Crystal plasticity finite element analysis of the effect of bainite size on coordinated deformation in medium carbon steel

Abstract To enhance the plastic coordination of wind turbine main shaft materials under multi-axis stress conditions, this study employs a combination of experimental and simulation methods to investigate the influence of bainite microstructure size on the mechanical properties of medium-carbon steel (Fe-0.42 C-1.05Cr-0.25Mo-0.8Mn, wt%). Experimental results show that at pre-deformation temperatures of 900 °C, 700 °C, 500 °C, and 400 °C, the length of the bainite–ferrite bundles decreases from approximately 31 μ m to 19 μ m, while the width remains between 2 and 3 μ m. Tensile simulations using a crystal plasticity finite element modeling model based on EBSD data indicate that shorter bainite bundles result in more concentrated interface Mises stress, with peak stress reaching 540 MPa at 400 °C, an approximately 15% increase compared to 900 °C. The yield strength in the Y -axis direction is higher than in the X -axis direction, with a maximum difference of approximately 30 MPa. After testing tensile, the polar density increased from 2.2 to 3.4, and the orientation became more concentrated. Low-temperature pre-deformation refines the bainite microstructure and increases the dislocation density, optimizing the crystal orientation distribution and slip coordination, significantly enhancing the material’s strength and anisotropy control capabilities.