In engineering applications, steels are commonly used in various areas. The mechanical members are exposed to different loading conditions and this subject can be investigated in fracture mechanics. Fracture toughness (KIC) is the important material property for fracture mechanics. Determination of this properties is possible using a compact tension specimen, a single edge notched bend or three-point loaded bend specimen, which are standardized by different institutions. Researchers underline that these standardized methods are complex, the manufacturing process is difficult, they require special fixtures for loading during the experiment and the test procedures are time consuming. Alternative methods are always being sought by researchers. In this work, two different approaches are investigated for S355 steels. In the first method, a circumferentially cracked round bar was loaded in tensile mode and pulled till failure. Using suitable equations, fracture toughness can be calculated. In the second method, a circumferentially notched bar specimen without fatigue pre-cracking was loaded in a tensile machine. By means of fracture load values, fracture toughness was determined by the proposed equations. It can be stated that these two different approaches for calculating fracture toughness are simple, fast and economical.

Fracture toughness determination of dual-phase DP450 steel using the essential work of fracture (EWF) methodology is the major focus of this research work. The EWF method is used for the determination of fracture toughness of thin sheets in a plane stress dominant condition. The EWF method is discussed in detail with the help of DP450 steel experimental results. Double edge notched tension (DENT) specimens with fatigue pre-crack and without fatigue crack (notched) have been used for testing. Specific essential work of fracture (w_e), crack tip opening displacement (${\delta }_c^e$) and crack tip opening angle (${\psi }^e$) parameters were used for the comparative analysis. High-intensity laser beam cutting technology was used for the preparation of notches. Fracture toughness values of fatigue pre-cracked and notched samples were compared. The effect of notch tip radius and fatigue crack on the fracture toughness values were analysed. Digital image correlation (DIC) technology was used for the identification of local strain distribution and validation of the methodology. Fractured surfaces were examined by a scanning electron microscope (SEM) to analyse the fracture morphology and stress state.

Thermomechanically processed high-strength steels feature specific fracture behavior. One of the decisive criteria for their application is their stability against internal defects during impact loads, especially in connection with the welding. The work is focused on experimental analyses of the influence of welding on static and dynamic fracture toughness of Strenx 700MC steel. The fracture toughness was determined using the circumferentially notched round bar specimens during static loads and two dynamic load levels. To achieve a homogeneous zone for the requirements of fracture toughness tests, simulation of the welding influence was performed. Fractographic and metallographic analyses described a specific fracture behavior controlled by the internal structural heterogeneity. A limiting degradation process due to welding was identified by the microstructural analysis.

En tr Boron steels are increasingly used material especially in industrial applications requiring high wear resistance. The main area of usage of this type of steel is tillage tools which are working in harsh conditions. In addition to the abrasive wear resistance, impact toughness is also required properties. In this study, the effect of cryogenic treatment on 30MnB5 boron steel used in agricultural mechanization is investigated in terms of the tribological and mechanical properties. Charpy impact test, the hardness and the abrasive wear tests are performed on untreated, heat treated and cryogenically treated of 30MnB5 steel. It is observed that the hardness of the specimen is slightly decreased but impact toughness is increased for the quenched and cryo treated specimen in comparison to conventionally heat-treated specimen. The usage amounts of boron steels are increasing gradually, especially in industrial applications requiring high wear resistance. One of the usages of this type of steel is tillage tools, which are working in harsh conditions. Prominent desired properties for materials that face the soil in agricultural machining are hardness, abrasive wear resistance, impact toughness. In this study, the tribological and mechanical properties of 30MnB5 boron steel used in agricultural mechanization are investigated, applying three different heat treatment procedures. The impact strength, hardness and abrasive wear resistance of the as supplied, quenched and quenched cryo treated-tempered samples are evaluated. It was observed that the quenching is an essential heat treatment for usage of boron steel in agricultural field. The tempering reduces hardness of the specimen and cyrogenic treatment and tempering increased the impact toughness.