In this thesis we investigated the high temperature oxidation of hot work steel
SITHERM S140R, manufactured by SIJ Metal Ravne. We studied the steel in the
condition of soft annealing, as it is also issued in this form by the manufacturer. We
used pure iron (99.9 wt. % Fe) as a comparative material. For steel, we first calculated
the equilibrium compositions of the resulting oxide layers by thermodynamic modelling
using the CALPHAD method. Subsequently, two samples were oxidised in a
simultaneous thermal analysis apparatus (STA) at temperatures of 500 and 700 °C.
Samples of the reference material - iron - were oxidised in a chamber furnace at a
temperature of 700 °C and removed from the furnace after three different times.
Subsequently, the change in mass that occurred during oxidation was measured by
means of weighing. Metallographic analysis was used to measure the thicknesses of
the oxide layers that had formed on two oxidised steel samples. Based on the results
obtained, we created a thermodynamic model for the steel studied at each
temperature. The model developed describes the kinetics of high-temperature
oxidation, which is also described by the results of the analysis performed with Thermo-Calc. The kinetics of the investigated steel can also be described with three
mathematical functions: exponential, parabolic or cubic function. Which mathematical
function best describes the oxidation kinetics depends on the chemical composition of
the steel and the oxidation temperature. Through tests, it was found that alloying
elements have a great influence on the oxidation kinetics.
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