Abstract
	Hot formability of the ledeburitic tool steel X155CrVMo12.1, which is determined for cold working, was investigated by means of three (3) methods. The first of them consisted in one-pass rolling of wedge-shaped samples provided with V-shape notches, produced by milling, on their side walls. These notches function as initiators for crack development. The special software, based on the computer raster image analysis of the rolled stock, was used for determination of geometric dimensions of the final rolled stock and calculation of its deformation characteristics. The results of wedge-shaped rolled samples were compared with those obtained by high-temperature tensile tests. Additional information was gained by means of the differential thermal analysis (DTA).
	Results of both mechanical test methods exhibit identical trends, showing a loss of cohesiveness of the investigated material in the temperature region above ca 1160 °C due to overheating and burning – see results of SEM analysis of fracture surfaces. The highest rollability was found with a sample of the investigated steel at the temperature of 1050 °C. Plasticity values, based on reduction of area in the place of fracture, are low (max. 60 %) in the whole range of the studied temperatures, at temperatures above ca 1130 °C no plasticity can be registered. Results of the differential thermal analysis demonstrate an influence of the matrix properties by progressive dissolving of the precipitated carbides; this process is finalized at temperatures above 1150 °C.
	The executed experiments confirmed a reduced hot formability of the ledeburitic tool steel 155CrVMo12.1 and led to a proposal of optimization of forming temperatures. Whereas normally recommended temperatures for this steel are 1050 – 850 °C, the carried out experiments show that with regard to plastic properties a real chance of increasing rolling temperatures by up to 100 °C exists.