Microstructure and mechanical properties of Fe–7Al based lightweight steel containing carbon

The effect of carbon on the microstructure and mechanical properties of lightweight steel based on Fe–7 wt-%Al produced by air induction melting with flux cover is investigated. The ingots were hot worked to plates and were characterised. Steel containing 0.02 wt-%C exhibited a single phase microstructure Fe–Al(α), whereas steel containing 0.5 and 1.0 wt-% carbon exhibited a two-phase microstructure containing significant amounts of Fe₃AlC_0.5 precipitates in Fe–Al(α) matrix. Microhardness of the matrix decreases with increasing carbon content due to depletion of aluminium from the matrix to form Fe₃AlC_0.5 carbides. The bulk hardness, room temperature strength increases and tensile elongation decreases with increasing carbon content. However, at 873 K the improvement in strength as well as creep properties with increasing carbon content is marginal.     

Melting,Processing, and Properties of Disordered Fe-Al and Fe-Al-C Based Alloys

This article presents a part of the research work conducted in our laboratory to develop lightweight steels based on Fe-Al alloys containing 7 wt.% and 9 wt.% aluminum for construction of advanced lightweight ground transportation systems, such as automotive vehicles and heavy-haul truck, and for civil engineering construction, such as bridges, tunnels, and buildings. The melting and casting of sound, porosity-free ingots of Fe-Al-based alloys was accomplished by a newly developed cost-effective technique. The technique consists of using a special flux cover and proprietary charging schedule during air induction melting. These alloys were also produced using a vacuum induction melting (VIM) process for comparison purposes. The effect of aluminum (7 wt.% and 9 wt.%) on melting, processing, and properties of disordered solid solution Fe-Al alloys has been studied in detail. Fe-7 wt.% Al alloy could be produced using air induction melting with a flux cover with the properties comparable to the alloy produced through the VIM route. This material could be further processed through hot and cold working to produce sheets and thin foils. The cold-rolled and annealed sheet exhibited excellent room-temperature ductility. The role of carbon in Fe-7 wt.% Al alloys has also been examined. The results indicate that Fe-Al and Fe-Al-C alloys containing about 7 wt.% Al are potential lightweight steels.     

Toughening and creep in multiphase intermetallics through microstructural control

The lack of engineering ductility in intermetallics has limited their structural applications, in spite of their attractive specific properties at high temperatures. Over the last decade, research in intermetallics has been stimulated by the discovery of remarkable ductilisation mechanisms in these materials. It has however often been the case that the process of ductilisation or toughening has also led to a decrease in high temperature properties, especially creep. In this paper we describe approaches to the ductilisation of two different classes of intermetallic alloys through alloying to introduce beneficial, second phase effects. The Ti₂AlNb based intermetallics in the Ti-Al-Nb system can be ductilised by stabilising thebcc phase of titanium into the structure. The principles of microstructural and compositional optimization developed to achieve adequate plasticity, while retaining creep properties of these alloys, are described. An entirely different approach has been successful in imparting plasticity to intermetallics based on Fe₃Al. The addition of carbon to form the Fe₃AlC_0.5 phase imparts ductility, while enhancing both tensile and creep strength.     

Effect of cerium and thermomechanical processing on microstructure and mechanical properties of Fe-10·5Al-0·8C alloy

The effect of cerium content and thermomechanical processing on structure and properties of Fe-10·5 wt.%Al-0·8 wt%C alloy has been investigated. Alloys were prepared by a combination of air induction melting with flux cover (AIMFC) and electroslag remelting (ESR). The ESR ingots were hot-forged and hot-rolled at 1373 K as well as warm-rolled at 923 K and heat-treated. Hot-rolled, warm-rolled and heat treated alloys were examined using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction to understand the microstructure of these alloys. The ternary, Fe-10·5 wt.%Al-0·8 wt.%C alloy showed the presence of two phases; Fe-Al with bcc structure, and large volume fraction of Fe₃AlC_0·5 precipitates. Addition of cerium to Fe-10·5 wt.%Al-0·8 wt.%C alloy resulted in three phases, the additional phase being small volume fraction of fine cerium oxy-carbide precipitates. Improvement in tensile elongation from 3–6·4% was achieved by increasing the cerium content from 0·01–0·2 wt.% and further improvement in tensile elongation from 6·4–10% was achieved by warm-rolling and heat treatment.     

Thermo-mechanical processing of Cu-Cr alloys prepared by using electro slag crucible melting

Cu-Cr ingots of Cr contents of up to 2 Wt % were prepared by melting copper scrap using electroslag crucible melting (ESCM). Chromium addition to copper was carried out by in-situ reduction of chromium oxide present in the slag. The Cu-Cr ingots produced were subjected to up to 90% rolling reduction using different combination of rolling and heat treatment. A range of microstructure and mechanical properties was obtained. Alloys with recrystallised microstructure exhibited lower strength and higher ductility. The alloys prepared by ESCM compare well with Cu-Cr alloys reported in the literature. The ESCM route is more attractive as it uses copper scrap for melting and in-situ reduction of chromium oxide for alloying of chromium. ESCM also enables preparation of alloy with high (up to 2%) Cr content.     

Effect of Carbon on the Long-Term Oxidation Behavior of Fe3Al Iron Aluminides

Electroslag, remelted-iron aluminides having the compositions: (1) Fe–16Al–0.05C, (2) Fe–16Al–0.14C, (3) Fe–16Al–0.5C, and (4) Fe–16Al–1.0C were investigated to understand the effect of carbon on their oxidation behavior in the temperature range 700–1000°C. The oxidation behavior of these aluminides was compared with that of 310 SS, a reference alloy used in the study. Regardless of carbon content, the iron aluminides exhibit marginally higher oxidation tendency than that of 310 SS at 700°C. However, between 800 and 1000°C, they exhibit better oxidation resistance than 310 SS. Although the oxidation resistance of aluminides at 1000°C is better than that of 310 SS, they suffer severe spallation during long-term exposure and C exacerbates this effect. Examination of the early stages of oxidation of the alloys at 800 and 900°C shows that they do not gain a corresponding weight as they do for a temperature rise from 700 to 800°C. A further rise to 1000°C leads to a marginal inversion in the oxidation tendency of the alloys. Based on the literature, this inversion is attributed to the possible dissolution and/or change in compo- sition of Fe₃AlC_0.69 carbide phase with temperature.     

Processing of Fe-Al-C-Ce alloys through air induction melting with flux cover (AIMFC) and electroslag remelting (ESR)

The effect of process parameters on recovery of reactive element, cerium, during air induction melting with flux cover (AIMFC) and electroslag remelting (ESR) of Fe-10.5 wt% Al-0.8 wt% C-(0.1 and 0.3) wt% Ce alloys and also the effect of melting techniques on hot workability, structure and tensile properties (at room temperature and at 873 K) of Fe-10.5 wt% Al-0.8 wt% C-0.3 wt% Ce alloy have been investigated. Good recovery of cerium was obtained by AIMFC. While conventional fluxes were found to be unsatisfactory, modified flux containing CeO₂ gave better recovery of cerium during ESR. The best recovery of cerium was achieved by using calcium as a deoxident during ESR. The combination of AIMFC and ESR yields a sound ingot of Fe-Al-C-Ce quaternary alloys free from gas and shrinkage porosity with very low oxygen, nitrogen and sulphur contents. Processing of AIMFC ingots through ESR has resulted in improved hot-workability. The ESR processed and hot-rolled alloy exhibited superior tensile elongation as compared to hot-rolled AIMFC alloy. This may be attributed to the comparatively sound, homogeneous and clean ingot, with a refined microstructure and fine uniform distribution of precipitates observed in hot-rolled ESR ingots.     

Effect of carbon on corrosion behaviour of Fe3Al intermetallics in 0.5 N sulphuric acid

Electrochemical corrosion behaviour of iron aluminides, produced by electroslag remelting technique, having the compositions (1) Fe-15.6Al-0.05C, (2) Fe-15.6Al-0.14C, (3) Fe-15.6Al-0.5C and (4) Fe-15.6Al-1C were investigated in 0.5 N H₂SO₄ media. Corrosion rates of these alloys were found to increase with carbon content. This was attributed to the preferential attack of the carbide phases. These alloys exhibited typical active-passive-transpassive behaviour. In addition, they displayed a secondary anodic current maxima during polarization. The resistance of aluminides to breakdown of passivity was assessed by varying addition of chloride ions in the same media.     

Microstructural evolution in iron aluminide Fe-28Al-2C after high-temperature hydrogen treatment

High-temperature hydrogen attack (HA) in a carbon-alloyed iron aluminide of composition Fe-28.1Al-2.1C (in at. pct) has been studied. Well-polished samples were exposed to hydrogen gas (1 atm) at 700 °C and 900 °C for different times. The characteristics of HA were evaluated by two-dimensional microstructural analysis, performed on the rolling plane of the as-received and hydrogen-treated samples. The carbon-alloyed iron aluminide contained carbides in two different morphologies: blocky and needle shaped. The compositions of these carbides have been determined. The blocky carbides were preferentially attacked along the {111} and {110} crystallographic planes. The interfaces between the blocky carbides and grains were mainly affected by the hydrogen treatment. The needle-shaped carbides dissolved in the matrix after relatively short times. The degree of attack generally increased with increases in treatment temperature and time of exposure, as long as the surface was not completely covered with a protective oxide layer.