Changes in strengthening mechanisms in creep of 9Cr-1.8W-0.5Mo-VNb steel tested over wide ranges of creep conditions

The present paper studies stress, temperature and heat dependence of creep rupture life 9Cr-1.8W-0.5Mo-VNb (Gr. 92) steel with data 4 heats reported in National Institute for Materials Science Creep Data Sheet 48B. In Gr. 92 there are four regions, H, M, L G, showing different stress life. increases increasing hardness after tempering Regions H M (high medium stress), prior austenite grain size long-term Region G. Its is insensitive to the low-stress L. lives formulated each region as a function metallurgical variable determining its Two types breakdown strength (substantial decrease exponent life) take place steel; one from L, other or Since used G steam power boilers, second engineering importance. Causes discussed grades enhanced ferritic steels. • Small detrimental Grade 91 strong grade steels increased amounts w B. Strengthening mechanism elucidated time range over 100,000 h. breakdowns occur