Orientation Dependence on Plastic Flow Behavior of Hydrogen-Precharged Micropillars of High-Mn Steel
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Orientation Dependence on Plastic Flow Behavior of Hydrogen‑Precharged Micropillars of High‑Mn Steel Daehwan Kim1 · Gyeong Hyeon Jang1 · Taekyung Lee2 · Chong Soo Lee1 Received: 19 September 2019 / Accepted: 23 October 2019 © The Korean Institute of Metals and Materials 2019
Abstract This study investigated the dependence of grain orientation on the hydrogen embrittlement (HE) characteristics of high-Mn twinning-induced plasticity steels. Single-crystal micropillars were fabricated to represent the five major texture components of face-centered cubic structure: brass, Goss, copper, cube, and S components. These were classified into three groups for discussion based on the microstructural and mechanical characteristics. The copper and cube micropillars showed the lowest HE resistance because of an exclusive formation of twin boundaries that led to a localized hydrogen concentration. Brass and Goss micropillars revealed multiple slips with increasing strain, which was different from the case of S orientation that exhibited the activation of single slip system. The results of this work suggest that increasing frequency of S component grains would enhance HE resistance owing to the inhibited twinning and suppressed dislocation mobility. This is supported by the superiority of S/cube bicrystal micropillar to Goss/cube micropillar in terms of HE resistance. Keywords Austenitic steels · Hydrogen embrittlement · Twinning · Orientation · Texture
1 Introduction Emergence of high-strength steels, including a high-Mn twinning-induced plasticity (TWIP) steel, has given rise to the issue of hydrogen embrittlement (HE) that limits their practical use. Internal hydrogen in high-strength steel deteriorates the mechanical properties and induces intergranular fracture, leading to unexpected catastrophic failure [1, 2]. Researchers have actively studied various methods to prevent the HE phenomenon, which can be classified into three broad strategies of (1) impeding hydrogen diffusion within a material utilizing irreversible trapping sites [3, 4], (2) increasing the grain-boundary resistance to decohesion [5–7] and (3) reducing the localized stress concentration [8–12]. * Taekyung Lee [email protected] * Chong Soo Lee [email protected] 1
Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
School of Mechanical Engineering, Pusan National University, Busan 46241, Republic of Korea
2
The third strategy focuses on the suppression of hydrogen-assisted stress concentration. One way to achieve this goal is the modification of alloying elements, since chemical composition determines phase transformation, twinning, slip mode, and many other material properties. The best example is the addition of Al to high-Mn carbon steels [11, 12]. The other way is tailoring the grain orientation, often referred to texture engineering [13]. However, the effect of grain orientation on HE has been considered limitedly owing to the difficulty in conducting investigations. Karaman
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