The technical conditions, which are imposed on the cast iron rolls in the exploitation period, are very different and often contradictory. The obtaining of various physical and mechanical properties at the different points of the same foundry product meets difficult technological problems in the industrial conditions. One of the parameters, which determine the structure of the irons destined for rolls casting, is the chemical composition. If we do not respect this composition, which guarantees the exploitation properties of each roll in the stand of rolling mill, it will lead to rejection. Alloying elements have in principle the same influence on structure and properties. This paper suggests a mathematical interpretation of the influence of the main alloying elements on the mechanical characteristics (the hardness on the crust of the rolls) of this nodular irons, resulting in the average values and average square aberration of the variables HB, and the main alloying elements (Cr, Ni, Mo), the equations of the hyper surface in the four dimensional space. For the statistical and mathematical analysis, there were used some industrial cases. The resulted surfaces, belonging to the three-dimensional space, can be represented and, therefore, interpreted by technologists. Knowing these level curves allows the correlation of the values of two independent variables so that HB can be obtained within the requested limits.