Abstract: Continuous cooling and isothermal dilatometry was performed for a binary Fe-0.3C alloy
and a ternary Fe-0.3C-1.0Mn alloy at slow (< 0.1 oC/s) cooling rates and isothermally at temperatures
below the equilibrium eutectoid reaction temperature but above the bainite start temperature (625 to
715 oC). Some of the test conditions produced an unusual morphology in which fine scale
‘sub-grains’ are decorated with carbide, with additional discrete carbide particles inside the
‘sub-grains’. A detailed investigation into the network carbide formation indicates formation during
austenite decomposition, as opposed to a post lamellar transformation coarsening or spheroidization
reaction, but only for select temperatures, and apparently only during isothermal conditions.
Abstract: The effect of hot rolling parameters on graphitization of a spray formed
ultra high carbon steels(UHCSs) was described. The number of graphite stringers and
graphite area fractions increased with the increase of rolling reduction. Graphite
stringers nucleated at small pores and grew by carbon diffusion from adjacent
austenite during hot rolling. Alloy contents, pores and hot deformation atγ+Fe3C
phase range are the key factors for graphitization.The graphite stringers of UHCSs
have little effect on tensile strength, but reduce the ductility at room temperature.
Abstract: The microstructural evolution and the softening behavior of hot rolled and 60% cold rolled
0.85wt% carbon pearlitic steels during spheroidization annealing have been investigated by using the
textural and microstructural information contained in the Orientation Imaging Microscopy (OIM)
scans. The local boundary energy map, recently suggested by the present authors, is used to monitor
the changes of stored plastic strain energy distribution in ferrite during the annealing process, which
shows that the spheroidization process of cementite is finished before the completion of
recrystallization of the 60% cold-rolled high carbon pearlitic steel.
Abstract: By employing the new developed relaxation-precipitation-controlling phase
transformation (RPC) technique in large scale production the bainitic steels with ultra fine bainite
has been obtained. These bainitic steels have good synergistic properties. With the aid of thermal
simulation the refinement mechanism of RPC technique has also been investigated. The optical
microscope, scanning electron microscope, transmission electron microscope and Electron back
scattering diffraction technique were employed to study the features of microstructure produced by
RPC technique, precipitation and the evolution of dislocation configuration during the relaxation.
The results show that when produced by RPC technique the microstructure of the steel is mainly
ultra-fine lath bainite packets, and these bainite packets block each other. It is also found that during
the relaxation the dislocation cells form and strain induced precipitation occurs, the dislocation cell
pinned by the precipitates can confine the bainite transformation. After the relaxation during the
cooling the acicular ferrite forms at first and in succeeding the bainite transformation is blocked by
the acicular ferrite and the bainite is refined effectively.
Abstract: This paper addresses the physical mechanisms of the transformation of deformed
austenite into allotriomorphic ferrite and Widmanstätten ferrite. The possible implementation of
deformation in currently available transformation models for allotriomorphic ferrite and
Widmanstätten ferrite is discussed based on a series of deformation dilatometry experiments. It is
concluded that a small amount of deformation already gives significantly faster transformation
kinetics and a significant decrease in fraction Widmanstätten ferrite, and that the key to
understanding the effect of deformation on transformation lies in the nucleation of allotriomorphic
and Widmanstätten ferrite. For Widmanstätten ferrite also the growth needs further study.
Abstract: Three-dimensional observations of proeutectoid ferrite formed at grain boundary in an
Fe-0.09%C-1.48%Mn vanadium microalloyed alloy was revealed by techniques of serial sectioning
along with computer-aided reconstruction. The ferrite allotriomorphs nucleated at grain boundary edges
were approximately prolate ellipsoids. Not all the ferrite allotriomorphs formed at grain boundary faces
were oblate ellipsoids. The growth kinetics of ferrite allotriomorphs nucleated at grain boundary edges
was greater than that of ferrite allotriomorphs nucleated at grain boundary faces.
Abstract: The model of the γ→α transformation calculated with the CATRAN program is
described. The expected effect of former austenite grain size on the transformation kinetics as well
as the final microstructure is analyzed and compared with experimental data. The effect of austenite
grain size distribution spread on the transformation kinetics is also considered and must be included
as the additional input parameter in the computer model of austenite decomposition. In particular,
probable variations of grain size non-uniformity should be taken into account when comparing
transformation kinetics observed in the dilatometer experiment and under industrial conditions.