics of severely hot-deformed austenite has been studiedby considering ferrite nucleation from dislocation cell blocks inside austenite grains. The size ofdislocation cell blocks and ferrite grain size just after phase transformation are acknowledged to beinversely proportional to the square root of dislocation density. It is found that the ferrite nucleationrate in this area can reach the saturated state at a high temperature just under Ae3, and the ferritetransformation finishes within a very short time. The kinetics of ferrite volume fraction and theferrite grain growth after phase transformation for plain carbon (0.1%C, 0.2%Si, 1.0%Mn) steelhave been studied using a THERMECMASTER hot-compression testing machine. These modelscan be applied to the hot and warm forming processes of plain carbon steel to predict the ferritetransformation from severely deformed austenite.

Abstract: A 0.12 wt.% C – 1.26 wt.% Mn steel was studied to evaluate phase transformations that occurred during a specific thermal processing method designed to simulate steel plate surface layer microstructural evolution during processing with intermediate cooling. All process simulations used a Gleeble thermomechanical simulator along with thermal practices developed previously. After intermediate cooling was completed during processing, slight reheating of the plate surface layer region would occur due to heat retained in the plate core. Microstructural evaluation of Gleeble samples quenched at several points along the thermal profile allowed interpretation of microstructural evolution during processing. The microstructure that was present at the point where deformation would be applied consisted of approximately 75% ferrite, 25% austenite and some small, undissolved cementite particles.