scholarly journals Intergranular and Pitting Corrosion in Sensitized and Unsensitized 20Cr-25Ni-Nb Austenitic Stainless Steel

CORROSION ◽  
10.5006/3725 ◽  
2021 ◽  
Author(s):  
Ronald Clark ◽  
Choen Chan ◽  
W. Walters ◽  
Dirk Engelberg ◽  
Geraint Williams
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Pitting Corrosion ◽  
Intergranular Corrosion ◽  
Niobium Carbide ◽  
Ion Concentration ◽  
Kelvin Probe ◽  
The Matrix

Advanced gas-cooled reactor (AGR) oxide fuels used in the UK are clad in bespoke grade 20%Cr-25%Ni-Nb austenitic stainless steel. Electrochemistry was first applied to correlate the breakdown potential with chloride ion concentration, temperature and pH for this alloy. At near-neutral pH the unsensitized material exhibited a linear E<sub>b</sub> = A + B log10[Cl<sup>-</sup>] relationship, where A = 0.7 V (vs. SCE), and B = 0.098 V/decade. Scanning Kelvin probe force microscopy revealed grain boundary regions in the heat-treated material up to 65 mV less noble to the matrix, whereas un-dissolved niobium carbide (NbC) precipitates were up to 55 mV more noble to the matrix. In-situ time-lapse microscopy and post-corrosion observations confirmed that sensitized grain boundaries were susceptible to pitting corrosion, further developing along intergranular corrosion pathways. It has however been shown that micro galvanic coupling between the Nb precipitates and matrix and / or sensitized grain boundary regions is not a factor in corrosion initiation as all experiments were performed under external potential control. Post corrosion observations showed the presence of pits at NbC precipitates promoting grain boundary corrosion. It is postulated that corrosion initiates at NbC precipitates as a pit, and when in close vicinity to Cr-depleted grain boundaries, then propagates along grain boundaries as intergranular corrosion.

Grain Boundary Engineering for Intergranular Corrosion Resistant Austenitic Stainless Steel

2004 ◽  
Vol 261-263 ◽  
pp. 1005-1010 ◽  
Author(s):  
Hiroyuki Kokawa ◽  
Masahiko Shimada ◽  
Zhan Jie Wang ◽  
Yutaka S. Sato ◽  
M. Michiuchi
Keyword(s):  
Stainless Steel ◽  
Corrosion Resistance ◽  
Sulfuric Acid ◽  
Austenitic Stainless Steel ◽  
Grain Boundary ◽  
Thermomechanical Treatment ◽  
Intergranular Corrosion ◽  
Ferric Sulfate ◽  
Grain Boundary Engineering ◽  
Intergranular Corrosion Resistance

Optimum parameters in the thermomechanical treatment during grain boundary engineering (GBE) were investigated for improvement of intergranular corrosion resistance of type 304 austenitic stainless steel. The grain boundary character distribution (GBCD) was examined by orientation imaging microscopy (OIM). The intergranular corrosion resistance was evaluated by electrochemical potentiokinetic reactivation (EPR) and ferric sulfate-sulfuric acid tests. The sensitivity to intergranular corrosion was reduced by the thermomechanical treatment and indicated a minimum at a small roll-reduction. The frequency of coincidence-site-lattice (CSL) boundaries indicated a maximum at the small pre-strain. The ferric sulfate-sulfuric acid test showed much smaller corrosion rate in the thermomechanical-treated specimen than in the base material for long time sensitization. The optimum thermomechanical treatment introduced a high frequency of CSL boundaries and the clear discontinuity of corrosive random boundary network in the material, and resulted in the high intergranular corrosion resistance arresting the propagation of intergranular corrosion from the surface.

The Effects of Sulfur and Phosphorus on the Intergranular Corrosion of 304 Stainless Steel

CORROSION ◽  
1980 ◽  
Vol 36 (9) ◽  
pp. 497-509 ◽  
Author(s):  
C. L. BRIANT
Keyword(s):  
Stainless Steel ◽  
Grain Boundaries ◽  
Intergranular Corrosion ◽  
304 Stainless Steel ◽  
Boundary Structure ◽  
Chromium Depletion ◽  
Grain Boundary Structure ◽  
The Matrix ◽  
Acid Test ◽  
Electrochemical Potentials

Abstract This paper reports a study of the effects of sulfur and phosphorus on the sensitization and intergranular corrosion of 304 stainless steel. It is shown that sulfur has little effect on the intergranular corrosion of the material, except at the high electrochemical potentials of the Huey test and oxalic acid test. At these potentials chromium sulfides precipitated at the grain boundaries and in the matrix are preferentially attacked. Phosphorus has little effect on intergranular corrosion as measured by the modified Strauss test, but it greatly accelerates intergranular corrosion in the Huey test. The magnitude of this effect depends on the extent of chromium depletion. It is also shown that in all of the alloys studied grain boundaries in a given sample corrode at varying rates. This variation appears to be a result of variation in grain boundary structure and hence in precipitation and segregation.

scholarly journals Testing of intergranular and pitting corrosion in sensitized welded joints of austenitic stainless steel

10.30544/274 ◽  
2017 ◽  
Vol 23 (2) ◽  
pp. 109-117 ◽  
Author(s):  
Bore V. Jegdic ◽  
Biljana Bobić ◽  
Milica Bošnjakov ◽  
Behar Alić
Keyword(s):  
Stainless Steel ◽  
Corrosion Resistance ◽  
Austenitic Stainless Steel ◽  
Weld Metal ◽  
Base Metal ◽  
Pitting Corrosion ◽  
Heat Affected Zone ◽  
Intergranular Corrosion ◽  
Chromium Concentration ◽  
Pitting Corrosion Resistance

Pitting corrosion resistance and intergranular corrosion of the austenitic stainless steel X5Cr Ni18-10 were tested on the base metal, heat affected zone and weld metal. Testing of pitting corrosion was performed by the potentiodynamic polarization method, while testing of intergranular corrosion was performed by the method of electrochemical potentiokinetic reactivation with double loop. The base metal was completely resistant to intergranular corrosion, while the heat affected zone showed a slight susceptibility to intergranular corrosion. Indicators of pitting corrosion resistance for the weld metal and the base metal were very similar, but their values are significantly higher than the values for the heat affected zone. This was caused by reduction of the chromium concentration in the grain boundary areas in the heat affected zone, even though the carbon content in the examined stainless steel is low (0.04 wt. % C).

Role of Grain Boundaries in Intergranular Corrosion in Austenitic Stainless Steels

2002 ◽  
Author(s):  
D. N. Wasnik ◽  
V. Kain ◽  
I. Samajdar
Keyword(s):  
Stainless Steel ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Intergranular Corrosion ◽  
Austenitic Stainless Steels ◽  
304 Stainless Steel ◽  
Grain Boundary Character Distribution ◽  
Orientation Imaging ◽  
Grain Boundary Character ◽  
Degree Of Sensitization

Grain boundaries play a very important role in intergranular corrosion. They determine whether the material is prone to intergranular corrosion or not. A study has been carried out to determine the influence of grain boundaries on the degree sensitization of Type 304 stainless steel (SS) and Type 316L stainless steel. The alloys were different thermomechanical treatment to obtain a variation in grain boundaries. They were then annealed and sensitized. The degree of sensitization was evaluated by using the Double Loop Electrochemical Potentiokinetic Reactivation (DL-EPR) technique and intergranular corrosion was evaluated by ferric sulfate-sulfuric acid test. In these tests, the degree of sensitization was measured by determining the ratio of the maximum current generated by a reactivation scan to that of the anodic scan, i.e. Ir: Ia, and intergranular corrosion was measured from weight loss of specimens. The grain boundary character distribution was measured with the help of Orientation Imaging Microscope (OIM). The degree of sensitization was then related to the grain boundary measurements. It was found that the degree of sensitization and intergranular corrosion is low at high angle grain boundaries in both types of stainless steel.

DISTRIBUTION AND CORROSION BEHAVIORS OF THE TRIPLE JUNCTIONS IN A GRAIN BOUNDARY ENGINEERED 304 STAINLESS STEEL

2009 ◽  
Vol 23 (06n07) ◽  
pp. 1110-1115 ◽  
Author(s):  
XIAOYING FANG ◽  
WEIGUO WANG ◽  
HONG GUO ◽  
CONGXIANG QIN ◽  
BANGXIN ZHOU
Keyword(s):  
Stainless Steel ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Intergranular Corrosion ◽  
Electron Back Scatter Diffraction ◽  
304 Stainless Steel ◽  
Grain Boundary Character Distribution ◽  
Triple Junctions ◽  
Grain Boundary Character ◽  
Character Distribution

Grain boundary character distribution (GBCD) and triple junction character distribution (TJCD) in a 304 stainless steel cold rolled with the thickness reduction of 6% and then annealed at 1323K for 5 minutes(GBE process) were analyzed by electron back scatter diffraction (EBSD). The intergranular corrosion (IGC) resistance of various triple junctions and grain boundaries were evaluated after sensitization treatment at 1073K for 30 minutes. The results showed special TJ containing 2 or 3 CSL boundaries exhibit higher resistance to IGC than other TJs. In addition, the {411} and {221} symmetrical tilt grain boundaries (STGBs) are more resistant to intergranular corrosion for Σ9 boundaries.

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