Influence of Induced Convection on Transformation Kinetics During Rapid Solidification of Steel Alloys: The Retained Dam
- PDF / 933,996 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 10 Downloads / 233 Views
https://doi.org/10.1007/s11837-020-04375-2 2020 The Minerals, Metals & Materials Society
SOLIDIFICATION BEHAVIOR IN THE PRESENCE OF EXTERNAL FIELDS
Influence of Induced Convection on Transformation Kinetics During Rapid Solidification of Steel Alloys: The Retained Damage Model DOUGLAS M. MATSON
1,2
1.—Mechanical Engineering Department, Tufts University, Medford, MA 02155, USA. 2.—e-mail: [email protected]
The Retained Damage Model successfully predicts the incubation delay during transformation from ferrite to austenite in the presence of an applied external flow field during rapid solidification of ternary stainless-steel alloys. The model incorporates two new features—conservation of the free energy associated with undercooling of the primary metastable phase, and use of a modified Read–Shockley approach to quantify defect energy induced by melt shear. Healing of the microstructure could reduce the amount of free energy retained, but, for the alloys considered in this work, it was found that the model is not sensitive to this phenomenon, and thus 100% of available free energy is retained to provide an additional transformation driving force, significantly shortening the incubation period. Use of a dimensionless approach allows comparison between systems with very different thermophysical properties, and highlights the similarity in response to local flow conditions over a wide range of compositions.
INTRODUCTION Electromagnetic stirring has been successfully used for many decades to improve product quality during continuous casting operations.1 One approach to investigating how convection influences metastable phase solidification, with subsequent transformation to a stable phase in steel alloys, is to utilize containerless levitation processing. Electromagnetic levitation (EML) leads to significant convection when compared to electrostatic levitation (ESL).2,3 Conducting EML experiments in space allows for investigation of a wide range of induced convection because the lack of gravity means levitation forces can be significantly reduced,4 with a concomitant reduction in both applied electromagnetic field strength and induced convection. In each of these approaches, magnetohydrodynamic modeling (MHD) is used to predict the level of convection and the rate of shear in the undercooled liquid during processing.5–7
(Received June 16, 2020; accepted September 2, 2020)
The hypo-eutectic FeCrNi stainless-steel alloy family solidifies in a two-step process known as double recalescence.8 The temperature profile exhibits a first rise during the formation of metastable bcc-ferrite from the undercooled liquid, followed by an almost immediate second rise during the formation of the stable fcc-austenite within the pre-existing metastable semi-solid. Because these alloys do not significantly partition, the second temperature rise associated with the transformation to the stable phase, DTs, is the difference between the metastable phase liquidus, TL,m, and stable phase liquidus, TL,s, as defined by the metastable extens
Data Loading...
