For petroleum refinery plants, the material with high resistance to sensitization is required. 347AP has been developed for this application, which shows good sensitization resistance due to its low-C content. However, more improvement of high temperature strength is needed for high temperature operations in complex refineries, such as delayed coker. Recently, the new austenitic stainless steel (low-C-18Cr-11Ni-3Cu-Mo-Nb-B-N, UNS No. S34752) with high sensitization resistance and high strength at elevated temperature has been developed. In this study, the mechanical properties and microstructure of the several aged specimens will be reported. Conducting the several aging heat treatments in the range of 550 \~ 750 °C for 300 \~ 10,000 hours on the developed steel, it was revealed that there were only a few coarse precipitates presumed as sigma phase even after the aging at 750 °C for 10,000 hours. This indicates that the newly developed steel has the superior phase stability. The developed steel drastically increased its Vickers hardness by short term aging treatment. By TEM observation, the fine precipitates of copper rich phase was observed dispersedly in the specimen ruptured at 700°C for 144 hours. Therefore, the increase of Vickers hardness in short term aging is possibly due to the disperse precipitation of copper rich phase. There was also increase of Vickers hardness by Z phase precipitation, but the increment was smaller than that by Cu phase. Being attributed by these precipitates, the newly developed alloy has showed excellent creep rupture strength even in the long-term tests around 30,000 hours.


Mechanical Properties and Microstructure of the Newly Developed Steel (Low-C-18cr-11ni-3cu-Mo-Nb-B-N) After Aging Treatment

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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