Abstract
In this report, the descaling conditions of annealed SUS 304 steel in electrolyte of sodium chloride and sodium nitrate are experimentally investigated.
The structures of the scale are determined by means of electron diffraction and X-ray diffraction.
The layer of the scale of the specimens are composed of two types of oxide; (1) oxide with a corundum structure, which is identified to be Cr2O3 and (Cr, Fe)2O3, (2) oxide with a spinel structure, which is identified to be Fe3O4 and FeCr2O4.
In the presence of some defects in the layer of the scale, the removal of scale on the steel can be accomplished by two stages of electrolytic descaling process; (1) 90% of the layer of the scale is removed by the electrolytic descaling in NaCl electrolyte. (2) To remove any remained scale and give passivity, it is electrolyzed at current density of 50 to 200mA/cm2 in NaNO3 electrolyte.
In the absence of any defect in the inner layer of the scale, the scale is removed by the dissolution of Cr-oxide of the scale during the electrolytic descaling in NaNO3 electrolyte.
