Various technological procedures may be used to improve the mechanical properties of metallic materials. In this thesis, we tested the properties of steels obtained by special heat treatment – deep cryogenic treatment.
We used various methods to determine the properties of steel materials. Corrosion properties were determined with electrochemical methods for measuring corrosion potential, linear polarization, electrochemical impedance spectroscopy and potentiodynamic measurements. We also used metallographic and spectroscopic methods for the microstructural analysis of materials. We tested steel specimens of three different compositions, labeled A, B, and C. The samples with composition A and B were tested with two different heat treatments and with added cryogenic treatment. Samples of steel B were prepared by powder metallurgy. Electrochemical methods were performed in a solution of sodium tetraborate with pH = 10.
We found that for steels of composition A, the industrial grade M2, the cryogenic treatment does not change the corrosion properties. The martensitic needles decrease due to cooling, the change in hardness is the result of different tempering temperatures. If we add cobalt to this composition – steel C (M35), the corrosion properties reduce after cryogenic treatment. There are no noticeable differences in the microstructure, nor is there any change in the hardness of the material. Steels of composition B, industrial grade M3: 2, exhibit a significant improvement in corrosion properties after deep cryogenic treatment. The number of carbides is visibly higher compared to steels A and C. The sample tempered at a lower temperature indicates an increase in hardness after cooling. Changes in hardness between the heat treatments are also evident due to different tempering temperatures.
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