PSI - Issue 69

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

118

continuously with rising solid-solution temperature. The yield strength (YS) initially increases, but a noticeable decline is observed above 900 °C. The total elongation (TE) and impact toughness ( Akv 2 ) both increase with solid solution temperature below 900 °C. Beyond 900 °C, TE remains nearly constant, while Akv 2 gradually decreases. At a solid-solution temperature of 900 °C, the quenched samples exhibit optimal comprehensive properties, with YS, UTS, TE, and Akv 2 values of 1332 ± 7 MPa, 1983 ± 2 MPa, 12.1 ± 0.42%, and 34 ± 1 J, respectively. In the aged condition, the effects of solid-solution temperature on the tensile and impact properties are consistent with those observed in the quenched condition. However, compared to the quenched samples, the aged samples exhibit significantly higher YS, UTS, and TE, while Akv 2 is markedly reduced. These changes are likely associated with the precipitation of M 2 C carbides and NiAl particles during aging, the formation of which has been demonstrated in similar steels[8, 10] and our prior studies[12, 13]. Although the precipitates enhance strength through precipitation strengthening, they simultaneously impede dislocation motion, reducing dislocation mobility and significantly deteriorating toughness. Although this enhances strength, it also reduces dislocation mobility, leading to a decline in toughness. Among the aged samples, those treated at a solid-solution temperature of 900 °C achieve the best strength toughness balance, with YS, UTS, TE, and Akv 2 values of 1875 ± 4 MPa, 2185 ± 3 MPa, 13.84 ± 0.4%, and 16.2 ± 0.8 J, respectively.

Fig. 6 The mechanical properties of the (a, b) quenched samples at different temperatures and (c, d) aged samples: (a, c) tensile properties; (b,d) impact properties.

Based on the above microstructural characterization, as the solid-solution temperature increases, although there is a slight increase in the retained austenite content in the quenched steel, its content remains around 2.0 vol.% (Fig. 3), which has a negligible impact on both strength and toughness. A qualitative analysis based on the Hall-Petch relationship reveals that the increased grain size leads to reduced strengthening. Below 900 °C, although the PAGs increases, the YS does not decrease. Specifically, in the aged condition, the YS actually increases, which is likely related to the dissolution of the primary M 7 C 3 carbides (Fig. 4). In the quenched condition, with increasing solid solution temperature, the dissolution of M 7 C 3 carbides results in reduced precipitation strengthening, but the carbon