A reduction of 1 mm in thickness was given to the samples during each pass. A Demag rolling mill was used to hot-roll the samples to a sheet of 2 mm thickness. The pancake samples were soaked in a furnace for 1 h at a temperature of 1100 ☌. A Leco CS-444 was used to measure the carbon content. The amount of Al and Nb present in the pancakes was determined by wet chemical analysis. Pancakes were checked for defects by Gamma-ray radiography using a 5-Curie Co 60 radioactive source. For each composition, the pancake was melted three times with periodic reversal of the pancake top. The alloy was cast as a pancake of 100 mm diameter and 10 mm thickness in a water-cooled copper crucible. A current of 850–900 amperes and voltage of 18–20 V were used during melting. The arc was initiated without direct contact between the tungsten electrode and the charge material. During melting, the argon gas pressure was maintained at 600 mbar. The process of evacuation and refilling was performed twice. The melting chamber was evacuated to 1 × 10 −3 mbar and refilled with argon. Non-consumable DC arc melting process with a thoriated tungsten electrode was used for melting the raw materials. High-purity raw materials such as iron, aluminum, graphite, and niobium were used for preparing steel pancakes of desired compositions. It is suggested that the melting of high aluminum low-density steels in a controlled atmosphere may be necessary to achieve improved mechanical properties. All the alloys studied in the present work exhibited significant (20% or more) tensile elongation. This may be related to their susceptibility to hydrogen embrittlement. Earlier attempts to add Nb to low-density steels resulted in very low ductility. In order to predict the formation of phases on Nb addition, thermodynamic calculations were performed using ThermoCalc software and compared with the experimental results. Here, we report the effect of Nb addition on microstructure and mechanical properties of a Fe–7wt.%Al–0.35wt.%C alloy (all compositions are in wt.%). We have earlier reported properties of Fe–7wt.%Al alloys with carbon addition. Further, they may also have potential defense applications. Reducing the weight of an automobile by 10% can hike the fuel economy by 6–8%, and therefore, these materials have applications in the automotive industry. Because of their low-density, high specific strength, and good corrosion resistance, these steels are considered potential structural materials in thermal power plants and petrochemical industry. Aluminum addition also leads to an improved corrosion resistance. Each wt.% addition of Al gives about 40 MPa increase in strength by solid solution strengthening and a density reduction of about 1.5%. ![]() The density of steel can be reduced by the addition of aluminum. Further, it is also important to maintain a high C/Nb ratio to avoid the formation of Laves phases. Melting of high aluminum low-density steels in a controlled atmosphere may lead to a considerable improvement in mechanical properties. ![]() This study demonstrates the advantages of adding Nb to Fe–Al–C-based low-density steels. Nb carbides present at rolling temperature resist grain growth and lead to improved mechanical properties. About 80% increase in the yield strength is observed as the Nb content increases from 0.2 to 1.0 wt.%. Niobium addition also resulted in a significant increase in strength and hardness of the hot-rolled steel. All the alloys exhibited a significant (20% or more) tensile elongation. ![]() The phases formed on adding Nb were predicted by thermodynamic calculations using ThermoCalc. A hot rolling temperature of 1100 ☌ was selected to carry out rolling in the intercritical (ferrite + austenite) region. The present work reports the effect of niobium addition on a Fe–7wt.%Al–0.35wt.%C-based low-density steel.
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