SEGREGATION ON THE SURFACE OF STEELS IN HEAT-TREATMENT AND OXIDATION

During annealing of steels different kinds of enrichments are observed on. steel surfaces. Equilibrium segregation of a dissolved element leads to enrichment in the range of a monolayer, two interacting elements can form two-dimensional compounds by cosegregation and also chemisorption induced segregation leads to monolayer surface compounds. If the concentrations or pressures are exceeded which are necessary for the formation of three-dimensional bulk compounds, enrichments occur due to surface precipitation resp. oxidation. On the other hand, oxidation can cause segregation or accumulations of dissolved elements beneath the oxide scale. These different phenomena are fundamentally discussed and examples are presented, which are important in the steel production and for the steel properties.