Prostorová mapa tvařitelnosti sestavená z výsledků zkoušek tahem za tepla

Abstract

This thesis deals with the experimental study of the hot deformation behavior of spring steel 51CrV4. In terms of formability of this material it is mainly about determining optimum conditions for its bulk forming by hot rolling. The first part of the experimental research was focused on the determination of the maximum possible forming temperature. For this purpose so-called nil strength temperature was determined, which corresponds to the heating temperature, above which the strength of the material substantially decreases to zero. In the case of the examined steel the value was determined as 1384 °C. In the second phase of the experiment was carried out a series of uniaxial tensile tests in the temperature range of 650-1380 °C and testing speed range of 1, 16 and 250 mm•s-1. The determined value of the nil strength temperature of 1384 °C then exactly corresponds with practically negligible formability, observed during tensile tests at temperatures of 1380 °C. The deformation behavior at temperatures below 800 °C is influenced by the occurrence of pearlite in the structure. Results of tensile tests were used to construct the 3D maps of strength and ductility. The 3D map of ductility shows the improvement of formability by growing strain rate (approximately from 0.1 to 22 s-1) at temperatures over 1000 °C. Upper rolling temperature up to 1270 °C can be recommended from the point of view of formability and flow stress in case of the steel 51CrV4.