Stress relaxation measurements were carried out on a plain carbon and four Ti steels over the temperature range 850 to 1050$ sp circ$C. The results show that the stress relaxation of plain carbon austenite after a 5% prestrain can be described by the relation $ sigma$ = $ sigma sb0$-$ alpha$ln(1 + $ beta$t). By contrast, in the solution-treated Ti steels, relaxation is arrested at the start of precipitation and is resumed when precipitation is complete. As a result, this new mechanical method is suitable for following carbonitride precipitation in microalloyed austenite at hot working temperatures. / PTT diagrams were determined by the present technique for the steels containing 0.05, 0.11, 0.18 and 0.25% Ti. The PTT curves obtained are C shaped for all the steels. The upper parts of these curves are shifted to significantly longer times as the Ti and C concentrations are reduced. By contrast, the positions of the lower arms of the curves are relatively independent of the current values of the solubility product (Ti) (C). This phenomenon is attributed to the catalytic effect of trace amounts of dissolved N on the nucleation rate of Ti(CN) in austenite. / Changes in the size distribution and morphology of the precipitates during relaxation of the 0.25% Ti steel were followed by means of electron microscopy. The cube shaped Ti(CN) precipitates were heterogeneously distributed in either a chain-like or a cell-like manner. Electron microanalysis was additionally carried out to determine the compositions of the Ti carbosulphide-Mn sulphide inclusions. / Finally, the experimental results are compared with the predictions of classical nucleation theory and of the diffusion controlled particle growth theory. Good agreement was obtained between the predictions of the theories and the experimental results. It is demonstrated by means of the thermodynamic analysis of nucleation that the Ti(CN) precipitate/austenite interface is of a semi-coherent nature. It is shown that the interface between a critical nucleus and the matrix can be characterized by the newly introduced coherency loss parameter C.

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The kinetics of dissolution of titanium and vanadium in liquid steel has been studied. Two periods were distinguished: the steel shell period and the free dissolution period. / In the case of titanium, it is shown that the customary frozen shell of steel encases the cylinder following its initial immersion. Premature internal dissolution then begins as a result of liquid eutectic of Fe(,0.3) Ti(,0.7) composition forming at the inner steel shell boundary. This phenomenon triggers an exothermic dissolution and erosion of the inner steel shell. The net result is considerable shortened shell melting times. During the free dissolution period, the temperature of the titanium dissolving at the interface increases and the dissolution process becomes self-accelerating. / During the steel shell period with pure vanadium and ferrovanadium alloys, no reaction was observed between the steel shell and vanadium. For low grade ferrovanadium alloys, the dissolution proceeds via a heat transfer mechanism. On the other hand, for high grades, ferrovanadium mass transfer mechanisms dominate. / A simplified mathematical model of the process has been developed to describe the coupled heat and mass transfer phenomena involved in the various systems studied.

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Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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