INFLUENCE OF DEFORMATION RATE, GRAIN SIZE AND TEMPERATURE ON MECHANICAL TWINNING IN ELECTRICAL STEEL E2412

Deformation features of fine-grained steel E2412 with 3.63 % silicon concentration and different grain sizes, mainly deforming by twinning, have been considered. Samples were stretched with In stron-5565 machine at deformation rates ≈ 0.002 . 0.660 s–1 during heating in temperature interval of 183 . 393 K. Constantly, two types of specimens among which are 80 % with grain sizes of 1,5 . 9 mmand 0,025 . 0,225 mm, have been experimentally studied. General connection between the number of crystal twins, step-like view of crystal load curve and deformation rate (for grains with dav1 = 3.55 mm) have been determined. Generation of steps is accompanied by detectable decrease of load due to high rate of twin forming at low rates of load. The value of load dropping decreases with increase of load rate. The value Δσ reverses the sign at deformation rate ≈ 0.04 s–1. The authors did not observe detectable load surges in finely crystalline steel at formation of twins (dav2 =0.12 mm). High-speed forming of twins and their small amounts lead to decrease of twin forming time in a single grain in finely crystalline material. Distribution histograms for twinned grains as functions of grain size, temperature and load rates have been plotted. It has been detected that distribution maximum of twinned grains shifts toward bigger grain against general size distribution in polycrystal. It has been determined that optimum grain size, being preferred for twinning and exceeding average grain size at initial size distribution, exists. It has been also shown that number of crystal twins depends on test temperature and deformation rate in a separate grain. Twinning intensity depends on temperature and deformation rate in maximum twinned sample. Deformation temperature, retaining constant number of crystal twins at main experimental rates, exists. 

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