A Radhakrishna

Processing of high carbon Fe3Al based intermetallic alloy

Abstract A melting procedure for air induction melting (AIM) of an Fe 3 Al based intermetallic alloy Fe-15.38 wt%Al-1.1 wt%C is described. Use of an appropriate slag cover during AIM results in elimination of hydrogen gas porosity in cast AIM ingots. Criteria for slag selection and slag to metal ratio are discussed. Refining by slag-metal reactions results in significant reduction in impurity levels (S, O, N) during AIM. Consequently, low cost raw materials such as mild steel scrap and commercial aluminium were used for melting the alloy. The AIM ingot exhibited excellent tensile properties. The ductility and hot workability of the ingot may be further improved by subsequent processing through electroslag remelting. It is also argued that the presence of carbon may be necessary to get AIM castings with desirable mechanical properties.

Effect of carbon and processing on structure and mechanical properities of Fe-11 wt.% Al alloy

Abstract Ingots of Fe–Al alloys containing 11 wt.% Al and 0.5 and 1.1 wt.% C were prepared by a combination of air induction melting with flux cover (AIM) and electroslag remelting (ESR). The ESR ingots were hot forged at 1373 K to 53% reduction and subsequently hot rolled at 1373 K to 53% rolling reduction. The cast ESR samples were placed in a hearth furnace at 873, 1073 and 1273 K for 24 h then furnace cooled to room temperature. The Fe-11 wt.% Al alloy containing 1.1 wt.% C exhibited a significant higher yield strength at test temperature up to 773 K than alloy containing 0.5 wt.% C. This may be attributed to the presence of large amount of hard Fe 3 AlC 0.5 precipitates in the alloy. The thermo-mechanical processing of cast ESR ingots has resulted in significant improvement in room temperature tensile ductility. This may be due to breaking of cast dendritic structure and more uniform distribution of Fe 3 AlC 0.5 precipitates. These high carbon Fe-11 wt.% Al alloys exhibited excellent resistance to decarburization up to 1273 K because of the formation of continuous protective Al 2 O 3 film on the surface. It would appear from the present work that thermo-mechanically processed high (1.1 wt.%) carbon ESR alloy exhibit an attractive combination of properties.

Effect of molybdenum addition on structure and properties of high carbon Fe3Al based intermetallic alloy

Abstract The effect of molybdenum addition on structure and properties of high (0.3 wt.%) carbon Fe 3 Al based intermetallic alloy containing about 16 wt.% aluminium has been studied. Three different alloys with the following compositions Fe–16.3 wt.% Al–0.27 wt.% C, Fe–16 wt.% Al–2.85 wt.%, Mo–0.3 wt.% C and Fe–15.8 wt.% Al–7.5 wt.% Mo–0.3 wt.% C were prepared by a combination of air induction melting with flux cover (AIM) and electroslag remelting (ESR). The alloys were characterized with respect to microstructure. Micro-analysis was carried out by electron probe microanalyser. A considerable amount of solid solubility for molybdenum was observed in the carbon containing Fe 3 Al alloy. At low (2.85 wt.%) concentration of Mo, Fe 3 AlC 0.5 precipitates with dissolved Mo and a small fraction of fine Mo 2 C precipitates was observed. At a high (7.5 wt.%) concentration of Mo, Fe 3 AlC 0.5 precipitates were totally absent and only Mo 2 C precipitates were observed. Significant improvements in strength on the addition of Mo has been achieved. This may be attributed to both solid solution strengthening and precipitation hardening.

High temperature tensile and creep properties of a cast aim and ESR intermetallic alloy based on Fe3Al

Abstract A high carbon intermetallic Fe-16 wt.% A1-1.1 wt.% C alloy based on Fe 3 Al was melted under a flux cover by air induction melting (AIM). The AIM ingots exhibited excellent elevated temperature tensile properties in the temperature range (600–800°C) studied, in contrast to poor properties expected in ingots melted without a flux cover. Subsequent processing of the AIM ingots through electroslag remelting (ESR) resulted in improvement in ductility. However, the AIM ingots exhibited better creep properties because of their coarser gain structure. The presence of large (1.1 wt.%) amount of carbon in the alloy resulted in significant improvement in elevated temperature tensile as well as creep properties over those reported for Fe 3 Al based intermetallic alloys with lower carbon contents. These improvements in mechanical properties are attributed to the extensive precipitation of Fe 3 AlC phase and to the formation of a duplex Fe 3 Al-Fe 3 AlC structure at such high levels of carbon. It is suggested that carbon may be an important alloying addition to Fe 3 Al-based intermetallic alloys.

Mechanical properties of high carbon Fe3Al-based intermetallic alloys

Abstract Fe-16 wt% Al alloys containing 0.074 to 1.1 wt% carbon were prepared by a combination of air induction melting and electroslag remelting (ESR). The cast ESR ingots exhibited a two-phase structure consisting of Fe 3 AlC 0.5 precipitate in an Fe 3 Al-based matrix. The precipitate volume fraction increased with increasing carbon content of the ingot. Most of the carbon was found to be present as the Fe 3 AlC 0.5 phase. The bulk hardness of these alloys increases linearly with increasing volume fraction of the precipitates. However, the Youngs modulus of these alloys was measured to be around 175 GPa and does not change significantly with change in volume fraction of the phases present. This is explained by arguing that both the matrix as well as precipitate exhibit the same modulus values for the alloys studied in the present work. Both the bulk hardness and Youngs modulus follow the rule of mixture for two phase alloys. However, the same may not be true for structure sensitive properties such as yield strength, ductility and creep resistance.

Effect of hot rolling and heat treatment on structure and properties of high carbon Fe–Al alloys

Iron–aluminium alloys with the following compositions, Fe–8.26 wt.% Al–0.46 wt.% C, Fe–7.2 wt.% Al–1.1 wt.% C, Fe–11.20 wt.% Al–0.5 wt.% C and Fe–10.83 wt.% Al–1.1 wt.% C were melted under a flux cover by air induction melting (AIM). The AIM ingots were subsequently processed through electroslag remelting (ESR). Both AIM and ESR ingots were hot forged and hot rolled at 1375 K to 92% reduction. ESR ingots exhibited better hot workability as compared with AIM ingots. This may be due to the axially oriented columnar grain structure relatively free from internal defects such as microporosity and non metallic inclusions observed in ESR ingots. About 14 ml thick ESR processed alloys in the hot-rolled condition also exhibited superior room temperature tensile elongation as compared with hot-rolled AIM alloys. This may be attributed to the comparatively homogeneous, clean ingot with a refined microstructure and a fine uniform distribution of Fe3AlC0.5 phase as observed after ESR. Further rolling of the ESR alloy to a 4-mm thickness has resulted in significant improvements in strength. The tensile elongation of hot rolled ESR alloys was reduced after heat treatment except in the case of Fe–7.2 wt.% Al–1.1 wt.% C alloy which exhibited a 17% improvement.

Effect of alloying additions on structure and mechanical properties of high carbon Fe-16 wt.% Al alloy

Abstract Effect of quaternary alloying elements Mn, Cr, Ni and Ti on structure and properties of Fe 3 Al-based alloy containing about l wt.% carbon have been investigated. Four different alloys were prepared. The composition of the quaternary alloying element was proposed to be ≈4 wt.% and was substituted for iron. Processing of Fe-16Al-4.1Mn-1.0C, Fe-16.5Al-3.5Cr-0.94C, Fe-16Al-4.0Ni-0.9C and Fe-15.6Al-2.8Ti-1.0C alloys through a combination of air induction melting with flux cover (AIM) and electroslag remelting (ESR) yields a sound ingot free from macro and microporosity with very low sulphur, oxygen and nitrogen. This process route also exhibited excellent recovery of alloying elements. As-cast alloys were examined using optical microscopy, X-ray diffraction, electron probe microanalyses (EPMA) and scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray analysis to understand the microstructure of these alloys. The as-cast ESR ingots of alloys containing Mn, Cr and Ni exhibited a two-phase structure of Fe 3 AlC 0.5 precipitate in the Fe 3 Al-based matrix. Both phases exhibited considerable amount of solid solubility for Mn, Cr and Ni, whereas the alloy containing Ti exhibited a three-phase microstructure of TiC particles and Fe 3 AlC precipitates in the Fe 3 Al-based matrix. This alloy has also exhibited very low solubility of Ti in the Fe 3 Al-based matrix and no solubility in the Fe 3 AlC precipitates. Several microcracks were observed in the as-cast ESR ingots of the high carbon Fe 3 Al alloy containing Ni and tensile tests could not be carried out for this composition. Tensile and creep tests were performed on the high carbon Fe 3 Al alloys containing Mn, Cr and Ti in the as-cast condition. No improvement in room temperature tensile strength and inferior high temperature strength and creep properties was observed by the addition of quaternary alloying elements.

Effect of carbon content on elevated temperature stability and tensile properties of Fe–8.5 Al Alloys

Abstract Fe–8.4Al–0.04C, Fe–8.26Al–0.46C and Fe–8.35Al–1.1C alloys were prepared by a combination of air induction melting and electroslag remelting. The low (0.04 wt.%) carbon alloy exhibited microcracks therefore it was not studied further. The ESR ingots of high (0.46 and 1.1 wt.%) carbon alloys exhibited a significant amount of Fe 3 AlC 0.5 precipitation. The cast ESR samples of Fe–8.26Al–0.46C and Fe–8.35Al–1.1 C were placed in a hearth furnace at 873, 1073 and 1273 K for 24 h and then furnace cooled. The high carbon alloys do not undergo decarburization and exhibit stable microstructure up to 873 K. Decarburization appears to be a problem only after exposure at temperatures of 1073 K and above. The ESR Fe–8.26Al–0.46C alloy exhibited greater elongation and significantly better elevated temperature strength up to 873 K than those reported for cast VIM low carbon multicomponent alloy with similar Al content. This may be due to the presence of a large volume fraction of stable Fe 3 AlC 0.5 precipitates. All the high carbon alloys exhibit a sharp drop in strength at 873 K regardless of carbon content. These alloys are therefore targeted for potential structural application at or below 873 K.

Effect of processing on mechanical properties of an Fe–8.5 wt.% Al–1.1 wt.% C alloy

Abstract A Fe–8.5 wt.% Al–1.1 wt.% C alloy was melted under a flux cover by air induction melting (AIM). Subsequent processing of the AIM ingots through electroslag remelting (ESR) resulted in a significant improvement in ductility. This may be attributed to the refined axially oriented grain structure, free from internal defects observed in the ESR ingots. The alloy exhibited a significantly higher yield strength at test temperatures up to 500°C than those reported for complex Fe–Al alloys with comparable aluminium contents. This may be due to dispersion strengthening caused by the presence of a large volume fraction of Fe3AlC0.5 precipitates in the alloy. Though the addition of carbon may decrease ductility, it allows commercial production of alloys with reasonable (8%) room temperature ductility, melted using cheap raw materials and a low cost melting procedure. The high carbon ESR alloy offers the best ductility reported for cast Fe–Al alloys with similar aluminium contents.

Effect of thermo-mechanical processing and heat treatment on structure and mechanical properties of an electroslag remelted Fe–8.5wt%Al–1.1wt%C alloy

Abstract Electroslag remelted (ESR) ingots of Fe–8.5wt%Al–1.1wt%C alloy were hot forged at 1373 K to 83% reduction. The forged ingots were hot rolled at 1373 K to 53% rolling reduction and heat treated at 1173 K for one h. The thermo-mechanical processing and heat treatment of the ESR alloy ingots resulted in breakdown of cast dendritic structure leading to a homogeneous microstructure with fine Fe 3 AlC 0.5 precipitates. This was accompanied by a significant improvement in ductility and strength of the alloy. It is shown that the addition of carbon to Fe–8.5wt%Al binary alloy does not result in a significant loss in ductility. The presence of Fe 3 AlC 0.5 precipitates results in an increase in strength and improvement in creep and stress rupture properties. The cast and wrought alloys exhibited similar creep and stress rupture properties. The reasons for this are discussed. An attractive combination of strength, ductility and creep and stress rupture properties not yet reported for Fe–Al alloys was achieved by thermomechanical processing and heat treatment.