日本金属学会誌

J. Japan Inst. Metals, Vol. 28, No. 12 (1964),
pp. 820-827

On the Deformation Twinning in Fe-Ni-C Martensite

Imao Tamura1, Hirofumi Yoshimura2, Nobuhiro Iwasaki3 and Masao Ibaraki4

1The Institute of Scientific & Industrial Research, Osaka University, Sakai; at the present, Faculty of Engineering, Kyoto University, Kyoto
2Postgraduate School of Osaka University, Sakai
3Faculty of Engineering, Osaka University, Osaka; at the present, Technical Research Institute,Nippon Kokan Kabushikikaisha, Kanagawa
4The Institute of Scientific & Industrial Research, Osaka University, Sakai

Abstract:

A deformed Fe-27.56%Ni-0.44%C martensite was examined by optical and transmission electron microscopy and the micro-hardness test. Optical micrographs showed that numerous parallel striations which would be due to twin faults (transformation twins) were slightly observed in the non-deformed martensite, and the spacing of their striations in the martensite increased remarkably and became clearly observable by 5%-deformation of the specimen. Beyond 5%-deformation, relatively wide parallel and crossed striations presumably due to deformation twins appeared.
Transmission electron micrographs and electron diffraction patterns in the selected area of the deformed martensite showed the following: (1) The wide parallel and the crossed striations observed by a optical microscope were deformation twins formed on {112} planes during deformation. (2) Three types of relationships between the deformation twin and the transformation twin were confirmed: (a) Both the twinning plane and the twinning shear direction were the same. Such a kind of deformation twins was easily formed at the beginning stage of deformation on the martensite, and the growth and the detwinning of the transformation twins occurred. (b) The twinning plane differed from each other and the twinning shear direction was the same, and (c) both the twinning plane and the twinning shear direction differed from each other. (3) In the deformed martensite, the deformation twins crossing with other deformation twins and transformation twins were also observed. (4) The deformation twins which were formed on {112} planes and were different from the twinning plane and shear direction of the transformation twins frequently showed kinds of habit planes deviated from {112} planes.
The results of micro-hardness tests showed that the deformed martensite was strain-softened by up to 5%-deformation, beyond this, the deformed martensite was strain-hardened rapidly and reached a constant hardness with the degree of deformation of the specimens.


(Received 1964/7/1)

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