Structural stability of dissimilar weld joints of steel P91

Characterisation of creep-weak zones (white bands) in grade 91 weld metal

“…fraction) can be obtained from the following equation 25 N Cr(eq)~NCr z0:386N Mn zN Mo z2:08N V z2:08N Nb Sopousek and Foret 27 as well as Sopousek et al 28 have calculated the carbon activities of steels with different chromium contents using the Calphad method, indicating that the chromium content significantly affected the carbon activity in steel. Foret et al 18 and Million et al 26 have confirmed the suitability of using a stationary model to predict carbon diffusion in dissimilar welding. It is proposed herein that this assumption is also applicable to the current case of relatively local inhomogeneities in substitutional element concentrations within the weld metal itself, which produces the diffusion of carbon and the dissolution of the carbides.…”

“…This suggests that the substitutional elements will have not migrated significantly during either the PWHT or the creep exposure; it has been argued elsewhere 16 that the inhomogeneities in their compositions are associated with poor mixing of the alloying elements contained in the flux in a thin layer close to the bead boundary. 17 However, significant diffusion of carbon may be expected to take place in the times over which the PWHT and the creep exposures took place, although, as argued by Foret et al, 18 redistribution times may have been significantly affected by the kinetics of carbide dissolution.…”

“…It is proposed herein that this assumption is also applicable to the current case of relatively local inhomogeneities in substitutional element concentrations within the weld metal itself, which produces the diffusion of carbon and the dissolution of the carbides. 18 In the case of the white bands, the volumes of the alloydepleted regions from which the carbon is diffusing are small, resulting in rapid attainment of local equilibrium in carbon.…”

“…The presence of chromium leads to a reduction in carbon activity, and thus to carbon migration down the activity gradient towards the high chromium side during high temperature exposure, resulting in a carbon-depleted zone on the low chromium side and carbon-rich zone on the high chromium side. 18,[20][21][22][23][24] The activity coefficient of carbon c C in such a steel can be expressed by Wagner's relationship 25 c c~e xp e Cr C N Cr(eq) Â Ã c C does not depend on carbon concentration but it is only a function of the concentration of a substitutional element, which, in this case, is the chromium equivalent N Cr(eq) (at. fraction).…”

Mechanical Properties of Bimetallic Weld Joint Between Sa 516 Grade 65 Carbon Steel and Ss 304 L for Steam Generator Application

“…Thermal cycling in power plant operation during the numerous startups and shut-downs thus plays a major role in premature service failure of these joints [12][13]. These cyclic stresses superimposed on the residual welding stresses, external loads and internal steam pressures cause the ultimate service failure of the dissimilar joint [13,19,20]. The service life of the joint can be improved by reducing the magnitude of cyclic thermal stresses through a gradual change in thermal expansion coefficients of the joint components.…”