Long-term creep deformation property of modified 9Cr-1Mo steel

The first volume of “Atlas of Creep Deformation Properties” was published on modified 9Cr-1Mo steels in March 2007, as a part of the NIMS (National Institute for Materials Science) Creep Data Sheet series. Creep deformation properties up to about 70,000 h have been investigated. No clear steady-state creep stage has been observed, and creep deformation of the steel consists of transient and accelerating creep stages. Good linear relationships between creep strain vs. time and creep rate vs. time were observed within a transient stage in a log-log plot. It was appropriately expressed by a power law rather than an exponential law, logarithmic law and Blackburn's equation. With decrease in stress, the magnitude of creep strain at the onset of accelerating creep stage decreased from about 2% in the short-term to less than 1% in the long-term region. Life fraction of the time to specific strain of 1% creep strain and 1% total strain, to time to rupture tended to increase with decrease in stress. The time to 1% total strain, that is an important parameter for design of high temperature components, was observed to lie in the transient creep stage in the short-term regime, however, it shifted to the accelerating creep stage in the long-term regime. For evaluation of long-term creep strength properties, an experimental creep test data should be extrapolated in consideration of the stress dependence of creep deformation properties.