Microstructure and mechanical properties of 9Cr heat-resistant steel strengthened by TiC nanoparticles

doi:10.13251/j.issn.0254-6051.2025.01.029

Abstract

Abstract: In order to improve the high temperature strength of heat-resistant steel for steam turbine, 9Cr heat-resistant steels with different contents of TiC nanoparticles (mass fraction of 0%, 0.01%, 0.05% and 0.1%) were prepared. The microstructure of the tested steel with 0.01%TiC nanoparticles was analyzed by using high temperature laser scanning confocal microscopy (LSCM), optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the mechanical properties were studied by tensile and impact tests. The results show that the addition of TiC nanoparticles can significantly enhance the high-temperature strength at 600 ℃ of the 9Cr heat-resistant steel, and when the addition amount is 0.01%, the maximum tensile strength is 356 MPa, and the strain at fracture is 38%. The martensite structure is obtained for the tested steel with 0.01% TiC nanoparticles under air-cooling conditions, the second-phase carbide category is M₆C, and the distribution of TiC nanoparticles in the grains plays a role in dispersive strengthening. The tested steel with an addition of 0.01%TiC nanoparticles has excellent comprehensive mechanical properties after annealing at 1040 ℃+normalizing at 990 ℃+tempering at 740 ℃, with the hardness, tensile strength, yield strength, elongation and reduction of area of 177 HBS, 734 MPa, 538 MPa, 15.45% and 31.15%, respectively, and a large number of dimples are observed in the tensile fracture, indicating ductile fracture. The impact absorbed energy at room temperature is 116 J, and the ductile-brittle transition temperature FATT₅₀ is -15 ℃.

Key words: nanoparticle strengthening, 9Cr heat-resistant steel, steam turbine, microstructure, mechanical properties

CLC Number:

TG142.4

Zhu Xiaolong, Wang Zhenghui, Wang Wenyan, Xie Jingpei, Diao Xiaogang, Zhang Feiyang. Microstructure and mechanical properties of 9Cr heat-resistant steel strengthened by TiC nanoparticles[J]. Heat Treatment of Metals, 2025, 50(1): 187-194.

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