HORNÍK Jakub Czech Technical University in Prague

Spoluautoři ZUNA Petr, JANDOŠ František, MÁLEK Jaroslav, JETMAR Tomáš

The paper deals with the problematic of weakening of the original austenite grain boundaries which often occurs during the processing of forgings. This phenomenon may cause development of intercrystalline fracture even before the final heat treatment of forgings. Samples cuted from forging made from steel 14-5 26NiCrMoV were at first processed by regime of austenitization at 1200 °C / 2 hours and oil quenched. Samples were then tempered at the temperatures in range (200 - 700) °C for 1, 10 and 100 hours. Microstructure of the material, impact energy and hardness of monitored steel in the individual stages of processing were evaluated. Microstructure and fracture surfaces were observed by light microscopy, scanning electron microscopy and eventually using transmission electron microscopy of thin foils and replicas. Decreasing of toughness at temperatures 300 and 400 °C was monitored. However, this slight decrease does not reach critical value for the initiation of intergranular rupture during the forging process.