Correlation of orientation relationships and strain-induced martensitic transformation sequences in a gradient austeniti
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Correlation of orientation relationships and strain-induced martensitic transformation sequences in a gradient austenitic stainless steel Yinsheng He1,* 1 2
, Kai Wang2, and Keesam Shin1,*
School of Nano and Advanced Materials Engineering, Changwon National University, Changwon 51140, Korea School of Mechatronics Engineering, Foshan University, Guangdong 528231, China
Received: 26 August 2020
ABSTRACT
Accepted: 9 November 2020
Orientation relationships (ORs) play a crucial role in the phase transformation of face-centered cubic austenite (c-fcc) to body-centered cubic martensite (a0 -bcc) upon plastic deformation. So far, ORs between c-fcc and a0 -bcc are reported frequently; however, the correlation to the transformation sequences is not clear. Here, the gradient structured austenitic stainless 304 steel prepared by ultrasonic nanocrystalline surface modification was examined to clarify the ORs that were involved in the strain-induced martensitic transformation (SIMT) behaviors. The results showed changes in the ORs from Nishiyama–Wassermann (NW) to Kurdjumov–Sachs (K-S) and Pitsch with an increase in depth from the top-treated surface. The OR of a0 -bcc formed directly on c-fcc was identified as N-W, while those via the hexagonal closed packed e-plate (e-hcp) were the K-S and Pitsch as they were nucleated at the single and two e-plates intersections, respectively. Thus, the SIMT sequence was the direct c ? a0 with the presence of the N-W OR in the high strain depth, while it was the c ? e ? a0 as the existence of K-S and Pitsch ORs in the low strain depth. The findings provide essential data for the in-depth and comprehensive study of the polymorphic martensitic transformation mechanisms in various steels and alloys.
Published online: 23 November 2020
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Springer Science+Business
Media, LLC, part of Springer Nature 2020
Introduction Strain-induced martensitic transformation (SIMT) is important for both ferrous and nonferrous alloys that has been extensively studied for over 50 years [1–8]. SIMT is known as a diffusion-less process that leads
to changes in the properties of materials [8, 9], for example, it enhances the strength and toughness of austenitic stainless steels [10, 11]. The transformed a0 martensite is considered as a body centered-cubic (bcc) structure derived from the face-centered-cubic (fcc) austenite (c) by homogeneous distortion [12], in
Handling Editor: Sophie Primig.
Address correspondence to E-mail: [email protected]; [email protected]
https://doi.org/10.1007/s10853-020-05551-0
J Mater Sci (2021) 56:4858–4870
4859
which a \ 001 [ axis of c-fcc is compressed by 20% to become the c-axis of a0 -bcc, and two \ 110 [ axes are extended by 12% to yield the a- and b-axes of a0 bcc (Fig. 1a). The process suggested by Bain indicates that a correspondence (Bain correspondence) between the fcc and bcc lattices exists [12] (Fig. 1a). And the martensite may exist orientation relationships (ORs) with respect to the austenite during the transformation [12–14]. The OR between the two phase
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