STUDY OF HEAT-RESISTING STEEL (XIII)

Abstract

The precipitated particles were determined by means of X-ray diffraction, electronic microscope, chemical analysis, and selective etching for both of regular 16-25-6 alloy and 16-25-6 alloy containing Ti. Samples for X-ray diffraction test and for an electronic microscope were extracted from aged specimens by electrolytic decomposition in 3% HCl solution. For X-ray diffraction test, there were two methods. One applied the usual X-ray diffraction tester using photograph film, and another used a tester which measured the diffraction and intensity automatically with Geiger counters. The author's data were compared with the known carabides crystallographic data (from ASM Diffaction Data Cards.)
It was concluded that precipitated particles in Timken 16-25-6 alloy contained two kinds of carbides, M₆C, (Fe, Cr)₂₃C₆, at least. These particles were also analysized chemically, and evidence of the presence of nitride was found simultaneously. Presence of σ phase was not found. On the other hand, the carbide M₆C was observed through microscope by using selective etching reagent. Thus, with the regular 16-25-6 alloy, it was concluded that precipitated particles perhaps were M₆C, (Fe, Cr)₂₃ C₆, and Cr MoN₂. In the case of 16-25-6 alloy contaning Ti, the intermetallic compound M₂Ti (perhaps Ni₂Ti) were observed apparently, besides carbides M₆C and M₂₃C₆.