X-ray-based measurement of composition during electron beam melting of AISI 316 stainless steel: Part I. Experimental se
- PDF / 316,781 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 41 Downloads / 151 Views
I. INTRODUCTION ELECTRON beam (EB) melting has emerged as an increasingly important method for producing specialty metals for high-performance applications. The combination of high vacuum, good control over the input power distribution, and relatively quiescent bath make the EB melting process well suited for the removal of low- and high-density inclusions. Removal of low- and high-density inclusions is critical in applications requiring good fatigue performance. Moreover, the EB melting process is versatile because high-quality alloy products can be produced from a variety of feeds (ranging from steel ingots to titanium scrap or sponge). Unfortunately, the high evaporation rates present during EB melting, which accelerate the removal of undesirable volatile elements such as hydrogen, nitrogen, and suboxides, can also lead to difficulties in maintaining compositional control of high vapor pressure alloying elements, such as aluminum in titanium alloys. To help overcome this shortcoming, accurate on-line composition measurement is needed to reduce and potentially eliminate composition related rejections. Furthermore, the capacity to have continuous on-line reading of alloy composition eliminates uncertainty as to the uniformity of the final ingot composition. The possibility of using the X-rays generated by the highpower electron beam when it interacts with the molten liquid
M. RITCHIE, Engineer and Technical Sales Specialist, is with North American Pipe and Steel, Delta, BC, Canada V4H 1B9. S.L. COCKCROFT, Associate Professor and Head, and A. MITCHELL, Emeritus Professor, are with the Department of Metals and Materials Engineering, University of British Columbia, Vancouver, BC, Canada V6T 1Z4. P.D. LEE, Senior Lecturer, is with the Department of Materials, Imperial College, London, United Kingdom SW7 2BP. Contact e-mail: [email protected] T. WANG, Development Engineering, is with Alstom Ltd., 5401 Baden, Switzerland. Manuscript submitted December 4, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS A
for in-situ compositional analysis has been investigated in this study. The method presents some unique challenges. The beam size and energy density in the melting process are both several orders of magnitude larger than those used in conventional energy dispersive X-ray (EDX) or wavelength dispersive X-ray (WDS) analysis, leading to an X-ray density, which is far too high for satisfactory analysis unless suitably attenuated. In addition, the detector/collimator/ attenuator system has to operate in a hostile environment, where it is exposed to high thermal radiation and vapor condensation reactions. And, since the melting chamber is necessarily much larger than that of the conventional EDX/ WDS analysis instruments, there is also the additional difficulty of a detector/collimator arrangement, which must be suitably focused at the beam target area over 1 m distant from the detector. In Part I, the design and construction of the attenuation/collimation and protection systems are described. The results from a series of expe
Data Loading...
