Some crystallographic characteristics of the (252) f martensite transformation in Fe-alloys
- PDF / 2,986,355 Bytes
- 9 Pages / 603.28 x 788 pts Page_size
- 50 Downloads / 175 Views
I.
INTRODUCTION
THE crystallography
of the (252)f martensite transformation has been extensively investigated and detailed experimental data on the habit plane, the orientation relationship, and the shape strain are available. 1-9 In spite of this, attempts to use the basic I~ or modified 12'13'14versions of the phenomenological theory of martensite for theoretical analysis of the crystallography have failed to provide a solution in satisfactory agreement with all experimental observations. 15,16 The term (252)f martensite is derived from the original work of Greninger and Troiano,l who reported a habit plane close to {252}f in Fe-C alloys. Subsequent works on an Fe-8Cr-1.1C alloy2'4'9 and Fe-C alloys3 reported habit planes between the (121)f and (252)f planes, and it was also established that the average habit plane may deviate from the exact []01]f zone by a small angle (~2 deg). The most extensive investigation on the martensite/ austenite orientation relationship has been performed by Dautovich and Bowles, 8 who reported an average orientation relationship (_l_lll)f 0.38 deg from (011)~ and [101]f 0.70 deg from [lll]b. These results, obtained for an Fe-6Mn-0.9C alloy, were in good agreement with previous results2'4 for an Fe-8Cr-1. IC alloy. Thus, both the habit plane and the orientation relationship have been determined with a high accuracy, and different investigations are highly consistent. Various investigations on the shape strain, on the other hand, have resulted in a considerable variation in shape strain directions. This variation can be observed even for different plates in the same alloy and has been demonstrated by Dunne and Bowles, 5 using Fe-Mn-C and Fe-C alloys, and by Muddle et al., 9 using an Fe-8Cr-I.IC alloy. The various shape strain directions approximately form a great circle close to the [lll]f zone and the spread is about 40 deg even when plates penetrating deeply into the specimen, representative of "bulk" martensite plates, are used for the measurements. 9 Dunne and Bowles could observe a re-
B. E J. SANDVIK, formerly with the University of Illinois, is now at the Laboratory of Physical Metallurgy, Helsinki University of Technology, Espoo 15, Finland. C. M. WAYMAN is with the Department of Metallurgy and Mining Engineering, University of Illinois at UrbanaChampaign, Urbana, IL 61801. Manuscript submitted February 1I, 1983. METALLURGICALTRANSACTIONSA
lationship between the shape strain direction and the surface orientation of the austenite grain used for the measurement, but this result was not supported by the larger number of measurements performed by Muddle et al. Thus, the reason for the spread in shape strain directions remains unknown. In spite of the inconsistency in shape strain directions, it has been established that the (252)f martensite shape strain is an invariant plane strain, i.e., the martensite habit plane is an invariant plane. 5-7'9 In the basic phenomenological crystallographic theories l~ the macroscopic martensite shape change can be expressed by the equation Pl
Data Loading...
