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 mi crostructure were investigated at high-temperature martensitic and low-carb on steels with 9% chrome and the further alloying elements molybdenium, van adium, niobium and partially tungsten. After austenitizing and subsequent a ir cooling the steels were tempered at temperatures below, at and above AC( 1b) for different times and finally a hardness test was performed. Making u se of the temperature dependence of the hardness tempering diagrams were co nstructed and the Hollomon-Jaffe-Parameter on the three steels was determin ed within its application limits, Micrographs of the structure shows the fo rmation 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 t he partial austenitizing was obtained. While hardening below AC(1b) the tem pering quality increases from P 91, NF616 to E911.