Hardness of iron and structural steels as functions of the parameters of ultradisperse structure

Strengthening of iron of various purity and of structural steels in which ultradisperse and coarse-grained structures of various types were produced by deformation and annealing have been investigated. Approximating dependences have been established, which permit one to estimate the hardness of these materials in various structural states at an equal size of structural constituents in a range of 0.05-1 mum and determine the contribution of grain-boundary (related to the refinement of structural constituents and to the nonequilibrium structure of boundaries), solid-solution, and carbide strengthening. The main contribution to the hardness of pure iron comes, irrespective of the microstructure type, from the refinement of structural constituents. Alloying iron with carbon changes the parameters of the Hall-Petch equation with changing type of microstructure. This is related to a redistribution of impurities between the solid solution, dislocations, and boundaries of microcrystallites upon deformation and to a change in the relative contribution of different types of strengthening.