Změny korozní odolnosti pro různě kryogenně upravené nástrojové oceli

Jurči Peter - Slovak Technik University of Trnava (Slovak Republik)

Corrosion resistance of tools may be of some importance if they operate in environments that contain acids, seawater or similar substances. Therefore it is appropriate to control this property carefully, by using proper heat treatment route. One of possible ways how to change the corrosion resistance of tool steels is the application of cryogenic treatment. This treatment reduces the retained austenite amount, produces extra carbides in steels microstructures, changes the precipitation of nano-sized carbides, and evokes an overall microstructural refinement. In this paper the impact of cryogenic treatments on corrosion resistance in 3.5% NaCl solution is demonstrated upon an example of Vanadis 6 steel. The steel was subjected to different combinations of cryogenic treatments (-75, 140, -196 or -269°C) and tempering (no, 170, 330, 450 or 530°C). Then, the specimens were tested by potentiodynamic polarization method. A general improvement of steel´s corrosion resistance was recorded due to cryogenic treatment, with the maximum after cryogenic treatment at -140°C. It was suggested that enhanced number and more uniform distribution of carbides can more than sufficiently compensate lowered retained austenite amounts, thus induce improved corrosion resistance. The obtained results are then compared and discussed with the findings on corrosion resistance of similar cryogenically treated materials.

Keywords: ledeburitic tool steels; cryogenic treatment; microstructure; potentiodynamic polarisation; corrosion resistance

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