Steel grade 14MoV6-3 is a low-carbon microalloyed steel with addition of chromium and molybdenum. This medium-strength steel exhibits a ferritic-bainitic microstructure after the heat treatment. This grade is designed mainly for power industry applications, withstanding operating temperatures up to 580 °C; in Železiarne Podbrezová, this particular grade is used for production of hot rolled seamless boiler tubes. In this paper we present the basic chemical concept of 14MoV6-3 steel along with its mechanical properties after the heat treatment. Further, analysis of the final microstructure, carbide phases and precipitation of vanadium is being presented as well. For this purpose, the yield stress theory has been proposed along with predictive nomograms for selected ferritic-bainitic phases. According to the results of DTA analyses, necessary conditions for heat treatment after rolling have been proposed. Finally, CCT diagrams for required ferritic-bainitic structure are presented as well.

Steel 7CrMoVTiB10-10 is a Cr-Mo medium alloy steel with addition of vanadium and titanium as microalloying elements and with further addition of boron. The resulting microstructure after the heat treatment takes the form of a tempered bainite. In hot rolling of seamless tubes using this particular steel grade, it is very important to find the optimum heat treatment parameters in order to obtain the final mechanical properties according to STN EN 10216-2+A2. In this paper, various optimization concepts regarding temperature and time of tempering are being presented. Results obtained were utilized in production of seamless steel tubes in Železiarne Podbrezová.