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.© Elsevie

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 700-1000degreesC. 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 700degreesC. However, between 800 and 1000degreesC, they exhibit better oxidation resistance than 310 SS. Although the oxidation resistance of aluminides at 1000degreesC 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 900degreesC shows that they do not gain a corresponding weight as they do for a temperature rise from 700 to 800degreesC. A further rise to 1000degreesC 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 Fe3AlC0.69 carbide phase with temperature

Effect of Al content on oxidation behaviour of ternary Fe-Al-C alloys

Iron aluminides produced by the electroslag refining technique, having the compositions: (1) Fe–16Al–1C, (2) Fe–10Al–1C, and (3) Fe–8Al–1C were used to investigate the effect of Al on the oxidation behaviour of the Fe–1C–Al system at 700 to 1000 °C. Prior to oxidation studies, phase and microstructure of alloys were analysed. The carbide phase, Fe3AlC0.69, was found to be distributed in the Fe3Al matrix in alloy 1 and α (Fe–Al) matrix in alloys 2 and 3. The low Al content alloys displayed inversion in the oxidation kinetics below 800 °C, while, high Al content alloy displayed inversion phenomena at 1000 °C. The mechanism involving inversion in oxidation kinetics was found to be different in the two cases. In the former, it was attributed to the preferential oxidation of Al, while in the latter, to the phase transformation within the Al2O3. Carbides in the alloy having low Al content showed instability during oxidation.© Elsevie

Effect of aluminium on electrochemical corrosion behaviour of Fe-0-5Cand Fe-1Calloys in 0.25M H2SO4

Electroslag remelted iron-aluminium alloys, with carbon contents of 0.5 and 1 wt-%, were used to investigate the effect of Al on the electrochemical corrosion behaviour in 0.25 M sulphuric acid solution. The alloy compositions were (wt-%): (I) Fe-16Al-0.5C, (2) Fe-10Al-0.5C, (3) Fe-8Al-0.5C, (4) Fe-16Al-1C, (5) Fe-10Al-1C, and (6) Fe-8Al-1C Lowering the Al content of the alloys resulted in a deterioration of the passivation behaviour during potentiodynamic polarisation testing. This deterioration vas attributed to the reduced Al content of the matrix phase on lowering the Al content of the alloy. Examination of the polarised surfaces via SEM revealed that in high Al content alloys carbides are preferentially attacked, while in low Al content allo, vs the attack is more general. Alloys with a carbon content of 1 wt-% displayed somewhat inferior passivation tendencies compared with those of alloys containing 0.5 wt-% carbon

Processing of Fe3Al based intermetallic alloys through electroslag remelting

A process comprising air induction melting (AIM) and electroslag remelting (ESR) for production of iron aluminides based on Fe3Al is reported. Extensive hydrogen gas porosity is observed in air induction melted electrodes, Electroslag remelting of AIM electrode results in ingots free from gas porosity. Possible mechanisms for elimination of gas porosity during electroslag remelting are discussed. The cast ESR ingots exhibit a marked susceptibility to cracking at high power inputs due to high thermal gradients prevailing in the ingot. This may be attributed to the relatively low thermal conductivity and high coefficient of thermal expansion of Fe3Al. At very low power levels the ESR ingots exhibited poor surface quality. Proper selection of process parameters during electroslag remelting of air induction melted electrodes results in sound ingots free from thermal cracks and exhibiting good surface quality

Effect of hot working on room temperature mechanical properties and stress-rupture behaviour of ESR processed Fe-16wt%Al intermetallic alloys

The effect of hot working (forging) on structure and mechanical properties of electroslag remelted (ESR) Fe3Al based intermetallic alloys containing approximately 16 wt% (28 at%) aluminium and 0.013 to 0.50 wt% carbon are reported. The ESR alloys having low (0.013 to 0.06 wt%) carbon content were severely cracked during forging probably due to the presence of pre-existing microcracks. ESR ingots with high (0.14 to 0.50 wt%) carbon content were successfully forged at 1000 degrees C. At high (60% or more) forging reductions the cast columnar structute of ESR alloys was transformed into recrystallized grain structure. The room temperature mechanical properties did not improve significantly after forging. During creep and stress-rupture tests carried out at 600 degrees C and 140 MPa, the cast ESR ingot with columnar structure exhibited lower minimum creep rate and higher creep life than those exhibited by the corresponding forged ingots with recrystallized grain structure. There is only a marginal improvement in creep life with increase in carbon content from 0.14 to 0.50 wt%. The stress-ruptured specimens exhibited predominantly ductile dimple failure with elongations in excess of 50%. The creep and stress-rupture properties of the alloys with high (0.14 to 0.50 wt%) carbon contents are better than those reported for wrought Fe-16 wt%Al alloys with low (< 0.01 wt%) carbon contents. This may be attributed to the presence of uniformly distributed Fe3AlC precipitates as well as the interstitial carbon present in the alloys

ELECTROSLAG REMELTING OF FE-28 ATMOSPHERIC-PERCENT-AL INTERMETALLIC ALLOY

Electroslag remelting (ESR) has been used to process an ordered Fe-28 at.-%Al intermetallic alloy. A commercial calcium fluoride based slag was used in the process. Oxygen, sulphur, and non-metallic inclusion levels were significantly reduced during ESR. The ingots exhibited a defect and segregation free structure with good surface finish. The mechanical properties of the ESR material, in the as cast condition, compared well with those reported for high purity wrought alloy of similar composition. The improved structure resulted in isotropic properties in the ESR processed material

Effect of TiB2 and ZrB2 additions on structure and properties of Fe-7Al based light weight steel

Microstructural modifications and their effect on tensile properties in an Fe-7 wt.% Al alloy by additions of 0.5% TiB2, 0.5% ZrB2 or both has been studied. Alloys are examined in the as-cast as well as in the hot-rolled and annealed conditions. Solidification structure of the Vacuum Arc Remelted pancake ingots was columnar dendritic. Further, boride modified alloys are found to have finer grains in as-cast as well as in hot-rolled and annealed conditions. In the annealed condition, boride containing alloys were found to have superior tensile yield strength, ductility and strain hardening behaviour. These property improvements are attributed to boride aided grain refinement during casting as well as during thermo-mechanical processing of the steels