Observation and Analysis of Nitrides in Steels Using the Non-aqueous Electrolyte-Potentiostatic Etching Method

Nitrides in carbon steels and stainless steels were observed and analyzed using the non-aqueous electrolyte-potentiostatic etching method (the SPEED method).The results obtained are summarized as follows:(1) Polarization curves of nitrides were measured by the electric conductive paint method in 10% acetylacetone-1% tetramethylammonium chloride-methyl alcohol electrolyte. Nitrides such as AlN, BN, β-Cr2N, Z-phase and TiN are found to be stable when the steel matrix is etched at potentials lower than +800 mV vs SCE.(2) In situ observation and analysis of the nitrides, especially film-like nitrides and duplex nitrides in steels were successfully conducted by the SPEED method.(3) The precipitation behavior and the morphology of the following nitrides were made clear by the SPEED method.(a) Fine AlN in low carbon steel heat-treated in a high temperature region (1100∼1500 K),(b) Z-phase in highly purified ferritic stainless steel (19%Cr-2%Mo-0.09%Nb) heat-treated in the temperature range of 650∼1300 K,(c) Dice-shaped Ti(C,N) in ferritic siainless steel (17%Cr-0.42%Ti).