Steels used in steam turbine applications are susceptible to temper embrittlement if operated at temperatures above 400°C. The cause of this embrittlement is the segregation of impurity elements, mainly phosphorus, to the prior austenite grain boundaries. Molybdenum can act as an effective scavenger for phosphorus, but the scavenging effect is lost when the molybdenum is precipitated in carbides during service at these elevated temperatures. Thus, the very slow temper embrittlement is controlled by the rates of alloy carbide formation, rather than by the diffusion of phosphorus. The presence of vanadium apparently retards the embrittlement process even more by interfering with the formation of the molybdenum-rich carbides. Vanadium carbonitrides, are small, only a few nanometers in size, and difficult to see by standard TEM contrast mechanisms. Analysis of segregating elements to the grain boundaries has to be carried out on areas which are devoid of precipitates, especially small V precipitates or other precipitates that could be interpreted as segregation rather than precipitation. One method of detecting precipitates in the matrix is by X-ray mapping areas of interest. This paper describes a new method of X-ray mapping of multi-component steels that have overlapping lines. The method has been found to be effective in removing thickness effects from the maps and discriminating between real and artificial compositional components, which are created by the overlapping lines.