Ductile-to-Brittle Transition and Impact Fracture Behavior of 3Mn–Si–Ni Low Carbon Martensitic Steel

Impact behavior related to crack initiation and growth of low carbon martensitic 3Mn–Si–Ni steel was investigated by instrumented impact Charpy V-notch tests. Load–displacement curves were acquired, so significant characteristic load parameters and impact absorbed energies in different fracture phases from 20~(−70)°C were determined. The ductile–brittle transition temperature (DBTT) was also investigated and the corresponding fractograph was obtained. The DBTT of the 3Mn–Si–Ni steel is −50°C. With the temperature decreased from 20 to −70°C, the maximum force F m increases and the difference between the F m and the crack stable propagation initial force F iu decreases. Higher force was used to trigger the crack and tended to be brittle fracture at lower temperature, such as −50 and −70°C. Also once the crack initiated, it will extend rapidly until fracture when the tested steel serves at very low temperature, especially below −20°C. With the impact temperature decreasing to −70°C, the crack unstable growth final force F a decreased to nearly zero and there isn’t distinct secondary fiber area.