Abstract
In this study, the fracture mechanisms of S355 ferritic steel were analyzed. In order to obtain different mechanisms of fracture (completely brittle, mixed brittle and ductile or completely ductile), tests were carried out over a temperature range of −120 to +20 °C. Our experimental research was supplemented with scanning electron microscopy (SEM) observations of the specimens’ fracture surfaces. Modeling and load simulations of specimens were performed using the finite element method (FEM) in the ABAQUS program, and accurate calibration of the true stress–strain material dependence was made. In addition, the development of mechanical fields before the crack tip of the cracking process in the steel was analyzed. The distributions of stresses and strains in the local area before the crack front were determined for specimens fractured according to different mechanisms. Finally, the conditions and characteristic values of stresses and strains which caused different mechanisms of fracture—fully brittle, mixed brittle and ductile or fully ductile—were determined.
Highlights
Structural elements made of ferritic steel are commonly used in various types of structures and mechanisms over a wide range of temperatures
Brittle cleavage fracture occurred (Figure 2b) in the ferritic steel specimens at temperatures corresponding the lower plateau of the brittle-to-ductile transition dependence
Brittle cleavage fracture (Figure ferritic steel specimens at temperatures heat-resistant ferritic steelsoccurred operated for a long2b) timeininthe high temperatures (e.g., 14MoV6-3, 14MoV69, DIN Standard), an increase time of the transition elements can result in a significant
Summary
Structural elements made of ferritic steel are commonly used in various types of structures and mechanisms over a wide range of temperatures. In order to design them correctly and ensure their safe operation, it is essential to provide information on strength characteristics and fracture toughness of the material within the range of service temperatures. Modern technologies of production and inspection do not allow the presence of crack-type defects in newly manufactured components. During long-term operation in conditions of cyclic loads and environmental impact, cracks in the elements may arise and develop from microstructural defects (e.g., from particles of large inclusions) [1,2]. A high risk of initiation and development of cracks in a component is found when inclusions are grouped in one plane, which leads to the development of internal delamination cracks [3,4,5,6]. Defects in the form of cracks often occur in welded joints as well [7,8]
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