Quxatitative Theory of Seasitization

1988 ◽  
Vol 125 ◽  
Author(s):  
Thomas M. Devine
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Carbide Precipitation ◽  
Experimental Results

ABSTRACTThe chromium composition along the grain boundaries of sensitized austenitic stainless steel are calculated using several different quantitative theories of sensitization. The results of the calculations are compared to measured values of the chromium composition along the grain boundary in an effort to assess the validity of the various theories. The experimental results point out two facts not previously emphasized in prior studies: (1) the amount of carbide precipitation required to sensitize austenitic stainless steel is small; (2) significant de-sensitization does not occur until after large amountsof carbide precipitation have occurred.

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.

scholarly journals Study of the Sensitization on the Grain Boundary in Austenitic Stainless Steel Aisi 316

2014 ◽  
Vol 22 (341) ◽  
pp. 131-136
Author(s):  
Edina Kocsisová ◽  
Mária Dománková ◽  
Ivan Slatkovský ◽  
Martin Sahul
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Structure ◽  
Secondary Phases ◽  
Electron Backscattered Diffraction ◽  
Steel Aisi ◽  
Aisi 316 ◽  
Stainless Steel Aisi

Abstract Intergranular corrosion (IGC) is one of the major problems in austenitic stainless steels. This type of corrosion is caused by precipitation of secondary phases on grain boundaries (GB). Precipitation of the secondary phases can lead to formation of chromium depleted zones in the vicinity of grain boundaries. Mount of the sensitization of material is characterized by the degree of sensitization (DOS). Austenitic stainless steel AISI 316 as experimental material had been chosen. The samples for the study of sensitization were solution annealed on 1100 °C for 60 min followed by water quenching and then sensitization by isothermal annealing on 700 °C and 650 °C with holding time from 15 to 600 min. Transmission electron microscopy (TEM) was used for identification of secondary phases. Electron backscattered diffraction (EBSD) was applied for characterization of grain boundary structure as one of the factors which influences on DOS.

Thermal Stability of Microstructure in Grain Boundary Character Distribution-Optimized and Cold-Worked Austenitic Stainless Steel Developed for Nuclear Reactor Application

2009 ◽  
Vol 1215 ◽  
Author(s):  
Shinichiro Yamashita ◽  
Yasuhide Yano ◽  
Ryusuke Tanikawa ◽  
Norihito Sakaguchi ◽  
Seiichi Watanabe ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Grain Boundary Character Distribution ◽  
Boundary Character ◽  
Grain Boundary Character ◽  
Character Distribution ◽  
Boundary Character Distribution ◽  
Cold Worked

AbstractGrain boundary character distribution-optimized (GBCD) Type 316 corresponding austenitic stainless steel and its cold-worked ones (GBCD+CW) are one of prospective nuclear materials to be considered for next generation energy systems. These steels were thermally-aged at 973 K for 1 and 100 h and were examined by transmission electron microscopy (TEM) to evaluate microstructural stability during high temperature exposure. TEM results revealed that microstructures of both specimens prior to ageing contained step-wise boundaries which is composed of coincidence site lattice (CSL) and random grain boundaries and also that the GBCD+CW specimens had dislocation cells and networks as well as deformation twins whereas as the GBCD one possessed few dislocations. After thermal ageing, the precipitates formed on not only random grain boundaries but also dislocations, contributing to prevent significant microstructural change occurring such as recrystallization and dislocation recovery.

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