High resolution characterization of pearlitic steels with increased copper content

The environmental challenges posed by climate change force the steel industry to significantly reduce carbon dioxide emissions, which account for approximately 30% of global industrial emissions. This has driven a shift from blast furnace to alternative production routes such as electric arc furnace. Electric arc furnace, which primarily uses scrap for steel production, provides notable environmental advantages, while facing unintentionally added impurities called tramp elements. Tramp elements are impractical or very costly to remove and affect the steels properties in a negative way. The aim of this thesis is the investigation of the precipitation behavior of tramp elements within the pearlitic microstructure. The primary focus is on copper within the pearlitic microstructure, with the aim of assessing its potential for precipitation. Therefore, a reference alloy is compared to two trial alloys with increased tramp element content, which imitates steel produced via a scrap-based production. The investigations include simulations with Thermo-Calc, optical microscopy, hardness measurements as well as atom probe tomography, transmission electron microscopy and high energy x-ray diffraction. Analysis with optical microscopy confirm the presence of a purely pearlitic microstructure. However, hardness measurements indicate a solid solution strengthening effect with the addition of tramp elements. The high-resolution techniques show that silicon and manganese show preferred solubility in ferrite and cementite, respectively. Copper was fully dissolved in the ferrite and did not precipitate. Other tramp elements, such as tin and nickel, exhibit a preference for the ferritic phase, whereas typical carbide-forming elements like vanadium, chromium demonstrate a strong tendency to diffuse into the cementite phase. Additionally, phosphorus shows a pronounced tendency to segregate at the ferrite/cementite interface.