TEM Image Analysis of Fracture Surfaces of P91 Steel and Comparison with Mechanical Properties

Abstract

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).