PROCESSING OF IRON ALUMINIDES BY INGOT METALLURGY ROUTE

摘要

A melting procedure for air induction melting (AIM) of Fe-Al-C based internnetallic alloys (containing 7 to 23 wt. percent Al, 0.01 to 1.0 wt. percent C and 0.02 to 4.0 wt. percent alloying elements such as Mo, W, Cu, Cr, Si, Ni, Mn, Nb, Ti, Zr, Ce and B) is described. Air induction melting resulted in the formation of hydrogen gas porosity in cast AIM ingots. Use of flux cover and proprietary charging schedule during air induction melting resulted in elimination of hydrogen gas porosity. Refining by flux-metal reactions results in significant reduction in impurity (S, O, N) levels during air induction melting with flux cover (AIMFC). Criteria for flux selection and flux to metal ratio are discussed. Processing of AIMFC ingots through electroslag remelting (ESR) has further improved the ductility and hot-workability. Excellent recovery of alloying elements has been achieved by both AIMFC and ESR. Proper selection and control of process parameter during eiectroslag remeiting of even highly porous AIM ingots resulted in clean, sound, homogenous and defect free ingots. Possible mechanisms for the elimination of hydrogen gas porosity during ESR have been discussed. The cast ESR ingots exhibit a marked susceptibility to cracking at high power inputs. The optimum power level for the alloys was found to be significantly lower than that of steels. The Fe-AI-C based intermetallic alloy ingots with low carbon content produced with combination of AIM / AIMFC and ESR exhibits microcracks. These micro cracks led to cracking of the ingots during fabrication of test samples by cutting and turning as well as during hot-forging. It is argued that the presence of carbon may be necessary to get AIM / AIMFC plus ESR castings with desirable mechanical properties. The process route and composition developed in the present work allows the use of inexpensive source of iron (such as steel scrap) and commercial aluminium for bulk production of Fe-AI-C based intermetallic alloys.