STRUCTURE AND PHASE COMPOSITION OF FERRITIC-PERLITIC STEEL SURFACE AFTER ELECTROLYTIC PLASMA QUENCHING

The paper presents the transmission electron microscopy investigations of the structure and phase composition of ferritic-perlitic ST2 steel surface after electrolytic plasma quenching. The steel in the initial state represents the material after hardening at 890[degrees]C for 2 or 2.5 hours and quenching in warm (30-60[degrees]C) water with subsequent tempering at 580[degrees]C for 2.5 or 3 hours. Electrolytic plasma quenching is carried out at 850-900[degrees]C in an aqueous salt solution for 4 seconds, at 320 V voltage and 40 A current. In the initial state, the morphology of the steel matrix consists of lamellar perlite and nonfragmented and fragmented ferrite. Electrolytic plasma quenching of the steel surface results in the martensite transformation, steel self-tempering, and the formation of cementite particles in all martensite crystals. This treatment also leads to the diffusion transformation of [gamma] [right arrow] [alpha] phases, the release of residual austenite ([gamma]-phase) along the low-temperature martensite laths and lamellas and in all crystals of lamellar martensite, the formation of [M.sub.23][C.sub.6] special carbides and, finally, to the enhancement of all parameters of the steel fine structure. Keywords: steel, electrolytic plasma quenching, morphology, phase composition, ferrite, perlite, martensite, residual austenite, cementite, particle, fine structure parameters.