Effect of chlorides on the stability of the passive state of low Mn steels

Abstract

Electrochemical measurements have shown that low Mn (-0.2% Mn) modified stainless steels with low (< 1.2% Mo) or no Mo exhibit a higher pitting resistance in NaCl aq (0.005 M up to 2 M NaCl) than the analoguous commercial steels with 1.4% Mn and -2.8% Mo. Microscopic examinations and X-ray microprobe analysis revealed a correlation between pitting resistance of the steels and the composition of the nonmetallic inclusions as well as of the adjacent matrix. They both differ considerably for the two groups of steels.Elektrochemische Messungen haben gezeigt , daB nichtrostende Stahle mit niedrigem Mangangehalt (etwa 0,2% Mn) mit Molybdangehalten unter 1,2% bzw. molybdanfrei in 0,005 m-2 m NaCl bestandiger gegen Lochkorrosion sind als die analogen handelsublichen Stahle mit 1,4% Mn und etwa 2,8% Mo. Mikroskopische Untersuchungen und Rontgenmikrosondenanalyse zeigen eine Beziehung zwischen der Widerstandsfahigkeit gegen Lochkorrosion und der Zusammensetzung der nichtmetallischen Einschliisse sowie der umgebenden Matrix der Stahle. Diese beiden GroRen sind bei den beiden Stahlgruppen sehr verschieden.

The Role of Oxide Films on TiS and Ti4C2S2Inclusions in the Pitting Corrosion Resistance of Stainless Steels

“…The addition of titanium to stainless steels also results in the formation of Ti-sulfides and/or carbosulfides instead of Mn-sulfide inclusions, in effect improving the pitting corrosion resistance of stainless steels. [1][2][3][4][5][6][7][8][9] Mn-sulfide inclusions are known to be preferential sites for pit initiation in chloride solutions. [10][11][12][13][14][15][16][17][18][19][20][21] Ti-sulfide and carbosulfide inclusions (e.g.…”

“…), however, have better pitting corrosion resistance than MnS inclusions. [1][2][3][4][5][6][7][8][9] Research by Baroux and Gorse indicated that Ti-sulfide inclusions are insoluble and do not act as the initiation sites for pitting in low chloride containing solutions (0.02 and 0.1 M NaCl). 5 They also demonstrated that the Ti-sulfide inclusions dissolve and act as preferential sites for pit initiation in a more concentrated 0.5 M NaCl solution.…”

Microelectrochemistry on CrS and MnS Inclusions and Its Relation with Pitting Potentials of Stainless Steels

“…Many other researchers have also reported that CrS inclusions are more resistant to pit initiation than MnS inclusions. [22][23][24][25][26][27] One possible reason for this is the difference in the solubility of the inclusions. CrS inclusions are either completely insoluble or poorly soluble in water: MnS inclusions are, however, soluble, in the process of dissolving, they release corrosive sulfur species.…”