February 5, 1996 Location: Anaheim Marriott Hotel
Session Chairperson: TBA
2:00 pm
CRYSTALLOGRAPY AND THREE- DIMENSIONAL RECONSTRUCTION OF PEARLITE COLONIES IN FE- C- X SYSTEMS: M. A. Mangan, G. J. Shiflet, Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22903
Previously, electron backscatter diffraction (EBSD) in a scanning electron microscope (SEM) has been applied to the pearlite transformation in Fe-.8C-12Mn to analyze the orientation relationship between ferrite and cementite lamellae in a single colony. This study has been extended to other Fe- C- X systems where X is Ni, Cr, Mn and Si. In addition, any ambiguity associated with the three- dimensional (3- D) development of a pearlite colony can be removed through repeated sectioning and subsequent reconstruction. The interlamellar spacing and colony size can now be measured unambiguously from the resulting volume, improving data for studies of growth kinetics. Combining the 3- D information with the orientation relationships between ferrite and cementite lamellae obtained through EBSD, the factors resulting in different ferrite/cementite relationships can be determined.
2:20 pm
PHASE TRANSFORMATION KINETICS AND MICROSTRUCTURAL EVOLUTION IN HYPOEUTECTOID STEELS: R. Pandi, M. Militzer, E. B. Hawbolt, T. R. Meadowcroft, The Centre for Metallurgical Process Engineering, The University of British Columbia Vancouver, B.C. V6T lZ4 Canada
The austenite- to- ferrite/pearlite phase transformation is characterized by nucleation and growth phenomena. Usually, early site saturation is obtained in the austenite decomposition and further progress of the phase transformation is followed by ferrite growth. In ferritic steels, the final microstructure can be evaluated by ferrite grain size and morphology. The ferrite grain size depends on the number of grains produced at the early stage of phase transformation. In other words, the ferrite nucleation rate determines the grain size of the final products. Chemical composition, austenite grain size, cooling rate and retained strain have major effects on the phase transformation kinetics and final microstructure. This work deals with modelling of the austenite decomposition kinetics and final microstructure of hypoeutectoid steels (low carbon, plain carbon and HSLA steels) by quantifying the above parameters. To follow the transformation kinetics experimentally, dilatometric continuous cooling transformation (CCT) tests have been performed on the Gleeble 1500 thermomechanical simulator. Both semi- empirical and fundamental approaches are proposed to describe the phase transformation behavior and good agreement between experimental data and model predictions are obtained.
2:40 pm
MODELING OF HEAT AFFECTED ZONE FORMATION IN FLAME CUTTING OF MILD STEEL: Peter Robinson, BOC Fabrication Technology Center, 24 Deer Park Road, London, UK SW19 3UF
A numerical model has been developed, using a finite- volume based approach, to simulate the conductive heat transfer leading to the formation of a heat- affected zone in oxy- acetylene cutting of steels. The model considers both the heat supplied by the iron- oxygen reaction, and that from the preheating flame. Phase transformations in the steel are considered, by the inclusion of non- linearities in the governing partial differential equation. Experimental validation has shown the model to be accurate in the prediction of both the size and shape of the heat affected zone. Correlations for dependence of heat affected zone size on processing parameters (cutting speed, flowrate of gas, steel alloy content and nozzle size) are discussed in relation to the model, and their effects are described.
3:00 pm
HIGH STRENGTH HIGH DUCTILITY COMPACTED GRAPHITE CAST IRON: MECHANICAL PROPERTIES: Cheng- Hsun Hsu, Shen- Chih Lee, Dept. of Materials Engineering, Tatung Inst. of Technology, Taipei, Taiwan 10451
This research applied alloy addition and heat treatment methods to obtain austenitic, upper/lower bainitic, and tempered martensitic compacted graphite (CG) cast irons. The effects of vermicularity (percentage of compacted graphite in total free carbon), and matrics on strength and ductility were evaluated. It was found that high nickel base austenitic CG iron resulted in lowest hardness and tensile strength, followed by as- cast pearlitic-ferritic iron. Bainitic CG iron exhibited both superior strength and ductility of all CG irons studied. As to tempered marten-sitic CG iron, the high strength grade would be accompanied by relatively low ductility as compared to bainitic one. Optical microscopy, SEM and X- ray diffractometry were carried out in order to correlate the microstructural features to that of the properties obtained.
3:20 pm BREAK
3:30 pm
HETEROGENEOUS NUCLEATION BEHAVIOR IN CAST IRON: Toshiaki Mizoguchi, John H. Perepezko, Deptartment of Materials Science and Engineering, University of Wisconsin- Madison, 1509 University Ave., Madison, WI 53706
During the solidification of cast iron a modest melt undercooling is a common observation, but the identity of the nucleation catalyst limiting the amount of undercooling has been elusive. In order to examine the undercooling behavior in a systematic study, a droplet method has been developed based upon an Al2O3SiO2- CaO slag containing a dispersion of 30- 300 um diameter droplets. For hypoeutectie alloys, primary [[gamma]]- Fe is a poor nueleant for both graphite and Fe3C based on a nucleation undercooling of 375deg.C below the eutectic. For hypereutectic alloys, primary graphite is catalytic for [[gamma]]-Fe and Fe3C at 8deg.C and 31deg.C undercooling respectively. The solidification microstructures have been examined to identify the reaction path. The support of the Nippon Steel Corp. and ARO(DAAH- 04- 93- G- 0296) is acknowledged.
3:50 pm
MORPHOLOGICAL DEVELOPMENT OF CELLULAR (DISCONTINUOUS) COLONIES IN A l9Cr- 5Ni AUSTENITE STEEL: S.Matsuoka, M. A. Mangan, G. J. Shiflet, Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22903
The dependence of grain boundary misorientation on the occurrence and morpho-logical development of cellular precipitation was studied using a combination of electron backscattered diffraction (EBSD) with an SEM and three- dimensional re-construction from serial sectioning of cellular colonies. In this study, cellular colony growth rates are shown to be dependent on the grain boundary misorientation forming the transformation growth front. The growth rate increases from about 20 degs. misorientation and reaches a maximum at 40 degs. By applying the repeated sectioning method and our computer graphic analysis program, a three- dimensional reconstruction of a cellular colony is obtained resulting in an improved perspective of the colony. Once the cellular colony is reconstructed, precipitate plate lengths and spacings can be accurately measured without the usual errors associated with single sectioning.
4:10 pm
THE EFFECT OF GRAIN SIZE AND LOAD ON THE TRANSIENT CURRENT RESPONSE AND MICROSTRUCTURES DURING THE IMPACT AND CONTINUOUS SCRATCHES IN Fe-18%Cr-5%Ni ALLOY AND 304 STAINLESS STEELS: Richard Raul Romero, S. K. Varma, Department of Metallurgical and Materials Engineering, The University of Texas at El Paso, El Paso, TX 79968- 0520
The scratch technique has been modified to include the continuous scratches
besides the conventional impact scratches to study the corrosive wear behavior
of Fe-18%Cr-5%Ni alloy and 304 stainless steel. The transient current generated
during the two different scratching processes have been compared to study the
depassivation kinetics. The near surface microstructures evolved as a result of
the scratches have been determined by the transmission electron microscopy
(TEM). The microstructural details at the TEM level have been examined to study
the effect of initial grain size and load on the transient current generated
due to depassivation. The load on the stylus and the grain size not only
influence the microstructures, they also affect the depassivation and
repassivation kinetics during the corrosive wear process. This research has
been supported by the National Science Foundation through the grant number HRD-
9353547.
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