The knowledge of the stress-and deformation-induced martensite formation in metastable austenitic steels including the formation temperatures and amounts formed is of considerable importance for the understanding of the transformation induced plasticity. For this purpose a stress-temperature-transformation (STT) and a deformation-temperature-transformation (DTT) diagram have been developed for the steel X5CrNi 18 10 (1.4301, AISI 304). It is shown that the Md-temperature for Y~E, E~a', Y~E~a' and y~a' martensite formation is defined by two stress-temperature curves which show a different temperature dependence. They specify the beginning and the end of the deformationinduced martensite formation in the range of uniform elongation. The intersection point defines the corresponding Md-temperature. The stress difference which results from the stresses for the end and the beginning of the martensite formation shows positive values below the Md-temperature. It defines the amount of martensite being formed. When the MdY-' temperature is reached and the formation of the first deformation-induced amount of e-martensite appears, an anomalous temperature dependence of the maximum uniform elongation starts. The highest values of the maximum uniform elongation are registered for the tested steel in the immediate vicinity of the Md y-a' or the Mdy-,-a' temperature -similar as in other metastable austenitic CrNi steels. At this temperature the highest amount of deformation-induced a-phase exists. The transformation plasticity in the test steel is considerably caused by the deformation-induced E and a' martensite formation. Using the new evaluation method, the increase of plasticity !1A (TRIP-effect) and strength !1R can be quantified.

The behaviors of several types of inclusions at a high temperature were examined using a confocal scanning laser microscope (CSLM, 1LM21H/SVF17SP). Although alumina inclusions tended to impact on each other, agglomerate, and grow quickly, no other inclusion type, such as spinel as well as solid and liquid calcium aluminate, was observed to attract each other. The results of confocal microscope study were compared with the industrial investigation. For this purpose, many steel samples were taken at different stages of ladle treatment. The samples were analyzed by scanning and light optical microscopes. Approximately 50,000 inclusions of several types were examined. Only alumina inclusions were attracted to each other and agglomerate. No agglomeration by attractive behavior was observed in the other types of inclusions, including liquid inclusions. Both the industrial data and the in situ observation by CSLM indicate that, although the attraction force and the agglomeration play a significant role in the growth of alumina inclusions, the agglomeration of spinel and calcium aluminate inclusions does not need special consideration in ladle treatment. The agglomeration of liquid calcium aluminate inclusions took place only when they occasionally met as a result of external force, which led to low collision probability. However, the agglomeration of the liquid calcium aluminate inclusions along with alumina particles could be detrimental in the casting process.

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