Determination of Carbides in High Speed Steels by Anodic Oxidation Technique

Abstract

In order to determine different types of carbides existing in annealed high speed steels, metallographic specimens were oxidized potentiostatically at various anodic potentials in a 1M sodium hydroxide solution and examined by electron microprobe analysis. The anodic oxidation behavior of carbides was discussed on the basis of the anodic polarization curves measured in the same solution. In addition, the volume fraction of M₆C was estimated as a function of quenching temperature by measuring the electric charge during anodic oxidation and by comparing the results obtained by point counting. The following conclusions are drawn from the results:
(1) The carbide particles stained brown to blue at 0 V vs SCE are identified to be M₆C.
(2) In the anodic polarization curves three current peaks are observed. These peaks are attributable to the dissolution of tungsten, molybdenum and vanadium in the matrix, M₆C and M₂₃C₆, respectively.
(3) The volume fraction of M₆C determined from the amount of electric charge is nearly equal to the value obtained by point counting.