The work aims to clarify the changes in mechanical properties of low activation martensitic (CLAM) steel strengthened by deformation heat treatment during high-temperature long-term service, and to study the microstructure evolution mechanism of CLAM steel strengthened by deformation heat treatment during high-temperature long-term thermal exposure. High-temperature long-term heat exposure tests were conducted on materials with a muffle furnace at different temperature (600 ℃, 650 ℃) and duration (1 100 h, 2 100 h). The microstructure of CLAM steel before and after thermal exposure was characterized and analyzed by OM, XRD, SEM, and TEM, and the changes in hardness were analyzed with a microhardness tester. As a result, with the extension of heat exposure duration and the increase of temperature, the deformation heat treatment strengthened CLAM steel showed a slight increase in grain size, an increase in precipitation phase size, a decrease in dislocation density, and other microstructural evolution laws,, accompanied by a decrease in hardness. Taking the 650 ℃-2 100 h heat exposure with the largest change amplitude as an example, the size of the M23C6 phase in CLAM steel increased by 65.8 nm, the size of the MX phase increased by 9.29 nm, the dislocation density decreased by 17.2%, and the hardness value decreased by 7.05%. However, as the CLAM steel after deformation heat treatment played a pinning role by precipitating excessive fine MX phases, the lath structure and some dislocations were well retained during the high temperature heat exposure process, which slowed down the decline rate of hardness and achieved a certain strengthening effect. In conclusion, the microstructure of CLAM steel strengthened by deformation heat treatment undergoes a certain degree of degradation during long-term high-temperature thermal exposure. However, the stability of the microstructure of the material under high-temperature thermal exposure is improved by the precipitation strengthening effect enhanced by deformation heat treatment.
Key words
CLAM steel /
high-temperature long-term thermal exposure /
deformation heat treatment /
microstructure /
hardness
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Funding
Guizhou Provincial Natural Science Foundation (ZK[2022]023, [2020]1Z046); Guizhou Provincial Science and Technology Plan ([2023]270)
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