MODELING AND METALLURGICAL CHARACTERIZATION OF THERMAL CYCLING BEHAVIOR OF THERMO-SOLAR BOILER STEEL

Nowadays "T22" is one of the common steels that manufacturing use to produce boilers, huge tanks to store water. This tanks go through nonstop cycles of heating and cooling, due to and because lack of protective coating layer an oxide scale forms that causes failure in the steel, as a result shortening its lifetime. Brightsource industries developed a protective coating for the purpose of preventing oxidation on boilers. The project focused on characterizing macroscopic and microscopic of the interface between thermo - solar boiler steels and Brightsource`s coating, and describing the changes at the interface using a mathematic - kinetic model.

The project goals are characterizing grain boundaries oxidation rate at the steel-coating interface, during isothermal storage at high temperatures (530^oc-600^oc), and, during isothermal soak at 530^oc and 600^oc, while performing thermal cycling, then composing a mathematical model, demonstrating the correlation between grain boundaries oxidation rate during isothermal storage, and oxidation rate at thermal cycling, and Verifying this mathematical model feasibility by literature comparison.

The research characterized grain boundaries oxidation rate in coated T22 steel models at the influence of three elevated temperatures during isothermal storage. By cutting the models and characterizing them with metallurgical microscope, it was possible to calculate the oxidation rate constant, activation energy (using Arrhenius equation) and acceleration factor. The model who is compatible to the grain boundary oxidation rate is the parabolic model d^2=k*t where d is the oxide thickness, t is time and k the parabolic constant. Using the model a comparison was made between isothermal storage oxidation rates to oxidation rate during isothermal soak while performing cycle, and indeed the rates match.

Key words: "T22", oxidation, protective coating.