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<p>This study investigates the influence of rotational speed (1000–2000&#xa0;rpm) on the microstructural evolution, crystallographic texture, recrystallization mechanisms, and microhardnessof dissimilar C45/E335 steel joints produced by rotary friction welding. Optical microscopy, energy-dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), and Vickers microhardness mapping were employed to establish quantitative process–structure–property relationships.Optical microscopy revealed that increasing rotational speed enhances interfacial mixing and promotes greater plastic deformation within the central weld zone. As rotational speed increases, the microstructure in this region becomes progressively refined and strain-affected.Hardness mapping demonstrated that the maximum hardness was consistently located in the thermo-mechanically affected zone (TMAZ), reaching 310 HV at 2000&#xa0;rpm. In contrast, lower hardness values were measured in theheat-affected zones(HAZ), reflecting thermally induced recovery and grain coarsening. Notably, the region of maximum hardness shifts toward the C45 steel side, whereas the E335 steel exhibits a wider HAZ and lower local hardness. Furthermore, hardness increases with increasing rotational speed, indicating stronger deformation-induced strengthening at higher thermomechanical inputs.EBSD-based analyses of grain orientation spread (GOS), low-angle grain boundary fraction, and geometrically necessary dislocation density revealed microstructural and crystallographic gradients across the weld seam, including variations in grain size, low-angle grain boundary fraction, geometrically necessary dislocation density, and texture intensity. Therefore, microstructural evolution in the TMAZ is dominated by continuous dynamic recrystallization (CDRX), characterized by subgrain rotation, progressive LAGB formation, and relatively diffuse texture components. With increasing rotational speed, enhanced thermal input promotes grain boundary mobility and selective growth of strain-free grains, indicating a transition toward discontinuous dynamic recrystallization (DDRX), particularly in regions experiencing elevated temperatures and lower deformation such as the HAZ. This CDRX-to-DDRX shift is reflected by changes in GOS distributions, texture sharpening along the γ-fiber, and local variations in hardness.Overall, the results demonstrate that rotational speed governs the development of asymmetric thermomechanical gradients, which in turn control recrystallization behavior, texture evolution, and local microhardnesswithin the welded joint.</p>

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Microstructural and mechanical assessment of a weld seam between two medium carbon steels using the rotary friction welding process

  • 期刊论文

  • 发表日期：

    2026年5月5日

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  • Zakaria Boumerzoug,
  • Yazid Helal,
  • Jairo Alberto Muñoz Bolaños,
  • José María Cabrera Marrero,
  • Raouache Elhadj,
  • Abdelhak Ayad,
  • Billel Cheniti

摘要

This study investigates the influence of rotational speed (1000–2000 rpm) on the microstructural evolution, crystallographic texture, recrystallization mechanisms, and microhardnessof dissimilar C45/E335 steel joints produced by rotary friction welding. Optical microscopy, energy-dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), and Vickers microhardness mapping were employed to establish quantitative process–structure–property relationships.Optical microscopy revealed that increasing rotational speed enhances interfacial mixing and promotes greater plastic deformation within the central weld zone. As rotational speed increases, the microstructure in this region becomes progressively refined and strain-affected.Hardness mapping demonstrated that the maximum hardness was consistently located in the thermo-mechanically affected zone (TMAZ), reaching 310 HV at 2000 rpm. In contrast, lower hardness values were measured in theheat-affected zones(HAZ), reflecting thermally induced recovery and grain coarsening. Notably, the region of maximum hardness shifts toward the C45 steel side, whereas the E335 steel exhibits a wider HAZ and lower local hardness. Furthermore, hardness increases with increasing rotational speed, indicating stronger deformation-induced strengthening at higher thermomechanical inputs.EBSD-based analyses of grain orientation spread (GOS), low-angle grain boundary fraction, and geometrically necessary dislocation density revealed microstructural and crystallographic gradients across the weld seam, including variations in grain size, low-angle grain boundary fraction, geometrically necessary dislocation density, and texture intensity. Therefore, microstructural evolution in the TMAZ is dominated by continuous dynamic recrystallization (CDRX), characterized by subgrain rotation, progressive LAGB formation, and relatively diffuse texture components. With increasing rotational speed, enhanced thermal input promotes grain boundary mobility and selective growth of strain-free grains, indicating a transition toward discontinuous dynamic recrystallization (DDRX), particularly in regions experiencing elevated temperatures and lower deformation such as the HAZ. This CDRX-to-DDRX shift is reflected by changes in GOS distributions, texture sharpening along the γ-fiber, and local variations in hardness.Overall, the results demonstrate that rotational speed governs the development of asymmetric thermomechanical gradients, which in turn control recrystallization behavior, texture evolution, and local microhardnesswithin the welded joint.