Numerical Prediction and Experiments on Casting Fe-Based Bulk Amorphous Strips on a Twin Roll Caster and on a Horizontal Single Belt Strip Caster

摘要

The purpose of this work was to investigate the possibility of casting Fe-based bulk amorphous strip material using either twin roll and/or horizontal single belt strip casting processes. Three kinds of Fe-based alloy were studied: ORNL-A1 (Fe-15B-7Co-7Mo-2Y-8Zr in at. %), Darval0l (Fe-6B-15C-15Cr-14Mo-2Y in at. %) and Darpa-Q21 (Fe-20B-2Zr-2Nb-1.5Cr-4.5V-2Y in at. %), respectively. The glass transition temperatures of the alloys were estimated as: 632℃, 570℃, 580℃ respectively, and their critical cooling rates for forming amorphous structures as: 400K/s, 150K/s and 140K/s respectively. Heat transfer rates from the melts into the cooling substrates (rolls and belt) were predicted theoretically, using the technique of numerical simulation, and were also measured physically in the case of the single belt casting process. Temperature variations within the moving mould were measured by embedded thermocouples, allowing interfacial heat fluxes during solidification to be calculated using the IHCP (Inverse Heat Conduction Problem) technique. The maximum thickness of amorphous strips possible to be cast was predicted for various operating conditions and compared with corresponding experiments. Darva10l strip samples were cast on a lab-scale twin roll caster. Further to this, all three alloys were cast on a horizontal single belt strip casting simulator, and strip samples of 0.2～2mm thick were obtained. The strip samples' microstructures were analyzed by microscopy, X-Ray Diffraction and SEM. Helium atmospheres were considered to be essential for enhancing cooling rates and for lowering melt temperatures below the T_g values noted above. The possibility of casting Fe-based amorphous strip via the two casting processes was confirmed.