Mapping of Creep Strain in Notched Specimens of Boron-Added P91 Steel
Tóm tắt
Boron-added modified 9Cr-1Mo (P91B) steel is being considered as an alternate candidate material for steam generators of sodium cooled fast reactors. As components in service consist of discontinuities in geometry, the creep behaviour of P91B steel was investigated by including discontinuity in the form of U-notch. The notch root radius (r) of notched specimens was varied as 0.25, 1.25 and 2.5 mm, while keeping the notch diameter and depth (h) as the same. The corresponding notch acuity ratios (h/r) are 6.7, 1.34 and 0.67 respectively. The creep tests were conducted on notched specimens at 923 K and at 240 and 260 MPa. A non-contact type video extensometer was used to measure the elongation in the different regions of the notched specimen. The creep strain in both the plain as well as notch regions were measured individually. It has been observed that the response of material to applied load was not uniform along the specimen length, due to existence of stress gradient in the presence of notch and was manifested as compressive strain in the plain region between the double U-notches in some tests. At the stress level of 240 MPa, the creep rupture life increased upto 1.5 times with increase in notch acuity ratio from 0.67 to 6.7.
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