In order to improve the efficiency of steam boilers in modern power plants, engineers have to use contemporary materials that enable exploitation at higher parameters, primarily operating temperature and pressure, with resistance to different forms of corrosion at the same time. For that purpose, contemporary 9-12Cr martensitic steels, designated P91, P92, E911, VM12-SHC, and SHM12, were developed.
The paper analyzes experimental research on the behavior of commercial ferritic steel P91 samples. Behavior data on the heat affect zone (HAZ) of welded joints were obtained by testing smooth specimens produced by simulation of the new material welding. A survey of testing hardness and tensile properties is given and images of the fracture surfaces of the samples were processed. Image analysis with ImagePro Plus confirmed experimental testing results for the grain size measured by the circle method and a comparative relationship between the percentage of carbides, precipitates, and lamellar diameters with respect to temperature is provided. The material that was PWHT (post-weld heat treatment) has the highest mean value of lamellar diameter, which indicates increased toughness and decreased hardness compared to BM and material without PWHT i.e (The higher lamellar diameter, the smaller material hardness).
This research will show the analytical way of determining the remaining life of a welded joint with a fatigue crack initiated in its heat affected zone. The calculation will be divided into two stages, since the fatigue crack propagated through the heat affected zone, and then through the parent material. The analysis will be related to specimens with different fatigue properties taken into account for both regions. These calculations included a number of models, since different crack lengths were used for the heat affected zone and the parent material. There were three pairs of different HAZ vs PM fatigue crack lengths, always with the assumption that the total crack length is 5 mm, due to measuring range of the used measuring foils. The aim of this analysis was to apply method typically used in fracture mechanics in order to determine the number of cycles in a welded joint with an initiated fatigue crack, depending on a number of parameters. Obtained results were then compared to the results from the numerical analysis for the same cases. While the total number of cycles was mostly unaffected by these changes, some noticeable differences were observed between individual welded joint regions in question, the heat affected zone and the parent material.
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