Electro-spheroidization effects on the mechanical property and microstructures in S50C medium‑carbon steels: A comparison with conventional subcritical spheroidization
IF 5.5 2区 材料科学Q1 MATERIALS SCIENCE, CHARACTERIZATION & TESTING
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引用次数: 0
Abstract
This study systematically investigated the microstructure evolution and mechanical softening of normalized S50C medium‑carbon steels subjected to direct current electro-treatment at current densities of 2.75–4.25 × 103 A/cm2 for 1 h. Compared to conventional subcritical spheroidization (700 °C for 24 h), electro-treatment achieved a 24.1 % micro-hardness reduction to 157.8 ± 0.6 HV at a significantly lower processing temperature (268.8 °C) and 96 % shorter duration. Electron backscatter diffraction analyses revealed complete ferrite recrystallization at high current densities, accompanied by grain boundary rearrangement and dislocation annihilation. Concurrently, the cementite morphology evolved from lamellar to spheroidized, with the spheroidization rate increasing from 3.4 ± 0.8 % to 99.5 ± 3.4 %, and the interlamellar spacing of pearlite expanding from 0.37 ± 0.10 μm to 1.45 ± 0.32 μm. These transformations followed a two-stage mechanism: electro-fragmentation at a moderate current density (2.75 × 103 A/cm2) and Ostwald ripening at higher levels (3.00–4.25 × 103 A/cm2). A composite Hall-Petch, Bailey-Hirsch, interlamellar spacing based model quantitatively captured the micro-hardness contributions from grain boundary strengthening, strain hardening, and interlamellar cementite strengthening in dual-phased medium‑carbon steels. A thermal benchmark experiment at 269 °C for 1 h confirmed that Joule heating alone could not trigger the observed changes, underscoring the dominant role of athermal effects in metallurgical behaviors. Literature-based thermodynamic analysis further suggests that electro-treatment introduces additional free energy, promoting interface destabilization and accelerated phase transformations. Overall, this method enables effective spheroidization and recrystallization while preventing severe grain growth, offering a low-temperature and high-efficiency alternative for sustainable processing of medium‑carbon steels.
期刊介绍:
Materials Characterization features original articles and state-of-the-art reviews on theoretical and practical aspects of the structure and behaviour of materials.
The Journal focuses on all characterization techniques, including all forms of microscopy (light, electron, acoustic, etc.,) and analysis (especially microanalysis and surface analytical techniques). Developments in both this wide range of techniques and their application to the quantification of the microstructure of materials are essential facets of the Journal.
The Journal provides the Materials Scientist/Engineer with up-to-date information on many types of materials with an underlying theme of explaining the behavior of materials using novel approaches. Materials covered by the journal include:
Metals & Alloys
Ceramics
Nanomaterials
Biomedical materials
Optical materials
Composites
Natural Materials.