1988 Volume 74 Issue 10 Pages 2001-2008
The effect of molybdenum content on creep-rupture properties and room-temperature toughness of high chromium ferritic heat resisting steels was investigated. Molybdenum content was varied from 1 to 2 wt%. In order to obtain 9Cr-Mo-V-Nb ferritic steels with both high creep-rupture strength and superior toughness, the amount of delta ferrite was controlled below 25%, and the optimum tempering condition and mechanical properties after simulated welding have been investigated. The influence of molybdenum content on creep-rupture strength and Charpy absorbed energy was investigated with respect to the ratio of delta ferrite to tempered martensite, the precipitates, and the microstructures.
Charpy absorbed energy of the 0.05C-9Cr-1Mo-0.15V-0.05Nb steel tempered at 800°C and then heated at 600 650°C for 104 h was as high as 20 30 kgf-m. By contrast, Charpy absorbed energy of 0.05C-9Cr-2Mo-0.15V-0.05Nb steel was reduced to about 4 kgf-m after heating at 600 650°C for 104 h. It is considered that the steel of 1Mo shows superior toughness because of its low carbon content and a single phase of martensite. It was concluded that combination of superior creep-rupture strength and toughness can be obtained by optimum heat treatment for the 9Cr-1Mo-V-Nb steel containing 0.05 wt%C.