25cr-35ni ˘ˇ ˆ

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Page 1: 25Cr-35Ni ˘ˇ ˆ

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Microstructural Effect on the Weldability of 25Cr-35Ni Cast Steel

M. Shamanian and A. Saidi

Department of Materials Engineering, Isfahan University of Technology

Abstract: The 25Cr-35Ni heat resistant steel has been widely used when resistance to oxidation and creep rapture at elevated temperatures is required. In this paper, the microstructural effect on the weldability of this alloy is investigated. The results of this study indicate that this steel has a perfect weldability in the as cast condition but does not possess good weldability in the aged condition. The as cast microstructure of 25Cr-35Ni steel consists of austenite matrix and a network of primary carbides, while the aged condition consists of austenite matrix and y primary and secondary carbides. The morphological change of primary

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Page 2: 25Cr-35Ni ˘ˇ ˆ

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carbides and the secondary carbides precipitate formation, reducing the elongation and ductility of aged steel, should have enhanced the steel susceptibility to cracking, particularly in the area of the eutectic carbides, and hence, the reduced weldability of the steel. The cracking observed was of the intergranular type and spread along the eutectic carbides. It was found that the carbides in the as cast steel consisted of NbC and M23C6, whereas that of the aged steel also exhibited Ni16Nb6Si7 and M23C6carbides.

Keywords: 25Cr-35Ni cast steel, Weldability, Microstructure, As cast, Aged

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Page 3: 25Cr-35Ni ˘ˇ ˆ

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Page 4: 25Cr-35Ni ˘ˇ ˆ

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Page 5: 25Cr-35Ni ˘ˇ ˆ

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1. petrochemical 2. gas turbines 3. reformers 4. direct reduction processes 5. supersaturated matrix 6. as cast 7. aged

8. welding procedure specification (WPS)

9. American Society for Mechanical Engineering (ASME)

10. gas tungsten arc welding (GTAW)

11. direct current electrode negative (DCEN)

12. optical microscopy 13. scanning electron microscopy 14. energy dispersive spectrometer 15. secondary electron (SE) 16. backscattered electron (BE) 17. ductility

Page 10: 25Cr-35Ni ˘ˇ ˆ

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