High alloyed materials are required by certain industrial sectors as is power, chemical and nuclear industry, etc. These materials have superior mechanical properties and are resistant to chemically aggressive environment in which it must accommodate the long term mechanical stresses at high temperatures. However, in the course of operating loading reduces their service life. Steels are losing their specific characteristics and in particular the toughness and corrosion resistance.This paper deals with the influence of the structure stay on electrochemical properties of steel, mainly the behaviour in the passivity area. The experiment was effected on the bearing body made from the high alloyed steel 440C. Specimens were treated to a different mode of heat treatment - quenching 930 °C to 1080 °C / 0,75 h / oil; following tempering 200 °C to 750 °C / 2 h / air; or freezing (-80 °C, 0.5 h). Microstructure was observed in two directions – on outside round surface and cross section. In addition to the optical microscopy have been used SEM and the EDX analysis. The volume of residual austenite was determined by XRD analysis. The changes of mechanical properties are verified by measurement of microhardness HV 0.01. Corrosion tests are proceeded out in hydrochloric and boric acid environment. Corrosion potential has been measured and corrosion loss (corrosion rate). The results showed that in the first environment corrosion occurs in the active area, in the second case in the passive. Also interesting connections were observed between corrosion rate and the development of hardness for each of the samples.Keywords: High alloyed steel, passive state, corrosion rate, corrosion potential, heat treatment
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