Fracture Energy Characteristics of High-Strength Steels Hardox 450 and Armox 500T Under Impact Bending

• Published in: Strength of materials 2022-11, Vol.54 (6), p.1009-1018
• Main Authors: Kravchuk, A. V., Kondryakov, E. O., Kharchenko, V. V.
• Format: Article
• Language: English
• Subjects: Abrasion resistant steels; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Crack initiation; Crack propagation; Data recording; Deformation; Ductile fracture; Ductile-brittle transition; Energy; Energy value; Fracture surfaces; High speed; High strength steels; Impact loads; Impact strength; Materials Science; Nucleation; Propagation; Propagation velocity; Solid Mechanics; Steel, High strength; Velocity
• ISSN: 0039-2316; 1573-9325
• DOI: 10.1007/s11223-023-00476-w

The processes of impact loading have been studied for a long time, but there are still many questions, the solution of which is vital for various industries, especially for the military. This paper presents the results of comprehensive experimental studies to determine the energy characteristics of fracture during crack initiation and propagation in Charpy specimens of high-strength steel Hardox 450 and armored steel Armox 500T, cut from sheets in two different directions, during impact bending tests. The tests were carried out on an instrumented vertical tester equipped with a high-speed data recording system in the temperature range from –196 to 300 °C. According to the test results, the load diagrams in the force-time coordinates were obtained. The total deformation and fracture energy and its components, nucleation energy, ductile growth, brittle crack slip, and ductile fracture energy of the specimen were calculated. Using quantitative fractography methods, the specimens’ fracture surfaces were studied, and the specific deformation and fracture energies and their components were determined. It is shown that the direction of cutting of specimens significantly affects the energy characteristics of fracture. On the upper shelf in the specimens cut in the longitudinal direction, the energy value is higher than for the transverse direction for both steels. This difference is approximately 38% for Hardox 450 and almost 118% for Armox 500T. Using a high-speed recording system allows us to determine the average crack propagation velocity and crack velocities in separate areas by comparing the corresponding zones on the load diagram and on the fracture surface of the specimens. The results showed that the average crack propagation velocity for specimens cut in the transverse direction was 10–15% higher than for specimens cut in the longitudinal direction for both steels.