Influence of tempering on microstructure and hardness of high-temperature 9%Cr-steels

The influences of temperature and duration of tempering on hard ness and microstructure were investigated at high-temperature martensitic and low-carbon steels with 9% chrome and the further alloying elements molybdenium, vanadium, niobium and partially tungsten. After austenitizing and subsequent air cooling the steels were tempered at temperatures below, at and above AC(1b) for different times and finally a hardness test was performed. Making use of the temperature dependence of the hardness tempering diagrams were constructed and the Hollomon-Jaffe-Parameter on the three steels was determined within its application limits, Micrographs of the structure shows the formation of the carbides and the martensite. At tempering temperatures below Ac-1b a decrease of hardness occurs, above AC(1b) a hardness rise due to the partial austenitizing was obtained. While hardening below AC(1b) the tempering quality increases from P 91, NF616 to E911.