Microstructure evolution of Cu-bearing low-carbon bulb flat steel during hot-rolling-induction heating-solid solution-tempering treatment was characterized using electron back-scattered diffraction(EBSD),field emission scanning electron microscopy(FE-SEM)and energy disperse spectroscopy(EDS).The difference between the bulb and flat was analyzed based on the strengthening mechanism.The results show that at different heat treatment stages,the grain size of flat is smaller than that of the bulb,while the precipitation of Cu-rich particles in the flat is improved.After aging at 680 ℃ for 2 h,compared with the bulb,the flat exhibit a higher strength and hardness and a relatively lower elongation.During hot-rolling-induction heating-solid solution-tempering process,the bulb flat steel undergoes thermal deformation,ferrite austenite transformation,martensitic transformation,and recovery stages in sequence.The strength difference of about 50 MPa between the flat and the blub is attributed to the major factor of the size difference of Cu-rich particles,the secondary factor of the difference in grain size and the weak factor of the difference in dislocation density.
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