Feng Han,Gu Yang,Song Zhigang,et al.The Effect of Isothermal Heat Treatment on the Microstructural Homogeneity and Mechanical Properties of 690 Alloy[J].Special Steel,2026,47(03):113-119.
Feng Han,Gu Yang,Song Zhigang,et al.The Effect of Isothermal Heat Treatment on the Microstructural Homogeneity and Mechanical Properties of 690 Alloy[J].Special Steel,2026,47(03):113-119. DOI: 10.20057/j.1003-8620.N250537.
The Effect of Isothermal Heat Treatment on the Microstructural Homogeneity and Mechanical Properties of 690 Alloy
In view of the complex service environment of the electrode in the Joule furnace for vitrification, to ensure the microstructural uniformity and performance stability of the 690 alloy electrode material, the effects of isothermal heat treatment temperatures (600 ℃, 800 ℃, 1 000 ℃, 1 100 ℃, and 1 200 ℃) on the microstructure including austenite grain size and carbide dissolution, as well as mechanical properties of the alloy were investigated using testing methods such as optical microscopy (OM), scanning electron microscopy (SEM), and room-temperature tensile test.The results show that the austenite grain size of the 690 alloy increases with the rise of temperature. From 600 ℃ to 1 000 ℃, the grain growth is slow, and the average grain size increases from 48.13 μm to 64.37 μm. At 1 100 ℃, the grains coarsen sharply, with the average size increasing to 225.21 μm, and further coarsening to 254.72 μm at 1 200 °C.The isothermal temperature significantly affects the composition, quantity, and distribution of the second phase. Between 600 ℃ and 800 ℃, a large number of second phases are distributed at the grain boundaries and within the grains of the alloy; the main phase at the grain boundaries is M₂₃C₆, while the dispersed granular second phases are a mixture of M₂₃C₆ and Ti(CN). When the temperature exceeds 1 000 ℃, the second phase at the grain boundaries basically disappears, and only a small amount of granular second phase remains in the matrix, and the titanium content decreases.Temperature variation mainly affects the tensile strength and reduction of area of the alloy. The tensile strength decreases with increasing temperature; when the temperature rises from 1 000 ℃ to 1 100 ℃, the tensile strength drops significantly from 638 MPa to 587 MPa, which is mainly attributed to the sharp coarsening of grains leading to a reduction in the grain refinement strengthening effect. The reduction of area shows a "first increase then decrease" trend, reaching a peak value of 78.5% at 1 000 ℃. This study provides an experimental basis for the optimization of the solution treatment process of the 690 alloy used in the electrodes of joule furnaces for vitrification.
Betova I , Bojinov M , Ikäläinen T , et al . Corrosion of alloy 690 in simulated steam generator crevices: Effect of applied potential, pH and Pb addition [J]. Journal of the Electrochemical Society , 2022 , 169 ( 2 ): 021502 .
Kuang W J , Was G S . The effect of grain boundary structure on the intergranular degradation behavior of solution annealed alloy 690 in high temperature, hydrogenated water [J]. Acta Materialia , 2020 , 182 : 120 - 130 .
Zhao X , Wang M , Hao X C , et al . Precipitation of dendritic M23C6 carbides in alloy 690 during continuous cooling [J]. Journal of Alloys and Compounds , 2021 , 851 : 156694 .
Kuo T Y , Lee H T . Effects of filler metal composition on joining properties of alloy 690 weldments [J]. Materials Science and Engineering: A , 2002 , 338 ( 1-2 ): 202 - 212 .
Jiang X , Di X J , Li C N , et al . Improvement of mechanical properties and corrosion resistance for wire arc additive manufactured nickel alloy 690 by adding TiC particles [J]. Journal of Alloys and Compounds , 2022 , 928 : 167198 .
Zener C . Grains, phases, and interfaces: An interpretation of microstructure [J]. metals technology , 1948 , 175 : 15 - 51 .
Hillert M . On the theory of normal and abnormal grain growth [J]. Acta Metallurgica , 1965 , 13 ( 3 ): 227 - 238 .
Gladman T . On the theory of the effect of precipitate particles on grain growth in metals [J]. Proceedings of the Royal Society of London Series A Mathematical and Physical Sciences , 1966 , 294 ( 1438 ): 298 - 309 .
Zhang J S , Li G Q , Wang H H , et al . Achieving superior cryogenic impact toughness and sufficient tensile properties in a novel high-Mn austenitic steel weld metal via cerium addition [J]. Journal of Materials Research and Technology , 2023 , 23 : 5016 - 5030 .