Tažnost oceli 42CrMo4 v širokém rozsahu deformační rychlosti a teploty

Abstract

By means of the uniaxial tensile tests performed on the hot deformation simulator Gleeble 3800, the formability of continuously cast steel with 0.43 % C – 0.80 % Mn – 0.27 % Si – 1.01 % Cr – 0.19 % Mo – 0.0044 % N. At first, the ductility of steel was investigated at constant rate of stroke of 20 mm•s-1 (i.e. at strain rate of ca 0.65 s-1) in temperature range of 800 – 1375 °C. Ductility increased steadily to a temperature about 1335 ° C and then dropped sharply as a result of overheating and burning of the material. The zero ductility temperature is probably between 1360 °C and 1370 °C. For temperatures corresponding to low respectively high formability (i.e., 900 °C or 1280 °C), tensile tests were performed at strain rate in the range of 0.00075 – 60 s-1. Even in the applied range of 5 orders, it was not possible to determine the value of the strain rate corresponding to the local maximum of formability. Metallographic analysis of samples and scanning electron micrographs of fracture surfaces confirmed the theoretical assumption that the effect of strain rate on formability of the studied steel depends on the development of the microstructure in the course of a tensile test.