We study the structure and character of failure of steels microalloyed with boron, rare-earth metals, zirconium, and molybdenum, depending on thermal treatment. On the basis of the developed invariant models, we obtain a quantitative estimate of the influence of grain sizes, the number of triple joints, and grain-boundary energy on the resistance of steels to intercrystalline cleavage. We show that the differences in the tendency of steels toward intergranular failure are conditioned by the different amount of carbides at the grain boundaries with a higher energy level.