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Increase of Wear Resistance and Contact-Fatigue Strength of Wheel Steel by Plasma Hardening

Metallographic studies of structural-phase states formed in the section of the flange of the wheel band during surface plasma hardening were conducted. It is shown that the formation of several structural zones of different micro hardness is distinctly observed in the depth of hardening, which indicates the formation of a graded-layered structure. It has been confirmed that at superfast heating rates that occur during surface plasma quenching, phase and structural transformations are shifted to high temperatures, greatly changing the kinetics of nucleation and growth of the new phase (austenite). This forms a fine-grained austenite, which turns into a highly disperse martensitic structure, unattainable by traditional methods of heat treatment. It is shown that the main factor leading to strong hardening of the surface layer during plasma treatment is the formation in the near-surface zone of a nonequilibrium metastable structure, which goes over to a narrow zone of complete and incomplete quenching with an inhomogeneous and distorted structure of highly disperse martensite with a high level of internal stresses. The complete wear of the unstressed flange of the tire wheel band is 1.9 mm in 1.1 years, and for hardened flanges, wear is 0.7 mm for 2.6 years.