Spray casting of steel strip: Process analysis |
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Authors: | Suresh Annavarapu Diran Apelian Alan Lawley |
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Affiliation: | (1) Department of Materials Engineering, Drexel University, 19104 Philadelphia, PA;(2) Worcester Polytechnic Institute, 01609 Worcester, MA |
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Abstract: | Near-net shape manufacturing (NNSM) of thin steel sections by spray casting eliminates casting as a separate step with attendant
improved microstructures and properties and significant energy savings. The process involves atomization of a stream of liquid
metal and deposition of droplets in the generated spray on a moving substrate at mass flow rates of 0.25 to 2.5 kg/s. In this
paper, NNSM of steel strip by the Osprey spray casting process is investigated by combining numerical simulation and experiments.
Critical input parameters for the computation are quantified utilizing existing state-of-the-art mathematical models and specific
experiments. Numerical computation of the consolidation of the spray at the substrate during manufacture of thin sections
is conducted using bothcontinuum anddiscrete event (“splat solidification”) approaches to predict: (1) variation of strip thickness in the transverse dimension and (2) isotherms
and cooling rates across the strip thickness. Predicted geometries of the strip simulated by the continuum model are in good
agreement with measurements. Predicted isotherms in narrow strip by the continuum approach are in reasonable agreement with
thermocouple measurements for intermediate thicknesses (2 to 5 mm), and the observed microstructure is consistent with predicted
cooling rates. The discrete event model predicts significantly higher cooling rates than the continuum model in the basal
portion of the strip. This is consistent with the observed grain size in thin strip (<l-mm thick) and in the basal portion
of thick strip. Beyond a threshold thickness, however, the discrete event model confirms the formation and persistence of
a partially liquid layer at the growing surface of the deposit with an attendant decrease in the cooling rate. The influence
of critical parameters on “splat solidification” is analyzed and assessed.
DIRAN APELIAN, formerly Howmet Professor of Materials Engineering at Drexel University |
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