THE INFLUENCE OF INTERNAL AND EXTERNAL CONVECTION IN THE TRANSFORMATION BEHAVIOR OF FE-CR-NI ALLOYS

摘要

A difference in the transformation delay times is observed between electromagnetic levitation (EML) and electrostatic levitation (ESL) experiments on steel alloys. This deviation is due to the difference in convection. Using high speed imaging, we can observe the frequency of nucleation as a function of declination angle measured from the equatorial plane and we can observe the delay between nucleation events. These measurements show no preference for location in ESL testing. For EML tests, primary recalescence preferentially occurs on the top hemisphere where cooling gas impinges on the surface. Delay times did not vary significantly between top and bottom hemispheres and thus external (gas phase) flow does not explain the deviation observed. For EML tests, the frequency of secondary nucleation appears to disfavor positions along the equator and both poles, where internal flows are minimized, indicating that internal convection is most likely to be responsible for the observed deviation.