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<p>This paper presents the results of comprehensive experimental studies to determine the energy characteristics of fracture at crack initiation and propagation in three types of specimens: standard Charpy, side-grooved, and small-sized specimens cut in three mutually perpendicular directions from a 15Kh2NMFA-A steel forging during impact bending tests. The tests were conducted on an instrumented vertical impact testing machine equipped with a high‑rate data‑acquisition system over the temperature range T = –100…150°C. From the tests, load–time diagrams were obtained, and the total deformation and fracture energy, as well as its components, were calculated: the energies of crack initiation, ductile growth, brittle propagation, and final ductile fracture of the specimen. Using quantitative fractography, we examined the fracture surfaces of specimens and determined the specific deformation and fracture energies, as well as their components. It is demonstrated that the cutting direction has a significant impact on the energy characteristics of fracture. Tests on the different specimen types show that the cutting direction affects the mechanism of side contraction formation of both standard Charpy specimens and small‑sized specimens, and that the value of deformation and fracture energy is influenced by the ductile‑fracture mechanism both in the side contraction zone and in the final‑fracture zone. The use of a high‑rate data‑acquisition system makes it possible to determine the average crack‑propagation rate and its local rate in separate intervals by correlating the corresponding zones on the load–time diagram with those on the fracture surface of specimens. It is shown that, for side‑grooved specimens, the propagation rate of a brittle crack is significantly higher than in other specimens and varies within 816–182 m/s. The propagation rate of a ductile crack is 0.6–130 m/s for Charpy specimens, 0.6–11 m/s for small‑sized specimens, and 6.2–21 m/s for side‑grooved specimens. Based on experimental studies and fractographic analysis using scanning electron microscopy, the fracture mechanisms and features of crack propagation in side‑grooved specimens were identified. The increase in the fracture energy of the specimens in the <i>Y</i> direction (<i>xOz</i> plane) is associated with microstructural heterogeneity that arose during thermomechanical processing of the steel.</p>

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Scale Factor and Stress State Type Effects on Energy Characteristics of 15Kh2NMFA-A Steel in Impact Bending Tests Considering Anisotropy

  • 期刊论文

  • 发表日期：

    2025年9月1日

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  • A. V. Kravchuk,
  • E. O. Kondryakov,
  • V. V. Kharchenko,
  • H. V. Chyzhyk

摘要

This paper presents the results of comprehensive experimental studies to determine the energy characteristics of fracture at crack initiation and propagation in three types of specimens: standard Charpy, side-grooved, and small-sized specimens cut in three mutually perpendicular directions from a 15Kh2NMFA-A steel forging during impact bending tests. The tests were conducted on an instrumented vertical impact testing machine equipped with a high‑rate data‑acquisition system over the temperature range T = –100…150°C. From the tests, load–time diagrams were obtained, and the total deformation and fracture energy, as well as its components, were calculated: the energies of crack initiation, ductile growth, brittle propagation, and final ductile fracture of the specimen. Using quantitative fractography, we examined the fracture surfaces of specimens and determined the specific deformation and fracture energies, as well as their components. It is demonstrated that the cutting direction has a significant impact on the energy characteristics of fracture. Tests on the different specimen types show that the cutting direction affects the mechanism of side contraction formation of both standard Charpy specimens and small‑sized specimens, and that the value of deformation and fracture energy is influenced by the ductile‑fracture mechanism both in the side contraction zone and in the final‑fracture zone. The use of a high‑rate data‑acquisition system makes it possible to determine the average crack‑propagation rate and its local rate in separate intervals by correlating the corresponding zones on the load–time diagram with those on the fracture surface of specimens. It is shown that, for side‑grooved specimens, the propagation rate of a brittle crack is significantly higher than in other specimens and varies within 816–182 m/s. The propagation rate of a ductile crack is 0.6–130 m/s for Charpy specimens, 0.6–11 m/s for small‑sized specimens, and 6.2–21 m/s for side‑grooved specimens. Based on experimental studies and fractographic analysis using scanning electron microscopy, the fracture mechanisms and features of crack propagation in side‑grooved specimens were identified. The increase in the fracture energy of the specimens in the Y direction (xOz plane) is associated with microstructural heterogeneity that arose during thermomechanical processing of the steel.