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    Transgranular Stress Corrosion Cracking of 316 L Stainless Steel in Chloride Environment at 80º C

    Eltaghoor, Fathi Mohamed Abdsalam

    [Thesis]. Manchester, UK: The University of Manchester; 2016.

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    Abstract

    Although the phenomena of stress corrosion cracking is known to occur in 316L stainless steel in chloride environments, there is little knowledge regarding the incubation stage, i.e. when the cracks are very short and about a few grains in length scale. The project aimed to determine whether Grain Boundary Engineering GBE, through thermo-mechanical processing, could improve resistance to transgranular chloride stress corrosion crack nucleation in austenitic stainless steels.The material studied is type 316L austenitic stainless steel, with cracking developing in conditions of controlled humidity at 80°C under saturated MgCl2 salt deposits. Three batches were used; as received (AR), Heat treated at 950ºC designated as TM950ºC, treated at 1075ºC; designated as TM1075ºC and also treated at 1150ºC; designated as TM1150ºC for modifying the structure.The thermo mechanical treatment resulted in increase of ∑(3-29) and ∑3 in both fractions by almost 20% as the annealing temperature increased between 950ºC to TM1150ºC, on the other hand (AR) has sustained on 10% improvement over the TM950ºC in both fractions CSL% = ∑(3-29) and ∑3.In-situ observations show that the short cracks may grow to larger scale length in the (AR), TM950ºCand TM1150ºC than can grow in TM1075ºC.DIC analysis was not suitable for testing in this environment might be due to many factors, such as salt content residual effects, evaporation of the salt liquid, surface detritions and lateral movements due to tensile testing. The interaction between short stress corrosion cracks and microstructure was characterised by Electron backscatter diffraction (EBSD). The high angle grain boundaries (HAGB) are shown to act as barriers to cracking resulting in hindering or deviating the crack tip, which slows the overall crack growth rate.The type of microstructure that would have superior TGSCC resistance would be that, possess much higher fraction of both fractions CSL%= ∑(3-29) and ∑3.

    Layman's Abstract

    Although the phenomena of stress corrosion cracking is known to occur in 316L stainless steel in chloride environments, there is little knowledge regarding the incubation stage, i.e. when the cracks are very short and about a few grains in length scale. The project aimed to determine whether Grain Boundary Engineering GBE, through thermo-mechanical processing, could improve resistance to transgranular chloride stress corrosion crack nucleation in austenitic stainless steels.The material studied is type 316L austenitic stainless steel, with cracking developing in conditions of controlled humidity at 80°C under saturated MgCl2 salt deposits. Three batches were used; as received (AR), Heat treated at 950ºC designated as TM950ºC, treated at 1075ºC; designated as TM1075ºC and also treated at 1150ºC; designated as TM1150ºC for modifying the structure.The thermo mechanical treatment resulted in increase of ∑(3-29) and ∑3 in both fractions by almost 20% as the annealing temperature increased between 950ºC to TM1150ºC, on the other hand (AR) has sustained on 10% improvement over the TM950ºC in both fractions CSL% = ∑(3-29) and ∑3.In-situ observations show that the short cracks may grow to larger scale length in the (AR), TM950ºCand TM1150ºC than can grow in TM1075ºC.DIC analysis was not suitable for testing in this environment might be due to many factors, such as salt content residual effects, evaporation of the salt liquid, surface detritions and lateral movements due to tensile testing. The interaction between short stress corrosion cracks and microstructure was characterised by Electron backscatter diffraction (EBSD). The high angle grain boundaries (HAGB) are shown to act as barriers to cracking resulting in hindering or deviating the crack tip, which slows the overall crack growth rate.The type of microstructure that would have superior TGSCC resistance would be that, possess much higher fraction of both fractions CSL%= ∑(3-29) and ∑3.

    Bibliographic metadata

    Type of resource:
    Content type:
    Form of thesis:
    Type of submission:
    Degree type:
    Doctor of Philosophy
    Degree programme:
    PhD Materials Science
    Publication date:
    Location:
    Manchester, UK
    Total pages:
    223
    Abstract:
    Although the phenomena of stress corrosion cracking is known to occur in 316L stainless steel in chloride environments, there is little knowledge regarding the incubation stage, i.e. when the cracks are very short and about a few grains in length scale. The project aimed to determine whether Grain Boundary Engineering GBE, through thermo-mechanical processing, could improve resistance to transgranular chloride stress corrosion crack nucleation in austenitic stainless steels.The material studied is type 316L austenitic stainless steel, with cracking developing in conditions of controlled humidity at 80°C under saturated MgCl2 salt deposits. Three batches were used; as received (AR), Heat treated at 950ºC designated as TM950ºC, treated at 1075ºC; designated as TM1075ºC and also treated at 1150ºC; designated as TM1150ºC for modifying the structure.The thermo mechanical treatment resulted in increase of ∑(3-29) and ∑3 in both fractions by almost 20% as the annealing temperature increased between 950ºC to TM1150ºC, on the other hand (AR) has sustained on 10% improvement over the TM950ºC in both fractions CSL% = ∑(3-29) and ∑3.In-situ observations show that the short cracks may grow to larger scale length in the (AR), TM950ºCand TM1150ºC than can grow in TM1075ºC.DIC analysis was not suitable for testing in this environment might be due to many factors, such as salt content residual effects, evaporation of the salt liquid, surface detritions and lateral movements due to tensile testing. The interaction between short stress corrosion cracks and microstructure was characterised by Electron backscatter diffraction (EBSD). The high angle grain boundaries (HAGB) are shown to act as barriers to cracking resulting in hindering or deviating the crack tip, which slows the overall crack growth rate.The type of microstructure that would have superior TGSCC resistance would be that, possess much higher fraction of both fractions CSL%= ∑(3-29) and ∑3.
    Layman's abstract:
    Although the phenomena of stress corrosion cracking is known to occur in 316L stainless steel in chloride environments, there is little knowledge regarding the incubation stage, i.e. when the cracks are very short and about a few grains in length scale. The project aimed to determine whether Grain Boundary Engineering GBE, through thermo-mechanical processing, could improve resistance to transgranular chloride stress corrosion crack nucleation in austenitic stainless steels.The material studied is type 316L austenitic stainless steel, with cracking developing in conditions of controlled humidity at 80°C under saturated MgCl2 salt deposits. Three batches were used; as received (AR), Heat treated at 950ºC designated as TM950ºC, treated at 1075ºC; designated as TM1075ºC and also treated at 1150ºC; designated as TM1150ºC for modifying the structure.The thermo mechanical treatment resulted in increase of ∑(3-29) and ∑3 in both fractions by almost 20% as the annealing temperature increased between 950ºC to TM1150ºC, on the other hand (AR) has sustained on 10% improvement over the TM950ºC in both fractions CSL% = ∑(3-29) and ∑3.In-situ observations show that the short cracks may grow to larger scale length in the (AR), TM950ºCand TM1150ºC than can grow in TM1075ºC.DIC analysis was not suitable for testing in this environment might be due to many factors, such as salt content residual effects, evaporation of the salt liquid, surface detritions and lateral movements due to tensile testing. The interaction between short stress corrosion cracks and microstructure was characterised by Electron backscatter diffraction (EBSD). The high angle grain boundaries (HAGB) are shown to act as barriers to cracking resulting in hindering or deviating the crack tip, which slows the overall crack growth rate.The type of microstructure that would have superior TGSCC resistance would be that, possess much higher fraction of both fractions CSL%= ∑(3-29) and ∑3.
    Thesis main supervisor(s):
    Funder(s):
    Language:
    en

    Institutional metadata

    University researcher(s):

    Record metadata

    Manchester eScholar ID:
    uk-ac-man-scw:303559
    Created by:
    Clayton, Leanda
    Created:
    6th September, 2016, 13:18:05
    Last modified by:
    Clayton, Leanda
    Last modified:
    30th September, 2016, 09:44:06

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