Papers by Author: Karel Matocha

Abstract: This article is focused on optimization of fundamental utility properties and technological process of advanced low alloy steel 15NiCuMoNb5 used for power engineering mainly for production of large capacity steam boilers. Consequently problem critical locality in weld after post weld heat treatment is studied. Optimization of welding technology is proposed. Fracture behaviour of welded joint made from boiler plates 80 mm in thickness of 15NiCuMoNb5 type steel after N + T PWHT regime after welding procedure were studied. Stable crack growth measurement and evaluation of fracture toughness of base material as well as weld metal in temperature region from 0 up 350°C were carried out. Unstable cleavage fracture and fracture toughness KJc of both parts of welded joint at test temperatures cover the transition region were evaluated. The reference temperature T0 approach was used for evaluation of temperature dependence of fracture toughness in transition range.

Abstract: The effect of intercritical annealing of 10GN2MFA grade steel on mechanical properties and impact notch toughness is studied in this paper. This type of low alloy banitic steel is used for production of collector bodies of steam generators for nuclear power station of VVER type. This article is focused on optimalization of fundamental utility properties and heat treatment process of the steel under investigation to increase toughness and critical temperature of brittleness. An intecritical annealing has been chosen as a useful tool for such improvement. Mechanical properties and impact notch toughness values after the intercritical annealing and conventional heat treatment regimes are compared. Effect of simulation of stress relieving including minimum and maximum allowable heating regimes are studied too. Intercritical annealing was added to the conventional quality heat treatment process, between quenching (normalizing) and tempering. The application of intercritical annealing improved the impact toughness significantly, an increase in the upper shelf energy and a decrease in transition temperature of steel under investigation.