Effect of electrolyte-plasma surface hardening on the structural-phase state of ferrite-perlite class steel

The study by means of transmission electron microscopy on thin foils was carried out to investigate the change in matrix morphology and phase composition occurring in ferrite-pearlitic steel of grade st2 (Russian grade) under plasma electrolytic surface quenching. In the original state st2 steel is given as material which underwent quenching under the temperature of 890 °C (2-2.5 h) with cooling into warm water (30-60 °C) and further tempering under the temperature of 580 ° (2.5-3 h). Surface quenching was conducted in aqueous salt solution during 4 seconds under the temperature of 850-900 °C, voltage of 320 W, and current rate of 40 A. In the original state morphological components of the steel matrix were lamellar pearlite and non-fragmented and fragmented ferrite. Surface hardening led to martensite transformation, to "self-shedding" of steel and extraction of cement particles inside all martensite crystals, to diffusion transformation and extraction of residual austenite (g-phase) along the borders of low-temperature martensite laths and plates and inside all plate martensite crystals and to extraction of special carbides of Me₂₃C₆ phase, as well as to increase of all parameters of fine structure of steel.

Keywords

Authors

References