Evaluation of the C* Parameter in Welded Joints of 9%Cr Steels Under Consideration of the Heat Affected Zone

In fracture mechanics based component assessment of parts containing microstructural defects subjected to elevated temperatures, the C* parameter is a common choice for describing the crack tip loading under steady-state creep conditions. Welded joints of ferritic-martensitic 9%Cr steels, commonly used in applications of up to 650°C operation temperature, comprise a rather complex and inhomogeneous microstructure in the heat affected zone, with wildly differing creep properties in comparison to the base materials. Therefore, the influence of the inhomogeneous material must be considered carefully when calculating C*. This paper is subjected to the evaluation of the C* parameter in compact tension fracture mechanics specimens for a welded joint made from two different 9%Cr steels with an additional buttering. Based on finite element simulations, different methods for calculating C* are assessed. It is shown that the application of methods disregarding the properties of the heat affecting zone leads to erroneous results.