Issue 36

F. Z. Liu et alii, Frattura ed Integrità Strutturale, 36 (2016) 139-150; DOI: 10.3221/IGF-ESIS.36.14 149 10 -7 , D 3 = 2.66 × 10 -7 and D 4 = 2.31 × 10 -7 cm 2 /s. Obviously, with the increase of tempering temperature, diffusion coefficients of experimental materials would decrease. To sum up, as for the improved Mn-B steel plate (1500 MPa), the delay fracture resistance of experimental material in quenching state is the lowest, but tempering processing can significantly enhance the delay crack resistance. The delay fracture resistance of the materials processed at 200 °C tempering temperature was the highest on the condition that the strength of experimental materials decreased slightly. When tempering temperature was too high, for example, 400 °C, then diffusion coefficient of hydrogen at room temperature was weakened due to the significant decrease of the strength, but the resistance was still high than that of materials processed by quenching. With the increase of tempering temperature, the diffusion coefficient of hydrogen at room temperature decreased. The content of non-diffusible hydrogen of experimental materials in corrosive fluid under critical stress showed an obvious improvement after loading. The quantity of hydrogen bearing by the samples in quenching state under critical stress was the lowest, while the quantity of hydrogen of the samples processed at 200 °C tempering temperature was the highest. Under the effect of critical stress and after 100-h loading in corrosive liquid, the content of hydrogen in samples showed a remarkable increase; besides, the quantity of hydrogen processed by heat forming was higher than that of samples processed by quenching and samples processed by quenching and 100 °C tempering, leading to the high delay fracture resistance. Hence, hot forming processing can ensure a high delay fracture resistance of experimental materials and tempering processing can further improve the delay fracture resistance of experimental materials. R EFERENCES [1] Koyama, M., Akiyama, E., Tsuzaki, K., Hydrogen-induced delayed fracture of a Fe–22Mn–0.6C steel pre-strained at different strain rates. Scripta Materialia, 66(11) (2012) 947-950. [2] Zhang, C. L., Liu, Y. Z., Chao, J., et al. Effects of Niobium and Vanadium on Hydrogen-Induced Delayed Fracture in High Strength Spring Stee l. Journal of Iron & Steel Research International, 18(6) (2011) 49-53. [3] Zhang, S., Huang, Y., Sun, B., et al. Effect of Nb on hydrogen-induced delayed fracture in high strength hot stamping steels. Materials Science & Engineering A, 626 (2015) 136-143. [4] Ogata, T., Evaluation of Hydrogen Embrittlement by Internal High-Pressure Hydrogen Environment in Specimen. Journal of the Japan Institute of Metals, 72(2) (2008) 125-131. [5] Araújo, B. 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