Mechanism of High Temperature Stability on Microstructures of 25Cr35NiNb Alloy Prepared by Laser Additive Manufacturing

The performance of static casting 25Cr35NiNb alloy pipe fittings with complex shapes for ethylene cracking furnace is insufficient, which affects the safe operation of equipment, and becomes an urgent problem to be solved in this field. Laser additive manufacturing (LAM) technique is suitable for the fabrication of complex components with high performance. 25Cr35NiNb alloy prepared by LAM is different from that prepared by static casting or centrifugal casting due to the solidification with the cooling rate of 102∼105 K/s in a tiny molten pool. In order to fabricate complex pipe fittings by LAM, the performance of 25Cr35NiNb alloy prepared by LAM needs to be clarified and the mechanism also needs to be revealed. This paper focuses on the mechanism of high temperature stability on microstructures of 25Cr35NiNb alloy prepared by LAM. Firstly, two kinds of 25Cr35NiNb alloy deposits were prepared by LAM with different processing parameters. Secondly, heat treatments were executed in the temperature range from 850°C to 1275°C for 25Cr35NiNb alloy deposits. Then, the microstructures of 25Cr35NiNb alloy were observed by optical microscope (OM) and scanning electron microscopy (SEM). It is found that the finer the microstructures of the original deposits was, the better the high temperature stability of microstructures was. The results of electron probe microanalysis (EPMA) show that the distribution of Nb and Ti elements in the original deposits affects the high temperature stability of microstructures. The finer microstructure has the more uniform distribution of Nb and Ti elements, which improves the high temperature microstructural stability.