Effects of Overall Grain Boundary Nature on Localized Corrosion in Austenitic Stainless Steels

2004 ◽  
Vol 467-470 ◽  
pp. 813-818 ◽  
Author(s):  
D.N. Wasnik ◽  
Vivekanand Kain ◽  
I. Samajdar ◽  
Bert Verlinden ◽  
P.K. De
Keyword(s):  
Stainless Steel ◽  
Grain Boundary ◽  
Cold Rolling ◽  
Grain Boundaries ◽  
Stainless Steels ◽  
Intergranular Corrosion ◽  
Localized Corrosion ◽  
Mechanical Processing ◽  
Type 316L ◽  
Type 304

Thermo-mechanical processing of type 304 and type 316L stainless steels done by (a) cold rolling to a reduction in thickness of 20 to 80 percent and (b) solution annealing to obtain a medium size of grains led to a considerable improvement in resistance to both sensitization and intergranular corrosion. The nature of the resultant grain boundaries was examined in a scanning electron microscope using orientation imaging microscopy in electron back scattered diffraction mode. Fraction of random and special grain boundaries were established for each set of thermo-mechanical processing. After appropriate sensitization treatments, the degrees of sensitization of these stainless steels were evaluated by double loop electrochemical potentiokinetic reactivation tests. Standard ASTM tests were used to evaluate susceptibility to intergranular corrosion (IGC) and intergranular stress corrosion cracking (IGSCC). These studies showed that a particular combination of thermomechanical processing led to formation of over 75 percent random grain boundaries in the steels and this imparted resistance to sensitization and to IGC and IGSCC. This opens a new concept in grain boundary (GB) engineering of a high fraction of random GB increasing the resistance to localized corrosion like IGC and IGSCC. Textural studies were carried out with the help of X-ray and MTM-FHM software. It showed significant change of texture in type 304 stainless steel, while no change in the texture of type 316L stainless steel after cold rolling and annealing.

Intergranular Corrosion of Nonsensitized Austenitic Stainless Steels — 1. Environmental Variables

CORROSION ◽  
1965 ◽  
Vol 21 (7) ◽  
pp. 235-244 ◽  
Author(s):  
J. S. ARMIJO
Keyword(s):  
Stainless Steel ◽  
Grain Boundary ◽  
Stainless Steels ◽  
Intergranular Corrosion ◽  
304 Stainless Steel ◽  
Intergranular Attack ◽  
Corrosion Reaction ◽  
Stress Levels ◽  
Type 304 ◽  
Type 304 Stainless Steel

Abstract Intergranular corrosion of nonsensitized stainless steels is reviewed, with emphasis on corrosion experienced in nitric-dichrornate solutions. Electrical resistance changes occurring during corrosion of Type 304 stainless ' steel in nitric-dichromate solutions are used to measure the rate of intergranular attack. Effects of HN03 concentration, Cr+6 concentration, temperature and stress on the intergranular corrosion reaction have been studied. The over-all corrosion reaction is found to consist of an incubation period, followed by a penetration period in which the rate of intergranular dissolution is linear. Measured activation energies for incubation and penetration periods are identical. The effect of applied stress is to increase both incubation and penetration rates. Low stress levels have greatest effect on the incubation rate, while high stress levels have greatest effect on the penetration rate. Appreciable grain boundary hardening is observed in nonsensitized Type 304 stainless steel. The grain boundary hardening is attributed to adsorbed impurities at grain boundaries. This segregation presents another variable which may be important in this type of intergranular attack.

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.

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.

Enhancing the Intergranular Corrosion Resistance of High-Nitrogen-Containing 316L Stainless Steels by Grain Boundary Engineering via Thermomechanical Treatment

CORROSION ◽  
10.5006/3487 ◽  
2020 ◽  
Vol 76 (9) ◽  
pp. 835-842
Author(s):  
A. Ravi Shankar ◽  
Vani Shankar ◽  
R.P. George ◽  
John Philip
Keyword(s):  
Grain Boundary ◽  
Nitrogen Content ◽  
Thermomechanical Treatment ◽  
Stainless Steels ◽  
Intergranular Corrosion ◽  
Boundary Energy ◽  
Cold Work ◽  
High Nitrogen ◽  
Increase With Increase ◽  
Type 316L

High-nitrogen-containing Type 316L stainless steels (SS) with 0.12% to 0.22% N are being developed as future structural material of fast breeder reactors because of their improved hardness and resistance to localized corrosion. However, stainless steels with higher nitrogen content are prone to intergranular corrosion (IGC) due to their tendency to get sensitized by enhanced precipitation of Cr2N. Thermomechanical treatment (TMT) of 6.5% cold-work and heat-treatment (1,323 K for 30 min) is evaluated in this study to enhance IGC resistance of 0.07%, 0.12%, 0.14%, and 0.22% nitrogen-containing Type 316L SS. The frequency of coincident site lattice (CSL) boundaries is found to increase with increase in nitrogen content in Type 316L SS. A maximum CSL increase of 35% was seen in 0.22% nitrogen containing stainless steel, as compared to samples containing 0.07% to 0.12% N. The effective grain boundary energy was the least (<0.1 μm−1) for Type 316L SS containing 0.22% N, which is attributed to the higher percentage of Σ3 boundaries. Double-loop electrochemical potentiokinetic reactivation (DL-EPR) tests conducted on the sensitized as-received and TMT samples showed a clear decrease in sensitization for TMT samples. The improved resistance to IGC visualized in the post-DL-EPR optical micrographs of TMT samples is attributed to the breakdown in the connectivity of attacked boundaries. The role of nitrogen in austenitic SS on twinning and generation of CSL boundaries is also discussed.

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.

Determination of Percolation Threshold for Random Boundary Network on the Basis of EBSD/OIM Observations

2007 ◽  
Vol 539-543 ◽  
pp. 2371-2376
Author(s):  
Sadahiro Tsurekawa ◽  
Shinya Nakamichi ◽  
Tadao Watanabe
Keyword(s):  
Stainless Steel ◽  
Grain Boundary ◽  
Percolation Threshold ◽  
Grain Boundaries ◽  
Intergranular Corrosion ◽  
Polycrystalline Materials ◽  
Grain Boundary Character Distribution ◽  
Grain Boundary Engineering ◽  
Triple Junctions ◽  
Random Boundary

Grain boundary engineering through the control of grain boundary character distribution (GBCD) has been extensively employed as a powerful tool for achieving enhanced properties and for development of high performance both structural and functional polycrystalline materials. Many efforts were made firstly to increase the frequency of low-energy CSL boundaries of polycrystalline materials in grain boundary engineering. However, the connectivity of grain boundaries can be an important microstructural parameter governing bulk properties of polycrystalline materials as well as the GBCD. In the present work, the connectivity of random grain boundaries was quantitatively evaluated using both the triple junction distribution and random boundary cluster length on the basis of SEM-EBSD/OIM observations, and then these evaluated parameters were linked to intergranular corrosion of SUS304 stainless steel. We have found that the length of the maximum random boundary cluster drastically decrease with increasing CSL boundaries in the fraction ranging 60 – 80% CSL boundaries, which leads to percolation threshold occurring at approximately 70±5% CSL boundary fraction (at 30±5% random boundary fraction). The experimentally observed percolation threshold is much higher than theoretically obtained one based on randomly assembled network (at 35% resistant bonds for a 2D hexagonal lattice). In addition, the fraction of resistant triple junctions is found to increase with increasing the the CSL boundary fraction. An increase in the frequency of resistant triple junctions can enhance intergranular corrosion resistance of polycrystalline austenitic stainless steel even if the GBCD is the same.

Strain-induced martensite effects on transgranular carbide precipitation in type 304 stainless steels

1991 ◽  
Vol 49 ◽  
pp. 604-605
Author(s):  
A.H. Advani ◽  
L.E. Murr ◽  
D. Matlock
Keyword(s):  
Heat Treatment ◽  
Grain Boundary ◽  
Stress Corrosion Cracking ◽  
Stainless Steels ◽  
Deformation Twin ◽  
Austenitic Stainless Steels ◽  
Carbide Precipitation ◽  
Strain Induced Martensite ◽  
Type 304

Thermomechanically induced strain is a key variable producing accelerated carbide precipitation, sensitization and stress corrosion cracking in austenitic stainless steels (SS). Recent work has indicated that higher levels of strain (above 20%) also produce transgranular (TG) carbide precipitation and corrosion simultaneous with the grain boundary phenomenon in 316 SS. Transgranular precipitates were noted to form primarily on deformation twin-fault planes and their intersections in 316 SS.Briant has indicated that TG precipitation in 316 SS is significantly different from 304 SS due to the formation of strain-induced martensite on 304 SS, though an understanding of the role of martensite on the process has not been developed. This study is concerned with evaluating the effects of strain and strain-induced martensite on TG carbide precipitation in 304 SS. The study was performed on samples of a 0.051%C-304 SS deformed to 33% followed by heat treatment at 670°C for 1 h.

Precipitation formation on ∑5 and ∑7 grain boundaries in 316L stainless steel and their roles on intergranular corrosion

2021 ◽  
pp. 116822
Author(s):  
Shao-Pu Tsai ◽  
Surendra Kumar Makineni ◽  
Baptiste Gault ◽  
Kaori Kawano-Miyata ◽  
Akira Taniyama ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Grain Boundaries ◽  
Intergranular Corrosion ◽  
316L Stainless Steel ◽  
Precipitation Formation
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