On the Stability of Reversely Formed Austenite and Related Mechanism of Transformation in an Fe-Ni-Mn Martensitic Steel
- PDF / 4,382,811 Bytes
- 14 Pages / 593.972 x 792 pts Page_size
- 68 Downloads / 152 Views
,
The stability of reversely formed austenite and related mechanism of transformation were investigated against temperature and time in an Fe-9.6Ni-7.1Mn (at. pct) martensitic steel during intercritical annealing at a dual-phase (a + c) region. Dilatometry, electron backscattering diffraction (EBSD), atom probe tomography (APT), and X-ray diffraction (XRD) were used to characterize the mechanism of reverse transformation. It was found that under intercritical annealing at 853 K (580 C), when the heating rate is 20 K/s (20 C/s), reverse transformation takes place through a mixed diffusion control mechanism, i.e., controlled by bulk diffusion and diffusion along the interface, where Ni controls the diffusion as its diffusivity is lower than that of Mn in the martensite and austenite. Increasing the intercritical annealing to 873 K (600 C) at an identical heating rate of 20 K/s (20 C/s) showed that reverse transformation occurs through a sequential combination of both martensitic and diffusional mechanisms. The transition temperature from diffusional to martensitic transformation was obtained close to 858 K (585 C). Experimental results revealed that the austenite formed by the diffusional mechanism at 853 K (580 C) mainly remains untransformed after cooling to ambient temperature due to the enrichment with Ni and Mn. It was also found that the stability of the reversely formed austenite by martensitic mechanism at 873 K (600 C) is related to grain refinement. DOI: 10.1007/s11661-017-4288-2 The Minerals, Metals & Materials Society and ASM International 2017
I.
INTRODUCTION
IN recent years, many scientists have been engaged in active research programs to seek ways to exploit commercially viable advanced steels with exceptional properties. HAMIDREZA KOOHDAR is with the School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, PO Box: 14395-731, Tehran, Iran. MAHMOUD NILI-AHMADABADI and MOHAMMAD HABIBI-PARSA are with the School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, and also with the Center of Excellence for High Performance Materials, School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, PO Box: 14395-731, Tehran, Iran. Contact e-mail: [email protected] HAMID REZA JAFARIAN is with the School of Metallurgy and Materials Engineering, Iran University of Science and Technology (IUST), Narmak, Tehran, Iran. TILAK BHATTACHARJEE and NOBUHIRO TSUJI are with the Department of Materials Science and Engineering, Kyoto University, Yoshida Hommachi, Sakyo-Ku, Kyoto 606-8501, Japan. Manuscript submitted January 21, 2017. Article published online August 28, 2017 5244—VOLUME 48A, NOVEMBER 2017
The practical motivation for these studies has been the need for structural steels with an outstanding combination of strength and toughness, e.g., the mixed structure of martensite and austenite in which martensite provides strength and austenite provides ductility and toughness.[1–4] It has been reported that martensitic st
Data Loading...
