PSI - Issue 69

Haofei Zhu et al. / Procedia Structural Integrity 69 (2025) 113–120

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that is released during dissolution re-enters the martensite, thereby enhancing solid-solution strengthening. As a result, when the quenching temperature increases from 870 °C to 900 °C, the marginal variation in yield strength may be attributed to a balanced competition between two strengthening mechanisms (precipitation and solid-solution strengthening). In the aged condition, the carbon that re-enters the matrix precipitates as fine M 2 C carbides [4], which, compared to the coarse M 7 C 3 carbides, provide a significant precipitation strengthening effect. Consequently, when the solid-solution treatment temperature increases from 870 °C to 900 °C, the YS of the aged samples increases. Above 900 °C, the M 7 C 3 carbides completely dissolve, and the PAGs increases significantly (Fig. 2 and Fig. 4), which leads to a rapid decrease in YS for both the quenched and aged states. Additionally, the impact toughness is closely related to the presence of M 7 C 3 carbides and the PAGs. Under impact loading, the large amount of M 7 C 3 initial carbides in the samples treated at 870 °C (both quenched and aged) causes stress concentration and initiates crack nucleation, resulting in poor toughness. For samples solid-solution treated above 900 °C, the dissolution of M 7 C 3 carbides significantly improves toughness. However, when the solution temperature exceeds 900 °C, the PAG coarsen significantly, leading to a reduction in high-angle grain boundary fraction. This reduces the ability to suppress crack propagation, slightly decreasing toughness[14]. Therefore, due to the superior strength-toughness balance, a solid-solution temperature of 900 °C is considered optimal. 4. Conclusions As the solid-solution temperature increases, the content of retained austenite slightly increases, but its impact on strength and toughness of the steel is minimal. At the same time, the dissolution of M 7 C 3 carbides contributes to the improvement of both strength and toughness. However, the coarsening of the prior austenite grain size has an adverse effect on both strength and toughness. Under the combined influence of these two factors, the solid-solution treatment at 900 °C results in an optimal strength-toughness balance for both quenched and aged states. In the quenched condition, the steel achieves YS of 1332 ± 7 MPa, UTS of 1983 ± 2 MPa, TE of 12.1 ± 0.42%, and Akv 2 of 34 ± 1 J. In the aged condition, the corresponding values are YS of 1875 ± 4 MPa, UTS of 2185 ± 3 MPa, TE of 13.84 ± 0.4%, and Akv 2 of 16.2 ± 0.8 J. Data availability Data will be made available on request.