Effect of Ni on solidification of duplex low-density steels
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Effect of Ni on solidification of duplex low‑density steels Tilen Balaško1 · Jaka Burja2 · Jožef Medved1 Received: 22 October 2019 / Accepted: 14 September 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Recently, low-density Fe–Mn–Al–C steels have attracted attention because of their low density with excellent combinations of strength and ductility. They can be divided into three categories: ferritic steels, duplex steels and austenitic steels, depending on the microstructure. The solidification of five duplex low-density steels was investigated. Five steels Fe–15Mn–10Al– 0.8C, Fe–15Mn–10Al–1.7Ni–0.8C, Fe–15Mn–10Al–3.9Ni–0.8C, Fe–15Mn–10Al–5.6Ni–0.8C and Fe–15Mn–10Al–8.6Ni– 0.8C were produced in a vacuum induction furnace under Ar atmosphere and remelted in a simultaneous thermal analyser (NETZSCH STA 449 C Jupiter). The influence of Ni on the solidification process was analysed using thermodynamic calculations and differential scanning calorimetry. The samples were analysed by light microscopy. The thermodynamic modelling was performed with commercial software Thermo-Calc using the CALPHAD method. The Thermo-Calc calculations show a better agreement for the liquidus temperatures at lower Ni additions, while the higher Ni additions show a better agreement for the solidus temperatures. The Ni additions slightly increase the density, reduce the distance of the secondary dendrite arms and lower both the solidus and liquidus temperatures, but do not influence the solidification interval. Keywords Low-density steels · Duplex steels · Solidification · DSC · CALPHAD
Introduction About 20% of the EU’s greenhouse gas emissions come from the transport sector, 72% of which is from road transport [1, 2]. The automotive industry is therefore reducing the mass of cars to cut CO2 emissions. Recently, low-density Fe–Mn–Al–C steels have attracted attention because of their low density with excellent combinations of strength and ductility [3–12]. One of the most effective ways to reduce the mass of steels is to add more aluminium (1.3% density reduction per 1 mass% Al) [3, 10]. Low-density Fe–Mn–Al–C steels can be divided into three categories: ferritic steels, duplex steels and austenitic steels [3, 6, 11]. The addition of Ni to low-density steels is relatively new, as Ni is not particularly advantageous for achieving low density. The steel with 5 mass% Ni addition was selected according to the promising results of Kim et al. [13] and Rahnama et al. * Tilen Balaško [email protected]‑lj.si 1
Faculty of Natural Sciences and Engineering, University of Ljubljana, Aškerčeva Cesta 12, 1000 Ljubljana, Slovenia
Institute of Metals and Technology, Lepi pot 11, 1000 Ljubljana, Slovenia
2
[14]. The Ni addition changes the precipitation of ordered phases in austenite and ferrite and their chemical compositions, which influence the mechanical properties [14]. The topic of hot working has been discussed by Mozumder et al. [15], but the topic of solidification has never been discussed. The microstructure in the as
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