Abstract
Through methods of modern materials science it is shown that plasma hardening of cast iron rolls of a rolling mill causes the formation of layers the structure of which is characterized by the regular change of mechanical characteristics, phase composition and defect substructure of the material and realized at different structure-scale levels: macro (the sample as a whole), meso (the state of the grain-subgrain ensemble), micro (the state of the carbide and dislocation subsystems), nano (the state of the solid solution). It is established that α, γ-phases, graphite and cementite are formed in cast iron rolls as a result of plasma hardening. The formation of nanocrystalline α-phase grain structure (with crystallite size of 35-40 nm) stabilized with 3-5 nm cementite particles is found in the surface layer. It is established that utilization of hardened cast iron rolls predictably changes the defect substructure and the phase composition of cast iron. The sources of far-ranging stress fields were identified which are created in a cast iron roll as a result of plasma treatment and further operation. It is shown that the largest stress fields are created in the surface layer in the structure of nanocrystalline ferrite grains. Application of the plasma surface hardening technique led to an increased wear resistance in cast iron rolls. The evolution of the structure-phase states and the defect substructure in the surface layer of cast iron rolls was analyzed in the case of large diameter rebars production.
Keywords
Structure, phase composition, cast iron rolls, plasma hardening
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