Abstract
In order to improve descalability of annealed austenitic stainless steels, this study investigated the effects of the contents of 0.2-1.0 mass% Si and 0.8-1.6 mass% Mn on the dissolution behavior of the scale of annealed Type304 steels on electrolysis in Na2SO4, solution and pickling in HNO3-HF acid solution in descaling process.
The results obtained are as follows:
(1) Descalability of annealed Type304 stainless steels decreased as the Si and Mn contents increased.
(2) The increase of Mn contents made an outer scale of spinel oxide thick. A dissolution rate of the spinel oxide by the Na2SO4 electrolysis was lower than that of an inner scale of corundum oxide, therefore the time required for electrolysis descaling was longer.
(3) The increase of Si contents made an inner scale of corundum oxide and amorphous Si oxide under the scale thick. As corundum oxide became thicker, the time required for descaling by the Na2SO4 electrolysis was longer. Besides a thick amorphous Si oxide obstructed permeation of HNO3-HF pickling solution into Cr depletion layer under Si oxide.
