Stress Corrosion Cracking of Type 304 Stainless Steel in Sulfuric Acid Solutions Containing Cyanide or Thiocyanate

Abstract

Behavior of stressed Type 304 steel in H2SO4 solutions with addition of cyanide or thiocyanate has been studied in view of the reported strong adsorption characteristics of these spiecies. Annealed Type 304 wire was examined at 353K in 1 to 4 kmol/m3 H2SO4 solutions with additions of different quantities of KCN, NH4SCN, or NaN3 (pseudohalides) mainly under open circuit conditions at a stress of 275 MPa.With increased additions of KCN or NH4SCN the attack morphology changed from heavy general corrosion to cracking or localized attack and the time or fracture was prolonged. KCN was a cathodic and anodic inhibitor and NH4SCN was a cathodic inhibitor. The latter was also an anodic inhibitor at and near the open circuit potential. In the solutions containing NaN3 Type 304 did not fail due to passivation resulting from the cathodic reaction stimulated by NaN3 or fractured by general corrosion at the small addition of NaN3. (Received November 28, 1987) Keywords: stainless steel, stress corrosion cracking, acid solutions, cyanide, thiocyanate, azide, inhibitorIn cyanide solutions, stress corresion cracking (SCC) occurs in mild steel(1)(2) and in a NH4SCN solution, SCC also occurs in high carbon steel(3), high manganese steel(3), and austenitic stainless steels (Type 304 and 316 aged at 773K)(4). It was also reported(5) that H2SO4 solutions containing NH4SCN caused (transgranular) SCC in 25Cr-14Ni stainless steel.Cyanide and NH4SCN are pseudohalides, the chemical behavior of which is generally like that of halides as is well known. CN-ion is very strongly adsorbed at active sites of the steel surface in its solutions(6) and SCNion or NCS-ligands of various isothiocyanatochromium (III) complex ions are also adsorbed on the Hg surface from their solutions(7).T he relative adsorptivity of anions on the Pt surface from their potassium salt solutions increases in increasing order of Cl-<Br-<I-< SCN-(8) and when these anions are characterized as the bases in the hard and soft acids and bases principle, the above order is the same as that(9) of their softness. CN-ion is softer than SCN-ion(9) and this may account for the reported strong adsorption of CN-on the steel surface. Halide ions, which have also adsorptivity, cause SCC in Type 304 steel corroding in H2SO4 solutions(10); hence, the reported SCC of 25Cr-14Ni steel may be similar to that of Type 304 steel in H2SO4-halide solutions in mechanism. This paper deals the effects of additions of cyanide, thiocyanate, or azide (which is also a pseudohalide) on the behavior of Type 304 steel stressed in H2SO4 solutions. Cracks or localized attack under applied stress were observed when corrosion of Type 304 steel was suppressed by cyanide or thiocyanate additions.Type 304 wires of 1mm diameter from different charges (charge marks, DR81 and 5H) were used. Their chemical compositions

Chloride-Induced Stress Corrosion Cracking of Friction Stir-Welded 304L Stainless Steel: Effect of Microstructure and Temperature

“…However, austenitic SS is susceptible to stress corrosion cracking (SCC). The SCC occurs when the susceptible microstructure of austenitic SS with adequate tensile stress encounters a chloride-containing environment such as NaCl and MgCl 2 or other specific environments such as H 2 S or H 2 O 2 , resulting in loss of ductility and brittle failure [1][2][3][4]. SUS 304L or 316L austenitic steel plates are used for the fabrication of canisters for intermittent dry storage of used nuclear fuels [5].…”