SURFACE SEGREGATION IN LOW-CARBON STEELS

We studied by Auger electron spectroscopy the surface segregation phen omena in two low carbon steels containing titanium or titanium and nio bium. The free elements dissolved in the matrix can segregate to the f ree surface; these elements are phosphorus, sulphur and titanium for t he steel without niobium. In addition to the previous elements, carbon is detected for the steel with niobium. The presence of dissolved car bon in one of the steels and its absence in the other constitutes the most important result of the study relating to the role of carbon in t he different properties of these steels. Free enthalpies of surface se gregation were evaluated for each element using the Guttmann approach for ternary or binary systems. We clearly revealed different kinds of interaction between segregated elements. Strong attractive interaction between Ti and P or Ti and S produces cosegregation of both elements. On the other hand, there is a repulsive interaction between C and P o r S and P. This repulsion strengthens a site competition phenomenon be tween the latter elements (S and P).