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Effect of heat treatment and cooling rate on microstructure and properties of T92 welded joint

Ma Chengyong, Wu Zhiquan, Qi Yanchang, Zhang Xin

Materials Science Poland

2023

Vol. 41, No. 1

124--139

The effects of heat treatment and cooling rate on the microstructure and properties of T92 welded joints were studied. Under the same tempering holding time, the diffusion ability in the deposited metal increased as the tempering temperature increased. The phase-change temperature was lower than the AC1 points. In the 5-20s range of t8/5, the deposited metal toughness decreased as the cooling rate increased. When the t8/5 was equal to 70s, the toughness increased and the hardness decreased. The higher heat input induced coarse grain tendency. The lower welding heat input should be used in conjunction with the reasonable post-weld heat treatment.

Weld defects and precipitates of deposited metal in 9Ni steel welded joint

Ma Chengyong, Qi Yanchang, Zhang Yuqing, Wu Zhiquan, Zhang Xin

Materials Science Poland

2022

Vol. 40, No. 1

25--48

Three kinds of electrode with different niobium contents were developed and compared, and the influence of alloying elements on microstructure and mechanical properties was summarized. Strong carbide elements such as Nb, Ti, and V were added to form stable precipitates. The existence of intercrystalline precipitates leads to pinning and zigzag of grain boundaries, hinders the propagation of cracks, and enhances the low temperature strength and impact toughness of the materials. The No. 1 and No. 2 ENiCrMo-6 electrodes meet the requirements of LNG (liquified natural gas) equipment. The tensile strength of the deposited metal reaches 687 MPa, while the average impact energy at −196°C is 131 J. Owing to fluctuations in the stress concentration at the junction of grain boundaries, cracks may easily form. MC carbide can retard the crack propagation. With the increase of Nb and other alloys, the strength and hardness increase gradually, but the plasticity and toughness are retarded to a certain extent.