Analysis of Martensite Pole Figure from Crystallographic View Point
- PDF / 432,425 Bytes
- 5 Pages / 593.972 x 792 pts Page_size
- 10 Downloads / 216 Views
have been published on the prediction of transformation texture in which the orientation relationship between austenite and martensite has been assumed to be the Kurdjumov–Sachs (KS) or NishiyamaWasserman (NW) type.[1–3] On the one hand assuming the orientation relationship (OR) to be KS or NW makes the texture modeling easier as the characteristics of this OR is known for a long period of time, but at the same it leaves us with some confusing and inadequate information. As He et al.[1] could not explain the observed pole figure of a in the plessite region of Gibeon meteorite, they came to the conclusion that in the a reflection, all five well-known ORs, namely KS, NW, Greninger–Troiano (GT), Pitch, and inverse GT, were present in almost equal intensities. Kitahara et al.[2] tried to explain the crystallography of lath martensite in low-carbon steel and came to the conclusion that the OR is somewhat like the K–S. They also pointed out that the orientation of martensite is broadly distributed around the ‘‘ideal’’ OR. The use of an incorrect crystallographic relationship has led Cayron et al.[3] to conclude that the two-stage theory can explain the crystallography of martensitic transformation better than the widely accepted phenomenological theory of martensite crystallography (PTMC).[4,5] It must be understood that there is no ‘‘ideal’’ OR between austenite and martensite. For every material, where
APPA RAO CHINTHA, Researcher, VIKRAM SHARMA, Senior Research Assistant, SAURABH KUNDU, Head of Research Group, Employees, are with the Research and Development Division, Tata Steel Ltd., Jamshedpur 831001, India. Contact e-mail: kundu. [email protected] Manuscript submitted May 28, 2013. Article published online August 20, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
c ! a0 transformation is thermodynamically possible, there is an unique OR between the parent and the product phase, and thus, it is incorrect to conclude that more than one popular OR is exists in a single alloy system. In the work of Kurdjumov and Sachs,[6] Nishiyama,[7] Wassermann[8] the ORs are determined based on measurements done on various materials with the help of an X-ray. For example, the KS OR was determined based on the investigations done in lowcarbon martensitic steel and the NW OR was determined based on the work done on Fe-Ni alloys. To make the ORs easy to understand, these are expressed rationally, which is shown in Table I. However, these are all empirical relationships and are based on the experiments done on different materials. It has been shown long ago that these ORs are not unique, and for different materials, different ORs can be observed experimentally.[9] Recently, Nolze has shown based on experiments done on a large number samples how the actual OR deviates from various popular ORs like KS or NW.[10] The deviation of actual ORs in various alloys from the popular ones can be explained with the help of PTMC.[4,5] It is known that for martensitic transformation, it is important to have one invariant line at the interface of the paren
Data Loading...
