INVESTIGATION IN HARDSURFACING A NICKEL-COPPER ALLOY (MONEL400).

CZAJKOWSKI,C. ; BUTTERS,M.

Brookhaven National Laboratory

关键词: Monel;    Alloys;    36 Materials Science;    Electron Microscopes;    Stellite 6;   

DOI  :  10.2172/791763
RP-ID  :  BNL--52651
RP-ID  :  AC02-98CH10886
RP-ID  :  791763

美国|英语

来源: UNT Digital Library

【 摘 要 】

Brookhaven National Laboratory (BNL) investigated the causes of weldability problems and materials failures encountered with the application of Monel (Ni-Cu) 400 as a base material and Stellite 6 (Co-Cr) as the hard-surfacing material when using the oxyacetylene welding process. This work was performed under a cooperative research and development agreement (CRADA) with the Target Rock Division of the Curtiss-Wright Flow Control Corporation. BNL evaluated two heats of Monel 400 material. One of the heats had performed well during manufacturing, producing an acceptable number of ''good'' parts. The second heat had produced some good parts but also exhibited a peculiar type of hardsurfacing/base metal collapse during the welding process. A review of the chemistry on the two heats of material indicated that they both met the chemical requirements for Monel400. During examination of the failed component, linear indications (cracks) were evident on the valve body, both on the circumferential area (top of valve body) and below the hard surfaced weld deposit. independent measurements also indicated that the two heats met the specification requirement for the material. The heat affected zone (HAZ) also contained linear discontinuities. The valve body was welded using the oxyacetylene welding process, a qualified and skilled welder, and had been given a pre-heat of between 1400-1600 F (760-871 C), which is the Target Rock qualified procedure requirement. Both original suppliers performed mechanical testing on their material that indicated the two heats also met the mechanical property requirements of the specification. The BNL investigation into the cause of the differences between these heats of material utilized the following techniques: (1) Heat Treatment of both heats of material; (2) Hardness testing; (3) Optical microscopy; (4) Scanning electron microscope (SEM)/Fractography; and (5) Energy dispersive spectroscopy (EDS). The report concludes that the cause of the failure of the valve body during welding is not obvious, however, it does not appear to be a welding issue. The observed inter-granular fractures indicate a grain boundary problem. Further research is recommended.