metals Article Enhancement of Uniform Elongation by Temperature Change during Tensile Deformation in a 0.2C TRIP Steel Noriyuki Tsuchida 1, * and Stefanus Harjo 2   Citation: Tsuchida, N.; Harjo, S. Enhancement of Uniform Elongation by Temperature Change during Tensile Deformation in a 0.2C TRIP Steel. Metals 2021, 11, 2053. https:// doi.org/10.3390/met11122053 Academic Editors: Zhenjia Xie, Marcello Cabibbo, Xueda Li and Xiangliang Wan Received: 18 November 2021 Accepted: 15 December 2021 Published: 18 December 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji 671-2280, Japan 2 J-PARC Center, Japan Atomic Energy Agency, 2-4 Shirane Shirakata, Tokai-mura, Ibaraki 319-1195, Japan; stefanus.harjo@j-parc.jp * Correspondence: tsuchida@eng.u-hyogo.ac.jp Abstract: It is important to control the deformation-induced martensitic transformation (DIMT) up to the latter part of the deformation to improve the uniform elongation (U.El) through the TRIP effect. In the present study, tensile tests with decreasing deformation temperatures were conducted to achieve continuous DIMT up to the latter part of the deformation. As a result, the U.El was improved by approximately 1.5 times compared with that in the tensile test conducted at 296 K. The enhancement of the U.El in the temperature change test was discussed with the use of neutron diffraction experiments. In the continuous DIMT behavior, a maximum transformation rate of about 0.4 was obtained at a true strain (ε) of 0.2, which was larger than that in the tensile test at 296 K. The tensile deformation behavior of ferrite (α), austenite (γ), and deformation-induced martensite (α ′ ) phases were investigated from the viewpoint of the fraction weighted phase stress. The tensile test with a decreasing deformation temperature caused the increase of the fraction weighted phase stress of α and that of α ′ , which was affected by the DIMT behavior, resulting in the increase in the work hardening, and also controlled the ductility of α and α ′ , resulting in the enhancement of the U.El. Especially, the α phase contributed to maintaining high strength instead of α ′ at a larger ε. Therefore, not only the DIMT behavior but also the deformation behavior of γ, α, and α ′ are important in order to improve U.El due to the TRIP effect. Keywords: TRIP effect; uniform elongation; deformation-induced martensitic transformation; deformation temperature; neutron diffraction experiments 1. Introduction The transformation-induced plasticity (TRIP) effect is a strengthening mechanism of metals that makes efficient use of the deformation-induced martensitic transformation (DIMT) of the retained austenite (γ R ) and is expected to improve the ductility or elonga- tion [1–6]. Because the TRIP effect also has been utilized in advanced high-strength steels, there is great interest in understanding how the DIMT controls and the constituent phases interact to obtain superior mechanical properties [2,4,7]. In various studies on the TRIP effect, the DIMT behavior of γ R is key information for discussing the enhancement of the uniform elongation (U.El) through the TRIP effect [4–12]. Blondé et al. investigated the mechanical stability of γ R using high-energy X-ray diffraction during tensile tests at various deformation temperatures [3]. They made clear that the mechanical stability of γ R was influenced by a complex interplay among the carbon concentration in γ R , the grain orientation, the load partitioning and the deformation temperature. Based on previous studies, it is desirable that γ R is stable in the early stage of deformation and that the DIMT is temporarily induced up to the latter part of the tensile deformation in order to obtain a better TRIP effect [8,13–15]. On the other hand, in cases where the improved U.El was obtained in various TRIP steels, all of the γ R was not necessarily transformed into deformation-induced martensite (α ′ ) at the maximum load point [7,9,16]. This means that the DIMT can be effectively used to improve the U.El through the TRIP effect. If such Metals 2021, 11, 2053. https://doi.org/10.3390/met11122053 https://www.mdpi.com/journal/metals