With using of tension tests, which were performed on universal plastometer Gleeble 3800, the influence of grain size on hot formability medium-carbon steel was investigated. From investigated steel were prepared 2 sets of samples, while the booth sets were made from the same melt. The first set of samples was made from hot rolled bars. The second set of samples was made from the subsurface area of the continuously cast billet. It can be assumed that the samples prepared from a cast billet should have a relatively coarse grain structure, whereas samples made from hot rolled bars should have relatively homogenous fine grain structure. The samples with the initial deformed structural state were heated directly to the selected deformation temperatures, whereas samples with initial cast structural state were uniformly austenitized by temperature 1300 °C and then were controlled cooled down to selected deformation temperatures. All hot tensile tests were performed at uniform tension rate 1000 mm·s-1. The samples from initial deformed structural state exhibited, with a comparison of samples from initial cast structural state, the higher hot ultimate tension strength and smaller hot ductility. The interesting results of hot ductility were obtained in the two-phase low-temperature region. In the case of samples from initial cast structural state, the ductility at low-temperature two-phase area decreased, whereas in the case of a sample from the initial deformed structural state the ductility unexpectedly increase.Keywords: grain size, hot formability, tension test, mechanical properties in hot condition.
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