PSI - Issue 69

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ScienceDirect

Procedia Structural Integrity 69 (2025) 113–120

13th European Symposium on Martensitic Transformation 2024 (ESOMAT 2024) Effect of solid-solution temperature on the microstructure and mechanical properties in low-cobalt secondary hardening ultra-high strength steel Haofei Zhu a , Zhiping Xiong a, b * , Jianwen Mao a , Xingwang Cheng a, b a National Key Laboratory of Science and Technology on Materials under Shock and Impact, School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, China b Tangshan Key Laboratory of High-Performance Metals and Ceramics, Tangshan Research Institute BIT, Tangshan 063000, China Abstract The effects of solid-solution temperature on the microstructure and mechanical properties of low-cobalt M 2 C and NiAl co precipitated secondary hardening steel were investigated. With increasing solid-solution temperature, the microstructure undergoes complex evolution, characterized by an increase in retained austenite, dissolution of primary M 7 C 3 carbides, and growth of prior austenite grains. Correspondingly, the yield strength and impact toughness in both quenched and aged conditions initially improve. This is attributed to the dissolution of the primary M 7 C 3 carbides, which enhances the precipitation strengthening of M 2 C carbides and inhibits crack nucleation, thereby improving both strength and toughness. However, when the solid-solution temperature exceeds 900 °C, the coarsening of prior austenite grains leads to a reduction in Hall-Petch strengthening and decreased crack propagation resistance, resulting in a decline in yield strength and toughness in the aged state. The optimal solid-solution temperature is found to be 900 °C, where an excellent balance between strength and toughness is achieved. © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Guest Editors

Keywords: Mn heterogeneity; pearlite; austenite; martensite;

* Corresponding author. Tel.: +86 68913951; fax: +86 68913951. E-mail address: zpxiong@bit.edu.cn, zuileniwota@126.com. # These authors contributed equally to this work and should be considered co-first authors.

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Guest Editors 10.1016/j.prostr.2025.07.016