The design of a new grade of low density steel and alloy composition

In this thesis, 3 different alloy designs were determined by examining the solidification structure of low-density steels and the casting of the determined alloys was carried out in the vacuum induction melting furnace. After castings, the samples were cut from the ingot parts and subjected to the macro etching process. Subsequently, 3 different regions were determined for each tablet sample. The chemical compositions of these regions were determined by OES and ICP wet analysis techniques, compared with the chemical compositions obtained during casting. Metallographic sample preparation processes were applied to the samples taken from the areas that did not show any defects. Microstructures of the prepared samples were determined by optical microscope and microhardness/impact strength values were measured. It was determined that the hardness distribution was homogeneous in the regions with dendritic solidification and equiaxed grains, and the variation between the microhardness values of the medium alloy casting (V025) was higher compared to the other castings. Casting with high aluminum content (V027) has the lowest impact strength with an average of 2.1 J, while casting with low aluminum content (V024) has an average impact strength of 7.03 J. Considering the impact strength of the samples, it was observed that the impact strength values decreased as the aluminum ratio increased. The segregation index is required to be in the range of 0.95-1.05. A good agreement was observed between the literature and the results obtained. Fe-C balance diagrams were created for each casting with ThermoCalc, CCT diagrams with J-Mat Pro, solidification structure diagrams and theorical density values with FactSage. Densities were calculated as 6.47, 6.30 and 5.81 g/cm3 respectively. In addition, visible defects occurred in the samples cut from ingot pieces and samples were taken from the defective areas. These samples were first examined macro, then optical microscope and SEM/EDS examination were made. After the examinations, it was determined that the defects on the samples were due to casting defects. No casting void was observed in the low alloy design (V024), but the dendritic structure was found to be dense. In the medium alloy design (V025), it was observed that the equiaxed grains were dense, but the casting cavity was deep at a single point. In the high alloy design (V027), it was observed that the defect was scattered and superficial, and the coaxial and dendritic structure were together. In this study; obtaining the ideal casting structure in low density steel quality, providing chemical homogenization and examining the elemental effect were presented.