20th International Forgemasters Meeting - IFM 2017

Over decades Böhler Special Steel has been a full package supplier of customized high quality special steels and forgings. Böhler Special Steel fosters close relationships to plant manufacturers with the aim to provide products ahead of its time. This paper provides some results of our research activities to raise the operating temperatures of 9% Cr steels from 625 °C (1157 °F) to 650 °C (1202 °F). Increasing the operating temperature requires adoptions of our processes and manufacturing methods to produce optimized microstructures which meet customer specifications and increase creep rupture strength at the same time. The microstructure of two Boron containing 9% Cr steels (FB2-2-LN and NPM1-LN) developed within the framework of our COST activities is compared after heat treatment and discussed after creep rupture. The results show a dependency of the creep rupture strength on the stability of precipitates and on the recovery of dislocations within the first 10 000 h of creep exposure at 650 °C. Heat treatment allows to reduce the total amount of dislocations and to decrease their recovery during creep. The creep rupture time of both steels was increased by more than 30% without negatively affecting the creep rupture strain and impact values.